Open joints

When we found this to be a problem with some QFP 100's (.020" pitch, and our first experience with fine pitch - 48 of them on a 2-up panel), we saw that the solder was running up the leads during reflow and staying there, leaving the fillets thin or nonexistant. We use HASL also, although we don't feel as though it's a big problem.

We monkeyed with the profile too, and it helped slightly, but eventually we determined the problem was a stencil design that had lousy release characteristics and even worse registration on our manual printer. We got a better printer, a new stencil, and the problem was gone. Not the cheapest fix, granted, but affective.

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We have had soldering problems with fine pitch QFP in the past [and probably will in the future]. Several questions leap to mind: * When you took your profile on the component pads, do you profile on the pads that did not solder well? * When you say the profile seemed OK, what were the numbers? * What is the solder paste that you use on this board? * What is your process up to the point of recognizing the problem we�re discussing? * How did other pads on the board solder? I assume everything soldered GREAT, except this fine pitch part. * Continuing with that thought, when you say �and the board as a poor HASL�, what specifically are your complaints with the solderability protection? * How do the leads on the fine pitch part solder when using a soldering iron? Or touching-up the connections on the board? * As Steve says, where is the paste going after reflow? * Continuing, what does the �open connection� pads look like [i.e., reddish-brown, silverfish, grayish, er what?] after reflow? * Is this a new problem with a new board? Old problem? New problem with an old board? Does this affect a single or multiple components / suppliers / etc?

Commenting: * Pad width of 0.010" on the fine pitch components should not be a problem. * Fine pitch components pad that are not all at the same height [length???] should not be a problem, providing they are roughly the same length and meet minimum requirements.

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