It All Adds Up at Count on Tools

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When you work from a home office, nothing is more enticing than an opportunity to “get out” and see a customer and take a facility tour. So, last week, “get out” I did and hit the road from Fayetteville, GA, up to participate in a tour of Count on Tools in Gainesville, GA.  (For those unfamiliar with Georgia geography and traffic – yes, that is a bit of a drive, but, thankfully, I-85 has been repaired.)

This tour was organized by the Georgia Manufacturing Alliance. This group serves manufacturing businesses in the state and provides monthly plant tours, educational sessions and networking opportunities  “designed to help make profitable business connections for our members.” They put on all sorts of very cool tours throughout the state – including one I was sorry I missed of the KIA plant. Jason Moss, the founder and CEO of GMA, has, in fact, been a great supporter of our local SMTA Atlanta Chapter as well as a featured keynote.

But, I digress. Back to Count on Tools – longtime CIRCUITS ASSEMBLY friend, supporter and 2017 Service Excellence Award winner for Automation and Handling Equipment. I was greeted warmly at the door by Curt Couch, president and CEO, and we chatted about how nice it was to see each other outside the confines of a busy trade show.  He and his wife, Rene, started this business about 26 years ago literally in their backyard. And what an amazing success story from such an unassuming but obviously visionary guy. He said he never expected this level of growth, but here they are today with about 40 employees and a 20,000-sq. ft. facility.

For those who may not know, COT is a precision component manufacturer specializing in CNC Swiss automatic machining using standard to exotic materials including stainless steel, titanium, Inconel and PEEK. They are a global supplier of precision engineering components to a wide range of industries. And, of course, in our industry we know them for their nozzles and tooling, automation tooling and component handling equipment. Just this month, they finished an expansion of their manufacturing facility.

The consistent comment from the tour group (which was comprised of professionals from other manufacturing and service facilities throughout Georgia) – “what a beautiful, clean facility, well run and organized.”  And, the camaraderie among the Count on Tools employees was evident as well.

Zach Shook, operations director, Marketing and IT was also on hand, and we discussed our upcoming travel plans for SMTAI and Productronica. I caught up with my friend Tom Foley from ASM, who is a customer of COT. Prime, a contract manufacturer here in Georgia, was also represented as well. (Shameless plug  – our next SMTA chapter meeting will be held at Prime, and our speaker with be Jeff Timms, managing director of ASM Americas.  He will speak on “Enabling the Digital World” which highlights many of the upcoming and future technologies which will drive the electronics assembly industry into the future.)

All In all, Count On Tools is an impressive manufacturing success story and a day well spent!  Thank you Curt, Rene, Zach and the Count on Tools team for your hospitality.

Frances Stewart is vice president for PCD&F/CIRCUITS ASSEMBLY.

QFN Center Pad Revisited

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The QFN (quad flat pack, no leads) package can no longer be considered exotic. It was when I first wrote about it a decade ago, but not anymore. In fact, with the wafer-scale BGA, it’s one of the more common packages for new chip designs.

Not all QFNs come with an exposed metal pad underneath, but most do, and that can cause problems with reflow solder. The pad itself isn’t the problem, but improper solder paste stencil layer design can be.

The default stencil layer in the CAD library footprint might have an opening the full size of the metal pad. If that’s the case, modify the footprint so that there will be 50% to 75% coverage with solder paste (Figure 1). If you don’t, it may result in yield problems. With a 100% open area, the likely result is too much solder in the middle. The part will ride up, or float, and may not connect with all of the pads on the sides of the part.

Figure 1

Figure 1. The optimal QFN footprint will have 50% to 75% solder paste coverage.

 

Figure 2 shows a stencil with too large an opening in the center, a segmented paste layer in the CAD footprint, and the resultant segmented stencil.

Figure 2

Figure 2. Stencils shown with too large an opening in the center (left), segmented paste layer (center), and the resultant segmented stencil (right).

 

You may note that I said to shoot for 50% to 75% coverage and ask: “Well, is it 50% or 75%? What gives?”

True, that is a bit of ambiguity. Anything in that range should be fine for prototype boards, however. If the assembly is headed for volume production, work with the manufacturer to tweak the design for best high-volume yield.

