Tin Whiskers 101: What Are They?

Folks,

Tin whiskers are very fine filaments or whiskers of tin that form out of the surface of the tin. See Figure 1. They are the result of stress release in the tin. Tin whiskers are a phenomenon that is surprising when first encountered, as their formation just doesn’t seem intuitive.

Figure 1. Note how thin a tin whisker can be compared to a human hair. The image is from the NASA Tin Whisker Website

They are a concern, as they can cause electrical short circuits or intermittent short circuits as a fusible link. Lead in tin-lead solder greatly suppresses tin whisker growth. Therefore, with the advent of lead-free solders there is a justifiable concern for decreasing reliability due to tin whisker growth in electronics.

Tin whiskers can vary in length and width, as is seen in Figure 2. Note that although only about 10% are as long a 1000 microns (1mm). That length and occurrence rate is such as to cause many reliability concerns.

Figure 2. The length and width of some tin whiskers. The source is also the NASA Tin Whisker Website.

Over the following weeks I plan to post how tin whiskers form and strategies to alleviate them. Most of the information I will post comes from a paper I presented with Annaka Balch at the SMTA PanPac 2019.

NASA has an excellent website that provides much information about tin whiskers and is a source for historic critical failures caused by tin whiskers.

Cheers,

Dr. Ron

The ‘Seers’

It’s always interesting when the seers, also known as the industry’s journalists, get together for a chat.

Hosted by Mike Konrad, I joined Trevor Galbraith, Phil Stoten and Eric Miscoll to discuss post-pandemic production, innovations in our industry, supply chain and labor shortages, and of course, some predictions.

The podcast can be listened to or downloaded from PCB Chat here: https://upmg.podbean.com/e/rm-76-meet-the-press/

Or, if you are really brave, you can see us in action here:

Reducing the Environmental Impact of Electronics Manufacturing

Manufacturers are increasingly evaluating the environmental effects of their practices as eco-consumerism becomes more widespread. Companies can increase their profits by making their product development more sustainable and supporting energy-efficient infrastructure development.

President Biden allocated trillions of dollars to the sustainability sector, promoting low emission production. Reaching carbon neutrality requires a restructuring of the electronic manufacturing sector. Before evaluating the impact of reduction methods, we must examine the degradation associated with commonly used devices.

Life Cycle Assessment

A significant portion of electronic development derives from material mining. Many devices contain lithium-ion batteries, linking manufacturing processes to ecological degradation. Inadequately maintained mining sites pollute local water supplies, like the Liqi River in Tibet. Here, a lithium mine generated a chemical leak, killing a significant quantity of marine life.

Mining also depletes local water sources in drought-ridden regions. Lithium derives from a saltwater brine, which workers extract. Over time, local farming operations suffer from low groundwater levels. The extraction process also pollutes the air, causing adverse health effects.

Inefficient manufacturing processes can also generate pollution by developing electronic waste. The U.S. produces the most e-waste in the world. Chemicals leach into the soil from electronic landfills, which degrades the environment and human health. These dumps contain lead, mercury, cadmium and more, polluting food sources and drinking water. They also contain persistent organic compounds from fire retardants. When consumed, the substances cause cognitive defects in children and behavior or motor skill challenges.

Another environmentally degrading factor of production derives from energy use. China manufactures the highest portion of electronics globally. Coal is China’s largest energy source, fueling many production facilities.

When products leave the center, they absorb a portion of the emissions generated. Fortunately, manufacturing facilities can increase the sustainability of their products by using renewable energy sources. Over time, their environmental impact will decrease.

Renewable Energy Sources

Large corporations recently adopted renewable energy systems in production, meeting eco-consumerism demands. Over the past year and a half, BMW used solar and wind power to decrease the emissions generated by its manufacturing facilities. It also increased the energy efficiency of their products, shrinking their carbon footprint throughout their life cycle.

If China’s electronic manufacturing facilities converted from coal-powered electricity toward renewable energy, they could significantly increase their practices’ sustainability. Reducing greenhouse gas emissions and adding energy-efficient appliances can decrease a company’s carbon footprint.

Some companies decrease their production facilities’ ecological impacts by swapping conventional lights with light-emitting diode (LED) bulbs. The bulbs absorb 75% less energy than incandescent lights and last 25 times longer.

Improve Product Longevity

The best way to target e-waste is through improving products’ longevity. Some companies utilize planned obsolescence to maintain a consistent revenue stream. The expiration date on electronics increases e-waste production and decreases their sustainability.

Some electronics companies source ceramic and glass for product development. The materials have a limited defense against electronic stressors and generate pollution over time. Replacing the materials with liquid silicone rubber can make a product last longer and eliminate the normalization of planned obsolescence.

Manufacturers can also sustain economic gains by increasing the price of long-lasting products. Customers are more likely to purchase sustainable goods over their less expensive counterparts. If we build products to last, it increases profitability while decreasing environmental impact.

Recycled Materials

Rather than mining lithium-ion battery elements each time we produce new electronics, we can utilize recycled materials. Environmental engineers and scientists are generating efficient lithium-ion recycling technology, extracting functional features from the devices. The Department of Energy (DOE) developed the first recycling center, increasing the industry’s profitability.

