Mechanism of Moisture Diffusion, Hygroscopic Swelling, and Adhesion Degradation in Epoxy Molding Compounds

Epoxy molding compounds (EMCs) are widely used as encapsulation materials for protecting the semiconductor chips of plastic encapsulated microcircuits (PEMs) against harsh environments and mechanical forces such as impact and pressure. Since PEMs are usually exposed to humid conditions during their storage and service life, they absorb moisture, which causes many reliability problems such as popcorn cracking and interfacial delamination during the solder reflow process. This chapter presents a comprehensive investigation of the mechanism of moisture diffusion in EMCs. The results from moisture diffusion tests during absorption, desorption, and re-sorption of various EMC samples are presented. The gravimetric results showed a non-Fickian behavior of the moisture diffusion in the EMCs. This non-Fickian behavior was found to induce a non-reversible effect by causing some residual moisture content upon baking these plastic parts. The gravimetric moisture diffusion results can be correlated to moisture-induced hygroscopic swelling and adhesion loss. Hygroscopic swelling of EMC and its reversibility was investigated using both bulk EMC samples and bi-material beams. Moreover, the effect of moisture on the adhesion of EMC/Cu interface was studied using a fracture mechanics approach. Two mechanisms of adhesion loss upon moisture diffusion can be observed. Some of the adhesion loss due to small amount of moisture content may be recovered via a proper annealing. However, upon long-term storage in humid conditions, where the second phase of non-Fickian behavior is activated at the interface, none of the adhesion loss can be recovered after baking the samples.

[1]  T. P. Ferguson.  MOISTURE AND INTERFACIAL ADHESION IN MICROELECTRONIC ASSEMBLIES , 2004 .

[2]  B. Wunderle,et al.  Modeling cure shrinkage and viscoelasticity to enhance the numerical methods for predicting delamination in semiconductor packages , 2009, EuroSimE 2009 - 10th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems.

[3]  H. Reichl,et al.  Molecular Dynamics Simulation for the diffusion of water in amorphous polymers examined at different Temperatures , 2007, 2007 International Conference on Thermal, Mechanical and Multi-Physics Simulation Experiments in Microelectronics and Micro-Systems. EuroSime 2007.

[4]  Xuejun Fan,et al.  Package structural integrity analysis considering moisture , 2008, 2008 58th Electronic Components and Technology Conference.

[5]  A. Evans,et al.  A Test Specimen for Determining the Fracture Resistance of Bimaterial Interfaces , 1989 .

[6]  Ken M. Takahashi.  ac impedance measurements of moisture in interfaces between epoxy and oxidized silicon , 1990 .

[7]  J. Vlassak,et al.  Water diffusion and fracture in organosilicate glass film stacks , 2007 .

[8]  J. Comyn,et al.  The effect of humidity on the durability of aluminium-epoxide joints , 1990 .

[9]  Salit Kark,et al.  A dissertation for the degree of Doctor of Philosophy , 2000 .

[10]  C. Soles,et al.  A discussion of the molecular mechanisms of moisture transport in epoxy resins , 2000 .

[11]  A. Nishimura,et al.  A New Method for Measuring Adhesion Strength of IC Molding Compounds , 1992 .

[12]  Anthony J. Rafanelli,et al.  Plastic Encapsulated Microelectronics; Materials, Processes, Quality, Reliability, and Application , 1997 .

[13]  M.G. Pecht,et al.  Characterization of hygroscopic swelling behavior of mold compounds and plastic packages , 2004, IEEE Transactions on Components and Packaging Technologies.

[14]  Y. Lin.  Investigation of the Moisture-Desorption Characteristics of Epoxy Resin , 2007 .

[15]  B. Michel,et al.  Characterization of dual-stage moisture diffusion, residual moisture content and hygroscopic swelling of epoxy molding compounds , 2008, EuroSimE 2008 - International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Micro-Systems.

[16]  Jiang Zhou,et al.  Investigation of nonuniform moisture distribution on determination of hygroscopic swelling coefficient and finite element modeling for a flip chip package , 2005, EuroSimE 2005. Proceedings of the 6th International Conference on Thermal, Mechanial and Multi-Physics Simulation and Experiments in Micro-Electronics and Micro-Systems, 2005..

[17]  Stuart Lyon,et al.  Effect of water and its activity on transport properties of glass/epoxy particulate composites , 1997 .

[18]  Linda Zhai,et al.  Moisture Absorption and Diffusion Characterization of Molding Compound , 2005 .

[19]  Peter Cawley,et al.  The Correlation of Non-Destructive Measurements and Toughness Changes in Adhesive Joints during Environmental Attack , 2001 .

[20]  Wen-li Wu,et al.  Water adsorption at a polyimide/silicon wafer interface , 1995 .

[21]  Xunqing Shi,et al.  Direct Concentration Approach of Moisture Diffusion and Whole-Field Vapor Pressure Modeling for Reflow Process—Part II: Application to 3D Ultrathin Stacked-Die Chip Scale Packages , 2009 .

[22]  M. Tencer,et al.  Moisture ingress into nonhermetic enclosures and packages. A quasi-steady state model for diffusion and attenuation of ambient humidity variations , 1994, 1994 Proceedings. 44th Electronic Components and Technology Conference.

[24]  M. Shanahan,et al.  Evaluation of adhesive shear modulus in a torsional joint - Influence of ageing , 1993 .

[26]  I. Ashcroft,et al.  Modelling anomalous moisture uptake, swelling and thermal characteristics of a rubber toughened epoxy adhesive , 2005 .

