Indium Corporation Blogs

It is no secret that automotive semiconductor customers are becoming increasingly demanding. The "under the hood / bonnet" electronics environment is arguably one of the most thermally stressful environments on the planet. Electronics close to the engine block can experience extremes ranging from frigid winter cold to tropical heat, with the added heat source of the adjacent internal combustion engine.

The moisture sensitivity level (MSL) standard from JEDEC / IPC was developed to cover the moisture-absorption and "popcorning" effects of polymeric overmolded materials, but has been expanded in usage to cover a variety of different packaging situations and failure modes. The standard does allow for a certain amount of delamination, even under the MSL1 conditions usually required by automotive semiconductor customers. However, now "zero tolerance for delam" is the most common request from automotive design engineers. In order to meet this need, both overmolding materials manufacturers and leadframe suppliers have been working on how to drive to zero delamination. Leadframe manufacturers have developed a variety of approaches to their products that enhance the adhesion between the leadframe metal itself and the overmolding compound. Usually, this takes the form of physical and chemical texturing of the copper, using a process such as brown oxide formation.

It is no surprise that this need for adhesion enhancement (AE) drives leadframe treatments that are antithetical to the need for formation of void-free, high conductivity electrical connections between the die and the leadframe - basically, it messes with the solderability of the preform or solder paste. In order to get around this issue, leadframe manufacturers have increasingly moved to the use of spot-plating of silver onto copper, with thicknesses ranging from 2-9microns. Why is the silver so thick, in comparison to silver sputtering onto the die surface? Simply because copper diffuses very quickly into the silver, so a thicker silver layer leads to a longer shelf-life for the leadframe. Note also that plating does not have as good process control as sputtering, but it is a lot cheaper and faster.

You can see (below) a schematic of solder paste printed onto one of these leadframes.

An emerging failure mode is one of incomplete wetting onto the leadframe, leading to failures at the sites where solder has failed to flow over the silver plated area completely - "delamination sites" - (below). The flat, shiny, silver finish is not a suitable surface for overmolding compounds to bond to.

So why isn't the solder wetting well? The answer becomes clear pretty quickly when you do some back-of-the-envelope calculations of the expected final silver content of the finished joint. Let's assume some bondline thicknesses (BLT) is (25,75microns) of a solder containing 2.5%Ag (such as Indalloy 151 or 163) and the plating thickness is (3-9)microns. Typical plating thicknesses of 2-9microns may be seen, based on a recent customer survey), with a mean around 3microns.

So what is the silver content of the final joint, assuming all the silver is dissolved?

The calculations, therefore, show that it is from 6 to 27% silver. The 27% level is well beyond the solubility limit of silver in these types of solder, and in fact in most solders, at the expected soldering temperatures. The mechanism of non-wetting is clear: solder can no longer wet onto silver, once it has become filled with insoluble intermetallic particles.

The message to power semiconductor component suppliers is:

• Maintain the silver thickness at a consistent, low level: set up tighter specifications on the silver spot-plating from your supplier.
• Update your incoming quality control inspection so you can be sure you are getting what you paid for in terms of thickness of silver and consistency.
• Manage leadframe inventory so you run leaner, so you do not run into leadframe lifetime issues with copper diffusing through the thin silver layer and oxidizing (solderability / voiding problems).

You do have an alternative (moving to an alternate solder type), but then you are into a lengthy requalification procedure.

As always, please contact me if you need assistance.

Cheers!  Andy

Being the Indium Corporation, we know what indium is, where it comes from, and how to use it.  But sometimes we forget that not everyone is as immersed in indium as we are.

So what is indium?  Of course it is an element with an atomic number of 49, an atomic weight of 114.818amu, a relative density of 7.31g/cm³, and a melting point of 157°C.  I have known that for most of the 27 years I have worked at Indium Corporation, but what exactly does that mean?

Well, the atomic number is important because it is the number of protons in the nucleus - and this is what gives each element its physical characteristics.  It also places it in the periodic table (directly to the left of indium on the chart is cadmium which has an atomic number of 48 and to the right is tin, which has an atomic number of 50).  This puts indium in the group of metals known as "Other Metals", along with bismuth, tin, zinc, antimony, gallium, and germanium.  The atomic weight is a measurement of the total number of particles in the nucleus of the atom.  If you want to know more about protons, electrons, and neutrons, go to the Jefferson Lab site.

The specific gravity or relative density of an element, which, in the case of indium, is 7.31g/cm³, depicts its relative density compared to water.  If the relative density of an element is less than one, then it will float in water.  If it is greater than 1 then it will sink.  If you compare indium's relative density to that of lead, which is 11.35, you will see that, if you had a piece of each material cut to the exact same dimensions, the lead would be heavier than the indium.

Between the atomic number and the specific gravity, I use the specific gravity more often.  It is used in a formula to find the weight of a solder part, or of a length of wire or ribbon.

So where does indium come from?  Since indium is an element, it comes from the earth's crust.  It is generally refined as a by-product of zinc ore mining.  There is an ongoing debate about the availability of indium.  But a lot of work is being done to create more efficient extraction methods and reclaim, particularly of ITO targets, to assure an adequate indium supply for existing and emerging technologies for decades to come.

Okay, now for the fun part. Where is indium used?  It would probably be shorter to say where it ISN'T used!  If you are involved in any of the following areas, you have a need for indium:

• Cryogenic sealing
• Hermetic sealing
• Low temperature soldering for temperature sensitive devices
• Step soldering
• Solar panels (CIS & CIGS)
• Coatings for displays and glass (ITO & IGZO)
• Pb-free soldering
• Fuses
• CTE mismatch when bonding dissimilar materials
• Thermal management

Indium is certainly one of the more versatile metals because it works and plays well with others.  Read more about indium:

Indium Solder and Sealing

Thermal Management

Heat Spring

Low Temperature Solder

We like new challenges and applications, so if we can help you (or you think you can stump us), email me at cgowans@indium.com.

