Indium Corporation Blogs

Folks,

We tend to think of mixing as something that can completely even out those things being mixed.  As an example, let’s assume you are making chocolate chip cookies and would like to have 10 chocolate chips in each large cookie.  You make enough batter for 100 cookies and then mix in 1,000 chocolate chips.  After mixing for a long time you put 100 dollops of the batter on the baking pan and bake up the cookies.  Upon inspecting the cookies, to your dismay, you find that you have only 13 cookies with 10 chocolate chips.  More than 40 cookies have 30 percent more or 30 percent less than 10 chips.  Worse yet, 3 cookies have 4 or less chocolate chips and 7 have 16 or more.  See the graph below. You decide that you did not mix them enough, so you make another batch and mix for 4 hours.  The results are the same.

Statistics tells us why the above scenario is so.  In a case like this one, the number of chips in a cookie is described by the Poisson distribution.  The mean will be 10 chips, since we are using the Poisson distribution, the standard deviation will be the square root of the mean or 10^0.5=3.16, or about 3 chips.  One way to assure a more even distribution of chocolate would be to divide each chip into 10, so we would have 10,000 smaller chips in a batch.  On average each cookie would now have 100 chips and the standard deviation would be 10.  Plus and minus one standard deviation is about two thirds of the data, so two thirds of the cookies would have +/- 10% of the desired amount of chocolate, a much better result.  If we divided the chips into even smaller sizes, we would further tighten the distribution.

How does any of this relate to solder preforms or solder paste?  In the new world of lead-free solder pastes, where it is common to have 3 or 4 alloying elements, some in very small concentrations, it can be difficult to control the concentration of the alloying elements throughout a sample of the alloy.  The limits of mixing are just part of several processes that are required to assure that a modern lead-free solder has a consistent formulation.  These are some of the topics you should discuss with your solder supplier to assure that you get consistency in any solder alloy you purchase.  Asking to see assay analysis of a solder alloy is often a good idea, too.

Cheers,

Dr. Ron

Folks,

A reader writes:

Dear Dr. Ron, I need to measure the void content of an alloy.  Is there an easy way to do it?

After a little thought, it occurred to me that the densities of the voided and unvoided material will likely hold the answer.  I derived the result below.  Assuming we know the density of the unvoided material, we can measure the density of the voided material with the Wet Gold Technique, discussed in recent posts, if the voids are not connected (closed cell.)  If the voids are connected (open cell), you could machine the foam to the shape of a rectangular parallelepiped and determine the density of the foam as the mass divided by the volume.

As an example, let’s say you have a closed cell aluminum foam. We use the wet gold technique to measure its density at 1.5g/cc. The density of solid Al is 2.7g/cc.

So the volume fraction of voids is:

Sadly, this technique could not be used to find void content in solder joints, or in BTC (e.g. QFN) thermal pad connections (which are so handily mitigated by using solder preforms.)

:   :   :   :   :   :   :

Global Warming Musings:  My recent post on GW generated many comments.   I will be sharing additional reasons why I am a skeptic at the end of posts like the one above. 

It is important to state the distinction between a GW Skeptic (me) and a GW Denier.  As a Skeptic, I am not convinced that the warming trends are alarming or unusual, especially since the atmosphere has not warmed in more than a decade.  Also, I am not convinced that the main driving force for the warming trend up to the late 1990s can conclusively be attributed to human activities.  Lastly, I’m not convinced that even with Draconian measures, we could affect a change that would matter.

The Carbon Cycle

In this post, I would like to share the data relating to how much carbon dioxide is produced and put into the atmosphere.  More specifically, what percent of carbon dioxide generated each year is from human activities. Would it be 30%, 40%, 50%?  The answer is 3%.  The remaining 97% of carbon dioxide generated on the earth each year is generated by natural processes in the oceans and on the land.  See the image below.  The GW argument is that even though human activities are only 3%, this amount offsets the delicate balance that nature provides.  Working with and modeling data all of the time, I find this argument unsatisfying.  Collecting accurate data and developing an accurate model on data like this is difficult.  Making incontrovertible conclusions (it is certain GW is caused by humans) more so. Freeman Dyson, arguably one of the most accomplished physicists of this era, has a similar view:

The models solve the equations of fluid dynamics, and they do a very good job of describing the fluid motions of the atmosphere and the oceans. They do a very poor job of describing the clouds, the dust, the chemistry and the biology of fields and farms and forests. They do not begin to describe the real world we live in...

