What is solder wetting? And how to prevent poor wetting?
Welding is a basic technology in electronic assembly, used to connect electronic components and mechanically connect them to a PCB (printed circuit board). A key step in this process is the concept of “solder wetting”. In this article, we will introduce the basic knowledge of solder wetting, the importance of solder wetting, the causes of poor wettability, and how to prevent wetting problems to ensure reliable solder joints and long life.
What is solder wetting?
Solder wetting refers to the process by which solder melts and diffuses to the surface of PCB components. Liquid solder tends to move freely on the surface containing the solder and forms a uniform shiny surface covering layer when cooled and combines with surface metallurgy. If the wettability is good, we can see that the solder is smooth and shiny. However, poor wettability is easy to find because its appearance is rough, dim, and granular.
Why is proper solder wetting important?
It is essential to achieve proper solder wetting for the following reasons：
Conductivity: Good wetting helps to increase conductivity because it helps reduce the risk of signal loss and resistance.
Mechanical strength: The strong and long-lasting bond formed by good wettability can withstand thermal cycling and mechanical stress.
Reliability: Properly wetted joints have a lower failure rate than cracked, cold joints, or intermittent connections.
Visual inspection: If the solder joints are fully wetted, the solder joints will look smooth and shiny, and the quality control operators can easily find defects.
Thermal management: Good wettability can also provide excellent heat dissipation performance, which is essential for temperature-sensitive components.
3 solder wetting problems you should know
Although the goal is to achieve the ideal solder wetting, various problems may occur during the welding process：
1. Poor wettability (insufficient wettability)
If the solder is not evenly distributed as expected, the process is called poor wettability. The result is a larger contact angle, a more uneven distribution of solder, and possible voids or gaps in the joint. A joint with poor wettability may work normally at first, but over time, it is more likely to fail.
2. Non-wetting welding
Non-wetting is a welding problem, and the solder cannot be bonded to the PCB metal alloy. However, if the terminals of electronic components and the pads of the PCB cannot be glued, attached, and firmly connected, the circuit board material will be exposed to the surface. The solder also looks dull or huge at the same time. In addition, direct voids are also caused by non-wetting. This is the process of creating holes in solder joints that may lack solder material.
领英推荐
3. Dehumidification
The dehumidification process is the process by which solder paste covers the component terminals and PCB pads, but leaves part of the solder. This will leave a thin surface solder and thick and irregular clumps on the metal alloy. The surface material of the PCB is usually not exposed all the time. However, when dehumidification occurs, it usually first affects the bonding of the solder and the quality of the solder feet.
Common factors that cause poor wettability of solder
How to prevent poor wetting of solder?
The key to welding lies in detail and control, and it must be handled in a good wetting manner. Here are some key strategies to prevent wetting problems：
First, clean the PCB surface and components. We can use general solvents to wipe to remove dirt, oil and any other contaminants.
Welding to the hot soldering iron head can prevent oxidation. Keep the tip of the soldering iron tinned so that the soldering iron is closed and the soldering iron is kept in a properly wetted state. This can save time and money, and avoid the extremely cumbersome process of constantly buying new soldering iron tips.
In this case, highly active solder pastes can provide better wettability and are also useful in situations where the surface finish is complex. In addition, highly active solder pastes will help avoid poor wettability during reflow.
The soldering iron must be preheated to the optimal temperature. The solder will not completely melt at the wrong temperature, resulting in cold solder joints. Therefore, its adhesion is unreliable.
We do have many welding strategies, but poor wettability of solder is inevitable. Don't worry-when the problem occurs, despite this, we can still fix it. To start again, just wait for the solder joint to cool, remove the flux, and reheat the solder joint.
conclusion
The correct solder wetting technology determines the assembly and working quality of electronic equipment. If you are engaged in the production of electronic products, what is really important is to understand how this basic process works. Technicians can understand the cause of wetting problems and should use best practices to improve the wettability of welding skills and obtain better and more reliable results. This is the powerful knowledge necessary to produce high-quality electronic components that meet industry standards and performance requirements.