Considerations for the long term reliability of PCBs in harsh environmental conditions

Creep corrosion failures have recently been seen on all surface finishes. The increase in occurrence of this phenomenon is a result of the convergence of alternative surface finishes, developed to support RoHS compliant, lead-free, fine-pitch technology and an overall increase in the use of electronics in harsh environments. It has taken time and extensive investigation to understand the root cause for these corrosion failures. There are many factors in play which affect the ability of an electronic assembly to withstand harsh environments. When reviewing an electronic assembly prior to it being placed in the field, the design, materials of construction, surface finish, surface finish application, final board cleaning and assembly process and materials all play a role in its long-term reliability. Many initial studies focused on single aspects of the assembly. It was discovered however, that a multi-tiered approach is required to achieve the most robust RoHS compliant assembly. The following paper is a discussion on surface finishes, assembly materials, test methods and assembly considerations for building more reliable circuit boards that meet the specific requirements of harsh environment deployment.