Automotive optoelectronic components submitted to thermal shock: Impact of component architecture on mechanical reliability

Abstract

New LED technologies & modules allow glare-free automotive lighting. Valeo solutions include the first high-definition LED lighting system. These LEDs technology endure extreme tests conditions in form of thermal shocks or mechanical vibrations to insure reliability under the lifetime of automotive usage. Strict regulations require lead-free solders. Advanced optimization of LEDs for automotive lighting led to multilayered and miniaturized stack-ups. The first lead-free solders were revealed as a weak part of the electronic components and LED assembly. Enormous efforts have been spent on optimizing the lead-free solder material, design and reflow process. However, component miniaturization can also lead to high thermal gradients. Present work analyses the relation between component architectures and thermal shock induced fatigue damage. First, damage after N1 and N2 thermal shock cycles was characterized experimentally. Genuine sample preparations by a Cross polisher followed by high-resolution SEM observations reveal void growth in the solder material and cracking in the current circuit Layer. A two-scale finite element model reproduces both damage types. Simulation results can help to provide design improvements on the component architectures and modules to avoid (minimize) both damage types.