Indium Corporation Blogs

Engineered solders are solders that can make a HUGE difference with your thermal management, IGBT, die-attach, medical device, hermetic sealing, or connector assembly application. The possibilities are endless.

One of my personal favorite engineered solders is Solder Fortification® Preforms. Obtaining the correct amount of solder to ensure a strong solder joint is critical in electronics manufacturing. Solder Fortification® Preforms are the solution for many challenging manufacturing issues from miniaturization to tightly fitted components to achieving just the right amount of solder in just the right place.

Solder Fortification® Preforms are generally rectangular pieces of alloyed metal that do not contain any flux. The preform is added to a deposit of solder paste using standard pick and place equipment. Since the alloy for both the preform and the solder paste is the same, the preform will reflow at the same temperature as the solder paste, with the solder paste providing the necessary flux. The preform increases the volume of solder over what could be achieved with solder paste alone, especially for stencils with a pitch of 0.3mm or less.

Tell me where engineered solders, especially Solder Fortification® Preforms, might help you. I'll take it from there.

Seth

Folks,

I am a global warming skeptic.  This term, however, requires some explanation.   I believe in climate change.  The climate is always changing.  However, I don’t think it is clear that the world has been getting warmer in the last decade.  I also am not convinced that humans are the main drivers of whatever  climate change has occurred.  The following explains why.

Point 1: For the Last 12 years the World Not Getting Warmer

The global warming scenario that exists today is that human emissions of carbon dioxide are the main reason that the climate is warming.  So, it is natural then to ask, is the climate really warming?  One look at USA Today’s cover story “Why You Should Sweat Climate Change” on 1 March 2013 would appear to settle the story.  Just look at  Figure 1 below.

Figure 1. Graph from USA Today Cover Story March 1,2013.

A quick scan of the graph shows 55.34°F last year and 50.56°F in 1895.  A 5 degree increase.  Wow!  A little closer analysis reveals that these temperatures are individual data points.  If you look at the years 1900 and 2010, you get 53°F for both years, essentially no change.  The thick red line is the long term trend and admittedly it increases from about 51.3°F to about 53°F in the 117 year period. 

Note the icon in the upper right corner, it shows the globe with a dramatic upward trend line.  However, this causes you to now note that this graph is for US temperatures, not world temperatures.  What was the world temperature like?  As this thought crosses your mind, you remember that 2012 brought Europe its coldest winter in recent memory. So you go on the internet and find out that 2012, for the world,  was the ninth hottest year on record.  Scary.  But then you think, “Wait a minute, that means that eight years were hotter.” So you wonder, what do the last 10 or so years look like for world temperatures.  The graph is below in Figure 2:

Figure 2. World Temperature 2001-2012. Graphed by Dr. Ron

Note that for the last twelve years, the trend is flat (actually a little down).  Where are all of the headlines sharing this important information?  So it is not clear that the world is continuing to get warmer.  

Am I the only one that finds it troubling that the media seem to universally tout the scary stories about global warming, but don’t seem to mention obvious counterpoints such as the graph above?  This information is profoundly important.

Point 2: In the Past, Nature Along has Delivered Stunning Climate Change by Itself

I am writing this post from my home Woodstock, VT. I look out my window and view two beautiful, large rocks, each about the size of a house.  These monoliths were likely left as the glaciers in the last ice age retreated, these rocks probably originated in Quebec.  Woodstock was under thousands of feet of ice during the last ice age, Canada was completely under ice.  New York State's Long Island is a glacial terminal moraine. The extent of the ice coverage is shown in Figure 3 below.  However, the forces of nature alone, raised the temperature of the earth by 12 degrees Celsius (with no help from mankind), melting the glaciers and allowing me to live in the Green Mountain State (Vermont = Ver (green) mont = mountain, in French.)  

Figure 3. The Extent of the Ice Coverage in the Last Ice Age  http://www.iceagenow.com/

The natural processes that caused the warming are many.  They include the precession of the earth on its axis, variation in the output of the sun, changes in the ocean and atmosphere, and others.  These processes  have resulted in the past temperature changes as shown in the Figure 4 below.

Figure 4. Temperature of the Earth in the Past 800,000 Years.

This figure shows as much as a 20°C (36°F!) temperature swing produced by nature alone.  The change in world temperature between 1900 and 2010 would be about as thick as the line in this figure. 

I find the proposition that the main driving force in global warming (if it is occurring)  being human produced CO₂ alone is hard to accept, when we see what mother nature has given us in the past.  It would be similar to someone taking the position that the only thing that affects stencil printing quality is the stencil.  When others point out that it might be the solder paste, or the print head, or separation speed, etc., they are shouted down as being unscientific.

Point 3: It was Warmer in the Middle Ages than Today

The United Nations commissioned a panel to study climate change in 1988.  The Intergovernmental Panel on Climate Change IPCC  was established.  In 1990, the panel came out with an assessment of past world temperatures as shown below in Figure 5.  The estimating of temperatures before the mid 1800s is difficult due to lack of records and thermometers before this time.

Figure 5. The First IPCC Assessment of World Temperatures, 800AD to the Present

There is some argument that the Medieval Warm period and Little Ice Age were local events, however they clearly existed and profoundly affected much of the Northern Hemisphere.  But more recent temperature IPCC plots lose them, as seen in Figure 6. below.   The Medieval Warm Period enable the Vikings to settle in Greenland and red wine to be grown in England. When the Little Ice Age came, the Vikings had to leave and England has not been as warm since. 

Figure 6. Third IPCC Temperature Assessment.  Note the Medieval Warm Period and Little Ice Age Disappear.  Because of the abrupt change in temperature after 1900, this graph has earned the moniker, The Hockey Stick Graph.

The controversy over the Hockey Stick graph  is interesting reading and is the source for Figures 4-6.  

In 2003, MacIntyre and McKitrick presented a detailed criticism of the IPCC 3^rd Assessment's Hockey Stick Graph in Figure 6 .  I find their criticism compelling.

I could go on and on,  but to summarize why I am a global warming skeptic:

• For the  past decade the world has not gotten warmer
• Natural forces overwhelm CO₂ as a driving force for climate change
• Sloppy science is behind the hockey stick graph

Please share your science- and fact-based comments.

Cheers,

Dr. Ron

When helping customers with the optimization of their soldering process, the question often comes up;

“What will my solder bond line thickness be when utilizing this material?” 

The amount of volume lost to flux content while utilizing a solder paste, in comparison to a flux-coated preform, is much greater.  Whereas a flux-coated preform only contains about 1-2% flux by weight, a stencil printing solder paste is approximately 10% flux by weight.   This may not sound like much, but when you consider the density of the powdered alloy in the solder paste (7.40 g/cm³ for SAC305) versus the density of the flux (~1 g/cm³), you end up with a material that is almost 50% flux by volume! 

Therefore, if you were to print a 0.5” x 0.25” deposit utilizing a 0.005” thick stencil (0.001in³ of printed solder paste volume), you would only end up with approximately 0.0005in³ of actual metal solder.  In short, your final bond line thickness will be half of the thickness of the solder paste printed.

For help determining your bond line thickness, or for help determining the appropriate solder material for your application, please contact AskUs@indium.com.

