原创 More on soldering practices

As a follow up to my previous post on engineers who cannot solder, I received an email from Jim Smith, president of Electronics Manufacturing Sciences Inc.

He said the people at his company focus on soldering, because it is both the heart of electronics manufacturing and the process that causes the most problems. For these reasons, his company specialises in soldering training/education, certification, and process development.

I reproduce Jim's email in its entirety as follows:

Hello Max. I came upon your column by fortuitous accident. You wrote with great insight into a critical problem in the US electronics industry. And, as I wrote hurriedly in my posted response, the problem is much greater than most people realise. Almost no one—not just engineers—knows how to solder. Most of those who take pride in their soldering skills are unaware that their technique is faulty.

I've been developing soldering processes, troubleshooting soldering process problems, and teaching all forms of soldering for close to 50 years. I've worked with hundreds of companies—from start-ups to the biggest corporations—all over the world, and I can tell you without fear of contradiction that lack of soldering knowledge is more prevalent now than ever.

The prevailing belief holds that a cosmetically attractive solder connection must be a good solder connection. But this is not necessarily true, especially if a soldering iron was involved in making that connection. At soldering iron temperatures, solder will stick to oxides and give the false appearance of a proper connection (you can read more in my document The Metallurgy of Heat-Induced Soldering). The compromised integrity of the solder bond itself affects reliability under conditions of vibration or thermal cycling, but the far more serious reliability consequence consists of degradation inside components, especially ICs. Applying such high temperature long enough to achieve adherence of solder to the oxidized surface causes the wire bonds inside ICs to degrade to an extent that would require decades of product use. The phenomenon is known as the "purple plague" (click here to see some discussions on this phenomenon). The damage is invisible, so everyone blames the component manufacturer when devices fail prematurely, but the root cause is improper soldering technique.

Today's hand soldering procedure was developed in the vacuum tube era for attaching wires to sockets. Those materials could not be damaged by overheating. Rather, the challenge was how to get enough heat into big metal objects using irons that were not very efficient at turning electricity into heat. The focus was entirely on keeping the parts hot enough, long enough so the solder would flow adequately without freezing.

When solid-state devices entered the picture, we began soldering the components themselves rather than their sockets. To prevent heat damage to the component, metal clips known as heat sinks were placed on leads next to the component body. This allowed the excess soldering heat to flow into the sink rather than stressing the component. As parts got smaller, however, there wasn't room for heat sinks, so they disappeared from the work instructions, but every trainee continued to be told to use the same technique developed for wiring vacuum tube assemblies. This is insane.

Complicating matters is the fact that electronics "soldering" has mostly been welding. Surfaces to be soldered have mostly been tin or tin/lead and those surfaces melted at or below 450°F (232.22°C), which is much lower than the temperature reached by those surfaces during "soldering." When a surface melts during application of solder, the heavy liquid solder easily pushes oxides and even contaminants aside; the liquid metals (solder and component surface) can then flow together. It's hard to imagine a less challenging application. But the lead-free movement and fear of tin whiskers have caused the use of new component surface metals that have much higher melting temperatures. Those surfaces don't melt during soldering, which means that the industry—for the first time in its history—must actually solder. But they (including most of the people who set industry standards) don't know how to solder; they only know how to weld.

In short, no one understands wetting forces and solderability. Nor do they have meaningful understanding of flux properties ranging from ionic contamination (acid residue) hazards to hygroscopic solids.

Soldering is the heart of electronics manufacturing, and lack of process knowledge is killing industry. Touchup (most of it unrecognised by management; what we used to call "the hidden factory") and rework are rampant.

Engineers get no coherent education about soldering. I don't know of any course aside from my company's Science of Soldering that teaches the chemistry, metallurgy, and physics of soldering. Operators and technicians get "certified" in the idiotic ritual of memorising A-610 or J-STD-001 acceptance rules so they can answer open-book multiple-choice questions. The training tells them the appearance of acceptable solder connections but provides no knowledge at all of how to meet those requirements (aside from pushing the solder around with the iron until it finally achieves a shape everyone can live with). Rather than rewarding operators who bring material and process problems to management's attention so the problems can be corrected, the industry places highest value on assemblers who can produce visually acceptable connections with un-solderable materials. The whole system is like teaching pilots how to fly simply by giving them route maps without any instructions about how to operate the plane itself. (My 2011 Assembly Magazine column about the damage done by A-610 and J-STD-001 training can be found by clicking here.)

To sum up, you've opened the journalistic door to the single most important challenge facing electronics manufacturing today. Thanks for your time and the outstanding column. Best wishes, Jim.

I don't know about you, but I think he is passionate about soldering. Also, since he says such nice things about me and my writings, I think it's fair to assume that he is a very clever and discerning person. However, I fear he has thrown down the gauntlet to some parties with an interest in certain industry standards. I await everyone's comments and feedback with bated breath.