Progress in ultrasonic bonding wire process and quality evaluation of bonding point

Abstract

Wire bonding is one of the most widely used methods in the field of electrical connecting in packaging. The main characteristics of common wire bonding materials and process parameters affecting the reliability of wire bonding are discussed and analyzed. The evaluation method of wire bonding quality is described, and the measures to enhance the reliability of wire bonding are put forward. The results show that of all the wire materials, gold wire (Au) has the best comprehensive performance which used most widely. Aluminum wire (Al) and copper wire (Cu) are ideal materials for the replacement of Au because of low cost. Platinum wire (Pt) is mainly used in low temperature packaging for its low heat loss. In terms of bonding process parameters, bonding force is an important parameter for the shape and strength of bonding point. Adjusting the bonding force is an effective method to solve the problem of pad damage and bonding interface slip. Ultrasonic power and time are the important factors affecting bonding strength. Usually it is easier to bond wires with higher bonding temperature, and appropriate temperature is exist due to the device’s tolerance temperature. In the wire bonding quality evaluation methods, microscopic observation is the simplest method to evaluate the bonding quality. The mechanical testing methods include wire pull test and ball shear test. Environmental tests include temperature cycling, electromagnetic resonance test and other testing. It is mainly used to evaluate the overall performance and fatigue properties of wire bonding. As a result, the mechanical testing and environmental testing are the effective methods to adjust the new bonding process , and microscopic inspection is an effective method for bonding quality assurance.