1. PCB assembly: Application of solder paste
First, solder paste (a small grain of solder paste mixed with flux) is applied to the board. For this application, most PCB manufacturers use stencils (available in several sizes, shapes, and specifications all to spec) that only apply the correct amount of solder paste to certain parts of the board.
2. PCB Assembly: Placement of components
Unlike in the past, this stage of the PCB assembly process is now fully automated. Picking and placing of parts, such as surface mount assemblies, was once done manually and is now performed by robotic pick and place machines. These machines place components accurately into pre-planned areas of the board.
3. PCB Assembly: Reflow
Now, the solder paste and all surface mount components are in place. what do you do next Curing the solder paste to the correct specifications is critical to properly adhering PCB components to it. It's this relevant part of the PCB assembly process - reflow soldering. To do this, the component with solder paste and the components on it are passed through a conveyor belt, which passes through an industrial grade reflow oven. A heater in the oven melts the solder in the solder paste. Once melting is complete, the components are again moved on the conveyor belt and exposed to a series of cooler heaters. The purpose of these coolers is to cool the molten solder and allow it to solidify.
4. PCB Assembly: Inspection
After the reflow process, the PCB should be inspected to check its functionality. This stage helps identify poor quality connections, misplaced components and shorts due to the continuous movement of the board during reflow. PCB manufacturers employ multiple inspection steps, such as manual inspection, automated optical inspection, and X-ray inspection, to check board functionality, identify lower-quality solder, and find out any potential hazards. Once inspections are complete, the assembly team will make crucial decisions. Often boards are scrapped with several functional errors. On the other hand, if there are minor errors, the board is sent again for rework.
5. PCB assembly: Through-hole component insertion
Certain types of PCBs require the insertion of through-hole components along with regular SMD components, and this stage is dedicated to the insertion of such components. To do this, vias are created with the aid of which PCB components carry signals from one side of the board to the other. PCB through-hole insertion typically utilizes manual or wave soldering to achieve results.
6. PCB Assembly: Final Inspection
Now is the time for a second level inspection. Here, the assembled board is functionally tested, or the PCB is thoroughly inspected to monitor its electrical characteristics, including voltage, current or signal output. Today's manufacturers utilize a variety of advanced testing equipment to help determine the success or failure of a finished board.
7. PCB Assembly: Cleaning
Since the soldering process can leave a lot of flux residue in the PCB, it is critical to thoroughly clean the components before delivering the final board to the customer. To do this, wash the PCBs in deionized water. After the cleaning process, the boards are thoroughly dried using compressed air. The PCB assembly is now ready for customer inspection and inspection. Although the PCB assembly process steps are almost the same for all types of boards, there are still some variations in THT assembly, SMT assembly, and hybrid techniques.