Enhanced Polymer Passivation Layer for Wafer Level Chip Scale ...

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5.2.2 Material Properties Elements used for simulation were the eight node SOLID45 brick and the VISCO107 elements. Other than the solder balls modeled by VISCO107, all the rest of the materials in the package were modeled by eight nodes SOLID45. As taken from the ANSYS element library, SOLID45 is used for 3-D modeling of solid structures. It is defined by eight noded elements and has three degrees of freedom at each node. It has the capability to model creep, plasticity, swelling, and other deformation features. The VISCO107 element also has eight nodes and three degrees of freedom at each node. It is used to model rate dependent plasticity. This element is chosen for solder defined with the Anand model, while the SOLID 45 element is used for solder defined with elastic-plastic-creep model. All of the materials in the package were modeled as isotropic except for the PCB which was modeled as orthotropic. For the Sn3.0Ag0.5Cu solder, material properties used in the Anand model are shown in Table 5.2. The material properties for the finite element models of both WLCSP packages are shown below in table 5.3. 110
5.2.3 Meshing Table 5.2 Anand constants SAC 305 [112] Table 5.3 Material Properties of models Material Elastic Modulus (GPa) 111 CTE ppm/ o C Possion’s Ratio PCB 17(x,z) , 7(y) 15(x,z) 67(y) 0.39 Solder Ball 30 25 0.35 Silicon Die 162 2.54 0.28 SolderBrace 4 14 0.3 PECVD SiO2 80 0.5 0.25 Accuracy of the FE model depends on not only the accuracy of the materials properties, but also the proper meshing. In this study, the model was built from the top down. The mesh
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Enhanced Polymer Passivation Layer
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SolderBrace coatings were low tempe
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Table of Contents Abstract ........
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4.4 Failure Analysis ..............
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List of Figures Figure 1.1 Trends i
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Figure 3.17 SAC305 Reflow profile .
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CHAPTER 1 INTRODUCTION In the era o
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This effect changes the package to
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1.4 Solder Joint Fatigue Figure 1.2
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leading to the solder joint failure
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umped wafers. The coating is stenci
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11 Bumped Wafer Print over ball Pre
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2.1 Chip Scale Package Technology C
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Mountable with conventional assembl
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Figure 2.3 Cross section of a typic
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Table 2.1 Comparison between tradit
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In-Situ Bumped Wafers Placed Prefor
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of solder joint failure, and they o
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(a) (b) Figure 2.8(a). Metalized ph
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"underfilled" structure distributes
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have generally been the modificatio
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are “low temperature” wafer lev
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2.3.4 Optimized SolderBrace Materia
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CHAPTER 3 WLCSP DIE FABRCIATION In
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Table 3.1 Test Die used for Reliabi
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Figure 3.4 Fabrication Process Flow
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spin coating. A layer of light sens
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layer, is investigated as a potenti
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10. Final cleaning: After the passi
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Cyclopentanone, a colorless liquid
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used to check the basic spin and ph
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Figure 3.7 SolderBrace film thickne
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6. Post-UV exposure bake: This step
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8. Pattern characterization: The su
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offers the optimum flux release cha
Page 71 and 72: fatigue resistance, lower cost SAC
Page 73 and 74: Figure 3.12 Solder Ball Placement M
Page 75 and 76: of solder balls to the holes on the
Page 77 and 78: of thermal shock. If the temperatur
Page 79 and 80: Figure 3.17 SAC305 Reflow profile -
Page 81 and 82: foaming and high performance cleane
Page 83 and 84: - Polish clean: used the optimized
Page 85 and 86: Figure 3.22 SolderBrace printed waf
Page 87 and 88: Voids Figure 3.25 SolderBrace Mater
Page 89 and 90: cutting speed was set at a low valu
Page 91 and 92: Figure 4.2 Process Flow of Board As
Page 93 and 94: pitch, and bump diameter), and subs
Page 95 and 96: 4.2.4 X-Ray Inspection Figure 4.5 R
Page 97 and 98: Figure 4.6 Air to air thermal cycli
Page 99 and 100: Figure 4.7 Thermal Cycling Setup 87
Page 101 and 102: 4.4 Failure Analysis The main purpo
Page 103 and 104: Figure 4.10 Pad cratering failure o
Page 105 and 106: CHAPTER 5 FINITE ELEMENT ANALYSIS I
Page 107 and 108: 5.1.1 Modeling Approaches Due to th
Page 109 and 110: are shown in Figure 5.2. However, t
Page 111 and 112: 5.1.2 Material Properties Many pack
Page 113 and 114: strain rate sensitivity. The evolut
Page 115 and 116: Morris et a1 [96] used a double pow
Page 117 and 118: focus on the time-dependent effects
Page 119 and 120: 5.2 Modeling Procedure In this proj
Page 121: Figure 5.6 The diagonal symmetry mo
Page 125 and 126: direction, but that the surface is
Page 127 and 128: PREP7 tref,398 ! set zero strain te
Page 129 and 130: 5.2.7 Thermal Fatigue Life Predicti
Page 131 and 132: CHAPTER 6 CONCLUSIONS Wafer level c
Page 133 and 134: References 1. Future Trends in Elec
Page 135 and 136: 23. Electronic Packaging and Interc
Page 137 and 138: 48. Ultra Low Stress and Low Temper
Page 139 and 140: 70. Factors for Successful Wafer-Le
Page 141 and 142: 92. Microstructural Dependendence o
Page 143: 111. Nonlinear Analysis of Full Mat
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Enhanced Polymer Passivation Layer for Wafer Level Chip Scale ...

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