Soldering forms a significant part of the manufacturing as well as assembly of a PCB. A cold joint solder is one of the most known issues during soldering. These solder joint types affect the PCB’s performance to a very large extent. Asides from this, the cold joints will increase the cost of your PCB assembly.
What Does PCB Soldering Mean?
PCB Soldering Involves the process, which forms electrical and mechanical connections on a PCB. Normally, manufacturers make use of a combination of Lead and Tin for binding all electronic components that should be placed on a PCB surface.
What Does Cold Solder Joint Mean?
Cold joint solders usually occur whenever solder doesn’t melt completely to form proper joints. This wrongly formed joint or cold solder joint could cause reliability issues for any electronic assembly. With a cold solder joint, there will be an increase in the solder joints’ electrical resistance. This then reduces the solder joints’ reliability.
Below are some of the factors, which could result in cold solder joints.
- Improper wetting, reflow, or melting of a joint’s solder
- Disturbances like vibrations whenever the solder cools down
- Too high process temperature results in the premature breakdown of the flux
- Too low process temperature of solder joints can result in incomplete wetting
You can detect a cold solder joint using magnifying glass or through visual checking. Cold solder joints may look deformed, convex, whitish, and dull, which is much different from the normal solder joint.
What Type of Cold Solder Joints are There?
You can classify this bad solder joint into different types. Each has its own specific behavior and causes. The main types include:
- Dry solder joints
- Cracked solder joints
- Cold solder joints
Dry Solder Joints
Dry solder joints can be described as joints that are soldered, but not with enough solder. Whenever molten solder gets inside or flows in the joints, the whole connection will wet, so that whenever it solidifies, there’ll be a reliable electrical connection established.
Dry solder also lacks enough metal, which in several cases, causes a circuit that is completely open. For other cases, this joint might have intermittent high resistance and electrical conductivity. This causes noise during operation. Also, a dry solder joint has a matt or dull finish that is easily identifiable.
Cracked solder joints
From the name, cracked solder joints are caused from stressed solder joints which yields forming a crack. Immediately the crack begins to set in, its pin gets detached partially from its board causing it to move freely. The movement could break or close the electrical connection; this depends on the crack’s profile.
This electrical connection stops and start will result in the failing or the working of that specific appliance on random occasions. Vertically mounted heavy components are the components that are most susceptible due to gravity. When the boards flip or move constantly, this issue becomes exaggerated as this crack widens.
The cracked solder joint is usually an issue when CRT monitors are on transit. Usually, these monitors are placed in padded boxes by manufacturers to help reduce vibrations as well as the chances of cracked solder joints happening.
Cold Solder Joints
Generally, cold solder connection joints could be both cracked and dry. Nevertheless all the cracked solder joints aren’t cold joints. However, this doesn’t stop the fact that cracked solder joints would be a problem at some point, if it isn’t attended to.
Factors that Could Lead to Cold Solder Joints
The major cause of a cold solder joint can be seen in this section.
Insufficient Solder Application
Weak solder condition is known whenever solder spots lack enough tin during the tinning of the board. Also, there are other possible cold solder joint causes; however, the one that is most frequent is inadequate heat provided throughout the process. Also, inadequate application of solder could lead to poor connection. This could also cause electrical shorts.
Insufficient heat
One soldering error which causes cold solder joints isn’t heating the two surfaces all at once, or the inability to heat them sufficiently. It happens whenever the soldering iron stands at a very low temperature or whenever you place the soldering iron on component pins for less time. You need reheating for this situation.
There’s another instance where the pin of the components isn’t heated even whenever the tip of the soldering iron is touching as well as heating the circuit board pad. Because of this, solder bonds properly to the circuit board pad and not the component’s pin. Also, this could happen another way, leading to the bonding of the solder to the component pin but not with the circuit board pad.
Poor Cleaning
At times, while trying to rush through the process of soldering and not being attentive to detail, the solder joint could come in contact with dirt. Also, contaminants like metal oxide, grease, and grime might prevent good soldered joints from happening. Normally, it becomes noticeable whenever the solder doesn’t bond with dirty surfaces due to the formation of globules or beads. In addition, this interference could make this solder to take so much time to wet this joint, which results in cold solder joint causes.
Asides from what we have already discussed, there are other predisposing factors that cold solder joints possess. The factors include:
- Selective soldering frames
- Contamination of the solder alloy
- Uncomely wetting, melting, and reflow at joints
- Relative disturbance found between the boards and its components before the complete solidification of the solder
- Soldering temperature is too low, which leads to incomplete wetting
- Soldering temperature is too high, which leads to the flux breaking down prematurely
Detecting and Testing Cold Solder Joints
At present, freelancers that meet tight deadlines usually get majority of electrical projects assigned to them. This freelancer will have to be very fast, in order not to mess the timelines of the client. More often, this quick results in the cold solder joint might be too difficult to notice during soldering.
