I would like to add a few general comments. I have been involved with electroless copper for a number of years, using most of the methods available for measurement. SPC of the thickness is frustrating to say the least. The process is so dynamic & also relies on more than just the copper bath to influence the thickness (although many of these variables have only nuance effects). The measurements vary so much that my real bottom line is: "I want to know if the bath/line has so much variation from one load to the next that something has just had a major screwup." That is, I am looking for those wide swings in thickness from one rack to another that indicate REAL problems (variation of 30-40 millionths or more). i.e. Did a replenishment pump die since the last load was processed? Did someone bump a calibration knob on one of the pumps? Was the wrong add made? etc. These are the things that you are REALLY interested in. The thickness of the Dep copper within 10 or 15 millionths of the target isn't really going to make much difference to your processing unless you are already on the verge of etching it out of the holes in your plating line, creating PTH voids. Matt Byrne Hadco, Owego ______________________________ Reply Separator _________________________________ Subject: FAB: follow-up on electroless thickness measurements Author: [log in to unmask] at SMTPLINK-HADCO Date: 4/1/96 06:20 PM 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 [log in to unmask]