PCB wave soldering parameter setting and precautions

Date：2022-09-01 15:55:00Views：761

In PCB processing, wave soldering is to make the welding surface of the plug-in board directly contact with high-temperature liquid tin to achieve the purpose of welding. The high-temperature liquid tin maintains a slope, and the liquid tin is shaped like waves by a special device. Therefore, it is called "wave soldering", and its main material is solder bar. In order to help you have a deeper understanding, the following contents are organized by Chuangxin testing network for your reference.

Setting method of PCB wave soldering parameters

1. Foaming air volume or flux spraying pressure: it shall be determined according to the condition that the flux contacts the bottom surface of the PCB, so that the flux can be uniformly applied to the bottom surface of the PCB. It can also be observed from the through hole on the PCB surface. A small amount of flux should penetrate upward from the through hole to the pad on the top surface of the through hole. However, it should be noted that the flux should not penetrate into the component body.

2. Preheating temperature: it is set according to the actual situation of the preheating area of the wave soldering machine. The PCB surface temperature is generally between 90 and 130 ℃, and the upper limit is taken for the assembly plate of large plate, thick plate and SMD components.

3. Conveyor belt speed: set according to different wave soldering machines and PCB to be welded, generally 0.8-1.92m/min.

4. Solder temperature: since the temperature sensor is in the tin pot, the temperature of the meter or liquid crystal display is about 5-10 ℃ higher than the actual temperature of the wave peak.

5. Measuring the peak height: adjust the peak height to exceed the bottom surface of the PCB, at 1 / 2 ~ 2 / 3 of the PCB thickness.

Precautions for wave soldering of PCB processing

After wave soldering, cleaning, storage and maintenance of PCB board, there may be white around the pad. These white substances are mainly caused by residues.

1. Causes of white pad caused by excessive wave soldering

1) Tin oxide floating on the surface of the wave crest;

2) Improper preheating temperature or curve parameters;

3) The flux flow is too high, the preheating temperature is low, and the tin eating time is too short;

4) Flux composition, inspection test and certification.

2. Causes of PCB pad whitening after cleaning

1) Rosin in flux:

Most of the white substances produced after cleaning, storage and solder joint failure are the inherent rosin in the flux.

2) Rosin denaturates:

This is the substance produced by the reaction between rosin and flux during the welding process of the board, and the solubility of this substance is generally very poor, which is not easy to be cleaned and remains on the board to form a white residue.

3) Organometallic salts:

The principle of removing oxide on welding surface is that organic acid reacts with metal oxide to form metal salt soluble in liquid rosin. After cooling, it forms solid solution with rosin and is removed with rosin during cleaning.

4) Metal inorganic salt:

These may be generated by the reaction of metal oxide in solder with halogen containing active agent in flux or solder paste, halogen ion in PCB pad, residual halogen ion in component surface coating, and halogen ion released by halogen containing material of FR4 at high temperature. Generally, the solubility in organic solvent is very small. If the cleaning agent is selected properly, the flux residue may be removed; Once the cleaning agent is not selected to match the residue, it may be difficult to remove these metal salts, leaving white spots on the board. The welding pad turns white after processing and welding, which is mainly caused by residual flux and unclean cleaning. It needs to be cleaned after welding.

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