The invention relates to IC packaging, particularly to IC packaging for high frequency applications.
Packaging for high-speed digital circuits running at 40 Gbps and beyond is still an open problem. The main problem in package design is the elimination of discontinuities along the high-frequency signal and ground paths from the integrated circuit, through the package, to the printed circuit board.
Specifically, what remains an open problem is the realization of a small form factor package with broadband characteristic (DC to 50 GHz and beyond) for high-speed digital integrated circuit with multiple I/Os. Having multiple I/Os requires the use of a packaging technology that allows using multiple metal layers for signal routing. On the other hand, the presence of multiple metal layers renders more difficult the design of broadband transitions due to discontinuities (bends, vias, transition from micro strip to stripline configuration, etc.) in the high-speed signal path. Also, the higher number of I/Os generally implies bigger footprint for the package and higher power dissipation. Those two requirements pose additional challenges to thermal management and second level joints reliability.
A few papers analyzing the electrical performance of transitions inside a multilayer ceramic structure are available in the literature [1,2]. Other researchers are addressing the problem of transition from the package to the board [3] using ball grid array (BGA) technology. One of the issues of BGA technology is the excitation of parallel plate mode between the package ground and the motherboard ground launched by the package solder balls. This limitation could be finally overcome by using smaller and smaller solder ball on a decreasing pitch, but this creates manufacturing problems.
[1] Interconnects and transitions in multilayer LTCC multichip modules for 24 GHz ISM-band applications
Simon, W.; Kulke, R.; Wien, A.; Rittweger, M.; Wolff I.; Girard, A.; Bertinet, J-P. Microwave Symposium Digest. 2000 IEEE MTT-S International, Volume: 2, Page(s): 1047-1050.
[2] RF/Microwave Characterization of Multilayer Ceramic-Based MCM Technology
Sutono A., Pham, A-V. H, Laskar, J., Smith, W. R. IEEE Transactions on Advanced Packaging, Vol. 2, August 1999, pp. 326-331.
[3] 50 GHz broadband SMT package for microwave applications
Yoshida, K.; Shirasaki, T.; Matsuzono, S.; Makihara, C. Electronic Components and Technology Conference, 2001. Proceedings. Page(s): 744-749