Standard for Surface Coating (Plating) of PCB Circuit Boards
From the process and inspection of soldering components onto PCB circuit board pads, the standard for surface coating (plating) of PCB circuit board pads mainly encompasses the following five aspects:
1. **Heat Resistance**
At high soldering temperatures, the surface coating (plating) should effectively protect the copper surface of the PCB circuit board pad from oxidation and allow the soldering material to bond with the copper (or metal) surface to establish a connection. The heat resistance of organic surface coatings (plating) refers to their melting point and thermal decomposition (volatility) temperature. The melting point should be close to or slightly lower than that of the PCB soldering material (tin), while the thermal decomposition temperature (≥350°C) should be significantly higher than both the melting point of the soldering material and the soldering temperature. This ensures that the copper surface does not oxidize during the soldering process. The heat resistance of metal surface coatings does not face this issue.
2. **Coverage**
For organic heat-resistant solderability coatings (including flux), the coating must completely cover the surface of the copper pad both before and during the soldering process to prevent oxidation and contamination by air. The coating should only decompose and volatilize when the molten solder material is applied to the copper pad, thereby floating (covering) the surface of the solder joint.
Therefore, to ensure the molten welding material is thoroughly fused onto the coupling disk, the surface tension of the molten organic surface coating layer must be low, and its decomposition temperature must be high to achieve good coverage before and during welding. Additionally, its specific gravity should be significantly lower than that of the molten solder material (tin) to enable the molten solder to squeeze and penetrate the copper surface. Thus, the coverage of the organic surface coating pertains to its properties at the soldering temperature, including surface tension, specific gravity, and other characteristics. During welding, the metal surface coating layer partially melts into the welding material or onto the barrier layer to form a connection.
• The Remains
The residue of the organic heat-resistant solderability coating (plating) refers to what is left on the soldering pad or the solder joint after soldering. Typically, these residues can be hazardous (such as organic acids or halides) and should be removed, necessitating cleaning measures post-welding. Nowadays, no-clean soldering technology is employed because the organic surface coating (plating) leaves minimal residue after welding, as most of it decomposes and volatilizes.
• Corrosiveness
The corrosiveness of the organic heat-resistant solderability coating (plating) refers to the corrosion of the PCB circuit board’s surface after welding, such as corrosion on the substrate and metal layer. This is due to the presence of halides or organic acids in the coating (intended to clean residual oxides and contaminants on the copper pad), but these acidic substances are hazardous post-welding. They must be cleaned and removed in addition to decomposing and volatilizing.
• Environmental Protection
Environmental protection regarding PCB surface coating (plating) involves ensuring that waste slag from the coating process and cleaning waste liquid after welding are easy to dispose of, cost-effective, and environmentally friendly.
PCB Giant Magnetoresistance Effect and Layer Structure Analysis
The giant magnetoresistance effect refers to the phenomenon where a material’s resistivity changes significantly under an external magnetic field compared to when no external magnetic field is present. It is generally defined as GMR = ρ(H)/ρ(0), where ρ(H) is the material’s resistivity under the magnetic field H, and ρ(0) is the resistivity without an external magnetic field. This significant resistance change in some magnetic materials due to an external magnetic field is a crucial aspect of magnetoelectronics. Various giant magnetoresistance materials exhibit this effect at room temperature, including multilayer, granular, oxide, and tunnel junction magnetoresistance materials.
The magnetoresistance effect describes how the resistance of a conductor or semiconductor changes in a magnetic field. Discovered independently by Peter Grünberg and Albert Fert in 1988, they won the 2007 Nobel Prize in Physics for this work. Research shows that in magnetic multilayer films like Fe/Cr and Co/Cu, the ferromagnetic layers are separated by nano-thin non-magnetic materials. Under specific conditions, the resistivity reduction can be up to 10 times greater than the magnetoresistance in typical magnetic metals and alloys. This phenomenon is known as the “giant magnetoresistance effect.”
The giant magnetoresistance effect can be explained by quantum mechanics. Each electron has a spin, and its scattering rate depends on the spin direction relative to the magnetization direction of the magnetic material. When the spin direction aligns with the magnetization direction, the scattering rate is low, allowing more electrons to pass through, resulting in low impedance. Conversely, when the spin direction opposes the magnetization direction, the scattering rate is high, reducing electron flow and increasing impedance.
Sensors based on the PCB giant magnetoresistance effect typically have three sensing layers: Reference Layer or Pinned Layer, Normal Layer, and Free Layer (where “Free” refers to the resistivity of the raw materials). An external magnetic field causes a significant resistivity change compared to no external magnetic field. It is usually defined as GMR = ρ(H)/ρ(0), where ρ(H) is the PCB material’s resistivity under the magnetic field H, and ρ(0) is the resistivity without an external magnetic field. The significant resistance change in some magnetic materials due to an external magnetic field is an essential aspect of magnetoelectronics. Many types of giant magnetoresistance materials are available at room temperature, including multilayer film, granular, oxide, and tunnel junction magnetoresistance materials.