Calculating the exact amount of solder paste needed for a given circuit board or for a full production run can be difficult for several reasons, including:

• print deposit variations
• paste left on the stencil and squeegees after the build is complete
• bead size needed for the build (which depends on the squeegee size)

The theoretical volume of solder paste can be calculated for each board using the Greely Formula and a simple volume calculation.

The Greely Formula:

Specific Gravity of the flux vehicle is generalized to 1. 

Example:

• Solder Paste: SAC305, Indium8.9HFA, Type 4.5, 87.75%
• Aperture Size: 0.012” Square
• Stencil Thickness: 0.004”

 

 

 

 

Solder Paste Specific Gravity = 4.14

 

Volume for this aperture can be calculated using the following formula:

Length x Width x Height

0.012” x 0.012” x 0.004” = 0.000000576 inches³

 

To get the theoretical weight of the solder paste for the 0.012” square aperture you must multiply the solder paste theoretical volume by the solder paste density. 

 0.000000576 inches³ * 4.14gm/cm³ = 0.000009439cm³ * 4.14gm/cm³ = 0.0000391gm

 

To calculate the theoretical amount of solder paste that will be used for each board, the weight of solder paste for each aperture on the board will need to be calculated.  Once all of the weights have been calculated they can be added together which will result in the amount of solder paste per board. 

Of course this is the theoretical value and not an actual value.  The easiest way to determine the actual paste weight per board is to weigh a board before the paste has been printed and then again after the paste has been printed.  The difference is the actual solder paste weight or consumption of solder paste per board. Of course, there will be some margin of error even in this calculation due to the weight tolerances of the board and the variations in solder paste deposits from print to print.

Let me know if I can help you calculate or estimate the amount of solder paste your project will consume.
Chris

Folks,

This year will mark the 10^th anniversary of SMTA’s SMT Process Certification Course.  This course was developed by Jim Hall, Phil Zarrow and me, Dr. Ron Lasky, in time for SMTAI 2002.  The workshop covers all of SMT from materials (strong emphasis on solder paste), components, soldering, stencil printing, component placement, reflow soldering, wave soldering, dispensing, test, and more.

The course assumes that the material is mostly review, so it is definitely not introductory level.   At the end of the workshop are an open book and closed book test.  Upon passing the test, you will have the privilege of adding the title: “Certified SMT Process Engineer*” to your business card.

Among the many benefits of SMTAI certification is being able to inform your customers that your product is manufactured by credentialed personnel. Since the SMT Process Certification Course is taught internationally, this credential is recognized globally.

So if you, or your team, are not already certified, join the tenth anniversary workshop at SMTAI 2012  at Disney World and get certified!

Cheers,

Dr. Ron

* In some countries, such as Canada, the term "engineer" has legal implications and cannot be used unless the person has a degree from an accredited university or a Professional Engineer's License.

Folks,

It is hard to believe that I have been blogging for over 7 years now.  In all this time it has surprised me how much interest there has been in the solder density calculator that I developed.  At the suggestion of Tim Jensen, I have added a feature that can calculate the volume of solder paste and flux if given their masses or vice versus.  The densities of the solder paste alloy and flux are also needed.  Most fluxes have a density of about 1 g/cm³.   If you are interested in this updated software tool, download it here.

Knowing the volume of the solder and flux in a solder paste is critical if you are using the Pin-in-Paste process, with or without solder preforms.  I have also developed a software package called StencilCoach™ that can calculate stencil parameters and the special parameters needed for the Pin-in-Paste process.  I will also send this free software tool to those that are interested.

The image shows the schematic for the solder volume calculations for the Pin-in-Paste Process.  The equations were developed by Creyr Innovation’s Jim McLenaghan.

Cheers,

Dr. Ron

Folks,

Patty is getting ready for her meeting on "Copy Exactly" with Mike Madigan.......

It was after 6:30 PM and Patty was just arriving home.  Since Patty was working late, Rob had agreed to make his signature dish, crispy macaroni and cheese.  Patty and Pete had just finished their project to develop a copy exactly strategy for ACME.  They would present it tomorrow to CEO Mike Madigan.  The local GM, Sam Watkins, would be there too.  Technically Mike was her boss in her Senior VP position, but since she had an office at the ACME facility in Exeter, NH, she reported to Sam - “dotted line.”  Patty had been working late for weeks on this project and was glad that the greatest portion of the work was over.

As she opened the door to her house, her twin 2 year old boys ran up to her in their excitement to see their mom and nearly knocked her over.  She tussled with them for a few minutes and then went to give Rob a hug.  He had the dinner on the table and they all quickly sat down.  Rob and Patty had a "no technology" rule at meals…..no mobile phones, iPads etc.  Meal time was family time.  After discussing the events of the day, Rob’s face lit up.

“I found out today that there is something we look at more than anything else,” Rob stated.

“OK, OK, let me guess,” Patty replied.

After a number of tries, she hadn’t gotten it.

Alright, I give up, Patty said with playful exasperation.

“Indium, or really Indium Tin Oxide (ITO), it is a transparent conductor of electricity.  We look through it when we look at our computer, tablet or mobile phone screens.  Think about it, for most of us we probably look through ITO for 8 to 10 hours a day.  It’s like we have a love affair with the stuff,” Rob explained.

Patty almost choked on some of the mac and cheese on the last comment.

“Why have you become such an expert on this stuff?” Patty asked.

“Well, you remember that ACME may go into component assembly? Sam asked me to look into indium thermal interface material (TIM)  for some of the component packages that need to dissipate a lot of heat,” Rob answered.

Patty knew a little bit about TIMs, but not about ITO.

“But why did you learn about ITO?” she asked.

“Sam is worried that Indium supplies may not be enough to satisfy TIM requirements, so he asked me to look into it,” Rob answered.

“What is the conclusion? Patty asked.

“Well, Indium is about as common in the earth’s crust as silver, but a little more difficult to extract.  This probably gives it the reputation of being rare.  Fortunately for me a recent analysis was performed that showed that the indium supply will be more than adequate for the next 75 years ,” Rob said.

Rob went on, “Indium is a very interesting material, it is one of the few materials that wets glass, so it enables metal sealing to glass.  It was only discovered in 1863 and it wasn’t until the 1930s that the first practical use for indium was discovered: aircraft bearing lubrication.  In a sense, it could be argued that it is one of the materials of the future, as we are just now learning about its potential.”

While he was talking, Rob reached into his backpack and took something out.

“Look at this, or rather listen,” Rob said.

With that, he took a thin bar of metal and bent it. A crackling sound came from the metal.  Patty was fascinated.

“What was that?" she asked.

“When a thin bar of indium is bent, it gives off a sound.  It is called “Indium Cry.”  The salesman for the TIMs we are using let me borrow it for a presentation I am giving to Sam Watkins next week,” Rob answered.

Dinner was soon finished and Patty had to get the boys to bed after playing with them for awhile.  Today was Spanish day and all of their discussions were in that language.  Another day was Mandarin Chinese day.  The boys already understood the three languages spoken at home.

A few hours later, Patty lay in bed - energized by the thought of her meeting tomorrow.

