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November 2004

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From:
Guy Ramsey <[log in to unmask]>
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Date:
Mon, 15 Nov 2004 14:51:28 -0500
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In addition to having a shorter toe-to-heel land the heel-to-heel distance
is reduced. This would minimize the solder in the heel fillets. This would
reduce the strength of the lead to land connection.  But, you say the solder
is strong enough to rip the pads and all off the board. The lead to land
connection is not the issue.

Sounds like you need the larger land pattern.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Steve Gregory
Sent: Monday, November 15, 2004 6:50 PM
To: [log in to unmask]
Subject: [TN] SOD323 problem...


Hi All!

(munch, munch...GULP) 'Scuse me, typing this email while I'm chowing down
some lunch.

We just recently built some boards here that have a handfull of SOD323
packaged Schottky diodes from International Rectifier on them, and have had
a pretty serious problem with the part and pads being ripped off the board.
It's been happening mostly during hand cleaning.

We have a open cased DC/DC converter that we have to hand solder, and then
hand clean. No, we can't use no-clean flux and leave the residues, the
customer won't allow it. But that's where it seems they are getting ripped
up. After the first couple of diodes got ripped up, we've made it known to
the operators who are working on these assemblies how easy it is to do this,
and that they need to be very careful when cleaning. We've got our best
operators working on these assemblies, and I know their skills. But even
when they try to be as careful and gentle as they can cleaning the
assemblies, parts are still getting ripped-up...it's really unbelievable how
fragile this part is.

Has anybody had similar experiences with this part?

I've got pictures of things on my page. Go and look at:

http://www.stevezeva.homestead.com/files/SOD323.jpg

There you will see a picture of the part. The part is kind of tall in
relation to the size of the two pads it gets soldered to.

Now look at:

http://www.stevezeva.homestead.com/files/InternationalRectifierFootprint.jpg

There you will see what International Rectifier recommends for a
footprint...pretty small pads huh?

Now look at:

http://www.stevezeva.homestead.com/files/footprintForSOD323.jpg

This is what I measured the footprint to be from the gerber for the board.
The pads are a little undersized from what International Rectifier
recommends, and they also are oriented 90-degrees out from the recommended
footprint, but do you think that difference explains why these things are so
easy to damage? Would you go with larger pads than what is recommended to
provide more surface area for the pads to provide more mechanical strength
to them?

Just curious if anybody else has had the same problems..

-Steve Gregory-

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