Page 171 - Bebop to The Boolean Boogie An Unconventional Guide to Electronics Fundamentals, Components, and Processes

152 Chapter Fourteen

One of the criteria used when selecting the adhesive is its ability to conduct
heat away from the die when the device is operating. An automatic wire bonding
tool connects the pads on the die to the leads on the lead frame with wire
bonds finer than a human hair.9 The whole assembly is then encapsulated in a
block of plastic or epoxy (Figure 14-15).

Figure 14-1 5. Wire bonding and encapsulation

A dimple or notch is formed at one end of the package so that the users will
know which end is which. The unused parts of the lead frame are cut away and
the device’s leads, or pins, are shaped as required; these operations are usually
performed at the same time (Figure 14- 16).

Discard unused
lead frame

Figure 14-1 6. Discard unused lead frame and shape pins

9 Human hairs range in thickness from around 0.07 mm to 0.1 mm. A hair from a typical blond
lady’s head is approximately 0.075 mm (three quarters of one tenth of a millimeter) in diameter.
By comparison, integrated circuit bonding wires are typically one-third this diameter, and they
can be even thinner.