During wave soldering, the solder is in the molten state, and the oxidation of its surface and the formation of some residues by its interaction with other metal elements (mainly Cu) are inevitable. However, the reasonable and correct use of wave soldering equipment and timely cleaning are also very important to reduce tin slag.

1. Strictly control the furnace temperature

For Sn63-Pb37 tin bar, its normal service temperature is 240-250oc. The user should often use a thermometer to measure the temperature in the furnace and evaluate the uniformity of the furnace temperature, that is, whether the temperature in the four corners of the furnace is consistent with that in the center of the furnace. We suggest that the deviation should be controlled within? Within 5 OC.

It should be pointed out that the display temperature of the instrument on the wave peak furnace can not be viewed alone, because in fact, there is usually a deviation between the display temperature of the instrument and the actual furnace temperature. This deviation is related to the equipment manufacturer and the service time of the equipment.

2. Control of crest height

The control of wave crest height is not only very important for welding quality, but also helpful to reduce tin slag. First of all, the wave crest should not be too high. Generally, it should not exceed 1 / 3 of the thickness direction of the printed circuit board, that is, the top of the wave crest should exceed the welding surface of the printed circuit board, but not the component surface.

At the same time, the stability of wave crest height is also very important, which mainly depends on the equipment manufacturer. In principle, the higher the wave crest, the larger the solder surface in contact with the air, the more serious the oxidation and the more tin slag. On the other hand, if the wave crest is unstable, when the liquid solder falls back from the peak, it is easy to bring air into the molten solder and accelerate the oxidation of solder.

3. Clean up

It is necessary to clean the surface of tin furnace regularly. Otherwise, the solder falling from the peak falls on the surface of the tin slag, and enters the semi solidified state due to the lack of good heat transfer. Such a vicious cycle will also lead to excessive tin slag.

4. Addition of tin bar

The height of the furnace surface should be checked before starting up every day / every time. Don't open the wave peak first, but add the tin bar to make the soldering tin in the tin furnace reach the full state. Then turn on the heating device to melt the tin bar.

Because the melting of the tin bar will absorb heat, the temperature in the furnace is very uneven at this time. The wave peak can not be opened until the tin bar is completely melted and the temperature in the furnace reaches a uniform state.

Timely replenishment of tin bars can help to reduce the height difference between the welding surface and the welding surface, that is, reduce the contact area between the soldering peak and the air, and also reduce the generation of tin slag.

5. Cleaning of bean curd residue like Sn Cu compounds

In the process of wave soldering, the copper on the surface of printed circuit board and the copper on the pins of electronic components will continue to dissolve into the molten solder. Cu6Sn5 intermetallic compound will be formed between Cu and Sn. The melting point of the compound is above 500oC, so it exists in solid state.

At the same time, since the density of the compound is 8.28g/cm3 and the density of Sn63-Pb37 solder is 8.80g/cm3, the compound will generally float on the surface of liquid solder in the form of tofu residue. Of course, some compounds will enter the solder due to the wave crest.

Therefore, the work of copper discharge is very important. The method is as follows: stop the wave crest, the heating device of the tin furnace operates normally, and first clean up all kinds of residues on the surface of the tin furnace to expose the mercury like mirror state.

Then reduce the tin furnace temperature to 190-200oc (at this time, the solder is still in liquid state), stir the solder with tools such as an iron spoon for 1-2 minutes (to help the Cu Sn compound inside the solder float up), and then stand for 3-5 hours.

Due to the low density of Cu Sn compound, the Cu Sn compound will float naturally on the solder surface after standing. At this time, the Cu Sn compound on the surface can be cleaned with tools such as iron spoon.

Source: Changjiang nonferrous metals network

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