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.
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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
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