It is interesting also to note that throughout history the temperature of the earth determined the carbon dioxide content in the atmosphere, not vice versa.

Cheers,

Dr. Ron

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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

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,

In my last post we saw how you could measure density with only a scale.  In this post, we will expand on that technique and learn how to measure metal content in gold/quartz ore.  In principle, this technique could be used for other ore, but the ores can only be two part (e.g. gold and quartz) systems.  Gold is a “natural” for this analysis as it is typically pure gold with quartz.

Gold is often found “veined” in quartz.  I was certain that this was the origin of the “Golden Fleece.”   The fleece being the white quartz with the gold on top.   However, a little research did not clarify this belief.

Anyway, let’s assume you take a few weeks off from work.  Leaving the world of solder paste, TIMS, ITO, wave solder flux and solder preforms behind, you set out for the west in search of some large gold nuggets.  Fate was with you in that, in a short time, you find a gold/quartz specimen as shown below.   The images, and the new “wet gold” weighing technique I will discuss, are from Bill and Linda Prospecting.

You are so excited you are shaking.  The only tools you brought are a scale, some string and a beaker.  To determine that gold content, you need to measure the weight of the gold in air and under water.  But you only have the scale as shown below.  What can you do?

After measuring the weight of the ore in air, fill the beaker part way with water, place it on the scale and zero the weight.  Then insert the ore on a string as shown below.  The scale will now read the weight of the volume of water that the ore displaces.  Let’s call this weight of the water displaced W_D .  The wet weight of gold (weight of gold under water) will be the weight in air minus W_D.  So we now have the weight in air and the weight in water.

The derivation of the equation that tells us how much gold is in the ore is at the end of this post.  The final equation we need is W_Au = 3.07W_W – 1.91W_Air.  For our ore sample W_Air = 25.1 pennyweight (pw). A pennyweight is 1/20^th of a troy oz.  W_D as shown in the photo above is 8.3 pw.  So W_W = W_Air – W_D = 25.1-8.3 = 16.8 pw.  So W_Au = 3.05*16.8 – 1.91*25.1 = 3.635 pw.  Subsequent analysis showed that the gold content was actually 3.9 pw and error less than 7%.  Not too bad for a simple field measurement.  At $1600/oz our ore sample contained. a little over $300 dollars of gold.

This technique could be used to measure the density of an alloy as in the last post.

Cheers,

Dr.Ron

The Derivation of the Equation

Folks,

In the category of interesting requests, Ron, a gold worker, from Guyana, sent me the following note:

Dr. Ron,

My colleagues use a “wet” gold technique to measure gold alloy density.  Is this valid?  Where does the formula come from?

Sincerely,

Ron

Well, to tell the truth, I had never heard of it and was skeptical.  How can you measure density (mass/volume) by only measuring weight?  So, I investigated. The technique claims that one can measure density with only a scale, by measuring the alloy’s weight in air and in water.

I could find no derivation, so I thought about it and derived it on my own.  As far as measurements go, as stated, you only have to measure the weight in air and water.  If you don’t have a scale that can handle being immersed in water, you can use a hanging scale (think weighing a fish).  So, after weighing the alloy in air, you immerse it in water. It will weigh the amount of water it displaces less.  The derivation is below:

As an example, let’s say you have a gold alloy ingot that weighs 1,000 grams (OK, I know grams is mass, but we are all sloppy and use it as weight, too) in air.  You weigh it in water and it weighs 930 grams. From the formula below, the alloys density is:

r = 1000/(1000-930) = 14.29g/cc

Since the density of gold is 19.3g/cc, the alloy is not pure gold.  If you knew the alloying element, say copper, you could use Indium’s Solder Alloy Density Calculator to determine that the alloy was 69.8% gold, 30.2% copper.  If there are multiple alloying elements, since most of the common elements have a density of about 9 g/cc, you can even estimate the fineness of the gold.

Could this technique be used to measure the alloy density of say a handful of solder preforms. Sure, you could put them in a woven bag of non-hygroscopic material and weigh them in air and water.  Admittedly, measuring the density of solder paste, with this technique, would be a challenge.

Next posting, I will show how this technique is used to measure the quantity of gold in gold/quartz ore.

