Original Date: 05/01/2000
Revision Date: 01/18/2007
Information : Circuit Card Assembly: Conformal Coating
Previously, Northrop Grumman Defensive Systems Division (DSD) used a manual spray method for applying conformal coating to circuit card assemblies. Per MIL-I-46058, this process was performed in a ventilated booth using an acrylic coating thinned with methylethyl ketone and toluene, both hazardous substances. When required, the conformal coating was removed by using Freon TMS, an ozone-depleting chemical (ODC). Additionally, the boards being coated were manually masked and demasked to keep coating out of specified areas of a given circuit card assembly (CCA). In 1996, Northrop Grumman DSD acquired a Nordson Select Coat System to automate its conformal coating process and eliminate environmental hazards.
The Nordson Select Coat System uses a robotic five-axis spray head to selectively apply conformal coating. This microprocessor-controlled system also utilizes a low pressure, non-atomized spray to flow coat the circuit card assemblies. Other process improvements included switching to a conformal coating material with lower levels of volatile organic compounds (VOCs); performing the process in a continuously ventilated work cell; and eliminating Freon TMS by changing to a semi-aqueous cleaner.
These changes to Northrop Grumman DSD’s conformal coating process has resulted in a 50% reduction in touch labor by dramatically reducing the assembly masking and demasking steps. Furthermore, the company eliminated the use of hazardous materials, substantially reduced VOCs and ODC emissions, and improved coating repeatability.
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