PCBA Tech - ​How to solder PCB circuit board chip components?

How to solder PCB circuit board chip components? SMD components soldering steps:

1.Clean and fix PCB (printed circuit board)

Before PCB soldering, check the PCB to be soldered to ensure that it is clean. The oily fingerprints and oxides on the surface should be removed so as not to affect the tin. When soldering the PCB by hand, if conditions permit, you can use a soldering station or the like to fix it to facilitate soldering. Generally, it is good to fix it by hand. It is worth noting that your fingers should not touch the pads on the PCB and affect the soldering.

2.Fixed SMD components

The fixation of PCB patch components is very important. According to the number of pins of the patch component, the fixing method can be roughly divided into two types-single-leg fixing method and multi-leg fixing method. For SMD components with a small number of pins (generally 2-5), such as resistors, capacitors, diodes, triodes, etc., a single-pin fixing method is generally used. That is, tin on one of the pads on the board first.

Then hold the PCB component with tweezers in your left hand and place it in the mounting position and lightly hold it against the circuit board. Use the soldering iron in your right hand to close the tinned pad and melt the solder to solder the pins. After soldering a pad, the component will not move, and the tweezers can be released at this time.

For SMD chips with many pins and distributed on multiple sides, it is difficult to fix the chip with a single pin. In this case, multi-pin fixing is required. Generally, the method of fixing the pins can be adopted. That is, after a pin is welded and fixed, the pin opposite to the pin is welded and fixed, so as to achieve the purpose of fixing the entire chip. It should be noted that for chips with many and dense pins, precise pin alignment to the pads is especially important, and should be checked carefully, because the quality of soldering is determined by this premise.

It is worth emphasizing that the pin of the chip must be judged correctly. For example, sometimes we fix the chip carefully and even complete the soldering. During inspection,we find that the pin corresponds to the error-the pin that is not the first pin is used as the first pin to solder! Regret too much! Therefore, these meticulous preliminary work must not be sloppy.

3.Solder the remaining pins

After the PCB components are fixed, the remaining pins should be soldered. For components with few pins, you can hold the soldering tin in your left hand and the soldering iron in your right hand, and then spot solder them in sequence. For chips with many and dense pins, in addition to spot welding, drag soldering can be used, that is, put enough tin on one pin and then use a soldering iron to melt the solder onto the remaining pins on that side. The molten solder can be Flow, so sometimes the board can be properly tilted to get rid of excess solder. It is worth noting that, regardless of spot welding or drag welding, it is easy to cause adjacent pins to be short circuited by tin. Don't worry about this, because it can be obtained. What needs to be concerned is that all the pins are well connected to the pads, and there is no virtual soldering.

4.Remove excess solder

In step 3, we mentioned the short circuit phenomenon caused by soldering. Now let's talk about how to deal with this excess solder. Generally speaking, you can use the above-mentioned suction tape to suck off the excess solder. The method of using the soldering tape is very simple. Add a proper amount of flux (such as rosin) to the soldering tape and then close it to the pad. Place a clean soldering iron tip on the soldering tape and wait for the soldering tape to be heated to absorb the pad. After the solder on the upper part has melted, slowly push and pull from one end of the pad to the other end, and the solder is sucked into the tape. It should be noted that after the soldering is finished, the soldering iron tip and the soldering tape should be evacuated from the pad at the same time. Then add flux to the soldering tape or reheat it with a soldering iron tip and then gently pull the soldering tape to make it free from the pad and prevent the surrounding PCB components from being burnt. If there is no special suction tape sold on the market, the thin copper wire in the wire can be used to make the suction tape. The self-made method is as follows: after peeling off the outer skin of the wire, the thin copper wire inside is exposed. At this time, use a soldering iron to melt some rosin on the copper wire. In addition, if you are not satisfied with the soldering results, you can reuse the suction tape to remove the solder and solder the components again.

5.Clean the welding place

After PCB soldering and removing excess solder, the chip is basically soldered. However, due to the use of rosin for soldering and tin suction tape, some rosin remains around the chip pins on the board. Although it does not affect the work and normal use of the chip, it is not beautiful. And it may cause inconvenience during inspection. Because it is necessary to clean up these residues. The common cleaning method can be washing plate water. Here, alcohol is used for cleaning. The cleaning tool can be a cotton swab or a toilet paper with tweezers. 

When cleaning and erasing,it should be noted that the amount of alcohol should be appropriate,and its concentration is best to be high,so as to quickly dissolve residues such as rosin. Secondly,the erasing force should be well controlled and not too large to avoid scratching the solder mask and damaging the chip pins. At this time, you can use a soldering iron or a hot air gun to properly heat the alcohol scrubbing position to allow the residual alcohol to evaporate quickly. At this point, the soldering of the chip is over.

If a short circuit occurs during soldering, treatment:

Basic steps for dealing with short circuits

When a short circuit occurs during soldering, the power supply must first be disconnected to ensure safety. Then, the entire PCB board should be carefully inspected for possible physical damage or soldering problems, including the appearance of loose solder joints and short circuits between wires. The use of a multimeter or circuit tester can help identify the location of the short circuit, thus ensuring the accuracy of the subsequent repair.

Short Circuit Repair Methods

Once the location of the short has been determined, the next step is to repair it. If the short is not a serious problem, simple repairs can be made to find the point of failure and fix it. If a component is deteriorated or damaged, it may be necessary to replace the component to completely solve the problem. When dealing with this, you also need to make sure that the solder joints are clean by using appropriate tools such as a soft bristle brush or compressed air to remove dust and debris from the board.

Precautions and Precautionary Measures

During the soldering process, in order to avoid short-circuiting phenomena, operators should receive the necessary training and familiarize themselves with the operation of the equipment. In addition, the amount of solder used during soldering should be controlled to avoid short circuits caused by excessive amounts of solder paste. The temperature during soldering should also be appropriate and should not be too low to ensure that the solder can be melted evenly to reduce the risk of potential short circuits.

Soldering chip components on PCB circuit boards is a task that requires care and patience, and it is critical to master the correct operating procedures and techniques. Before soldering, make sure the pads are clean and apply the right amount of flux, which can improve the quality of soldering and reduce the risk of short-circuit. During the soldering process, keep the temperature of the soldering iron moderate to ensure the stability and reliability of each solder joint. At the same time, check the soldering joints thoroughly after the soldering is completed to make sure there is no leakage or false soldering. Through these meticulous steps, you can ensure the performance and reliability of the circuit board, which in turn improves the quality of the entire electronic product.