Cheers,

Dr. Ron

NanoFoil^® can be packaged in tape & reel, bulk containers, or waffle packages. Here are the main advantages of each type of packaging:

• Tape & Reel: great choice for high-volume automated pick & place equipment

• Waffle Pack: perfect for hand placement or low-volume automated placement machines

• Bulk: most economical way to order

Packaging NanoFoil^® is actually a lot like packaging standard solder preforms. (Here is a complete list of our packaging options for preforms.)

Folks,

Our discussion of Weibull Analysis continues.....Let’s say you have worked hard and assembled some SMT lead-free PCBs for thermal cycle testing.  You used the best lead-free solder paste, and some lead-free solder preforms as you assembled several through-hole components with the Pin-in Paste process.  You were a little concerned with the assembly process as the board was thermally and physically massive and the reflow process needed to be a bit above the recommended temperature and time.

The results of the thermal cycle testing are shown in Figure 1 below.  You dutifully report the characteristic life (or scale) as 2,387 cycles and the first fail at 300 cycles.  You were quite disappointed, as in the past similar, but slightly smaller boards, had a slightly higher scale, but more importantly, the first fail was about 1,000 cycles.  Anyway, you write you report up and file it away.

Figure 1. A Weibull Plot of the Thermal Cycle Data

Hold on!  The data are screaming at you the something is going on.  Look at the same data in Figure 2.  Note two distinct lines shown in green.  These two separate lines suggest very strongly that there are multiple failure modes.  The line furthest to the right is likely the typical failure mode observed in the past.  The line to the left is a new early failure mode.  It could be due to something like oxidized pads or some other phenomena not seen when testing similar but smaller boards.  Root cause failure analysis should be performed to try and understand to new failure mode.

Figure 2. A Weibull Plot of the Thermal Cycle Data with Multiple Failure Modes Noted

Now for a human interest note:

One of the rewarding aspects of being a professor at Dartmouth is the outstanding nature of many of the students.  They are not just good academically, but often are talented artistically, athletically, etc.  This point was brought home to me recently.  In a class I teach, ENGS 1: The Technology of Everyday Things, we were recently discussing the conservation of angular momentum (CoAM).  One of the most striking ways to demonstrate CoAM is an ice skater’s spin.  I went on the internet and could not find a good video of a spin.  I then remembered that one of my former students, Julia Zaskorski was on Dartmouth’s figure skating team.  I asked her if she had a video she could share.  It appears below.  She is a materials science and physics major.  Who knows, maybe we will see her at APEX or SMTAI in a few years. 

Here is a little bio in her own words:

               My name is Julia Zaskorski, and I’m a junior from Wellesley College taking part in the 12 College Exchange Program at Dartmouth.  At Wellesley I am majoring in physics with the intent to pursue mechanical engineering.  Despite Wellesley’s relationship with nearby MIT, Wellesley does not have its own engineering program, so I sought out the more self-contained curriculum and atmosphere at the Thayer School of Engineering.  In addition to the draw of the Thayer School, the Dartmouth Figure Skating team was also a hugely motivating factor for my exchange, as Wellesley does not have a team, let alone a rink.  I have known the coach of the Dartmouth team for several years now, and to finally see my name on the roster for the team is a dream come true.  The engineers, as well as the winter activities here in Hanover, pulled my heart to Dartmouth long before I’d ever set foot on campus. 

  Cheers,

  Dr .Ron                           

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

Folks,

In continuing our discussion on Weibull Analysis, let’s assume we assembled some SMT and through-hole PCBs with lead-free solder paste.  On this board are also some bottom-side terminated (BTC) components (often called QFNs), that are also assembled with solder preforms.  A stress test is performed to test the BTCs.  In such a test, the first fail in Weibull analysis is the most important data point.  No matter the results of remainder of the data, these later fails cannot undo the effect of a very early first fail. 

To understand this concept, let’s look at the Weibull chart below.  In many high reliability applications, there may be a requirement that some small percentage of the components under test have at least some minimum reliability.

Figure 1.  Weibull Analysis with an Early Fail.

As an example, let’s say that 1% of the components cannot have less than 500 cycles of life.  By looking at Figure 1, we see that 1% have less than 150 cycles of life (see arrow.)  This one early outlier dramatically affects the Weibull Analysis.

