What are the reasons for PCB bad soldering(cold soldering)？

Reasons:

Bad soldering or cold soldering means that after the components are soldered on the PCB board, the surface looks very good and there is no problem, but the internal connection is not really well connected to the circuit, or the connection is unstable and intermittent. In this case, PCBA cannot work stably and normally. These are invisible problems. Let’s summarize the various reasons for bad soldering. It is mainly the answer summed up by our factory over the past 25 years.

1:Caused by poor soldering or less tin. 

This includes the SMT part and the DIP part. In the SMT part, precise high-quality stencil should be made according to the thickness of the PCB and the packaging of the components, which will help the tin on some precision components. In addition, in the DIP part, skilled workers will master the welding time and the direction of pulling the solder wire, so that the solder joints are full and fully melted.

2:Another reason should be seen from the material aspect.

PCB pads of good quality are flat and vacuum-packed without oxidation. And there is no board warping, so that the components can be welded very firmly. Another point is the quality of the components, the pins of the components are not oxidized, so that the quality of welding will also be guaranteed.

3:The third reason is that after long-term use, the pins of some components with large heat generation are seriously aging, and they are directly peeled from the pads.

How to find the position of bad soldering?

When a batch of PCBA production is over, the factory usually conducts functional tests on these PCBAs. Bad soldering/cold soldering is a very common cause of failure. Let’s talk about the method to find out the position of the bad soldering.

1. Judge the rough scope of the fault based on the occurrence of the fault phenomenon;

Engineers will determine the location and components of the problem based on the fault phenomenon. Combine the schematic diagram to analyze the cause of the problem.

 

2. Observe the appearance, focus on the larger components and the components with a large amount of heat;

Through observation, focus on the components that have a high temperature to the touch, a large current passing through them, and a large amount of heat. These components are likely to peel off the pad due to overheating.

 

3. Use a magnifying glass to observe;

Use a magnifying glass to check the soldering condition of the pad.

 

4. Use X-Ray to detect the welding quality of chip and BGA.

Because of the special package of some chips, it is impossible to observe through a magnifying glass. Components with very small pitch are also high incidence locations for poor soldering.

5. Shake the suspicious component by hand, and observe whether the pin solder joints are loose.

Wear an anti-static wristband and gloves. Lightly touch or shake components that may be soldered. Determine whether the pins are poorly welded or loose.

Methods to solve the Bad soldering of PCBA

1. The components must be stored in moisture-proof;

Regular circuit board production factories will use vacuum packaging, and there are moisture-proof bags inside, which can prevent moisture and oxygen from damaging the PCB.

2. The pins of DIP components can be slightly polished;

For DIP type components, you can slightly polish it.

 

3. When soldering, solder paste and flux can be used, preferably reflow soldering, manual soldering requires good technology;

 

4. Choose a good board to make PCB, and choose a good surface treatment according to the accuracy of the component. Such as ENIG.

 

In the PCBA processing process, virtual soldering is an important reason that affects the quality of the circuit board. Once the virtual soldering phenomenon occurs, it needs to be reworked, repaired or reproduced. In this way, the production efficiency is not high, the cost will increase, and the delivery time will be prolonged, which will cause losses to both the enterprise and the customer. Therefore, it is necessary to avoid the occurrence of false welding as much as possible and do a good job of inspection. Once the false welding occurs, the cause needs to be found and solved immediately .

 

The above is the entire content of this article. If you have any questions or suggestions, you can contact us at any time.