This thesis demonstrates the feasibility of using finite element analysis to model the
thenno-mechanica1 effects of manufacturing processes on electronics interconnection.
The thesis has two significant complementary parts. The first of these explores
the modelling of heat transfer in a commercial solder reflow furnace to contribute to
the understanding of the non-unifonn distribution of heat on a printed circuit board
within the furnace. The second part of the thesis identifies the thermal stresses in a die
attach assembly using an electrically conductive adhesive, typically cured in a reflow
furnace, thereby indicating potential points of failure.
The first part of the thesis reports the calibrated modelling of a reflow furnace of commercial
complexity as part of the demonstration of the feasibility of creating a concurrent
engineering design tool for electronic interconnection. The application of a
technique using area proportional thermal conductances to model the convective heat
transfer between the furnace and board is demonstrated. The model explores the
effects of the mechanisms of heat transfer within the oven to show that this is more
uniform with the addition of convection and that edge heaters appear to have little
effect. In the second part of the thesis the effect of the material properties of glass transition
temperature, Youngs Modulus and coefficient of thermal expansion were quantified
using finite element modelling, to show that these properties significantly affect the
structural integrity of the interconnections constructed using conductive adhesives.
Electronic Speckle Pattern Interferometry (ESPI) methods are also shown to be an
effective method of validating such finite element models. This work required the
measurement of the viscoelastic properties of typical materials using novel specimen
preparation techniques. It is anticipated that the conclusions presented are conservative
because of the assumptions and sensitivity analyses made during the modelling
The combined results of the two parts of this work demonstrates the feasibility of
modelling the solder reflow process and highlights the potential of electrically conductive
adhesives as replacement for solder in high temperature applications. Promising
avenues for further work include improved non-linear modelling of
interconnection systems and understanding of the effect of rework, including reliability
assessment. In addition, further work remains to be carried out in the determination
of relevant material properties in representative configurations.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.