For RF devices applications, underfill materials shall possess low dielectric constants to improve RC delay, power consumption, and crosstalk noise, besides excellent mechanical strength. By the utilization of zeeospheres and porous silica as the fillers, porosity was successfully introduced into the underfill materials by pore sealing pretreatment to reduce their dielectric constants.
For the pore-sealing treatment of low-k underfill materials, the selection of an appropriate material to seal the pores was the most critical. The temperature-dependent viscosity and the curing reaction were found to be important in the selection of sacrificial material, while the curing profile for pore-sealing pretreatment could be determined by DSC and rheometer measurements. The material, employed for pore-sealing treatment, shall possess the properties described below:
(1) The material must have proper melting point such that it could sealed the interconnected pores, and appropriate boiling point to ensure that it could be removed thermally during the curing reaction of underfill materials.
(2) The materials should possess poor compatibility with epoxy resins which can hinder the epoxy resins to flow into the pores.
(3) The molecular size of the material must be smaller than the pore size of porous silica so that it can enter the pores easily to seal the pores.
(4) The material cannot react with epoxy resins degrading the mechanical strength of underfill materials.
In this thesis, a pore-sealing pretreatment for porous silica was developed by employing D3, with melting point, 60 ~ 70 ℃, and boiling point, 130 ~ 140 ℃. The
molecular size of D3 was below 1nm, which was far smaller than the pore size of porous silica (6.6nm), indicating that D3 could easily get into the pores to seal them.
Moreover, it was good that D3 didn’t react with the epoxy resins unlike N-butanol.
These properties made D3 to protect and retain the porosity successfully. The mechanisms for retaining porosity in the underfill system could be illustrated in two stages; namely.
(1) The sacrificial material, D3, heated at 95 ℃, easily flowed into the pores and sealed over the pores such that the flowing epoxy resins could not enter the pores at room temperature. Upon the cooling step after pre-treatment, D3 trapped in the larger pores would slightly outgas leaving a layer of D3 onto the sidewall of pores.
Some degree of epoxy backflow into larger pore was likely.
(2) D3 outgassed at boiling point, 120 ~ 140 ℃, at which large gas pressure out of pores hindered the reflow of the epoxy resins during the curing reaction until the high viscosity of epoxy resins resulting from crosslinking.
The pore-sealing pretreatment by D3 had successfully retained pores to reduce the dielectric constants of underfill materials such as low-k underfill materials C and D.
However, D3 also led to 30-40% degradation of mechanical strength due to the poor adhesion at epoxy/porous silica interface caused by D3 outgassing. The hypothesis was further confirmed by loss factor, tanδ using DMA, which was an indicator to estimate the interface condition of composite materials. The higher tanδ meant more energy dissipated and poor adhesion between the components. For low-k underfill materials B, C, and D, tanδ data of low-k underfill material C and D (0.04 and 0.06) were larger than that of low-k underfill material B (0.02) which indicated that D3 vaporized and diffused out of pores during curing reaction, and therefore, destroyed the adhesion between epoxy and fillers.
In summary, we have successfully developed a pore-sealing pretreatment for porous silica fillers by D3 to reduce dielectric constant from 3.2 to 2.86 (~10.6%) with 15 wt% porous fillers in this thesis. However, the mechanical strength was reduced from 3.0 GPa to 1.5 GPa. because of poor adhesion at porous silica/epoxy interfaces caused by D3 ougassing during the curing reaction step.
References
[1] D. J. Frank, R. Puri, and D. Toma, Proceedings of the 2006 IEEE/ACM international conference on Computer-aided design, 329 (2006).
[2] L. T. Manzione, Plastic Packaging of Microelectronic Devices (Van Nostrand Reinhold, New York 1990).
[3] J. H. Lau, Flip Chip Technologies (McGraw-Hill, New York 1996).
[4] 黃淑禎, 李巡天, 陳凱琪, 新世代半導體封裝材料與發展趨勢, 工業材料 170, 86 (2001).
[5] 郭嘉龍, 半導體封裝工程 (全華科技圖書公司, 台北市 1999).
[6] S. Luo, Tsuyoshi Yamashita, and C. P. Wong, Adhesive Joining and Coating Technology in Electronics Manufacturing, 70 (2000).
[7] 楊正杰, 張鼎張, 鄭晃忠, 銅金屬與低介電常數材料與製程, 毫微米通訊 7, 40 (2000).
[8] D. R. Frear, Future Fab Intl. 16, 10 (2004).
[9] R. Kultzow and B. Mainguy, Electrical Insulation Conference and Electrical Manufacturing and Coil Winding Conference, 291 (2001)
[10] R. R. Tummala, Fundamentals of Microsystems Packaging (McGraw-Hill, New York 2001).
