Bell Labs' first positive gain semiconductor amplifier was of the point contact type where the n−type germanium base contact was conductively bonded to a metallic plate and the emitter and collector connections were made by point contact "cat whiskers." Such a contact is not mechanically robust and would not be a long term solution to semiconductor manufacturing. This full-page advertisement appearing in a 1958 issue of Radio & TV News magazine touts Bell Labs' development of a thermocompression wire bonding process whereby the combination of heat and concentrated pressure causes an atomic-level reaction between the semiconductor material and a gold interconnect wire. It proved to be very effective and reliable and paved the way for greater circuit density and packaging diversity (plastic and ceramic encapsulation vs. metal cans). Thermosonic wire bonding eventually replaced thermocompression wire bonding as the dominant process used in the semiconductor industry due to its lower stress on the semiconductor substrate and requiring less lateral separation on the die surface (pad pitch).
A 1953 ad told of Bell Labs' development of wire-wrapping.
Bell Telephone Laboratories Ad
Thermo-compression bonding -
Wire bonded to germanium by thermo-compression technique (enlarged). Wires only 1/10 the breadth of a human hair have been successfully anchored to germanium wafers only three hairs thick. The bond may be an ohmic contact or rectifying contact by adding suitable impurities to the wire and the semiconductor.
One method of thermo-compression bonding. A heated wedge presses a wire against a heated semiconductor with enough force to deform the wire. Adhesion occurs in seconds.
new way to join metal to semiconductors
Thermo-compression bonding provides a new way to attach a wire to a semiconductor. It calls for heat and pressure - nothing else. The wire and the semiconductor are moderately heated, then pressed together under moderate pressure. The resulting bond is very strong - stronger actually than the wire. No chemical flux or molten metal is required.
Eliminating molten metal provides an enormous advantage in fixing electrical connections to transistors. That's because molten metal tends to spatter and spread uncontrollably over the surface of a semiconductor. And it may alloy with the semiconductor to alter its all-important crystalline structure and chemical purity. Thermo-compression bonding easily and quickly makes a strong permanent electrical connection without damaging the semiconductor. Furthermore, the lead may be attached to microscopic areas and precisely positioned, a most valuable aid in the construction of high-frequency transistors.
At Bell Labs Howard Christensen and Orson Anderson discuss their discovery of new bonding principle with Peter Andreatch, Jr., who collaborated in the studies.
Thermo-compression bonding will speed the production of transistors ... the transistors needed to fill all the new jobs Bell Laboratories finds for them in the quest to provide still better telephone service to our growing country.
Bell Telephone Laboratories
World Center of Communications Research and Development
Posted January 9, 2020