Gold Embrittlement

Gold embrittlement of solder joints still appears as a problem from time to time even though the issue has been understood for many decades. We diagnose this problem by using SEM/EDS to estimate the amount of gold in the solder joint. If the gold level exceeds about 3 wt% in the bulk solder joint then the joint is considered to be embrittled.

gold-embrittlement-1

We also diagnose gold embrittlement by using BSE SEM images to estimate the area fraction of AuSn4 intermetallic compound in the solder joint.

gold-embrittlement-2

There is a relationship between the wt % of gold in the bulk solder joint and the area fraction of AuSn4 intermetallic compound in the solder microstructure.

gold-embrittlement-3

For eutectic tin-lead solder the relationship is as shown in the above figure, suggesting that 3 wt% Au corresponds with ~ 12% area fraction of AuSn4 intermetallic compound in the solder microstructure. AuSn4 is a relatively hard/brittle phase in a softer Sn & Pb matrix, so when the AuSn4 exceeds ~ 12% the integrity of the solder joint begins to suffer.

See also GOLD EMBRITTLEMENT OF SOLDER JOINTS.

Check out SEM Lab, Inc.  to learn more.

Leave a Reply

Your email address will not be published. Required fields are marked *