I recently noticed something that appeared in a 3^rd party lab report that a customer shared with me. This lab report was an analysis of a NanoBond^® the customer had performed and sent out to verify. The thing that struck me was that the technician reported “This sample exhibited small fractures in the [NanoFoil^®] core material which we have seen before…” I started thinking about this, and there are very few products in the solder world other than NanoFoil that you would like to crack. In this case, cracking is a good thing!

You wouldn’t expect most soldering products to crack, but NanoFoil^® isn’t like other soldering products. As the aluminum and nickel layers react, the foil shrinks and tends to curl. Since the curling action of the foil is restricted, the foil cracks. Solder flows between the cracks and bonds to the reacted NanoFoil^® as well, creating a sort of micro-scale concrete.

Pretty interesting, huh? Here’s a link to learn more.

…And here’s a link to try it out!

Folks,

I was at APEX 2013 San Diego this past week.  San Diego is a great venue for the show, but I always forget how cold it can be (55-65°F) this time of year.  The folks at iConnect 007 interviewed me at the show; the topic was lead-free reliability and has cost for consumer electronics been demonstrated.  You can see the interview here.

These are topics I think about often, so let’s discuss them a bit. First, let’s consider reliability.  RoHS was enacted on 01 July 2006, more than 6 ½ years ago.  Each year more than $1 trillion-worth of electronics are made, therefore, in this period of time, something over $3 trillion worth of consumer electronics have been manufactured.  There have been no “the sky is falling”-type of reliability issues in this time.  How can I say this?  Well, my office at the Thayer School of Engineering at Dartmouth is across the hall from the IT (information Technology) Dept.  They purchase all of the millions of dollars worth of PCs, printers, displays etc. that Thayer uses.  Several years ago (say early 2011) I stopped by when most of the department was in and cheerfully asked if the reliability of the equipment they purchase has gone down since lead-free assembly was enacted.  They asked me in unison, “What’s lead-free assembly.”  After I explained what lead-free assembly was, they confirmed that they have noticed no changes in reliability.  Since RoHS, my family has purchase about 100+ electronic devices, a few have had reliability problems, about as many as in the past.  Most were attributed to hard drive fails.  Of the scores of friends and colleagues I have, no one has ever commented that they have noticed an increase in electronics fails. So, my conclusion is that consumer product reliability is not "practically" worse if my family and  these many  other folks haven’t noticed it.

I have made an informal study of reliability data of lead-free vis-a-vis tin-lead solders published in papers.  A statement from Rockwell Collin’s JCAA/JGF-PP No Lead solder Project: -55C-125C Thermal Cycle Testing Final Report  sums up my overview conclusion nicely: “Test vehicles assembled with lead-free materials (notably tin-silver-copper) exhibited lower reliability under some test conditions.”  Nay sayers might be quick to suggest that this statement  says that lead-free is no good.  However, the statement could be reworded to say: “In considerably more than half of the test conditions, test vehicles assembled with lead-free materials had higher reliability." Counting the comparisons in the Rockwell Collins paper shows lead-free better in 51 cases, tin-lead better in 31 cases, and one draw.  However, it is disturbing that a small percentage of lead-free assembled test vehicles had much much worse reliability than tin-lead test vehicles.  This later information makes me believe that lead-free is not yet ready for mission-critical, high-reliability, long-life products.  These small numbers of much poorer reliability assemblies must be understood and corrected before lead-free is ready for mission-critical prime time.  The much shorter life cycle of today’s consumer electronics may also mask this concern.

What about cost?  I don’t at all want to minimize the expense that many went through to go lead-free and RoHS compliant.  In about 2007, one of our colleagues estimated that it cost the electronics industry $20 billion to become RoHS compliant.  I think this number is low, but, from a consumer’s perspective, there has been no cost hardship.  The price of a PC continued to go down during and after RoHS implementation, as shown in the figure below.  While performing my non-scientific survey of co-workers, family, and friends on reliability, I also asked about cost.  All agreed, electronics are cheaper than ever.

Challenges still exist, even in consumer electronics with the Head-in-Pillow, Graping, non wet opens, and other defects.  However, we can all purchase lead-free, RoHS compliant products at a reasonable cost and reliability.

Cheers,

Dr. Ron

The source for the image is :http://thomaslah.wordpress.com/2010/02/03/apple-and-intel-defying-gravity/

The 2013 IPC APEX Expo , the premiere electronics assembly event, is right around the corner - and our technology experts are ready to share their experience and knowledge on a variety of topics.

Ning-Cheng Lee, PhD, VP of Technology will present a paper on voiding control in mixed solder alloy systems. He will also present on the hot topic of QFN voiding.     Dr. Lee is a world-renown soldering expert (EVERYBODY knows Dr. Lee!).  In addition to his work at Indium with solders (for 27 years), he is also an expert on polymers, underfills, and adhesives.

Ronald Lasky, PhD, PE, Senior Technologist will be presenting a paper on Material and Process Optimization for Head-In-Pillow Minimization.  Dr. Lasky is one of our most popular bloggers, check out his blog!  He approaches the world of electronics assembly from some interesting directions, including the exploits of Patty and the Professor.  Dr. Lasky will also talk about Applications of Solder Preforms to Improve Reliability, and A Focus on Productivity: Several Case Studies.  He has also found some time to teach two professional development courses: An Introduction of DOE, SPC and Weibull Analysis; and Manufacturing for High Yields in Assembly. Another busy man!

Senior Technical Support Engineer, Eric Bastow will be presenting on The Effects of Human Induced Contamination on PCB Assembly Electrical Reliability.  Eric has looked at the impact of oil, grease, and hand creams and how they can create reliability issues in small components.  Eric provides technical support to our customers by phone and in person. 

