checking QFP's for opens

"I think the best is to make sure the oven profile and other factors are set up so as to avoid any opens in the first place."

I think you answered your own question.

The difficulty (from my limited experience, anyway) in adequately qualifying your process lies first in identifying everything that you have to control....program selection, stencil washing, paste control, bare board quality, etc., then getting the resources to control it all.

Edited to add that if you have problems and decide you need to inspect everything, a microscope is a much safer method. If you feel like you must poke and prod, do it under a scope, limit it to suspect joints and be prepared to touch up (not a good thing in and of itself) every one of them.

We had a problem once at my last employer and it became the normal process to drag solder all 4 sides of every (there were 12) QFP 100 after reflow, on every board....with an OA flux. A new layout, a couple iterations of stencil design, and a new printer later, we stopped drag soldering. I won't tell you what happened when we had washer problems.

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oops.

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