Proper procedures must be used when building integrated assemblies that incorporate gallium-arsenide (GaAs) or gallium-nitride (GaN) monolithic microwave integrated circuits (MMICs). Hence, this topic is the subject of Qorvo’s white paper titled, “GaAs and GaN Die Assembly and Handling Procedures.” In it, Qorvo discusses component placement, attachment, and interconnect techniques that can be utilized to successfully build assemblies containing GaAs or GaN MMICs.
The white paper begins by discussing component placement, which involves picking up and then placing MMICs into microwave circuits or modules. It explains that both GaAs and GaN MMICs should be picked up by using either an automatic or semi-automated pick system along with an appropriate pick tool (e.g, a vacuum pencil or collet).
Solder attachment is the next topic presented. The white paper recommends that solvent cleaning of solder preforms and substrates/packages be performed to remove any existing surface contaminants. Moreover, gold-tin (AuSn 80/20) is the alloy that is most commonly used when soldering GaAs and GaN MMICs. AuSn solder is usually available as a preform, with common thickness values ranging from 0.5 to 2 mils. One additional point of emphasis involves choosing a substrate or base-plate material with a suitable coefficient of thermal expansion (CTE).
Epoxy attachment is another technique that can be used to attach GaAs and GaN MMICs to a surface. In the past, this technique was recommended only for low-power applications. However, advancements in technology have made expoy attachment a viable option for high-power MMICs—as long as proper measures are taken. Furthermore, the document notes that epoxies cure at temperatures ranging from +100°C to +200°C. Curing should take place in a convection oven with proper exhaust.
Lastly, interconnection techniques are discussed. Thermosonic ball bonding is the preferred interconnect technique, according to the white paper. Critical factors when using bonding equipment are force, time, and ultrasonic power. Acceptable wire diameters with respect to the bond-pad size on a device are discussed as well.
Qorvo Inc., 7628 Thorndike Road, Greensboro, NC 27409; (336) 664-1233