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?