The APEX Expo will feature over 400 exhibitors and lots of technical sessions. It provides you the opportunity to have face-to-face discussions with many of our materials experts, so bring your soldering challenges and visit us at Booth 1127.

Can't make it to San Diego?  Call or email us and we can help you anytime!

Carol Gowans

February 2013

Today I thought I’d take a break from talking about soldering materials for a minute to reflect on how we arrived at Blog Post #415.

Back in 2007 I was asked to try out blogging. I was given free rein to discuss whatever related to soldering. Since then, almost everything about blogging has changed for me. We use different software now, I write about different subjects now, and I have noticed my style has changed quite a bit over the years. Older posts were mostly short, abstract, and open-ended. As years passed it became clear that you, the audience, wanted more technical details and links to additional information.

I’ve been really lucky: blogging has surprised me many times in the last 5 years. There have been so many interesting people that I’ve had a chance to meet and work with. There have been perks too - once I received a video camera for writing some guest posts, and, a few times, I have been offered products to review. To top it all I met the love of my life because of blogging; someday I’ll find the words to share that story. In all, I’m glad I was asked to blog for Indium Corporation, it has been one of the best parts of my career, so far.

By the way, the picture I included has nothing to do with the post – because I’m feeling frivolous today. It’s a picture of me snowboarding, which is an activity I’ve vowed to not do on my birthday (which happens to be today). Maybe tomorrow though…

~Jim

Using NanoFoil^® can be very easy, and there are many things you can do yourself to make prototyping or production easier, save money, and get the results you want quickly – without outsourcing services.

1. Electroplating NanoFoil^®
2. Immersion Tin Plating NanoFoil^®
3. Hand Cutting NanoFoil^®
4. Masking a  NanoBond^® Area
5. Applying Solder to Copper, Nickel, and Platinum (Flux)
6. Applying Solder to Aluminum and Aluminum Alloys (Scrubbing)
7. Applying Solder to ­­Molybdenum, Titanium, and Tungsten (Ultrasonic Soldering)
8. Determining What NanoFoil^® You Have
9. Connecting NanoFoil^®

These ideas will help you save money and feel confident about processing and using NanoFoil^® in different ways. They'll also help make you more successful and powerful in your job.

For more information about NanoBonding, check out the NanoBond^® Process Series. For a NanoFoil^® kit to get you started, click here.

All the best,

          ~Jim

Tin-coated NanoFoil^® is not one, but two very different products, combined. It is a heat source and a form of solder. In the world of interconnection, this is quite unique. (Shown in the picture here: Uncoated NanoFoil^® on the left, tin-coated NanoFoil^® on the right. Note the matte finish of the tin coating.)

It is important to remember that even with tin coating, NanoFoil^® should be used with properly metallized parts. If this condition is met, there is no need for traditional soldering equipment or materials. No reflow oven, soldering iron, solder wire, or flux. Interesting huh? To learn more, check out The NanoBond^® Process Series, and then contact us to answer any questions.

~Jim

Folks,

Let’s see how Pete is handling the wave solder crisis.

Pete had to admit that he was surprised by the positive outcome of his meeting with Fred Castle.  He had sent Patty a text the day before, after he took the operators to lunch, before meeting Fred.  The text was a little negative.  So he was eager to send her the good news about the surprises in his two meetings with Fred since then.  He was frustrated that he kept on getting her voice mail.  Finally she answered.

“Advanced Processes,” Patty speaking.

“Hey, kiddo, it’s your favorite process genius!” Pete responded cheerfully.

“Oh, this must be Oscar Patterson!” Patty joked, and they both laughed. Patterson was an annoying chap they had to deal with a few years ago.  He topped their list of most annoying people. Pete had almost come to fisticuffs with him.

“How is it going there?” Patty asked.

“Shockingly well. My meetings with Fred Castle were very productive” Pete answered.

“Well, that is shockingly positive news. But I thought he said, ‘I’ve forgotten more about wave soldering than you’ll ever know,’” Patty responded.

“That’s the first thing he said to me when we shook hands, but he was clearly teasing.  He slapped me on the back at the same time and chuckled. He went on to say that he had worked in wave soldering for over 30 years, typically at companies that had processes that were out of control.  It was clear that he understood a lot about wave.  We talked for 30 minutes about what makes a good wave process. As far as I could tell he was right on in everything he said.  I think the operators didn’t pick up on his teasing, by the way,” Pete elaborated.

“What about special cause vs common cause?” Patty queried.

“He didn’t have a clue,” Pete replied.

Patty was bracing herself.  She was concerned that Pete might have insulted Castle.

“And you didn’t tell him he was an idiot?’ Patty teased.

“Patricia! I’m shocked you could even think such a thought,” Pete replied.

Pete went on, “We bonded, and he admitted that he was frustrated with the yield loss increasing.  He was studying the situation and spending a lot of time trying to figure out the issues.  He said he was having trouble sleeping.  He mentioned that, in his last job, he was responsible for the wave processes at 10 locations.  He was constantly fighting fires and got good at it.  He had never worked at company that performed DOEs and developed optimized processes.”

“I’m dying to know how this situation worked out,” she interrupted.

“Patience, patience,” Pete admonished jokingly. He continued, ”It was clear that Fred likes to learn, so  I mentioned that, recently, The Professor had mentioned the importance of understanding the differences between common cause and special cause variation when trouble shooting a process.  I suggested that maybe studying these topics might help. So I gave him a few links to The Professor’s posts on common cause and special cause.” (Dr. Ron note, it will be helpful understanding this story to read The Professor's post, if you are not familiar with common cause and special cause fails.)

“What happened then?” Patty asked, the impatience in her voice apparent.

“Remember, this is now the end of my first day. I watched the process in the morning, took Molly and Chuck to lunch, and then met with Fred.  On the second day I had a morning meeting with the quality director, Pam. Then Castle and I went to lunch,” Pete elaborated.

