System Design Issues for Harsh Environment Electronics Employing Metal-Backed Laminate Substrates

Designing harsh environment electronics continue to increase in difficulty to a rapid increase in feature content while electronics packaging technologies are often providing less reliability. In addition, restricted under-the-hood airflow and integrated (mechatronic) designs are significantly increasing operating temperatures toward their maximum operating capability. To provide a cost effective design, automotive electronics designers are pursuing circuit board assemblies directly attached to a metal plate. For cost purposes, this metal plate can also be used as part of the module housing to provide protection, as well as thermal efficiency. Unfortunately, the metal backing can often further reduce component reliability due to increases in substrate coefficient of thermal expansion. The paper investigates the impact of metal attachment on component reliability as it investigates the use of several board attachment options. These analyses are compared to finite element modeling to further understand the causes of earlier failure. In addition, the impact of additional component encapsulants and conformal coatings are investigated. Because all attachment materials must meet a certain thermal performance (both initial design and long-term performance) the thermal efficiencies of these design options are investigated, as well as the delamination due to product life. Finally, failure analyses are presented and ensure that failures match expected characteristics.