Wire bonding is a widely used interconnection technology in electronic packaging. Due to the advantages of fast bonding process, high productivity, good electrical and thermal performance, Au wire bonding has been widely applied to various electronic packaging applications, such as Multi chip module (MCM), B all grid array (BGA) and Chip-on-board (COB). The organic substrates for Printed Circuit Boards (PCB) have a low glass transitional temperature, T_g, typically 130°C. This imposes limitations on the wire bonding process because wire bonding must be performed at temperatures far below the T_gof the substrate to avoid softening of the materials. Meanwhile, a substrate with a high T_g incurs additional cost arising from material and fabrication processes....[ Read more ]

Wire bonding is a widely used interconnection technology in electronic packaging. Due to the advantages of fast bonding process, high productivity, good electrical and thermal performance, Au wire bonding has been widely applied to various electronic packaging applications, such as Multi chip module (MCM), B all grid array (BGA) and Chip-on-board (COB). The organic substrates for Printed Circuit Boards (PCB) have a low glass transitional temperature, T_g, typically 130°C. This imposes limitations on the wire bonding process because wire bonding must be performed at temperatures far below the T_gof the substrate to avoid softening of the materials. Meanwhile, a substrate with a high T_g incurs additional cost arising from material and fabrication processes.

The objective of this thesis is to optimize metallization and process variables to enhance wire bondability and product yields of low temperature Au wedge thermosonic bonding. The wire bond strength with various metallization characteristics were correlated to establish the process window for successful low temperature wire bonding. The technological understanding acquired in this thesis can be used as a practical guideline for PCB metallization plating and processing conditions.

The research was carried out in four stages. The first stage examined the surface characteristics of various metallization schemes on conventional FR-4 PCBs. The second stage investigated the interrelation between the metallization characteristics and the wire bonding process variables. The third stage studied the improvement in wire bonding by plasma cleaning. The last stage was a study of high temperature wire bonding on Bismaleimide triazine (BT) substrate. Based on the bond tests and process windows established, optimizing bonding parameters for acceptable wire bond strengths at low temperatures were identified. Specific recommendations were made on the optimum surface and elemental characteristics of metallization that can improve wire bondability.

Keywords: Wire Bonding, Wedge Bond, Printed Circuit board, Plasma Cleaning, Surface Characterization, Wire Bond Strength