1. Remind everyone to check the appearance first after getting the PCB bare board to see whether there is short circuit, circuit break and other problems. Then get familiar with the development board schematic diagram, and compare the schematic diagram with the PCB screen printing layer to avoid the discrepancy between the schematic diagram and PCB.
2. After the materials required for reflow oven are ready, the components should be classified. All components can be divided into several categories according to their sizes for the convenience of subsequent welding. A complete material list needs to be printed. In the welding process, if no welding is completed, cross out the corresponding options with a pen, so as to facilitate the subsequent welding operation.
3. Before reflow soldering machine, take esd measures, such as wearing an esd ring, to prevent electrostatic damage to components. After all welding equipment is ready, ensure that the soldering iron head is clean and tidy. It is recommended to choose a flat Angle soldering iron for the initial welding. When welding encapsulated components such as 0603 type, the soldering iron can better contact the welding pad, which is convenient for welding. Of course, for the master, this is not a problem.
4. When selecting components for welding, weld them in order from low to high and from small to large. In order to avoid the welding inconvenience of the welded larger components to the smaller components. Preferentially weld integrated circuit chips.
5. Before welding integrated circuit chips, ensure that the chips are placed in the correct direction. For the chip screen printing layer, the general rectangular pad represents the beginning of the pin. During welding, one pin of the chip should be fixed first. After fine-tuning the position of the components, the diagonal pins of the chip should be fixed so that the components are accurately connected to the position before welding.
6. There is no positive or negative electrode in ceramic chip capacitors and regulator diodes in voltage regulator circuits, but it is necessary to distinguish positive and negative electrode for leds, tantalum capacitors and electrolytic capacitors. For capacitors and diode components, the marked end shall generally be negative. In the package of SMT LED, there is a positive – negative direction along the direction of the lamp. For the encapsulated components with silk screen identification of diode circuit diagram, the negative diode extreme should be placed at the end of the vertical line.
7. for crystal oscillator, passive crystal oscillator generally only two pins, and no positive and negative points. The active crystal oscillator generally has four pins. Pay attention to the definition of each pin to avoid welding errors.
8. For the welding of plug-in components, such as power module related components, the pin of the device can be modified before welding. After the components are placed and fixed, the solder is melted by the soldering iron on the back and integrated into the front by the solder pad. Don’t put too much solder, but first the components should be stable.
9. PCB design problems found during welding should be recorded in time, such as installation interference, incorrect pad size design, component packaging errors, etc., for subsequent improvement.
10. after welding, use a magnifying glass to check the solder joints and check whether there is any weld defect or short circuit.
11. after the completion of the circuit board welding work, alcohol and other cleaning agent should be used to clean the surface of the circuit board, to prevent the circuit board surface attached to the iron chip short circuit, but also can make the circuit board more clean and beautiful.
Post time: Aug-17-2021