However, if that outlier was removed, as seen in Figure 2, the data suggest that 1% of the components will have a life of 900 cycles.  We can see the dramatic effect the first fail has on this result.  Note that the first fail does not affect the “scale” or characteristic life much (2647 vs 2682).  Hence, the characteristic life, is not a robust metric to use in a high reliability environment.  However, the shape or slope is dramatically affected by the early fail as it changes from 2.22 to 4.23 when the early fail is “censored.” 

Figure 2. Weibull Analysis with the Early Fail Removed (Censored).

Why might an outlier like this exist?  Almost certainly there is something unusual about the early fail.  It might be something like an oxidized pad preventing good wetting of the solder.  Perhaps something like this failure mode might be discovered in root cause failure analysis.  However, I am typically opposed to censoring data, even with supportive failure analysis.  I think the test should be done over.  It is often too easy to talk yourself into accepting inconclusive failure analysis.

What is your opinion?

Cheers,

Dr. Ron

Folks,

A while ago I discussed the Weibull Distribution and its importance in electronics reliability analysis.  This distribution has been used to evaluate the life of solder joints whether formed in SMT, wave, or even using solder preforms. In the next few posts, I would like to discuss how to interpret Weibull plots.

Let’s consider two Weibull plots from thermal cycle testing of lead-free solder joints as seen below in Figure 1.

Figure 1.  A Weibull Plot of Thermal Cycle Data for Alloy 2 and Alloy 4.

Both alloys have almost exactly the same scale, or characteristic life. You will remember that characteristic life is the number of cycles at which 63% of the test subjects fail.  For Alloy 2 it is 2,593 cycles and for Alloy 4 it is slightly better at 2,629 cycles.  However, these two alloys performed dramatically differently.  The most striking difference is in their “spread.”  We see this much greater spread for Alloy 4, when we plot a fit to the data as a normal distribution, as in Figure 2 below.

Figure 2. The Best Fit Normal Distribution Plot for Alloy 2 and Alloy 4.

In the Weibull plot, the data for Alloy 2 has a very steep slope or shape factor, this indicates a tight distribution.  A tight distribution is desirable as it facilitates more accurate prediction of thermal cycle life.  Alloy 2 is clearly superior.  So, in a Weibull distribution, not only is a large scale factor or characteristic life desired, but so is a steep slope or larger shape factor.

Next time we will talk about outliers.

Cheers,

Dr. Ron

Folks,

Let’s step away from electronics assembly challenges, and deep considerations of solder paste, solder preforms, and wave soldering, to ponder where electronics have gone in the last decade or so. 

The mobile phone of the early 2000s was just that, a phone. Today it is a phone, music player, PalmPilot-type organizer, camera (still and video), video player, gamer, TV remote, GPS system, web portal, etc.  There is almost nothing electronic that it can’t do.  The USB memory stick of 2002 with 0.5GB of memory cost $500, today $5 will get you 4GB one, a cost reduction of 800 to one, the equivalent of halving in price about every year.

There is no reason to expect any less dramatic advancements in the future.  But, predicting the future of electronics is never easy.  In the January 2013 edition of Scientific American  Ed Regis wrote an article titled, The Bold and Foolish Effort to Predict the Future of Computing. In this article, Regis interviewed eight computer luminaries, including Stephen Wolfram and Nathan Myhrvold,  to ascertain their perspectives on where computing will be in 150 years.  The conclusion was that no one can predict the future of computing, as interviewee George Dyson said, “All I can guarantee is that any prediction will be wrong."

One person less humbled by the difficulties of computing predictions is Ray Kurzweil.  His prediction success level of more than 80% would seem to support such confidence.  Kurzweil also just got a new job at Google. I am finishing his new book “How to Create a Mind: The Secret of Human Thought Revealed” and, while I  finding it fascinating, I think he goes too far.  He believes the mind is a sophisticated computer and that, when computers get to a certain point equaling and surpassing the human mind's computational ability, they will be considered human.

Supporting this point, he hopes to, someday, resurrect his father, as Bloomberg states:

“Among the stranger things Ray Kurzweil will say to your face is that he intends to bring his father back to life. The famed inventor has a storage locker full of memorabilia—family photographs, letters, even utility bills—tied to his father, Fredric, who died in 1970. Someday, Kurzweil hopes to feed this data trove into a computer that will reconstruct a virtual rendering of dear old Dad.”

