What is cold Solder, what causes it, and how can you avoid it?
A PCB features closely packed parts, and soldering gone wrong will significantly impact its performance.
Therefore, soldering a PCB is an art that requires expertise to avoid common issues, such as forming cold solder joints.
Today, we will highlight this issue and how to avoid a cold solder joint. Let’s get started.
What Is Cold Solder And Why it Should Be Avoided
Sometimes when soldering, the Solder may fail to melt appropriately, which will, in turn, cause an imperfect joint on the circuit board (cold solder joint).
You can tell a cold solder from the following features:
- It has a rugged/rough and dull appearance.
- Also, it features an uneven appearance and may sometimes drip into unintended parts of the circuit board.
Best Soldering Procedures
Soldering circuit board electronic components.
The ideal solder joint should feature a concave shape appearance when soldering through-hole components.
You should align your Solder at an angle of between 40 and 70 degrees to the PCB.
Also, it would be best to heat your soldering iron to a peak temperature of approximately 15 degrees above its melting point.
This will ensure it melts to a fluid that easily spreads on the soldering spot.
The approach for soldering surface mount components is slightly different.
We apply reflow soldering for this; therefore, you don’t expect the solder joint to be concave-shaped.
Why You Should Avoid a Cold Solder Joint
- A cold joint limits the PCBs and devices’ overall performance and efficiency.
- Also, it can lead to increased electrical resistance, which leads to joint failures, because cold joints are prone to malfunctioning.
Causes of Cold Solder Joint
Here are the three leading causes of cold solder joints in electronics assembly.
Soldering with a hot iron.
Ideally, it would be best to heat the Solder and the circuit board simultaneously and properly.
So how does insufficient heat cause cold solder joints?
The issue is prevalent in three main ways:
- First, it occurs when the soldering iron temperature is way below the necessary heat volume enough to melt the Solder efficiently.
- Also, cold soldering happens when you don’t allow the hot soldering iron to stay on the circuit board’s surface long enough for optimal heating.
- Lastly, insufficient heat can cause the component’s pin that you’re soldering to the board not to warm up. When this happens, the Solder will heat and attach to the circuit board’s pad rather than the component’s pin.
Hasty or careless cleaning can leave substances such as metal oxides on the PCB’s surface, preventing an excellent bond formation.
Moreover, if the soldering happens in an unclean environment with grease and grime, the Solder will not dry well and then causes a cold soldered joint.
Inadequate Solder Application
A smoking soldering iron.
Thirdly, cold Solder joint problems can result from applying insufficient wetting material (Solder).
It will cause a thin film which is a precursor to issues such as electrical shorts and poor connection of the components to the electronic circuit.
What leads to insufficient Solder? Primarily it’s because of inadequate heating.
Other reasons for cold soldering include the following.
- Overheated joint: Applying more heat than needed on the Solder will prompt it to melt improperly. It leads to melting the PCBs flux and, ultimately, a cold solder joint.
- Disturbed Joint: If you tamper with the soldered joint before it dries, you’ll likely experience a cold solder joint.
- Insufficient wetting: Heat the circuit board and the pin to the same temperatures when soldering to prevent this issue.
Different Cold Solder Joints
We have three main cold solder joints.
Distributed Cold Joints
It happens when the soldering iron moves off the designated soldering point resulting in a concave-shaped joint.
Often this is due to the displacement of the PCB during the soldering process.
Therefore, its remedy is to hold the PCB firmly on a vice during soldering.
You can use a PCB holder or a wall-mounted soldering vice.
Cracked Solder Joint
Applying mechanical stress during soldering can lead to a cracked solder joint.
Also, using inadequate Solder can induce cracking.
Thirdly a cracked solder joint could be due to gravitational forces from heavy PCB components on the circuit board.
Finally, a cracked solder joint will increase if the electronic component experiences constant vibration.
The main issue with a cracked solder joint is that the component pin doesn’t connect effectively to the board, which can interfere with the electrical connection.
Lay a cathode ray tube on your solder pad to minimize the vibrations that produce cracked solder joints during soldering.
Repairing and soldering with a soldering station
Dry Solder Joint
This joint in PCB manufacturing is often because of insufficient Solder.
They increase the circuit’s electrical resistance, cause incomplete circuits and hamper the current flow.
Most cold solder connections are a combination of cracked and dry solder joints.
Can you outright identify the type of cold solder situation that you have at hand?
If not, consider seeking the help of an assembly services expert’s assistance with identification which is imperative in crafting a solution.
Identification of Cold Solder Joint
Identifying a cold solder early enough is critical in limiting the imperfections of faulty PCBs, especially if you’re dealing with the mass production of circuit boards.
Here are the main methods of Cold Solder Joints Identification.
It is the easiest and fastest way to identify solder joints in PCBs.
First, assemble the components necessary for this operation. These are a light source and magnifying glass.
- Shine the light on the joints and observe it via the magnifying lens. If the light penetrates the joint, there’s a chance it’s a cold joint.
- Next, check if the joint is smooth enough. If it’s rough, this indicates inadequate heating during soldering.
- Finally, check if there’s a PCB solder joint that spills to another joint. The issue can lead to electrical shorts and malfunctioning of the PCB.
A digital multimeter.
Next, you can use a multimeter to check if the cold solder connection has rendered the joint inoperational.