When she woke up the next day, she exercised at home, ate breakfast, and took the boys to day care.  See arrived at the office 30 minutes before the big meeting.  After checking emails, she went to the conference room where the meeting would be held, to set up her computer.  At precisely 8AM, Mike Madigan and Sam Watkins arrived.

“OK Coleman, let’s get this show on the road,” Madigan commanded.

“Since our last meeting we have analyzed assembly equipment and materials to determine which ones would be best for a copy exactly strategy,” Patty began.

She then showed her third slide and spoke to it.

“The winner for component placement equipment is Optoplace, as are their stencil printer and reflow ovens.  Exactotest makes the winning testers and ElectoMaterials the best solder paste and solder preforms,” Patty went on.

“Can you explain your methodology?” Sam asked.

“We looked at what The Professor calls ‘Profit Potential,’ simply the equipment and material that gives the most profit, assuming you are running a well tuned organization.  Fortunately, since ACME has 80 assembly lines we were able to get real process performance data on all of the major machines available, ” Patty answered.

“You answer seems a little evasive, why didn’t you use ‘Cost of Ownership?’” Madigan challenged.

“Some machines cost less to own, but they are down more for assists and when they need repair, we have to wait longer for the repair man.  From what The Professor taught us, uptime is very important. Anything that hurts uptime, like a late repairman or a machine that needs more assist time, will hurt profits.  The same is true for materials like solder paste.  If they cost less, but result in line downtime for response to pause issues or some other fault, they hurt profitability.” Patty responded.

Just then Sam’s administrative assistant, Clare Perkins opened the door.

“As you requested Mr. Madigan, your guest is joining the meeting,” Clare said.

“Well Torant, looks like Coleman said you lost,” Madigan said to the new arrival.

Upon seeing Rex Torant, Patty became a little unsettled and Pete turned his famous crimson red.  Patty and Pete called him “Rex the Torrent” as he spoke so rapidly when trying to sell them something.  Both found this manufacturer’s “rep” annoying.

“Everyone, I invited Rex to the meeting.  We met at the airport last night and started chatting.  He assured me that his Pinnacle equipment line and Ultima solder paste would be the winners today since they have the lowest cost of ownership,” Madigan explained.

Torant saw the slide announce Optoplace, Exactotest and ElectoMaterials as the winners.

“My products are just as reliable and cost 30% a year less to own,” Torant fumed at Patty.

Patty had not anticipated Torant’s attendance at the meeting but had prepared for this type of question.

“Mr. Torant is correct, however Pinnacle’s component placement machines have more downtime for machine assists and, when the equipment does malfunction, it is down for repairs on average for 28 hrs, whereas Optoplace is only down for 14 hrs.  All in all, Optoplace machines are up 6 hrs more a week in a two shift operation,” Patty calmly responded.

Will Patty’s arguments win the day?  Can a 30% more expensive machine really have more “Profit Potential?”  And what about the solder paste and materials?  Stay tuned.

Cheers,

Dr. Ron

 

image

Folks,

Let’s see how Patty is doing with the latest crisis……

Upon hearing Claire Perkins inform her that Rob was in the hospital, Patty froze and her face looked ashen. She quickly recovered and got her cell phone out to call Rob’s mother.

“Mom, what has happened to Rob?” Patty said, her voice quavering a little.

“He hurt his back at the gym, he can hardly walk. He collapsed under a heavy barbell. His head was injured too. He was unconscious for five minutes. I’m almost at the hospital now,” Rob’s mother, Hilde Gunther replied.

“I’ll see you there,” Patty said.

Both Sam and Mike insisted that someone take her to the hospital, but Patty refused. 

Patty looked at her watch, it was 9AM. Rob was working a “swing shift” for six weeks and didn’t have to go into work until 10AM, so he went to the gym from 7:30 to 9AM most days. Patty had been teasing Rob that his workouts were getting too vigorous. She knew he was trying to snatch over 250 pounds as he was in a friendly competition with one of his friends, Fred, to see who would be the first to accomplish this significant feat. She wondered if this goal led to his accident.

The drive seemed to take forever, but soon she was at his emergency room bed. Rob was awake but his face was black and blue.  Patty didn’t notice her mother-in-law, as she quickly ran to Rob's side.

“Rob, what happened?” Patty cried.

“The good news is, I snatched 250!” he chuckled, which caused him to grimace in pain. “It was 260 pounds that was my downfall, I collapsed under the weight,” Rob went on.

“How bad are your injures?” Patty asked, a little frustrated with Rob’s levity.

“My back hurts so much, I can hardly walk, my face just looks bad. I’m going for an MRI in a few minutes, they’re worried I might have a slipped disk,” Rob answered, becoming much more serious.

Just then an MRI tech came.

“Well Mr. Gunther, we are going to squeeze you in, so I need to put you ‘On Deck’ for an MRI that opens up. Realistically, it could be two or three hours,” the tech commented.

Both Patty and his mother kissed Rob on the part of his head that wasn’t black and blue as he left. After Rob was taken away, Patty chatted with her mother-in-law for about 30 minutes.

Even though to some people it would seem strange, Patty had a way of compartmentalizing things, she knew she could not help Rob, except to pray for him which she had already done. So, she decided to do some work on her laptop. Fortunately the hospital had WiFi.

Patty had some unfinished business from what she learned on her trip investigating NMAC/I/O. She wrote an email to the GMs of the sites that were using that cheaper solder paste that had the response to pause problems or that required kneading before being used, suggesting that they change to one of two corporate approved pastes that didn’t have these issues. She also wrote a note to the people that were using a full wavesoldering process for a PWB that had only two through-hole components, solder preforms should be used with the reflow process for a PWB like this she told them.

As Patty finished the emails she needed to send, she observed the activities of the MRI section of the hospital where she was waiting for Rob. It occurred to her that this was a process just like assembling electronics. Instead of stencil printers and component placement machines, there was an MRI machine. There were techs that ran the MRI machines just like there were operators. The nurses were like the process engineers, and there were some medical doctors that were like the mangers and execs at her company. Instead of producing electronics, the MRI section was producing MRI scans. There was really little difference.

Patty got curious and she decided to ask the scheduling assistant a few questions.

“Excuse me, my husband is getting an MRI and I have a few questions,” she asked Sara Carter the assistant.

“Sure,” Sarah said, “go ahead.”

“About how much does an MRI scan cost?” Patty asked.

“It varies depending on the extent of the scans needed, but $3,000 is a good estimate,” Sarah responded.

Patty asked more questions and learned that there were 5 MRI units and she assessed the headcount and floorspace needed to support the MRI unit. She also found out that each of the 5 MRI units averaged 9 scans per day. It then occurred to her that she could use ProfitPro to estimate the cost of a typical MRI scan. Under The Professor’s tutelage she has gotten quite good at estimating burden labor rates, etc, which would be needed for the calculation. She got her laptop out and using ProftiPro, in a few minutes estimated that the hospital’s cost of an MRI scan should be only $390!

“Why does it cost our insurance $3,000?” she thought.

It then occurred to her that her good friend from her days at Tech, Emily Chen, was a radiology resident at the hospital. She decided to send her a note and, in addition to telling her about Rob, ask about the MRI scan cost. 

