Evaluating the Effects of Plasma Treatment Prior to Conformal Coating on Electronic Assemblies to Enhance Conformity of Coverage
Authors: John D. Vanderford, MSEE, Ann E. Paxton, and Dave Selestak Company: Desich SMART Center and Nordson MARCH Date Published: 9/27/2015
Abstract: The corrosion of Nickel-Palladium-Gold (Ni-Pd-Au) finish terminals in humid environments is known to be reduced with the application of a conformal coating such as acrylic. Corrosion has a higher rate of occurrence around the terminal ‘knee’ of a surface mount component, which may be reduced with the application of conformal coatings. Although radio frequency (RF) plasma processing is generally known to enhance conformity of conformal coating to surfaces through ionic bombardment, the effect on the functionality of assembled printed circuit boards (PCB) is not as well known. The purpose of this study is to assess whether RF plasma processing can enhance the adhesive and coverage qualities of an acrylic conformal coating on PCBs, specifically on Ni-Pd-Au terminals with a knee, and if plasma processing has an effect on the electrical functionality of components and fully assembled PCB. Optical metrology was used to quantify and photograph the enhanced knee surface after boards were plasma processed and conformally coated with acrylic; electrical testing of printed circuit boards was used to determine electrical functionality. Results show that plasma processing can enhance the quality of the conformal coating as well as increase thickness of the coating around the knee of a terminal. Settings of RF power, process gas, process pressure, and plasma process time were used to come to this result.