由於扇出型(Fan-out)晶圓級封裝在電性與封裝尺寸上的優勢，近年來在封裝體系中成為主要研究技術之一。在典型的扇出型封裝中，矽晶(Si)外圍使用環氧樹脂封膠(Epoxy molding compound, EMC)包覆，並且在重佈線層(Redistribution layer, RDL)中使用聚醯亞胺(Polyimide, PI)薄膜和銅導線組合而成，由於不同材料之間密度與膨脹係數不同，在封裝或使用過程中產生熱機械應力，造成裂開或脫層失效的風險更高，且高分子材料具有吸濕性，可能降低材料之間的界面黏著力與增加應力，因此探討材料界面因為水汽和熱引起的應力並且評估失效風險和封裝結構可靠度勢必很重要。
為評估扇出型封裝結構之吸濕可靠度，本論文主要目標為建立一套基於有限元素法的水汽、熱和力學耦合模型，用以評估在扇出型封裝結構之界面水汽濃度與相關應力。首先針對環氧樹脂封膠在不同溫濕度環境下進行一連串吸濕實驗，根據實驗結果擬合相關材料特性包括吸濕擴散係數、水汽濃度模型和吸濕膨脹係數，接著將以上參數結合至有限元素模型中，考慮在濕度敏感等級條件下進行水汽、熱和力學模擬，分析吸濕擴散之暫態反應、應力和翹曲變化與封膠-矽晶和聚醯亞胺-銅界面角落與邊緣處之剝離應力(peel stress)，評估由吸濕造成界面脫層之驅動力，此外，本研究也針對封裝結構幾何分析對於剝離應力之影響。本研究建立之實驗擬合模型與水汽、熱和力學耦合模型對於封裝結構之幾何設計、材料選擇和評估水汽失效風險有相當大的幫助。

For evaluating the hygro-thermo-mechanical reliability of fan-out (FO) wafer-level package, a coupled-field finite element (FE) model was developed to evaluate the moisture concentration and stresses at materials interfaces in a FO package structure. A series of moisture absorption experiments were first carried out on epoxy molding compound (EMC) under various temperature and relative humidity (RH) conditions. Material parameters for moisture absorption models including saturation concentration, diffusivity and coefficient of hygroscopic swelling (CHS) were obtained from fitting to the experimental results. These models were then implemented in a coupled FE simulation to estimate the evolutions of moisture concentration, package warpage and peel stresses at EMC-Si and polyimide (PI)-Cu interface corners under moisture sensitivity level (MSL) testing. The peel stresses were considered as the driving forces of the interface delaminations caused by moisture absorption. The experimentally fitted moisture diffusion model and the coupled hygro-thermo-mechanical simulation model established in this study can be used for evaluate the effects of geometry and materials on the moisture sensitivity of FO wafer level packages.

[1] Y. Diamant, G. Marom, and L. Broutman, “The effect of network structure on moisture absorption of epoxy resins,” Journal of Applied Polymer Science, vol. 26, pp. 3015-3025, 1981.
[2] C.-H. Shen and G. S. Springer, “Moisture absorption and desorption of composite materials,” Journal of composite materials, vol. 101, pp. 2-20, 1976.
[3] M. Shirangi and B. Michel, “Mechanism of moisture diffusion, hygroscopic swelling, and adhesion degradation in epoxy molding compounds,” in Moisture sensitivity of plastic packages of IC Devices: Springer, 2010, pp. 29-69.
[4] M. D. Placette, X. Fan, J.-H. Zhao, and D. Edwards, “Dual stage modeling of moisture absorption and desorption in epoxy mold compounds,” Microelectronics Reliability, vol. 52, pp. 1401-1408, 2012.
[5] P. Bhargava, K. C. Chuang, K. Chen, and A. Zehnder, “Moisture diffusion properties of HFPE‐II‐52 polyimide,” Journal of applied polymer science, vol. 102, pp. 3471-3479, 2006.
[6] Y. He and X. Fan, “Real-time characterization of moisture absorption and desorption,” in Moisture Sensitivity of Plastic Packages of IC Devices: Springer, 2010, pp. 71-89.
[7] R. Gannamani and M. Pecht, “An experimental study of popcorning in plastic encapsulated microcircuits,” IEEE Transactions on Components, Packaging, and Manufacturing Technology: Part A, vol. 19, pp. 194-201, 1996.
[8] B. P. Rice and C. W. Lee, “Study of blister initiation and growth in a high-temperature polyimide,” in International Sampe Technical Conference, 1997, vol. 29: Sampe Society For The Advancement Of Material, pp. 675-685.
[9] I. Fukuzawa, S. Ishiguro, and S. Nanbu, “Moisture resistance degradation of plastic LSIs by reflow soldering,” in 23rd International Reliability Physics Symposium, 1985: IEEE, pp. 192-197.
