And “chippy,” in this context, refers to chip caps and any other tiny two-connector components. When considering surface mount, most people think of the many-connector parts, like BGAs and QFNs as the challenging components. That’s mostly true. However, the little passives can be big bears too if not treated properly.

You could have tombstoning problems. This can be caused by unequal sized pads, unequal sized traces going to the pads or inequality in copper plane in a different layer. A big part on one side can cause tombstoning too — the big part’s thermal mass may slow the solder paste melt on one side of the part, leading to tombstoning.

Via-in-pad is still a problem too. Open vias can lead to unreliable connections, tombstoning or crooked  parts.

Solder mask can cause problems too. Too thick a solder mask can prevent the part from reaching the solder and can cause tombstoning. Too think a solder mask can also interfere with outgassing in the reflow oven which can cause solder ball splatter. (A = okay, B = not okay).

Duane Benson
It just goes to show you…
It’s always something.

http://blog.screamingcircuits.com/