Meaning
Lead-free solder finishes on printed circuit boards and component terminals can spontaneously grow crystalline filaments that cause electrical short circuits. Employing tin whisker mitigation techniques is necessary to prevent these conductive microstructures from bridging adjacent conductor paths. This process is particularly critical in aerospace and medical applications where high reliability is required.
The boundary of this mitigation involves the choices of metal alloys and the application of protective conformal coatings.
Physical Prevention
Stress gradients within the electroplated tin layer drive the growth of these metallic filaments. Effective tin whisker mitigation begins with the selection of appropriate underplating materials, such as nickel barriers between the copper substrate and the tin finish. This intermediate layer prevents zinc or copper migration that would otherwise increase the compressive stress.
This barrier significantly delays the initiation of whisker growth.
Protective Coating
Application of a thick polymer or silicone conformal coating provides a physical barrier that prevents whiskers from escaping the surface or contacting other leads. This layer of tin whisker mitigation is applied during the final board assembly stage. The coating must be applied uniformly to ensure no pinholes are left where a filament could emerge.
This mechanical defense protects adjacent high-density solder joints from shorting.
Reliability Handover
Compliance is verified through long-term environmental stress testing under high temperature and humidity conditions. This test is followed by visual inspections under scanning electron microscopes to confirm the absence of filament growth. This qualification report is required before the design can be approved for aerospace deployment.
