On Tue, 8 Oct 2002 11:18:07 -0700, you wrote:

>Some boardhouses may still "dip" or submerge the board into an "etchant
>tank", where the board simply sits in the etchant, however, there should be
>enough "agitation" or "circulation" of the etchant to prevent what they are
>describing from happening.

Nothing you can do will eliminate the problem, just hope to reduce the
effects. A lot of copper in one area of the PCB will take longer to etch
resulting in over etching (undercutting) in areas with less copper. The
board house can't afford to over etch because some tracks will undercut
unacceptably (or even completely and fall off the board), under etching
risks leaving shorts in the dense areas. You are giving them process
control and yield problems seems reasonable they want you to pay extra. 

Before the etching problem there is a similar problem with plating. Need
100A for the copper on one side of the board and 5A for the other - how do
you arrange that? I think the only thing they can do is fiddle around with
anode spacing on each side of the board to try to balance it a bit. They
can't plate at 100A anyway because it puts too much current through the
sparse areas and leaves the tracks with an uneven 'frazzled' appearance. 

Again you are giving them process control and yield problems and slowing
them down. 


Cheers, Terry.

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