Daan,
        Our customer specs for pretinning plastic package parts used in
high-rel applications are to within .050" - .070" (1.27 - 1.78mm). This
reduces thermal transmission through the leadframe to the internal die,
prevents stress points at the package/lead demarcation, and reduces
opportunity for flux encroachment inside the package. Overall, just good
practices to follow for good reasons....

Mike

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Sauer, Steven T.
Sent: Wednesday, November 26, 2003 10:18 AM
To: [log in to unmask]
Subject: Re: [TN] Pretinning height on fine-pitch gull wing leads


Hi again Daan,
Let's try this from another angle, Common Sense 101.  I would look at
the requirement in 6.1.1 that specifies that the component shall meet
the part specification AND the intent behind the requirement in 9.2.6.8
Note 4 (that discusses the solder touching the pkg or seal).  The intent
of the requirement is to focus on what an excessive amount of solder
does to the stress relief of the lead bend NOT that solder has wetted
past the upper bend to the lead/body interface. Another hearty Good
Luck.

Steve
-----Original Message-----
From: d. terstegge [mailto:[log in to unmask]]
Sent: Wednesday, November 26, 2003 10:29 AM
To: [log in to unmask]; [log in to unmask]
Subject: RE: [TN] Pretinning height on fine-pitch gull wing leads


Hi Steve,

I forgot to tell that my problem is that our QA rejects parts because
the solder has wicked to far onto the leads during pretinning. It's
treated like a solder fillet that touches the body, which to my opinion
makes no sense. It's not a problem with gold embrittlement.

Daan Terstegge
Thales Communications
Unclassified mail
Personal Website: http://www.smtinfo.net

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