Call me a religious fanatic, but I think there is something more to each of us than our memories and our brains computing ability. 

Kurzweil endorses IBM's computer system, Watson’s victory in Jeopardy  in February of 2011 as a major step in the direction of computers as humans.  IBM provided commercial support for these Jeopardy episodes.  In the commercials they strongly reminded us that Watson was not thinking, but only doing what it (not “he”) was programmed to do.  Someone summed it up nicely, Watson won, but did he know he won?

I think there are a few major things that people like Kurzweil minimize when they propose that computers will be recognized as human.  These points are:

1. Humans are sentient (they would know whether or not they won or lost Jeopardy, we have emotions and feelings).  I know of no progress in sentience development for machines.
2. Humans have a will.  We get up in the morning, we decide what we will do that day and do it.  There is no progress (thankfully?) in giving computers a will.
3. Humans have a biological body.  We smell the newly cut grass, feel a refreshing breeze, get tired, enjoy a meal, enjoy sports etc.   It is easy for some to minimize the importance of the body in being human. Again no progress in this area.

However, I don’t want to minimize much of what Kurzweil predicts.  In her ground breaking book, Alone Together, Sherry Turkle tells us that, in addition to the fact that the average teenager in the US sends 200 text messages a day, electronic companions already exist.  As time goes by they will become more realistic and will be capable of interesting and stimulating speech and interaction.  Having all of the world’s knowledge at their fingertips (pun intended), these companions will likely be more stimulating than people, they will easily pass the Turing Test, and, for good or ill, will make us more “alone together” than ever.  But our companion will not love, fear, hate, or know that it is a companion.

As has been pointed out, this brave new world is coming whether we like it or not.

BTW, on another topic,  the History Channel has produced a terrific video series, Men Who Built America http://www.history.com/shows/men-who-built-america.  It is a the spell-binding story of Vanderbilt, Rockefeller, Carnegie, J. P. Morgan, Edison, and Henry Ford.  If you missed it, it is coming out in DVD in January.

Cheers and Best for the New Year,

Dr. Ron

We’ve heard about the solder paste “graping” defect, but the same oxidation challenge occurs in other solder forms as well, such as solder washer preforms used to attach small connectors. 

Solder graping is a defect that arose as a result of small solder paste deposits and higher (than were used in the past) reflow temperatures.  The peak reflow temperature for SnPb alloys were just over 200°C, but. with SnAgCu alloys, that peak is as high as 260°C.  New solder pastes have been developed that address this defect by utilizing flux chemistries that function as an oxidation barrier.

But what about other solder forms? 

I was recently working with a customer who was evaluating solder preforms for a connector application.  These solder washers (outside diameter of 0.025”), like the small solder paste deposits, had a large surface area with a tendency to oxidize on their heated journey to melting.  These washers were made of SnAgCu, so the peak temperature required of them was no different than it would be for Pb-Free solder paste.

I found that the same 1°C ramp that causes graping of solder paste can do so for preforms as well.  The difference though, is that the non-molten portion of solder takes the shape of its un-reflowed form, that of a small washer in this case, as opposed to the “grapes” of aggregated solder powder.  

Fortunately, the issue can be addressed in 3 ways, and I encouraged my customer in this case to process their assembly using the combination:

1. Adjust the reflow profile. Ed Briggs' recommendations work well here.  Further, use a fast ramp to peak. I tested the reflow on a hot plate set to 250°C; this improved the wetting.  Preforms are unique from solder paste in that they are solid metal, as opposed to a mixture of metal and flux.  They do not benefit from the same heating controls that solder paste requires. 
2. Reflow in nitrogen.  By purging out the environmental oxygen during the reflow process, the solder preform will not oxidize.
3. Apply a tacky RMA flux, such as Tac007.  RMA fluxes provide stronger oxidation barriers than other non-rosin flux types. 

In the second image here, it is evident the improvement these changes made in terms of the spread and coalescence of the solder preforms. Note that the addition of tacky flux left an amber-colored no-clean residue, however, this can easily be washed away using a mild solvent.

Any questions?  AskUs@indium.com!

Over the years, solder alloy choices have been pretty stable.  In the last century, SN63 and SN62 could be found at any company making any kind of electronic device, and both alloys were the backbone of every company making solders.

