Package assembly involves attaching components to the next-level assembly, usually printed wiring boards. Assembly includes active plastic and ceramic components containing logic and memory chips as well as nonactive components like capacitors, resistors, and inductors. The assembly itself involves either surface mount or pin-through-hole (PTH) attachment. PTH is expensive, space-consuming, and heavy compared to SMT. Given the need for both low cost and portability in consumer products, Japan has invested very heavily in and has continually improved the technology to achieve assembly densities of 20 components/sq. cm as in Sony's Video TR-5, based on 0.5 mm QFP pitch and passive component sizes of 1.0 x 0.5 mm. This trend in increasing density is illustrated in Figure 4.31 for notebooks, palmtops, cellular phones, organizers, and camcorders. Assembly density in Japan is expected to reach 50 components/sq. cm by the year 2000.
Figure 4.31. Japanese consumer product component
density trend (Sony).
Consumer products require thin and lightweight packaging. Plastic packages such as QFP that are surface-mounted onto PWB have effectively met consumer product requirements. The Japanese vision of next-generation products requires packages that are smaller and cheaper than in the past, roughly 50% smaller for each new generation. Given Japan's past investments in PWB and SMT technologies, and given increased global cost-competitive pressures, Japan is expected to pursue the use of plastic packages to the ultimate limit. The ultimate limit accepted by Japan currently is 0.15 mm leadframe pitch, giving rise to 800 pins in 30 sq. mm and 1000 pins in 38 sq. mm sizes.
The continued use of P-QFP beyond the current 0.4 mm pitch toward 0.15 mm pitch, however, requires major enhancements in SMT pick and placement tools, solder deposition technologies, reflow tools and technologies, inspection, solder repair for opens and shorts, and electromigration resistance of both the plastic package and the printed wiring board. Contrary to what U.S. companies might expect, Japanese industry will incrementally enhance each of these to a level that will guarantee high yield and high reliability. This conclusion is supported by (1) Sony's advancements in factory automation and (2) Oki's single-PPM-defect-soldering systems. These systems and processes have lowered assembly defects to less than 20 PPM, as shown in Figure 4.32. Sony's precision robots have improved placement repeatability to 0.01 mm from 0.05 mm during the last six years. Matsushita's new SMT machine has 11 placement heads with 0.01 mm repeatability. Toshiba's advanced TAB equipment can place 0.2 mm pitch parts using CCD vision, since pitch size has reached the limits of human vision.
Figure 4.32. Soldering defect improvement achieved at Oki.
With increased miniaturization, soldering technologies continue to evolve. For example, Oki's single PPM defect technology includes developments in the following:
Figure 4.33 illustrates the general trend in soldering techniques that the Japanese micro-electronics industry is expected to follow, shifting from reflow to local soldering tech-niques in order to meet ultrafine pitch assembly requirements.
Figure 4.33. Soldering technology trend in Japan (Hitachi).