After sending the email, she asked her mother-in-law if she would like to get a cup of coffee. In a short time, they were heading to the hospital cafeteria. Before they left, they found out that Rob was just starting his 45 minute MRI scan. 

Fifteen minutes later they returned, and Patty was surprised that she had already received an answer from Emily.

“Patty, I’m so sorry to hear about Rob. You probably won’t hear the official news on his MRI until tomorrow, but I will take a look at it and call you later today. BTW, my boyfriend works in the finance department here. I’ll find out about the cost. But, your numbers sound way off.”

Twenty minutes later Rob was finished. His doctor had given him some pain killers and muscle relaxers, so Rob was a little more comfortable, but the doctor wanted Rob to stay overnight for observation. Rob soon fell asleep from the medication. Patty decided to stay with Rob and by 4PM, she asked her mother-in-law if she could pick the boys up from day care.

At 4:30 PM another email arrived from Emily.

“Patty, good news. I looked at Rob’s MRI scan and it looks fine. He probably just severely strained a muscle. He’ll be as good as new in a month or so” Emily’s note began. Emily’s note went on, ”My boyfriend looked up the cost for the hospital to run an MRI scan. You were close, it costs $410. Neither of us can believe it. Where does the extra $2600 go?”

Dr. Ron note: I have done some investigations into MRI scan costs. As surprising as it sounds, these numbers are about right, the base cost for a hospital to perform an MRI scan is in the $400 range, but they have to charge $3,000 to break even. Considering that many hospitals are non profits and are losing money adds to the confusion.  At this point, I don’t claim to understand the cost structure of running a hospital, but one would think that one of the most critical questions in the current healthcare cost crisis in the United States, would be to understand why $3,000 must be charged for a $400 procedure to break even.  

The image is of Yegeny Chigishyov snatching about 450 pounds in the 2008 Olympics.

Cheers,

Dr. Ron

Solder paste is comprised of powdered solder alloy suspended in a flux vehicle. There is a group of flux ingredients that is generically identified as "activators". It is the activators whose primary function is to remove oxides not only on the surfaces that are being soldered but any oxides that may be present on the solder powder, itself. These activators are generally "activated" by heat. The flux chemist knowingly selects activators that are relatively dormant at room temperature but become very active at soldering temperatures. Their level of activity is often directly related to temperature.

Given that the flux is in direct contact with the solder powder, this allows for the flux activators to interact with the solder powder even while the solder paste sits on the shelf. Those activators can begin to "react" with the powder, and, given enough time, can "clean" the powder surface to the point where the solder particles will actually "weld" together. So, now instead of the paste containing free-flowing powder, it contains clumps of welded together solder particles. Those clumps often increase the viscosity and can clog stencil apertures and dispensing needles. For these reasons, the paste manufacturer will require refrigerated storage of the paste in order to realize the optimum shelf life.


As a rule water-washable solder pastes often include activators that are more aggressive than the activators found in no-clean and RMA type solder pastes. This is because water-washable flux residues are designed to be washed off. So, there is no concern about the flux causing corrosion over the life of the product. On the other hand, a no-clean flux generally has milder activators, because the flux residue may remain on the device indefinitely; where corrosion would be detrimental to the performance and life of the device. As a result, no-clean type solder pastes typically have a longer shelf life and are more tolerant to higher storage temperatures than water-soluble/washable solder pastes.

A solder paste typically has a shelf life of 6 months when refrigerated. One may ask what happens if the paste has been refrigerated for 2 months, then thawed to room temperature, remains at room temperature for 12 hours and is then re-refrigerated....Will it still have a 6 month shelf life? That is a very difficult question to answer. The same situation could arise with a perishable food item that requires refrigeration, such as milk. Lets say that one buys a container of milk at the store and it has an expiration date that is 5 days away. After having it home, properly refrigerated, for 2 days, one of the kids leaves the milk on the counter for 3 hours before anybody notices it and puts it back in the refrigerator. Can one expect the milk to stay good for the remaining 3 days? What about if it is left out of the refrigerator for 1 hour? or 5 hours? You can see how difficult the questions become to answer. What is the impact if a solder paste is exposed to elevated temperatures when it is 3 days old or 3 weeks old or 3 months old or with 3 days left to expiration????? The answer is not fully known. It is impossible for the solder paste manufacturer to study every possible scenario for its impact on the shelf life of the paste.

The best and only sure approach is to refrigerate solder paste immediately upon receipt and only thaw when needed, in amounts that will be completely consumed. Avoid thawing and re-refrigerating pastes as much as possible, in order to take advantage of the full shelf life.

The particle (mesh) size of the solder powder can also impact shelf life. As the powder size decreases, the surface area per volume or mass of powder drastically increases. More powder surface area means more area for the flux to react with, and more surface area for welding to occur. Therefore, a type 3 solder paste that has a shelf life of 6 months may not provide a full 6 months of shelf life with a type 6 solder powder, all other things being equal.

For the most part, solder paste manufacturers are conservative in assigning shelf life. It is highly unlikely that a properly stored solder paste's performance is going to collapse 1 day after the expiration date. In fact, depending on the paste, it may still be good for months beyond the expiration date.

How does one know if their solder paste is still usable? This can be determined rather easily. As mentioned earlier, one artifact of a degrading paste is a rise in viscosity. So one can perform a simple printing or dispensing test to see if it still performs adequately in that regard. Another aspect that often suffers is coalescence. As the flux degrades it looses its ability to adequately remove oxides on the solder powder. In order to gauge the degradation, it is best to put a small amount of paste on a non-wettable substrate, like a piece of ceramic. Reflow the paste and see how well it coalesces. If coalescence is good, the solder paste will reflow into a ball, surrounded by a flux pool that is relatively free of uncoalesced solder particles. If the paste has significantly degraded, the paste will not coalesce well and there will be a significant amount of uncoalesced solder particles in the flux pool.

Please see this IPC test method for determining the coalescent properties of a solder paste.

Folks,

Rob heads to Guadalajara to solve the QFN voiding problem......

As Rob sat on the airplane, he was excited to go to GDL (Guadalajara, Mexico) to help solve the voiding problem. He knew Patty would be a little peeved that he asked for Pete to come along, but she was gracious, recognizing that Rob would benefit from a success in this effort.

As the plane circled for a landing, Rob was preparing for the somewhat comical trip through customs. He always thought that the red light/green light method of determining if they were going to search you bags was unusual. Oh well, go with the flow.

The ride from the airport was about 40 kilometers to the factory through GDL’s bustling traffic. After arriving at the plant Rob was relieved to see that Miguel Mendoza was there to meet him and Pete. Rob had worked with Miguel in the past and respected him as a process engineer. Miguel told them that a kick-off meeting was scheduled with the site GM, a fellow from the US named Grant Wilson.

As the meeting started, Rob introduced himself to Wilson in Spanish.

“Wow,” Wilson chuckled, “when asked if I am bilingual, trilingual or American, I have to say I am American.” “But, I am taking Spanish lessons,” he continued.

Rob looked at Miguel and saw him roll his eyes. But Rob thought it was at least a nice gesture that Wilson was taking Spanish lessons.

“Perhaps someone could share what actions have been taken and what the status is,” Rob suggested.

