I’ve done around 4 complex boards and 8 or so “Let me test this chip” or “connector break-out” boards in KiCad. I recently (summer of 2020) made a power supply to run a server in a mobile/vehicle environment. It has two 50W boost-buck supplies so that cranking the car doesn’t affect the output voltage. An on-board micro allows configuration of output voltages, monitoring of current and temperature sensors and also does all the mimicking of the front panel button to bring the server up and take it down.
The board is a 4-layer, use OSHpark to make it and also did a stencil for assembly. I have a cheap (too cheap, I need to get a better one) hot air reflow that I got used to on the 4 complex boards. The power supply board has a lot of 0402 and some parts with pins on the bottom of the package. The main power supply chip is the TI TPS55288.
The proto was easy to assemble. I made the placement so that I could cut the stencil into pieces to populate the micro processor, the power supply and control circuitry, and each of the 50W supplies separately so I could bring the board up in stages. This was a huge win, since there wasn’t the “Turn everything on at once and hope” moment.
I over-cooked on of the main power supplies chip, damaging a FET. I was able to test it in buck mode, which let me know the wiring was OK but in boost mode the main external FETS just got nice and hot. Fortuatnly, the other supply worked 100% so I could test it.
It was much cheaper to be able to proto the PCB my self than to have a stuff house make 2 or 3 boards. The extra effort to allow for incremental power-up was not too bad and really did not waist any board space or make the board larger. The board had to fit in the extra space in a chassis designed for an ATX-FLEX when there was only an ATX-MINI motherboard present. The chassis was a SuperMicro SCE300 and the motherboard is a SuperMicro A2SDI-8C-HLN4F.
I got 25 boards back from the assembly house (“stuff house”) and so far all 3 i’ve tested worked. I made some BOM errors, and need to write some software to cross check a .csv version of the BOM with the Pick and Place to find errors in counts and parts omitted fro the BOM. Somehow, I dropped 5 parts. All but 1 were 0603 or 0805, the one was an 0402. Never blew a BOM in 40 years, just must be getting old. Software will let me make the minor BOM changes from a proto without having to start from scratch and should help the transition from prototype to fab. I should also be able to re-format both the BOM & P&P to whatever format the stuff house wants.
I had the house work with the PCB group of their choice, and just pointed to the OSH park stack-up for the 4-layer board. I also left the panalization up to them. A little extra $$s but the stuff house can get things in a form that works best for them. The only change I made from the OSHpark stack-up was the top and bottom layers went to 2 oz copper due to the high currents. The production boards tested better than the proto due to this change. I also went from just using 10 mill hole vias in the high power traces to also using 38 mil vias along the path. This resulted in lower via resistance and inductance. Never thought to do this until now. When both supplies are running 12V at 4 Amps, and the input goes down to 6 volts, the DC power draw off the battery is 20 amps. Normally, with Unix running and the vehicle idling, not cranking, the maximum possible from the battery current current draw is around 7 amps. The idle current from the server PCB (and the 4 fans in the chassis) when Unix is running is about 1.7 amps at +12, about 1.5 amps for that supply from the vehicle battery. A “fun” project with high currents, uP control, lots of EMI to worry about, and tight integration with the server motherboard and vehicle battery/ignition/tempurature.
Just wanted to share this “proto to production” story with everyone. Enclosed is gratuitous pix of the PCB.