PCB Technical - How to solder circuit board?

Circuit board soldering refers to the manufacturing process and technology of joining metal or other thermoplastic materials through heating, high temperature, high pressure, and other methods. Soldering is a very important process in PCB production. Without welding, various devices cannot converge on the board and cannot form the so-called circuit board.

Common processes for soldering circuit boards

1. arc soldering

Arc soldering uses the heat of the arc to melt the workpiece to realize the connection. Arc soldering is a commonly used soldering method. There are two basic types. One is the melting electrode arc. The electrode is melted by the heat of the arc. The molten electrode metal passes through the arc and transfers to the molten pool. Another type is non-melting electrode arc, where the electrode does not melt and the filler metal needs to be added separately to the molten pool.

2. Plasma soldering

Plasma soldering belongs to flash arc welding, which is a soldering method of melting base metal by highly concentrated plasma arc. Plasma soldering has high welding speed, no groove, excellent weld performance, small weld Heat-affected zone, small soldering deformation and residual stress, and can weld a variety of metals.

3. High-frequency soldering

High-frequency soldering includes high-frequency resistance soldering and high-frequency induction welding. It utilizes the "skin effect" of a high-frequency current of 60-500KHz to concentrate the current and heat the surface of the metal to be welded, causing it to melt instantly, and then pressurize and weld it together. It is used for soldering straight seam welded pipes (round pipes, square pipes, shaped pipes, shaped steel, etc.) with high production efficiency. When the surface treatment of the metal to be welded before soldering is clean, there is no soldering fume generated.

4. Gas soldering

Gas soldering is a type of soldering method that uses or burns gas flames to melt workpieces for connection. There are various methods for this type of soldering, among which oxygen-acetylene soldering and oxygen-hydrogen welding are classified according to the type of combustible gas. The heat of a flame is generated through chemical reactions, usually using acetylene as a combustible gas.

5. Argon arc soldering

Argon arc soldering belongs to flash soldering, which generates strong ultraviolet radiation during welding. It is divided into non-consumable argon arc soldering and consumable argon arc soldering. Argon arc soldering can use a mobile soldering fume purifier, and at the same time, it is necessary to ensure good local ventilation at the welding station to ensure the health of the welder.

6. Resistance soldering

Resistance soldering is a type of soldering method that utilizes the pressure applied to the electrode and the resistance heat generated by the soldering current to achieve joint, including spot soldering, seam soldering, projection soldering, resistance butt welding, etc. Resistance soldering is generally automatic soldering, as various resistance soldering equipment is equipped with complete electrical control systems and mechanical control devices.

Soldering process flow of circuit board

preparation

1. Soldering materials

1) The solder usually uses Sn60 or Sn63 solder that meets the general American standard or HL-SnPb39 tin-lead solder.

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

3) The cleaning agent should ensure no corrosion and pollution to the circuit board and generally use cleaning agents such as anhydrous ethanol (industrial alcohol), trichlorotrifluoroethane, isopropanol (IPA), aviation washing gasoline, and deionized water for cleaning. The specific cleaning agent to be used for cleaning should be selected according to the process requirements.

2. Soldering tools and equipment

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

2) Wave soldering and reflow soldering machines are welding equipment suitable for industrial mass production.

3. Key operating points for circuit board soldering

1) Manual soldering

① Before soldering, insulation materials should be checked in advance to avoid any signs of burns, scorching, deformation, cracks, etc. During soldering, it is not allowed to burn or damage components.

② The soldering temperature should usually be controlled at around 260 ℃ and should not be too high or too low, otherwise it will affect the soldering quality.

③ The soldering time is usually controlled within 3 seconds. For welding components with large heat capacity such as multi-layer boards, the entire soldering process can be controlled within 5 seconds; The entire process of soldering components for integrated circuits and thermal components should not exceed 2 seconds. If the welding is not completed within the specified time, the welding point should be allowed to cool down before soldering, and the quality standard for re-soldering should be the same as that of the welding point during the first welding. Obviously, due to factors such as differences in soldering iron power and heat capacity of solder joints, there is no fixed rule to follow in mastering the welding temperature in practice, and specific conditions must be taken into account.

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

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

2) Wave soldering

① To ensure that the board surface and the lead surface are rapidly and completely soaked by solder, flux must be coated. Generally, rosin flux or water-soluble flux with a relative density of 0.81~0.87 is used.

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

③ During the welding process, the temperature of the solder should generally be controlled within the range of 250 ℃± 5 ℃, and its suitability directly affects the welding quality; The inclination angle of the welding fixture entering the wave crest should be adjusted to 6. about; The welding line speed should be controlled between 1-1.6 n/min; The peak height of the solder trough tin surface wave is about lama, and the peak is generally controlled at 1/2 to 213 of the circuit board thickness. If it is too high, it will cause molten solder to flow to the surface of the circuit board, forming a "bridge".

④ After wave soldering, the circuit board must undergo appropriate strong wind cooling.

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

3) Reflow soldering

① Before welding, the surface of the solder and the welded part must be clean, otherwise it will directly affect the soldering quality.

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

③ Local heating sources can be used, so different soldering methods can be used on the same substrate for soldering.

④ The solder used for reflow soldering is a solder paste that ensures the correct composition and generally does not mix with impurities.

4. Board cleaning

After the circuit board is soldered, it must be thoroughly cleaned promptly to remove residual flux, oil stains, and dust. The specific cleaning process is carried out according to the process requirements.

In the process of manufacturing circuit boards, circuit board soldering is a crucial task, which determines the performance and reliability of the circuit board. In the future, with the increasing demand for miniaturization, high performance, and high reliability in electronic devices, circuit board solderingtechnology will continue to develop and innovate.