Bondability of Cu wire on Cu substrate with Sn plating by ultrasonic

Abstract

Bondability of Cu wire on Cu substrate with Sn plating by ultrasonic by FUJIWARA Shinichi and DAUSKARDT Reinhold H. This study evaluated both the joint strength of copper wire on a copper substrate with tin plating and the joint reliability of copper wire bonding after heat treatment. The suitable tin thickness and bonding conditions, which are stage temperature, wire bonding power and bonding time, were chosen by the peel test after copper wire bonding. Tin thickness of 10 microns showed a high bonding rate under the conditions of stage temperature 373 K, bonding power 500 to 700 mW and bonding time 30 to 50 ms. Before heat treatment, the peel strength of the copper wire on the copper substrate with tin plating conditions was weaker than that of gold wire on a gold substrate. After heat treatment for more than 70 hours at 298 K, the peel strength of the copper wire became higher than that of the gold wire and twice as high as the initial bonding strength. The tin layer remained between the copper wire and copper substrate before heat treatment. When the samples were held at 298 K, tin reacted with copper and turned into a Cu-Sn intermetallic compound. Upon completion of this reaction at 298 K for over 70 hours, the soft tin layer between the copper wire and copper substrate disappeared. Therefore, the peel strength of copper wire after heat treatment increased. These results were observed by SEM images of the interface between the copper wire and copper substrate before and after heat treatment.

Microstructure of Joint between Stranded Wire and Substrate Welded by Ultrasonic Welding

“…Cu wires can be directly welded to Cu substrates [5,[10][11][12]. Further, coating of Cu wires or substrates by several metal layers for ultrasonic welding was developed to improve the weldability [4,8,9,[13][14][15]. To develop the welding techniques for the joint between the coaxial connector and the wire with low loss transmission of high frequency signal, we firstly applied the ultrasonic welding to the fine stranded Cu wire.…”

Interface Structure of Cu Wire Bonding on Cu Substrate with Sn Plating

“…911) In previous investigations, 12) the Cu wires were bonded after suppressing the formation of oxide films on Cu by Sn-plating the Cu substrate, and parameters for bonding the Cu wire to the Cu substrate but leaving residual Sn at the joint interface were derived. In this study, the joint cross sections were examined in detail by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to understand the bonding state after initial bonding.…”