What Should be Paid Attention to in PCB Soldering by Hand?
These You Should Pay Attention to in Handly PCB Soldering
PCB soldering is one of the most important parts of the electronic manufacturing. Some people may think that PCB soldering by hand is very easy, there is no technical content - not absolutely. Without the proper PCB soldering process quality assurance, it is difficult to achieve design goals in any well-designed electronic device.
1. Double-check the appearance of the bare PCB to see if any short circuit or open circuit. Then compare the schematic with the PCB to avoid any defect.
2. After the materials required are ready, the components should be classified, which is convenient for subsequent welding. Print the BOM, marked the unwelded parts in the process.
3. Wear antistatic measures such as anlistatig loop before PCB soldering to prevent static electricity from harming components.
4. When selecting components for PCB soldering, soldering should be performed in the order of components from low to high and from small to large.
5. Before soldering the integrated circuit chip, it is necessary to ensure the correct orientation of the chip. For a chip silkscreen, a generally rectangular pad represents the starting pin. When soldering on the circuit board, fix one pin of the chip first, fine-tune the position of the component, and fix the diagonal pin of the chip so that the component is accurately connected and soldered.
SMD ceramic capacitors and voltage regulator circuits have no positive and negative poles. The LEDs, tantalum capacitors and electrolytic capacitors need to distinguish between positive and negative electrodes. For capacitors and diode components, the one that is generally marked should be negative. In the package of the chip LED, the direction along the lamp is in the positive-negative direction. For the silk screen identification component of the diode circuit diagram package, the negative terminal of the diode should be placed at one end of the vertical line. For the crystal oscillator, the passive crystal oscillator generally has only two pins, and there is no positive or negative. The active crystal oscillator generally has four pins, so pay attention to each pin definition to avoid PCB soldering errors.
For soldering plug-in components, such as power module related components, the device pins can be modified before PCB soldering. After the components are placed and fixed, the solder is usually melted on the back side by a soldering iron and then integrated into the front surface by the pads. Solder does not have to be placed too much, but the components should first be stabilized.
6. The design problems found in PCB soldering process should be recorded in time for subsequent improvement.
7. After PCB soldering, check the solder joints by a magnifying glass to check if there are any solder joints and short circuits.
8. When the PCB soldering is completed, the surface of the circuit board should be cleaned with a cleaning agent such as alcohol to prevent the iron scraps attached to the surface of the circuit board from short-circuiting the circuit.
In PCB soldering, you must also be aware of some details as below
A. Although the weldability is good, it is also necessary to ensure the cleaning of the welding surface.
Due to the long-term storage and pollution, it is very likely that a harmful oxide film or oil stain will be produced on the surface of the soldering piece. Therefore, it is necessary to clean the surface of the soldering piece before the next step of PCB soldering, otherwise, it is difficult to ensure the quality.
B. The temperature and time of soldering should be appropriate.
When the welding is uniform, the solder and the weld metal are heated to the soldering temperature, so that the molten solder is immersed and diffused onto the surface of the solder metal and forms a metal compound. Therefore, in order to ensure a firm solder joint, an appropriate PCB soldering temperature must be provided. At a sufficiently high temperature, the solder can be wetted and diffused to form an alloy layer. The temperature is too high for PCB soldering. The soldering time has a great influence on the solder, the wettability of the soldered component and the formation of the bonding layer. Properly mastering the welding time is the key to high-quality PCB soldering.
C. The solder joint must have sufficient mechanical strength.
In order to ensure that the welded parts do not fall off and loose under vibration or impact, it is necessary to have sufficient solder joint mechanical strength. In order to have sufficient mechanical strength of the solder joint, a method of bending the lead terminal of the component can be generally employed, but excessive solder cannot be accumulated, which easily causes a short circuit between the solder joint and the short circuit.
D. PCB soldering must be reliable and ensure electrical conductivity.
In order to make the solder joints have good electrical conductivity, the most important point is that the solder joint must be prevented. Virtual soldering means that there is no alloy structure between the solder and the solder surface but simply adheres to the solder metal surface. In the PCB soldering, if only a part of the alloy is formed and the rest is not formed, the result is that the solder joint can pass current in a short time, and it is difficult to find the problem of the instrument. However, as time passes, the surface where no alloy is formed will be oxidized, which will cause time to open and break, which inevitably causes quality problems in the product.