“Miguel, could you give Rob an overview of where we are” Wilson asked.

Miguel began, “The warranty send back rate is 5% on Druid phones. Almost all of these failures have been traced to high powered QFNs that have significant voiding under the thermal pad. The voiding percentage is about 50-70%. About a week ago we obtained Derrick Herron, Dr Yan Liu and Dr Ning-Cheng Lee’s recent paper, Voiding Control at QFN Assembly, at SMTAI 2011.  We changed our stencil design, as suggested in the paper, to allow for venting of the solder paste volatiles and voiding went down to 30 to 50%.”

“What level of voiding would be acceptable?” Rob asked.

“We’re not sure,” Miguel answered.

“So it seems we have two issues, one is to determine if 30 to 50% voiding is OK and the other is to see if we can reduce it further,” Grant Wilson reasonably commented.

“My sense is that we need to be in the less than 30% range,” Rob added. “This may require that we use solder preforms. Voiding is caused by outgassing but also by insufficient solder,” Rob finished.

“OK, you two go and solve the problem and get back to me. You have 3 days,” Wilson commanded.

Rob, Pete, and Miguel headed off to get started on their assignment. Rob was really glad Pete was there.  He was an expert in setting up and optimizing the component placement machines that were at this site.  Fortunately, Rob had also brought some solder preforms with him, expecting that they would be required. A call to the QFN vendor confirmed that less than 30% voiding should be the target. Rob looked at the data and x-ray images of the work that Miguel and his team did to reduce the voiding by improving the venting of the flux volatiles. He was impressed. But he didn’t think it would be enough.

(Dialogue translated from Spanish)

“Miguel, I’m almost certain that we will need to use solder preforms on the two most critical QFNs,” Rob began. “There are two major reasons for voiding, the first is flux volatiles forming voids, the second is solder starvation. Most people don’t realize that solder paste is only 50% by volume metal. In cases like this, where we really need low voiding, often the only path to success is to use solder preforms to add solder metal,” he finished.

Rob then showed Miguel Seth Homer’s SMTAI 2011 paper Minimizing Voiding in QFN Packages Using Solder Preforms. This paper describes the process steps needed to achieve a successful QFN solder preform process. Rob and Miguel spent the better part of a day setting up one assembly line to assemble with the solder preforms using this paper as a guide. They assembled 100 phones and the voiding level was 10.5%.

Early the next morning, they met with Grant Wilson.

“By the smiles on both of your faces, I gather you were successful?” Wilson asked.

Rob went on to explain how they determined that solder preforms were needed. He explained the process and waited for questions.

“What do solder preforms cost?” Grant asked.

“They are about $0.02 (US) in quantity, but understand that your warranty cost per $200 phone is at least $10 right now (0.05x200),” Rob answered.

“Did you have to slow the process done?” Wilson asked. “I have been a fan of the work that you and Patty Coleman have done with The Professor, you have convinced me of the importance of throughput,” he finished.

“The Professor has pointed out that almost never is a line completely balanced. Your flexible placers were waiting four seconds for the chip shooters. We put the preforms on the flexible placer and tuned up both machines by optimizing the feeder placement. The cycle time is now 1.25 seconds faster for the 3 phone per PCB card,” Rob answered.

“I’m curious, what was the greatest challenge?” Grant asked.

“Rob pointed out that the correct placement of the preform on the solder paste deposit for the heat sink part of the QFN is critical. We needed to assure that the preform was pushed into the paste far enough to leave a ring of paste around the preform to assure good mating with the QFN.  We couldn't have done this without Pete, he really knows the placement machines,” Miguel answered.

Miguel then showed Wilson an image from Seth Homer’s paper that displays this situation .

“Guys thanks for the great work. I have to admit that I didn’t really know anything about solder preforms, before today. In certain cases it is obvious that they can be lifesavers!” Grant summed up the situation.

“To celebrate your success, I’m treating for dinner tonight at the Santo Coyote, let’s meet there at 7PM,” Wilson suggested.

“Thanks,” Rob, Pete, and Miguel said in unison.

Santo Coyote was Rob’s favorite restaurant in Guadalajara, but it was Patty’s too. Rob was a little sad she couldn’t join them.

 Epilogue: Three months later it was confirmed that warranty send back rate was approaching zero.  Miguel was promoted to senior engineer for his part in the solution to this costly problem.

Cheers,

Dr. Ron

 

 

Last week I spent some time in the simulation lab with Eric Bastow, verifying the printing characteristics of our newest low temp metallization paste LT-918. Due to its current success with a variety of customers, we needed to take production capacity to the next level. New equipment was purchased to keep up with the demand, but there is always the chance that material may not perform the same when it is made in substantially larger batches. Our testing confirmed the printing characteristics of the material made on the new equipment surpassed that of previous batches. That’s good news for everybody.

As you can see from the picture, we used a standard printer designed for stencil printing solder paste onto electronic circuit boards. The printer was not the only similarity to solder paste printing though. An interesting characteristic of LT-918 is that it has a higher viscosity than most metallization pastes, which helps with print definition. The high viscosity of LT-918 helps it print like a solder paste, this is great for solder paste printers (like Eric and I, and many of you for that matter) from the SMT and semiconductor assembly industries.

In my opinion, LT-918 is the best metallization paste currently available for interconnecting thin-film cells. It has not only excelled in printing, it also has industry-leading resistivity scores, and has passed customer reliability testing including thermal cycling, damp heat stability, and accelerated UV tests. Much of the data that we can share will be available soon as a product brochure that we hope to have ready for you at EU-PVSEC in September.

Solder starvation is a serious electronics assembly issue - with a very simple solution.

Solder starvation occurs when adequate volumes of solder are not available to effect a perfectly-shaped solder joint. The consequences include:

• weak solder joint strength
• open solder joints
• intermittent short circuits
• reduced first-pass yields
• increased inspection
• increased rework
• field failures
• damage to your company's brand & image
• reduced sales and profits

Frequently, solder starvation occurs in Surface Mount Technology (SMT) when solder paste deposits are inadequate.  This happens because: 

• The single-thickness stencil is designed for the majority of smaller components, starving the few larger components of solder volume.
• High-use interfaces, such as connectors and USB ports, require extra solder - to assure their solder joints survive the constant use in the field.
• Smaller, more tightly compacted circuit boards don't allow for deposition of enough solder paste.

So, how do you solve this increasingly common problem without impacting your process or your cost? 

Solder Fortification® preforms are the simple answer:

• You can add solder just where you need it without overprinting solder paste or working with step stencils.
• Preforms deliver precise, repeatable volumes of solder.
• Preforms can be added during your existing SMT process with existing pick & place equipment.
• Preforms eliminate the need for rework or hand soldering at the end of the process.

For more information, contact me at solderfortification@indium.com or visit our web site at www.indium.com/solderfortification.

Carol Gowans
Market Manager

Folks,

When the industry was preparing to transition to lead-free solders almost ten years ago (can it have been that long), tin-bismuth solders were serious candidates. Their low melting point, of about 138C, made these solders interesting candidates to replace tin-lead solder. However, if contaminated with lead, tin-bismuth solders can produce a eutectic phase that melts at 96C. In such situations the resulting solder joint exhibits poor performance in thermal cycle testing. Since early in the transition to lead-free solders it was expected that there would be numerous components and PWBs with lead-based surface finishes, this property made tin-bismuth solders unacceptable.

