Bill:
After reading notes 2 & 6, I would have called you for two reasons;
#1 I would have asked what kind of mask do you require
#2 I would have asked can I change the plating to SMOBC.
That's all.
Charlie McMahon
Brooks,Bill wrote:
>I raised the issue in the open forum for a reason. (OBTW ... It's not my
>design)
>
>One, I may be able to locate someone else who has had this problem before
>and knew of a spec that would enlighten the folks involved in reviewing
>this.
>
>Two, I may find that there is no spec and we are at fault for not specifying
>SMOBC and that we have been enormously lucky all these years that the vendor
>we were using interpreted our preference for assemblies that don't short out
>under the soldermask after wave soldering....
>
> I went to the IPC specs looking for guidance on this and found little that
>I could interpret to be related to this scenario.
>
>Here are the notes off the actual drawing... Maybe you guys can shed some
>light on the results we received... (it was a new vendor)
>
>NOTES: UNLESS OTHERWISE SPECIFIED
>1. Material: .062 FR-4 C2/C2 Finished
>2. Solder Plate exposed copper .0003 to .0005
>3. Hole sizes are after plating, Min. wall .001 thk
>4. Finished board to comply with IPC-A-600, Class II
>5. Component side shown
>6. Solder Mask Both Sides
>7. Silkscreen component side with white epoxy ink
>8. Tolerances: Front to Back: +/- .005
> Hole location: +/- .003
> Hole Diameter: +/- .003
>
>
>That's all there was... I didn't create the notes, I have only been here 2
>years, it was created before 1996 by another designer.
>So any speculation on why one vendor used SMOBC and another used SOS... ?
>- BB
>
>
>
>Bill Brooks
>
>
>
>-----Original Message-----
>From: Barmuta, Mike [mailto:[log in to unmask]]
>Sent: Tuesday, October 22, 2002 12:57 PM
>To: 'TechNet E-Mail Forum.'; 'Brooks,Bill'
>Cc: Barmuta, Mike
>Subject: RE: [TN] Solder UNDER Soldermask Accept/Reject Criteria?
>
>
>Bill:
>1. Since this board has been made for over 10 years, did you change
>fabricators? If so the new fab shop obviously was not aware of your SMOBC
>desire. Although a good board supplier should have reviewed your drawing and
>questioned you as to what style of fab and final finish you wanted. Never
>assume what someone's default process is.
>
>2. From your description this sounds like an electroplated fused Sn/Pb board
>with soldermask. At least I hope it's fused. If the fab shop is set up for
>this process it's cheaper to build than an SMOBC board. Did somebody try to
>get a lower cost on this board?
>
>3. Soldermask over fused Sn/Pb is not necessarily a bad thing. If done
>properly it should have better solderability and shelf life than HASL. The
>issue of wrinkling mask in the wavesolder process could be a problem.
>However it depends on the board design. If you don't have large features or
>groundplanes on the bottom wavesolder side of the board you should not see
>much, if any loss of mask.
>
>
>
>
>Regards
>
>Michael Barmuta
>
>Staff Engineer
>
>Fluke Corp.
>
>Everett WA
>
>425-446-6076
>
>
>
>-----Original Message-----
>From: Brooks,Bill [mailto:[log in to unmask]]
>Sent: Tuesday, October 22, 2002 12:20 PM
>To: [log in to unmask]
>Subject: Re: [TN] Solder UNDER Soldermask Accept/Reject Criteria?
>
>
>I guess I should clarify also that this is a board that has been made for
>years. Without the soldermask coming in over solder. The board has been
>around more than 10 years and this was a shock to the manufacturing folks
>when it happened... we just don't see this sort of thing happen anymore....
>I think the last time I saw this was in 1985. We all learned to call out
>SMOBC to get the vendors to avoid making the boards with solder under the
>soldermask. In fact, it took some convincing of some engineers that the
>board would be fine without a solder coat over the entire copper surface,
>and that they only needed the solder where the component lead was...
>I'm sure there are some of you guys that are my age (46) that remember this
>stuff... its just so surprising to see it in this day and age... :)
>
>
>Bill Brooks
>
>
>
>-----Original Message-----
>From: Brooks,Bill [mailto:[log in to unmask]]
>Sent: Tuesday, October 22, 2002 12:08 PM
>To: [log in to unmask]
>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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