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October 2002

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Subject:
From:
John Parsons <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 22 Oct 2002 13:40:57 -0700
Content-Type:
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OK, how many people out there were quite happy with life, until someone
decided that they could get a component "cheaper", particularly one that has
been in production a long time - raise your hand :o)

Bill,  while the notes do imply SMOBC "2. Solder Plate exposed copper .0003
to .0005", clearly something went wrong.  Apparently there are board shops
out there still building old tech boards with the reflowed Sn/Pb process -
it probably was cheap though!  Isn't that the only criteria these days?

We could speculate this to death on this forum but you really need to bring
your purchaser and the fab shop in on the discussion (if you have not
already) and troubleshoot it that way.  Who knows, maybe their quote
indicated that the board would be built this way and your purchasing
department missed it.  I personally don't think there is anything really
"wrong" with your notes so who knows, maybe the fab shop will come good on
this and remake them for you.

If this is the first time this has happened to you then let it be a lesson
to your purchasing department, sometimes you get what you pay for.

John Parsons

> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of Brooks,Bill
> Sent: October 22, 2002 1:20 PM
> To: [log in to unmask]
> Subject: Re: [TN] Solder UNDER Soldermask Accept/Reject Criteria?
>
>
> 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

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