Down the Drain

Figure 1 shows a closeup photo of a PCB assembly, it seems as though solder has flowed “down the drain” and away from the solder joint where it’s needed.

In fact it has, because the customer has inconveniently located a via right through the center of one of the two topside SMT pads for a surface mount component. When the assembled PCB is run through reflow, the molten solder drains away through the barrel of the via and out the other side of the PCB. There isn’t enough solder remaining post-reflow to create an acceptable solder joint per IPC-A-610. The joint is “starved”; this is unacceptable. What to do?

Figure 1. Insufficient solder, i.e., "starved" solder joint on an SMD pad.

Figure 1. Insufficient solder, i.e., “starved” solder joint on an SMD pad.

The via is there to stay, by virtue of the customer design. So, no matter how many times solder is added to the joint, every time the PCB is run through the reflow oven the solder is going to drain away because the PCB , including the via, is at reflow temperature.

Obviously, more than one run through the oven makes no sense. The only practical solution is to manually add solder to the individual solder joint, post-reflow, without running the entire PCB through another thermal cycle. It’s a touchup procedure that’s required to create a robust SMT solder joint that meets acceptability criteria. This is a manual PCB assembly soldering process that should be performed by a skilled hand-soldering or rework operator. Solder is added only to the joint, via cored wire solder or solid wire with flux, in order to build up the volume of solder at the solder joint to provide strength, connectivity, and an acceptable meniscus per IPC standards, covering the via drain-hole. The solder won’t flow through the via because only the surface joint area is heated.

Figure 2. The solution: Add solder to the joint manually via a touchup procedure.

Figure 2. The solution: Add solder to the joint manually via a touchup procedure.

It may seem tedious, but a skilled operator can touch up the joint in a few seconds, and if there is only one instance per assembly it won’t appreciably cause production delays.

Roy

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The Cost of Misunderstanding Standards

An article in the latest issue of Assembly magazine asserts that use of standards, specifically IPC-A-610 and J-STD-001, raises the cost for US manufacturers and has led to the widespread offshoring of assembly.

The premise of the article, authored by a Dr. James A. Smith of Electronics Manufacturing Services Inc., is that standards drive up costs. This is stunning in that it completely mischaracterizes a core reason standards exist: to ensure widespread uniformity to a predefined level of quality.

Indeed, as someone who has traveled extensively abroad — I have spent more nights in Shanghai than any city other than the ones I have actually lived in — I can unequivocally state that manufacturers in China, Taiwan, Malaysia and so forth use IPC-A-600 and IPC-A-610 almost exclusively. And the reason is, those are the standards that their Western customers demand. Southeast Asia might offer lower labor rates, but that has nothing to do with IPC-A-610. As they used to tell me in stats class, correlation isn’t causation. I’m surprised Dr. Smith’s grad school teachers didn’t drill that conceit into him.

In the article, Dr. Smith asserts that “cost-plus” contracts reward poor manufacturing by ensuring that the assembler gets paid a set margin even if low yields lead to high rework costs. Besides being expensive, rework, of course, can be detrimental to the long-term board quality. Says Dr. Smith:

Some types of heat damage—lifted pads, delaminated circuit boards, and melted component bodies to name a few—are easily recognized. However, soldering iron heat causes serious degradation inside components such as ICs where the damage can’t be seen. The most prominent example of such damage is accelerated growth of the intermetallic (“purple plague”) between the gold wire bond and the aluminum pad on the chip substrate. As the intermetallic grows, electrical resistance inside the connection increases and switching characteristics change; depending on the sensitivity of the circuit, this change alone can be fatal. Even worse, Kirkendall voids develop in place of the pad material and breaks develop around the edges of the pad.

Therein lies the problem: Dr. Smith gets the technical details right and yet extrapolates from them a complete fallacy, writing “touchup and rework are all about deceiving the customer who, unwittingly, receives product with higher probability of premature failure.”

I am a former member of the IPC technical staff responsible for IPC-A-610 and J-STD-001. Having spent many a weekend in J-STD-001 meetings, I can state from experience that many defense contractors pushed to ease certain requirements in order both to save money and improve reliability. In one instance that springs to mind, Boeing provided ample evidence that minimum hole fill could be reduced because, they found, although a higher percentage of hole fill was seen as more reliable, in practice inspectors would have the rework technicians hit nonconforming holes with the solder gun, and the additional temperature excursion *reduced* long-term reliability more so than the greater volume of solder in the hole could increase it. These types of discussions don’t show up in the final boxscore, but you can’t understand the outcome of the game without knowing them. If Dr. Smith hasn’t been able to “unearth the data” behind the standards, it is because he hasn’t attended the meetings.

He also takes aim at the American industry for ignoring the teaching of the great quality gurus. “Instead of the focus on results emphasized by Deming and Juran, industry has embraced paperwork bureaucracy.” In fact, Dr. Deming focused on process, with the idea being a perfect process would net perfect results, and his “knowledge of vriation” concept runs through J-STD-001. At its core, J-STD-001 is a process driven document; a company that doesn’t understand SPC and process deviations has no hope of properly instituting it.

This all indirectly raises a separate point, however, namely: that it is critical for the US to maintain control of the standards. As my old friend Dieter Bergman used to tell me, he who controls the minutes controls the meeting. By authoring the standards (and making sure that the key Western OEMs are active contributors), the US can ensure a place at the international table far superior to the one our depleted manufacturing base would otherwise allow.