Saturday, May 31, 2008

Composition of Printed Wire Board Plating

Excessive amount of organic additives or the decomposition products associated with the additives can result in brittle deposits. Possibly the biggest pitfalls in studying the causes of these deposits are the difficulties in analyzing the addition agents and identifying the culpable decomposition product. The researcher disclosed an analytical scheme for controlling solid or aqueous stock solutions of ore additive (2-mercaptobenzimidazole), while others claimed that the key was the use of only a minimum amount of proprietary leveler.

Optimum ductility has been obtained by using solutions free of organic additives. In some cases continuous carbon filtration is also used, in another, multistage and periodic reverse current. However, even with these precautions, brittle copper deposits could be obtained. Along this line, showed that multilayer boards containing excess ammonia and a low pyrophosphate to copper ratio failed much more quickly by cracking than did boards plated with ductile copper. To minimized cracking in the plated through holes by applying a thin deposit of copper pyrophosphate (5-7.5 µm) followed by 25 µm of ductile cyanide copper. Plated through hole copper cyanide deposits were less susceptible to cracking than pyrophosphate deposits.

Brittle copper deposit for the way solder peeled away from copper surfaces during adhesion test and solder joint divorced themselves from copper pads. The failure were eliminated when copper pyrophosphate plating was done with no organic additives in the bath, or by use of a nickel diffusion barrier from a pyrophosphate bath. It was postulated that brittle copper obtained with organic additives exhibits a diffusion rate different from that of pyrophosphate copper without organic additives. Skip printing is occasionally encountered when plating printed circuit boards. This problem manifests itself as depressions in the form of teardrops around the plated through holes. The depressions are probably caused by variable thickness of the cathode film during plating. Interfaces produced by cavitations in the solution due to high agitation around the holes are immediately filled with desorbed brighteners and are thereby locally insulated. The primary causes of the variable cathode film which lead to skip plating are excessive or decomposed brighteners, improper current density, agitation or both eliminated skip plating. Test method for printed circuit boards with plated through holes are given in various specifications. Item such as electrical continuity, temperature cycling, bend strength, and plating thickness are checked.

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