The DOE also developed a program influencing professionals to develop advanced lithium-ion recycling technology. It offered the winner a $5.5 million reward to expand the system’s efficiency. When using recycled materials, manufacturers can reduce their reliance on ecologically degrading mining practices.

Where to Start

Manufacturers can begin decreasing the environmental impact of their practices by leaving fossil fuel-derived electricity sources behind. Renewable energy is abundant and currently cost-effective, improving sustainability rates while reducing utility costs. It also helps companies immediately reduce greenhouse gas emissions, shrinking their carbon footprint and making them more appealing to a new generation of consumers.

Jane Marsh is the founder and editor-in-chief of Environment.co where she covers topics in green technology, energy and environmental sustainability.

EMS on Overdrive

The EMS industry has posted several straight months of what some consider excessively high book-to-bill ratios. The April peak of 1.62 has only marginally fallen over the past couple months and, as of this writing, was 1.48 in June, the most recent data available.

As a refresher, the ratio is calculated by dividing the amount (in dollars) of bookings by the amount in shipments. In other words, if over a set time period a company gets $110 worth of orders and ships $100 worth of product, its book-to-bill ratio would be 1.10. A ratio over 1.0 is considered an indicator of future market growth.

So a positive ratio is a good sign, generally speaking, but too much of a good thing makes folks nervous. And ratios in the 1.40 and above range are historically at the high end.

Some are concerned of an overheated market, but conversations with several leading EMS firms suggest instead that OEMs are offering longer forecasts, which are inflating the numerator. For instance, if the typical window was six months, it might be nine or even 12 months now. That pushes more “orders” into the data pile, but it’s a mathematical anomaly, not a sign of double-booking.

I don’t expect the sky to fall, at least this time.

Hypothesis and Confidence Interval Calculations for Cp and Cpks

Folks,

I am reposting an updated blog post on Cp and Cpk calculations with Excel, as I have improved the Excel spreadsheet. If you would like the new spreadsheet, send me an email at rlasky@indium.com.

One of the best metrics to determine the quality of data is Cpk. So, I developed an Excel spreadsheet that calculates and compares Cps and Cpks.

———————————————————————————————————-

Folks,

It is accepted as fact by everyone that I know that 2/3 of all SMT defects can be traced back to the stencil printing process. A number of us have tried to find a reference for this posit, with no success. If any reader knows of one, please let me know. Assuming this adage is true, the right amount of solder paste, squarely printed on the pad, is a profoundly important metric.

In light of this perspective, some time ago, I wrote a post on calculating the confidence interval of the Cpk of the transfer efficiency in stencil printing. As a reminder, transfer efficiency is the ratio of the volume of the solder paste deposit divided by the volume of the stencil aperture. See Figure 1. Typically the goal would be 100% with upper and lower specs being 150% and 50% respectively.

Figure 1. The transfer efficiency in stencil printing is the volume of the solder paste deposit divided by the volume of the stencil aperture. Typically 100% is the goal.

I chose Cpk as the best metric to evaluate stencil printing transfer efficiency as it incorporates both the average and the standard deviation (i.e. the “spread”). Figure 2 shows the distribution for paste A, which has a good Cpk as its data are centered between the specifications and has a sharp distribution, whereas paste B’s distribution is not centered between the specs and the distribution is broad.

Figure 2. Paste A has the better transfer efficiency as its data are centered between the upper and lower specs, and it has a sharper distribution.

Recently, I decided to develop the math to produce an Excel® spreadsheet that would perform hypothesis tests of Cpks. As far as I know, this has never been done before.

A hypothesis test might look something like the following. The null hypothesis (Ho) would be that the Cpk of the transfer efficiency is 1.00. The alternative hypothesis, H1, could be that the Cpk is not equal to 1.00. H1 could also be that H1 was less than or greater than 1.00.

As an example, let’s say that you want the Cpk of the transfer efficiency to be 1.00. You analyze 1000 prints and get a Cpk of 0.98. Is all lost? Not necessarily. Since this was a statistical sampling, you should perform a hypothesis test. See Figure 3. In cell B16, the Cpk = 0.98 was entered; in cell B17, the sample size n = 1000 is entered; and in cell B18, the null hypothesis: Cpk = 1.00 is entered. Cell B21 shows that the null hypothesis cannot be rejected as false as the alternative hypothesis is false. So, we cannot say statistically that the Cpk is not equal to 1.00.

Figure 3. A Cpk = 0.98 is statistically the same as a Cpk of 1.00 as the null hypothesis, Ho, cannot be rejected.

How much different from 1.00 would the Cpk have to be in this 1000 sample example to say that it is statistically not equal to 1.00? Figure 4 shows us that the Cpk would have to be 0.95 (or 1.05) to be statistically different from 1.00.

Figure 4. If the Cpk is only 0.95, the Cpk is statistically different from a Cpk = 1.00.

