i am getting *so* much rework practice out of the current board design on the bench.

first batch reflow cycle was bad, baked the flux out before reaching temperature
tried to rework those, because shorts all over the place, but gave up after three days.

today, pasted and placed one more board. got too much paste on it, but Zoé helped me fix the worst solder bridges.
tested it, has some strange behaviour, rework some more and so on.
check schematic again, forgot a diode (thought it was just a tvs diode and left it out).

soldered on the diode, checked again, still bad.

checked diode orientation, of course it's the wrong way around... now it's on the right way, but the board is still cooling down. let's see if it's any better then :D


one more time. measured some more and now i'm pretty sure the 5V regulator does something weird. that pesky 2x2mm QFN package really hates too much paste...

· · Web · 2 · 0 · 5

squeezed out a bunch of solder paste & cleaned it up. 9-pins in a 4mm² package is fun :D (especially with the large one in the middle)

it works \o/ now i'd just like to know if i fried the MCU somewhere along the way. i'm still waiting for my debug adapter boards but i'll probably just make a cable tomorrow and get started with writing some code to enable the output and trace efficiency.

@ln its always the power people with the weird packages

uusually for good reason

@steph it's always power dissipation and EMI. it's this part btw: ti.com/lit/ds/symlink/lmr36503

extremely efficient if you don't need much power, and still good even at 300mA

@ln wow thats the silliest hotrod package layout ive seen, they're usually a lot better than this
@ln not the actual package, i meant the pinout choice :P
@ln for example the example layout makes the switchnode huge for no reason, which will increase common-mode noise...

@steph it's not *that* bad, and you can make the switchnode smaller with a different layout too. also the LDO i have on it has something like 95dB PSRR and the current sense amps 120dB CMRR, noise won't be the issue. except ADC noise, because that's really the weakest part.

@ln its more of an EMI issue off-board than on-board

@steph *slaps sticker "test equipment" on it* there you go, emission problems solved ;)

@ln everything looks so solderable when you're in CAD with 0.2mm traces :P

@steph hey, it basically just comes down to my bad pasting skills. de-soldering and placing it again is easy. even with that really cheap hot air and pre-heater.

Sign in to participate in the conversation

chaos.social – a Fediverse instance for & by the Chaos community