Package Functions and Design

There are four basic functions performed by a semiconductor package. They are to provide:

1. A substantial lead system
2. Physical protection
3. Environmental protection
4. Heat dissipation

1.Substantial lead system

The primary function of the package is to allow connection of the chip to a circuit board or directly to an electronic product. This connection cannot be made directly, due to the thin and fragile metal system used to interconnect the components on the chip surface.This difference in wiring sizes is the reason why the chip wiring terminates in the larger bonding pads.

2. Physical protection

The second function of the package is the physical protection of the chip from breakage, particulate contamination, and abuse. Physical protection needs vary from low, as in the case of consumer products, to very stringent, as in the case of automobile circuits, space rockets, and military uses. The protection function is accomplished by securing the chip to a die-attachment area and surrounding the chip, wire bonds, and inner package leads with an appropriate enclosure. The size and eventual use of the chip dictate the choice of materials for the enclosure and the design and size of the package.

3. Environmental protection
Environmental protection of the chip from chemicals, moisture, and gases that may interfere with the chip functioning is provided by the package enclosure.

4. Heat dissipation

Every semiconductor chip generates some heat during operation. Some generate large quantities. The package enclosure materials serve to draw the heat away from most chips. Indeed, one of the factors in choosing a package material is its thermal dissipation property. The chips that generate large quantities of heat require additional consideration in the package design. This consideration will influence the size of the package and will often require the addition of metal heat-dissipating fins or blocks on the package.