Solderability of tin - based composite coating was studied by adding TUM series of additives to the soldering bath. The 3 second wetting force of the composite coating almost reached the theoretical value
with its solderability approaching the best level. The effect of inner factors (surface oxidic film
"tin pest")on solderability was investigated. The microcrys-talline structure and surface oxidation were examined with X - ray diffraction and ion probe
and the mechanism of the effect of composite particles on solderability was studied.