Evaluation of Glob Top and Underfill Encapsulated Active and Passive Structures for Millimeter Wave Applications

The protection of active devices against mechanical and environmental influences is necessary to guarantee a proper performance and life time. Packaging of the devices however is a very cost intensive factor and therefore it is very important to search for more economical packaging methods for RF-applications, too. In order to investigate the influence of epoxy encapsulation material we have characterized active and passive devices, which are wire bonded with subsequent glob top encapsulation as well as flip chip bonded with underfill encapsulation. The devices have been measured up to 70 GHz in order to evaluate the change of RF-transmission line characteristics and device parameters due to mounting and encapsulation. With a parameter extraction method the elements of an equivalent electrical circuit for the inner active device and the parasitics are determined. A change of impedance for encapsulated transmission lines of about 3 ¿ for a 50 ¿ line was found. Wire bonded devices exhibit a stronger variation of parasitics due to encapsulation in comparison to flip chip bonded devices, a reduction in Gmax of 1.2 dB and 0.2 dB at 20 GHz were found, respectively. For both HEMT and MESFET the inner device was unchanged. For MMIC and hybrid circuit packaging epoxy encapsulation is suitable even for mmwave range. For circuit design modified parameters should be considered.