Page 98 - Power Electronics Handbook

Smartpower 91
squeegee 7
Angle of attack '\
Screen opening Paste

(a)

Paste
Screen Frame

Carriage

(c)
Figure 3.13 Stages in thick film printing: (a) start of stroke, e) during stroke, (c) end of
stroke

area to which the die is to be attached is gold-plated and the chip is then
pressed and scrubbed onto it to form the eutectic bond. Alternative
techniques for die bonding include using silicon or epoxy adhesives, and
soldering, which requires both the back of the die and the area on the
substrate to be gold-plated.
The terminals on the die can be wire bonded to the package pins or hybrid
tracks, using thermocompression or ultrasonic techniques. Thermocompres-
sion ball bonding uses gold wires and relies on heat and pressure to form the
bonds. Ultrasonic bonding does not require the substrate to be heated and it
uses aluminium wire. The wire is pressed and scrubbed at high frequency
against the metal contact area and this removes surface oxides and results in
a strong molecular bond. Instead of using wires for bonding, flip chip