Here are my thoughts. The acceptance criteria in J-STD-001 and IPC-A-610
are visual acceptance criteria.
They presume certain things about the materials, methods and designs of
subject products.
When a design does not conform to the presumptions, how the criteria cannot
be applied? Is the absence of a heel fillet, when the design does not
provide for one, a cause for rejection?
Given a good overlap and a good solder connection, the resulting bond
between the component lead and the board land pattern may well exceed the
peel strength of the metal foil.
The problem is we cannot infer the quality of the connection from the
physical appearance of the connection. The design does not provide us with
the proper features from which we observe evidence of wetting, from which we
infer IM formation and bond.
Is this different from many new packages with no leads at all? Perhaps the
problem is not one addressed in IPC J-STD-001 but IPC-D-279 or perhaps
SM-785.
Guy
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Reuven Rokah
Sent: Thursday, August 25, 2011 9:46 AM
To: [log in to unmask]
Subject: Re: [TN] Gull Wing Lead - no heel fillet
Do you have two side fillets instead? or only bottom IMC?
Reuven
On Wed, Aug 24, 2011 at 11:57 PM, Phil Bavaro
<[log in to unmask]>wrote:
> Hypothetical situation:
>
> Gull wing lead, land pattern error, zero heel (also zero toe) fillet.
> Hardware would not meet Class 3 workmanship requirements.
>
> An equation is being used to decide if the pad to gull wing lead lap
> solder joint is adequate to survive the intended thermal cycling
> environment.
>
> This would have been a question for Werner but I am sure there are
> others here who can shed some light on this for me.
>
> I know that part of the justification for why we have set our IPC
> standards where they are is partly based on years of testing.
>
> How could a mathematical calculation such as "Steinberg equation"
> justify a lack of Class 3 gull wing lead heel fillet?
>
> Any help is appreciated.
>
>
>
>
>
>
>
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