Tomio Iizuka

Influence of ball-forming conditions on the hardness of copper balls

Effect of ball‐forming conditions on the microstructure and the hardness of balls has been investigated in order to obtain soft balls suitable for a reliable ball‐bonding process using copper wire. Copper balls formed in a room‐temperature shield gas are found to be harder by 6 Hv than fully annealed copper wires of the same purity. This is caused by many dislocation loops which are generated in balls due to inclusion of gaseous impurities from the atmosphere and due to rapid solidification. On the other hand, copper balls formed in a shield gas heated above 175 °C are found to be softer by the amount of 4.5 Hv than balls formed in a room‐temperature shield gas. This is due to disappearance of dislocation loops caused by the reduction of solidification rate and by elimination of gaseous impurities from the balls during solidification. Impurities, especially oxygen, are found to have a strong influence on the hardening of copper balls. From these results, we conclude that copper balls formed in a shield ga...

Investigation of Aluminum Ball Bonding Mechanism

The effects of various factors, e.g., ball hardness, amount of ball deformation, thickness, and surface cleanliness of the aluminum electrode, which can influence bonding strength were investigated. Metallurgical bonding between balls and electrodes occurs by rupturing the oxide film existing on the aluminum electrodes and proceeds from outside, inwards to the center of the bonds. The bonding strength is found to be a linear function of the true bonded area between balls and electrodes. The factors increasing the true bonded area are a high ball hardness, a large amount of deformation, a thick aluminum electrode, and a clean electrode surface. In addition, a high strength ball bonding comparable to gold can be realized by using aluminum alloy wires containing magnesium.

Ball Formation in Aluminum Ball Bonding

The effects of various factors, i.e., shield gas, current density, wire polarity, and wire material, which can influence oxidation of ball surfaces were investigated. Good quality aluminum balls were found to be formed if optimum electric and shield gas conditions were employed; for example, current density geq 2.5 GA/m2wire polarity: cathode; shield gas: Ar+H 2 . Good quality aluminum balls of 1.7 to 2.5 times the wire diameter could be formed by varying discharge time and/or current density. It was found that they could be obtained independently of the wire material. The relation between morphologies of aluminum balls and the degree Of oxidation was also investigated in order to examine the mechanism for obtaining a good quality bail. A close correlation was found between ball morphologies, i.e., eccentricity, sphericity, and constriction, and the degree of oxidation. The morphologies were significantly improved as the oxide film thickness was reduced.

Self-Limiting Power Excursion Characteristics of Light Water Reactor, (III) Instrumentation for HTR-Pulse Operation

The Hitachi Training Reactor (HTR) provided with pulse operation capability was utilized for an experimental study on the excursion characteristics of light water reactors. Measurements were performed on reactor power, reactor period, released energy, fuel temperature, fuel cladding strain, pressure in water channel and water activities. The reliability of the instruments and devices employed was confirmed to be satisfactory through pulse operation tests repeated 300 times, with inserted reactivities up to 1.50

Laser beam reflection system

, with reactor periods down to 15 msec, and hot spot fuel temperatures up to 1,300°C. A description is also given of the instrumentation for the measurements and reactor operation.