Handling MMICs:
GaAs MMICs may be destroyed or damaged by electrostatic discharge (ESD). Proper ESD precautions should be employed when handling GaAs MMICs. Grounding is critical for all work surfaces, bonding and handling equipment and machinery. Operators should always wear wrist or foot ground straps. ESD test equipment should be available to insure proper ESD grounding at all times.

During GaAs MMIC assembly, handle the die along the edge; do not touch the surface of the die. Use tweezers or a vacuum collet sized to contact the edges of the die so that plated airbridges are not damaged or deformed during handling and assembly.

MMIC Die Attach:
The recommended method for attaching these GaAs MMICs to microcircuit packages or pedestals is by using epoxy. Historically, solder die attach has been the industry standard and only method of MMIC die attach. In recent years, there have been significant advances in epoxy technology for this application. As a result, epoxy die attach has become the preferred die attach method in most MMIC applications.

Epoxy Die Attach:
Advantages of epoxy include production efficiency, reliability, reduced rework, increased placement accuracy, and less sensitivity to thermal expansion mismatch of the GaAs MMIC to its mounting substrate.

The perceived disadvantage of epoxies is their relatively high thermal resistance. This is largely a misconception when one considers the very thin layer of epoxy which results in small temperature gradients through the die attach layer.

Die attach epoxies are available as a pre-form or in a mixing dispenser. The major consideration when using epoxies is the final die attach layer thickness. This layer needs to be considerably less than one mil thick. The accepted target is one-fourth to three fourths of a mil thick.

There are a number of companies supplying die attach epoxies. Ablestick Corporation manufactures a variety of die attach and microcircuit adhesives. Ablestick 84-1LMI adhesive is widely accepted and used at Centellax.

Wire Bonding:
Thermosonic wire bonding is the acceptable method to attach wires to MMIC bond pads. Two thermosonic bonding tools are in common use: wedge and capillary. Manufacturers of wire bonding equipment provide technical information, which serves as a good starting point for successful wire bonding to MMIC bond pads. The recommended gold wire diameter is 0.7 mils.