Peter:
I suspect you've just encountered a classic example of requirements
mindlessly transferred when product technologies change.
As all us old-timers remember, back in the days of single-sided
through-hole boards there was debate about the maximum allowable gap in
the solder where it crossed the (non-plated) hole. (Exactly why the gap
should be a concern was never clear to me inasmuch as the bottleneck for
electrical flow has always been the traces. Moreover, the "problem" was
easily resolved by reducing the hole diameter relative lead size. But I
digress.) The generally established requirement was 75% coverage (though
some companies settled on 50% or so), one of many ill-conceived
decisions that ensured job security for touchup operators.
When double-sided and ultimately multi-layer through-hole assemblies
arrived, the same debate took place with respect to minimum permissible
solder flow up plated through-holes. The requirement was basically
derived from the single-sided requirement. That is, 75% fill (or, in
some companies, 50% or so). Of course, the traces continue to be the
electrical bottleneck regardless of the amount of solder (unless the
flow is prevented by breaks in hole plating, in which case it doesn't
matter where the flow is halted).
Now we get to surface mount assemblies and -- surprise -- you've got a
customer who wants to see 75% solder flow up the end caps. That kind of
thinking has been inevitable and I imagine it's more widespread than any
of us realizes.
Oh yes, I almost forgot: touchup operators still have job security.
Best wishes,
Jim Smith
Managing Director
Cambridge Management Sciences, Inc.
4285 45th St. S.
St. Petersburg, FL 33711-4431
Tel: (727)866-6502 ext. 21
Fax: (727)867-7890
eMail: [log in to unmask]
Peter Lee wrote:
> Technet,
>
> One of our customers is requesting 75% solder fillet height on all the
> SMT Porcelain capacitors (0805 package size with taller profile) used
> for a RF application. We told them based on our experience that the
> excess paste volume (and wetting) can not be achieved by our SMT stencil
> process. IPC only requires 25% for class 2 products. But they are now
> specifying hand soldering these components.
>
> Can anyone see any reason for doing this? I am prepared to go back to
> our customer to convince them otherwise (reasons such as extra labour,
> process inefficiency, solder joint reliability etc.)
>
> Rgds,
> Peter
>
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