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Tin Electrochemical Migration

Material Name: Sn
Record No.: 189
Primary Chemical Element in Material: Sn
Sample Type: Bulk
Uses: No data
Etchant Name: None
Etching Method: No data
Etchant (Electrolyte) Composition: No data
Procedure (Condition): No data
Note: Tin electrochemical migration mechanism is similar to that of Cu, but is much more prevalent because Sn constitutes a major portion of several commercial solder compositions such as 62SnPb2Ag, 10SnPb, Sn3.5Ag0.7Cu, etc. In addition, exposed Sn is more widespread on an assembled PWB as compared to Cu. The particular example shown in Figure 1 is from a test vehicle that failed upon exposure to damp heat testing. In this case, the potential difference between the terminals of a resistor with Sn termination resulted in the migration of Sn from the cathode towards the anode. It can be seen from the EDX elemental maps (Sn) that one of the resistors is shorted.
Reference: Sridhar Canumalla and Puligandla Viswanadham, Board Level Failure Mechanisms and Analysis in Hand-held Electronic Products, Richard J. Ross (Editor), Microelectronics Failure Analysis, Desk Reference, Sixth Edition, ASM International, 2011, pp. 23-33.


Figure 1: Tin electrochemical migration on a resistor with pure tin termination.