Patent ID: 8603315

Claim:
A method for electrochemically plating tin or tin alloy onto a workpiece, comprising: immersing the workpiece in an electroplating bath comprising stannous ions and devoid of organic additives other than alkane sulfonic acid and a wetting agent; immersing a counter electrode in said electroplating bath; and passing a succession of mediated pulsed currents between said workpiece and said counter electrode sufficient to provide a tin or tin alloy deposit on said workpiece, the pulsed current having a cathodic peak currents density in the range of about 5 to 150 milliamperes per square centimeter, a cathodic on-time in the range of about 0.05 to 10 milliseconds, an anodic peak current density in the range of greater than 0 to about 30 milliamperes per square centimeter, an anodic on-time in the range of about 0.05 to 10 milliseconds, wherein said deposit has an outer surface and an interface between the workpiece and the deposit and, wherein the pulsed currents are mediated such that the deposit has a stress gradient from the interface between said workpiece and said deposit to the outer surface of said deposit; the stress gradient being within the deposit.