Immediately the board is completed, this electrical engineer will then go ahead to handle the issue of the board not working. First, conduct tests. But how can you achieve this?
Visual Checking
The solder joints of printed circuit boards are usually tiny. This is why you will need a spotlight and magnifying lens. First, check the joints’ color, As mentioned earlier, dry solder joints are dull.
Next check the solder joint’s shape. It is deformed or lacks a concave shape, then the solder alloy failed to melt sufficiently as a result of improper heating. It could cause cracking and will eventually detach from the board whenever the joint is heated up by resistance.
Next, make use of a magnifying lens and torch to see whether light is passing through any of the joints. If light truly passes, then the joint is inadequately bonded.
Lastly, tilt this board and check if the joint detaches partially from the board’s base. Also, you may check for any overspills top make sure that short circuits were not created. This is because they can ruin this board completely.
Check using a multimeter
Multimeter helps in checking the continuity and resistance across joints. By this, you will be able to know if there is something wrong about the joint.
Testing for the resistance
On resistance mode, set your multimeter to 1000. To be sure your device is functioning effectively, try to interconnect this testing probe. You ought to get a reading of zero. Connect a testing terminal on one of the joints to the second terminal through another component.
When this component isn’t a resistor, you will get a reading of zero all the time. Once your reading is higher than zero, then there’s a high chance that there’s a cold joint.
Testing the Device’s continuity
Here, you will switch the device to the continuity mode. This is to test the functionality of your device through connection of the test terminals. Normally, this gives a beep sound. Now, connect both test terminals to any of the solder joint’s ends. It you don’t get a beep, then there is need for rework on that joint.
Repairing the Cold Solder Joint
The most common type of cold solder joints are the disturbed and normal cold solder joints.
Normal Cold Solder Joint
The two major causes of cold solder joints is the inadequate heating of the soldering iron as well as contaminated soldering tips. Before use, ensure that the tip of the soldering iron is very clean. After use, make sure the tool is stored in a box. This is to prevent particles of dust from getting to the tip.
Furthermore, make sure that the tip of the soldering iron is well heated before use. You can even use any soldering station having a working temperature that is easy for you to regulate. Once you are able to achieve the ideal heat, reheat this solder and mount it. Also, if you discover that the soldering iron is cooling fast, make use of the SN96 lead-free solder alloy. The alloy will melt at lower temperature as well as exhibit plastic time of transition.
In addition, the cold solder joint feature high resistance. This is happening due to the solder iron not melting completely. This high resistance could lead to excessive heating, which could ruin the board or the component immediately or later on. It will also lead to high consumption of power.
Disturbed Cold Solder Joint
They usually happen whenever the soldered components or board is moved before the sufficient solidification of the solder. Here, the most important feature is its concave shape as well as a tilted pin within a solder spool. In order to prevent this problem, the board has to be soldered on tightly fixed tables or wall-mounted soldering vices where space could be an issue.
Ways you can Prevent Cold Solder for Electrical Connections
There are some simple strategies to work with to avoid and prevent cold solder for electrical connections. These include:
Pay attention
During the application of solder, take time and pay attention to whatever joint you will be manipulating. Ensure this solder has melted sufficiently as you apply it carefully to your desi8red location. Also, ensure that you’re working with flat surfaces. With this setup, you will be able to reduce runoff as well as prevent the dripping of the solder onto the other areas of your component.
Work with high-quality equipment
Just like all other devices, as they age, the solders could be prone to experiencing failure, and therefore may not heat the filler material efficiently. Also, devices not function effectively have a higher chance of producing cold solder joints. This is why it is important to work with high quality equipment. Also, if the soldering equipment isn’t functioning the way it should be, then replace it quickly.
Attend some certification classes
To become an expert at soldering as well as reduce the possibility of creating any co9ld solder joint, there is a need to attend some certification classes. While attending these classes, you’ll learn and understand those soldering techniques which will assist you in creating solder joints of high quality, which will also help in improving the outlook of your career.
Adequate Application of Heat
Cold Joint results whenever the solder applied don’t melt completely. One reliable way of preventing this is to make sure that your soldering iron has been properly pre-heated with enough power. This is to achieve the best possible soldering temperature. Its peak temperature has to be kept at a minimum of 15 degrees Celsius above the melting point of alloy for a minimum of 45 seconds. By so doing, you will be able to avoid any unreliable solder.
Conclusion
Cold solder joints results due to the improper execution of the soldering process of the PCB components. As we have already explained in our article, the cold solder joint can increase the solder joint’s electrical resistance, which will affect the solder joint’s reliability adversely.