“And?” Patty asked impatiently.

“Castle was all excited.  After studying common cause and special cause all night, he realized that he was seeing common cause fails in his detailed scrutiny of the wave line. By adjusting the process parameters slightly when he found a common cause fail, he was moving away from the optimized process settings that were determined by a DOE, so the failure rate got worse.  In his previous job, he was mostly seeing special cause fails, as the processes were not optimized, so he was used to intervening,” Pete explained.

“It seems like he won’t have enough to do now,” Patty commented.

“I suggested he help quality.  They are stretched thin and he is a detailed-oriented fellow.  He keeps meticulous Pareto charts of the fails,” Pete said.

So, where are things now?’ Patty asked.

“Yesterday and today, first pass yields are at 96%.  Fred also started helping quality today. It felt good to help and not offend,” Pete finished.

Patty thanked Pete for the great job he did and complimented him strongly for being successful and making friends at the same time.  As she hung up the phone, she saw an email from Pam Olinski in her in box.  It was a kind note thanking her and Pete for his help.  It recounted much of what Pete had said.

She wistfully looked out her window.  She was happy and grateful for all of her success, but, to be truthful, she missed the action of being out on the shop floor solving these types for problems.

She was jolted from her chair when she suddenly remembered it was her turn to take her twin sons to karate lessons.  So she packed up quickly to pick them up at her mother-in-law's, to get them to the gym by 5PM.

Cheers,

Dr. Ron

image

Folks,

It's been a while. Let's look in on Patty......

Patty stared, bleary eyed, at her laptop screen.  It was the day after the election.  She and Rob were following the election closely as a “statistical thinking” exercise.  They had met at a conference with The Professor in late October and agreed that following the election would test their statistical thinking skills.  They established beforehand that they would not discuss who they favored, just the data.

All agreed that Mitt Romney had a greater challenge than President Obama.

As Rob said, “Of the six most populated states, even the Republicans agree that Obama will win California (1), New York (3), Illinois (5), and Pennsylvania (6).  Romney is only a shoe-in for Texas (2).  Only Florida (4) is a toss up”

“I thought some analysts were saying that Pennsylvania is in play,” The Professor commented.

“They’re dreaming,” Patty said with conviction.  “Pennsylvania has too many big cities; typical democratic strong holds,” she continued.

“Many pollsters have 255 electoral votes in Obama’s column and only a little over 200 for Romney. It’s hard to see a Romney path to victory.  It is statistically unlikely he could win all of the swing states” Rob added.

The Professor beamed as he listened to his protégés' intelligently analyze and argue the situation.

They all agreed that it was hard to understand why many were referring to it as a close race, although voter turnout could change everything.

As election night went on, Patty felt she could call the election at 8PM EST.  However, she was sympathetic that the networks needed a high level of certainty. The major networks were finally calling it at 10PM.  When they did, Romney was ahead in the popular vote by about 1 million.  Patty chuckled to herself, when a renowned TV anchor commented that it might be a governing challenge to Obama to win the electoral college and not the popular vote.  Clearly he had not factored in the fact that, although California was “called” for Obama around 10PM EST, it was called with only a few percent of the votes in.  The networks were using exit polls and statistical analysis to make a projection.  By the time all of the west coast votes were counted, Obama will comfortably win the popular vote - because of California’s large population.  Patty thought this should be obvious to the pundits.

Patty had stayed up until about 11PM to watch the results.  It was comforting that her analysis was spot on.  However, she was so “wound up” that she couldn’t fall asleep and she was now paying the price.

As her attention shifted back to the email she was writing.

Suddenly, she was jarred by a loud, cheerful voice.

“Hey kiddo, pack your bags, looks like we’re on the road again,” Pete said loudly.

As usual Patty thought,” How does Pete always know these things before I do…..I’m the boss!”

“What’s the scoop?” Patty asked.

“Remember our facility in Ohio?  They are having wave soldering yield and throughput problems,” Pete answered.

“What!” Patty shouted.  “We spent a lot of time there six months ago optimizing their wave soldering operation and teaching them the appropriate use of solder preforms. What happened?” She finished.

“Not sure,” Pete responded. “I thought we worked really well with their team and developed a good process.  It seemed to me it was one of the more productive projects I was involved in in quite awhile,” Pete finished.

“And you didn’t even offend any of the senior managers,” Patty teased.

Pete chuckled but his cheeks did turn a little red.  Pete was a terrific process engineer, but he had a little bit of a “short fuse,” although he was usually right.

“In talking to some of my buddies there, they told me that senior management hired a very senior fellow who is considered an expert in wave.  Strangely, things fell apart right after he joined,” Pete explained.

“Well, you are on your own for this one.  I've got a number of family commitments over the next two weeks,” Patty said with a little sadness in her voice.  Patty enjoyed these types of challenges.

“As soon as I get the official request, you’ll be on your way,” Patty said.

“Oh, and don’t offend anyone,” she teasingly finished.

As Pete left her office, she checked her emails. Sure enough, there was a note from Mike Madigan asking her to intervene in this wave soldering problem.

Two days later Pete was in ACME’s Ohio facility sitting in the office of Pam Olinski, the site's quality manager.

“Pete, I’m so glad you could come.  Three months ago our wave soldering first pass yield was 95% and our production was about 2,000 boards per day.  Yield is now 90% and production is off 15%. “Help!” Pam said.

“Tell me about the new guy?” Pete asked.

“Fred Castle; he has very impressive credentials, but he has been running the wave process like a dictator. He stops the process a lot to adjust the wave machine.  I think he will be offended that you are here to audit the process,” Pam finished.

Because of this concern, they agreed that it might be best to have Pete initially view the process from afar.  So, they decided that Pete would be given an operator’s smock and walk around the shop floor for half a day or so.

