Why did the SMT pad fall off easily when soldering the PCB boards?

PAD fall off?

The general double panel or single panel is easy to fall off the pad. Therefor, the multi-layer plate has a large area of floor, fast heat dissipation, welding temperature is also high, not so easy to fall off. Today, we have focused on wave welding to discuss why the solder pad is easy to fall off.

Wave peak welding off parts


In one case, during wave soldering the parts are dropped . According to my experience, the reasons are as follows:

1.SMT red adhesive is not enough!

2. The furnace temperature is too high!

3 wave peak too low will rub the original off

It is also possible that the organic acids of the flux used will react with the red glue.

The preheating of the wave peak is not turned on, and the guide element suddenly heats up and jumps up.

Personally, I think the answer to red glue can be obtained from the tensile test of red glue. If red glue has nothing to do with the flux problem, more.

6. The temperature exceeds the curing temperature of the red glue process, resulting in the drop of parts

7. Mount offset. The design of components and pads is not reasonable

8. The height of the part body exceeds the SMD protection wall and is scraped off.

9. The melting point of solder paste is lower than the peak soldering temperature

10.SMT mount blank welding.And the grave.

11. Damaged parts of external force before wave welding furnace.

12. Thermal impact causes parts cracking, mainly because SMT red glue can not withstand high temperature shock wave welding. Especially the thermal conductivity of glass two tube is very fast. So SMT red glue deep can not stand the temperature, the guide element will fall.

13. The red adhesive patch board is lost due to improper operation during the transfer operation.

SMT wave peak welding patch drop prevention

1. Whether the temperature curve is in line with the requirements during reflow welding!The temperature is too high to make the glue brittle.As a result, there will be cracks in packing and packing, and they will fall off when welding over the wave crest. If there are missing parts, can we check whether they fall off in the preheating area or in the tin furnace?

2, the bottom of the peak height to reduce the momentum.

3. The bottom of the track is so that the bottom component of the PCB board and the nozzle of the tin furnace collide and fall off. If this reason increases the height of the track.

4, when the pin is installed, it collided with the bottom element. The offset of the patch will cause this situation. The production process need improved. First of all, the PCB products produced by the red glue process. It will not fall off under normal circumstances if there is no external force. Even if the amount of glue is small, or other adverse factors exist, as long as they are not impacted or squeezed by external force, they will not fall off. If we open the package again, we suggest that the production operator start from the packaging, PCB may be squeezed in the packaging, inverted in the transportation process and other factors.

In addition, the analysis is relatively fixed position, is the component larger? The amount of glue can also apropriatly improve. There is also a red glue after solidification, the contact area with the element is also a problem to consider.

In SMT SMT process, red glue process is often used to complete, but when the mounted components of red glue process are welded over the wave crest, electronic components (especially glass diodes) often encounter the problem of falling off parts, which is a very vexing problem for SMT engineers.

Now we special for the red rubber plate over the wave peak welding when the reason and solution to make a detailed analysis and solution here:

Analysis of the reasons for the red glue plate falling:

1. If the patch element falls off with the green oil (welding oil) of the PCB board, it indicates that there is a problem with the material of the PCB board itself (the adhesion of the green oil is not enough);

2. Watch whether there is scratch on the position where the PCB board patch element falls. Scratch on the position where the PCB board patch element falls will also make the adhesion of the green oil insufficient;

3. Watch whether the PCB patch elements fall regularly. 

4, the patch element fell off, but the red glue is still well stuck on it, the reason is: the patch element incoming material has a problem (patch element surface treatment has a problem, such as a release agent, affect the adhesion of red glue);

5. The patch element falls regularly, the hole of red rubber steel mesh is blocked, and the amount of red rubber is too little;

6, if the patch element does not fall regularly, you have to consider whether the viscosity of the red glue is not enough, the red glue has expired, the temperature of the red glue is not enough and other reasons;

7, patch components in the process of transportation. Such as (glass diode), it is necessary to place the PCB board no stacked. Use of bubble bags or other buffered packaging materials to package the circuit board, avoid components collision and parts;

8, patch components fall because :PCB board after the patch storage time is too long, generally seven days after the patch need to pass tin, if more than time, red glue will slowly lose viscosity and paste instability resulting in bad parts.

At end

Electronic products manufacturers or electronic patch processing plants can make a comprehensive analysis and test of the products according to the above eight reasons before the red-rubber plate over the wave crest welding, which can greatly avoid the chance of the red-rubber plate over the wave crest welding, improve production efficiency and reduce the rate of defective products