Handbook of Printed Circuits 3rd edition says" Once the standard of industry pyrocopper has been almost entirely replaced by acid copper except for military and special applications. Pyrocopper continues to be used because of it's resistance to cracking, high throwing power, and purity." Rothschild in Electronic Packaging and Production magazine in August 1975 says pyrocopper with PY61H (the most common additive) had an average tensile strength of 87,000 psi and an elongation of 5-18%. Handbook says acid copper is 40-50,000psi and 10-25% . The major cause of the switch was really, in my opinion waste treatment issues, with it's ammonia pyrocopper is harder to treat than acid copper. Pyrocopper is still in specifications reportedly because those with high reliability applications still specify it. Pyro also was at a disadvantage in fine pitch applications requiring pattern plate once to semiaqueous photoresists were less available as it is a fine resist remover for aqueous resists. When we had a shop we used pyro on lots of 0.093 thick boards with success. You can get arguments on reliability because a whole lot depends on how you maintain either acid copper or pyro and either bath run outside its parameters can make marginal product. Pyro does provide a challenge from the control stand point both from the additive and the chemistry side. Atotech is a good contact on pyro I believe. With etchback you need to know what type, Anderson, etal in Purification of acid copper baths in Plating and Surface Finishing December 1983 says even moderate levels of manganese in acid copper baths exerts a significant detrimental effect on tensile properties of the deposit for instance. This indicates potassium Permanganate desmear process need to be well maintained and in control also. NOTE: Opinions are those of the author who used pyro for many years and may or may not represent those of his employer. ---------- From: [log in to unmask] To: [log in to unmask] Subject: Copper Plating Date: Tuesday, June 04, 1996 4:44PM Does anyone know of reliability differences between pyro and acid copper plating in severe thermal environments (i.e., military avionics) on multilayer pwbs up to .080 thick? I've read that pyro provides a challenge when it comes to elongation but my information may be old and may have been overcome in recent years. Also does etchback play any role in the selection of pyro or acid copper plate? Bill Dieffenbacher, Lockheed Martin Control Systems [log in to unmask] Phone 607-770-2961 Fax 2056 _______________________________________________________________