1. 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

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

3. 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

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

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

6. 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

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

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

9. 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”

10. 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

11. 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

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

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

14. 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

15. 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]

16. 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 Int. Microwave Theory Tech. Symp. Dig., Orlando, FL, May 1995, pp
[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
[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 Microwave Application Seminars.

17. Thank you !