Proper Wetting During Soldering in Board Assembly
Wetting is the process in which molten solder bonds to metal surfaces on printed circuit board (PCB) pads and components. Proper wetting is vital for ensuring the correct function and longevity of board assembly. However, this process is often plagued with various problems that prevent it from functioning properly. These common issues can be corrected and mitigated using targeted solutions and preventive strategies.
The most common errors associated with board assembly are cold and burnt joints. These errors can occur due to a variety of reasons, but typically result from the solder not reaching the required temperature during the wetting process. This can be caused by not properly preheating the iron, a lack of proper solder paste application or an incompatible iron for the job. In either case, a cold or burned joint will look dull or flaky and will not have the sheen of a well-made joint.
Another common error is the failure to use a pick-and-place machine. A pick-and-place machine uses mechanical or even vacuum-based movements to take a component from the feeder and place it on the pad where it is to be soldered, eliminating the need for a human hand and significantly increasing efficiency and accuracy. The use of a pick-and-place machine can also help reduce the costs associated with human error.
When a surface mount component is placed on a PCB, the copper area where it sits needs to be thoroughly cleaned and degreased to ensure that it is clean and free of contaminants and oxides. In order for the wetting process to be successful, these areas must be completely cleaned prior to soldering. When this step is overlooked, it can lead to a number of problems, including lifted pads and poor reflow performance.
How to Ensure Proper Wetting During Soldering in Board Assembly
Solder pads are the small copper areas that connect components to a PCB. These are usually located in designated spots on the board and require precise placement in order to ensure that the correct electrical connections are made. If too much heat is applied to these pads during the soldering process, they can become detached from the component’s leads. This is referred to as pad lifting and is a very common problem that can be prevented with careful placement and assembly processes.
A plethora of other issues can also affect the quality of a solder joint. A common issue is a lack of a soaking zone, which allows the preheat temperature to be maintained for longer periods of time in order to provide the necessary conditions for a successful wetting process. The use of an incompatible solder alloy for the reflow process can also have a negative impact on wetting performance.
In addition to addressing these issues, it is important to have a thorough inspection of the board prior to assembly. This is done through a combination of visual inspection and testing for continuity to detect any defects or irregularities that may hinder the wetting process. Additionally, the use of a stencil and properly calibrated solder paste application are essential for ensuring that the correct amount of melted solder is applied to each part of the board.