PCBA Tech - SMT patch or lead component welding and solder paste storage

Welding method of SMT chip components and lead components

SMT chip plus middle components are particularly small in size and light in weight, and chip components are easier to solder than lead components. SMD components also have a very important advantage, that is, to improve the stability and reliability of the circuit, which is to improve the success rate of production. This is because the SMD components have no leads, thereby reducing stray electric fields and stray magnetic fields, which is especially obvious in high-frequency analog circuits and high-speed digital circuits.

The method of soldering SMT chip components is to put the components on the pads, and then apply the adjusted patch solder paste on the contact between the component pins and the pads (be careful not to apply too much to prevent short circuits), and then use The 20W internal heating electric soldering iron heats the joint between the pad and the SMT chip component (the temperature should be 220~230 degree Celsius). After seeing the solder melt, the electric soldering iron can be removed, and the soldering is completed after the solder solidifies. After soldering, you can use tweezers to clamp a clip of the soldered patch component to see if there is any looseness. If there is no looseness (it should be very strong), it means that the soldering is good.

SMT lead component soldering method: when starting to solder all the pins, solder should be added to the tip of the soldering iron, and all the pins should be coated with flux to keep the pins moist. Touch the end of each pin of the chip with the tip of a soldering iron until you see the solder flowing into the pin. When soldering, keep the tip of the soldering iron parallel to the soldered pin to prevent overlap due to excessive soldering.

After all the pins are soldered, soak all the pins with flux to clean the solder. Suck off the excess solder where needed to eliminate any short circuits and overlaps. Finally, use tweezers to check whether there is any false soldering. After the inspection is completed, remove the flux from the circuit board, and soak the hard brush with alcohol and wipe it carefully along the pin direction until the flux disappears.

Use and storage of solder paste on PCB circuit boards

Solder paste is an indispensable auxiliary material in the process of PCB circuit board production. Its function is to melt the patch glue, so that the surface mount components and the PCB board are firmly bonded together, which has a great impact on the electrical performance of the circuit board. So how to use and store the solder paste of the PCB circuit board? Let's understand it together.

The solder paste coating technology most commonly used by PCB circuit board manufacturers is steel plate or screen printing. In addition, other related technologies are also used, including dispensing method, point-to-point transfer method, roller coating method, etc.

1. The practice of steel plate printing is derived from the concept of screen printing. Compared with screen printing, the use of steel plate printing can accurately control the amount of solder paste coating, and is suitable for fine-pitch parts assembly printing operations.

2. The printed steel plate is generally made of thin metal material, and the pattern of the metal opening matches the solder pad that needs to be coated with solder paste on the circuit board. The steel plate is aligned with the circuit board before printing, and then the solder paste is applied to the entire steel plate with a squeegee, and the solder paste passing through the opening of the steel plate is transferred to the required area. Finally, the circuit board is separated from the steel plate, and the solder paste stays on the corresponding solder pad.

3. The dispensing and coating technology is to press the solder paste magazine and squeeze the solder paste through the needle to perform fixed-point and quantitative coating operations. The operating principles and design methods of the dispensing system are very diversified. Generally, as long as the system is used to confirm that it can meet the stable, fast, and suitable volume supply capacity required by the application, this system can be the system of choice. Dispensing coating is a very versatile technology. It can be coated on uneven surfaces. At the same time, it can be programmed to perform random coating operations with indefinite points and non-quantitative quantities. But because the work speed is slower than printing, it is often used in parts manufacturing or heavy work.

4. The point-to-point transfer method is a good choice for small parts with larger spacing. It can transfer the solder paste to the required position. Using this technology, a set of pins are installed on the fixed board, and the position of the pin points and the pads to be soldered correspond to each other. During operation, a certain thickness of solder paste is built up on the flat-bottomed container, and then the set of pins is stably immersed in the solder paste and then lifted up, and the solder paste attached to the tip of the needle will remain at the top of the pin. Then these pins with solder paste will transfer the solder paste to the solder pads, and then repeat the next cycle.

Storage method of solder paste:

PCB solder paste is very sensitive to heat, air, and humidity in the exposed environment. Heat will cause the reaction between the flux and the tin powder, and also cause the flux and the tin powder to separate. If exposed to air or humid environment, it will cause dryness, oxidation, moisture absorption and other problems. It is recommended to store in a refrigerated environment. Before being exposed to the air, the temperature should be balanced with the ambient temperature before opening, so as to avoid condensation. The time required for rewarming varies depending on the size of the container and the storage temperature. The time required for thawing can range from one hour to several hours.