Assembly Material/Flux Interactions and the Impact on Reliability
Authors: Ian J. Wilding, Gavin J. Jackson, Katherine Day, Richard Boyle, Michael Carter, Daniel Buckland Company: Henkel Ltd Date Published: 9/28/2014
Abstract: Extending long-term reliability of electronic assemblies is becoming more and more critical, especially within automotive electronics. This is driven by the general trends of higher operating temperatures, miniaturisation, increasing voltages and proliferation of the number of life-critical functions within a standard vehicle. Significant amounts of research have been dedicated to the development of high reliability alloys, fluxes and peripheral materials for use on standard printed circuit boards, such as conformal coatings, potting compounds and underfills. In isolation each of these materials offer specific significant benefits with regard to particular requirements pertaining to extended functional life; such as: thermal cycle resistance, electrochemical migration and impermeability to moisture ingress. Every material that is applied to a printed circuit board is a mixture of complex chemicals and has the potential for insitu reactions to occur with other assembly materials. The natural assumption is that all materials applied to a printed circuit board are inherently benign with regards to the other materials, in practicality this is not the case. In fact, evidence is already available to show that combinations of some materials that on paper would confer improved final assembly reliability can have the opposite effect. There are numerous potential interactions that can occur when combining organic materials onto a printed circuit board, such as inhibition of cure, reduced dielectric properties or changes within the physical properties of the assembly materials. This paper details some of the potential chemical interactions that can occur, the results of tests that quantify the effect of both positive and negative compatibility results, and a glimpse into the future of further understanding the role of consumable compatibility and electrical assembly reliability.