TWI Industrial Member Report Summary 446/1992
By R G Clements and S T Riches
Background
The development of integrated circuits for microwave/optoelectronic and VLSI type devices has placed demands on the interconnection techniques due to the reduction in bonding pad size (as small as 10 µm for some microwave type devices) and increased density of interconnection. Normal wire bonding techniques using 25µm diameter Au and Al-1%Si wires are encountering difficulties in meeting the requirements of the microwave/optoelectronic type devices and a reduction in wire diameter to 12 µm diameter without modification to wire bonding equipment has resulted in overdeformation of bonds as bonding forces below 150mN could not be obtained.
For the high density interconnections required for VLSI type devices (500I/0's, 100µm pitch) limitations in the maximum density of interconnect achievable by conventional wire bonding techniques have been revealed and tape automated bonding technology is only being gradually implemented. An alternative technique which could combine the flexibility of wire bonding with the electrical characteristics and fine feature sizes of leadframes is ribbon bonding. One advantage of ribbon bonding is the use of standard integrated circuits (ie no requirement for bumped chips or leadframes).
However, the selection of bonding conditions for fine ribbons (30µm wide) and the placement accuracy and feeding mechanisms for manual and automatic wire bonding equipment for fine pitch components have not been established.
This programme of work was undertaken to examine the feasibility of ultrasonic bonding 7µm diameter wire where modifications have been made to the wire bonding equipment, to allow low forces to be applied, and to wedge bonding tools. The feasibility of using fine Au, Al-1%Si and Cu ribbons (30µm wide) for device interconnection is also reported.