SMT007 Magazine

SMT007-Aug2019

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66 SMT007 MAGAZINE I AUGUST 2019 Feature by Marissa Pati and Ana "Lety" Campuzano-Contreras BAE SYSTEMS, AUSTIN, TEXAS Abstract The development of an automated cir- cuit card assembly (CCA) conformal coat- ing process using a low-outgassing polyure- thane material was essential for meeting the increase in customer demand from 3,000 to 60,000 units per year. Low-outgassing poly- urethane conformal coating is used for protec- tion against humidity and tin whisker mitiga- tion. When increasing production throughput requirements, it is necessary to eliminate vari- ation and increase production capacity by automating processes. Manual processes in manufacturing can lead to defects, increased variability, and additional manufacturing time. To begin the process improvement of automating spraying a low-outgassing poly - urethane conformal coating, several machine and material parameters were considered dur- ing the evaluation. A selective conformal coat- ing machine was chosen and the following parameters were determined to be critical to the process: thinner-to-material ratio, atomiz- ing air pressure, material syringe pressure, noz- zle distance from the substrate, nozzle speed, material flow rate, number of coats, and cur- ing requirements. These parameters were ver- ified by performing an adhesion by tape test per ASTM D3359-17 (Standard Test Methods for Rating Adhesion by Tape Test) in addi- tion to verifying conformal coat thickness and defects per J-STD-001 (Joint Industry Standard Requirements for Soldered Electrical and Elec- tronic Assemblies) requirements. Implement- ing a selective polyurethane conformal coat- ing spraying process has increased capacity capabilities and eliminated variations induced from the manual process. Background In the manufacturing of Class 3 circuit card assemblies, conformal coating can be criti- cal to the lifespan of the circuit card. For cir- cuit cards to withstand environmental factors Automated Conformal Coating of CCAs Using Polyurethane

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