| Isothermal solidification (IS) is a process whereby reaction or/and diffusion take place between a liquid of low melting component and a solid of high melting one at a constant temperature slightly above the low melting point, to form intermetallic compound or solid solution. For some specific systems, a distinct feature characterized by IS is that the finally formed phases would remelt at a high temperature than that at which they form. This phenomenon makes it possible that a joint be made at a low temperature while capable of withstanding high operation temperature. Based on the theory of IS, this thesis aims at exploiting a new die bonding method of practical value in consistence with most common technique used in modem electronic package manufacture at present. According to IS theory as well as die bond requirement in reality, Au/In was chosen by virtue of appropriate equilibrium diagram and high reaction rate from a variety of binary alloy systems as die bond media. To match CET of chip material of silicon, alloy 42 (Iron-Nickel) rather than copper ?2 kinds of lead-frame materials in most common usage, was selected as substrate. Considering cost and feasibility of the method in packaging, galvanic plating was preferred in fabrication of gold and indium films; mechanical vibration was taken to assist in bonding. Thus, the key problem梕asy oxidation of indium in Au/In bonding was resolved in a way with advantages of low cost and high speed. Ultrasonic microscope along with test of shear strength were used to optimize bonding parameters, and contribution of each parameter was evaluated. Microstructures with two different indium thickness were analyzed in detail in the thesis, from which various appeared features were studied. A reaction model was then established to describe the bonding reaction mechanism. Tests of shear strength, thermal cycle, high temperature annealing, unbonding were performed to evaluate reliability of the bond, incorporating with further microstructure analysis. VI Based on above experiments, conclusion is drawn as follows: bonding can be achieved in 10 seconds at 250C. The produced joint has the strength satisfying the criterion of American Military Standards, resistance to withstand 1000 cycles of thermal cycle from ?5~C to 150~C and 1450 cycles from ?50C to 1250C. No failure was observed after 1000 hours annealing at 300 0C. The remelting temperature of the joint reaches up to 51 0~C. At last, larger die of 3 >( 3mm2 was tried for bonding. Preliminary results show the strength satisfies American Military Standard (MIL STD 883) and no delamination was found after 1450 cycles of thermal cycle between -550C to 125 .c. Through material selection, film fabrication, parameter optimization, microstructure analysis and reliability evaluation, this thesis has completed the exploitation of the new die bond method. The unique features lie in the marriage of isothermal solidification and mechanical vibration. The process is oriented to production. The advantages fall into the following aspects: low bonding temperature in relative to hard solder; high strength and high resistance to thermal fatigue to softer solder; high thermal dissipation and electrical conductivity to organic adhesives. This method not only suits for attachment between silicon and alloy...
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