As Pete arrived on the shop floor, almost immediately he saw Fred stop the wave machine and make some adjustments.  While  making the adjustments, Fred held a board in his hand - and he looked at occasionally.  After the wave machine was running again, Pete saw that Fred looked carefully at every board.

Pete saw one of the wave operators was going on a break.  Pete remembered Molly Stark from his visit to optimize the wave process six months ago, so he stopped her and ask if she could join in for lunch.

The morning passed quickly, and Pete was off to lunch with Molly.  As Pete had suggested, Molly brought another operator, Chuck Petrus to lunch.  Pete insisted on treating, so Molly and Chuck left their brown bags behind. 

In total, Fred stopped the line four times during the almost 4 hours of Pete's observations. Each time he made adjustments on the wave machine. After exchanging pleasantries Pete asked, “Why was that fellow stopping the wave line so often?”

Molly got quite animated and answered, “That’s Fred Castle, the supposed wave genius. He stops the line every time there is a defect and adjusts the wave machine parameters.  A number of us complained to him that he shouldn’t make adjustments on the machine that with just one fail.  That’s what you taught us.”

“What did he say?” Pete asked.

“ ‘I’ve forgotten more about wave soldering than you will ever know’……No one has said a word since,” Chuck responded.

“You and Patty taught us about special cause and common cause variation. I don’t think Fred understands that,” Molly commented.

“He’s also a knob twiddler,” Chuck added.

Does Fred know the difference between common and special cause variation?  Is that the root of the yield and throughput problems? 

What is a knob twiddler? Stay tuned to find out.

Cheers,

Dr. Ron

One of the key points to understanding a NanoBond^® application is understanding the reaction that takes place. When NanoFoil^® is activated, the nickel and aluminum bilayers (picture on left) start a self-sustaining reaction that quickly consumes the material.

After the reaction takes place, the aluminum and nickel layers form a brittle intermetallic (picture on right). This bi-product, nickel aluminide, shrinks and cracks allowing solder to flow between and complete the interconnection.

Through a series of posts, we will discuss:

• Wave Propagation
• Heat Penetration
• Heat Dissipation

I know this doesn’t cover everything you’d ever want to know about the reaction of NanoFoil^®, but that’s what we are here for! Let us know if you have a question.

*This post is part of the NanoBond^® Process series

It seems like a fairly simple thing to do.  What could be difficult about soldering a wire to a pad? 

Well, I hear three common complaints and expressions of frustration:

POSITIONING: Typically, in this process, a soldering iron is used. The first problem arises from trying to hold onto the soldering iron AND the wire to be joined to the prefluxed pad AND the solid-core solder wire you are using.  An extra hand would be nice! Some people use a system of fixtures or clips to hold the wire and the pad in the appropriate position. (see image and link, below)*.

COLD SOLDER JOINT: Another common complaint is that, after soldering, the wire easily pulls out of the solder joint.  This is due to the poor wetting of the solder to the wire and the pad - it never really "soldered".  A solution that I share is to pretin both the pad and the wire with the solder, using a flux.  To pretin the wire, I suggest melting some of the solder in a crucible or solder pot.  Dip the wire in the flux and then into the molten solder.  A teardrop should form on the end of the wire.  It can also be pretinned using the soldering iron. Next, pretin the pad. Both pretinned surfaces will have a coating of post-reflow flux residue.  If required, this residue can easily be removed using a suitable solvent.  Now that you have pretinned both surfaces, the pad should be heated with the soldering iron and, when the proper temperature is reached, the pretinned wire should be pressed to the pretinned pad.  The solder on both the pad and the wire will melt together and, when the heat is removed, the joint will be formed.  Usually this can be accomplished without adding additional flux.

INCONSISTENT VOLUME: A third issue is that the volume of solder in the joint is not uniform from piece to piece. If this is your concern, consider using a flux-coated solder preform. They can be produced with the exact solder volume, and the precise dimensions to fit onto the wire you are joining to the pad.  Similar to the process described above, when the pad and the wire are heated, the flux will be activated (removing the oxides) and the solder preform will melt, forming a consistent and perfect solder joint.

Please contact our technical support group with any questions you may have.  We are always ready to help you solve your soldering problem, whether it is large or small.

For more background, read these blog posts on hand soldering:

• soldering iron tip temperature
• hand soldering flux selection
• hand soldering tech support
• the importance of a clean soldering iron tip

Paul Socha

*Image: Harbor Freight sells a product called "Helping Hands" for (US) $6.99, as of this writing. Other companies offer similar products. Consider buying more clamps to hold the wire in place, freeing you to hold only the solder wire and the soldering iron.

Printed circuit boards containing both surface mounted and through-hole components are common, and are often referred to as "mixed technology" boards.  In mixed technology assembly, solder paste is used to attach the components to the surfaces and wave soldering attaches the components that are inserted through holes in the board.  For low volume production, hand soldering is often utilized - for the attachment of through-hole components.  Both of these methods require additional steps after the original reflow of the solder paste.

To increase your profits (saving you time and money while improving your quality and productivity) InTEGRATED PREFORMS^® have found a place in mixed technology assembly.  InTEGRATED PREFORMS^® are interconnected solder washers, designed to fit the pin pattern of a through-hole component.  These arrayed solder washers are sized to deliver the precise solder volume required to fill the holes and to produce excellent solder fillets at each joint. 

In some cases, to add even more solder, solder paste is deposited over the holes and the InTEGRATED PREFORM^® is placed into the paste. The component is then inserted through the solder preform, the solder paste, and the hole. 

In other applications, TacFlux® (that is compatible with the solder paste's flux vehicle) is applied to the preform before it is placed on the component's pins, or is placed directly on the board, and the component is inserted as described above.  Whichever method is used, only one reflow step and only one cleaning step are required.

