3 ms·
This is an actual technique used for these small packages! It's called "via in pad." Unfortunately it's not as simple as putting a hole in the pad because durin
by thrtythreeforty 5y ago
This is an actual technique used for these small packages! It's called "via in pad." Unfortunately it's not as simple as putting a hole in the pad because during solder reflow, the hole will wick the solder ball away from the chip, causing an open connection and possibly sucking the chip down and causing other pads to fail too.
Proper via-in-pad is a cost adder, because there's an extra step to backfill the vias with metal. Unfortunately it hasn't trickled down to hobbyist 4-layer processes yet.
- kragen 5y agoCouldn't you fill the via with solder with a soldering iron before you place the chip if you're doing a hobbyist 4-layer process? Or do you mean the kind of hobbyist 4-layer process where JLCPCB solders the parts on too?
- thrtythreeforty 5y agoHmm, maybe you could. I haven't tried it. You'd need to make sure that both sides of the via are un-tented (no green solder mask) so that the solder would flow through. The via would need to end up flat so the solder ball on the part would stick. And you still might get solder bleeding through when you reflow. For high-ball-count FPGAs, it sounds super tedious to prep. And obviously it's a no-go for machine assembly. But for smaller stuff it sounds feasible!