solder pop out from via hole at secondary reflow

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Hi Guys, We prints solder paste on via hole as the holes ... - Jul 08, 2002 by Yngwie

See what happens when you take a couple of days off? Yo... - Jul 08, 2002 by davef

Thanx Dave F. ... - Jul 09, 2002 by Yngwie

Yngwie

#20617

solder pop out from via hole at secondary reflow | 8 July, 2002

Hi Guys,

We prints solder paste on via hole as the holes are used as the test points. This is a clean process.

In normal production, upon completion of a primary side, board will proceed to secondary process immediately.

The problem happened when brds which were completed primary side and brd sent to wash as we have a 3 days vacation. After the vacation, brd were then proceeded for secondary process ( without baking ). Via hole were also printed on the secondary site. What we found was solder pop-out to the primary side from the via hole ( pop-corn ), and caused shorting to the primary side. Could it due to the entrapped water in the via hole vapourised and form a high pressure effect in the via barrel, and the energy is strong enough to push the molten solder out from the barrel ?

Experts your comments pls.

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davef

#20619

solder pop out from via hole at secondary reflow | 8 July, 2002

See what happens when you take a couple of days off?

Your theory sounds reasonable, but someone else could make an equally valid case that you are blasting your solder plug across the room with the force of the expansion of entapped air between the two solder plugs.

Regardless of which of us is correct, consider solder plugging only one side, because partially filled via are more reliable than fully plugged via. Search the fine SMTnetnet Archives for a reference to a study by Roger Wild at IBM that showed an unfilled via to be the most reliable, a completely filled via was almost as reliable as an unfilled via, and a partially filled via was not at all reliable.

See the more we talk, you end-up being better off by not even filling the via at all.

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Yngwie

#20624

solder pop out from via hole at secondary reflow | 9 July, 2002

Thanx Dave F.

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