In traditional wave soldering, components with long pins are a special challenge because they are very difficult to attach without getting alloy on the pins during wave or hand soldering.  InTEGRATED PREFORMS^® can be applied to the top or bottom side of the board and are reflowed along with the components held down with solder paste.

InTEGRATED PREFORMS^®  are designed and built to address the unique characteristics of each specific application.  To build your InTEGRATED PREFORMS® we require the following information, so the solder volume and washer spacing are correct for your specific pin configuration:

• Hole size
• Pin size
• Board thickness
• Center to center spacing of the pins (within the row, and row to row)
• Solder Alloy
• Is the preform going to be used to add to the volume of solder from the paste?

Separate (individual) solder washers can also be used in place of connected InTEGRATED PREFORMS^®.  They can be designed to deliver the same consistent volume of solder required for each joint.   Care must be taken, however, to place only one preform on a pin, and not miss any.  This is what makes InTEGRATED PREFORMS^® desirable.  The solder washer array is designed and manufactured to fit the pin configuration so only one washer goes on a pin.  If extra solder volume is required, InTEGRATED PREFORMS^® can be easily stacked.

With today's drive to optimize profits, InTEGRATED PREFORMS^® present an excellent opportunity.  The biggest advantage of InTEGRATED PREFORMS^® is the fact that quality can be improved while costs are reduced.  If you are looking for any easy way to cut costs, increase production, improve quality, improve customer satisfaction, and, ultimately, increase your profits, talk to me about InTEGRATED PREFORMS^®.

Paul Socha psocha@indium.com

BONUS: Read our white papers regarding InTEGRATED PREFORMS^® .

Attaining consistent and accurate solder (and flux) volume uniformity in hand soldering has long been a critical quality and performance issue.  Traditional hand soldering creates consistency and quality issues from operator to operator, from shift to shift, from day to day, and even within the same operator within the same day!

Hand soldering always delivers inconsistent solder volume.The human factor is a major contributor to this non-uniformity.

Solder preforms:

• offer a solution to the need for consistent solder volume.
• are the preferred solution in tens of thousands of applications where the uniformity of solder volume is critical.
• provide the correct alloy, the right size, and the exact volume of solder that you require.
• are available in custom sizes, shapes, volumes, and packaging, to suit your production needs.
• can be flux coated with a consistent and precise volume, and type, of flux. Flux-coated solder preforms reduce process time by eliminating a separate flux application step. They can also reduce total flux usage.
• can be ganged together (InTEGRATED^® Solder Preforms) for mass placement. I blog about that here and here.
• can be manufactured using a fugitive dye (in the flux coating) imparting a visible color for easy identification. This helps distinguish visibly-similar but different (alloy, dimensions, etc.) solder preforms.
• can be clad to a dissimilar metal, providing extra strength and/or the ability to bridge gaps.

Using,  applying, positioning, and reflowing solder preforms (and flux) is simple. Simply place the solder preform at the joint site (by hand or robotically), and apply heat.  It’s really that simple.  Each joint will have precisely the same solder volume regardless of who is doing the soldering.

Manage your 1st-pass yields, your quality, your field failure rates, your customer satisfaction, and your profitability by putting solder preforms to work for you.

Paul Socha

23 October 2012

While on a recent trip to Malaysia, I interviewed two colleagues regarding trends in semiconductor assembly. My previously-published interview with Sze-Pei Lim appears here.

This time, while on a visit to a logic device manufacturer in the North West, I [ACM] talked briefly to Sehar Samiappan [SS], Indium Corporation's Area Technical Manager, about our recently-developed water-soluble pin-transfer Ball-Attach Flux, WS446-NRD, which is designed for BGA applications of 0.5mm pitch, and greater than 1500  I/Os.

[ACM] What is the origin of WS446-NRD?

[SS] The development was driven by a customer need for a guaranteed good quality BGA (ball-grid array) solder joint, but with reduced environmental impact. Our very quality-focused customer uses several different suppliers of organic FC-BGA substrates with copper OSP pads. The customer had serious concerns about occasional poor solderability of SAC305 solder spheres onto substrates. The key defect seen was poor wetting onto the OSP-coated copper pad, which would give rise to variability in both joint strength and bump coplanarity,  and even (in worse cases) missing-ball / “big ball” effects. Some of the pad finishes were seen to be highly oxidized, severely restricting solder wetting during reflow. Variability in the surface finish was found to be not just from supplier to supplier, but also showed up as lot-to-lot variability from lower cost suppliers.

Some of the differences seen could be attributed to the method of mask desmear from the C4 “cage” of the flip-chip (top side) area, which was either a plasma-based desmear or an oxidizing inorganic acid dip, that was clearly having effects on solderability of the opposite (bottom) BGA side of the substrate.

[ACM] What steps have customers previously taken to get around this issue?

[SS] This is a serious issue for many ball-attach flux users, and some customers have gone to the lengths of using a special fluxing step to remove contaminants such as oxide and OSP (organic solderability protectant) coatings. These liquid fluxes are very reactive, but require  separate spraying, reflow, and cleaning stages that add cost and time. The halogenated ball-attach fluxes of the WS446 series have an established good chemistry that allows wetting of SAC105, 305, and 405 onto a variety of metallizations. In the semiconductor assembly industry, the WS446 fluxes are well-known in Taiwan, and throughout South East Asia, for their good solderability and long pot-life in a variety of FC-BGA applications.

[ACM] What was different about WS446-NRD, and why was it developed?

[SS] WS446 fluxes are all colored, using a bright red dye, so the flux can be seen by eye and automatically detected by vision systems. Red coloration also allows automated ball-attach flux dipping replenishment systems to detect flux levels. Normally, colored fluxes are not a problem, but the customer had some environmental concerns with the red color contaminating the water-wash equipment, and building up in their water-recycling system. WS446-NRD was developed from the basic WS446 flux series chemistry, but  without the red dye. The solderability performance of WS446-NRD was excellent, eliminating the variations in OSP solderability without requiring any additional processing steps. WS446-NRD also passed internal process and product requirements, such as cleanability, and the customer was very pleased with Indium’s ability to rapidly tailor a chemistry to their specific requirements.

