The Use of Cobalt in Plated Copper to Inhibit the Formation of Brittle Copper-Tin Intermetallic Compounds - at the Copper-Solder Interface on Printed Circuit Boards 710793
The formation of copper-tin intermetallic compounds of the Cu6Sn5 and the Cu3Sn type at the interface between copper and solder on printed circuit (PC) boards has been previously documented, as have the circumstances under which these brittle layers can cause peeling of the solder and greatly reduce the solderability of the PC boards shown.
The formation of these intermetallic layers is caused by diffusion, mainly of the copper into the solder, and is a function of time and temperature.
Inhibiting the diffusion will inhibit the formation of the intermetallics. Several methods have been tried, such as the use of a metallic barrier layer. This paper will show that one of the more successful methods is the codepositing of small amounts of cobalt (0.05-0.5%) with the copper.
This process is similar to the use of cobalt in wrought copper alloys to reduce solid-state mobility during thermal processes.
These small amounts of cobalt do not reduce the solderability, increase the difficulty of achieving sound plated through holes, or react differently to standard etching solutions than pure copper.
Citation: Breen, J., Toledo, E., and White, V., "The Use of Cobalt in Plated Copper to Inhibit the Formation of Brittle Copper-Tin Intermetallic Compounds - at the Copper-Solder Interface on Printed Circuit Boards," SAE Technical Paper 710793, 1971, https://doi.org/10.4271/710793. Download Citation
Author(s):
J. E. Breen, E. Toledo, V. White
Affiliated:
Raytheon Co.
Pages: 5
Event:
National Aeronautical and Space Engineering and Manufacturing Meeting
ISSN:
0148-7191
e-ISSN:
2688-3627
Also in:
SAE 1971 Transactions-V80-A
Related Topics:
Wrought alloys
Copper
Plating
Joining
SAE MOBILUS
Subscribers can view annotate, and download all of SAE's content.
Learn More »
