Tin-whiskers are often a hidden risk of failure in electronic components. The growth of these hair like crystalline structures is a phenomenon that until recently was less of a concern.
Before the RoHS Directive, the growth of tin whiskers was controlled very much by accident using lead solders; quite an effective suppressant. However the use of lead-free solders has seen the risk of tin whiskers become more prevalent.
It is uncertain exactly what causes the growth of these metal structures, which can grow several millimetres to between 1-10µm in diameter from the base of the finished surface.
Found in other metals such as Zinc, Cadmium, Indium, Aluminium and Silver the metal whisker can break off forming a bridge between two or more adjacent circuit elements causing them to short circuit.
Protection with conformal coatings
The application of a conformal coating can slow metal whisker growth but there are significant variations depending on the coating thickness and environmental conditions. For its ultra-thin coating thickness and truly uniform layer, Parylene surpasses other coatings in suppressing growth and insulating the rest of the assembly where a metal whisker has penetrated.
Parylene is the coating of choice for mission critical electronics being applied in the medical market for pace makers, active implants and diagnostics equipment and for ground electronics and avionics systems used in the aerospace and defence markets.
Parylene improves the life in Lead free solder joints
In tests carried out by Curtiss-Wright Controls involving a range of conformal coatings, they found that under thermal shock testing involving continuous cycling between -40 and 125C, Parylene improved the joint life of lead free solder joints by an average of 200% that of any other coating tested.
Parylene ruggedizes electronic assemblies, providing the reliability needed in critical applications; protecting from gases, chemicals, liquids and the risk of bridging posed by tin whiskers.