Reduction of Soldering Joint Defects Using in Situ Observation

Abstract

Brass has excellent ductility and workability. Lead–free brass containing Bi and Si has been put into practical use to comply with environmental regulations such as water quality standards. For actual use, brass soldering with lead–free solder is required. Therefore, a method is needed to estimate the solderability of the solder on brass. In the previous report, the experiment was performed using parallel two–plate specimens. The voids in the soldering area are classified into four types： “（Ⅰ） voids that can be used as soldering areas”, “（II） spherical voids”, “（Ⅲ） non–spherical voids”, and “（Ⅳ） heat shrinkage voids”. It was found that the number of spherical voids decreased when the amount of solvent in the flux was reduced. It is known that voids form when the temperature rises. The purpose of this study was to investigate the effect of heating rate on soldering using in situ observations.

In–situ observations and soldering experiments were performed. The experiment was conducted using a parallel two–plate specimen. A hot plate was used as a heat source. In–situ observation experiments revealed that the state of the specimen changed when the heating rate changed. In the soldering experiment, X–ray transmission images were acquired and evaluated. However, detailed evaluation was not possible with the conventional evaluation method. Therefore, a new evaluation method called “solder spread linear velocity” was defined. When we evaluated using this evaluation method, we were able to evaluate this experiment. The heating rate has a large effect on solder wetting. It was found that the higher the heating rate, the higher the spread linear velocity of the solder and the larger the spread of the solder.