TWI Frequently asked questions
by Jim Foster
Ribbon bonding has potential for the interconnection of high lead count, small pad size (less than 50µm) devices - especially for small-batch production. It combines the flexibility of wire bonding with the mechanical (structural rigidity) and electrical (HF application) characteristics and fine feature sizes of lead frames.
Applications include the interconnection of high lead count, small feature size VLSI devices, and the intra- and inter-connection of high speed, high frequency microwave devices (where conductor surface area is more important than cross-sectional area).
The need for an interconnection technique for VLSI circuits, where up to 500 I/Os on <100µm pitch (50µm track, 50µm spacing) are required to be connected, has revealed limitations in conventional wire bonding. This has led to the gradual change from wire to ribbon bonding.
Tape automated bonding (TAB) is claimed to meet the requirements for high density interconnections to small bond pads, using either a bumped chip or bumped tape approach. But for small batches of application-specific integrated circuits, the tooling changes for lead frame manufacture can become prohibitively high.
Ribbon bonding offers an alternative to tape automated bonding (TAB) and is attractive since many conventional ultrasonic wedge/wedge wire bonding equipments can be easily adapted to handle ribbons. The process achieves the required density of interconnections for both inner and outer bonds. At the same time, it eliminates the need for either bumped chips or tape, and it avoids the tooling costs normally associated with TAB.
Ribbon bonding has great potential in the manufacture of devices with small bond pads and/or high density interconnections.
Ribbon bonding investigations carried out at TWI include the ultrasonic bonding of:
- gold ribbon (30x8µm) to aluminium thin film on silicon
- copper ribbon (30x8µm) to copper tracks on printed circuit boards
- aluminium -1% silicon ribbon (30x8µm) to copper tracks on alumina substrates
