Encapsulation in electronic packaging using finite element analysis
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Date
2002-03
Authors
Liew, Kong Ken
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Abstract
One of the problems in encapsulation is incomplete filling of the cavities. Incomplete
filling (short shot) or packing in just a few cavities effectively ruins all of the devices
loaded onto the tool. Thus it is necessary to find a way to minimize this problem. One of
the ways is by achieving balar.ced mold filling through gate designs, which is shown in
the present work. Both nllinerical method and empirical method are used in the analysis.
Finite element method is used to carry out flow analysis in the present work.
Two-dimensional Hele-Shaw approach is used in view of a very thin thickness of flow.
The pressure distributions and velocity distributions in th~ domain are predicted through
the analysis. The pseudo-concentration technique with an artificial diffusion term has
been used to track the liquid front during mold filling. The involvement of the artificial
diffusion term in the front tracking process prevents fluid sticking to the wall during
mold filling and also smoothens numerical oscillations. The first part of the analysis has
been carried out on the molding tools, namely the runner and the gate. Good
comparisons exist between the experimental results (Manzione, 1990) and the predicted
results for the flow in the runner and the gate. Gate width and depth are found to be the
most important parameters to control the pressure drop through the gate. However, gate
width is the preferred parameter as it has little effect on gate break off.
The above methodology has been extended to an industrial problem to study the
flow in a six-~avity transfer molding process. An empirical method which is a onedimensional
balanced filling algorithm has been used to design the gate widths. By
applying the appropriate boundary conditions, the polymer front was tracked at a certain
time to see if balanced filling of the six-cavity transfer molding process could be
achieved through the new gate widths. The results show that balanced filling could be
achieved through the algorithm.
The methodology described in the thesis for the mold filling can also be used in
other processes as in the injection molding process.
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Keywords
Finite element method is used to carry out , flow analysis in the present work