Impact of surface texture on ultrasonic wire bonding process

Abstract

Due to the complex mechanisms, the ultrasonic (US) wire bonding process is usually optimized in the way of varying the processing parameters including normal force, US power, and processing time. In this study, a new way by creating different surface textures on substrates was used to alter the bonding process and improvements of the bonding process were detected. Three different surface textures including deposited strips, straight ditches at different angles, and elliptic ditches were designed and created on glass substrates. The results showed that the elliptic ditches hardly influence the bonding process while the deposited strips and straight ditches significantly alter the bonding process. The deposited strips help break the oxide scale and facilitate the transportation of oxides to the outside of contact. With the straight ditches, the oxide removal efficiency was significantly enhanced. Especially when the driving current exceeded 0.45 A, long chips from the ditches were clearly observed during the bonding process. The chips were aluminum and aluminum oxide which were continuously cut from the wire, accumulated in the ditches, pressed and squeezed to the outside of the contact. With a different angle of the straight ditches, the shape of the bonding footprint can be changed correspondingly. Compared to the bonding on smooth surfaces, the bonding strength on substrates with deposited strips and straight ditches was a few times higher and had a smaller deviation. The bonding process window was significantly enlarged.