"Welding knowledge" PCB circuit board welding process and method

Date：2022-06-10 16:00:00Views：883

Welding, also known as fusion, fusion, is a manufacturing process and technology for joining metals or other thermoplastic materials such as plastics by heating, high temperature or high pressure. People who have just come into contact often don't know what needs to be prepared and how to do it during the PCB welding process, which is what we often call the process flow. Here is a brief introduction to the process flow of circuit board welding:

preparation:

1. Welding materials

1) Sn60 or Sn63 solder conforming to American general standards or hl-snpb39 tin lead solder is usually used.

2) The flux can usually be rosin flux or water-soluble flux, which is generally only used for wave soldering.

3) The cleaning agent shall ensure no corrosion and pollution to the circuit board. Generally, absolute ethanol (industrial alcohol), trichlorotrifluoroethane, isopropanol (IPA), aviation washing gasoline, deionized water and other cleaning agents are used for cleaning. The specific cleaning agent shall be selected according to the process requirements.

2. Welding tools and equipment

1) Reasonable selection of power and type of electric soldering iron is directly related to the improvement of welding quality and efficiency. It is recommended to use low-voltage temperature controlled electric soldering iron. The soldering iron head can be made of nickel plated, iron plated or red copper. The shape should be determined according to the needs of welding.

2) Wave soldering machine and reflow soldering machine are one of the welding equipment suitable for industrial mass production.

3. Operation points of PCB electronic circuit board welding

1) Manual welding

① Before welding, the insulation materials shall be checked in advance, and there shall be no scalding, scorching, deformation, cracks and other phenomena. It is not allowed to scald or damage components during welding.

② Generally, the welding temperature shall be controlled at about 260 ℃, which shall not be too high or too low, otherwise the welding quality will be affected.

③ The welding time is usually controlled within 3S. For weldments with large heat capacity such as multilayer plates, the whole welding process can be controlled within 5S; For weldments of integrated circuits and thermal components, the whole process shall not exceed 2S. If the welding is not completed within the specified time, the welding joint shall be re welded after cooling, and the quality standard of re welding shall be the same as that of the first welding. Obviously, due to the differences of soldering iron power and solder joint heat capacity, there is no definite rule to follow in actually mastering the welding temperature, which must be treated according to specific conditions.

④ During welding, adjacent components, printed boards, etc. shall be prevented from being affected by overheating, and necessary heat dissipation measures shall be taken for thermal components.

⑤ Before the solder cools and solidifies, the welded part must be fixed reliably without swinging and shaking. The solder joint should be cooled naturally. If necessary, heat dissipation measures can be taken to speed up the cooling.

2) Wave soldering

① In order to ensure that the board surface and lead surface are quickly and completely wetted by solder, flux must be applied. Generally, the relative density is 0 81 ~ 0.87 rosin type flux or water-soluble flux.

② The circuit board coated with flux shall be preheated, generally controlled at 90 ~ 110 ℃. Mastering the preheating temperature can reduce or avoid the occurrence of sharp points and round defects.

③ During the welding process, the solder temperature shall generally be controlled within the range of 250 ℃± 5 ℃. Whether the temperature is suitable directly affects the welding quality; The inclination angle of the welding fixture entering the wave crest port shall be adjusted to 6. about; The welding line speed shall be controlled within 1 ~ 1.6 n / min; The height of the wave crest on the tin surface of the solder trough is about lomm, and the peak is generally controlled at 1 / 2 ~ 213 of the thickness of the circuit board. Too much will cause the molten solder to flow to the surface of the circuit board, forming a "bridge".

④ After wave soldering, the circuit board must be properly cooled by strong wind.

⑤ The cooled circuit board needs to cut off the component leads.

3) Reflow welding

① Before welding, the surface of solder and weldment must be clean, otherwise the welding quality will be directly affected.

② It can control the amount of solder applied in the previous process and reduce the welding defects such as false welding and bridging, so the welding quality is good and the reliability is high.

③ Local heating heat source can be used, so different welding methods can be used on the same substrate.

④ The solder for reflow soldering is a solder paste that can ensure the correct composition, and generally will not be mixed with impurities.

4. Plate surface cleaning

After the circuit board is welded, the circuit board must be thoroughly cleaned in time to remove the residual flux, oil stain, dust and other dirt. The specific cleaning process shall be carried out according to the process requirements.

The above is the content related to PCB circuit board welding organized by the creative core testing team. I hope it will be helpful to you. Shenzhen Chuangxin Online Testing Technology Co., Ltd. is a well-known professional testing institution for electronic components in China, with 3 standardized laboratories covering an area of more than 1000 square meters. The scope of testing services covers: testing and verification of electronic components, IC authenticity identification, material selection for product design, failure analysis, function testing, factory incoming material inspection, X-ray testing of components and parts, tape braiding and other testing items.