Tin Whisker Mitigation

Why Tin Whiskers Form and What Actually Stops Them

Tin whiskers grow spontaneously from pure tin surfaces. The precise mechanism is still not fully understood, but the recognised contributing factors include compressive stress within the plating, intermetallic compound formation at the tin and substrate boundary, thin or uneven plating, mechanical stress and vibration, and thermal cycling where materials with different expansion coefficients are joined. NASA's NEPP programme maintains the most extensive public body of research and failure imagery on the subject.

The industry moved to pure tin finishes largely as a consequence of RoHS legislation restricting lead. For most commercial electronics that is not a problem. For equipment expected to run for decades in defence, aerospace, rail and medical applications, it introduced a long-term failure mode that may not appear until years into service.

Two common responses do not solve it. Conformal coating can slow whisker growth and contain shorter whiskers, but it delays the problem rather than removing it. Hand-dipping components in solder is inconsistent by nature, which is why GEIA-STD-0006, the standard covering replacement of undesirable surface finishes, addresses robotic and semi-automatic solder dip processes and specifically excludes purely manual dipping.

Converting the finish to a tin-lead alloy addresses the root cause directly. Under GEIA-STD-0005-2, complete conversion of terminations from pure tin or lead-free solder to SnPb permits components to be used at any control level without further whisker mitigation. Our alloy conversion and re-tinning service performs that conversion, with XRF analysis confirming the resulting composition.

Our Tin Whisker Mitigation Process

Tin Whisker Testing and Verification

"Tin whisker testing" covers two different things, and it is worth knowing which one you actually need.

Verifying a mitigated finish. Once a pure tin finish has been converted to tin-lead, we verify the result rather than ask you to take it on trust. XRF analysis confirms the elemental composition of the new finish, giving you measured evidence that the pure tin has been replaced. Solderability testing can be added to confirm the converted finish still wets correctly. Results are recorded and supplied with the parts for your quality file.

Accelerated whisker growth testing. This is a different discipline. JESD201 sets the acceptance criteria and JESD22-A121 the measurement method, using long-duration environmental exposure, temperature cycling plus thousands of hours at elevated temperature and humidity, followed by microscope measurement of whisker length. It answers the question "is this finish whisker-prone?", takes months, and needs an environmental test laboratory. We do not perform JESD201 or JESD22-A121 whisker growth testing. If a customer or approval body requires it, that work belongs with an accredited environmental test house.

In practice most buyers searching for tin whisker testing want the first of these: evidence that a known-risk pure tin finish has been dealt with. Alloy conversion with XRF verification removes the risk rather than measuring it, and gives you the documentation to prove it.