Soldering Tips and Precautions for Printed Circuit Boards

Soldering Tips and Precautions for Printed Circuit Boards

Summary

This article specifically introduces the soldering skills and precautions of printed circuit boards to avoid virtual soldering of printed circuit boards

the soldering skills and precautions of printed circuit boards in detail

The soldering of printed circuit boards is related to the performance in the future. If there is poor soldering, it will cause the use effect to fail to reach the expected situation. Next, we will introduce the soldering skills and precautions of printed circuit boards in detail.

Welding skills

1. The process flow of selective soldering includes: flux spraying, circuit board preheating, dip soldering, and drag soldering. Flux coating process In selective soldering, the flux coating process plays an important role.

At the end of the soldering heat and soldering, the flux should be active enough to prevent bridging and prevent oxidation of the circuit board. Flux spraying is carried by the X/Y manipulator to pass the circuit board over the flux nozzle, and the flux is sprayed to the soldering position of the PCB circuit board.

2. In the microwave peak selection after the reflow process, it is important that the flux is sprayed accurately, and the micro-hole spray type will not contaminate the area outside the solder joints.

The diameter of the micro-sprayed flux spot pattern is greater than 2mm, so the positional accuracy of the flux deposited on the circuit board is ±0.5mm to ensure that the flux always covers the welded part.

3. The process characteristics of selective soldering can be understood by comparing it with wave soldering. The obvious difference between the two is that in wave soldering, the lower part of the circuit board is completely immersed in liquid solder, while in selective soldering, there are only some specific areas. contact with the solder wave.

Since the circuit board itself is a poor thermally conductive medium, it does not heat and melt the solder joints adjacent to components and areas of the circuit board when soldering.

4. Flux must also be pre-applied before soldering. Compared with wave soldering, the flux is only applied to the lower part of the circuit board to be soldered, not the entire PCB circuit board.

Precautions

1. Remind everyone that after getting the bare PCB board, you should first perform a visual inspection to see if there are problems such as short circuits and open circuits, and then familiarize yourself with the schematic diagram of the development board, and compare the schematic diagram with the PCB silkscreen layer to avoid the schematic diagram and PCB.

2. After the materials required for PCB welding are ready, the components should be classified, and all components can be divided into several categories according to their size, which is convenient for subsequent welding. A complete bill of materials needs to be printed. During the welding process, if an item is not welded, use a pen to cross out the corresponding option, which is convenient for subsequent welding operations.

3. Before welding, anti-static measures such as wearing an electrostatic ring should be taken to avoid damage to components caused by static electricity. After the equipment required for welding is ready, the tip of the soldering iron should be kept clean and tidy. It is recommended to use a flat-angle soldering iron for the initial soldering. When soldering components such as 0603-type packages, the soldering iron can better contact the pads, which is convenient for soldering.

4. When selecting components for welding, the components should be welded in the order from low to high and from small to large. So as not to bring inconvenience to the welding of smaller components by welding larger components. Priority is given to soldering IC chips.

5. Before welding the integrated circuit chip, it is necessary to ensure that the chip placement direction is correct. For the chip silkscreen layer, generally, the rectangular pad represents the starting pin. When welding, one pin of the chip should be fixed first, and the position of the components should be fine-tuned and then the diagonal pins of the chip should be fixed, so that the components are accurately connected and then welded.

6. There are no positive and negative poles for SMD ceramic capacitors and Zener diodes in voltage regulator circuits, while LEDs, tantalum capacitors, and electrolytic capacitors need to distinguish between positive and negative poles.

For capacitor and diode components, generally, the end with a prominent mark should be negative. In the package of SMD LEDs, the direction along the lamp is the positive-negative direction. For the packaged components identified by the silkscreen as the diode circuit diagram, the negative end of the diode should be placed at one end of the vertical line.

7. For crystal oscillators, passive crystal oscillators generally have only two pins, and there is no positive or negative. Active crystal oscillators generally have 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, you can modify the device pins before welding. After the components are placed and fixed, the solder is generally melted by a soldering iron on the back and then the pads are integrated into the front. You don't have to put too much solder, but the components should be stabilized first.

9. During the welding process, the PCB design problems found, such as installation interference, incorrect pad size design, component packaging errors, etc., should be recorded in time for subsequent improvement.

10. After welding, use a magnifying glass to check the solder joints to check whether there is any false soldering or short circuit.

11. After the welding of the circuit board is completed, the surface of the circuit board should be cleaned with a cleaning agent such as alcohol to prevent the iron filings attached to the surface of the circuit board from short-circuiting the circuit, and at the same time, the circuit board can be made cleaner and more beautiful.

If the printed circuit board is soldered, it will lead to poor contact of the working circuit, so we need to deal with it for specific reasons.

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