[ACM] Sehar: thank you. I look forward to sharing a durian with you again when they are back in season.

Folks,

Let's see how Patty and Pete are making out on their latest adventure....

“Here is the ProfitPro™ output," Dave Ferris said as he pointed to a PowerPoint slide on the screen.

Just then, the site general manager, Sally Wilson, and the head of purchasing, Blaine Ellis, arrived. 

“Long time no see,” Pete said to Ellis.

Ellis acknowledged Pete, but appeared to be in a foul mood.  Everyone settled down and the meeting came to order. Patty was again surprised, Pete always seemed to know everybody.

After introductions, Sally kicked off the meeting.

“As you know, we have a new corporate award program for saving money.  Dave is a candidate to win the first award.  But Blaine won’t sign off on it, because his solder paste expenses have, in his word, ‘skyrocketed' ”, Sally started.

Ellis exclaimed, “My solder paste costs are through the roof.  Last year we used 3,000 kilograms and this year we are using 3,100 kilograms and each kilogram costs $10.00 more.  That’s more than $40,000 dollars more.  How is this saving money?”

“How has the overall site profitability changed?” Patty asked.

“It’s pretty consistent with what Dave’s PowerPoint® slide shows", Sally answered.  "His result is for one of our six lines.  We are using the new solder paste on all of the lines now and profitability is up about 8%, or more than $6 million for a year.”

“A lot of the added profit is from cost savings that purchasing has implemented,” Blaine shot in.

“You don’t realize the pressure I am under to reduce the cost of purchased goods.  Components, PWBs, connectors, solder paste, flux, packaging, etc, is over 80% of all of our total cost. Corporate has been all over me because of the increase in solder paste cost,” Ellis went on in frustration.

“Part of the increased cost of solder paste is because we ship more product, we actually use less paste per board with the new paste,” Dave responded.

“How so?” asked Sally.

“The old paste had poor response to pause.  If we stopped the line for a few minutes, the first one or two prints afterward would be poor because the paste stiffened up.  We would have to wipe the paste off those boards and reprint them.  This would happen a couple of times per day.  The ProfitPro™ output shows the increased productivity and profitability for the line for which I am responsible. Note that the profits are up $841K!” Dave Ferris went on.

“But my purchasing expenses have gone through the roof!” Blaine Ellis blurted as he stormed out of the room.

Patty, Pete, Dave, and Sally, sat there dumbfounded, looking at each other.

Pete finally spoke up, “Let me go talk to Blaine,” he said as he left the room.

“One of the issues is that Mr. Ellis should not be criticized if a consumable costs more money if it increases profitability. That doesn’t make sense,” Patty said.

“I agree” said Sally, “But much of the pressure comes from ‘Corporate.’”

As Sally was speaking, it occurred to Patty, that, in her new role, she may be able to impact this ineffective corporate policy.  As she was mulling over this thought, Pete and Blaine Ellis returned to the room.

Ellis spoke first.

“After discussing the situation with Pete, it occurs to me that young Ferris’s profitability argument may have merit,” Ellis started.

“But Dr. Coleman, I need your help,” Ellis implored.

At this Patty’s ears perked up.  First, she is not used to being called by her last name and second, she was unaware that she had a PhD!

“I think I know what you need,” Patty responded.  “We need to change the corporate criteria for evaluating the effectiveness of purchasing, to include situations like this.  I’m quite sure I can do it,” Patty finished cheerfully.

The meeting concluded with all agreeing that Dave Ferris should be given the corporate award and Patty reaffirming her commitment to change the corporate policy.

In several hours, Patty and Pete were on an airplane heading home.

"OK, out with it," Patty teased Pete.

"What?" was Pete's sheepish reply.

"How did you know Blaine?" Patty asked.

"Remember, when I told you that I tried out for Olympic volleyball years ago?" Pete responded.

"Yes, " Patty replied.

"So did Blaine. I'm not sure which one of us was more humbled by the experience," Pete chuckled.

Cheers,

Dr. Ron

It is summer time again in the Northern Hemisphere and many places, especially in North America, are experiencing record heat. It also seems that most locations in the Southern Hemisphere stay reasonably warm even during their winter. What does that mean if you are a solder paste supplier? It means that, even with the best practices, there will be occasional shipments of paste that arrive at the customer’s dock “warm”. And this can be alarming to customers.

Solder paste is a heat sensitive product. Make no mistake about it. Excessive and prolonged heat can, and does, damage solder paste. Solder paste is a “perishable” item much the same as are milk and eggs. And we, the solder paste manufacturer, know that. So, we do many things to make sure that the paste arrives at the customer’s dock in its most viable condition. The intent is for the paste to arrive at <25C, not cold or cool. Here is a list of practices commonly employed to insure that the paste is not thermally damaged during transit:

1. Overnight Shipping
2. Thermally Protective Packaging (styrofoam coolers, etc.)
3. Cold Packs
4. Refrigeration of Paste Prior to Shipping (when appropriate)
5. Inclusion of Temperature Strips (when appropriate)

Given all the safe guards that we put in place, it is extremely rare that a solder paste delivered “warm” has been damaged. It is almost always related to something having gone amiss in the delivery. For example, the solder paste, even though shipped with overnight delivery, gets “lost” by the carrier and spends a few days in the back of a truck, at the height of summer in Arizona, before it gets delivered. In such an irregular scenario as this, it is possible that the solder paste may have been damaged.

Thermally damaged paste is not a subtle thing. It is not something that will sneak up and cause some sort of unforeseen product failure in the field. It is quite obvious. There are 2 things that are evident with thermally damaged paste:

1) The viscosity changes noticeably (usually increases or “thickens”) - manifesting itself during the printing or dispensing process.