- Connect the multimeter to the joint’s ends and listen for a beep sound. If present, the cold-soldered joint is still effectively passing current. If the beep sound is not continuous, it means some parts of the joint are detached, and finally, if there is no sound, you must fix the cold joint as no current is passing.
- Alternatively, test the joint resistance by connecting a multimeter set at 1000 Ohms to both ends. Ideally, you should obtain zero reading if the joint is operational.
Effects of Cold Solder Joint
The performance of your PCB will dip if it has imperfections, such as cold joints.
It will happen in the following two main ways.
A PCB with cold joints is prone to bending fatigue and can barely withstand vibrations and movement during device use.
Therefore, joint failure due to the mechanical instability of such a circuit board is highly prevalent.
Also, due to the weakness at the joints, irregular temperature changes can affect its overall performance.
Electrical conductivity problems
Cold soldering leads to gaps in the joint which can cause an air gap to develop.
This gap will induce rusting, affecting the joints’ electrical conductivity.
Such a circuit board becomes unreliable as it’s likely to break down during use.
Prevention of Cold Solder Joint
Now let us look at how to keep the cold soldering issue at bay.
Effective Cleaning of the Components
Cleaning a circuit board.
Grease and grime are contaminants that can lead to a cold joint on the circuit board.
Therefore, thoroughly clean the soldering tools and the components with a solvent.
Also, after use, always ensure that your tools are in a dust-free storage area to prevent introducing contaminants into the joints during service.
Heat the Joint Adequately
You must always ensure that your Solder melts entirely by providing the right temperature and adequate duration.
Ideally, the optimal soldering temperature should be at least 15°C above the melting point of your soldering alloy.
Also, it would be best to allow the soldering iron to stay at this temperature for at least a minute before embarking on the soldering.
Use enough Solder
Over-soldering is a critical issue as it can cause a joint to slip over to another joint which can lead to short-circuiting.
Similarly, applying less Solder than necessary can lead to a cold joint as the connection of the component to the board will be weak.
Therefore, use the optimal Solder under the right temperatures for the best results.
When soldering, it is essential to ensure that the PCB rests on a stable platform and there are minimal vibrations which are precursors to cold solders.
Also, you must be exquisitely perfect when soldering the individual parts to the board, as this is critical in the optimal performance of the circuit board.
This doesn’t outright reduce cold soldering, but it is essential as lead is one of the contaminants that industries should strive to phase out.
Go for green soldering options to keep our environment safe.
You must maintain your cool to avoid shaking during the soldering process.
Otherwise, you’ll introduce cold joints to the circuit board.
How to Repair Cold Solder Joints?
Repairing and soldering.
There’s no one-solution-fits-all for cold solder joint repair, as the technique relies on the cold soldering issues at hand.
Therefore, choose the ideal one for your situation from the repair methods below.
|Cold Solder Problem||Solution|
|Excessive Solder||Heat the excess Solder with a hot iron tip. Alternatively, you can use a solder remover or wick to dislodge the excess Solder from the joint.|
|Distributed Cold Solder||Heat the excess solder with a hot iron tip. Alternatively, you can use a solder remover or wick to dislodge the excess Solder from the joint.|
|Starved Solder Joint||Hold the PCB firmly as you apply Solder using a PCB holder or a soldering vice.|
|Typical Cold Solder||You can fix this primarily by upholding proper soldering practices. Hence, heat it effectively and use sufficient lead-free soldering wire. Use a lead-free solder alloy with a relatively low melting point for best results.|
Other Types of Soldering Issues
A Soldering Vector.
In addition to cold solder joint issues, there are additional soldering problems.
You can identify overheated solder joints from their dull appearance.
They lack the shiny metallic luster familiar in other well-soldered joints.
Overheating also leaves a burned flux on the circuit board, making the joint weak and brittle.
The remedy to an overheated solder joint is to remove it and resolder it again correctly.
Ensure you subject the Solder and the component’s pin to the same temperature and Solder at the right point to prevent the Solder overflowing.
Solder starved joints
As the name suggests, this joint doesn’t have sufficient Solder to hold the component well in place.
It could be due to poor heating while soldering or applying the wrong solder type.
Again, like a cold joint, a starved joint is dull and less pronounced.
You can treat a solder-starved joint by applying more Solder to the surface.
Disturbed solder joint
If your PCB moves during the soldering process, you’ll likely have a disturbed solder joint.
It can also result from low temperatures of the soldering iron.
Lastly, a disturbed solder joint can result from a dirty surface.
It happens when a solder overflows and connects to another on the PCB, leading to an unwanted link (solder bridge) between two points. The causes for the issue include:
- Using excess Solder.
- The improper soldering technique (Having your soldering tip touch two pads simultaneously).
- Poor cleaning of PCB after soldering, causing the accumulation of solder flux.
To fix it, carefully remove the excess solder flux to separate the two points.
They are common in SMD soldering and result from excessive heat on the pad, which causes it to lift.
Depending on the flux material, you can fix the issue by soldering at optimal temperatures.
Lastly, you will have untrimmed joints if you don’t trim the component pins or wires after soldering.
It predisposes your board to short-circuit if the wire touches another transmitting point on the PCB.
Simply trim the exposed ends of your solder wires/components to fix the problem.
A cold solder is a menace in many ways explained above.
But it is easy to fix as all you need is to follow the recommendations highlighted in the article.
In a nutshell, use the right soldering temperature, operate cleanly, remove excess flux from the circuit boards, and hold the circuit board firmly when soldering.
Thanks for reading to the end.