3 THE IC PACKAGE [1,2]

Starting with the transistor, the package has functioned as both a carrier and as an enclosure. As a carrier it allows the device s functionality to be fully accessed and to be assembled and electrically interconnected to other devices (Level 2.0). As an enclosure it provides protection from physical damage and a supportive and controlled operating environment for the device. The earliest ICs followed the same packaging format as the transistor (a TO-5 metal package) differing only in the number of leads (Figure 3-1).

Figure 3-1: Transistor and an Early IC Package (TO-5 Outline)

Physically the package has undergone many changes, responding to the needs of the IC, the end product, and certainly cost considerations. Ideally the guidelines have always been to:

• Provide a package that fully supports the IC, responding to inherent thermal, mechanical and electrical requirements,

• Avoid, if possible, having the package limit chip performance,

• Make the package as small as possible, and finally,

• Provide a cost-effective package that does not represent a substantial percentage of the final device s selling price.

3.1 Trends in IC Packaging [3 4]

Figure 3-2 graphically presents the industry s past history and current trends in IC packages. In particular, it shows the influence of accommodating both increasing I/O count and miniaturization.

Figure 3-2: IC Package History and Trends

The package miniaturization has been driven by the continuing demand for smaller, better, cheaper end product. Miniaturization is marked not only by a smaller package, but...