Study of RF flip-chip assembly with underfill epoxy

Flip-chip assembly technology is becoming more and more important to radio frequency (RF) MCM with the following advantages: automated assembly, compact size, low cost, low crosstalk, and low insertion loss. However, flip-chip assembly also demands careful evaluation of solder joint reliability. For an assembly with a large MMIC chip or with a polymer substrate, underfill epoxy should be used to enhance the solder joint reliability. For a GaAs-on-Duraid flip-chip assembly with a chip size of 1.38 mm/spl times/4.7 mm, fatigue life could be increased from 1,300 to 11,000 cycles by the use of epoxy. Epoxy enhances solder reliability; however, it may affect electrical performance. Experimental studies have been conducted to measure the additional insertion loss resulting from the underfill epoxy. The additional loss is less than 1 dB, and it is acceptable for many RF applications.