[10] J. E. Galloway and B. M. Miles, “Moisture absorption and desorption predictions for plastic ball grid array packages,” in InterSociety Conference on Thermal Phenomena in Electronic Systems, I-THERM V, 1996: IEEE, pp. 180-186.
[11] M. Shirangi, W. Müller, and B. Michel, “Determination of Copper/EMC interface fracture toughness during manufacturing, moisture preconditioning and solder reflow process of semiconductor packages,” in ICF12, Ottawa 2009, 2009.
[12] X. Fan, S. Lee, and Q. Han, “Experimental investigations and model study of moisture behaviors in polymeric materials,” Microelectronics Reliability, vol. 49, pp. 861-871, 2009.
[13] X. Fan, “Mechanics of moisture for polymers: fundamental concepts and model study,” in EuroSimE 2008-International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Micro-Systems, 2008: IEEE, pp. 1-14.
[14] H. Ardebili, E. H. Wong, and M. Pecht, “Hygroscopic swelling and sorption characteristics of epoxy molding compounds used in electronic packaging,” IEEE Transactions on Components and Packaging Technologies, vol. 26, pp. 206-214, 2003.
[15] C. Jang, S. Yoon, and B. Han, “Measurement of the hygroscopic swelling coefficient of thin film polymers used in semiconductor packaging,” IEEE Transactions on Components and Packaging Technologies, vol. 33, pp. 340-346, 2010.
[16] J. B. Kwak and S. Park, “Integrated hygro-swelling and thermo-mechanical behavior of mold compound for MEMS package during reflow after moisture preconditioning,” Microelectronics International, vol. 32, pp. 8-17, 2015.
[17] R. Liu, H. Wang, J.Wang, H. Lee, S. Park and X. Xue “Moisture diffusion and hygroscopic swelling of adhesives in electronics packaging,” in 2016 IEEE 66th Electronic Components and Technology Conference (ECTC), 2016: IEEE, pp. 2203-2209.
[18] C. Jang and B. Han, “Modeling of moisture diffusion and moisture-induced stresses in semiconductor and MEMS packages,” in Moisture Sensitivity of Plastic Packages of IC Devices: Springer, 2010, pp. 181-219.
[19] Z. Huo, V. Bheemreddy, K. Chandrashekhara, and R. Brack, “Modelling of concentration-dependent moisture diffusion in hybrid fibre-reinforced polymer composites,” Journal of Composite Materials, vol. 49, pp. 321-333, 2015.
[20] C. Jang, B. Han, and S. Yoon, “Comprehensive moisture diffusion characteristics of epoxy molding compounds over solder reflow process temperature,” IEEE Transactions on Components and Packaging Technologies, vol. 33, pp. 809-818, 2010.
[21] X. Fan and V. Nagaraj, “Finite element modeling of anomalous moisture diffusion with dual stage model,” in 2012 IEEE 62nd Electronic Components and Technology Conference, 2012: IEEE, pp. 1190-1193.
[22] X. Fan and S. Lee, “Fundamental characteristics of moisture transport, diffusion, and the moisture-induced damages in polymeric materials in electronic packaging,” in Moisture Sensitivity of Plastic Packages of IC Devices: Springer, 2010, pp. 1-28.
[23] G. Papanicolaou, T. V. Kosmidou, A. Vatalis, and C. Delides, “Water absorption mechanism and some anomalous effects on the mechanical and viscoelastic behavior of an epoxy system,” Journal of Applied Polymer Science, vol. 99, pp. 1328-1339, 2006.
[24] Z. Ahmad, M. P. Ansell, and D. Smedley, “Moisture absorption characteristics of epoxy based adhesive reinforced with CTBN and ceramic particles for bonded-in timber connection: Fickian or non-fickian behaviour,” in IOP Conference Series: Materials Science and Engineering, 2011, vol. 17: IOP Publishing, p. 012011.
[25] G. Van der Wel and O. Adan, “Moisture in organic coatings—a review,” Progress in organic coatings, vol. 37, pp. 1-14, 1999.
[26] P. Jacobs and E. Jones, “Diffusion of moisture into two-phase polymers,” Journal of materials Science, vol. 24, pp. 2343-2347, 1989.
[27] A. Berens and H. Hopfenberg, “Diffusion and relaxation in glassy polymer powders: 2. Separation of diffusion and relaxation parameters,” Polymer, vol. 19, pp. 489-496, 1978.
[28] D. A. Bond and P. A. Smith, “Modeling the transport of low-molecular-weight penetrants within polymer matrix composites,” Applied Mechanics Reviews, vol. 59, pp. 249-268, 2006.
[29] A. A. C. Pereira and J. R. M. d’Almeida, “Effect of the hardener to epoxy monomer ratio on the water absorption behavior of the DGEBA/TETA epoxy system,” Polímeros, vol. 26, pp. 30-37, 2016.
[30] C. Maggana and P. Pissis, “Water sorption and diffusion studies in an epoxy resin system,” Journal of Polymer Science Part B: Polymer Physics, vol. 37, pp. 1165-1182, 1999.