Is There a Perfect Ribbon-Bond Design?

What Was Investigated?

The study uses Finite Element Analysis (FEA) to investigate how ribbon thickness and loop height influence the temperature and equivalent plastic strain of aluminium ribbon bonds under power and thermal cycling. For the design optimization, these parameters are treated as competing objectives.

The Technical Trade-Off

At constant ribbon width, a lower ribbon thickness leads to a higher ribbon temperature, while a greater ribbon thickness increases the equivalent plastic strain at the bond interface.

A greater loop height slightly increases the ribbon temperature and also increases the equivalent plastic strain only slightly. Ribbon thickness therefore has a stronger influence on equivalent plastic strain than loop height.

Why Is There No Single Optimal Design?

In the multi-objective optimization, ribbon temperature and equivalent plastic strain are minimized simultaneously. The resulting Pareto front shows that improving one objective can lead to a deterioration of the other.

The paper therefore does not identify a single solution that optimizes both objectives simultaneously. Instead, it results in a set of Pareto-optimal solutions between which a technical trade-off must be selected.

Practical Significance

The Pareto front can be used to select suitable combinations of ribbon thickness and loop height.

However, the paper explicitly points out that additional constraints such as manufacturability, available bonding tools, ribbon width, and available package space must be included in the final design decision. The effects of a selected geometry on the overall power module should also be evaluated.