It is easy to make some errors when there is a huge task of modifying hundreds of PCBs. As a result, you may experience a pcb soldering defect when embarking on these tasks.
Even workers that are more advanced may make mistakes at times like under or overheating a pad or pin or covering with too much or too little molten solder.
In order to ensure that these mistakes or errors are avoided, and to master the most appropriate solder joint, then it is very important that you learn ways of understanding soldering problems and identifying bad solder joints.
12 Types of Soldering Defects
If your eye is properly trained, you will easily spot the well known types of soldering defects or soldering problems. Joints that are properly soldered will be symmetrical and have a concave shape.
It will also be orderly and clean in contrast to its neighbors. So also, a joint that is improperly soldered will look messy and feature some abnormality like long stems and very swollen shape.
Below are the 12 major soldering defects or mistakes
Disturbed Joint
A very common issue along a solder joints’ rows and columns is a disturbed joint. This usually comes with a distorted, bloated, and at times a flaky appearance. Also, the main cause of any disturbed joint is when there is a movement during the solder application.
If there are circuit boards mounted on a non-stable soldering surface and somehow swerves or shakes during the solder application, then this could result in a disturbed joint thereby making it lose the composition.
There could also be a disturbance when the board experiences some vibrations or movements during the drying of the solder mask.
Note that disturbed joints are not the same as cold joints. Though their appearance is similar, they are caused by different problems. There are cases whereby this issue is corrected by simply reheating the joint and leaving it to harden without more disturbances.
To avoid the occurrence of disturbed joints any other time, make sure that during the solder application, the joints are stable and immobilized.
Untrimmed Leads
A very dangerous error that is usually seen on the soldered joints can happen due to untrimmed leads. This usually sticks out just like horns. You can spot them easily with your naked eyes.
For normal leads, they possess a concave shape, however for untrimmed leads, they usually stick out more and higher and oftentimes, they have a little sideways tilt.
Now, if two out of all the untrimmed tips contract each other, then you could have a short circuit. Even if these leads stand upright, they can be bent easily with time and then make contact.
Rectifying untrimmed leads is easy. You can achieve this when you trim them to the right size for any standard joint. Take this same tool used in solder trimming and then pare each of them down to bring down the joint to a similar height as others present on the circuit boards.
Overheated Joint
This is another soldering defect. Across solder joints that are newly soldered, one of the well-known possible issues is an overheated joint. This usually forms during solder application whereby the individual applying the solder mask, applied too much heat.
Explaining further, this means that the iron was preheated in excess just before applying the solder mask. These overheated joints usually look burnt, having malformed and lumpy joints.
To solve for overheated joints, all you need to do is to scrape the burnt flux off using the tip of any of your working tools.
Also, another method is using a solution like isopropyl alcohol to get rid of your burnt flux. However, the best way to solve this problem is applying alcohol using a mini toothbrush
An overheated joint usually poses a problem to repair them. This is why you should avoid it the best possible way. To make sure that this doesn’t happen again, ensure your iron is heated to the right temperature.
Also, try to double check to ensure the cleanliness of the solder joints before you apply the solder. Insufficient heat isn’t good either.
Insufficient Wetting of the Surface Mount
If the pin is heated without the pad when applying the solder, this could lead to insufficient wetting of the surface mount.
Here, the surface mount components did not flow to the solder pad. Also, you can identify the site easily if you discover irregularities present in some row of mounts.
If some of these mounts flow properly to the pad, and one or about two more mounts retain their initial pin composition, then the problem might have been caused by a pad that is not properly wetted.
To solve the pad with less wetting as expected, preheat your iron tip to reach the required heat level. After this apply it onto the solder pad.
Furthermore, add more solder onto the solder pad, then allow it to flow into place and then melt into the right shape with the pin’s solder. To ensure that this problem never happens again, make sure that you heat the pad even before you heat the pin.
Cold Joint
A cold joint is another problem usually seen on boards that are newly soldered. This usually features a lumpy and at times a shapeless appearance. These cold joints form during the application stage whereby the solder doesn’t reach the right melting state.
Apart from their strange appearance, the cold joints have problems because they cannot fulfill their purpose. Furthermore, cold joints lack enough bonding ability. Also, over time, they develop cracks.
At times, cold joints can be repaired by reapplying some heat onto it. This can be accomplished by the application of hot iron to the cold joints until the flowing of the solder into place happens. At times, cold joints also have too much solder. If this is the case, you can get rid of it using the hot tip of an iron. In order to prevent cold joints from happening in the future, ensure the iron is heated to the right temperature before the application of the solder.
