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
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
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
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
At Bell Labs Howard Christensen and Orson Anderson discuss their
discovery of new bonding principle with Peter Andreatch, Jr., who collaborated in
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