Steve Berry and Sandra Winkler Contributing Editors

The invention of the transistor in the 1950's, followed by the integrated circuit, has transformed practically every aspect of our daily lives, from automobiles and airplanes to medical science and telephony.

Much of this transformation has been driven by the realization of Moore's Law within the "front-end" of semiconductor processing. But the front-end of semiconductor manufacturing must also be enabled by new methods in semiconductor packaging.

The Shrinking End Product

Since the IC package is responsible for setting the footprint to the PWB, reduced package size also enables the shrinkage of the final product, to the point where we now have numerous hand-held electronics, such as the cellular telephone, that we carry with us throughout our daily lives.

Reduced IC package size and new packaging formats have been a key element in the portability of cellular phones. (Motorola)

IC packaging has also evolved in ways that can actually simplify front-end manufacturing and bring products to market faster than trying to integrate technologies together on a single chip. This is the case for the Systems-in-Package (SIP) and the stacked package.

SIPs have one or more semiconductor die along with passive components (resistors and capacitors integrated into a single packaged unit). A SIP can be thought of as a functional block operating as a "system" to achieve a performance level beyond what can be accomplished by placing the components into individual packages.

Like the older multichip modules (MCMs), fewer leads are required going into and out of SIPs compared to independently packaged devices. SIPs are somewhat customized packages, and generally the system designer must work closely with the package designer.

Stacked packages also offer the advantage of saving precious board space on hand-held items and permit component placement in very close proximity. Stacked packages are essentially a vertical multichip package (MCP). They come in many forms, from stacked MCMs and stacked TSOPs to individual die that is stacked within a single FBGA.

Traditionally, memory has been placed in stacked packages. Combining a flash memory and a static random-access memory (SRAM) within a single FBGA is the most common stacked semiconductor product. Most stacks are only two-die high, although three or more layers are becoming commonplace as technologies are developed to accommodate this approach.

Increasingly, what is evolving is a package stack, where two or more packages are stacked on top of each other.

Multiple Components

Each individual package can also have multiple components. The point of this is to separate dissimilar technologies, such as logic and memory, so that testing of each can be done on each package separately. Separating devices into separate packages also enables purchasing different devices from different manufacturers with greater ease.

SIPs and stacked packages are specialty packages, and thus are not produced in the large volumes of standard packages. But these advanced packages are extremely beneficial in products that are short on space and require a high degree of performance. As a result, SIPs and stacked packages should demonstrate growth rates in excess of 20 percent annually (see table).

So, while front-end manufacturing has bragging rights over many new advances, the back-end should also receive praise for its own innovations.