Optimization of flip-chip laser soldering process

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Dr. Gordon Péter Róbert
Department of Electronics Technology

In my thesis work I had to verify experimentally a pre-defined simulation model in order to confirm the validity of this model. I studied the operation of the model, I tried to find correlation between input and output parameters. I have found those parameters in the model that has to be measured

I examined whether the modification of the structure of the model can affects the results. The feasibility of using traditional FR4 substrate instead of low-temperature resistant polymethyl methacrylate substrate was evaluated .

I designed an experiment, which was performed systematically with modified parameters. During a test cycle lead-free solder paste was printed on the substrate manually. Then the IC was placed into proper position by a Fine Placer equipment. The soldering of the IC was made by a Coherent AVIA UV Nd:YAG solid state laser at 355 nm wavelength. The soldering process was optimized for the maximum shear strength of the flip-chip because the theory of the model was also established for this parameter. After the soldering push off shear test was performed. At a given energy the soldering time was swept and a definite maximum shear strength was observed The soldering times (which belong the maximum shear strength) were plotted in the function of supplied energy then a curve was fitted .

After the appropriate modification the trend of the fitted curve was compared to the corresponding results of the model. This curve determines how much soldering time needed at a given pulse energy in order to get the maximum value of the shear strength.

After some numerical correction I found that the model describes the laser soldering process of the flip-chip onto PMMA substrate well.

I consider the verification of the theoretical model success, because the mathematical mapping of the experiments is similar to the mapping of the model.


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