Hi Ben,
All Au goes into solution with Sn to form AuSn4 IMCs [the same is true for Ag forming Ag3Sn], unless there is no more Sn left, during the soldering process. These IMCs form patelete-like structures [they often appear as needles in cross-sections] and act as internal 'notches' resulting in stress concentrations. The concentration of these IMC-platelets, and thus the concentration of notches, produce what is called 'Au-embrittlement.'
Whether you solder to Cu or Ni has no influence on this. The intermetalic layers forming the metallurgical bond between the bulk solder and the base metal do typically not contain any Au [or Ag].

Werner



 


 

-----Original Message-----
From: Gumpert, Ben <[log in to unmask]>
To: [log in to unmask]
Sent: Fri, 24 Oct 2008 10:58 am
Subject: [TN] Au embrittlement on Copper vs Nickel










Technetters,

Anyone care to share some comments on Au embrittlement?
Specifically, what is the relative difference between joints on copper
vs nickel? (For a SnPb joint)

Does Cu inhibit AuSn4 from forming in the bulk solder? Does this have
any effect on Au in the intermetallic layer?
Do the intermetallic compounds containing Au of each joint result in a
similar brittleness?
Do the joints have the same propensity for growth of intermetallic
compounds containing Au?

Any thoughts are welcome.
Ben



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