From the process and inspection of soldering components onto PCB circuit board pads, the standard for surface coating (plating) of PCB circuit board pads mainly encompasses the following five aspects:
1. **Heat Resistance**
At high soldering temperatures, the surface coating (plating) should effectively protect the copper surface of the PCB circuit board pad from oxidation and allow the soldering material to bond with the copper (or metal) surface to establish a connection. The heat resistance of organic surface coatings (plating) refers to their melting point and thermal decomposition (volatility) temperature. The melting point should be close to or slightly lower than that of the PCB soldering material (tin), while the thermal decomposition temperature (≥350°C) should be significantly higher than both the melting point of the soldering material and the soldering temperature. This ensures that the copper surface does not oxidize during the soldering process. The heat resistance of metal surface coatings does not face this issue.
2. **Coverage**
For organic heat-resistant solderability coatings (including flux), the coating must completely cover the surface of the copper pad both before and during the soldering process to prevent oxidation and contamination by air. The coating should only decompose and volatilize when the molten solder material is applied to the copper pad, thereby floating (covering) the surface of the solder joint.
Therefore, to ensure the molten welding material is thoroughly fused onto the coupling disk, the surface tension of the molten organic surface coating layer must be low, and its decomposition temperature must be high to achieve good coverage before and during welding. Additionally, its specific gravity should be significantly lower than that of the molten solder material (tin) to enable the molten solder to squeeze and penetrate the copper surface. Thus, the coverage of the organic surface coating pertains to its properties at the soldering temperature, including surface tension, specific gravity, and other characteristics. During welding, the metal surface coating layer partially melts into the welding material or onto the barrier layer to form a connection.
• The Remains
The residue of the organic heat-resistant solderability coating (plating) refers to what is left on the soldering pad or the solder joint after soldering. Typically, these residues can be hazardous (such as organic acids or halides) and should be removed, necessitating cleaning measures post-welding. Nowadays, no-clean soldering technology is employed because the organic surface coating (plating) leaves minimal residue after welding, as most of it decomposes and volatilizes.
• Corrosiveness
The corrosiveness of the organic heat-resistant solderability coating (plating) refers to the corrosion of the PCB circuit board’s surface after welding, such as corrosion on the substrate and metal layer. This is due to the presence of halides or organic acids in the coating (intended to clean residual oxides and contaminants on the copper pad), but these acidic substances are hazardous post-welding. They must be cleaned and removed in addition to decomposing and volatilizing.
• Environmental Protection
Environmental protection regarding PCB surface coating (plating) involves ensuring that waste slag from the coating process and cleaning waste liquid after welding are easy to dispose of, cost-effective, and environmentally friendly.
PCB Giant Magnetoresistance Effect and Layer Structure Analysis
The giant magnetoresistance effect refers to the phenomenon where a material’s resistivity changes significantly under an external magnetic field compared to when no external magnetic field is present. It is generally defined as GMR = ρ(H)/ρ(0), where ρ(H) is the material’s resistivity under the magnetic field H, and ρ(0) is the resistivity without an external magnetic field. This significant resistance change in some magnetic materials due to an external magnetic field is a crucial aspect of magnetoelectronics. Various giant magnetoresistance materials exhibit this effect at room temperature, including multilayer, granular, oxide, and tunnel junction magnetoresistance materials.
The magnetoresistance effect describes how the resistance of a conductor or semiconductor changes in a magnetic field. Discovered independently by Peter Grünberg and Albert Fert in 1988, they won the 2007 Nobel Prize in Physics for this work. Research shows that in magnetic multilayer films like Fe/Cr and Co/Cu, the ferromagnetic layers are separated by nano-thin non-magnetic materials. Under specific conditions, the resistivity reduction can be up to 10 times greater than the magnetoresistance in typical magnetic metals and alloys. This phenomenon is known as the “giant magnetoresistance effect.”
The giant magnetoresistance effect can be explained by quantum mechanics. Each electron has a spin, and its scattering rate depends on the spin direction relative to the magnetization direction of the magnetic material. When the spin direction aligns with the magnetization direction, the scattering rate is low, allowing more electrons to pass through, resulting in low impedance. Conversely, when the spin direction opposes the magnetization direction, the scattering rate is high, reducing electron flow and increasing impedance.
Sensors based on the PCB giant magnetoresistance effect typically have three sensing layers: Reference Layer or Pinned Layer, Normal Layer, and Free Layer (where “Free” refers to the resistivity of the raw materials). An external magnetic field causes a significant resistivity change compared to no external magnetic field. It is usually defined as GMR = ρ(H)/ρ(0), where ρ(H) is the PCB material’s resistivity under the magnetic field H, and ρ(0) is the resistivity without an external magnetic field. The significant resistance change in some magnetic materials due to an external magnetic field is an essential aspect of magnetoelectronics. Many types of giant magnetoresistance materials are available at room temperature, including multilayer film, granular, oxide, and tunnel junction magnetoresistance materials.
