Case Study: Tools to Assure Compatibility of Conformal Coatings and No-Clean Lead-Free Solder PastesAuthors: Emmanuelle Guene and Celine Puechagut
Company: Inventec Performance Chemicals
Date Published: 4/21/2015 Conference: SMTA China
Conformal coatings have been used for many years in markets requiring high reliability like automotive, military, aerospace and energy, to protect Printed Circuit Board Assemblies (PCBAs) operating under harsh environmental conditions such as high humidity, vibrations, presence of solvents, corrosive atmosphere... Use of conformal coating will increase in the coming years due to the demand to improve performance and lifetime of electronics, also to increase reliability of circuits due to miniaturization, and the growth of some markets including inverters, electronics in automotive, etc To ensure an optimal performance of a coating over a PCBA, cleaning the flux residues as well as all the contaminants before coating is a must. However, due to the additional costs of this cleaning step, sometimes it is not considered as an option in several markets (i.e, Automotive, Energy) using today no clean materials. This paper describes the performance of several kinds of conformal coatings (acrylics, polyurethanes, UV cured) over no-clean lead free solder paste residues. The physical and chemical compatibility will be assessed using several techniques.
After a description of the coatings and pastes chemistries used in the study, the compatibility before curing will be investigated (influence of viscosity, surface tension, thickness ... ) Second, the adhesion properties of the coatings after curing on different surfaces including lead free solder paste residues will be evaluated. Finally, Surface Insulation Resistance (SIR), Electrochemical Migration (ECM) tests and Bono corrosion test - which has been proven to better differentiate the nature of solder pastes residues- will be used for the chemical compatibility. It will be shown that several tools are necessary and complementary to anticipate the performance of conformal coatings with no-clean pastes residues due to the different kinds of coatings and pastes chemistries.
conformal coating, solder paste, compatibility, reliability, adhesion
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