Customer Issue: The helpline received a call from Naval Supply Systems Command to provide assistance in removing 300 pin edge connectors from PWB's. "I am looking for an assist in the removal of some connectors from 12 NON-RFI CCA's. I need the connectors to be able to be re-used. The current contractor lacks the skills, materials, and processes to remove the connectors without damaging them. Can you help?"
by Michael Morrison
Initial Inspection
Initial inspection of the circuit card assembly highlighted several challenges involved in removing the flex to rigid edge connector.
1. The connector mates to the board on both sides with flex ribbon style routing.
2. The board is covered with conformal coating, including the edge fingers and flex cable terminations mounted to the board.
3. The flex cable terminations are fragile and easily dam aged.
4. The rigid portion of the connector is riveted to the circuit board assembly in three places.
5. Adjacent components interfere with access to some of the flex termination pins.
6. The board has heavy ground planes on both sides.
Step 1
 The first step was removing the conformal coating from the flex connection terminations. IPC-7721 procedure 2.3.1 was used to determine the type of coating and the best method for removal. The flex cable was tested to ensure it would not have a negative reaction to using solvents for coating removal. Acetone (solvent method 2.3.2) was used to remove the bulk of the coating. The connector was immersed in the solvent while the flex terminations were scrubbed with an acid brush. Any residual coating was removed using the thermal method (2.3.4). After the conformal coating was successfully removed, the board was thoroughly cleaned with isopropyl alcohol.
Step 2
Any components interfering with access to the connector flex terminations were removed and saved. These components were not required to be "salvaged" or re-used, but our customer did want all components and wiring removed from the CCA to be saved and returned upon project completion.
Step 3
Once the coating and adjacent components were removed, the next step was to remove the solder from the flex terminations and board edge fingers. IPC-7711 procedure 4.1.3 was used as a guideline. RMA flux was liberally applied to the termination area to aid in heat transfer. Solder wick impregnated with RMA flux was selected to ensure compatibility with the external RMA flux already applied. Additional flux was applied to the wick as needed to ensure fast and complete solder removal from each land site.
Step 4
After all excess solder had been removed from the flex termination/CCA land site, the connector was ready for step 5. A small solder fillet was evident between the flex termination and the CCA land. In this step each flex "finger" is heated while a sharp probe is used to lift the finger off the land site. As soon as the "finger" or termination is lifted the soldering iron is moved to the next site. This action was repeated until the entire row of fingers had been lifted from the board land sites.
Step 5
The connector was now completely de-soldered but still hard mounted to the CCA with three rivets. These rivets were removed by drilling out the swagged rivet flange using a mini drill press.
Step 6
The next step was separation. Once the flex was de-soldered and the rivets drilled out, the connector was ready to fall off the CCA. The board was placed on a flat surface and the connector was pulled from the CCA taking care not to damage any of the now free flex connector terminations.
Step 7
The connectors were then thoroughly inspected. A few fingers had exposed copper which occurred during the conformal coating removal process. A solder coating was re-applied to all the connector fingers using the solder pot dip method. This restored the connector to its original condition and provided insurance against future solderability issues.
Conclusion
Upon receipt of the connectors, the NSSC responded, indicating that the EMPF was able to fulfill their requirements, saving them valuable time and avoiding unnecessary expense. Since the connectors were removed from the circuit boards without damaging any of the components, the NSSC was not required to prepare new test modules for bench/flight testing. New test modules would have taken three months to develop, and would have cost approximately $40,000.
 Sometimes a call to the EMPF Helpline can make all the difference. If you find yourself in a jam and you do not know which way to turn, call the EMPF Helpline at 610-362-1320. We are always ready to put our team of Engineers and Technicians on your problem, no matter how big or small.
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