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Comment by murderfs | Hacker News Reader

> Given tantalum is a rare earth metal, it might be nice to replace it with a ceramic and maybe a 4 Ω resistor in series. I’d love any input here.

USB allows for 10uF of capacitance, and you don't seem to have an LDO on your board, so you don't need a minimum amount of ESR to maintain stability. I don't think there's any reason you can't just replace the tantalum with a ceramic?

> https://chadaustin.me/images/sculpt/pcbway-top.jpeg

This is shockingly bad. I was thinking of using PCBWay to assemble a run of a dozen or so PCBs, because JLCPCB is limited on solder mask color and part selection, but this has pretty firmly turned me away from that.

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> This is shockingly bad.

What is so bad about it? I suppose they ordered prototype quality.

Look at the first long trace in the top left sector. It is detached from the board. That is a rather serious manufacturing defect.

Yes, that's bad indeed.

However, I've ordered from PCBWAY quite a lot recently, and I've never experienced anything like this, even on prototyping-quality boards. Also, the solder mask is much thicker (pcbs don't look semi-transparent like this one), and look more professional (I didn't order any assembled boards so I can't say anything about their soldering job). How long ago did the author order these pcbs?

The defect could also be the result of the author trying to fit the pcb into the keyboard.

Anyway, rest assured, on current PCBWAY boards traces are covered under a thick layer of solder mask and it is extremely difficult to remove them from the board (I just tried with a sharp metal tip on an old board).

Yeah, I was disappointed by the lifted trace. It was only on the assembled one. The others all look fine to my untrained eyes.

Because I had low confidence in my circuit, I ordered the cheapest possible assembly. I assume hand-assembled or a mix, given one of each part.

I’m hoping to attempt hand assembly myself soon. Picked up a hot air station and a new set of parts from Digi-Key. :)

If you're using stencils (and as long as your boards are relatively small, there's almost no reason not to with how cheap they are from jlcpcb/oshstencils), I highly recommend buying a jar of Loctite GC-10: it's the best solder paste I've ever used, and it lasts forever. I have a jar that expired 2 years ago and is still great.

Also, the T-962 reflow oven is pretty good for its price, with a bit of modding (flashing open source firmware (https://github.com/UnifiedEngineering/T-962-improvements), removing masking tape that melts and stinks, and adding a thermocouple for cold junction compensation).

Did you try SAC-305 solder pastes from different brands?

I'm quite happy with my current SAC-305 solder paste from ChipQuik, but curious if I could find an ever better one.

Checking my fridge drawer: I've used leaded mechanic paste, and SAC-305 mechanic, SRA, and MG chemicals (plus chipquik low temperature bismuth paste, but it was terrible: I had parts literally falling off the board).

They're all significantly worse for stenciling than GC-10. If you're manually applying paste with a syringe, you might be better off with other paste, because it's significantly thicker than the usual pastes I've tried, but I usually just hand solder instead of waiting an hour for refrigerated paste to be better.

When this tub of GC-10 actually has any symptoms of being expired, I'm definitely going to buy another (or maybe GC-18, which seems to be the new shiny version? I don't see any ebay listings for cheap almost-expired GC-18, sadly.)

The thing that confuses me is that this obviously happened as part of PCB production (there's solder mask under where the trace should be). However, the assembly looks like it was done by hand: tons of solder on D1, and R5 is facing the wrong way. How could you possibly not notice that??

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