copper and induim intermetallic

[Alex299]

Can any of you folks tell me what conditions would cause an intermetallic bewteen copper and indduim? Temperature, humidity, etc.. What about indium and brass? Also, how to prevent it?

Thanks, Alex.

 

[kenvlach]

At least 5 intermetallics can occur according to the Cu-In phase diagram given in ASM Handbook vol 3. Most only form at elevated temperatures, but Cu₁₁In₉ and CuIn may form at soldering temperatures. See the article (abstract is free):

http://www.springerlink.com/content/e3775x7221135062/

Two methods prevent intermetallic formation:
1) Keep the Cu-In contact at absolute zero (0 K). Maybe impractical.
2) Provide a diffusion barrier. One method is to plate a Ni buffer layer and Cr blocking layer onto the copper or copper alloy.

http://tinyurl.com/2stsmy

Electronics people also use more exotic metals such as Pd and Ta as diffusion barriers on copper. If high temperature exposure only occurs during soldering, a layer of nickel plating may suffice. Also, do a search

http://www.google.com/search?source...34,GGLG:en&q=copper+indium+diffusion+barrier+

 

[Alex299]

Thank you. We are testing new components and running into some trouble. We have a copper component with indium alloy solder, soldered to a silver surface. This is then run through a temp. shock test of -40C to +90C, and then humidity chambered at 95%RH. 3 questions: Is the intermetallic with Cu/In harsher than Cu/SiPB solder? Does the humidity have any effect on intermetallic formation? Is there an effect with the silver surface?