Semiconductor Die Bonding IDCOnline（半导体芯片焊接IDCOnline）.pdfVIP

Semiconductor Die Bonding The term ‘die bonding’ describes the operation of attaching the semi-conductor die either to its package or to some substrate such as tape carrier for tape automated bonding. The die is first picked from a separated wafer or waffle tray, aligned to a target pad on the carrier or substrate, and then permanently attached, usually by means of a solder or epoxy bond. The requirements for the die bond are that it: • Must not transmit destructive stress to the fragile chip. • Must make intimate contact between the chip and substrate materials, with no voids, and adhere well to both. • Has to withstand temperature extremes without degrading. • Should exhibit good thermal conductivity, to remove heat generated within the chip. • Should be either a good electrical conductor or a good insulator, depending on the application. A number of materials have been developed for die bonding. This section concentrates on the use of conductive epoxies, as used for plastic packages, but some alternatives are discussed in Die bonding materials. Choice of adhesive Adhesive die attach materials are suspensions of metal particles in a carrier. The particles are several µm in size, usually in the form of thin flakes of silver. The carrier provides adhesion and cohesion to make a bond with the correct mechanical strength, while the metal particles provide electrical and thermal conductivity. It is noticeable that conductive resins are now often used where no electrical connection is required, just to get the benefit of enhanced thermal performance. The carrier is now most frequently a solvent-free, high purity epoxy resin, the trend being fuelled by the need to cut costs, shorten cure cycles, and provide stress relief. • Solvent-free materials give reduced incidence of voids underneath the die, with better heat transfer leading to enhanced device reliability. • Purity is c