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Critical Considerations for Conformal Coating Reliability

Presenter: Jason Keeping, P. Eng.
Company: Celestica Inc.
Date Published: 3/22/2011

Description: Conformal Coating is a very mature process and application technique, however the importance of conformal coating is now re-emerging as the industry is coping to deal with changes associated with Pb-free and to drive cost out of the associated coating processes. Two key requirements for this success is for the Conformal Coating material to be where required as per design along with adhere and maintain this coverage for its intended expectancy, both for the assembly and the Conformal Coating material.

Cleaning is a key input process for Conformal Coating. The single most common deterrent to Conformal Coating adhesion being surface contamination (lack of surface energy) that may lead to corrosion, insulation breakdown, poor adhesion and subsequently, failure of the Conformal Coating. This information is critical for Aerospace, Military, Industrial customers and any other products that may be exposed to harsh environmental conditions with either lead free or mixed conditions requiring Conformal Coating.

This paper will describe the results of extensive review of Industry information on surface energy requirements; raw card manufacturing techniques with specific focus on solder mask type and finish properties (i.e. gloss, satin, and matte finish) and their interaction with various environmental tests to increase the reliability of a Conformal Coating process along with identify defects that may require further investigation for manufacturability optimization.

Eleven solder masks from ten key suppliers were investigated. This paper will discuss the outcomes of the evaluation and the critical variables that were tested utilizing a specific profile for a Harsh Product HASS test along with various requirements from both IPC-HDBK-830 and IPC-CC-830 standards that were used to execute the test plan. Overall, not all product qualification tests associated with HARSH were completed, but did provide fundamental reliability data on this topic for future review and work that can be completed.

Key Words: 

Conformal Coating, Surface Energy, Surface Tension, Process Yields/Reliability

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