The State of the Art and Future Prospects for Laser Direct-Write for Industrial and Commercial Applications
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Overview of LDW in Industry Recently, increasing demand for small size, light weight, and high speed in electronic appliances such as cellular telephones, digital cameras, and notebook-type personal computers (PCs) is establishing laser direct-write (LDW) as an attractive technology in the microelectronics and optoelectronics industries due to its excellent features of high speed, high flexibility, high precision, high reliability, and use of fewer chemicals and fewer process steps compared with conventional semiconductor processing based on photolithography. Table I summarizes representative applications of LDW in microelectronics and optoelectronics. One of the biggest markets for LDW is laser drilling of via holes for stacked or built-up printed circuit boards (PCBs).
Built-up PCBs are primarily used in cellular telephones, digital video cameras, and digital still cameras.1 Currently, ⬃250–300 production systems for high-throughput laser drilling of via holes are put in operation each year worldwide, and the number is expected to increase.2 Back in 1998, most of the $1 billion total output of PCBs in the world was produced in Japan, while in 2005 the output increased to $7 billion, but Japan’s share was reduced to 40%. Taiwan, China, and South Korea generated 50%, and the remaining 10% was produced in Europe, the United States, and other countries. Currently, pulsed CO2 lasers are mainly used for drilling via holes with diameters in the range of ⬃75–150 μm, but in several years, these will be replaced by UV Nd:YAG lasers as
MRS BULLETIN • VOLUME 32 • JANUARY 2007 • www.mrs.org/bulletin
via-hole diameters smaller than 50 μm become commonplace. The other important markets for LDW are photomask repair, memory repair, marking, trimming, patterning of solar cells, microwelding, and rapid prototyping.3 The repair of photomasks is driven by two different applications, large-scale integration (LSI) in semiconductor integrated circuits and in liquid-crystal displays (LCDs). High-precision repair with accuracy better than ⫾0.1 μm is required for LSI photomasks, while highthroughput repair is necessary to process LCD masks exceeding 600 mm. Opaque defects are repaired by ablation of excess material, while clear defects are corrected by laser chemical vapor deposition (LCVD). Memory repair using LDW is also becoming necessary in order to improve yields in 64-Mbit and 256-Mbit dynamic random-access memories (DRAMs). It should be noted that the largest share of laser-based manufacturing systems installed in industry is dedicated to laser marking of semiconductor wafers, integrated circuit (IC) packages, chip-scale packages (CSPs), and other components (see Table I). 4 Recently, the introduction of laser marking systems to production lines in the electronics and semiconductor industries has rapidly enhanced labeling of IC packages and wafers. Laser trimming of small-size chip resistors and ultralowresistance resistors is also a growing application for the manufacture of cellular telephones, digital video cameras, and notebo
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