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June 2010

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Subject:
From:
Mike Fenner <[log in to unmask]>
Reply To:
Date:
Tue, 29 Jun 2010 11:02:25 +0100
Content-Type:
text/plain
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text/plain (157 lines)
Yep, effectively solder flows towards heat. 
At least it melts first in the hottest area and then, now being mobile,
surface tension/wetting forces will tend to pull it there. The flux, which
is temperature activated, will also be most effective initially in the first
heated areas.
Eventually heated area becomes uniform, all the solder will melt, and then
things may even up [as much as the geometry of wettable area and remaining
flux effectiveness allows].


Regards
 
Mike

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
Sent: Monday, June 28, 2010 7:11 PM
To: [log in to unmask]
Subject: Re: [TN] QFP short at top of the leads

Hi,

 That dull gray makes me thing of reflow without any flux. Was that SAC
paste with PbSn on the parts? If so maybe the PbSn reflowed first and for
some reason was pulled to the body. (Does solder really flow towards the
heat?)

Bob Kondner

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Jerry Dengler
Sent: Monday, June 28, 2010 7:40 AM
To: [log in to unmask]
Subject: Re: [TN] QFP short at top of the leads

Jowan,

Was this part dipped in solder before placing?  It looks like solder has
coated the whole lead right up to the body.

Jerry

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Iven, Jowan
Sent: Monday, June 28, 2010 5:08 AM
To: [log in to unmask]
Subject: [TN] QFP short at top of the leads

Has anyone ever seen a QFP where shorts occur after soldering at the top
of the leads?
And the leads look pretty dull after soldering.  Any ideas?


A picture is available at
http://ipc-technet.groupsite.com/uploads/galleries/x/000/020/5ba/technet
01.jpg

Jowan Iven 




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