Evaluation of soldering properties with various types of metallization

We have studied the soldering properties of Sn-Ag-Cu lead-free solders with various types of metallization. We investigated the effects of metallization thickness on soldering properties in a variety of lead-free metallization materials. When no oxide film has formed, the metallization thickness affects the wetting speed at the initial phase but has no effect on the ultimate wetting state. Better wetting can be achieved by setting the flux activity to a suitable level than by increasing the soldering temperature. With Sn-Bi metallizations, the amount of Bi at the connecting parts increases as the metallization becomes thicker, causing the connection strength to decrease. Also, with a Bi content of 5%, the strength is low regardless of the metallization thickness.