Hmmmm..... another coupon dilemma. You know Ralph, this always seems to be an ongoing issue. Frankly I feel way too much emphases is placed on these dang coupons.
Coupons are a good if used as a process indicator. They don't by any stretch of the imagination ( in my opinion ) mean the board is good. I don't care where you place them.
I wonder just how many of us can tell stories of countless dollars lost due to coupons.
Some customer will section a board regardless of what your coupons look like and if the board shows a non-compliant condition ... guess what? Typically there would be a push to scrap the entire lot. After all, if your coupon is acceptable and the holes sectioned from the board is not.... well then.... You coupons obviously have no bearing on acceptability. Now on the other hand, if the coupons shows unacceptable, there is a tendency by many to scrap the lot regardless if the board sections good or not.
If the parts you are referring to are commercial and not military and your are not having any issues with functionality I really would not waste a lot of time on where the coupons were placed on the panel. The coupons will only provide a fairly good picture regarding the desmear/etchback process and a general idea of plating thickness and annular ring. I have found that as far plating thickness the coupon rarely mirrors all the holes on the actual parts due to the many current density issues on most designs. As far as annular ring, well at least you know your coupon doesn't break out. That doesn't mean the functional part of the panel does't have some isolated breakout at egress due to drill wonder, material movement, and/or artwork distortion. I have seen panels with great looking coupons and yet scrapped parts due to internal registration and may effect only a couple of parts on the panel.
Just my two cents.
Ed Cosper
----------
From: Vaughan, Ralph H[SMTP:[log in to unmask]]
Sent: Friday, May 08, 1998 8:44 AM
To: [log in to unmask]
Subject: [TN] PWB Test Coupons
Greets
How about a relatively non-technical arguement to chew on?
For years we have procured pwb's to the mil- or ipc-d 275 rules from
several very reputable suppliers. All the boards are delivered with a 1
to 2 inch wide manufacturing panel surrounding the board, which is
routed off after we complete assembly. In all cases, the shops have
regarded this panelized board as "the board" and have placed the test
coupons one-half inch from the"the board", as the spec requires. We
have always concurred with this, as we didn't particularly want our
manufacturing panel cut up to remove coupons, and we understand that
this is pretty much industry practice, and also feel that having the
coupon one inch closer to the circuitry makes no real dif. Now,
another faction of my company with a more purist attitude tells me none
of my boards are spec compliant because of coupon placement. We have
already gone to the needless trouble and expense of modifying drawing
notes to allow this condition, so I'm not in a panic, but I'd still
like the decision from the jury.
Thoughts?
Thanks
Ralph
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