日本語
Is there any rule of thumb when deciding the size of the solder paste aperture for large pads, especially like with exposed pad QFN packages? I've seen recommendations to break up larger areas into a number of smaller ones, but nothing that talks about how large/small to make the smaller areas, or what percentage coverage to aim for vs the original.
- Comments(1)
A****min
Mar 14.2019, 09:57:08
For QFNs with exposed pad under the chip, the amount of solder paste must be reduced a LOT, or the chip will pull down and squeeze the solder out to the rows of pads, shorting everything out. Many people make "window frames" by making a number of squares with clear stripes between them. This arranges for the solder to be spread across the pad but still reduces the total solder volume to prevent the shorts.
Larger parts can use 100% aperture to pad size, as the lead pitch is reduced, then you have to make the apertures smaller to prevent bridging. I sometimes have to go down to about 50% area for 0.5 and 0.4mm lead pitch.