But, when lead was identified as causing health issues, it was legislated out of everything from paint to gasoline to electronics, including solders.  In 2003, RoHS (Restriction of Hazardous Substances) was passed in Europe to restrict the use of lead (as well as mercury, cadmium, hexavalent chromium, and polybrominated diphenyl ethers: PBDE) in electronics and electronic equipment.

The electronics industry is now focused on SAC alloys (so named because they contain Sn, Ag, and Cu).  But, there is also SnAg, which was used in the lead era when a higher melting point was required.  The addition of the copper (in SAC) offers the benefit of improving wetting and potentially reducing the silver content from a non-copper alloy like 96.5Sn 3.5Ag. 

But, there are many applications where SnAg works well. Changing from it would require customer and/or government approval, and that involves a lot of extra money and time. This lead-free alloy works well in the assembly of a variety of medical devices that use non-traditional metallizations and fluxes.  The Cu addition (in a SAC alloy) probably would not improve the results enough to warrant the cost of requalifying an existing medical device through government agencies, so they stay with what works. 

So, if you are using 96.5Sn 3.5Ag (or 96Sn 4Ag), don't be afraid to stick with it.  Indium Corporation offers both of these solder alloys (and over 250 other alloys) in a variety of forms: preforms, wire, paste, and ribbon.   And, if you want to look at the SAC alloy family to see if it works better in your application, we will help you with that, too.  Just contact our Application Engineering Staff for help.

Carol

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

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

It is hard to believe, but 50 years ago, on October 9th, the first visible light LED was demonstrated by Nick Holonyak, Jr. of GE Advanced Semiconductor Laboratory in Syracuse, NY (just down the road from Indium Corporation's global headquarters).  Fortunately, he did not listen to his critics who said mixing gallium arsenide and gallium phosphide would not work to make a visible light LED, because they were wrong!

According to Roberto Baldwin at www.wired.com, Holonyak predicted that LEDs would one day replace the incandescent light.  Today there are many efforts underway to make that happen.

Today, Indium Corporation is involved in several LED applications:

1) NanoFoil®:   High brightness LEDs use NanoFoil® to bond thermal pads to heat-sinking substrates.  By using the NanoFoil®, the standard reflow process (that can negatively impact brightness, color, and life time) is avoided.

2) Gallium Trichloride: This is used as the starting material for making gallium-based metal organic precursors, such as tri-methyl gallium, which are used in the LED industry.

3) Indium Trichloride Also used as a starting material, but for indium-based metal organic precursors such as tri-methyl indium.  These compounds are also used in the manufacture of LED lighting as well as batteries and other applications.

4) Engineered Solder Materials: Attaching an LED to a substrate can also be done by using a variety of specialty solders, including bismuth-based (low temperature) solder preforms or solder pastes.  We also have a variety of thermal solutions that can help dissipate the heat generated by the LED.  Flux-coated solder preforms provide solder and flux in a consistent volume, for use under larger LEDs to reduce or eliminate voiding. 

It may have taken 50 years to see the widespread adoption of this technology, but there is no doubt that it is here to stay!

Contact us for more information or visit www.indium.com and see our new web site.

cgowans@indium .com

Carol Gowans

One of the biggest misconceptions about NanoFoil^® is that it is a form of solder. While it may contain a solder coating if specified (usually tin), it is really a heat source. A NanoBond^® requires solder, whether it comes from a plating on the joining surfaces, additional solder preforms, or on the NanoFoil^® itself.

Surface Coating

There are many ways to deposit solderable coatings onto parts that will be NanoBonded. Sputtering, thermal evaporation, thermal spray, plating, and HASL (hot air solder leveling) are just a few of the options. Coating the parts that will later be bonded tends to make assembly a bit easier.

Solder Preforms

If the parts have a gold or silver surface finish already, a thin solder preform is a very simple way to apply solder in the assembly. Preforms are sold as custom-shaped foil for your application.

NanoFoil^® Coating

Although Sn is the most popular solder coating for NanoFoil^®, it has been custom plated for individual customer applications with indium, traditional solder alloys, and even Au/Sn.

By the way, make sure there is solder on both sides of the NanoFoil^®. I almost overlooked this very point today while I was bonding a set of industrial batteries. There was solder on the battery terminal, and I was about to use bare NanoFoil^® to bond it to a gold plated board. Luckily we had some tin plated NanoFoil^® that I used instead – to ensure there was sufficient solder on the board side of the interface.

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