What are the reasons for PCB voids in SMT processing?
First of all, we need to understand the process of SMT processing. SMT (Surface Mount Technology) is a method of mounting electronic components directly on the surface of printed circuit boards. The technology has the advantages of simple structure, small size, fast signal transmission rate, etc., and has become the main way in modern electronic manufacturing.
In SMT processing, the generation of PCB voids is mainly related to the placement process. The SMD process generally consists of three steps: Unloading, mounting and soldering.
Step 1: Unloading. In the process of SMD processing, it is necessary to use an automatic discharging machine to take out the components from the material tray, due to the material surface adsorption of air and dust and other impurities, thus leaving a larger number of tiny air holes on the surface of the material.
The second step: mounting. In the mounting process, the components are clamped by the positioning device and moved to a predetermined position after being positioned. However, due to the presence of tiny air holes on the surface of the component, when the component comes into contact with the PCB surface, the air between it and the PCB surface is squeezed out, forming a hole.
Step 3: Soldering. During the soldering process, the holes are further heated, and under the action of the brazing material, the metal between the brazing material and the PCB pads is melted, and the component is soldered to the PCB surface.
In short, in the process of SMT processing, the generation of voids is mainly due to the existence of tiny air holes on the surface of the component, when the component is in contact with the surface of the PCB, the air between it and the surface of the PCB is squeezed out, forming a void.
There are also other reasons for PCB voids:
Insufficient Flux Activation:
Voids can form when the flux, a chemical substance used in soldering, is not adequately activated. Flux is essential for removing oxides and promoting proper wetting of the solder to the surfaces being joined.
Trapped Volatiles:
Certain materials, such as moisture or solvents, can become trapped within the solder paste. During the soldering process, these materials can turn into gas, creating voids in the solder joint.
Inadequate Preheating:
Inconsistent preheating of the PCB and components can lead to rapid vaporization of volatile substances in the solder paste, resulting in void formation.
Incorrect Solder Paste Composition:
The composition of the solder paste, including the type and size of solder particles, can influence void formation. Using the wrong solder paste for specific applications may increase the likelihood of voids.
What are the effects of PCB voids?
Reduced Mechanical Strength:
Voids can compromise the mechanical strength of the solder joint. The presence of air pockets may weaken the bond between the components and the PCB, leading to potential joint failure under mechanical stress.
Degraded Thermal Performance:
Voids act as insulators, reducing the thermal conductivity of the solder joint. This can impact the component’s ability to dissipate heat, potentially leading to overheating issues.
Electrical Performance Issues:
Voids may alter the electrical characteristics of the solder joint, affecting conductivity and potentially leading to electrical failures or intermittent connections.
How to avoid the generation of PCB voids?
To avoid the generation of PCB void, first of all should pay attention to keep the SMD processing site clean and hygienic. In the process of discharging and mounting to avoid dust, grease, fingerprints and other contaminants, and at the same time should be selected with good quality, smooth surface, no air holes in the components.
In addition, vacuum suction port or handling suction port can be used to reduce the contamination of the component surface and air atmospheric experiments on the extrusion of air holes. At the same time, in the placement process to maintain the proper regulation of the board pressure and temperature, can also effectively avoid the generation of voids.
PCB void, although a common problem, but as long as the patch processing process pay attention to a variety of details, you can effectively avoid its generation, to ensure the quality and reliability of patch processing.
Addressing and preventing voids in PCB solder joints require a holistic approach, involving careful consideration of materials, process parameters, and equipment. Continuous improvement and adherence to industry standards contribute to minimizing voids and ensuring the reliability of electronic assemblies.