PCB assembly requires an organized process to make sure that each component is arranged and soldered properly on the board. Here are a few guidelines to follow to ensure a properly assembled printed circuit board.
1. Avoid contaminating the surface of the board. Handle it by the edges. Contaminates such as oils makes it more difficult to solder. The solder joints may not be properly bonded to the board and detach easily, taking the component off the circuit.
2. Inspect the printed board for any errors. This would include any dents and bumps, discolorations, scratches and signs that the layers of the PCB have separated.
3. Further checks can be made, such as checking for any shorts and for continuity. This can be done through the use of an ohm meter.
4. Based on the PCB assembly design, gather all the components and arrange them in a neat and organized fashion. For example, group all resistors together and the capacitor in another. It will be good to have small separate containers for each of the components to prevent them from rolling all over the work surface. Locating them would also be much easier. Make sure that these containers are static proof, especially for semiconductors. Static can damage these components.
5. Next, start positioning the components on the board. Some people prefer to start arranging the passive components first, such as the resistors.
6. When using through-hole components, bend the component’s leads at the body at a 90-degree angle. Carefully insert the bent leads into the designated area of the printed circuit board. Pull the component through the hole so that it is tight against the surface of the board. If the component is likely to get hot when the PCB is in operation, mount it off the board by about a quarter of an inch. This will allow air to circulate around the component to prevent overheating, damage and burning. Slightly bend the component’s leads once through the hole so that the component is held in place while it is being soldered.
7. Carefully flip the board over so that the side where the leads is facing up. Solder the leads in place. Trim off extra lengths of the lead. As much as possible, trim close to the board.
8. Reworking may be needed when assembling PCBs. Some instances that would require a rework include diodes positioned backwards, misplaced resistors, or incorrect trace connections. There are a few things that can help in reworking during PCB assembly. These include a solder of braided copper tape and a solder sucker.
A solder wick acts like a sponge. This material is heated and then placed next to the soldered components. The wick will absorb the solder, removing the connection between the component and the board. This works well with single-sided PCBs but not effective when reworking 2-sided printed circuit boards that have plated though holes.
The best way to rework plated through holes is by using a solder sucker. This device has a plunger, which creates a vacuum that sucks the errant component off the board.
Another way to rework 2-sided boards with plated through holes is to carefully cut out the component. The board is flipped and the solder joint is heated just enough for the lead to be pulled out through the hole. This method may work, but often, the melted solder may occlude the hole and difficult to remove. If the new component is to be placed in this same area, the solder left behind can be reheated and the lead of the new component is pushed into the hole. Solder the leads again to make sure that the connection is good.
The PCB assembly process requires careful detail and attention to each step to make sure the product functions well. It takes time, patience, and more practice to get the techniques down pat.