PCB Technical - What do you know about the soldering skills of the latest double-sided PCB in 2021?

What do you know about the soldering skills of the latest double-sided PCB in 2021?

1. Circuit board welding skills

1. The selective soldering process 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 soldering heating and soldering, the flux should have sufficient activity to prevent bridging and prevent oxidation of the circuit board. Flux spraying is carried by the X/Y manipulator to carry the circuit board through the flux nozzle, and the flux is sprayed onto the soldering position of the PCB circuit board.

2. For the microwave peak selective soldering after the reflow soldering 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-spot sprayed flux dot pattern is greater than 2mm, so the position accuracy of the sprayed flux deposited on the circuit board is ±0.5mm to ensure that the flux is always covered on the welded part.

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

Since the circuit board itself is a poor heat transfer medium, it will not heat and melt the solder joints adjacent to the components and the circuit board area during soldering.

The flux must also be pre-coated before soldering. Compared with wave soldering, the flux is only coated on the lower part of the circuit board to be soldered, rather than the entire PCB circuit board.

In addition, selective soldering is only suitable for the soldering of plug-in components. Selective soldering is a brand new method. A thorough understanding of selective soldering processes and equipment is necessary for successful soldering.

Two, circuit board welding matters needing attention

1. Remind everyone that after getting the bare PCB board, you should first check the appearance to see if there are short-circuit or open circuit problems, and then familiarize yourself with the schematic diagram of the development board. Compare the schematic diagram with the PCB silk screen layer to avoid discrepancies between the schematic diagram and the PCB.

2. After the materials required for PCB soldering are ready, the components should be classified. All components can be divided into several categories according to their size to facilitate subsequent soldering. Need to print a complete list of materials. In the welding process, if one item is not completed, use a pen to cross out the corresponding option, which is convenient for subsequent welding operations.

3. Before welding, take anti-static measures such as wearing a static ring to avoid damage to the 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 first soldering. When soldering components such as 0603 packaged components, the soldering iron can better contact the pads and facilitate soldering. Of course, for masters, this is not a problem.

4. When selecting components for soldering, the components should be soldered in the order from low to high and from small to large. In order to avoid the welding of smaller components caused by welding of larger components. Priority is given to soldering integrated circuit chips.

5. Before welding the integrated circuit chip, it is necessary to ensure that the chip placement direction is correct. For the chip silk screen layer, generally rectangular pads indicate the starting pins. When soldering, 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 then soldered.

6. SMD ceramic capacitors and voltage stabilizing diodes have no positive and negative poles in the voltage stabilizing circuit. Light-emitting diodes, tantalum capacitors and electrolytic capacitors need to be distinguished between positive and negative poles. For capacitors and diode components, generally the marked end should be negative. In the package of SMD LED, the direction along the lamp is the positive-negative direction. For packaged components marked as diode circuit diagram by silk screen, the negative end of the diode should be placed at the end with a vertical line.

7. For crystal oscillators, passive crystal oscillators generally have only two pins, and there is no difference between positive and negative. Active crystal oscillators generally have four pins. Pay attention to the definition of each pin to avoid soldering errors.

8. For the welding of plug-in components, such as power module related components, the pins of the device can be modified before welding. After the components are placed and fixed, the solder is generally melted by a soldering iron on the back and then merged into the front by the pad. There is no need to put too much solder, but the components should be stable first.

9. The PCB design problems found during the soldering process should be recorded in time, such as installation interference, incorrect pad size design, component packaging errors, etc., for subsequent improvements.

10. After soldering, use a magnifying glass to check the solder joints to check whether there are false soldering and short-circuit conditions.

11. After the circuit board welding 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 it can also make the circuit board cleaner and more beautiful.

Three, double-sided circuit board characteristics

The difference between single-sided circuit boards and double-sided circuit boards is the number of copper layers. The double-sided circuit board has copper on both sides of the circuit board, which can be connected through via holes. However, there is only one layer of copper on one side, which can only be used for simple circuits, and the holes made can only be used for plug-in connections.

The technical requirements for double-sided circuit boards are that the wiring density becomes larger, the aperture is smaller, and the aperture of the metallized hole becomes smaller and smaller. The quality of the metallized holes on which the layer-to-layer interconnection relies is directly related to the reliability of the printed board.

With the shrinking of the pore size, the debris that did not affect the larger pore size, such as brush debris and volcanic ash, once left in the small hole will cause the electroless copper and electroplating to lose its effect, and there will be holes without copper and become holes. The deadly killer of metallization.

Fourth, the welding method of double-sided circuit board

Double-sided circuit board In order to ensure the reliable conductive effect of double-sided circuit, it is recommended to weld the connection holes on the double-sided board with wires or the like (that is, the through-hole part of the metallization process), and cut off the protruding part of the connection line to avoid Injury the operator's hand, this is the preparation for the connection of the board.

The essentials of double-sided circuit board welding:

1. For devices that require shaping, they should be processed according to the requirements of the process drawings; that is, they must be shaped first and then plug-in.

2. After shaping, the model side of the diode should face up, and there should be no discrepancies in the length of the two pins.

3. When inserting devices with polarity requirements, pay attention to their polarity not to be reversed. Roll integrated block components, after inserting, no matter it is a vertical or horizontal device, there must be no obvious tilt.

4. The power of the soldering iron used for soldering is between 25~40W. The temperature of the soldering iron tip should be controlled at about 242 degree Celsius. If the temperature is too high, the tip is easy to "die", and the solder cannot be melted if the temperature is low. The soldering time should be controlled at 3 ~4 seconds.

5. During the formal welding, generally operate according to the welding principle of the device from short to high and from the inside out. The welding time should be mastered. If the time is too long, the device will be burnt, and the copper line on the copper clad board will also be burnt.

6. Because it is double-sided welding, a process frame or the like for placing the circuit board should also be made, so as not to squeeze the components underneath.

7. After the circuit board is soldered, a comprehensive check-in check should be carried out to check for missing insertion and soldering. After confirmation, trim the redundant device pins and the like on the circuit board, and then flow into the next process.

8. In the specific operation, the relevant process standards should be strictly followed to ensure the welding quality of the product.

With the rapid development of high technology, electronic products that are closely related to the public are constantly being updated. The public also needs electronic products with high performance, small size and multiple functions, which puts forward new requirements on circuit boards.

This is why the double-sided circuit board was born. Due to the wide application of double-sided circuit boards, the manufacture of printed circuit boards has also become lighter, thinner, shorter and smaller.