Enhanced Polymer Passivation Layer for Wafer Level Chip Scale ...
Enhanced Polymer Passivation Layer for Wafer Level Chip Scale ... Enhanced Polymer Passivation Layer for Wafer Level Chip Scale ...
the bumping pads. The peak temperature should be high enough for good wetting, but it should not be so high as to cause assembly damage or excessive intermetallic growth, which reduces the solder joint fatigue resistance and makes the solder joint brittle. In the cooling phase the parts should be cooled down as fast as possible in order to acheive small metal grains and hence a higher fatigue resistance of the solder joint. Too slow a cooling ramp will decrease the strength and give the joint a rough surface. In addition, reflow in nitrogen can help to prevent oxidation of the solder ball surface [73-74]. A nitrogen purged Heller 1800 reflow oven with nine heating zones was used for this work. - Reflow profile: The reflow profile is one of the important variables that significantly impacts product yield in the manufacturing process. In soldering, it is a complex set of time-temperature data related with an objected heat up and cool down. It is often measured as temperature values for a variety of process dimensions including slope, soak, time above liquidus, and peak [75]. Figure 3.17 is the reflow profile used in this research to form the solder joint on the wafer that met the requirement provided by the solder sphere vendor. 66
Figure 3.17 SAC305 Reflow profile - Solder wetting with different fluxes: Figure 3.18 shows the solder wettability with TSF-6592 no-clean flux and Lord no-flow flux after thermal reflow. Obviously, the no-clean flux had a very good solder wetting performance while the no-flow flux did not wet the solder onto the bumping sites. To investigate the root cause, different heating methods and bond pad cleaning processes were tried such as hotplate, higher reflow temperature, acid cleaning with various levels, etc. However none of these resolved the problem. 67
- Page 27 and 28: Mountable with conventional assembl
- Page 29 and 30: Figure 2.3 Cross section of a typic
- Page 31 and 32: Table 2.1 Comparison between tradit
- Page 33 and 34: In-Situ Bumped Wafers Placed Prefor
- Page 35 and 36: of solder joint failure, and they o
- Page 37 and 38: (a) (b) Figure 2.8(a). Metalized ph
- Page 39 and 40: "underfilled" structure distributes
- Page 41 and 42: have generally been the modificatio
- Page 43 and 44: are “low temperature” wafer lev
- Page 45 and 46: 2.3.4 Optimized SolderBrace Materia
- Page 47 and 48: CHAPTER 3 WLCSP DIE FABRCIATION In
- Page 49 and 50: Table 3.1 Test Die used for Reliabi
- Page 51 and 52: Figure 3.4 Fabrication Process Flow
- Page 53 and 54: spin coating. A layer of light sens
- Page 55 and 56: layer, is investigated as a potenti
- Page 57 and 58: 10. Final cleaning: After the passi
- Page 59 and 60: Cyclopentanone, a colorless liquid
- Page 61 and 62: used to check the basic spin and ph
- Page 63 and 64: Figure 3.7 SolderBrace film thickne
- Page 65 and 66: 6. Post-UV exposure bake: This step
- Page 67 and 68: 8. Pattern characterization: The su
- Page 69 and 70: 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: of thermal shock. If the temperatur
- 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 and 122: Figure 5.6 The diagonal symmetry mo
- Page 123 and 124: 5.2.3 Meshing Table 5.2 Anand const
- Page 125 and 126: direction, but that the surface is
- Page 127 and 128: PREP7 tref,398 ! set zero strain te
Figure 3.17 SAC305 Reflow profile<br />
- Solder wetting with different fluxes: Figure 3.18 shows the solder wettability with<br />
TSF-6592 no-clean flux and Lord no-flow flux after thermal reflow. Obviously, the<br />
no-clean flux had a very good solder wetting per<strong>for</strong>mance while the no-flow flux did<br />
not wet the solder onto the bumping sites. To investigate the root cause, different<br />
heating methods and bond pad cleaning processes were tried such as hotplate, higher<br />
reflow temperature, acid cleaning with various levels, etc. However none of these<br />
resolved the problem.<br />
67
Change language