| abstract |
An electrode is applied to the surface of an electrical device such as a semi-conductor integrated circuit by a process comprising the steps of applying a metal layer 8 to the body 1 to be contacted, applying a metal mask 9 over the layer 8, depositing metal 20 on to the portion of the layer 8 exposed through the mask 9, and dipping the arrangement in a molten solder which adheres only to the deposited metal 20 to form a coating thereon but does not adhere to the mask 9. The embodiment comprises an N- type Si body 1 having a diffused P-type zone 4, the layer 8 and mask 9 respectively comprising vapour deposited layers of Ag and Al. Apertures are etched through the Al layer 9 to form the mask, and a further mask is applied over the layer 9 to define the regions where subsequent metal deposition is to occur. The metal parts 20, 21 may be applied by electroless coating or by electrolytic deposition of Cu from an aqueous solution of CuSO 4 containing H 2 SO 4 . The second mask is then removed and the arrangement is dipped into a molten solder comprising 60% Sn, 40% Pb by weight, which adheres only to the surface of the parts 20, 21. The A1 masking layer 9 and the exposed portions of the Ag layer 8 are finally removed by etching or using a water jet. |