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10 Common Soldering Problems To Avoid On Your PCBs

10 Most Common Soldering Problems10 Most Common Soldering Problems

We have encountered many common soldering problems throughout our years in the industry.

Soldering is the integral application that can make or break the functionality of your PCB. High quality craftsmanship of the soldering process ensures for a fully functioning and well-crafted electronic device.

For the longevity of the device, quality checking the soldering work, to ensure that all connections have the perfect solder joint, is essential.

In this guide we will break down the most common soldering issues that we hear of, along with how to remedy them.

But Firstly, What Is The Perfect Soldering Joint?

There are several characteristics that form the basis of the perfect soldering joint. They are as follows:

  • Finished wetting process
  • Neat concave fillet
  • Shiny and clean joint

To achieve this, the correct solder should be used, along with the right technique and a correctly prepared process.

So, What Are The Common Soldering Problems

Now that you know what the perfect solder joint is, let’s dive into the common problems and mistakes that can be made through the soldering process.

1 - Solder Bridging

Solder bridging occurs where two individual joints melt together. This can then create an unwanted connection that effects the functionality of your PCB.

If this problem is left without a solution, then your board could be at risk of either short circuiting or burning out.

This issue is more prominent where smaller components are being used. Usually, the root cause of this is too much solder being used. Alternatively, it can also be the result of a soldering tip that is too large or wide being used, or even the soldering iron being withdrawn at an angle that leaves residue.

Identifying possible solder bridges on your PCB can be a challenging task, as they can sometimes be microscopic in size.

When found, solder bridges will require a solder wick to remove the unwanted solder and drag it away.

2 - Solder Balling

Solder balling is one of the most common defects that can occur in largescale PCB manufacturing.

This is a process that often occurs with reflow or wave soldering. Small spheres of solder will appear around the pad and component.

There could be a multitude of reasons as to why these occur. However, the most common cause is where either air or water vapour gets stuck between the layer of solder paste and PCB, before the board is heated.

Preheating your PCB can help to prevent this from occurring, along with ensuring that the correct amount of flux has been applied.

3 - Too Much Solder Or Solder Starved Joints

Similarly to heat, there is a fine balance for the right amount of solder that is required. Using too much or too little can both create issues on your PCB. It is a balancing act that must be adhered to. As a rule of thumb, you should ensure that you have used enough solder to adequately wet the pin, with a concave surface on the PCB.

  • Too Much – Excessive solder can often be the result of an over enthusiastic operator, where too much solder is applied to the pin or lead. This is often as a result of the solder being withdrawn too late. A common misconception is that the more solder the better the connection. However, this can lead to solder bridging or solder balling (both of which are outlined above). Too much solder can mask other underlying issues with the joint, such as insufficient wetting. Not to mention, soldering this way also wastes a lot of solder.
  • Too Little – Where too little solder is used to form the connection to the PCB, this is referred to as solder starved. This can mean that a solid electrical connection is not formed.
    Whilst it is still possible that sufficient connection has been achieved for the solder joint to work, the long-term integrity of the solder connection is likely poor. Over time this can lead to crack as the overall mechanical strength of the joint is insufficient. Thankfully this common soldering problem can be easily rectified by reheating the joint and applying more solder. Just ensure that you get the balance right and do not overcompensate! This can be the result of several instances including:
    • Application of insufficient heat to the lead.
    • Premature solder withdrawal during the application process.
    • Use of insufficient flux for the application.

4 - Cold Or Overheated Joints

Both ends of the spectrum are not ideal. You can think of a solder joint as needing the goldilocks treatment. Too much heat is bad, whereas too little is not great either, but the middle ground is just right!

Outlined below are the results of these types of solder joints.

 

Cold – Where a solder joint has been formed at a lower than optimal soldering temperature, it can lead to a dull, lumpy or uneven joint.

These solder joints have not formed properly as the solder has insufficiently melted. Therefore, the solder joint becomes at risk of both cracking or failing completely.

To remedy this, you can reheat the joint until the solder flows again.

 

Overheated Joints – The other end of the scale is just as bad, with too much heat making your joints susceptible to burning.

You can usually tell an overheated joint by a whiter appearance and a rougher edge.

Above all, should these joints be overheated, you run the risk of lifting the pad entirely from the surface of the PCB, often rendering your board surplus in the process.

5 - Insufficient Wetting For Throughhole & SMD Components

Wetting of a solder joint is integral.

Often this is a novice solderers mistake. It inhibits the ability for a proper connection to be performed between the PCB pad and the component.

Where insufficient wetting has taken place, the performance of the electrical device becomes compromised, impacting on the device’s reliability and longevity.

Often you can remedy this by selecting the correct solder type for your application.

6 - Tomb Stoned Components

This is a common soldering problem when using surface mounted components. When soldering these kinds of components, such as a resistor, solder will be applied to both pads and the wetting process will begin.

However, should one side not have finished this process, the component can become lifted on one side. This gives the illusion of a tombstone, hence the name.

To summarise, tombstoning occurs when one end of the component completes the wetting process before the other.

One of the most common causes of this involves an uneven heating during the reflow process, leading to premature wetting on some areas of the PCB.

Avoid and remedy tombstoning once identified. It can lead to a drop in thermal performance of the PCB, along with affecting the longevity of the soldering joint.

7 - Solder Skips

Often, solder skips occur within the automated soldering process. But they can also occur from a less experienced soldering operator.

Whether it be lack of communication or a poorly configured robot, skipped joints happen, rendering certain areas of the PCB non-functional.

Solder skips can also occur during the wave soldering process, were there is an incorrect wave height between the board and the soldering wave.

8 - Lifted Pads

A lifted pad on your PCB provides a catastrophic failure to the entirety of the board.

They are often the result of using too much heat or excessive heating whilst soldering. This extreme thermal or physical stress leads to the pad lifting entirely from the surface of the PCB. This renders the PCB with an improper connection to the lead.

Heating the board reduces copper adhesion. This can lead to a lifted pad.

To avoid this problem, after you have soldered, ensure that the PCB is handled with care until the solder has solidified completely.

9 - Solder Splashing Or Webbing

This common soldering problem is where bits of solder become stuck to the solder mask, resembling that of a spider web, or splashes of solidified liquid.

There are two main causes of splashing or webbing on your PCB:

  1. Use of an insufficient flux agent.
  2. Pollutants have contaminated the PCB you are working on.

The messy aesthetics they leave behind are not your only worry. This webbing or splashing can lead to short circuit hazards that can damage the PCB you are working on!

Consequently, ensuring that you select the correct flux, along with cleaning your PCB before the soldering process will help you to avoid this problem.

10 - Pin Holes & Blow Holes

Pin holes are another common soldering problem regarding the wave soldering process.

This looks like small pin holes, or larger openings (blow holes). Where moisture is present on the PCB, once inside the reflow oven, it turns into vapor.

This gas then escapes through the solder before it has had time to harden, forming these voids of varying severity.

As a result, these can lead to poor conductivity.

Preheating the board sufficiently before the wave soldering process can remove the moisture. Reducing the copper plating thickness on the PCB is also another viable option.

To Conclude

We hope that this article has helped familiarise you with the problems that can occur whilst soldering.

Similarly, when performing any quality control checks, you should now have a far better idea for potential catastrophic PCB soldering problems.

If this is useful, keep an eye out for our next post regarding the ways you can avoid these issues.

For any help or further information around selecting soldering products, contact our team today.