Assembly of two individually encapsulated silicon-chip transistors produces silicon power-transistor that has low electrical resistance and low thermal impedance. Electrical resistance and thermal impedance are low because of short lead lengths, and external contact surfaces are plated to reduce resistance at interfaces

Ferree, H.

Stonebraker, E.

Stoneburner, D.

English

NASA Technical Reports Server

July 1973	 B73-10295 
•	 NASA TECH BRIEF 
NASA Pasadena Office
	 -4r 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Silicon Switching Transistor with High Power
and Low Saturation Voltage 
.
The problem: 
To construct a silicon power-transistor that has low 
electrical resistance and low thermal impedance. 
The solution: 
An assembly of two individually encapsulated 
silicon-chip transistors. 
How it's done: 
Each encapsulated chip is a disc-shaped hermet-
ically-sealed package with the emitter connected to 
one side and the collector to the opposite side. The 
use of two individual chips permits close matching 
of performance and ease of replacement should one 
unit fail. Electrical resistance and thermal impedance 
are low because of short lead lengths, and the external 
contact surfaces are plated to reduce resistance at the 
interfaces. Both units are mounted to the same heat 
sink so that their temperatures will most probably be 
equal. Since each unit is individually capable of 
carrying the rated current, emitter ballast resistors 
(which might increase saturation voltage) are not re-
quired; current sharing is assured because the chips 
are matched. 
A compression-bond—encapsulation technique is 
used for contacting the collector, base, and emitter of 
the basic transistor fusion. The emitter and collector 
contact faces of the unit are identical, and therefore 
interchangeable, which makes possible use of a 
mounting in which the emitters are directly in contact 
with a grounded heat sink. A commercially available 
aluminum heat sink may be used. A narrow profile 
offers advantages in electrical resistance, thermal re-
sistance, and lead wire inductance. The insulated
base lead passes through a pressure contact and 
makes contact to the weld flange of the emitter seal. 
The top portion of the assembly is a copper col-
lector-contact bar which provides a low-resistance 
contact to the collector of the units. Since the thermal 
conductivity of copper is about twice that of alumi-
num, heat is conducted to the heat sink much faster 
and over a much larger area than if the devices were 
mounted directly on the heat sink. The units are lo-
cated on the collector contact bar, and an emitter 
contact bar is located on the emitter contact area of 
the flat package. The top compression bar is located 
and held in position over the emitter contact bar by 
two dowel pins which fit in a milled groove on both 
the emitter and top bars. Alignment of the assembly 
is accomplished by a compression bolt and insulator. 
The required force on the units is maintained by the 
bolt along with the compression nut and Belleville 
springs; the force required to provide low thermal 
and electrical resistance is about 900 kg (2000 ibs). 
Notes: 
1. The following documentation may be obtained 
from: 
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $6.00 
(or microfiche $0.95) 
Reference: NASA CR-112870 (N70-86859), Design 
and Development of a High Power, Low Satura-
tion Voltage, Multi-Chip Switching Transistor. 
Patent status: 
NASA has decided not to apply for a patent. 
(continued overleäf) 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19730000295 2020-03-17T07:00:43+00:00Z
Source: E. Stonebraker, D. Stoneburner, 
and H. Ferree of 
Westinghouse Electric Corp./Semiconductor Division
under contract to

NASA Pasadena Office 
(NPO.11565)
. 
. 
B73-10295	 Category 01


Silicon switching transistor with high power and low saturation voltage

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server