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April 2008

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Subject:
From:
"Gumpert, Ben" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Gumpert, Ben
Date:
Fri, 11 Apr 2008 07:03:17 -0400
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Wayne,

How about turning the board over and shaking it? But that will only give
you evidence that at least one pad is wetted.

On a more serious note.. The types of defects that I have seen with
these style parts are obvious - parts way up off the pads. I have not
seen any purely non-wetting defects.

But if you can't see enough to find evidence of wetting, perhaps a lack
of evidence of non-wetting is enough? If the part is in the correct
position and any observable solder (pads should extend out from under
the part) appears normal - the shape is consistent with other locations
- then is that evidence enough?

Ben

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wayne Thayer
Sent: Thursday, April 10, 2008 10:35 PM
To: [log in to unmask]
Subject: [TN] FN Parts--Evidence of Wetting

Relevant IPC specs claim that no toe fillet is required for DFN/QFN
parts and there is no minimum solder joint height.  The only requirement
for the joint other than alignment/pad size is "evidence of wetting".
How do I get this evidence without a toe fillet?  I suppose if I have
enough joint height I can see under the part like a BGA, but I've never
seen a FN part mounted that high.

Would be nice if the spec included some pix/examples of this "evidence".

Any recommendations would be very much appreciated.

Thanks,

Wayne Thayer

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