Microwave techniques for high-density electronics interconnect bonding and hybridization

Microwave Bonding Instruments, Inc. (MBI), has been investigating die-to-die (Level-0) bonding of independent devices, or device-substrate hybridization, as part of a system-on-a-package (SOP). MBI applies microwaves to selectively heat the interconnect metal to bond the substrates. MBI bonded a 320×256 array of indium bump of infrared detectors made of GaAs to the CMOS readout on silicon substrates. This selective heating technique has doubled the bump-to-bump bond strength to 0.2 g/bump and minimized the processing time (less than 15 s) at an overall low-substrate temperature (86°C). The thermal mismatch between substrates is reduced in this bonding process. The technique was also applied to higher melting temperature metals. Bonding of gold-tin-to-gold-tin all the way up to gold-to-gold has been demonstrated on parts up to 400×400 bumps. A SOP for advanced electronics requiring a variety of substrates will benefit from this technology.