Today the first preproduction batch of my devices, consisting of four PCBs (Printed Circuit Boards), was finally completely mounted, and I began to power them up in order to test the mounting accuracy and device functionality. It was revealed during mounting that I had placed some components too close to each other, although this will not prevent embedded software developers from using the devices to debug their firmware. When I started to bring the live into the device, I found that at one position, on all devices, stabilitrons were mounted in opposite polarity. It seems that assemblers who performed actual soldering, are accustomed to the fact that diodes' Anode pole are usually goes to positive polarity, and Cathode pole - to negative. This is true for simple forward usage of regular and shottky diodes, but stabilitrons need to be used in reverse direction. I marked where the Anode should be on assembly drawing, nevertheless it seems that assembler was guided by datasheet, where Anode mark is showed, and polarity of PCB padstacks. I'm thinking about resorting to using SOT-23 case for this component in second version of a scheme (for those who are not familiar with it: this is 3-leads case, it have 2 leads on one side and one on another, thus it is impossible to place it in wrong orientation). It may be _slightly_ more expensive than currently used 2-leads case, but it will leave us from necessity to think about right orientation and to control it.
It seems, that many engineering decisions are often driven by similar motivation - to ease manufacturing and/or repairing processes, at price of slightly increasing components cost.
It also reminds me that responsibility of everyone who design any type of interfaces, is to make every interface as clean and consistent as possible, and to make sure that working with this interface requires from user absolutely minimum of possible knowledge of a system.
SOT-23 drawing
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