I'm having issues with making a pcb that has a 100 pin tqfp part on it. I'm using the manufacturers recommended pad / mask layout for the part. The problem is inconsistency. I, very often, get boards that have both too little solder on some pins and bridging on others. What i think is happening is that when the solder pre-heats and sort of "spreads" out, it touches the paste from adjacent pad. Then during the acutal reflow portion, one of 3 things happens:
1. The paste gets wicked all to one pin, leaving the other with none
2. The paste bridges the two pins
3. It reflows properly.
So, I though the answer would be a thinner stencil, but that created two other issues:
1. The stencil printer drags the paste up out of the apertures if the pressure is too high
2. The stencil printer leaves paste attached to the paste in the apertures on top of the stencil, which causes no-release.
And if the pressure is "just right" I get a combination of the two scenarios.
Can anyone tell me what I'm doing wrong?
1. The paste gets wicked all to one pin, leaving the other with none
2. The paste bridges the two pins
3. It reflows properly.
So, I though the answer would be a thinner stencil, but that created two other issues:
1. The stencil printer drags the paste up out of the apertures if the pressure is too high
2. The stencil printer leaves paste attached to the paste in the apertures on top of the stencil, which causes no-release.
And if the pressure is "just right" I get a combination of the two scenarios.
Can anyone tell me what I'm doing wrong?