Another aspect of tin-bismuth solders is that they expand on cooling. This phenomenon can result in fillet lift in through-hole solder joints.

However, as we are now well into 2011, almost no components or PWBs have lead-containing finishes and many portable electronic devices have no through-hole components, so it may be time to reconsider tin-bismuth for some applications.

Some years ago, Hewlett Packard (HP) had performed work to show that adding 1% silver to tin-bismuth solder enabled this alloy to outperform eutectic tin-lead solder in 0 to 100C thermal cycle testing. Even at these low reflow temperatures, HP demonstrated solder joint strength with SAC BGA solder balls that was 65% that of tin-lead solder. Expanding on this work, Indium Corporation's Ed Briggs and Brook Sandy performed stencil printing and reflow experiments consistent with the requirements of current miniaturized components using this 57Bi-42Sn-1Ag solder. All of their results were promising. Ed presented a paper at SMTA Toronto,summarized the Hewlett Packard work, and reviewed the results of this new work.

So for applications consistent with 0-100C thermal cycling, 57Bi-42Sn-1Ag solder may be something to consider if the high temperature of SAC solder paste is an issue to components or PWBs in a product

Cheers,

Dr. Ron 

PS: Read my follow-on posting about bismuth.

The image is of a bismuth crystal with an iridescent oxide surface from http://en.wikipedia.org/wiki/File:Wismut_Kristall_und_1cm3_Wuerfel.jpg

Here's an example of a hot new B2C video, being shown on Air New Zealand flights. It features fitness guru Richard Simmons, up to his usual antics. The same old message delivered in a captivating, entertaining way.




Can this sort of thing be done in the B2B arena?


Let me know if this next vid makes sense to you:



All such vids need to be understood "in context". The Richard Simmons/ANZ vid needs to be viewed on a flight, of course. And knowing something about traditional (booooring) safety vids AND Richard help deliver the punchline.

In my case, being a surface mount technologist (an electronics assembler) who is familiar with stencil printing solder paste is required to "get it". They are my exact target audience. And the persona used in this branding video is an engineer who actually has a life, but who thinks about his/her work at odd times throughout the week.  Poking fun at that is the theme.

Share your thoughts and examples. Thanks!

Folks,

Patty had been working with engineering on a new product that needed a very precise and controlled volume of the stencil printed “brick” of solder paste on the PWB pads.  The product had many 01005 passives and CSPs with 30 mil spacings and the application was “mission critical.” So solder joint integrity was critical. The critical factor in obtaining this solder joint integrity was a consistent volume in the stencil printed brick. Her favorite solder paste gave a Cp and Cpk of 1.5 in 500 prints. The upper and lower spec limits were 60% and 140% of the aperture volume.

Purchasing called to tell her that XLK company just announced a solder paste with a Cp and Cpk greater than 3, under the same printing conditions that this product required. Needless to say Patty was skeptical. When she looked at the report, she groaned. The data were collected by Mort Bittler. She had seen him give several presentations and he always seemed to misrepresent the data to make his company’s solder paste look better than it was. She was on her way to a team meeting and expected that this new “break through” would be discussed.

As the meeting came to order, the VP of Engineering, Todd Hamilton, spoke.

“I saw this new data from XLK with a printing Cpk = of 3.72, we will use this paste,” Todd commanded.

“What a minute,” Patty responded, “the decision on which solder paste to use is with my group.”

“But you group has dropped the ball, how could you not know about this superior paste?” Hamilton challenged.

“We have evaluated their pastes continuously, they have always been second rate,” Patty shot back.

“Well things have changed, get with it Coleman, this project is too important,” Todd shouted.

Patty was really angry, technically Todd was her superior, but she found his attitude and words insulting. Using her last name was a bit unfriendly too.

“I’ll travel to XLK tomorrow and review their data,” Patty responded, her voice shaking more from anger than anything else.

She called Mort Bittler and he was available, so he agreed to meet with her the next day.

As she hung up, Pete showed up at the door, “Hey kiddo, how’s it going?” Pete asked.

“You were at the meeting, so what do you think? Hamilton impugned all of us,” Patty said flatly.

“Anyway I can help?” Pete asked.

“Why don’t you go with me to XLK tomorrow, it might be good to have two people check the data.

Fortunately XLK was only 120 miles south of their southern New Hampshire office.  

Pete had become one of her best friend’s in the past year. They spoke in Spanish the whole way to XLK to get their skill level up. Patty had also taught Pete some Mandarin, but it was slow going. After 120 minutes of discussing the PGA Tour vis a vis Tiger Woods, in Spanish, they arrived at XLK. Mort was waiting.

Mort was 45 years old, with a thick Boston accent. He came across as being knowledgeable ….. to someone who wasn’t knowledgeable.   

After brief pleasantries, Patty asked to see the raw data.

“Patty, I already made the calculations, why do you need to see the raw data?” Mort asked.

“The Professor always told me to ‘look at the raw data,’” often one can glean things that the final calculations don’t show,” Patty answered evenly.

“Well maybe later, let me show you how we took the data first,” replied Mort evasively.

Patty and Mort went to the printing lab and Patty noticed that Pete was not with them.

After verifying that the printing process was reasonable, Patty asked if she could have a little time with Pete……if she could find him.

Patty and Mort found Pete in the break room. 

“Pete let’s pow-wow for a while,” Patty said.

Mort said he would go answer some emails and they would meet in 30 minutes.

“Pete, where have you been? You’re not going to embarrass me again are you?” Patty pleaded.

“Me embarrass anyone?” Pete sheepishly replied.

“I found the person who took the data, Beth Thompson,” Pete went on, “she told me they average Cpks.”

“Not again, Patty groaned, we just went through that with a vendor last week, when will they learn that it’s wrong to average Cpks.

In 30 minutes they went to Mort’s office. All agreed to go lunch.

After ordering, Patty asked, “Mort what are your thoughts on averaging Cpks?”

Mort seemed defensive, and he squirmed a little, finally he said, “seems OK to me, it’s just like averaging golf scores.”

“What about the non linearity of the standard deviation in the Cpk equation?” Patty asked.

Mort was clearly not grasping the issue.

Patty continued, “If you have two sets of data and calculate the Cpk of each and average them, you will not get the same result as if you calculated the Cpk of the data added together. One of the reasons is that the standard deviation is non-linear. For the same reason it is wrong to add Cpks together”

Patty came right out and asked, “Did you average the Cpks?”

“Yes,” Mort said glumly.

“Let’s look at the data when we get back from lunch,” Patty insisted.

When they looked at the data it showed Patty’s point, four runs, of 100 samples each, had Cpk’s of around 1.2 to 1.3 and one run had a Cpk of 15.56. The average Cpk was 3.73, but if one takes the data all together, the Cpk is 1.58. Patty had calculated the total Cpk on the spot with Minitab.

The Cp and Cpk Data.  The correct results, calculated by Patty, are in the last row.

“But the 1.58 still is quite good,” Mort pleaded.

