Abstract
This study deals with nondestructive evaluation of the solder ball joints in BGA package. In order to establish the fast, two-dimensional, non-contact and non-destructive method for the evaluation of solder joints, a new technique based on the infrared thermograph was developed, in which the surface temperature of solder ball joints was measured in the thermal cycle with abrupt cooling after heating. Two parameters were used to evaluate the bonding state of the solder ball joints. One parameter is the temperature change of solder ball in the thermal cycle with the thermal shock due to abrupt cooling, which shows large decrease in poor bonding and slight decrease in good bonding. Another one is the temperature ratio between the solder ball and surrounding molded area, or dimensionless temperature. This value decreases with applying the thermal shock to poor bonding joints, while good solder ball joints keeps constant values regardless of thermal shock. These differences in two parameters are caused from the different thermal conductivity at the bonding interface of solder ball, which were confirmed by the FEM analyses of solder ball joints. It was also confirmed that the second parameter was a preferable parameter for the evaluation of solder ball joints, since the initial heating temperature as well as cooling time did not influence it.
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