Flip Chip Technology Kim Dong Hwan Microwave Device Term Project 2005/6/16 Kim Dong Hwan School of Electrical Engineering and Computer Science Seoul National University, Korea

Contents Introduction Wire Bonding vs. Flip Chip interconnect Flip Chip Process (SSB & MSB) Conclusion

Introduction Advancements in the packaging of semiconductor devices  traditionally use wire bonds to provide the interconnect from device to substrate or to other devices Along with the rapid advances in microwave and millimeter wave subsystem development  a growing interest concerning chip interconnection techniques has developed. The importance of quality of these interconnects  a large impact on the performance of the entire subsystem, especially at high frequencies. Flip chip offers advantages over traditional interconnect schemes.  A smaller overall footprints, better thermal heat transfer

Introduction Wire Bonding vs. Flip Chip interconnect Flip Chip Process (SSB & MSB) Conclusion

Wire Bonding Bond ribbon [Coplanar Waveguide Model] Wire length loss

Flip Chip Interconnection Compared to the Bond Wire MMIC(2mm 50 CPW line) Motherboard on 20-cm Si wafer Bump CPW Small Big [Flip Chip Interconnection of Coplanar MMIC] [EM-Simulation Structure for RF test] [Gold(Stud) Bumps attached] Ref. Songsub Song

Flip Chip Interconnection Bump Height ≥ Spacing ☞ The influence of substrate surface -> negligible {Bump height ≥ Ground to ground spacing of the transmission lines}

Flip Chip Interconnection Versus Wire Bonding Insertion loss Return loss Beyond 100GHz → Below 0.5dB

Proximity Effect in Flip-Chip Structure [ Change rate of characteristic impedance as a function of air-gap for a flip-chip mounted CPW MMIC ] Air gap (mm) Change in Z0 ( % ) 50  CPW (D= 80mm) Alumina substrate ~ 3 % change at 20 mm [ E-field distribution for a flip-chip mounted CPW MMIC ] D Motherboard MMIC or Device Height of flip-chip bump (air-gap) Ref. Sangsub Song, “The Flip-Chip Mounted MMIC Technology using the Modified MCM-D Substrate for Compact and Low-Cost W-band Transceivers”

Why Flip Chip Technology? [ Flip-Chip Bonding Technology ] [ Wire-Bonding Technology ] m-strip MMIC Wire -Bonding 50 ~ 100 mm Via CPW MMIC Ground Flip-Chip Bump ~ 650 mm  Advantages of Flip Chip Bonging Technology.  Short Interconnection Length  Better Electrical Performances  High reproducibility  High Yield & Less Tuning  Compact size  High Packaging density  Passive components are made in dielectric substrate such as alumina Ceramics, SiO2 and BCB  Low Cost

Wire Bonding Technology Comparison Flip Chip Technology Wire Bonding Technology Advantages High density High performance Noise control Thin profile Area array technology Small device foot prints Self alignment Mature Technology Infrastructure exists Flexible for new devices Flexible for new bonding patterns Disadvantages Additional Equipment Additional processes Rework after encapsulation is difficult Die shrink Rework is difficult I/O limitation

Introduction Wire Bonding vs. Flip Chip interconnect Flip Chip Process (SSB & MSB) Conclusion

Stud Bump Bonding Technology [Cross-sectional SEM photograph of the bonding portion by SBB] [Process flow of the SBB]

Micro Bump Bonding Technology -To cure the resin [Cross-sectional SEM photograph of the bonding portion by MBB] [Process flow of the MBB] ☞ Further requirements for miniaturization and higher frequency operation

Conclusion The need for smaller packaging Flip chip interconnect process → more compact fashion Improved electrical performance Reduced interconnect length → lower inductance and reduced signal loss → lower power requirements The demands of high frequency applications Limitation of the wire interconnect → flip-chip bump connection [Wire connection] [Flip Chip Bump Connection]

References [1] Mark S. Hauhe, “Flip Chip Technology Vendor Overview,” [2] R. Sturdivant, “Reducing the effects of the mounting substrate on the performance of GaAs MMIC flip chips,” in Proc. 1995 Int. Microwave Theory Tech. Symp. Dig., Orlando, FL, May 1995, pp. 1591-1594. [3] Hideki Kusamitsu, et al., “The Flip-Chip Bump Interconnection for Millimeter Wave GaAs MMIC,” IEEE Transactions on Electronics Packaging Manufact- uring, VOL. 22, NO .1, January 1999. [4] T. Krems, et al., “Millimeter-Wave Performance of Chip Interconnections Using Wire Bonding and Flip Chip,” IEEE MTT-S Digest. pp. 247-250. [5] Hiroyuki Sakai., “High Frequency Flip-Chip Bonding Technologies and Their Application to Microwave/Millimeter-wave ICs,” IEICE TRANS. Electron., VOL. E81-C, NO. 6 June 1998. [6] Kiyomitsu Onodera, et al., “Novel Flip-Chip Bonding Technology for W-Band Interconnections Using Alternate Lead-Free Solder Bumps,” IEEE Microwave and Wireless Components Letters, VOL.12, NO. 10, October 2002. [7] Sangsub Song, “The Flip-Chip Mounted MMIC Technology using the Modified MCM-D Substrate for Compact and Low-Cost W-band Transceivers” IEEE IMS 2005. Microwave Application Seminars.

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