PCB Rework and Repair Guide [pdf]
intertronics.co.uk
intertronics.co.uk
The techniques here are also way beyond basics I think- like, you look at most guides for repair and it's "idk just solder some bodge wires on there, here's what a good joint should look like"
Edit: here's the thread. It's a 6 layer PCB with a short on L5 that needs to be fixed from the L1 side.
If the parts all have pads on their perimeter, then a jumper wire can replace internal traces. If the pads are underneath the part, and the trace is only internal, than a jumper may not be feasible, unless the damage happens from the surface in, in which case each layer can be jumpered at the damage.
BGa pad repairing is very common, here is one example: https://www.facebook.com/watch/?v=1077341457703029 (sorry can't find non-facebook link)
- Heating becomes easier. There's no large sinks to take the heat away. It's also easier to overheat things.
- You need finer tweezers, and don't drop them because if you do the tips will bend.
- The solder's surface tension does more of the work. It feels a lot more like sticking together things with tiny droplets of glue. Having the correct amount of solder in the right place is critical.
- Solder and flux become two separate things you have to care about individually
- It is easier to burn yourself
- learning how to brace your hand against something in a way that gives you very fine control. One reason soldering with an iron can be difficult is because your hand is so far away from the tip, like trying to write with a pen held by the end.
I now highly recommend learning it to anyone doing electronics. It's well worth the (small) time investment and makes things a lot easier, opening lots of doors. Even for a hobbyist you immediately get benefits. Everything becomes more compact, 2 sided boards are much more usable, and, of course, it opens up a lot of repairability (and recycling. Are you really a hobbyist if you aren't desoldering and reclaiming parts?).
Fun memory from who-knows-how-many years ago:
While installing a Playstation mod chip, I accidentally dislodged a nearby surface mount resistor, pulling off one of its metal contacts in the process. (Is that what happens when you overheat them?) I didn't think that was fixable, and since it was Sunday, the local electronics shop was closed. I ended up disassembling an old junk digital camera that hadn't yet been taken to the e-waste recycling drop, and finding inside it a resistor that seemed close enough to maybe work. The transplant was a success, and the Playstation ran great thereafter. Very satisfying.
When you hand someone a board with 0603s on it that you hand-assembled, it seems like magic to people who stop to think about it.
I believe this is why I have an easier time hand-soldering BGA than QF[np]: I can't screw up solder amount/evenness.
Important caveat: The downside to this is you can't inspect it (without an x-ray machine), and if you screw up, you're going to need a new chip (Re-balling does not look approachable/time-efficient)
Also, it seems to not melt if you don't flux the pads prior. Not really sure why.
Some people also just put solder paste on the PCB with a stencil and reflow that into solder bumps that you then solder the chip to. I find that method suspect but if it works it works
More generally, with iron soldering only the iron and the last couple joints are hot. For SMD, there's more places for the heat to go; sometimes the entire board can be hot. Sometimes, you might need to balance being close enough in to get a good grip on the tiny parts, but far enough to not get burnt. You will feel the heat when SMD soldering - it's not always dangerous but another thing to pay attention to.
Newer irons, especially for SMD work, have gotten smaller and the grip-to-tip distance also shrunk; here's a good visual comparison:
https://www.eevblog.com/forum/reviews/grip-to-tip-distance-o...
It's worth noting that the longest one there is already much shorter than the classic mid-century unregulated irons, and all of those can be held like a pencil.
I see the flaw in your clever plan...
If it's an SO package, e.g. SSOP, TSOP, etc., Desolder the IC, add the jumper wire, bend the pins down enough to account for the thickness of the jumper wire, and resolder the IC.
Either way, make sure you have enough thermal mass connected to it for thermal dissipation. If there's components on the opposite side of the PCB, it's probably not much.
Less than 3000 volts cannot be felt by humans? Should be 3000 millivolts right? i.e. 3 volts...
That's not 3 volts.
For discharge that you can feel and see, the energy is even higher, but damage can be done far below this level.
If you're replacing one, it's easiest to cut all of the plastic off first, then desolder the contacts one at a time. Sometimes you can even pull the plastic off, without damaging it. It's usually necessary to preheat the board.
I like to melt the original solder one contact or area at a time, add a little bit of fresh flux-containing solder if needed, and as soon as it gets to the consistency of mercury, vacuum it clean out with a good soldersucker.