Page 343 - A Practical Guide from Design Planning to Manufacturing

Microprocessor Packaging 313

Substrate type
The types of interconnects used between the package leads and the die
are determined in part by the choice of substrate. The most common
package substrates are molded plastic, ceramic laminates, and organic
laminates. Plastic packages are the least expensive but can be used
only with low-power, low-performance chips. Ceramic laminates have
the best performance but are the most expensive. Organic laminates
offer intermediate performance and cost.
Plastic packages are formed by attaching the die to a leadframe and
then encasing the die and part of the leadframe in protective case of
hard plastic. The basic steps to forming a plastic package are shown in
Fig. 10-5.

Step #1 Step #2
Leadframe formation Die attach and wire bond
Strip rail

Tie Internal
bar Die lead
paddle Die

Strip rail
External lead

Step #3 Step #4
Plastic molding Trim leadframe

Plastic
encapsulation

External lead
Figure 10-5 Plastic package assembly.