Circuit Card Assembly

Necessary Supplies for Circuit Card Assembly (CCA)

• Printed Circuit Board (PCB) for the desired CCA
• Component layout drawing for the CCA
• Solder mask stencil(s) for the CCA
• PCB stenciling fixture
• Tape for attaching the stencil to the fixture
• A larger scrap PCB to serve as a spacer and platform for the CCA's PCB
• Solder paste and a mud pan
• A tool (such as a putty knife or razor blade) for applying and removing excess solder paste
• All electronic components required for the CCA
• A white sheet of paper
• Tweezers (type "2AD" are ideal)

Assembly Instructions

1. Place the spacer PCB into the fixture's corner so that the CCA's PCB height will be flush with the top of the fixture's edge guides.
2. Apply tape to one edge of the stencil; this will serve as a hinge.
3. Position the CCA's PCB in the fixture's corner on top of the spacer PCB.
4. Align the holes in the stencil with the component solder pads on the PCB.
5. Tape down the edge of the stencil to secure it to the fixture.
6. Open the solder paste container and remove the plastic surface shield.
7. Use the tool to take a small amount of paste from the container or from the plastic shield.
8. Apply the solder paste to the top edge of the mud pan.
9. Return the plastic shield to the paste container, ensuring it is closed tightly.
10. Spread a bead of paste into the holes in the stencil, ensuring it fills the holes completely.
11. Using the tool, remove the excess solder paste from the stencil surface by scraping it off at a steeper angle.
12. Lift the stencil slowly and carefully off the PCB.
13. If you have additional PCBs of the same type, repeat the steps above to apply solder paste to them.
14. Place the solder-pasted PCBs on a white sheet of paper.
15. Use the tweezers to gently place the components onto the solder paste on the PCB, aligning them with the correct solder pads.
16. Pay attention to component values and orientation, ensuring they match the indicators on the PCB.
17. Once all components are placed, transfer the paper with the populated PCBs to the re-flow oven station.
18. Follow the reflow solder procedure:
    1. Turn off the external cooling fan.
    2. Load the populated PCBs onto the oven tray, ensuring they are properly elevated using existing PCBs in the oven.
    3. Set the top dial to Convection Bake and adjust the temperature dial to 180 °C.
    4. Turn on the thermometer and confirm it reads in Celsius.
    5. Switch on the oven power and wait for the thermometer to reach 180 °C (approximately 4 minutes).
    6. Turn the temperature dial to the "Toast" setting.
    7. Switch off the oven power when the temperature reaches 230 °C.
    8. Wait for the temperature to fall to 215 °C.
    9. Open the oven door and turn on the external cooling fan to "High".
    10. Wait for the temperature to fall below 80 °C.
    11. Using large tweezers, transfer the circuit card assemblies to a granite slab for further cooling.
19. The PCBs have now been transformed into circuit card assemblies (CCAs).
20. Carefully inspect each CCA for any solder bridges, lifted leads, and missing or crooked components using an eye loop. If any imperfections are found, make the necessary corrections using the soldering station.

Connectors

• Refer to the model of the circuit card to determine the correct locations for the connectors. (A screenshot of the specific CCA model should be present at the end of this general instruction.
• Solder the connectors onto the circuit card following these steps:

1. Prepare the connectors by ensuring they are clean and free from any dirt or debris.
2. Place the circuit card on a stable work surface and secure it in place.
3. Apply flux to the solder pads where the connectors will be soldered. Flux helps to improve solder flow and wetting.
4. Position the connectors on the solder pads, aligning the pins or terminals with the corresponding holes or pads on the circuit card.
5. Secure the connectors in place temporarily using small pieces of tape, a suitable fixture, or by first soldering one or two pins to prevent them from moving during the soldering process.
6. Prepare your soldering iron or soldering station by ensuring it is heated to the appropriate temperature for the solder you are using.
7. Take a small amount of solder on the tip of the soldering iron and touch it to the solder pad and connector pin simultaneously.
8. Allow the solder to flow and create a good joint between the pad and the connector pin. The solder should form a smooth, shiny fillet around the joint.
9. Repeat the soldering process for each pin or terminal of the connector, ensuring proper heat and solder flow for each joint.
10. Inspect the solder joints visually to ensure they are smooth, shiny, and free from any cold solder joints or solder bridges.
11. Once you have completed soldering all the connectors, allow the circuit card to cool down before further handling.
12. Perform a thorough inspection of the soldered connectors and surrounding areas to ensure the connections are secure and there are no visible defects.

CCA Cleaning Protocol

1. Put on nitrile gloves before starting the cleaning process. This step is optional but recommended to protect your hands from drying out and potential irritation caused by the cleaning solutions.
2. Manually remove any heavy brown or black flux deposits from each CCA using isopropyl alcohol (IPA) and a stiff brush or cotton swabs.
3. Rinse the CCAs with IPA to wash away any remaining sticky residue.
4. Turn on the heat for the ultrasonic cleaner.
5. Place the CCAs into the IPA bath and seal the container.
6. Place the IPA bath into the ultrasonic cleaner and sonicate the CCAs for 3 minutes at an ideal bath temperature of about 50°C.
7. Rinse both sides of each CCA with clean IPA as it is removed from the sonication bath.
8. Blow dry each CCA individually with compressed air to remove any remaining moisture.
9. Place the CCAs into the base wash, which is a pH 9 to pH 11 solution of sodium hydroxide (NaOH), and seal the container.
10. Place the base wash into the ultrasonic cleaner and sonicate the CCAs for 3 minutes at an ideal bath temperature of about 50°C.
11. Use tweezers to transfer the CCAs to a rinse bucket.
12. Rinse the CCAs thoroughly with a large amount of tap water.
13. Sonicate the CCAs in clean distilled water for 3 minutes at an ideal bath temperature of about 50°C.
14. Test the pH of the water and ensure it is below 6. If the pH is 6 or higher, or if any discoloration, cloudiness, or particles appear in the water, replace it.
15. Blow dry the CCAs with clean, compressed air to actively remove all remaining moisture. Do not let them "air dry" by evaporation.
16. Remember to turn off the heat for the ultrasonic cleaner once the cleaning process is complete.
17. Inspect the CCAs for any remaining flux residue. If needed, repeat the cleaning process.