Thanks to all who responded to my question about measuring thickness of 
electroless copper.

Here are some comments.

1.  Coupons must be all the same size, routed, not sheared.  Shearing may 
not make a big difference, but routing is best.

2.  Deposition varies with material:  epoxy-glass, polyimide-glass, etc.  
My thought is that, with different materials, you may need different SPC 
chart for each material.  Most of what our plant processes, almost all, 
is epoxy-glass, so we can evade this problem.

3.  Deposition may vary from lot to lot of the same material.  When 
setting up an SPC chart, may want to get a mix of lots to use for 
coupons.  That way, variability in those lots will be included in the SPC 
chart even when you don't know what the variability is.

4.  Bake the coupon before weighing.  Will the copper-clad coupon have 
enough water on the surface to make a difference?  If the coupon is baked 
(and weighed) before deposition, will it not absorb water when it is put 
through the wet process?


Thanks again to all who contributed.

Louis Hart
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