“Whiskers”, first identified in electroplated cadmium components during the late 1940’s, appear to essentially be an extrusion, or hairlike growth emanating from the surface of the tin plate. They can sometimes grow long enough to cause a short circuit between leads, or may break off and cause damage elsewhere in the device. It is generally agreed that pure tin finishes (and other high-tin content lead-free alloy finishes) present a risk of tin-whisker failures in electronics, particularly those demanding high reliability.

There are accelerated methods to test lead-free devices for tin whisker growth. Several manufacturers comprising the iNEMI Tin Whisker Users Group (http://www.nemi.org) have come up with recommendations that pertain to tin whisker testing requirements along with acceptance criteria for the evaluation of devices with tin finishes.

Three tests, in conjunction with SEM (Scanning Electron Microscopy), are generally accepted at this time for tin whisker testing per JEDEC Standard JESD201 and A121:

1. Storage at 55° C and 85% RH for 1500 hours for Class 1 & 2 products and 1000 hours for Class 1A products.
2. Storage at ambient temperature (30° C) and 60% RH for Class 1 & 2 products and 1000 hours for Class 1A products.
3. Temperature Cycling (-40° C to +85° C or -55° C to +85° C) for 500 cycles for Class 1, 1A and 2 products.