CPW
Delamination
& Crack
Figure 6.3 Average resistances from bump contacts on RO3210 with humidity test at different hours (168 hours, 336 hours and 504 hours)
Chapter 7
Conclusions
1. An evaluation of flip chip packages on RO3210 substrate (Dk = 10.2, tan δ = 0.0027) has been performed, including electrical (microwave application up to 60 GHz) and mechanical performances (reliability issue).
2. COB technique utilizes low cost organic substrate and integrates high electrical performance architecture (flip chip) into fabrication.
3. By definition, the loss in the flip-chip assembly includes mismatch loss (reflection) and real loss (attenuation). Mismatch loss can be improved by chip impedance matching and substrate circuit design. Meantime, selection of materials (chip/
substrate/ encapsulant) determines the real loss contribution.
4. Comparing with conventional microwave substrate (Al2O3), RO3210 demonstrates feasibility of application up to 40 GHz (reflection loss S11 = -20 dB).
Small degradation occurred after 40 GHz- 67 GHz (extra insertion loss S12 = -0.3 dB).
5. With suitable compensation layout (compensation at signal width (Cw) , ground pad overlap (lob) and ground pad shrinkage (SL)), the microwave performance can be improved up to 50 GHz application, even higher frequencies appear to be possible, at the expense of bandwidth, of course.
6. Quantitatively, the performances of three improved optimized designs:
compensation at signal width (Cw) , ground pad overlap (lob) and ground pad shrinkage (SL) are showed by the table below:
7. The encapsulating resin degrades the RF performance as the dissipation factor of the glob top/ underfill resin increases the transmission loss (Insertion loss, S21
degrades extra -0.3 dB). Meantime, glob top can be treated as ―natural compensation‖ to improve the reflection loss, S11.
8. The rule of thumb of chip impedance matching by taking into the consideration of the effect of underfill in the pre-design has successfully enhanced the S parameters performance from DC to 67 GHz broadband application (insertion loss is improved -1.0 dB) proposed packaging structure well suitable for millimeter wave application.
Optimized
11. Bump joint reliability testing shows the failure in non-encapsulated (2/3 samples) and glob top (3/3 samples) assemblies up to 400 thermal cycling. That bonding degradation is clearly due to the higher mismatch between the CTE of GaAs chip and RO3210 substrate. The thermal cycles induce stresses on the bump interconnect. The failure mechanisms at CPW transmission line caused by higher CTE glob top properties include delamination and crack.
12. There is no observable significant variation on measured bump resistance in humidity testing. Organic substrate and organic encapsulation demonstrates applicable in the 85 %RH/ 85 °C environment. All samples survive the harsh environment.
References
[1] Wolfgang Heinrich, ―The Flip-Chip Approach for Millimeter-Wave Packaging‖, IEEE Microwave Magazine, 05, pp1527-3342, September 2005
[2] Z.P. Zeng, W. Zhang, B.Z. Su, K.C.Gupta and Y.C.Lee, ―RF and Mechanical Characterization of Flip-Chip Interconnects in CPW Circuits with Underfill‖, IEEE MTT-S Digest, pp 1823-1826, 1998.
[3] H. Kusamitsu, Y.Morishita, K.Maruhashi, M.Ito and K.Ohata, ―The Flip Chip Bump Interconnection for Millimeter-wave GaAs MMIC,‘ International Conference on Multichip Modules and High Density Packaging, pp47-52, 1998.
[4] P. Monfraix, J.Monsarrat, J.L.Muraro, C.Dreavon, S.Dareys, M.Billot and J.L.Cazaux, ―Is Hermetic Encapsulation of GaAs MMIC still required for Space applications?‖ IEEE, pp2163-2166, 2005.
[5] K. Yoshida, T.Shirasaki, S. Matsuzono and C.Makihara,―50 GHz Broadband SMT Package for Microwave Applications‖, Electronic Components and Technology Conference, 2001.
[6] S.H.Shin and Y.S.Kwon, ―Selectively Anodized Aluminium Substrates for Microwave Power Module Package,‖ Electronic Components and Technology Conference, pp1904-1908, 2005.
[7] M. G. Pecht, H.Ardebili, A.A.Shukla, J.K.Hagge and D.Jennings, ―Moisture Ingress Into Organic Laminates‖, IEEE Transactions on Components and Packaging Technology, vol.22, No.1, pp104-110, March 1999.
