With the coming elimination of lead (Pb) in electronic components by July 1, 2006, led by two European Union directives, all manufacturers of IC’s are working the problems associated with tin (Sn) plated leads, specifically the creation of “tin whiskers”. These “whiskers” appear to be essentially an extrusion, or hairlike growth, emanating from the surface of the tin plate. They can potentially 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, particular those demanding high reliability.

There are accelerated methods to test your device for tin whisker growth. Several manufacturers comprising the iNEMI Tin Whisker Users Group have come up with recommendations that pertain to tin whisker testing requirements along with acceptance criteria* for the evaluation of devices with tin finishes. The three generally accepted tests, per JEDEC Standard JESD201, are:

1) Storage at 55°C and 85% RH for up to 4000 hours.
2) Storage at ambient temperature (30°C) and 60% RH for up to 4000 hours.
3) Temperature Cycling (-55°C to +85° C) for up to 1500 cycles.

To view tin whisker creation, a SEM (Scanning Electron Microscope) at 300x is typically used to identify the type (hillock, odd-shaped eruption, whisker filament, etc.) of growth and to record growth measurements. Due to the fundamental mechanisms for growth not being fully understood at this time, measurements are normally taken at regular intervals throughout each of the above tests.

Clients can be confident that Silicon Cert’s experienced and knowledgeable engineering staff will perform their tin whisker evaluation testing in a professional and timely manner. A complete report will be provided at the completion of the tests. Information can also be provided to clients on an interim basis because of the overall duration of the tests.

* Criteria for inspection/measurement based on JEDEC Standard # JESD22-A121 entitled “Measuring Whisker Growth on Tin and Tin Alloy Surface Finishes” of October 2005.