The good news on this front is that many QFN manufacturers and parts library creators have taken notice. It’s far more likely now than it was 10 years ago to find a datasheet correctly illustrating this, and footprints created correctly. But, always check your footprints to make sure.

Duane Benson

http://blog.screamingcircuits.com

How Far Can We Go to Replace Lead?

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The end is nigh for lead in solder, as our columnist Tim O’Neill writes this month in CIRCUITS ASSEMBLY.

Rules governing use of the materials — Directive 2015/863, aka RoHS 3 — are coming online and will be in full force by 2019.

Suppliers have until July 22, 2019 to meet the stricter provisions, which includes no more than 0.1% lead in medical devices, which are joining consumer, industrial and other electronics products on the effectively banned list.

The question Tim poses is, What comes next? Already, the future of commonplace unleaded alloys such as SAC is being questioned. As Tim writes, “It is even feasible SAC 305 will be dislodged by a new de facto alloy that better serves the needs of the market.”

A Norwegian scientist believes he may have the answer. As noted in Phys.org this week, Dr. Henrik Soensteby of the University of Oslo is working on an alternative alloy that contains nothing but common — and essentially benign — elements. In conjuring up his alloy, Soensteby is mixing sodium, potassium and oxygen with niobium, a very strong metal typically used in steel. While niobium dust is reported to cause eye and skin irritation, it reportedly is nontoxic, at least in the volumes used.

It’s not so clear yet how much niobium would be needed. Brazil is the biggest supplier of niobium, producing more than 85% of it each year. Other sources include Zaire, Russia, Nigeria and Canada. World production is relatively light: around 25,000 tonnes per year. Some scientists believe there are ample supplies still in the ground. There’d better be: Some 5 million tonnes a year of lead ores are mined each year, although obviously not all that goes into electronics.

Soensteby is optimistic he can use atomic layer deposition (ALD), a vapor phase method that uses gas at controlled temperatures to stimulate a reaction with the substrate; the output is thin films. It is an emerging technology in semiconductor manufacturing. There are many, many questions, of course. First and foremost, does the alloy actually, you know, work? Also, ALD typically involves higher temperatures than are used in electronics assembly: Would it work with today’s packaging? Will other technologies such as 3D printing or Joe Fjelstad’s solderless Occam process supplant the need for solder in any form?

Still, materials science is the most exciting area of electronics today. We may make fun of folks who walk around with smartphones seemingly permanently tethered to their ears, but we also have them to thank.

 

Register now for PCB West the Silicon Valley’s largest PCB industry trade show: pcbwest.com! Now with full-day electronics assembly tutorials!

 

Intermetallics and Kirkendall Voids Continue to Grow at Room Temperature

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Folks,

In my last post, I discussed intermetallic compounds (IMCs) and what I referred to as the “miracle of soldering.” I also mentioned that research focused on the brittle nature of IMCs suggests that failures in stress tests are more likely due to failures between the interfaces of the IMCs and the solder, the IMCs and the copper, or the IMCs (Cu6Sn5 with Cu3Sn) themselves and are not related to any perceived brittle nature of the IMCs.

Another weakening mechanism in soldering and thermal aging of solder joints is Kirkendall voids. Kirkendall voids form when one metal diffuses more rapidly into another metal than vice versa. A copper-tin interface displays such a mechanism. Copper diffuses into the tin more rapidly than the tin into the copper. This mechanism can result in actual voids in the copper at the metal interface. See the image below. In addition to causing a possible weakness at the interface, the excess copper that diffuses into the tin creates compressive stresses than can result in tin whiskers.

Kirkendall voids

(Source: http://www.jfe-tec.co.jp/en/electronic-component/case/img/case_solder_02.png)

IMCs and Kirkendall voids are formed quite quickly at soldering temperatures. However, even at room temperature IMCs and Kirkendall voids continue to grow, albeit at a much reduced rate. The reason for this continued growth is that on the absolute temperature or Kelvin scale, room temperature is a considerable fraction of the melting temperature of solders. As an example, the melting temperature of SAC is about 219°C, this temperature is equal to 492K (219+273), whereas room temperature is 295°K, so room temperature is 60% of the way to the melting point of SAC solder (295/492 = 0.60). Compare this situation to steel, which melts at about 1480°C. The steel would be red hot at 60% (780°C) of its melting point on the absolute scale. So, since room temperature is 60% of the way to melting, the IMC and Kirkendall forming processes don’t stop at room temperature. Hence, IMCs and Kirkendall voids continue to grow, as do related effects such as tin whiskers.