[27]  Xuejun Fan,et al.  Mechanics of moisture for polymers: Fundamental concepts and model study , 2008, EuroSimE 2008 - International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Micro-Systems.

[28]  Xuejun Fan,et al.  In-situ Characterization of Moisture Absorption and Desorption in a Thin BT Core Substrate , 2007, 2007 Proceedings 57th Electronic Components and Technology Conference.

[29]  Michael J. Adamson,et al.  Thermal expansion and swelling of cured epoxy resin used in graphite/epoxy composite materials , 1980 .

[30]  M. Pecht,et al.  A comparison of the theory of moisture diffusion in plastic encapsulated microelectronics with moisture sensor chip and weight-gain measurements , 2002 .

[31]  G. Q. Zhang,et al.  Multi-physics modeling in virtual prototyping of electronic packages--combined thermal, thermo-mechanical and vapor pressure modeling , 2004, Microelectron. Reliab..

[32]  Wei Zhou,et al.  Effect of Hygrothermal Aging on Interfacial Reliability of Silicon/Underfill/FR-4 Assembly , 2008, IEEE Transactions on Components and Packaging Technologies.

[33]  Thiam Beng Lim,et al.  Moisture diffusion and vapour pressure modeling of IC packaging , 1998, 1998 Proceedings. 48th Electronic Components and Technology Conference (Cat. No.98CH36206).

[34]  Walter G. McDonough,et al.  Interfacial Water and Adhesion Loss of Polymer Coatings on a Siliceous Substrate , 1995 .

[35]  Jianmin Qu,et al.  Predictive model for adhesion loss of molding compounds from exposure to humid environments , 2006, 56th Electronic Components and Technology Conference 2006.

[36]  G. D. Davis,et al.  Electrochemical Sensors for Nondestructive Evaluation of Adhesive Bonds , 2000 .

[37]  JAMES M. Macaulay.  Adsorption of Water Vapour on Solid Surfaces , 1951, Nature.

[38]  Seán J. Martin,et al.  Understanding hydrated polymers: the perspective of NMR , 1999 .

[39]  Q. Han,et al.  Experimental investigations and model study of moisture behaviors in polymeric materials , 2009, Microelectron. Reliab..

[40]  H. Reichl,et al.  Nano-particle enhanced encapsulants for improved humidity resistance , 2008, 2008 58th Electronic Components and Technology Conference.

[41]  J. Bauer,et al.  Structure property correlation of epoxy resins under the influence of moisture and temperature; and comparison of diffusion coefficient with MD-simulations , 2008, 2008 2nd Electronics System-Integration Technology Conference.

[42]  Michael Pecht,et al.  Hygroscopic swelling and sorption characteristics of epoxy molding compounds used in electronic packaging , 2003 .

[43]  W.D. van Driel,et al.  Interfacial Delamination Mechanisms During Soldering Reflow With Moisture Preconditioning , 2008, IEEE Transactions on Components and Packaging Technologies.

[44]  Jiang Zhou,et al.  Sequentially-Coupled Finite Element Transient Analysis with Hygroscopic Swelling , 2006, EuroSime 2006 - 7th International Conference on Thermal, Mechanical and Multiphysics Simulation and Experiments in Micro-Electronics and Micro-Systems.

[45]  Xunqing Shi,et al.  Direct Concentration Approach of Moisture Diffusion and Whole-Field Vapor Pressure Modeling for Reflow Process—Part I: Theory and Numerical Implementation , 2009 .

[46]  E. O'brien.  Durability of Adhesive Joints Subjected to Environemntal Stress , 2003 .

[47]  M. Yuen,et al.  Study of Interfacial Moisture Diffusion at Cu/Epoxy Interface by FTIR-MIR Technique , 2007, 2007 Proceedings 57th Electronic Components and Technology Conference.

[48]  A. Kinloch.  Interfacial Fracture Mechanical Aspects of Adhesive Bonded Joints—A Review , 1979 .

[49]  J. Fan,et al.  Direct Concentration Approach of Moisture Diffusion and Whole-Field Vapor Pressure Modeling for Reflow Process — Part II : Application to 3 D Ultrathin Stacked-Die Chip Scale Packages , 2009 .

[50]  G. Springer,et al.  Moisture Absorption and Desorption of Composite Materials , 1976 .

[51]  Y. J. Weitsman,et al.  Anomalous fluid sorption in polymeric composites and its relation to fluid-induced damage , 2006 .

[52]  Xuejun Fan,et al.  A Micromechanics-Based Vapor Pressure Model in Electronic Packages , 2005 .

[53]  J. Payer,et al.  The Effect of Immersion on the Breaking Force and Failure Locus in an Epoxy/Mild Steel System , 1992 .

[54]  Xin Lu,et al.  Moisture–absorption, dielectric relaxation, and thermal conductivity studies of polymer composites , 1998 .

[55]  Jiang Zhou,et al.  Effect of Non-Uniform Moisture Distribution on the Hygroscopic Swelling Coefficient , 2008, IEEE Transactions on Components and Packaging Technologies.

[56]  Jianmin Qu,et al.  Elastic modulus variation due to moisture absorption and permanent changes upon redrying in an epoxy based underfill , 2006, IEEE Transactions on Components and Packaging Technologies.

[57]  K. Takahashi,et al.  The critical humidity effect in the adhesion of epoxy to glass: role of hydrogen bonding , 2000 .

[58]  J. Bauer,et al.  Structure property correlation of epoxy resins under the influence of moisture; and comparison of diffusion coefficient with MD-simulations , 2008, EuroSimE 2008 - International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Micro-Systems.