Original Date: 05/01/2000
Revision Date: 01/18/2007
Information : Circuit Card Assembly: Cleaning
Prior to the Montreal Protocol, Northrop Grumman Defensive Systems Division (DSD) used Freon TMS to clean contaminants (predominately flux) from circuit card assemblies. This procedure was performed after each soldering operation within prescribed time limits. With the initiation of ozone depleting chemical (ODC) regulatory mandates in the mid-1990s, the company began developing a non-ODC cleaning process to replace its traditional chlorofluorocarbon cleaning methods.
Northrop Grumman DSD replaced its previous circuit card assembly (CCA) cleaning method with an automated semi-aqueous process that used a non-ODC compound (Axarel) and a closed-loop, zero-discharge system for the process liquids. This approach improved the cleaning process capability twenty-fold, eliminated more than half of the associated operations, and decreased ODC emissions by 39 tons per year (Figure 2-3). Additionally, the closed- looped system provided a significant reduction in process waste. The entire system only needs to be shutdown approximately every 12 to 18 months for cleaning and solvent replacement.
By changing to an automated, non-ODC-based cleaning system, Northrop Grumman DSD increased its cleaning performance, reduced the cleaning operation steps by 56%, and realized more than $2 million in conservation savings on ODCs. Lessons learned from using this process include: Equipment design and ventilation helped minimize the cleaning agent odors.
Since closed-loop filter membranes did not last as long as expected, they were replaced with carbon/mix bed resins.
Bacteria growth must be monitored in solution tanks, and can be controlled through periodic heating and chlorine-flushing during solution replacement.
Although higher temperatures clean and rinse better, they must be weighed against increased air emissions.
Application limitations exist with some assemblies due to non-submersible parts.
Figure 2-3. In-line Cleanliness Data
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