原创 PCB test jigs & my China experience

2014-11-12 17:16 991 1 1 分类: 消费电子

A comment that is even vaguely critical of industry in China always seems to be welcomed by an avalanche of responses in its defence. Often, they fight fire with fire, and so I write this blog with some trepidation.

Let me say at the outset that all my experiences are based on the statistically insignificant sample of two. If you are dealing with companies like Foxconn, then I can't believe you would see any of what I am about to describe. Perhaps you won't even see it at much smaller companies—but it did happen to us.

Apparently, it is very difficult to ship equipment into China, and it is really complicated to ship PCs even if they form part of some test equipment. Somehow we have managed to do it. In one case we had a test jig comprising a PC plus some electronics plus a bed of nails. Since the unit was based on obsolete PC ISA bus technology, and because we were planning on shipping it over long distances, we upgraded the system to an industrial computer (with a solid state disc) so that it certainly did not look like a PC.

This test jig was in use for several years, moving from one manufacturer to another. Eventually, the jig failed, so it was shipped it back to Canada. At the same time, we dispatched our duplicate jig to China. Imagine our surprise when the original jig arrived and we discovered that the PC was a beaten-up, non-functional, commercial-grade PC with a dead disc drive. No one knows when or where the substitution occurred.

In another case of test jig malfunction, I tried to perform some diagnostics over the phone. The conversation would go like this: I would ask the interpreter here in Toronto to ask the technician in China if a particular LED on a relay was on. This was communicated via a relatively lengthy conversation, which I presume was defining exactly which LED to look at. The conversation would then pause for about five minutes. The technician would then come back on the phone and there would be another conversation before I got the answer. This carried on for quite some time.

Eventually, I asked why there was always the long hang time before we received an answer. It turned out that the phone was about two minutes' walk away from the test jig—the technician had to walk over, take a look, and then return! Based on this experience, we reappraised the intercontinental exchange of test jigs.

The production facilities that I have seen in China are not climate-controlled. Not only is the shop hot and humid in summer and cold in winter, there is dust as well. Due to this, our test jigs became grimy and even rusty. Some of the gold-plated relays failed well before their rated operational life in one of the failures described above. We were actually asked (after our complaints) if we wanted the test jigs to be stored in air-conditioned storerooms.

We have an ongoing problem with printed circuit boards (PCBs). We email the Gerber plots to our subcontractor, who farms them out to a board shop. For some reason, the board shop moves tracks around. There is no logic to the changes and I can think of no justifiable reason to do this without the customer's permission, but it is especially concerning when your products carry UL/CSA agency approvals. To counteract these spurious changes, once the Gerbers have been reproduced, they are transmitted back to us and we have to check by overlaying the original against the new. This is wasteful and prone to human error, so occasionally unwanted, unrequested, and unauthorised changes do sneak through.

Of course, there is also the ongoing issue of fake parts, but this dropped off after we demanded that our subcontractor should not use brokers, but only official distributors. Nevertheless, you can end up with unexpected substitutions.

We connected (still do in fact) a TO-220 package to a commercially available heat sink with a metal clip made by the heat sink manufacturer. In an attempt to shave costs, our subcontractor had asked a metal shop to reproduce the clip. Unfortunately, the metal shop didn't anneal the part and the clips broke in shipping. It was bad enough that the TO-220 was no longer connected to its heat sink; even worse, there was now a fairly large piece of metal floating around in a 300V environment!

We once asked our subcontractor to design a test jig to generate an AC current of up to 15 amps. Despite advice we gave to the contrary, the subcontractor opted for a resistive load with a stepped down AC voltage. The photographs below show the internals of the resulting test jig:




It turned out that they had made their own custom rheostats using a power resistor with an exposed element, and then they'd used a carbon brush as a wiper. The brush was mounted on a threaded rod mounted in holes drilled into the box. To top it all, in order to dissipate the power, they connected two rheostats in parallel. The end result is that, in order to adjust the current, you have to turn both threaded rods (isolated by heat shrink). Unfortunately, the pressure on the brush changes and—because the width of the brush is less than the turns spacing—it loses contact for periods, you have to turn both rods to try to distribute the current equally. This all makes for a very erratic adjustment process.

This last issue has become the bane of my life. To prevent random semiconductor substitutions, we insist that nothing is substituted without our permission (or ECN), but this has backfired on us. The resistor manufacturers that we use in North America are not generally the preferred ones in China. The sub's favoured manufacturer also changes, and then—just to compound the issue—manufacturers have stopped making 5% resistors. The number of change requests at times can make your head spin.

Our relationship with our subcontractor has become more stable over time as we've become accustomed to each other's practices, and obviously the experience is profitable for us. So, have you had experience with Asian manufacturers and—if so—were your experiences better or worse than mine?

Aubrey Kagan is Engineering Manager at Emphatec


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