That is good enough to make this doable. The failures I had while developing a BGA soldering process were due to using the wrong amount of solder paste or not putting it on evenly enough. I also have cooked a PCB once (causing delamination), though that was a more complicated situation.maxreason:
Almost all the non-trivial SMT parts are on the same side, but not quite. All the BGAs and QFNs are on the same side of the PCBs, except for two 28-pad QFN chips (max8717s). And I have oodles of 0603, 0402 and 0201 bypass capacitors and a few less funky packages on the opposite side too (less funky meaning I can see and touch the leads (like SO8, SOIC, TSSOP).NleahciM:
Please tell me that all leadless ICs (BGAs, LGAs, QFNs, DFNs, etc) are on one side of the PCB. If that is the case, a hot plate should be enough to do your prototypes. Getting the BGA to solder properly will require experimentation. I’d recommend getting some scrap PCBs to practice on. If you have leadless parts on both sides, a hot plate will probably not work, especially considering the large size of one of your PCBs. In that case, a pre-heater and a hot air station will do it, but it will be trickier.The keyword here is practice. You’re gonna have a few dead boards. Maybe many.
All the “heavy” (BGA) parts that might “fall off” if inverted in a reflow oven are on the same side. Actually, I just received the parts, and I am rather amazed at how tiny and lightweight even the biggest, baddest, heaviest component is. Even the 256-ball BGA is a tiny featherweight little thing. Working on the PCB layout at 3200% to 10,000% obviously distorted my impression of how tiny these things are. I can barely even see the 0201 bypass capacitors unless I take my glasses off so I can look closer (5.50 diopters).
Absent some vibration or jarring, I’d bet solder surface tension would keep even those components on the bottom side of the PCB in a reflow oven, if necessary. However, no need for that, except perhaps for those two teenie weenie little 5mm square QFNs, which weight about 1/10 gram, I’d guess.
Do you think the extensive “practice” and “scrap” is mostly due to “placement precision errors”? Or “overheating and thereby destroying components”? Or what? And what is the best way to avoid those problems (besides a $30,000 pick-and-place machine)?
It is funny how looking at zoomed in PCBs can really distort your sense of size. It can be tricky when making really dense PCBs to keep your components placed far enough away from each other to be solderable.
My advice would be to concentrate on the BGAs before anything else. If your process works for BGAs, most likely everything else is fine. I’d suggest even destructively testing a successfully soldered PCB (or sending it out for X-ray) to be absolutely sure everything is working. I pried up the BGAs to examine them. This would rip pads off the PCB and balls off of the BGA. This made examination a breeze.
I used a timed, air powered solder paste dispenser to put on paste - but a stencil should work too. Probably faster as well (dropping 276 balls of solder paste, one by one, is actually a lot of work!)
As for self centering - yes self centering works OK for most things. One time a colleague messed up his LGA footprint so we couldn’t tell how to center it. But we were soldering it on a hotplate, and when the solder went moltent you could tap the PCB a teeny bit and it’d snap into place. What was even more interesting was taking some tweezers and pushing the component. It felt like you were pushing a ball over a sinusoid. Pretty cool.
One more word of warning: your silkscreen markers showing the outline of the component may not be good enough. Many PCB fabs have pretty bad registration between the soldermask and the copper. I prefer to put copper corner marks to show the corners of BGAs, as I’m sure those will be aligned with the pads of the BGA.