Page 66 - Power Electronics Handbook

Power semiconductor packaging 59
silicon dice of diameter D, cycled through a temperature range dT, is
given, for hard-soldered joints, by equation (1.29) where K is a constant.

(1.29)

Connections to the emitter and base of a transistor, or the gate and
cathode of a thyristor, are usually made by ultrasonic bonding using
aluminium or aluminium-magnesium wire. Aluminium wire is needed for
the gate terminal of a thyristor to ensure a non-rectifying contact.
For very large devices, such as the hockey puck package shown in Figure
1.36. the silicon dice is held in contact with the package using pressure only,
usually in the form of springs or washers. This is known as compression
bonding, and the absence of all solders makes this arrangement specially
suitable for large thermal stresses.

(f 1
(0)
Figurn 1.36 Power scmiconductor packages: (a) and @) T0220; (c) press fit; (d) stud; (e) and
(f) hockey puck; (g) high-frequency