“But the data suggest, that run 5 is a fluke, it is clearly not from the same population as runs 1-4. Let’s go out to the lab and run another 100 data points to see if we can reproduce run 5,” Patty asked, while essentially insisted.

 

They ran another 100 and the Cpk was 1.28. On the way over Pete whispered in Patty’s ear that he had more vital intel to share with her on the way home.

With the end of the data collection, Patty and Pete were done, so they headed home.

“OK, what is the vital intel you need to share with me?  she asked Pete in Spanish?

“While you were collecting data with Mort, I visited Beth again. She told me that Mort had her collect 150 data points on run 5 and he threw out the 50 points furthest from the mean. You were right, run 5 was from another population, a cheating one,” Pete chuckled.

“Well, I guess we will still use our favorite solder paste,” Patty summed up.

 

Cheers,

Dr. Ron

Tombstoning, simply, is the wetting of one side of a component before the other side, which causes the setting forces of the solder to lift the component like a drawbridge.  Sometimes, it even cause the component to complete stand, like a tombstone.

There are several ways to counteract whatever cause is making the defect occur.  All of them include either getting the component to come to the same temperature at the same time, or allow for flexibility in the melting point of the solder during reflow.

Below are some ideas on how tombstoning can be eliminated.

 

1.   Eliminate Nitrogen reflow - Nitrogen reflow prevents the additional build up of new oxides on surfaces and the solder alloy, and allows more activator to be used for wetting, increasing the wetting force.

2.   Lower the delta-T across the board and component to <10°C -  This allows for more stable temperatures through liquidus, which equalizes the wetting on both sides of the affected components.

3.   Slowing the ramp rate of the components through reflow to ~0.5°C/s - This allows both sides of the component to come to temperature simultaneously.

4.   Introduce an anti-tombstoning alloy, such as the Ind100 (62.6Sn 37Pb 0.4Ag, which has a 4-6°C plastic range.

5.   Increase placement pressure and depth, which uses the tackiness of the paste to hold the component in place.

6.   Proper placement ensures that the component is centered between the pads.

7.   Stencil design ideas, such as home plate or reverse home plate, takes advantage of the alloy’s wettability and uses it to your advantage to solder the part to board, rather than using the wetting of the alloy to lift the part.

8.  Ensuring proper board and Pad design makes sure that there is not solder-robbing, where the solder flows along a trace, and doesn’t leave enough for the component.

 

These are tried and true methods that I have used in the past with customers that have seen tombstoning.

Folks,

Let’s assume you are trying to improve the productivity of your SMT assembly lines. You work at a facility that manufactures high volume products with a high mix. The first aspect of your process that you attack is stencil printing. You find that your current paste stiffens up when the printing process pauses. So, after a pause, you have to wipe the solder paste off of the board and reprint the board.  

Let’s then assume that you replace this paste with a better one that has good response to pause (i.e. you don’t have to reprint a board after a pause). Let’s also assume that this elimination of reprinting boards results in a modest increase in productivity, say 2%. In other words, you are able to process 2% more boards in the same amount of time. No big deal right? Hardly matters? Wrong! In a typical assembly facility, a 2% increase in productivity results in more than a 6% increase in profits!

You continue working and garner 2% more increase in productivity by balancing your placement machines, improving assist time, and developing a preventive maintenance plan. You have now increased productivity by 8%, but profitability increases by more than 24%!

The calculations that support these conclusions, from ProfitPro,™ are shown as a graph of profitability increase versus productivity increases. All of these calculations support the “Law of Exponential Profits.” This “law” (OK it was developed by me, so maybe it isn’t a law) states that an incremental (e.g. 2%) increase in productivity results in an exponential (e.g. 6%) increase in profits.   The results will vary depending on the assembly facility, but the basic idea is always true.

The bottom line: Investing in productivity always pays.

How is your productivity improvement plan coming?

Cheers,

Dr. Ron

Folks,

The conclusion of the Bob and Fred break saga......

Phil stared, “The uptime on AXI's four SMT production lines is…….”

Fred and Bob were waiting for the good news of 38.1%.

“…9.8%.” finished Phil.

At this, Fred and Bob became red in the face and immediately shouted at Phil.

“We saw the numbers that Sarah took they showed a 38.1% uptime,” yelled Bob.

Neither Bob or Fred had noticed the different colored entries.

“That’s your ‘excuses uptime’,” said Phil.

“Your ‘no excuses uptime’ is 9.8%. It was 9.9%, but yesterday was a really bad day, and it went down %0.1% for the total time Sarah was tracking it.

“@#X*&^%,” said Fred and he looked like he might take a swing at Phil.

Finally Karl Hermann interrupted. He was a thoughtful, kind man, but when he spoke, Bob and Fred fell silent.

“Where are we losing the time?” he asked Phil.

Phil then went into a detailed discussion of misplaced stencils, component shortages, solder paste response to pause problems, etc, etc. 

Phil then showed some profit calculations from ProfitPro™ software that he had performed the day before. Phil had essentially made a cost model of the entire AXI assembly business. To assure the accuracy of his model, he checked the final figures with AXI’s CEO. 

 

“Currently each of AXI’s four lines produces $25M in sales and about $1.22M or about 5% profit, with uptime at 9.8%. The first line in the ProfitPro™ output shows these results,” Phil started.

He continued, “If we can increase uptime to at least 15%, which should be easy, we will achieve the results in the second line. Production increases by a little more than 50%, but profitability more than doubles. Oh, and this includes giving everyone a 50% raise.”

Phil had checked with Karl, to see if it was OK to share this interesting tid-bit. Karl had agreed, that would be the plan, if the gang could get uptime to 15% or more, the 50% salary input would stand.

Fred was digesting this and then said, “That’s impossible, profits can’t double if we only produce 50% more product.” But he was smiling at the thought of a 50% raise.

Phil responded politely, “Fred, you must not be aware of the ‘Exponential Law of Profits’.”

“The only Expo I know about is the one I went to a few years ago and drank a lot of beer,” Fred said with a smile.

After the chuckles died down, Phil continued. “When a small increase, say 3%, occurs in production, with no increase in fixed costs, such as labor, overhead, etc, each unit costs dramatically less to manufacture, versus the previous units, and 3% more are produced to sell, the result is often a 5 to 7% increase in profits.”

There was a murmur of understanding in the room.

Karl then asked, “But how do we improve our uptime?”

Phil suggested that he felt that the best way to solve the problem was to implement the productivity improvement plan as a Kaizen event with Fred and Bob as the lead implementers. At this note both Fred and Bob perked up. Phil then discussed his proposed action plan. All in the meeting added their suggestions and it was agreed that the Kaizen event would be immediately enacted.

In a Kaizen event, changes are made and implemented rapidly, typically off shift. As Fred and Bob normally worked from 7AM to 3:45PM, the Kaizen event started a 4PM and was to end at 10PM. The team asked Phil to lead a brainstorming session to identify lost time. Sarah and Juan participated enthusiastically in the process.

Phil wasn’t worried that they would get the uptime to 15%. He knew that having a systematic approach to manufacturing was critical, however, he rightly believed that if Fred and Bob were motivated to solve the misplaced stencils, component shortages at the line, etc, uptime would likely easily be 20% or more.