2) The solder paste does not coalesce properly during reflow.

Both of these properties can be easily measured and observed by the customer. Becoming alarmed and contacting the supplier is not necessary if the paste is printing/dispensing and coalescing fine. So, if you receive "warm" solder paste that dispenses or prints properly, you are in good shape. You only need to consult with your supplier of your solder paste exhibits one or both of these behaviors.

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,

It has been a while, let's look in on Patty......

Patty had to admit that she was very fortunate.  She had yet to turn 30 and she was a Senior Vice President at ACME.  There was even a small article about her in Fortune magazine.  But she had to admit that, at some level, she was bored.  She missed the action of being out on the line and solving problems. 

With these thoughts she headed toward the lunch room.  She had avoided eating lunch with the execs and still ate lunch with the young engineers that were her age. No one thought it strange.  Pete was occasionally the old timer in the group, as he was approaching 45 years old. 

As she sat at lunch with her friends, Patty also had to admit that she was jealous of all of the group's talk about solving technical problems.  She was now responsible for corporate strategies and seldom got her “hands dirty.”  So she missed the technical challenges on the shop floor. 

After lunch she stopped Pete.

“Hey, Pete, could you stop by my office?” Patty asked.

“Kiddo, for you anything….even that,” he answered and they both chuckled.

As Pete sat down in Patty’s office, she asked him, “How do you like your new job?”

“What’s not to like? Twice as much money and working with you!” Pete answered.

“But don’t you miss ... ,” Patty stopped and struggled to gain her composure.

Peter helped her, “Working on the shop floor solving process problems?”

“Yes, so much so that I could almost cry,” Pete finished.

They were silent for awhile.

Then Pete suggested, “Why don’t I see if I can find us a problem.”

Patty smiled. Pete was always well connected.

A few days passed and Patty had just about forgotten about their meeting.  There was a knock on her door and Pete stuck his head in.

“Hey kiddo, we have an assignment,” Pete shouted cheerfully.

Patty perked right up.

“What’s the scoop?” she asked.

“You know the new program that rewards cost savings?” Pete asked.

“Sure, I think it is a great idea,” Patty responded.

“There is a conflict in our plant in Santa Clara. Management wants to give a $10,000 reward and the senior purchase manager is blocking it,” Pete elaborated.

“Why?’ Patty asked.

“The engineer deserving of the reward purchased a solder paste that improved uptime,” Pete said.

“Sounds great, what is the issue?" Patty asked. "Let me guess. The better solder paste costs more?” she asked.

“Yep!” Pete responded, “One penny per gram.”

“Mike Madigan wants someone to negotiate the situation. Why not us?” Pete asked.

Patty quickly sent Mike an email offering to help.  He gave her the go ahead shortly thereafter.

In a matter of days the arrangements were made and Patty and Pete were on a jet from Boston’s Logan airport to San Jose, California. 

Their flight had taken off and they were enjoying a snack, when Pete commented, “Let’s hope we don’t find someone there like the guy who wanted to assemble the boards without the boards,” Pete chuckled.

At this comment, Patty almost choked on her sparkling water.  About four years ago, when Patty was just starting out, they were working on a critical project.  The manager in charge wanted the boards to be assembled on a certain date.  Unfortunately, the PWBs did not arrive on time, even though all other components, connectors, and the other hardware where ready.  The manager, in frustration, came out to the line on the scheduled start date and was furious that the boards were not being assembled.

The manager asked the lead engineer, “Why aren’t the boards being assembled?”

The lead engineer responded, “The PWBs did not arrive from the vendor.”

To this the manager responded, “Aren’t you going to assemble them anyway?” (See note below.*)

This was their favorite story about the occasional comedy in electronics assembly.

It seemed like no time at all and Patty and Pete were sitting in the conference room that had been reserved for the meeting.  They introduced themselves to a young engineer who was sitting in the room waiting for the meeting to start. His name was Dave Ferris.

“So Dave, you are the cause of this meeting, eh?” Pete teased.

“I guess so. I can’t believe how hard it is to sell productivity here.  The amount of time the new solder paste saves enables us to produce 1,000 more units per year on each line. And these boards are super expensive, with high margins.   Admittedly the solder paste costs $0.01 more per gram, but the additional profit is over $800,000 per year for each of our three lines,” Dave Ferris explained.

“How did you perform the calculations,” Patty asked.

“I went to a workshop run by this quirky, cheerful guy everyone calls ‘The Professor.’ He was amazing,” Ferris replied.

Pete and Patty both chuckled.

“We know The Professor well,” they chimed in unison.

“We assume you used “ProfitPro™ for the calculations?” Pete asked.

“Yes,” Dave responded with a surprise in his voice that they would know about such things.

Will Patty and Pete save the day?  Will Dave get his award?  Stay tuned to see.

Cheers,

Dr. Ron

*As hard as it is to believe, the story about building the boards without the PWBs is true.  Thanks to ITM.

As a primarily METALS materials supplier, we are used to most of our products appearing rather, well, boring. We see many shades of gray!

From solder paste to CIG targets, from solder wire to tabbing ribbon - they're mostly gray!

The indium sulfide (In₂S₃) that we produce for use as a buffer layer in thin film solar cells is quite unlike many of our other products. Visually, it is a bright orange powder or pellet. (The text in the picture is made from indium sulfide powder.) Chemically, it is like many of our other products in our metals and compounds division.

Indium Sulfide is supplied in various forms such as powder, thermal evaporation pellets, or sputtering targets. Since the powder form is very important as a starting material for other forms, we focus on achieving very high purity. We also focus on one other secret detail that helps our customers build better solar cells. (I can’t give everything away, right?)

If you’d like to know more about indium sulfide, feel free to send me an email @ jhisert@indium.com.