Product Assurance for Electronics in Harsh Environments
Dr. Pradeep Lall
Commercial electronics is increasing being used for the design, sustenance and life-extension of military systems. In most cases, the materials and interfaces in the commercial electronics are evolving faster than the availability of tools for life-prediction and risk mitigation for operation in harsh environments. Further, the tools and techniques developed for the reliability assessment in the commercial space are targeted for operating lifetime of 1-2 years, which are far shorter than the lifetimes expected in military systems. It is not uncommon for systems to be stored for long periods. High reliability is expected to assure mission readiness.
One of the technologies which is impacting the use of commercial electronics in military systems is the transition of the electronics to the use of copper-aluminum wirebonding. The existing wire-pull test standards are geared towards the use of gold wire and aluminum wire. The acceleration factors, quality assurance methods and the qualification test protocols for assurance of reliability of copper-aluminum wirebonds in harsh environments need development. The physics of failure based methods need to be rolled into existing standards and methods documents for mitigation of risk with the use of copper aluminum wirebonding.
Second of the technologies impacting semiconductor packaging is the introduction of leadfree solders. With the commercial electronics transitioning to leadfree solder and the declining availability of latest electronics technologies in leaded solder interconnects, tools and techniques are needed for the assessment and mitigation of risk related to the use of leadfree solders.
Research will focus on the study of the physics of failure mechanisms in Copper-Aluminum wirebonds and solder joints for the development of acceleration factors to allow for assurance of long-term storage reliability in harsh environments.
Correlation of the high-temperature and high-humidity with the operational reliability of copper-aluminum wirebonds will be established. Damage proxies for the initiation and progression of damage in wirebonds will be developed to allow for identification of pathways for ascertaining the accrued damage in components and assemblies that have been stored for long periods of time. The polarization curves and Tafel parameters will be measured for the copper-aluminum wirebond system for a number of commonly encountered pH values, and contamination concentrations and storage times. The measurements will be used for development of a multiphysics model for life prediction and assessment of remaining useful life.
High strain rate properties of solder will be measured for characterization of the stress-strain behavior, development of constitutive models and incorporation in finite element models for prediction of survivability of electronics. Focus will be on leadfree alloys after exposure to thermal aging similar to that experienced in storage of electronics.