Advanced IC packaging: Markets and trends
04/01/2001
Sandra Winkler, Electronic Trend Publications, San Jose, California
As applications for ICs continue to proliferate at an astonishing rate, the number of IC packages needed to support their varied requirements also proliferates. Over the last few years, these requirements have brought BGAs, CSPs, flip chip packages, and stacked packages into mainstream usage.
Although a few packages within each of these types have been used in specialty situations for years, they are still considered key elements of the "advanced package" market. Their volumes will have the greatest growth in the coming years, but are still small compared to the total IC volume of 86 billion units.
This article forecasts unit production and packaging revenues for these advanced packages. Also included is a revenue forecast for the interposers/substrates used in BGAs and CSPs. This market has been of great interest and concern to the companies involved in the IC packaging market, as it represents an entirely different infrastructure from the leadframes used in the majority of IC packages.
 Figure 1. BGA and CSP units. |
BGA and CSP
Description. Ball grid array (BGA) packages encompass all surface-mount array packages of greater than chip-scale size. In most cases, the packages have solderballs on the underside of the substrate. Also included in this category are other formats such as land grid array (LGA) and column grid array (CGA). Land grid array packages are essentially BGA packages without the solderballs. They can be socketed to a printed circuit board (PCB), have fewer joint fatigue problems than BGAs, and are generally used for microprocessors and other high-end chips.
 Figure 2. BGA and CSP packaging revenue. |
Chip-scale packages (CSPs) come in many forms and have a number of definitions. Basically, the CSP is a minimal package that approximates the size of the die. CSPs can be divided into two groups, those that hold onto a fixed footprint and those that alter with die shrinks. A more substantial division focuses on the package structure itself: array packages with a flexible interposer (flex CSP), array packages with a rigid interposer (rigid CSP), leadframe CSPs, and wafer-level packages (WLPs). The flex CSP and WLPs alter in size with every die shrink, while the rigid CSP and leadframe CSPs tend to hold onto a standard footprint size.
Figure 1 presents a summary forecast of BGA and CSP production through 2004.
Packaging revenue. BGA and CSP packaging revenue is shown in Fig. 2. Although CSP packaging revenue will have the highest growth rate over the next five years, total CSP packaging revenue will remain well below that of BGAs. This is primarily due to the lower average I/O count for CSPs.
Interposers. BT resin was the original substrate material for the BGA and has gone through many improvements over the years. However, as the BGA has expanded into an increasing number of IC product and application markets, the requirements of these markets have led to a proliferation of substrate materials.
The first CSPs were modeled after the array style of the BGA, but the earliest CSP developed was the flex CSP, not BT resin. The polyimide flex interposer offers inherent high density for these tiny packages, which must fit into very small spaces. The die size and the I/O requirement on a CSP are considerably lower than those for BGAs; therefore, thermal issues are not as much of a consideration for CSPs as for BGAs. In most cases, the heat is expected to dissipate into the PCB, with very little resistance through a very thin interposer.
Flex tape is still the most common type of interposer for CSPs, but like the BGA, options have proliferated. The high cost of the flex tape, coupled with expensive package designs, has aided in this proliferation. Since the CSP is still new and stylish, its packaging engineers and marketers are always looking for new markets, and new designs seem to sprout continuously.
Substrate revenue
Substrate revenue is dependent on area (among other factors, such as density and number of layers). Total substrate revenues encompass the area contributed by pin grid array (PGA), as well as by BGA and CSP packages. The dominance of BT resin is greater by area than by units. While flex tape was in second position by units, it is behind ceramic materials by area, due to the large area of the typical ceramic PGA package.
Substrate revenue is generated by multiplying the cm2 usage by the price/cm2. The pricing of substrates is highly specific to each package design. Factors include volume, total area/substrate, number of wiring layers, and wiring density. Multiplying the average price/substrate area by the substrate area produces the substrate revenue forecast given in Fig. 3. Judged by revenue, flex tape will move into a solid second position behind BT resin.
 Figure 4. Total flip chip forecast. |
Flip chip
Flip chip has been around for approximately 40 years, although early usage was primarily by IBM. The total flip chip market consists of two elements — flip chip in package (FCIP) and flip chips used in direct chip attach (DCA). Flip chip usage in the DCA category includes those on PCBs, flex tape, or ceramic material, and display drivers that are placed via tape-automated bond (TAB) packaging or directly on liquid crystal display (LCD) glass panels — flip chip on glass (FCOG). The size of the display driver market has soared recently, leading to a significant increase in the total flip chip forecast (Fig. 4).
Stacked packages
Stacked packages are a very small subset of the overall IC packaging market. Their rapid growth in certain products, however, makes them an item of interest in the advanced packaging market. Stacked packages contain multiple die in a vertically stacked arrangement. Most stacked packages contain only two- and three-die stacks, although some companies offer a greater number of die. The average is usually two-die/stack. Memory/memory combinations are by far the most popular stacks, but memory/logic and memory/
ASIC combinations are also available and on the roadmaps of companies producing stacked packages. The use of high-density substrates is also planned.
 Figure 3. Substrate revenue by type. |
The combination of devices typically produces a substantial reduction of I/Os, as the die can share many common signal routes. Flash/SRAM combinations, for instance, can share more than 50% of the I/Os. The I/Os are gathered in the substrate before routing to the PCB, so that both die share a common I/O. Flash/SRAM combinations, the high drivers in this market, are popular for cellular telephones.
Sharp Corp. has become the volume leader in stacked packages. The company's first version was stacked thin small-outline packages (TSOPs); current arrangements include stacking multiple bare die within a single TSOP or a single CSP. Only a few companies produced sizable numbers of stacked packages in 1999. In 2000, however, other players began to produce significant revenue. Most come from the flash and/or SRAM markets and include Intel, Mitsubishi, NEC, Fujitsu, and Toshiba.
The stacked packaging revenue numbers show that this revenue was $154 million in 1999, $282 million in 2000, and is expected to grow to $451 million in 2001, $669 million in 2002, $894 million in 2003, and $964 million in 2004. Revenue shown was developed using an average I/O and a price per I/O. Stacked package pricing, however, is not derived in this manner in many cases. Numerous packages are customized, low-volume products, so other methods of pricing are used. Adding a price premium over single-chip packaging is one method of pricing (the amount of the premium will drop with time and higher volumes). The price premium covers the additional material and process costs incurred.
Each advanced IC package category is important to needs in the semiconductor industry. BGA represents the largest value to the packaging industry as a whole; CSPs represent another widespread opportunity. Flip chip and stacked packaging will remain limited to specific areas. All will be impacted by this year's slowdown, but far less than the packages used in the majority of the industry's overstocked products.
For more information on the fourth edition of the report, Advanced IC Packaging Markets and Trends, contact Electronic Trend Publications Inc., 1975 Hamilton Ave., Suite 6, San Jose, CA 95125; ph 408/369-7000, fax 408/369-8021.