Ripening‐assisted asymmetric spalling of Cu‐Sn compound spheroids in solder joints on Si wafers

In reacting eutectic SnPb solder with Ti/Cu and Cr/Cu/Au thin film metallization on Si wafers, we have observed spalling of Cu6Sn5 spheroids when the solder consumes the Cu. The formation of the spheroids is assisted by the ripening reaction among the compound grains. In addition we have observed an asymmetric spalling phenomenon using a sandwich structure, in which two wafers were soldered face‐to‐face. The spalling occurs predominantly at the interface at the bottom of the solder joint. It suggests that gravity plays a role.