Step 1: Solder Paste Printing Solder paste printing is the first step in PCBA processing. We apply solder paste to the area of the printed circuit board where components need to be assembled. This step is accomplished by applying solder paste on the stainless steel template, which corresponds to the circuit board, and the solder paste drips from the holes of the template onto the PCB. 96.5% tin is gray and it contains 3% silver and 0.5% copper. In order to protect the environment, FS Technology uses lead-free solder paste. The solder paste will be heated and melted in step 3 and form a strong joint
Step 2: Pick and Place of Components The second step of the PCBA processing flow is to place the components on the PCB, which is completed by a high-speed SMT placement machine. At design time, the PCB designer creates a file, which is used to control the SMT device. The file identifies the X, Y coordinates of the PCB assembly, and thanks to this information, the pick and place machine accurately places the SMD components on top of the solder paste through the vacuum nozzle.
At the beginning, humans completed the picking and placement of components by manual soldering, but this is obviously not good for large-volume orders. In order to ensure fast turnaround, we use SMT assembly machines, which can ensure the consistency and accuracy of PCBA.
Step 3: Reflow oven melts and cures solder paste We need to use a reflow oven to melt and solidify the solder paste. It is best to use equipment with ten temperature zones for this process. The PCB is transferred to the reflow oven through the docking station. The oven can generate a maximum temperature of 250 degrees Celsius, which is enough to completely melt the solder paste. The melted solder paste will form a joint at the junction of the PCB and the component, forming a strong solidified solder joint after entering the cooler, which will create a permanent joint between the SMD component and the PCB.
Step 4: QC Check Due to the influence of many factors, the soldering quality of the circuit board may be poor. Since the circuit board is an essential component in electronic equipment, no matter how small the error is, it will lead to a circuit board short. Therefore, we need to use a variety of detection methods to ensure its quality.
Manual Inspection Almost all formal PCBA processing companies will require operators to conduct detailed and comprehensive PCB manual inspections. For a well-equipped assembly plant, the purpose of manual inspection is just a guarantee. Different components are installed on the PCBA board, while SMD patch components are smaller, and visual inspection of the circuit board may cause inaccurate detection due to fatigue of technicians. This detection method is more friendly to DIP components.
AOI Optical Inspection In high-volume assembly orders, AOI inspection is considered effective. This detection method refracts light through the PCBA solder joints, and observes the solder joints from multiple angles to ensure consistency with the standard board. The biggest advantage of this detection method is that it is fast and can process batch orders in a short time.
X-Ray Inspection: X-ray machines allow operators to observe the internal structure of printed circuit boards to find defects in their inner layers. This kind of testing equipment requires customers to pay extra fees, and usually we use it in complex and advanced circuit boards. If your assembly plant does not have skilled inspectors, please do not attempt this method of PCB inspection as it may result in rework or scrapped PCBs.
Step 5: Component Soldering Component introduction The PCB itself does not function and provides a carrier for electrical connections to electronic components. Various components are installed on different PCBA boards, including DIP components and SMD components.
DIP components are a larger and more common circuit board component that are mounted to a circuit board through through hole assembly. These holes are classified as plated through holes (PTH) and non-plated through holes (NPTH). The operator passes the pins of the DIP component through the holes in the PCB. These holes are connected to other holes and vias with copper traces. When these DIP components are inserted and soldered on the PCB, they make electrical connections with other holes in the same PCB as the designed circuit.
SMD components are the most popular electronic components in modern electronic equipment. The IC chip we often say is one of the SMD components. These components are soldered on the surface of the PCB in the form of patches. With the development of miniaturization trend, SMT assembly technology has gradually replaced DIP assembly.
Welding type The three most common soldering processes are manual soldering, wave soldering and reflow soldering.
Manual soldering is a way for electronics enthusiasts to make their own PCBA boards. Electronic enthusiasts insert the pins of the DIP component into the holes of the PCB, and then solder the pins on the soldering surface to death by a welding machine.
Reflow soldering is usually used in the SMT assembly process, which can easily complete the soldering of SMD components and ensure that these components are not damaged. When you choose a PCBA processing factory, please pay attention to whether the reflow soldering equipment used by the service provider is in ten temperature zones. Wave soldering is an upgraded version of manual soldering, which can complete the soldering work automatically. Once the PTH components are placed on the PCB, the PCB is placed on a conveyor belt and moved to a dedicated oven. Here, a wave of molten solder splashes onto the bottom layer of the PCB, where the component leads are located. This will solder all pins at once.
Step 6: PCB Functional Test When the PCBA is manufactured we need to test it. Functional test is an essential PCB test, which refers to checking whether the assembled PCBA can operate according to the design.
If any parameter of the PCBA shows unacceptable results, discard or scrap the PCBA following company standard procedures. The testing stage is very important because it determines the success or failure of the whole PCBA process.