Motorola Corporation

William O Rogers

Earl K Davis

Duane C Silvis

Nickel layers used in electronic devices are frequently plated in solutions containing phosphorus. Residual phosphorus trapped in the plated nickel layer reduces solderability with respect to Pb-Sn solders. Voids are frequently found in the soldered joints. Solderability of such phosphorus containing nickel layers is enhanced and the number of voids is much reduced by heating the nickel surface first in an oxidizing atmosphere and then in a reducing atmosphere prior to soldering. The oxidation temperature should exceed 347.degree. C. in order to oxidize the residual phosphorus and drive off the volatile phosphorus oxides. Hydrocarbons and volatile sulfides are also removed. The reducing step removes the non-volatile nickel oxides, leaving a clean surface for soldering which is substantially free of nickel oxide, phosphorus and phosphorus oxides, sulfides, and organics.

Method for enhancing the solderability of nickel layers

An improved molded-in insulated bushing is provided to electrically isolate the mounting fastener used to attach the metallic heat spreader of a semiconductor power device to an external heat sink. The bushing has at one end a flange protruding from one surface of the heat spreader and of sufficient height to exceed the required flash-over voltage. The other end fills a chamfered portion of the heat spreader, and is flush with or relieved from the heat spreader surface which contacts the external heat sink. This shape increases the surface flash-over distance and voltage above that of bushings of the prior art and retains the bushing in the heat spreader. The bushing is advantageously formed during molding of the plastic device encapsulation, but is separated from the encapsulation so that mounting forces are not transmitted through the encapsulation to the semiconductor die and lead wires.

Molded-in isolation bushing for semiconductor devices

An insulating or passivation glass consisting of 36 to 40 volume percent zircon and the balance is a base glass consisting essentially of 2 to 6 percent-SiO.sub.2, 70 to 75 percent-PbO 5 to 9 percent-ZnO, 0 to 4 percent-BaO, 2 to 5 percent-CdO, 0 to 2 percent-TiO.sub.2 and 10 to 14 percent-B.sub.2 O.sub.3, all of said percentages being weight percent.

Growing community of inventors

Tempe, AZ, United States of America

William O Rogers