[11] 呂宗興, 電子構裝技術的發展歷程, 工業材料 115, 49 (1996).
[12] J. H. Lau, Ball Grid Array Technology (McGraw-Hill, New York 1995).
[13] 鐘文仁, 陳佑任, IC 封裝製程與 CAE 應用 (全華科技圖書公司, 台北市 2005).
[14] Y. Liu, D. Desbiens, S. Irving, and T. Luk, IEEE Proc. of 55th ECTC, 861 (2005).
[15] 孔令臣, Flip Chip Bumping Technology, 工業材料 139, 155 (1998).
[16] C. P. Wong, S. Lou, and Z. Zhang, Science 290, 2269 (2000).
[17] J. W. Nah, K. Chen, and K. N. Tu, J. Mater. Res 22, 763 (2007).
[18] J. H. Lau, Low Cost Flip Chip Technologies (McGraw-Hill, New York 2000).
[19] Z. Zhang and C. P. Wong, IEEE T. Adv. Packaging 27, 515 (2004).
[20] H. Lu, G. Glinski, and C. Bailey, APACK 2001 Conference on Advances in Packaging, 245 (2001).
[21] Y. San, Study on the Nancomposite Underfill for Flip-Chip Application, Georgia Institute of Technology (2006).
[22] 賴耿陽, 環氧樹脂應用實務 EPOXY RESINS (復漢, 台南市 1993).
[23] E.J.A Pope and J.D. Mackenzie, Journal of Non-Crystalline Solids 87, 185 (1986).
[24] K.C. Chen, T. Tsuchiya, and J.D. Mackenzie, Journal of Non-Crystalline Solids 81, 227 (1986).
[25] A. H. Boonstra and T. T. M. Bernards, Journal of Non-Crystalline Solids 105, 207 (1988).
[26] D. Suryanarayana, R. Hsiao, T. P. Gall, and J. M, Mccreary, IEEE Transaction of Components and Hrbrid and Manufacturing Technology 16, 858 (1993).
[27] K. M. Chen, D. S. Jiang, N. H. Kao, and J. Y. Lai, Microelectronics Reliability 46, 155 (2006)
[28] P. S. Ho, J. Leu, and W. W. Lee, Low Dielectric Constant Materials for IC Applications (Springer, Berlin, 2003)
[29] P.-H. Tsao, C. Huang, M.-J. Lii, B. Su, and N.-S. Tsai, Electronic Components and Technology Conference, 767 (2004)
[30] C. George and T. Michael, IEEE/SEMI Int'l Electronics Manufacturing Technology Symposium, 10 (2004)
[31] H. Kusamitsu, Y. Morishita, K. Maruhashi, M. Ito, and K Ohata, IEEE T.
Electron Pack. 22, 23 (1999).
[32] S. P. Murarka, M. Eizenberg, and A.K. Shinha, Interlayer Dielectrics for Semiconductor Technologies (Elsevier, London 2003).
[33] J. Lou and W. Chen, IEEE Design and Test of Computers 21, 24 (2004).
[34] Z. Tao, L. Fan, and S. Yang, 7th International Conference on Electronics Packaging Technology, 1 (2006)
[35] J. R. Lee, F. L. Jin, S. J. Park, and J. M. Park, Surface and Coatings Technology 180, 650 (2004)
[36] International Technology Roadmap for Semiconductors (2003)
[37] I. Sugiura, N. Misawa, and Y. Nakata, Microelectronic Eng. 82, 380 (2005) [38] S. Li, Z. Li, and Y. Yan, Adv. Mater. 15, 1528 (2003).
[39] Bershtein, Vladimir A., and Victor M., Differential Scanning Calorimetry of Polymers/Physics, Chemistry, Analysis, Technology (Ellis Horwood, New York, 1994)
[40] J. M. Dealy, Rheometers Molten Plastics: A Practical Guide to Testing and Property Measurement ( Van Nostrand Reinhold Company, New York 1982) [41] Y. L. Sun, A Room-Temperature Gas Sensor Based on Solid-State Lanthanum
Fluoride Electrolyte, National Cheng Kung University (2002).
[42] N. Ku and K. Shi, RF Impedance/Material Analyzer (Hewlett Packard, Japan 1998)
[43] K. P. Menard. Dynamic Mechanical Analysis: A Practical Introduction (CRC Press, New York 1999)
[44] T. Murayama, Dynamic Mechanical Analysis of Polymeric Material (ELSEVIER, New York 1978)
[45] Y. Rao, J. Qu, T. Marinis, and C. P. Wang, IEEE T. Compon. Pack. 23, 680 (2000)
[46] R. A. Caruso, A. Susha, and F. Caruso, Chem. Mater. 13, 400 (2001)
[47] W. D William and J. Callister, Materials Science and Engineering: An Introduction (Wiley, New York, 2003)