Size effect of Ag nanoparticles on laser sintering and wire bondability

The present research aims to develop a dry process for forming wire-bonding pads on a Cu leadframe, where the dry process is defined as the use of the paste with metal nanoparticles and solvents and its laser sintering under air or argon atmosphere. In this report, the influence of Ag particle size on laser sintering and wire bondability is extensively investigated. Two types of Ag nanoparticles paste, φ 5 nm or φ 100 nm in average diameter, were coated on a Cu leadframe. Then, a focused near-infrared CW laser once scans the coated lead to make the paste metalized. Wire bondability between an Au wire and the Ag pad is examined by a pull test. Mechanisms of sintering as well as adhesion to the Cu substrate are discussed. Finally, these characteristics are compared with those of an Ag electroplated pad. As a result, the laser-sintered functional film using the φ5-nm-particle paste yields a crystallized structure and wire bondability similar to those of electroplating, whereas a porous structure with lower wire bondability tends to be produced by the φ100-nm-particle paste.