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Technology Convergence: Changing the Assembly Scene
December 31, 1969 |Estimated reading time: 5 minutes
Products continue evolving, blurring the lines of assembly technology and resulting in new challenges for both assemblers and suppliers.
By Jacques Coderre
Assembly technology no longer can be classified neatly as component, board and final assembly. Driven by the convergence of products, electronic assembly boundaries are collapsing as board assemblers struggle to gain expertise in semiconductor-related technology while component assemblers learn to handle passive components and solder screen printing. Clearly, the distinction between various levels of assembly blurs as manufacturers work to meet the demands of the marketplace. The impact is felt not only on the technology front but also in operations and quality control.
Consumer-driven Products
Consumer products drive technology, as opposed to high-end computing applications of latter years. Early adopters are purchasing mobile devices that incorporate telephony, personal-digital-assistance, photography, wireless communication, MP3 playing and other functions. The trend is not restricted to hand-held devices, however. Indeed, novel automotive electronics products are emerging that combine navigation technology, telephony, computing, auto-cruise and collision detection. New home game stations are yet another example of increasing performance and functionality. The next-generation Playstation 3 will include an IBM system-on-a-chip, with more power than the Deep Blue supercomputer (capacity of at least 1 teraflop has been reported). Production of this new 0.10 µm chip is expected to start in 2004. Convergence of computing, data, voice and video transmissions is fueling the industry so that increased functionality must be added to the smaller-faster-cheaper mantra.
CBA Impact
What does this have to do with circuit board assembly, you might ask? Performance and size-driven, these end products drive the technology inside. Direct chip attach (DCA), for example, is increasingly adopted whereby the semiconductor devices interconnect directly to the board, eliminating one level of packaging altogether. A typical system-in-a-package module (Bluetooth, GPS, Power amplifier) may have one to three flip chip devices alongside 0201s and other passives, mounted on an organic substrate. Circuit board assemblers claim they have the know-how to assemble such modules because it really does look like a board (especially when panelized). The installed manufacturing infrastructure and skill set is well suited to handle passives and the flexible fine-pitch machine possibly can be adapted to handle the flip chip process.
An FA-10 die is mounted to a test board. The device is a fully populated flip chip with 125 µm bumps on a 250 µm pitch (10 mil pitch).
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Component assemblers, on the other hand, feel they have what it takes to assemble these boards because they have been doing modules for a while. Paste printing, tape-fed components and chipshooters are foreign to them, however, and old process problems, such as tombstones, are seen as a new challenge. Suddenly, traditional semiconductor assembly houses compete with contract manufacturers to get the business from the fabless designers or OEMs. Some silicon-on-silicon applications drive the need to handle wafers as we handle boards today, bringing a whole new set of "board handling" challenges. Component stacking also is emerging.
Array packaging is evolving in many ways. Chip scale packages (CSP) with 0.4 mm ball pitch are on the horizon. There are some indications that such fine-pitch devices may require fluxing prior to placement instead of placing into paste as is done with 0.5 mm devices. With the advent of wafer-level packaging and test, some CSPs may be presented directly from wafers, similar to unpackaged flip chips.
The introduction of flip chip drives the need for underfill, designed to improve solder joint reliability by alleviating stress caused by coefficient of thermal expansion (CTE) mismatches. In a sense, the underfill process replaces the level package. Capillary underfills, the most commonly used, are deposited and cured after die placement and typically are done in a dedicated underfill line consisting of a unique dispensing system and a curing oven. A new set of no-flow underfills promises to simplify the process by enabling deposition prior to die placement or even at the wafer level. Underfill is quite different than anything typically seen in a circuit board shop. It requires increased engineering attention to be introduced effectively into a high-volume circuit board assembly shop. The process is tricky, with significant reliability impacts when loosely controlled. As shown in the figure, test vehicles, such as FA-10 and PB-8 die, are used to study and qualify such processes and much is known about their performance.
Tighter quality control is needed. Supplier quality assurance changes as well, with increased focus on such parameters as bump height variation, solder mask registration and materials. In many cases, the floor itself may have to be upgraded to a clean room level. Finally, novel lab equipment must be available, either onsite or through a third party. Access to a scanning acoustic microscope (C-SAM), an X-ray tool and thermal cycling equipment must be available. Access to a scanning electron microscope (C-SEM) is desirable.
Individual assembly machines differ from the traditional offerings as well. For example, components are not always in tape-and-reel or JEDEC tray formats anymore. Devices sometimes are picked directly from wafers. Vision algorithms and camera resolution enable fine-pitch and asymetrical bump pattern resolution.
Supplier quality assurance, production control and operations are all affected in such a change.
Equipment Supplier Impact
Similar to the assemblers themselves, equipment suppliers need to gain knowledge on the wide span of processes now used in the electronics assembly industry, not just circuit board or component assembly. Equipment specifications, such as accuracy and throughput, may differ as well. Recently, customers have begun requesting flexibility of both their lines and individual machines. Machines need to seamlessly handle flip chip devices and surface mount components. Assemblies also are migrating to 3-D, and board densities are being measured increasingly as components per cubic inches instead of square inches.
Conclusion
Traditional packaging levels are no longer clearly defined. As such, assemblers must learn new skills, master new technology and deal with new competitors. Similarly, suppliers must learn to handle new requirements that cross the traditional boundaries. Semiconductor and optical devices increasingly are handled at the board level and discrete devices appear at the component level. New materials are handled and changes to quality control schemes are common. As we prepare for the next growth cycle, those that have learned to manage convergence and partner with the right suppliers will succeed.
Jacques Coderre, product manager, may be contacted at Universal Instruments Corp., Advanced Semiconductor Assembly Div., P.O. Box 825, Binghamton, NY 13902; (607) 779-4362; Fax:(607) 771-8116; E-mail: coderre@uic.com; Web site: www.uic.com.