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Following from the EMPF HelpLine in Indianapolis, prepared by Jeff Kukelhan:
I would like to point out that both the EIA and IPC consider the "toe" area
of gull wing leads as non-critical (per ANSI/J-STD-001 and ANSI/J-STD-002).
In otherwords, the "toes" do not have to accept solder in either
solderability tests or production assembly operations to meet these
specifications. I think we may eventually determine that the "toe" joint is
critical to long term performance, particularly for fine pitch devices. But
for the time being commercial specifications do not require a toe joint. If
you want to maximize "toe" joint formation without pretinning, look for
vendors that apply 500 to 1000 microinches of fusible plating, and then trim
the lead from the bottom up. This bottom-up trimming motion will smear some
of the thick plating over the lower half of the toe, and will generally
facilitate the formation of a solder joint half way up the thickness of the
toe.
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From: TechNet-request
To: TechNet
Subject: Non solderable toes on QFP's
Date: 19 Dec 95 8:25AM
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Date: Tue, 19 Dec 95 08:25:01 GMT
From: "John Burke" <[log in to unmask]>
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Subject: Non solderable toes on QFP's
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--
Hi all,
Wonder if you can help. We occasionally experience problems with
solderability of joint toes on QFP's where the lead frame has been
cropped after packaging, which leaves non solderable nickel iron lead
frame at the toe of the joint.
My questions are :-
1 Is there any post cropping process which will avoid this
condition??
2 What practical problems has this caused in production??
3 Which manufacturers if any are worse than others in this respect??
Hope you can help.
If I don't come on the net again before have a good Christmas and new
year.
Kind regards.
John Burke.
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