[8] H.P. Chang, Q.B.A.Cetiner, F.D.Flaviis, M.Bachman and G.P.Li, ―Design and Process Considerations for Fabricating RF MEMS Switches on Printed Circuit
Boards,‖ Journal of Microelectromechanical Systems, vol.14, No.6, pp1311-1322, Dec 2005
[9] E. Valletta et al., ―Design of Planar Marchand Balun for MMIC Applications‖, http://www.ims-chips.de/content/pdfpublication/116375148.pdf, 22th July 2008.
[10] Y. K. Song and C. C. Lee, ―RF Modeling and Design of Flip Chip Configurations of Microwave Devices on PCBs‖, IEEE Electronic Components and Technology Conference, pp1837-1841, 2004.
[11] R. Bairavasubramanian, S.Pinel, J.Papapolymerou, J.Laskar, C.Quendo, E.Rius, A.Manchec and C.Person, ―Dual-Bands Filters for WLAN Applications on Liquid Crystal Polymer Technology,‖ IEEE, pp533-536, 2005
[12] G. Wang, D. Thompson, E.M.Tentzeris and J.Papapolymerou, ―Low Cost RF MEMS Switches Using LCP Substrate,‖ 34th European Microwave Conference-Amsterdam, pp1441-1444, 2004
[13]M. S. Hauhe, ―Flip Chip Technology Vendor Overview ―, Advanced Concepts &
Technology, http://www.gaasmantech.org/Digests/2005/2005papers/9.1.pdf, 23th July 2008.
[14]G.Baumann, E.Muller, F.Buchali, D.Ferling, H.Ritcher and W.Heinrich,
―Evaluation of Glob Top and Underfill Encapsulated Active and Passive Structures for Millimeter Wave Applications,‖ Microwave Conference and Exhibition, 27th European, pp26-31, 1997
[15]A.Jentzsch and H.Wolfgang, ―Theory and Measurements of Flip Chip Interconnects for Frequencies up to 100GHz‖, IEEE Transactions on Microwave Theory and Techniques, Vol.49, No.5, May 2001.
[16] B. Daigle, ―Printed Circuit Board Material and Design Considerations for Wireless Applications,‖ IEEE Electronic Components and Technology Conference, pp354-357,1996
[17] R.Hartley, ―Base Material for High Speed, High Frequency PC Boards,‖
http://www.speedingedge.com/PDF-Files/Materials_RickH2.pdf, March 2002 [18] N.Suthiwongsunthorn, N.Klibey and A.Cordery ―Study of the Electrical
Performance of Chip on Board (COB) Devices‖, IEEE Transactions on Components and Packaging Technologies, Vol 26, No.3, SEPT 2003.
[19] Y.H.Suh, D.Richardson, A.Dadello, S.Mahon and J.T.Harvey, ―A Low Cost High performance GaAs MMIC package using Air-Cavity Ceramic Quad Flat Non-Leaded Package up to 40GHz,‘‘2005.
[20] A.Wong and D.Linton, ―Copper Flip Chip Bump Interconnect Technology for Microwave Subsystems Including RF Characterization‖, Electronics Packaging Technology Conference, pp.335-338,2000.
[21] R.Sturdivant, C.Quan and J.Wooldridge, ―Investigation of MMIC Flip Chips with Sealants for Improved Reliability without Hermeticity‖, IEEE MTT-S Digest, 1996.
[22] Y.C. Hu, ―Using BCB and LCP as new underfill material for high frequency flip chip interconnects‖, NCTU, Master, 2007.
[23] R.Doyle, B.O.Flynn, W.Lawton,J.Barrett and J.Buckley ―Glob top Reliability Characterization: Evaluation and Analysis Methods‖, IEEE Transactions on Components, Packaging and Manufacturing Technology-Part A, vol21, No.2, June 1998.
[24] Sidharth Dalmia, Seok Hee Lee, Swapan Bhattacharya, Farrokh Ayazi and Madhavan Swaminathan, ― High-Q RF Passives on Organic Substrates Using a Low-Cost Low-Temperature Laminate Prcoess‖, http://www.ece.gatech.edu/
research/ integrated-mems/ conference%20papers/dalmia_dtip2002.pdf, School of Electrical and Computer Engineering Packaging Research Center, Georgia Institute of Technology.