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What is the reason for solider bridge of wave soldering ? How to Control it?

PCB Wave soldering is to make the soldering surface of the board directly contact with high-temperature liquid tin for welding purposes. The high-temperature liquid tin maintains a slope, and the liquid tin forms a wave-like phenomenon by special means, so it is called “wave soldering”. The main material is solder bars. This article mainly introduces the content of wave soldering and tinning. Firstly, it introduces the phenomenon of wave soldering and solder touch. Secondly, it introduces the reason of wave soldering. Finally, it explains the wave soldering to remove solder tough technology and how to reduce tin tough .

Wave soldering

Wave soldering solder touch phenomenon

1. Due to the phenomenon that the electronic component pin are too long when the board is over-wave soldering, the component trimming should be pre-processed: the extension length of the component pins is 1.5-2 mm, which does not exceed this height. There will be no phenomenon

Wave soldering solder touch phenomenon

2.Because the circuit board process design is more and more complicated, the lead pin spacing is getting denser and denser, and the wave soldering phenomenon is touchedafter the soldering. Changing the pad design is the solution. For example, reducing the pad size, increasing the length of the pad exiting the wave side, increasing the flux activity/reducing the pin extension length is also a solution.

pin spacing is getting denser

3. The phenomenon of solder touched between the components formed after the molten tin is wetted to the surface of the circuit board in wave soldering. The main reason for this phenomenon is that the inner diameter of the pad is too large, or the outer diameter of the component is too small.

The phenomenon of solder touched

4.  The component pin solder tin touch after the dense foot components are densely packed in a region to form a wave

component pin solder tin

5.Wave soldering solder touched due to excessive pad size

Wave soldering

6. The phenomenon soldering touch after wave soldering due to poor solderability of component pins

poor solderability of component pin

What is the reason for wave soldering solder touch?

1.Flux activity is not enough.

2. The wettability of the flux is not enough.

3. The flux applied is toolittle.

4. Non-uniform coating of flux. .

5. Part of the circuit board can not be coated with flux

6. the circuit board area is be coated with tin

7. Some pads or solder pin are heavily oxidized

8.  Unreasonable layout of circuit boards (unreasonable distribution of parts

9. The direction of working board is wrong.

10. the tin is not enough, or copper exceeds the standard; [excessive impurities cause the melting point of the tin liquid to rise]

11. The foaming tube is clogged and the foaming is uneven, leading the uneven coating of the flux on the circuit board.

12. 1 The air knife setting is unreasonable (the flux is not evenly sprayed). .

13. The board speed and preheating are not matched.

14. Improper operation when immersion tin by hand.

15. The inclination of the chain is unreasonable.

16.  the wave peak is not flat.

pcb assembly soldering machine

Wave soldering removal solder touch technology

There are many advanced supplement options in various machine types. For example, a patented hot air knife to bridge technology is provided to remove bridging and solder joint damage testing. The air knife is located at the exit of the solder bath to emit a narrow hot air of 0.4572 mm toward the solder joint at an angle of 40 to 90 degrees from the horizontal. It allows all re-filled solder joints that are not sufficiently soldered at the first time due to air retention, without affecting normal solder joints. However, it must be noted that in order to achieve a significant increase in solder joint quality, there is no need to set more options on the wave soldering equipment. And for all production equipment, it is also important to check the true accuracy of each engineering data. A good method is to run the board first with the machine before purchase.

How to reduce the wave soldering solder touch

1. Design according to PCB design specifications. The long axes of the two end Chips are perpendicular to the welding direction, and the long axes of the SOT and SOP should be parallel to the welding direction. Widen the pad on the back of the SOP (design a scratch pad)

2.The pins of the plug-in components should be formed according to the pitch of the printed board and the assembly requirements. For example, the short-insertion sub-welding process is adopted, and the surface of the soldering surface component is exposed to the surface of the printed board by 0.8~3mm, and the component body is required for the insertion. correct.

3.Set the preheating temperature according to the PCB size, whether the multi-layer pcb board, the number of components, and the mounted components.

4. The temperature of tin wave is 250±5°C, and the welding time is 3~5s. When the temperature is slightly lower, the conveyor speed should be slower.

5. Replace the flux.