"Effects of warpage on fatigue reliability of solder bumps: experimental and analytical studies".Abstract: PWB (Printed Wiring Board) An alternate term for printed circuit board. See printed circuit board. and component warpage results principally from CTE (Coefficient of Thermal Expansion) The difference between the way two materials expand when heat is applied. This is very critical when chips are mounted to printed circuit boards, because the silicon chip expands at a different rate than the plastic board. mismatch among the materials that make up the assembly. Warpage occurring during surface-mount reflow (1) The process of heating and melting the solder that has been screen printed onto a printed circuit board in order to bond chips and other components to the board. Surface mount chips (SMT) use the reflow method. Contrast with wave soldering. See also reflowable text. processes and normal operations may lead to severe solder bump reliability problems. This research studied the effect of initial PWB warpage on the low cycle thermal fatigue reliability of solder bumps in plastic PBGA PBGA Plastic Ball Grid Array packages, using experimental and analytical methods. A real-time projection moire Pronounced "mor-ray" and spelled "moiré." In computer graphics, a visible distortion. It results from a variety of conditions; for example, when scanning halftones at a resolution not consistent with the eventual printed resolution or when superimposing curved patterns on one warpage measurement system was used to measure the surface topology of assembly samples at different temperatures. The thermal fatigue reliability of solder bumps was evaluated from experimental thermal cycling tests and finite element simulation results. 3-D models of PCBs with varying board warpage were used to estimate solder bump fatigue life for different types of PBGAs mounted on PWBs. To improve the accuracy of FE results, the projection moire method was used to measure the initial warpage of PWBs, and this warpage was used as a geometric input to the FEM FEM Female FEM Finite Element Method FEM Feminine FEM Finite Element Model FEM Fédération Européenne des Métallurgistes (European Metalworkers' Federation) FEM Faculdade de Engenharia Mecânica (Brasil) . The simulation results were validated and correlated with the experimental results obtained using the projection moire technique and accelerated thermal cycling tests. An advanced prediction model was generated to predicted board level solder bump fatigue life based on the initial PWB warpage, package dimensions and locations, and solder bump materials. (Electronic Components & Technology Conference, May 2008) Authors: Wei Tan, I. Charles Ume, Ying Hung and C. F. Jeff Wu; charles.ume@me.gatech.edu. |
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