Stay tuned. Next time we will discuss IMC growth rates and resulting effects in stress testing as we wrap up this series on IMCs.

Cheers,

Dr. Ron

 

So Long, Sola

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I have to say, I didn’t think Jure Sola would or could last this long. The cofounder of Sanmina, Sola was one of the poster boys for wanton M&A excess, snatching up more than a dozen companies or OEM plants during the late 1990s and early 2000s. The spree culminated in the purchase of SCI Systems in mid 2001, a $6 billion deal that saddled the company with so much debt, when the ensuring tech collapse occurred, it was forced to take 20 straight quarters of “one-time” charges.

Most execs couldn’t have survived such a bloodletting. Sola wasn’t most execs, however. He continued to place his bets on fabricating in the US — in a memorable line, he told an IPC Printed Circuit Expo audience that “plating was in his blood” — and Sanmina remains the second (or third) largest board supplier in North America. Moreover, he correctly swung to the military and aerospace markets, eschewing the PCs that SCI was so dominant in.

Today the company is half the size in revenue of its peak, but consistently profitable.

Come October Sola will ride off into the sunset with his legacy intact, perhaps not the most beloved man to run a major PCB company, but a success nonetheless. In this era, that’s no small thing.

 

Green Herring

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For those newbies, Bob Herring was the perfect example of good timing, building up and selling not one but two board shops. The first, Industrial Circuits, was sold in 1989 for $60 million. The latter one, Herco Technology (which we profiled multiple times in PC Fab), went for $122 million in 2000, just a year before the tech crash. (The buyer of Herco, Teradyne, closed it less than two years later. The former Industrial Circuits lasted less than one year longer before Toppan shut the doors.)

In case you were wondering where Bob went, well, he started his own network cable news channel. It now is televised in some 30 million homes.

Guess there is life after PCBs!

 

 

Copper-Tin Intermetallics: The Miracle of Soldering

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Most articles discussing the copper-tin intermetallics that form during soldering refer to them as a necessary evil. The evil being the perception that intermetallics are brittle and can lead to failures in thermal cycling or drop shock.

I view the situation differently. From my perspective, the formation of copper-tin intermetallics is the miracle of soldering. Look at it this way, to assemble electronics, bonding copper to copper (the leads on the components to the pads on the PWB) in the presence of polymers (the PWB epoxies and the component cases) is required. These polymer materials can only take about 250°C for a few minutes. Copper melts at 1083°C, so bonding copper to copper in the presence of polymers would appear to be quite a challenge. Enter tin-based solder.

Lead-free (tin-based) solder, say SAC305, melts at about 219°C. So, with a peak temperature of about 245°C, in the reflow oven, solder can be melted and form an electrical and mechanical bond with the copper in the leads and pads. At 245°C, the many polymer materials are unharmed for the 90 seconds or so that soldering requires at this temperature.

But, what about the material properties of the intermetallics that are formed? Aren’t they too brittle? Lee et al* performed analyses that suggest that the intermetallics formed in soldering are not brittle. Their work also suggests that the failure modes are not in the intermetallics, but in the interfaces between the intermetallics and the solder, copper, or the different intermetallic compounds, Cu3Sn and Cu6Sn5. These two intermetallic compounds are shown in the figure below.

Copper tin intermetallics from Roubaud et al, “Impact of IM Growth on the Mech. Strength of Pb-Free Assemblies,” APEX 2001.

 

It has long been assumed that the thicker the intermetallics, the greater the risk of failure due to the intermetallic thickness. Lee’s work would appear to bring this concern into question.

Stay tuned for a continued discussion on intermetallics and their effect on reliability.

*Lee, C. C. et al, “Are Intermetallics Really Brittle,” IEEE Electronics Components and Technology Conference, 2007, pp. 648.

Cheers,
Dr. Ron

Jim Raby, RIP

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I’m saddened to get the news this morning that Jim Raby has passed away. As longtime readers will know, Jim was one of my favorite persons, not just in the industry but in life. What a tremendous fighter he was for doing things right! I will always miss him. 

My sincere condolences to his wife Ellen, son David and everyone at STI on this sad day. We have lost a fine engineer, gentleman and human being.