Self-alignment Ability of Copper Ball on Soldering for Packaging-on-Packaging and Measurement of Oxidation Layer Thickness by Lightness Value

Abstract

Cu balls showed unique soldering behavior that was different from the conventional solder as the semiconductor devices. On soldering on pad by the solder balls, solder balls move to the center position because of their self-alignment ability. On the contrary, Cu balls tend to move to the outer position from the mounted center position. We have achieved arranging of Cu balls at the center position using their self-alignment ability. It requires a thin oxidation layer on Cu balls. We also developed the simple and easy method to measure the thickness of the oxidation layers by utilizing the lightness.