Cold Solder: How To Identify and Prevent

cold solder

Cold soldering is a common issue experienced by unskilled manufacturers and technicians. It results in subpar products that do not deliver in terms of reliable output, high-quality performance, and most certainly not in terms of customer satisfaction. Soldering is an essential step in PCB assembly, and without effective execution, products can, at best, experience irregular function, and at worst complete failure or fire-sparking short circuits.

So, what is cold soldering exactly, why does it cause the issues that it does, why does it occur especially in off-brand products, and how can such issues be addressed? These are all great questions, and we will aim to cover them here.

What Is Soldering?

Before diving into anything related to cold soldering, it is important to comprehend what soldering is. Nearly all modern electronics contain a circuit board on which electronic components are linked with molten and pasted connectors made up of an alloy with conductive properties such as tin and lead in the form of paste (reflow soldering), bar (wave soldering), or wire (hand soldering).

These parts are often very tiny and need special tools to precisely accomplish connecting them to one another. It needs to be done correctly to conduct a clean, healthy flow of current. One tool is the soldering iron, an instrument with a pen-like shape that delivers molten alloy by linking it between the electrical connection components. These joints must be tight, tidy, and complete to allow for a consistent, effective flow of energy through them. Reflow and wave soldering generally require more industrialized equipment to execute properly. That equipment includes stencils, printers, reflow ovens, and wave solder machines.

What Is Cold Solder And Why Does It Occur?

When the connection joint is not efficiently linked, such as when the molten solder is course, sloppy, or lumpy, they do not perform efficiently for a long period of time. The lumps’ constitution is compromised as it gradually cracks, lessening the electrical flow. This type of poorly linked connection is known as a cold solder.

This discrepancy is fairly common in unskilled assembly. There are several reasons why they would occur. One is the usage of low-quality soldering materials, like sub-standard solder wires, another is the use of inefficient or faulty soldering irons.

“Budget” contract manufacturers may not have the training or the processes in placguarantee repeatable quality of PCBAs. They often bid low to win as many projects as they can. This leads to them rushing projects to make a sliver of a profit. Soldering is all about precision and care, something that budget manufacturers under the timeline gun do not usually have. Therefore, the jobs are often done quicker than they should be, resulting in shotty soldering.

More experienced manufacturers have a lot more resources, and entire teams to conduct quality assurance testing to make certain that the soldering is performed optimally. When such options and double-checks are not part of the production process, cold soldering is a far too common and unfortunate result.

Detecting And Testing Cold Solder

Though hobbyists and engineers often can do basic soldering, it takes hours of practice and training for precision soldering work. That does not mean there are no methods by which they can either detect or test the component connections after their soldering is complete. After all, any PCB Assembly should get some form of testing to assure its intended functionality. Failing to do so will cost the engineer/company further business with their customers, so it is in their best interest to test and verify their work before sending out the final product. There are two primary methods by which the cold solder can be tested.

Visual Observation

The first test is a visual one. It is the most practical and the simplest method to detect potential cold soldering issues and determine the viability of connections. Basic visual observation can help to detect if the connection will be regarded as a cold solder if it looks uneven, lumpy, or non-geometrical.

While a visual confirmation is a great start, because the parts involved are so small, certain tools are required to conduct this job properly. These include a adequate lighting and a magnifying glass. Shining a bright light from the flashlight onto a particular area that is observed through a magnifying lens can reveal the poorly shaped, defective, or uneven joint connections. The light shining on the joint should not be able to penetrate it. If it can do so, then the solder joint’s bond is inadequate or insufficient. Also, if the solder joints have rough blocks, it is an indication of inadequate heat being applied during the soldering process. This is unsafe because once an item gets hot from the heat generated by passing currents, the solder covering can crack and break away.

Multimeter Testing

This testing method for solder is applied primarily in two ways. The first involves setting the multimeter to resistance of 1000 ohms. You then interconnect the two terminals and look for a reading of 0 ohms to ensure it is working. Now you can connect each terminal to the opposing joints. If the reading shows 0 ohms, then the connection is viable.

The other testing method involves switching the multimeter into continuity mode, interconnecting two terminals, and listening for a beep. If there is a beep, then continuity has been confirmed. Connecting to the two ends of a suspected cold solder joint may not return a beep, meaning that the joint must be redone. If there is a beep, then the joint will be normally functional.

Repairing Cold Solder Joints

If cold solder joints have been identified, they need to be addressed to avoid poor functionality. Before the repair, it’s important to understand the type of cold solder joint one is dealing with.

Distributed Cold Solder

One type of cold solder occurs when the electrician is pasting the molten soldering alloy and the soldering iron moves. This is known as a distributed cold solder and it is distinguished by a tilted pin and a concave shape, and a crystalline, frosted appearance. Because this occurs due to the movement of the board, a stable positioning will help avoid a distributed cold solder altogether. To stabilize it, perform the soldering either on a stable table affixed to the ground or a wall-mounted soldering vice. The latter is especially preferable for those struggling to find a space to perform stable work.

Dry Cold Solder

When there is not enough solder applied. It lacks the amount of metal necessary for connectivity, resulting in an incompletely open circuit. These typically have a dull appearance. A viable solder is wet when it flows into the circuit so it can solidify for optimal connection. Even if a dry circuit lets current through, it conducts electricity intermittently, meeting it with a lot of resistance, resulting in the signals being noisy.

Typical Cold Solder

If the positioning of the tool is stable, the tool being used to perform the job may not be sufficient. In that sense, it is the primary tool (the soldering iron) that may be to blame. To avoid cold solders caused by a soldering iron, it is important to clean the iron’s tip before starting a job. The device’s performance can be easily affected by dust, so to minimize the necessity for an extensive cleaning, the soldering iron should be kept in an airtight box or container with minimal exposure to dust particles when not in use.

Additionally, the soldering iron needs to be heated sufficiently to experience optimum performance depending on the soldering material one is working with. For instance, SN96 solder, a lead-free solder alloy, has a lower plastic transition time due to its melting point being comparatively low to other materials.

Other Types of Cold Soldering Issues

While less common, if the resistance is far too high on solder joints, then the complete combustion is not achieved with the alloy. This can lead to the shortening of the life of an electronic, and can even result in its immediate ceasing to work. The cold solders resulting from such resistance issues end up leading to more power being consumed by the electronic and overheated circuits.

Best Practices

Cold soldering is an undesirable result of rushed, unprecise work, typically by people who are trying to get the work done quickly. Too many cold soldering issues can lead to product failure and then monetary and reputational losses for the brand selling such products.

To avoid cold solder issues as often as possible, there are a few best practices recommended when working on soldering electronic components.

  • Partner with a trusted contract manufacturer like Vinatronic
  • Use the best equipment and materials. Premium materials result in more conductive solder joints.
  • The less solder used, the fewer chances of excess solder causing a cold solder situation.
  • Keep the wires, rods, and soldering irons in an air-tight box, free of moisture.
  • Assure that the soldering item is sufficiently heated.
  • Invest in heat guns that quickly heat the conductive materials.
  • Perform the soldering on a stable desk or in an entirely stationary environment.

Final Thoughts

Using wrong or subpar materials, as well as performing the work in haste results in poor electrical connections after soldering is complete. As the cold solder joints deteriorate, the product overconsumes power, leading to overheating and malfunction, ultimately landing products in a state of disrepair. By following this article’s tips, the party performing the soldering can help them achieve an effectively soldered product.

Vinatronic’s expert team of solder technicians can build your boards to spec everytime. If you are having problems soldering yourself or having issues with an existing manufacturer, our team is available to help.

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