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October 2002

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Subject:
From:
"Valerie St.Cyr" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 22 Oct 2002 15:25:59 -0400
Content-Type:
text/plain
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text/plain (116 lines)
Bill,

There is no commonly understood acronym as "SOS" - Soldermask Over Solder"
- BUT
it used to be in the good old days that all boards were soldermask over
solder. The solder
was plated and reflowed, then the soldermask was applied. That was common
practice.

You said: "The implication is that the order of the notes IMPLIES that we
want soldermask after
the solder coating process" - while I would argue that notes never imply
anything, nevertheless,
you did get soldermask after solder coating; SMOBC is a soldermask BEFORE
solder coating.

Did the print say Hot Air Solder Level (HASL or something to that effect)
or Solder and/or the
words "plated" or "reflowed"? If the later, then your print will definitely
be intrepreted as asking for
soldermask over solder ...

The best course of action going foward is to clearly state SMOBC and then
the other finish:
eg: solder, silver, OSP etc...

Valerie







"Brooks,Bill" <[log in to unmask]>@IPC.ORG> on 10/22/2002 03:07:38 PM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
      to "Brooks,Bill" <[log in to unmask]>

Sent by:  TechNet <[log in to unmask]>


To:   [log in to unmask]
cc:

Subject:  Re: [TN] Solder UNDER Soldermask Accept/Reject Criteria?



The Print did not specify SMOBC. But it also didn't specify SOS (Soldermask
over solder) either! The implication is that the order of the notes IMPLIES
that we want soldermask after the solder coating process.  Don't all
PCB vendors know that the solder under the soldermask will reflow, wrinkle
and damage the soldermask in assembly?  If we have soldermask on a thru
hole technology board.... we are going to wave solder the board. Why would
a vendor interpret the drawing in such a way as to compromise the
performance of the board? I can't believe this is still happening in 2002.
I thought we learned our lesson back in 1980.....the first time I ever saw
anyone DO that...

 Doesn't IPC have a spec that tells us not to do it that way?

Bill Brooks

-----Original Message-----
From: Steve Gregory [mailto:[log in to unmask]]
Sent: Tuesday, October 22, 2002 11:44 AM
To: [log in to unmask]
Subject: Re: [TN] Solder UNDER Soldermask Accept/Reject Criteria?


Hi Bill!

Was that called out on the fab drawing? I've ran across a few boards here
that still call that out on the drawing, and TRY and get that changed
before the boards are fabbed...most of the time I've been lucky, but
there's been a few that slipped by me.

Bottomline, if it's called out on the drawing, you don't have much
recourse...

-Steve Gregory-


Anyone aware of a spec that sets the accept/reject criteria for boards that
come in with solder UNDER the soldermask? Is this actually done as a
legitimate practice? WHY would a vendor make the boards this way? Shouldn't
we be making all boards to be SMOBC when there is a soldermask?

Bill Brooks


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