Screaming Circuits: Little Chippy Challenges


Little Chippy Challenges

And in terms of "Chippy", in this context, I'm referring to chip-caps and any other tiny little 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.

Two part tombstone You can 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.H Skewed passive via in pad

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

Soldermask tombstoning for blog Solder mask can cause problems too. Too thick a solder mask can prevent the part from reaching the solder and can cause tombstoning. That thick solder mask can also interfere with out-gassing in the reflow oven which can cause solder ball splatter. (A = okay, B = at risk if mask is too thick).

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

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Comments

At my company, we are now required to route tracks that are parallel to the part. That is, the tracks come into the pads as if they are going to go through the two.
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This, among other things like temp monitoring etc, has been found to dramatically reduce the tombstoning we have seen on our boards within the company.

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