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Floating 144-pin QFPs

Steve Cheung

#13514

Floating 144-pin QFPs | 13 November, 1998

We are experiencing 'lifting' on one or more sides of a QFP. Poor lead co-planarity has been ruled out by independent tests. Please tell me which of the two remaining failure modes is the most probrable?

1. Expansion of gases in vias underneath device

2. Solderability issue

A hearty thank you from England!

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Chrys

#13515

Re: Floating 144-pin QFPs | 13 November, 1998

| We are experiencing 'lifting' on one or more sides of a QFP. Poor lead co-planarity has been ruled out by independent tests. Please tell me which of the two remaining failure modes is the most probrable? | | 1. Expansion of gases in vias underneath device | | 2. Solderability issue | | A hearty thank you from England! | Steve,

without more info, I'm just taking guesses. I'm assuming this is happening in reflow, not wave soldering. I'm assuming these are blind vias. Expansion of gasses seems highly improbable, since the package doesn't sit flat on the board.

Solderability - hmmm, you said the leads are coplanar, but is the board? Is it Hot Air Levelled or a flatter finish? It would have to be a pretty lousy leveling job to prevent you from printing enough paste (but not to be ruled out). It is highly doubtful that solderability could vary so much on a single part or a local area of board to cause one side to solder and not another.

If it is after wave soldering, check the wave profile - you're probably reflowing the parts by pumping too much heat in the board at the wave - A very common problem.

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karlin

#13516

Re: Floating 144-pin QFPs | 19 November, 1998

| | We are experiencing 'lifting' on one or more sides of a QFP. Poor lead co-planarity has been ruled out by independent tests. Please tell me which of the two remaining failure modes is the most probrable? | | | | 1. Expansion of gases in vias underneath device | | | | 2. Solderability issue | | | | A hearty thank you from England! | | | Steve, | | without more info, I'm just taking guesses. I'm assuming this is happening in reflow, not wave soldering. I'm assuming these are blind vias. Expansion of gasses seems highly improbable, since the package doesn't sit flat on the board. | | Solderability - hmmm, you said the leads are coplanar, but is the board? Is it Hot Air Levelled or a flatter finish? It would have to be a pretty lousy leveling job to prevent you from printing enough paste (but not to be ruled out). It is highly doubtful that solderability could vary so much on a single part or a local area of board to cause one side to solder and not another. | | If it is after wave soldering, check the wave profile - you're probably reflowing the parts by pumping too much heat in the board at the wave - A very common problem. |

Steve,

I presume that you are refering to the reflow process. Try to bake the QFP at 120 �C for 4 hours. If it is caused by expansion of gases in via during reflow. The lifting problem would resolved by itself.

rgs, karlin

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