Two tricks to get the welding solder beads, easy to learn!

"Solder beads" appear during the "wave soldering" process

 In the "wave soldering" process, "solder beads".There are two situations: one is that when the board is just in contact with the tin liquid, due to the excessive moisture of the flux or the plate itself, or the high boiling point solvent is not fully volatilized, it suddenly volatilizes when it encounters the high temperature tin liquid, and the large temperature difference causes the liquid solder to splash out and form tiny tin beads; The other is that when the circuit board leaves the liquid solder, when the circuit board is separated from the tin wave, the circuit board will pull out the tin pillar along the extension direction of the pin, and under the wetting effect of the flux and the fluidity of the tin liquid itself, the excess solder will fall back into the tin cylinder, and the splashed solder will sometimes fall on the circuit board, and then form "tin beads". Therefore, we can find that in the prevention and control of "solder beads" in "wave soldering", we should start from two aspects, one is the selection of raw materials such as flux, and the other is the process control of wave soldering.

(1) Cause analysis and prevention and control methods of flux

<!--[if !supportLists]-->1.<!--[endif]-->The moisture content in the flux is large or exceeded, and it fails to fully volatilize during preheating;

<!--[if !supportLists]-->2.<!--[endif]-->There are substances with high boiling points or non-volatile substances in the flux, which cannot be fully volatilized during preheating.

These two causes are caused by the "quality" of the flux itself, which can be solved by "increasing the preheating temperature or slowing down the board speed" in the actual soldering process. In addition, before selecting flux, the actual process should be confirmed for the samples provided by the supplier, and the standard process at the time of trial should be recorded, and in the absence of "solder balls", other instructions provided by the supplier should be reviewed, and the supplier's initial instructions should be checked in the subsequent receipt and acceptance process.

(2) Process cause analysis and prevention and control methods

<!--[if !supportLists]-->1.<!--[endif]-->The preheating temperature is low, and the solvent part in the flux is not completely volatilized;

<!--[if !supportLists]-->2.<!--[endif]-->The speed of the board is too fast, and the preheating effect is not achieved;

<!--[if !supportLists]-->3.<!--[endif]-->The inclination angle of the chain (or PCB board surface) is too small, and there are bubbles in the middle when the tin liquid is in contact with the soldering surface, and tin beads are generated after the bubbles burst;

<!--[if !supportLists]-->4.<!--[endif]-->The amount of flux applied is too large, and the excess flux does not flow away completely or the air knife does not blow the excess flux off.

The occurrence of these four undesirable reasons are related to the determination of the standardized process, in the actual production process, the parameters should be corrected in strict accordance with the work instruction documents that have been formulated, and the parameters that have been set can not be changed at will, and the relevant parameters and technical aspects involved are mainly as follows:

(1) About preheating: generally set at 90 - 110 degrees Celsius, where the "temperature" refers to the actual heating temperature of the soldering surface of the PCB board after preheating, rather than the "apparent" temperature; If the preheating temperature does not meet the requirements, it is easy to produce solder beads after welding.

(2) About the walking speed: In general, it is recommended that the user set the walking speed at 1.1 - 1.4 m/min, but this is not an absolute value; If you want to change the speed of the board, it should usually be matched by changing the preheating temperature; For example, in order to speed up the speed of board walking, in order to ensure that the preheating temperature of the PCB soldering surface can reach the predetermined value, the preheating temperature should be appropriately increased; If the preheating temperature remains the same, the flux may not evaporate completely when the board is too fast, resulting in the formation of "solder beads" during soldering.

(3) Regarding the inclination angle of the chain (or PCB board surface): This inclination angle refers to the angle between the chain (or PCB board surface) and the tin liquid plane, when the PCB board passes through the tin liquid plane, it should be ensured that the PCB part surface and the tin liquid plane have only one tangent point, and there can be no large contact surface; If there is no inclination angle or the inclination angle is too small, it is easy to cause bubbles in the middle of the contact between the tin liquid and the soldering surface, and the bubbles will burst to produce "tin beads". (4) In the use of wave furnace, the main function of the "air knife" is to blow off the excess flux on the PCB board surface, and make the flux evenly coated on the PCB part surface; Under normal circumstances, the inclination angle of the air knife should be about 10 degrees; If the angle adjustment of the "air knife" is unreasonable, it will cause too much flux on the surface of the PCB or uneven coating, which will not only be easy to drip on the heating element when passing through the preheating area, affecting the life of the heating tube, but also easy to cause the phenomenon of "fried tin" when immersed in the tin liquid. This in turn produces "tin beads".

In the wave soldering process, the generation of solder beads can be divided into two situations: when the board just comes into contact with the tin liquid and when it leaves the liquid tin liquid. In order to solve this problem, prevention and control can start from two aspects: flux raw material selection and wave soldering process control. In terms of flux, large or excessive moisture content, substances with high boiling points or non-volatile substances are quality problems, which can be solved by increasing the preheating temperature or slowing down the speed of board walking, and it is necessary to do a good job in supplier sample trial and data review. In terms of process, the four undesirable reasons are low preheating temperature, fast board walking speed, small inclination angle of chain (or PCB board surface), and large flux coating amount, which are related to the determination of standardized process. In the actual production, the parameters should be corrected in strict accordance with the work instruction documents, including the preheating temperature should be 90 - 110 degrees Celsius (refers to the actual heating temperature of the PCB board welding surface), the board walking speed is generally 1.1 - 1.4 m/min and the change speed should be adjusted with the preheating temperature, the inclination angle between the chain (or PCB board surface) and the tin liquid plane should ensure that the PCB part surface and the tin liquid plane have only one tangent point, and the air knife inclination angle is generally inAbout 10 degrees and the angle adjustment is not reasonable, there will be many adverse effects. Through the detailed analysis and control of these aspects, the generation of solder beads in the wave soldering process can be effectively reduced, the welding quality can be improved, and the stability and reliability of the product can be guaranteed. This is critical for related industries such as electronics manufacturing, where solder beads can cause problems such as short circuits in circuits that can affect product performance.