A method forms a micropad to an external contact of a first semiconductor device. A stud of copper is formed over the external contact. The stud extends above a surface of the first semiconductor device. The stud of copper is immersed in a solution of tin. The tin replaces at least 95 percent of the copper of the stud and preferably more than 99 percent. The result is a tin micropad that has less than 5 percent copper by weight. Since the micropad is substantially pure tin, intermetallic bonds will not form during the time while the micropads of the first semiconductor device are not bonded. Smaller micropad dimensions result since intermetallic bonds do not form. When the first semiconductor device is bonded to an overlying second semiconductor device, the bond dimensions do not significantly increase the height of stacked chips.