Steve/all, lots of good
comments on this; I want to add some more considerations based on standards
development committee meeting discussions.
1. The terms "side joint
length" and "end joint length" are not the same as "fillet height". Unless
specifically stated as in J001C 9.2.6.5, don't assume that solder climb up a
lead is required. Unless otherwise stated it most likely refers to what you can
see between the surfaces being soldered (bottom of lead to top of land). This
raises a discussion point for the committees to consider on future revisions to
J001 and A-610; usually dimension F minimum fillet height location is not
specified whether it is side/toe, but it is specific as the heel location for
some component types. This is an opportunity to improve the
documents.
2. Stamped copper leads
(comments about whether you "should" use them notwithstanding) should wet with
your process under control. Kovar (tm)/Alloy 42 base metals used in some
components is not wettable. If components with leads stamped from nonwettable
material are specified on the BOM, drawings take precedence. On discussion, the
committees determined that they didn't want to fill the standard listing
"drawings take precedence" for every criterion that is listed. So the "by
design" words were removed from Rev C of both documents.
3. Steve, you may not have
copper leads; under normal lighting conditions Kovar/Alloy 42/copper look about
the same. Looking at those leads using different lighting color
temperatures varying from 3,000 deg K to 4,500 deg K will differentiate
between the metals. The concern should be whether it is known to be wettable and
it won't. If the sides of some leads on the same components wet and others
don't, you have a process problem to troubleshoot.
Jack Crawford
Director, Professional Development and Assembly
Technology
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APEX 2003 March 31-April 2 Anaheim
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IPC Printed Circuits EXPO March 25-27 Long Beach
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Hi All!
I've got a situation here with a SMT socket. It's a SAMTEC
CLT-105-02-L-D. The leads are made from stamped pre-plated stock, so the sides
and toes of the leads have exposed copper, and of course doesn't wet during
reflow.
In J-STD-001B, it used to say under 9.2.6.1 Flat, Ribbon, "L"
and Gull Wing Leads:
"Leads not having wettable sides or ends by design
(such as leads stamped or sheared from pre-plated stock) are not required to
have side or end fillets.
In J-STD-001C it has no mention of that under
the same section, in J-STD-001C the section number has changed, it's 9.2.6.8.
So if you have leads that are made from pre-plated stock and have the
sides and toes not wet because of the exposed copper, is it now a defect? If it
is, how in the heck are you going to get the sides and toes to wet?
Thanks!
-Steve Gregory-
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