Have you ever experienced the frustration of intermittent electronic device malfunctions? Then you might be dealing with a "cold solder joint".

　　According to recent studies, nearly 70% of electronic failures are due to insufficient soldering. Considering these statistics, we assume you are also suffering from the same problem and are looking for a simple solution. So, let's delve into this topic to learn more.

　 　What is a cold solder joint?

　　A cold solder joint is one where the solder has not fully melted to form a perfect joint. In a cold solder joint, the solder fails to create a strong and reliable connection between the components or leads being joined. This lack of proper bonding can lead to various issues, including increased resistance, unstable functionality, and a higher likelihood of component failure.

　　Some variables that may lead to cold solder joints include:

　　● Insufficient solder wetting, insufficient reflow, or insufficient melting of the joint.

　　● Vibration or other disturbances as the solder cools.

　　● When the process temperature is too high, the flux will decompose prematurely.

　　● Too low a process temperature will result in insufficient wetting of the solder joint.

　　Common characteristics of cold solder joints include a dull and grainy appearance, rather than the smooth and shiny surface of a good solder joint. These joints typically exhibit weaker mechanical and electrical properties and may not provide the conductivity needed for the electrical components to function.

　　You can identify cold solder joints using a magnifying glass. Another method is to move the soldered component to check for cold solder joints; if the joint is weak, the component will move slightly.

　 　Different Types of Cold Solder Joints

　　Now that you know what a cold solder joint is, let's look at some of its types.

　　 1. Distributed Cold Joint

　　A distributed cold solder joint refers to a situation where insufficient heating during the soldering process results in inadequate bonding of multiple solder joints in a circuit. In this case, "distributed" indicates that the problem is spread across various solder joints rather than confined to a specific area. This phenomenon typically occurs when the solder in multiple solder joints fails to heat and melt during the assembly of electronic components.

　　Identifying distributed cold solder joints requires visual inspection of the entire circuit board. These solder joints may exhibit a dull and grainy appearance, characterized by weakened connections due to incomplete bonding. To address this, the repair process involves applying flux to the affected areas and systematically reheating and resoldering each solder joint to ensure even heating and establish reliable connections across the circuit board.

　　 2. Solder Joint Cracking

　　Solder joint cracking refers to the presence of one or more visible or microscopic cracks in the solder of a soldered connection in an electronic device. Due to these cracks, your circuit board may compromise the integrity of the solder joint and cause a range of problems in your device. The causes of solder joint cracking are

　　manifold, including thermal stress, mechanical stress, or repeated cycles of expansion or contraction. Factors such as temperature changes, physical impacts, or insufficient stress relief can all contribute to the formation of cracks in the solder.

　　The consequences of solder joint cracking can include increased resistance, intermittent functionality, and potential open circuits. However, visual inspection is commonly used to identify them when you want to view the cracks. In some cases, however, advanced techniques such as X-ray inspection may be necessary to detect microscopic cracks.

　 　3. Dry Solder Joint

　　This soldering problem occurs due to insufficient solder. There is insufficient metal content in the solder, resulting in a broken connection and causing accidents. In other cases, this joint may occasionally exhibit high conductivity and high resistance. Therefore, they will produce a crackling sound when in use.

　　 Factors Leading to Cold Solder Joints

　　Cold solder joints can be caused by a variety of factors, and understanding these issues is crucial for achieving reliable and lasting connections in electronic components. Here are some common factors that contribute to the formation of cold solder joints:

　 　1. Insufficient Heat

　　Insufficient heating of one or both surfaces is a typical soldering error that leads to cold solder joints. This happens when you set your soldering iron too low or don't give it enough time to connect the solder to the component leads. In this case, reheating is required.

　　There are also cases where the soldering iron tip contacts and heats the pad on the circuit board, but the leads of the component remain unheated. As a result, the solder adheres to the pad on the circuit board, not the leads of the component. Conversely, this may also occur, in which case the solder will connect to the leads of the component, not the circuit board pad.

　 　2. Improper Cleaning

　　If the soldering is done too quickly or without attention to detail, dirt may enter the solder joint. The presence of contaminants such as grease, dirt, and metal oxides can affect the quality of the solder joint. Typically, this becomes apparent when the solder forms small balls or beads and fails to adhere to the dirty surface. Cold solder joints can also be caused by interference, causing the solder to drop onto the joint too slowly.

　　 3. Insufficient Solder Usage

　　After tin plating the circuit board, insufficient solder in the solder joint is considered a sign of poor soldering. While there can be many reasons for this, a common cause is insufficient heat applied throughout the operation. Therefore, improper solder application can lead to electrical and connection failures.

　　 How to Prevent Cold Solder Joints

　　While frequent cold solder joint repairs are indeed an unfortunate reality, there are some preventive measures that can be taken. Let's find out more about them.

　　1. Using the Appropriate Reflow Profile

　　One effective measure is to use an appropriate reflow profile during the soldering process. A reflow profile refers to the temperature-time curve applied during soldering. Ensure that the solder paste reaches and maintains the required temperature for a sufficient duration to achieve proper wetting and bonding.

　　This can be achieved by following the recommended reflow profile provided by the solder manufacturer or component datasheet. Pay attention to the preheating, soak, and reflow phases, as deviations in temperature or duration in any phase can lead to insufficient solder flow, resulting in cold solder.

　　2. Correctly Clean Components

　　Clean components appropriately using a general-purpose solvent to remove grease or any impurities that may interfere with the soldering process. Soldering tools should be cleaned regularly and stored in a dry, dust-free case to prevent contamination.

　 　3. Remove Vibration Sources

　　Another cause of cold solder joints is vibration and movement during the cooling process that interferes with the solder joint. To prevent this, you should invest in a sturdy workspace to eliminate vibration sources. If using precision components, consider using anti-static tools such as grounding mats or wrist straps. You can also use solder mask to prevent further interference during the cooling process.