maxtherabbit wrote:pcrob wrote:Thanks for the advice! I reckon you might be onto something regarding the BGA joint. I'll test that tonight.
If it turns out that's the culprit, do you reckon I could just blast it with some hot air? I don't have a hot air reflow station, but I've wanted one for ages so I might invest in one finally.
might work, but generally speaking when BGA joints fail the only enduring solution is to remove the chip completely and re-ball it
I agree, that's the textbook way of doing it.
Still with a good amount of flux and some experience chances are you'll get the joint resoldered just as good as new solder balls would. Especially on such an old chip with rather large contacts.
If you're paying money for it you shouldn't accept a simple reflow but if you're doing it yourself or having somebody do it for you as a favour I'd say it's fine if it works.
Reflowing a large BGA chip isn't very easy though - I still have two cards I'd like to reflow but I haven't found the nerve yet. I watched somebody else do it a couple of times but I'm still worried to get something wrong and break the card even though I'm pretty confident with regular SMD soldering by now.
You'll have to pre heat the board to around 120-140°C, apply flux around the chip you're reflowing so it gets pulled under the chip and then evenly heat the chip from above and the board from below until all the solder balls liquify/soak for a couple of seconds. Then you'll have to remove the heat source from the chip and let the whole card cool down slowly. Let it sit undisturbed until it has cooled down. During the whole process you have to pay attention not to move the chip. That's why professional equipment doesn't use hot air but infrared light to heat the chip. You also have to have a heat source that will heat up the chip fast enough so it isn't slowly cooked but can be controlled well enough so it doesn't overheat the chip. Normally you'd use soldering temperatures between 220-350°C on the chip and 200-280°C on the PCB. After pre heating the PCB the whole soldering process shouldn't take more than a minute (including the couple of seconds of soak) before letting the whole board cool down slowly.
If you don't care too much about the card you can also try to just use a hot air station or even a temperature controlled heat gun to heat the chip until the solder balls melt. Sometimes that works just fine but it also increases the risk of frying the chip or getting new cracks due to tension from having too much of a temperature difference between chip and PCB.
Personally I'm planning on practicing on some cheap cards first before I move on to the cards I actually want to repair. 😁 😉
