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FIRST THERMOPLASTIC CHIP-CARRIER OF ZENITE CUTS PRODUCTION COSTS AND BOOSTS RELIABILITY
The high-temperature resistance, dimensional stability, easy melt-flow and good dielectric properties of DuPont Zenite liquid crystal polymer persuaded Siemens Dematic AG of Nuremberg to use this DuPont polymer for its new tightly-packed Polymer Stud Grid Array integrated circuit housings. These packages, which are only about 20 per cent bigger than the chip itself, are the first time a thermoplastic resin has been used as a chip carrier. The core of Siemens Dematic's trend-setting PSGA technology is the 0,4 mm wide and about 0,4 mm high matrix arrangement of contact studs on the underside of the housing of Zenite. These studs are produced in a single high-precision injection-moulding cycle, as an integral part of the whole chip-carrier. Held in a stabilising frame, up to 64 carriers are moulded per shot. Each weighs less than one gramme. The complete frames are first metallised, then structured by laser; then the chips are fixed and provided with contacts. As the last step of the manufacturing process, the finished packages are separated into single units. The special type of Zenite for this application was developed jointly by Siemens Dematic and an international DuPont team led by Hans-Jürgen Huber. The dimensional stability and high-temperature resistance of parts made from this resin ensure that the contact studs stay precisely positioned even at extreme temperatures up to 260 C, which can occur during reflow soldering with the new lead-free solder types. The fact that the type of Zenite used here has a similar thermal expansion coefficient as the circuit board also contributes substantially to the high reliability of the package. Apart from this, due to the material's flexibility, the studs compensate for dimensional changes between the housing and the circuit board, even after repeated temperature cycling. This practically eliminates the possibility of malfunctions resulting from mechanical stresses on the conducting elements. Siemens Dematic compared the properties of liquid crystal polymers with those of syndiotactic polystyrene and polyphthalamide in extensive tests. "Only the LCPs met our processability needs for both thermo-mechanical and electrical properties," comments Joachim Krause, Siemens Dematic's marketing manager. "They absorb no moisture, which would lead to 'pop-corning' in the reflow-solder process." According to Krause, another factor in favour of Zenite was the DuPont resin's low free ion content compared to other LCPs, which made it acceptable to semiconductor manufacturers. "Compared to conventional carriers made of thermoset resins, our advanced PSGA technology allows cost-effective production with few manufacturing steps and low reject rates," Krause states. "A further advantage is that this process is highly flexible, allowing the manufacture of flip chips, and cavity-up or cavity-down types." Siemens Dematic licenses its PSGA technology to semiconductor manufacturers and contract manufacturers of IC housings. It also supplies core equipment for production lines and the relevant process know-how. The first PSGA licence went to Custom Silicon Configuration Services. This Belgian company offers advanced packaging and test services for semiconductors. Together with other pilot users, CS2 supports the qualification of PSGA housings of Zenite. Siemens Dematic AG, headquartered at Nuremberg, is the world's largest supplier of automation systems for production and logistics. The company was formed in May 2001 by the merger of Siemens Production and Logistics Systems AG and Mannesmann Dematic AG. As systems integrator, Siemens Dematic supplies the whole range of individual products and systems up to complete turnkey installations. Apart from the company's activities in electronics assembly systems, it operates in four other major areas: materials handling automation, postal automation, cranes & components and mobile cranes. The new company has about 21 000 employees worldwide and sales of roughly 5 billion EUR.
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