Insufficient Wetting of the Pad
Note that if the solder pad does not get enough wetting when soldering is ongoing, then the joint will look uneven, which indicates that there is no bonding potential. Most of the time, a large quantity of solder brings enough solder wets to the leads. However, the pad won’t have enough bonding strength.
Usually, wetting issues could happen if the solder is applied onto a stained or dirty circuit board. Because there are dirts present on the board, this solder won’t bond properly. There are times where this pad will not get enough wetting. This can happen if the pin and pad lacks the right heat during the application.
In order to reverse this issue of a non-sufficiently wetted pad, the iron bar’s tip will be heated to the right temperature and then placed onto the base of the joint. Also, allow the solder to flow over your pad. Now, to ensure that this issue never happens again, ensure that the board is neat before you go ahead with the application. Also, make sure that you preheat the pad and the pin to the right temperature level.
Solder Starved
The joint is solder starved, if the joint does not have enough and therefore needs more solder. When a joint doesn’t have the expected amount of solder, it won’t have the necessary strength to serve or function the way it should.
When you don’t add the right quantity of solder, then a joint can crack when under stress. This can cause failure to the board. Though joints that are solder starved may have a good conductivity, the board will still not be useful unless this problem is rectified by reapplying the solder to that specific joint.
In order to fix this joint, preheat it using your iron’s tip. Then apply extra solder to this same spot just like the initial application. After this has been completed, this joint ought to be more consistent and stronger with others present on the board. Furthermore, the joint should now handle stress and ensure safe use in any computing device.
Insufficient Wetting for the Pin
Whenever there is a poor or insufficient wetting process of the pad and then there’s no wetting on the pin, you will most likely see a case whereby the pin didn’t get enough heat-treatment. Therefore, this leads to not enough wetting for the pin.
This is the kind of problem that occurs when you fail to give enough heat to the pin. What results is not allowing the right time for the flowing of the solder into place.
Now, to correct this, reheat the tip of the iron to the right level of temperature and then apply more solder. Also, when doing this reapplication, ensure that the hot iron’s tip touches both the pad and the pin. This measure is very necessary to help in conditioning the surface mount component for the right application.
Furthermore, to ensure that this problem doesn’t happen again, ensure that the pin and pad are heated to the right level when applying solder.
Too Much Solder
Another huge problem that involves the solder quantity has to do with a large amount or excess solder. You can easily spot these kinds of joints on the board.
This is because this joint will look swelled and round similar to what a bubble looks like. Healthy joints, on the other hand, that have the right solder amount usually forms a concave shape.
Furthermore, when you use too much solder to cover a joint, then it may lack the required electrical conductivity. Although the joint may not fall for stress cracks, this joint will fail to deliver on its true purpose.
Now, to help fix joints that are overly soldered, there’s a need to get rid of some solder present and pare this joint down to form the right concave shape.
In order to pare down this solder, get the tip of the soldering iron heated and then make use of it to trim off some excess solder.
Continue with this till the joint forms a different look asides being inflated and round. With solder-sucker you find it easier to remove any excess solder.
Solder Bridge
Solder bridging is when too much solder melts in-between a board’s neighboring joints, this could help in winding up a solder bridge.
On a printed circuit board, there’s a reason why the joints are usually separate. If a contact is unintentionally formed between the two joints during the solder application, then this problem, solder bridging has to be rectified immediately. If not, this board will be unusable.
Lifted Pads
Asides having issues with joints, this is another one of the soldering problems. you may discover spots whereby these solder pads are separated from the board.
Also, in spots whereby a joint has been overworked, or the solder has experienced several treatments from hot iron, then you may end up having a lifted pad.
A lifted pad usually happens as a result of constant and excess stress placed onto the board. Take for instance, if a solder bridge is removed with hot iron and the lateral bleed-over is scaled away from the joints, then you may lift it too much accidentally. This could cause the solder joint to dislodge from the circuit board altogether.
A lifted pad is very common for boards having thin copper layers and where through-plating does not exist. You can repair lifted pads, although the task may be a challenging one.
The repair method that is most practical is folding of the solder lead and bonding it to a copper trace that is still intact.
Stray Solder
There are soldering problems where you have bits of solder present on the circuit board due to messy oversights coming up when soldering. This is called stray solder.
The unintended bits will not be attached to the copper trace and they are usually bonded with the flux residue. If you haven’t joined the bits to something else on the circuit board, it is important that you still remove them even before making use of the board.
Conclusion
Joints that are properly soldered on PCBs are necessary to conduct currents safely, as well as serve as intended in a computing as well as electronic components or device. We at RayMing PCB offer electronic repair and PCB design services and if you wish to learn more about our services, please reach out to us here.
