We developed an infrared measuring system and proposed an appropriate parameter for the evaluation of bonding rate between the solder ball and the substrate in the BGA. In this system, the thermal stimulation due to the short period cooling was applied to ball joint, the temperature response of which was used to discriminate the bonding state in the sound or poor ball joints in the BGA device. The dimensionless temperature given by the temperature ratio enabled the evaluation of bonding rate between the solder ball and the jointing pad in the substrate. The results was confirmed by the numerical calculations of this process, also which suggested that this method is possible to detect the ball joints with bonding rate less than 50〜60%.
