Thermal Electric Analysis of Bond Wires Used in Automotive Electronic Modules

Bond wires are used in automotive electronic modules to carry current from external harness to components where flexibility under thermal cyclic loading is very essential between PCB (Printed Circuit Board) and connectors. They are very thin wires (few μm) made up of gold, aluminum or copper and have to undergo mechanical reliability to withstand extreme mechanical and thermal loads during different vehicle operation scenarios. Thermal reliability of bond wire is to make sure that it can withstand prescribed electric current under given boundary conditions without fusing thereby retaining electronic module's functionality. While carrying current, bond wire by virtue of its nature resists electric current flow and generates heat also called as joule heating. Joule heating is proportional to current flow and electrical resistance and if not handled properly can lead to thermal run away conditions.

In the present scenario the goal is to examine thermal reliability for bond wire when current flows for few milliseconds. Apart from dimensions of bond wire, its joule heating that varies with temperature makes thermal analysis complicated and hence emphases to consider coupled thermal electrical analysis. This paper focuses on formulation of numerical equation using finite difference method and solving using forward explicit scheme. While solving the numerical equation it is found that the nominal stability criteria i.e. Fo (Fourier number) < 0.5 is not valid and hence a new stability criterion is developed. The numerical equation was solved using Javascript™ and the calculations were in good agreement with experiment results & analysis tools. The developed equations can be useful for bench marking analysis tools before using them for detailed simulations.