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

[This e-mail is confidential and may also be privileged. If you are not the
intended recipient, please delete it and notify us immediately; you should
not copy or use it for any purpose, nor disclose its contents to any other
person. Thank you.]

---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------