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Gold Flash with QFN28 problem

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Dan

#40753

Gold Flash with QFN28 problem | 30 March, 2006

We have this panel that is Gold Flash. Am I correct in assuming this is technically a lead-free panel then? We are running a WS paste, and the QFN28 has balls of solder instead of a fillet. My Max temp is 216, and the TAL was between 52-57 secs with 6 probes. The QFN28 is also a lead free part. I have tried to increase the speed and add more heat to the last two zones(10 more degrees), but the panel still looks the same...Any thoughts are appreciated.. Thanks.

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RDR

#40756

Gold Flash with QFN28 problem | 30 March, 2006

So you have solder balls at the outer edge of the part right where the pad goes underneath? If so you just have too much solder but I wouldn't worry about them. the solder usually does not wet to the edges of these parts because of the exposed copper instead of plated finish

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Dan

#40757

Gold Flash with QFN28 problem | 30 March, 2006

Dan

#40758

Gold Flash with QFN28 problem | 30 March, 2006

Yes the balls are at the outer edge. The chips we have are not showing exposed copper, but the lead-free finish...

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RDR

#40759

Gold Flash with QFN28 problem | 30 March, 2006

Not arguing dan, but are you positive that they are not copper? anyway, what is happening is as the parts sucks down onto the board from reflow the extra paste is notnecessarily sqeezed out but it has no place to go. So it will form this ball on the outer edge. if you must fix, there are a couple of options, reduce stencil thickness and /or aperture size, add extra pad length to the outside and use same stencil design, this will allow for the solder to wet out onto the pad and give you a more typical looking solder joint.

i personally don't think uyu should worry about it if the bottom connects are good. no shorts/opens

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Dan

#40760

Gold Flash with QFN28 problem | 30 March, 2006

Sorry about that(My bad), they are copper. I believe the same thing, we need to reduce the appatures as we are already at 5mil. Our main problem is the customer...Their tests were failing and for some reason they touched that part up, and then the units passed test. Go figure, so we had to touch them all up. I think more info from the customer would also help. Im not so sure if these fail a class 3 spec or not. Thanks for the help. Dan.

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