Epoxy Die Attach Considerations For HPA MMICs

MMICs have been traditionally mounted on a RF circuit board, or directly to a plated metal carrier, using a wide range of conductive epoxies, or eutectic solder (e.g. AuGe, AuSn). Eutectic and epoxy has been used in both commercial, military and space applications for many years. Over the last decade with the onset of commercial power amplifiers for handsets and base station products, microelectronic assembly houses which deal with the assembly of modules containing MMICs have moved to epoxy attachment wherever possible.

Major benefits from the use of epoxy over eutectic solder are:

1. Lower MMIC stress (especially on larger MMIC's with via holes)
   
2. Less MMIC pollution
   
3. Simple and well controlled assembly process
   
4. Lower curing temperatures
   
5. Pb free and RoHs compliant

Because of these advantages in the assembly process, developments in thermally conductive epoxies have closed the traditional performance gap between epoxy and eutectic solder for HPA MMIC attachment. Accordingly, the use of these thermal epoxies for HPA MMIC attachment is commonplace and the result is a more uniform die attach with no lowering of the device MTTF or degradation of performance at elevated ambient temperatures.