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The Challenge in Packaging and Assembling the Advanced Power Amplifiers

Abstract:

Transistors have been widely employed in the areas of power amplifiers and power electronics. Packaging and assembly technologies become critical to the success of such applications where high power dissipation (in the form of heat) is involved while operating the transistors. With the ever increasing output power of such applications, heat dissipated from the transistors needs to be more effectively transferred out of the package so that the junction temperature in the transistors can be maintained at a reasonable low level. This is necessary in order to prolong the life time of the transistor devices.

Using higher activation energy materials and operating at lower temperature result in longer life time. The well-known outstanding performance of GaAs MMIC has activation energy of 1.6–1.9 eV, but its low power density typically makes GaAs non-completive with Si-based LDMOS and BJT in L-band for higher power amplification needs. In recent years, GaN on SiC with activation energy of 0.9–2.2 eV have become an excellent choice as RF transistors for high power amplifier applications due to their higher activation energy with about four times or more power density than GaAs. GaN on SiC also enable higher operating temperature due to the excellent thermal conductivity and high melting temperature of SiC, and it is able to perform at high frequency and wide bandwidth. Therefore, LDMOS, BJTs and GaN on SiC are the choice for high power amplifiers in the range of hundreds to thousand Watts. Lowering the operating temperature of a power amplifier module (PAM) is essential: not only can it prolong the transistors’ life time, but it also a global benefit to all electronic components on the module since the lower temperature leads to lower creep and fatigue failure rates for packaging and assembly materials. High power density of GaN power amplifiers demands the package substrate and packaging materials possess superior thermal properties. This paper focuses on the challenges that we are facing in manufacturing high power PAMs for RF and microwave applications.