Flux: chemical substance that can assist and promote the welding process in the welding process, has a protective effect and prevents oxidation reaction.
The flow can be divided into solid, liquid and gaseous.
It mainly includes “auxiliary heat conduction”, “oxide removal”, “reducing the surface tension of the welded material”, “removing oil stains on the surface of the welded material, increasing the welding area” and “reoxidation prevention”.
The two main functions in these aspects are “removing oxides” and “reducing the surface tension of the welded material”.
Stream selection
The role of flux is to improve welding performance and increase welding solidity.
Flux can remove oxides from the metal surface and prevent further oxidation, increasing weld and metal surface activity, thereby increasing wettability and adhesion.
Fluxes include strong acid flux, weak acid flux and neutral flux.
Commonly used soldering fluxes for electricians include rosin, rosin solution, solder paste and solder oil, etc.
Its scope of application is shown in the table and can be reasonably selected according to different welding objects.
Solder paste and soldering oil have certain corrosiveness and cannot be used to solder electronic components and circuit boards.
After welding, the residual solder paste and soldering oil must be cleaned off.
Rosin should be used as solder flux when tinning component pins.
If the printed circuit board has been coated with rosin solution, it is not necessary to use flux when soldering components.
Table 4-1 Scope of Application of Common Flows
| Flow type | Scope of application |
| colophony | Welding of electronic components, installation and welding of printed circuit boards, welding of connecting wires inside electronic equipment, welding of thinner wire ends, etc. |
| resin solution | Oxidation treatment of printed circuit boards, welding of thinner wire ends, etc. |
| Solder paste and slag | Welding thicker wire ends, welding larger terminals of electrical equipment, welding equipment housings, etc. |
For the manufacturer, there is no way to test the composition of the flux.
If you want to know whether the solvent in the flux is volatile, simply measure the specific gravity.
If the specific gravity increases too much, it can be concluded that the solvent is volatile.
When selecting the flow, the following suggestions are given to the manufacturer:
1. Smell
It is preliminarily determined which solvent is used, such as methanol, which has a small but suffocating taste, and isopropanol, which has a strong taste.
Although the supplier may also use mixed solvents, the supplier is required to provide an ingredient report, which is generally provided by the supplier;
However, the price of isopropanol is about 3-4 times that of methanol.
If the price is severely depressed with suppliers, it can be difficult to tell what is involved.
2. Determine the sample
This is also the most fundamental method for many manufacturers to select flux.
When confirming the sample, the supplier should request the supplier to provide the relevant parameter report and compare it with the sample.
If the sample is confirmed as OK, the subsequent delivery must be compared with the original parameters.
In case of any abnormality, the specific gravity, acidity value, etc., must be checked.
Smoke generation from the stream is also an important indicator.
3. The flow market is mixed, so the qualification of suppliers must be accurately understood when selecting
If necessary, you can visit the manufacturer.
If they are irregular flow manufacturers, they will be afraid of it.
Flow Usage
Before introducing the usage method, let's talk about flow classification.
It can be divided into a series of electrodeless fluxes, which are sold on the market as “welding oil”.
After use, pay attention to cleaning, otherwise it is easy to cause corrosion and damage the welded objects.
The other is organic series flow, which can decompose quickly and leave inactive residues.
The other is resin active series flux, which is non-corrosive, highly insulating and has long-term stability.
The most commonly used flux is rosin flux.
Generally speaking, the use of aluminum flux is relatively simple.
First, wipe the alcohol on the welding to remove the oil stain, then apply the flux to the surface to be welded, and then you can weld.
However, remember to clean it after welding and pay attention to safety during use. Do not let it get into your mouth, nose, throat or skin.
When not in use, it can be sealed and placed in a cool and ventilated place.
The key of the tin bar welding circuit is to clean the welding part, heat and melt the resin on the welding part or coat the flux on the object to be welded, and then use a soldering iron to eat the tin and point it at the point to be welded.
Generally, rosin is used to solder small components and flux is used to solder large components.
The resin is used in the circuit board and the flux is used for single-piece soldering.
And explain:
1. Sealed storage life is half a year. Do not freeze the product.
The best storage temperature is 18℃ – 25℃, and the best storage humidity is 75% – 85%.
2. After the flux is stored for a long time, its specific gravity should be measured before use, and the specific gravity should be adjusted to normal by adding diluent.
3. Solvent flux is a flammable chemical material. It must be operated in a well-ventilated environment, away from fire and direct sunlight.
4. When the flux is used in the sealed tank, pay attention to adjusting the spraying amount and spraying pressure reasonably according to the performance of the wave oven and the characteristics of the product.
5. When flux is continuously added to the sealed tank, a small amount of sediment in the flux will accumulate at the bottom of the sealed tank.
The longer the time, the more sediment will accumulate, which can cause blockage of the peak furnace spray system.
To prevent sediment from blocking the peak furnace spray system, affecting the spray quantity and spray status, and causing PCB soldering problems, it is necessary to regularly clean and maintain the spray system such as the sealed tank and the filter screen.
It is recommended to do this once a week and replace the flux with sediment at the bottom of the seal tank.
For manual welding operations:
1. Try not to pour too much flow at once, and add and top up according to the output;
2. 1/4 of diluent should be added every 1 hour, and the appropriate flow should be added every 2 hours;
3. Before the afternoon and evening break or when use is stopped, try to seal and cover the flow;
4. Before leaving work at night, carefully pour the plate flux back into the bucket and install it, and wipe the immersion plate with a clean cloth to wait;
5. When using the flux used yesterday, 1/4 thinner and more than twice the new unused flux should be added at the same time, so that the flux used yesterday can be fully utilized to avoid waste.
6. When coating flux with spray and foam processes, regularly check the air pressure of the air compressor.
It is better to filter water and oil stains in the air with more than two precision screening programs.
Use clean, dry, oil-free, anhydrous compressed air to avoid affecting the flow structure and performance.
7. When spraying, pay attention to the spray adjustment and ensure that the flow is evenly distributed on the surface of the PCB.
8. The tin wave is smooth and the PCB is not deformed, so a more uniform surface effect can be obtained.
9. In case of severe oxidation of tin-plated PCB, conduct appropriate pretreatment to ensure quality and solderability.
10. Unsealed flux must be sealed before storage. The used flux must not be poured into the original packaging to ensure the cleanliness of the original solution.
11. Discarded flux shall be disposed of by special personnel and shall not be randomly disposed of to pollute the environment.
12. During operation, the bare board and the base of the parts should be prevented from being polluted by sweat, hand stains, face cream, grease or other materials.
After welding, keep it clean and do not contaminate it with your hands before it dries completely.
13. The amount of flux coating depends on product demand.
The recommended flow amount for single panel is 25-55ml/min, and the recommended flow amount for dual panel is 35-65ml/min.
14. When the flow is a foam coating process, the specific gravity of the flow must be controlled to prevent the structure and performance of the flow from being affected by the volatilization of the solvent in the flow, the increase in specific gravity, and the increase in flow concentration.
It is recommended to check the specific gravity of the flow when the foam has been used for approximately 2 hours.
When the specific gravity increases, add the appropriate amount of diluent for adjustment.
The recommended range of specific gravity control is ±0.01 of the specific gravity of the stock solution specification.
15. The flow preheating temperature: 75-105 ℃ for single panel bottom (60-90 ℃ for single panel surface), 85-120 ℃ for double panel bottom (70-95 ℃ for single panel surface double).
