Hello Peter.
I have been building complex boards seems like all my life. I understand
completely how the processes your fab shop used could result in difficulty
etching the patterns. I also understand how designers are capable of making
board production nearly impossible. If you are serious and would like real
help in determining if a better process exists for this particular board
then I am willing to devote a few hours of study to your problem-- but I
will need real information. I invite you to send me a fab drawing showing
the stack-ups and finished hole sizes, the various layer interconnections,
etc. In addition, if there aren't major confidentiality issues, I also
invite you to visit our web site and use the Data Transfer Menu to send us
the CAD Data for the part. We will load it onto our systems and check the
layout for plating-related issues.
It could well be that there is no better process than the fab house has
already chosen, but I also think they might have "overlooked" some viable
solutions to the problem. Only your fab drawing and data will tell for sure.
My web site is: www.protoengineering.com
My fax is USA: (408) 738-1290
At 10:26 AM 11/16/01 +0800, you wrote:
>Dear All,
>
>I have another problem for you PCB Fab guru's. The sister board to the
>warped one of my previous posting has the problem of being over-etched in
>some areas. Some pads are half the width they should be. It is 12 layer,
>ENIG finished, with 3 different blind via depths from the bottom of the
>board and two from the top, as well as the through-hole group. They are
>laminated conventionally - i.e. each blind group is laminated. drilled and
>plated before lamination for the next hole group, and so on, so there is
>considerable variance in surface copper weight by the time the board is
>fully laminated.
>
>Our fab house tried remaking the boards by laminating the entire board at
>once, then laser drilling to depth and plating. The result was a total
>failure, and once again we're faced with a re-make using the previous
>processes.
>
>Does anyone know how we can reduce the variance in surface copper weight
>such that, in final etch, there isn't such a poor compromise between
>getting the widths and spacings of the heavier copper areas right, without
>over-etching the lighter copper areas? I tentatively suggested selective
>masking of some kind for the areas already plated, but I have no idea if
>that's feasible or not. How do other fab houses deal with this situation?
>
>Thanks as ever for your invaluable help.
>
>Peter Duncan
>
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