TWI Industrial Member Report Summary 615/1997
R G Clements and N R Stockham
With the increase in interest in chip-on-board (COB) technology, wire bond interconnections are required to a wide range of printed circuit boards. This report demonstrates that successful bonds can be made to rigid, flexible and compliant boards, once optimised procedures are established.
The use of chip-on-board (COB) technology in the electronics industry is increasing due to its low cost and the potential for increasing packing densities. The ultrasonic bonding of fine Au and Al wires (e.g. 25-33 µm diameter) on these organic based printed circuit boards has, in many cases, proved to be difficult. The relatively poor yields appear to be associated with the inherently soft and flexible nature of the material and the surface finish of the conductors.
TWI's many years experience in wire bonding has indicated that a high proportion of these problems could be overcome by establishing correct board clamping procedures and optimising bonding conditions (machine parameters and surface finish of tracks). This project aimed to establish the bondability of very thin (low cost) Au metallised Cu conductor tracks on FR4 (rigid), Kapton (flexible) and RT Duroid (soft) boards. This report deals with the techniques employed to establish satisfactory wire bonding to these substrates, discusses the issues involved and gives a best practice guide for wire bonding chip-on-board applications.
To develop fine wire (25µm diameter) bonding techniques to enable interconnection to rigid, flexible and compliant boards with thin (0.3-0.9µm ) Au metallisation.