The spreadsheet will also calculate Cps and Cpks from process data. See Figure 5. The user enters the upper and lower specification limits (USL, LSL) in the blue cells as shown. Typically the USL will be 150% and the LSL 50% for TEs. The average and standard deviation are also added in the blue cells as shown. The spreadsheet calculates the Cp, Cpk, number of defects, defects per million and the process sigma level as seen in the gray cells. By entering the defect level (see the blue cell), the Cpk and process sigma can also be calculated. 

Figure 5. Cps and Cpks calculated from process data.

The spreadsheet can also calculate 95% confidence intervals on Cpks and compare two Cpks to determine if they are statistically different at greater than 95% confidence. See Figure 6. The Cpks and sample sizes are entered into the blue cells and the confidence intervals are shown in the gray cells. Note that the statistical comparison of the two cells is shown to the right of Figure 6.

Figure 6. Cpk Confidence Intervals and Cpk comparisons can be calculated with the spreadsheet.

This spreadsheet should be useful to those who are interested in monitoring transfer efficiency Cpks to reduce end-of-line soldering defects. It is not limited to calculating Cps and Cpks of TE, but can be used for any Cps and Cpks. I will send a copy of this spreadsheet to readers who are interested. If you would like one, send me an email request at rlasky@indium.com.

Cheers,

Dr. Ron

An Antidote to a Complex Environment

Years ago, ahead of a US election, I used this space to pen an open letter to the new president. I wrote that the race for office was heated and intense, but the winner should put aside any ill feelings and work toward the betterment of all Americans.

The column was timed to hit readers’ desks in November, just after the election results were announced. Magazine deadlines being what they were, of course, I wrote it in early October – more than four weeks prior to election day. In short, I submitted it to the printer having no clue who was actually going to win.

More than a few readers didn’t catch that little nuance, and they filled my inbox with screeds both positive and negative about the outcome, projecting their own biases on my musings and utterly missing the point I was trying to make about leadership.

Since then, I’ve stayed away – far away – from anything that even hints of politics, sensing it’s too charged a subject to use even as a metaphor for a larger point.

So, when an industry friend whom I respect more than he will ever know suggested I write an editorial about electronics companies requiring vaccination, and, in his words, “come out swinging in favor of it,” my first reaction was indifference.

Then we conducted a survey of US readers and found just under 60% plan to attend face-to-face events this year, and the top reason for staying home is, of course, Covid-19. That’s no way to get business done, not when there’s a perfectly good vaccine – more than one, actually – available and in most cases free.

As Covid-19 cases increase across the nation, primarily with unvaccinated persons, it’s hard not to be frustrated at the current state of the world. This is a largely preventable disease, , provided we choose to prevent it.

Although I will probably pay dearly for using this space as a soapbox for something that goes beyond electronics engineering, I can’t keep quiet knowing just how badly it’s affecting our industry, not to mention our world.

With that, I strongly encourage all companies – not just US-based ones – to mandate vaccinations for all workers, full-time, part-time and contract-based. Any visitors to their offices should be required to show proof of vaccination too. 

I realize that the unvaccinated have their reasons, and I’m not going to argue with them. But let it be known I wholly disagree with their stance. We must ensure we are doing everything we can to protect the health of our employees and each other. It’s time to take a stand.

Would-Be Foxconn Beneficiaries: Always A Bridesmaid

The University of Wisconsin this week became the latest would-be benefactor of Foxconn’s pretend largesse to acknowledge that it has been, in fact, jilted.

A UW-Madison response to a public records request by the Wisconsin State Journal on Monday shows the Taiwanese electronics company gave $700,000 in the first year of a five-year agreement and no money in the second or third year. The amount to date represents less than 1% of the original commitment.

“I am not at this point expecting to receive that gift,” Blank said in an interview with the State Journal editorial board last week. “It’d be nice. I think it’s unlikely.”

— UW Chancellor Rebecca Blank

UW should feel no embarrassment at falling for the Taiwanese ODM’s promises of riches — in this case, $100 million in grants. The list of brides left standing at the altar by Foxconn is long and global.

Perhaps one day, when Foxconn comes knocking, the prospective bride will demand the ring — and the cash — upfront.

Somehow, however, I tend to doubt it.

From Boards to Brews

In case you were wondering whatever happened to IBM’s once sprawling campuses in Endicott, East Fishkill, and other western New York towns, where Big Blue made everything from semiconductors to laminates to circuit boards, the New York Times has the story.

Spoiler alert: Like so many other old mill buildings, breweries, among other businesses, are moving in.

Solution to Moore’s Law

Folks,

In a recent post, I discussed Moore’s Law. I challenged readers to solve for “a” and “b” from the equation a*2^(b*(year-1970)) from the graph in Figure 1.

Figure 1. Moore’s Law: Note that in 1982, ICs had about 100,000 transistors, whereas in 2016, they had about 10^10.

Moore’s Law posits that the number of transistors doubles every two years. If so, “b” should be 0.5. It ends up that “b”, from the solution in Figure 2, is 0.4885, so a double occurs about 1/0.4885 =2.047 years, but this number is really close to two years. The solution follows:

Figure 2. The Solution of a and b in the Moore’s law equation. 

BTW, congrats to Indium Corporation’s Dr. Huaguang Wang as he got a close solution.

Cheers,

Dr. Ron