Silicon Cert Ltd. - Testing for Tin Whisker Growth

With the elimination of lead (Pb) in electronic components in 2006 as a result of two European Union directives, 1) RoHS (Restriction on use of certain Hazardous Substances) and 2) WEEE (Waste from Electrical and Electronic Equipment), all manufacturers of IC’s have been working the problems associated with tin (Sn) plated leads, specifically the creation of “tin whiskers”.

“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: Storage at 55 degrees C and 85% RH for a minimum of 4000 hours. Storage at ambient temperature (30 degrees C) and 60% RH for a minimum of 4000 hours. Temperature Cycling (-40C to +85C or -55 to +85 C) for a minimum of 1500 cycles.

To view tin whisker creation, a SEM at a minimum magnification of 300x is typically used to identify the type (hillock, odd-shaped eruption, whisker filament, etc.) of growth and to record growth measurements. Since the fundamental mechanisms for growth are not fully understood at this time, measurements are normally taken at regular intervals throughout each of the above tests. JEDEC Standard JESD22-A121.01 is normally followed for this measurement procedure.

Clients can be confident that SCL’s experienced and knowledgeable engineering staff will expertly perform their tin whisker testing requirements. A complete report is provided at the completion of the tests. Information is also provided to clients on an interim basis due to the overall duration of the tests.