since lead - tin solder was outlawed , electronic circuits constructed with lead - free tin solders have been plagued growth of whiskers of tin emanating from the tin soldered and / or tin coated surfaces . such whiskers often short out the electronic circuits when present . the growth of tin whiskers in such electronic circuits ( i . e ., those fully or partially populated with components is addressed here by depositing a tin - whisker - impenetrable metal cap on all exposed tin coated surfaces in the circuit . in the process , metal surfaces where no cap is desired are masked , where after all exposed metal surfaces are cleaned , followed by immersing the entire circuit in an electroless bath , e . g ., a nickel electroless bath , for a time sufficient to form a metal cap on all exposed metal surfaces , removing the circuit from the bath , rinsing and de - masking covered surfaces .