Epilogue:

After the Kaizen event, line uptime went to 21% and steadily grew to 25% or better. Everyone did get a 50% raise as Karl had promised.   Karl even implemented an additional incentive, at the end of each month if uptime was greater than 20% the workers were awarded a bonus tied to the uptime percentage.

Cheers,
Dr. Ron

(continued from previous post)

“Fred break, Bob break?” Phil asked.

Folks,

The "Fred and Bob Breaks" saga continues,

“Fred is the tech responsible for the stencil printer and AOI unit, whereas Bob owns component placement through test,” Chuck started. “The job on line 2 was ready to go, but Fred had the wrong stencil. It typically takes him 30 minutes to find it, so we went on a break. Line 2 is our line.” Chuck finished.

At that the group chanted, “Line 2, Line 2.” The camaraderie and spirit of the team was obvious. A good thing, Phil noted.

“But actually we get more breaks because of that crummy new solder paste,” another fellow, Ivan, chimed in, with a slight Russian accent.

At that everyone groaned. There were murmurs of, “that stuff is crap," etc.

“Why is that?" Phil asked.

“Well, if the line is down for a few minutes for replenishing the components on the placement machines or some other reason, the paste stiffens up and it takes 30 minutes to knead it or replace it with fresh paste and then to get an acceptable print on the AOI. The new paste is $0.015/gram cheaper than the old one, but it seems like we are losing a lot of time with it.” Chuck replied.

Everyone shook their head in agreement.

“But look on the bright side, Juan wouldn’t be getting his degree if it weren’t for Fred and Bob breaks. And he wouldn’t have Sarah as a girl friend,” a chap named Andy added.

Everyone burst into laughter again, and a few whistled. Sarah turned as red as a rose. 

At that point Bob burst into the room and said that line 2 was back up and the group went back to work. As Juan left the room, Sarah introduced him to Phil.

Phil then asked, “What is a Bob break?”

“A ‘Bob Break’ occurs when the line goes down because of a lack of components, or a test or oven issue. It seems as though AXI is quite organized, with the white boards being used for preparing for future jobs. However, both Bob and Fred will fill in the white board and then, when it comes time to run the line, the stencil or components are still missing. They don’t seem to get it that this lack of attention to detail kills productivity,” Sarah summarized.

“Why was Juan in the back of the break room by himself?” Phil asked.

Sarah turned red again and answered, “He got is two-year degree four years ago at Tyler Community College. He now goes to Tech taking 2 or 3 classes at a time for his BS in engineering. Mr. Hermann kindly lets him work flexible shifts to accommodate his studies. We get so many Bob and Fred breaks that he does his homework then.” She almost stopped talking and then she blurted out, “OK, OK, we’re dating.” She looked relieved to get it out in the open.

She then went on to explain how Juan was an operator, but Karl Hermann told him he would become an engineer when he finished his courses this term. Phil chuckled inside to be a witness to this little romance.

He then told Sarah that he wanted to go back to the shop floor, but he made an appointment with her to discuss the uptime numbers that she had measured for the past two weeks.

He continued to observe a few Bob and Fred breaks, and that few lines seemed to be running. On the plus side, all lines seemed to be time balanced between the component placement machines, and the evidence of good Lean Sigma practices like 5S and the 7 Mudas was impressive.

As 4PM approached, Phil headed to his meeting with Sarah. She opened an Excel spreadsheet on her laptop and Phil was shocked to see an uptime of 38.1% prominently displayed. He then looked at the entries and saw that many of the 1s (a “1” indicating that a line was up when Sarah checked it) where colored, some blue, some red, and a few green. All of these colored 1s also had an Excel comment flag. Phil could see it coming.

“Why the colored 1s?” he asked Sarah.

“Fred and Bob came to me all during the days I was recording the data. I would score a “0” (the line is not running) and they would say that I should score a “1” because they couldn’t find the stencil or components, etc, etc. When they told me to do this, I would score a 1, but if it was a Fred break, it was a blue 1, a Bob break, a red 1 and something else would a green 1. Fred and Bob argued that many times when I scored a 0, that it wasn’t normal it was just a fluke. So they insisted I put a 1 in, I did but I color coded them. A fluke, right, look at the colored 1s, everything is a fluke then!” she finished in disgust.

Sarah was skilled in Excel however, and she wrote a formula in one cell that would only count the black (non-colored) 1s. This cell showed that the uptime was only 9.9%.

Phil quit for the day and went to his hotel. The next day he planned to observe the line some more and develop his suggested action plan.

On the third day he gave a summary to Karl Hermann, Fred, Bob, some of the managers, and most of the engineers. Phil started off by discussing uptime. Fred and Bob had been to some SMTA and IPC meetings and knew that 30-35% uptime was quite good, so they were anticipating praise to be heaped on them by Phil.

Phil stared, “The uptime on the four lines that AXI has is…….”

Fred and Bob were waiting for the good news of 38.1%.

Will Fred and Bob be happy with the uptime numbers?  Stay tuned.

Cheers,

Dr. Ron

I just visited a customer that was converting from water soluble solder paste to no-clean. Not exactly a slam dunk transition as this customer found out.

During my visit, solder balls and solder beads were observed in the no-clean flux residue adjacent to discrete components (capacitor/resistors). These could potentially be a reliability concern…electrical shorts.

In water soluble processes, solder defects such as solder balling and beading can be washed away in the cleaning process…no worries. However, introducing a no-clean solder paste often requires that the process be “cleaned” up a bit. Here are some ways to do it:

STENCIL DESIGN:
My first step was to investigate the stencil design for these discrete components. Why? Because, since water soluble post-reflow residues (including solder balls & beads) are washed away, many customers will opt to place as much solder (1:1 ratio) as possible on the pads - to achieve a good solder joint. This is especially true for military or medical applications where a robust solder joint fillet is vital. However, because no-clean residues are typically not cleaned, the solder balls and solder beads remain in the flux residue and may produce electrical shorts.

When printing in a 1:1 ratio, especially if the stencil is thicker than average, solder paste is often pushed under the component and onto the solder mask during component placement. Upon reflow, the sub-component solder paste may not pull back into the solder joint. This is one way that solder balls/solder beads are produced.

No one wants to hear that they need to buy new stencils with reduced apertures, but I did recommend, in this case, that some aperture reduction be considered (generally down to 0402 components). Usually a 10-15% reduction, with home-plate or similar design, is common. Many stencil manufacturers are fully aware of the issue and can make suggestions on aperture designs.

REFLOW PROFILE:
Simultaneously, the reflow profile often needs to be adjusted. In the preheat portion of the typical reflow profile, the first few oven zones are used to drive off flux volatiles, making the paste less "mobile". A balance in the ramp rate is vital; too fast - and small “explosions” may cause paste to spatter into other areas; too slow - and two bad things happen: the flux will spread excessively and the flux activity can be exhausted.

Good Starting Points:

• Ramp rate (IMPORTANT: not max slope, see "Best Practices Reflow Profiling for Lead-Free SMT Assembly" for reference): 1°C/s
• Initial first zone setting: 100-110°C

COMMENT to share your solder paste transitioning story or question. Thanks!