1. **Hot Air Leveling**
Hot air leveling is a technique that involves applying molten tin-lead solder to the PCB surface and then leveling it using heated compressed air. This process creates a coating layer that resists copper oxidation and ensures good solderability. During hot air leveling, a copper-tin metal compound forms at the interface between the solder and copper, with a thickness of approximately 1 to 2 mils.
2. **Advantages: Low Cost**
The primary advantage of this method is its cost-effectiveness.
3. **Shortcomings:**
1. Pads treated with HASL technology may not achieve sufficient flatness, resulting in coplanarity issues that fail to meet the requirements for fine-pitch pads.
2. The process is not environmentally friendly, as lead poses environmental hazards.
4. **Gold-Plated Boards**
Gold plating utilizes real gold, even if only in a thin layer, which constitutes nearly 10% of the circuit board’s total cost. The use of gold as a plating layer serves two primary purposes: facilitating soldering and preventing corrosion. Even the golden fingers of memory sticks, after several years of use, remain shiny.
**Advantages:** Gold offers strong conductivity and excellent oxidation resistance. Its dense and wear-resistant coating is commonly used in bonding, welding, and plugging applications.
**Disadvantages:** The main drawbacks are the higher costs and lower welding strength.
**Five, Chemical Gold/Immersion Gold**
Chemical nickel immersion gold, also referred to as chemical nickel gold or immersion nickel gold, is often abbreviated as chemical gold or immersion gold. This process involves chemically depositing gold onto the copper surface, using a thick layer of nickel-gold alloy that provides good electrical properties and long-term PCB protection. The typical deposition thickness for the inner nickel layer ranges from 120 to 240 μin (approximately 3 to 6 μm), while the outer layer of gold is generally 2 to 4 μin (0.05 to 0.1 μm).
**Advantages:**
1. PCBs treated with gold exhibit a very flat surface and good coplanarity, making them ideal for button contact surfaces.
2. Chemical gold offers excellent solderability; the gold quickly merges with molten solder, forming a Ni/Sn metal compound with the solder.
**Disadvantages:** The process is complex, requiring strict control of parameters for optimal results. A significant concern is the tendency for gold-treated PCB surfaces to develop black pad issues during ENIG or soldering processes, which can lead to excessive oxidation of nickel and overabundance of gold, compromising solder joint integrity and reliability.
**Six, Electroless Nickel Palladium Plating**
Electroless nickel and palladium introduce a palladium layer between the nickel and gold. During the replacement gold deposition reaction, the electroless palladium layer protects the nickel from excessive corrosion. Palladium effectively mitigates corrosion from the replacement reaction while preparing for immersion gold. The deposition thickness for nickel typically falls between 120 to 240 μin (about 3 to 6 μm), while palladium thickness ranges from 4 to 20 μin (about 0.1 to 0.5 μm), and gold is generally deposited at 1 to 4 μin (0.02 to 0.1 μm).
**Advantages:** This treatment has a wide range of applications. The chemical nickel-palladium-gold surface treatment effectively prevents reliability issues linked to black pad defects and can substitute for nickel-gold treatments.
**Disadvantages:** Despite its advantages, ENEPIG has its drawbacks; palladium is expensive and a scarce resource. Additionally, it demands strict process control similar to that required for nickel-gold.
**Seven, Spray Tin Circuit Board**
The term “spray tin board” refers to silver boards that have a layer of tin sprayed onto the outer layer of the copper circuit, aiding soldering. However, it does not provide long-term contact reliability like gold does. This type is mainly used in small digital products, primarily because of its low cost.
**Advantages:** It offers a lower price and good soldering performance.
**Disadvantages:** Spray tin is not suitable for soldering pins with fine gaps or very small components, as its surface flatness is inferior. Tin beads can easily form during PCB processing, increasing the risk of short circuits in components with closely spaced pins.
Hot air leveling is a technique that involves applying molten tin-lead solder to the PCB surface and then leveling it using heated compressed air. This process creates a coating layer that resists copper oxidation and ensures good solderability. During hot air leveling, a copper-tin metal compound forms at the interface between the solder and copper, with a thickness of approximately 1 to 2 mils.
2. **Advantages: Low Cost**
The primary advantage of this method is its cost-effectiveness.
3. **Shortcomings:**
1. Pads treated with HASL technology may not achieve sufficient flatness, resulting in coplanarity issues that fail to meet the requirements for fine-pitch pads.
2. The process is not environmentally friendly, as lead poses environmental hazards.
4. **Gold-Plated Boards**
Gold plating utilizes real gold, even if only in a thin layer, which constitutes nearly 10% of the circuit board’s total cost. The use of gold as a plating layer serves two primary purposes: facilitating soldering and preventing corrosion. Even the golden fingers of memory sticks, after several years of use, remain shiny.
**Advantages:** Gold offers strong conductivity and excellent oxidation resistance. Its dense and wear-resistant coating is commonly used in bonding, welding, and plugging applications.
**Disadvantages:** The main drawbacks are the higher costs and lower welding strength.
**Five, Chemical Gold/Immersion Gold**
Chemical nickel immersion gold, also referred to as chemical nickel gold or immersion nickel gold, is often abbreviated as chemical gold or immersion gold. This process involves chemically depositing gold onto the copper surface, using a thick layer of nickel-gold alloy that provides good electrical properties and long-term PCB protection. The typical deposition thickness for the inner nickel layer ranges from 120 to 240 μin (approximately 3 to 6 μm), while the outer layer of gold is generally 2 to 4 μin (0.05 to 0.1 μm).
**Advantages:**
1. PCBs treated with gold exhibit a very flat surface and good coplanarity, making them ideal for button contact surfaces.
2. Chemical gold offers excellent solderability; the gold quickly merges with molten solder, forming a Ni/Sn metal compound with the solder.
**Disadvantages:** The process is complex, requiring strict control of parameters for optimal results. A significant concern is the tendency for gold-treated PCB surfaces to develop black pad issues during ENIG or soldering processes, which can lead to excessive oxidation of nickel and overabundance of gold, compromising solder joint integrity and reliability.
**Six, Electroless Nickel Palladium Plating**
Electroless nickel and palladium introduce a palladium layer between the nickel and gold. During the replacement gold deposition reaction, the electroless palladium layer protects the nickel from excessive corrosion. Palladium effectively mitigates corrosion from the replacement reaction while preparing for immersion gold. The deposition thickness for nickel typically falls between 120 to 240 μin (about 3 to 6 μm), while palladium thickness ranges from 4 to 20 μin (about 0.1 to 0.5 μm), and gold is generally deposited at 1 to 4 μin (0.02 to 0.1 μm).
**Advantages:** This treatment has a wide range of applications. The chemical nickel-palladium-gold surface treatment effectively prevents reliability issues linked to black pad defects and can substitute for nickel-gold treatments.
**Disadvantages:** Despite its advantages, ENEPIG has its drawbacks; palladium is expensive and a scarce resource. Additionally, it demands strict process control similar to that required for nickel-gold.
**Seven, Spray Tin Circuit Board**
The term “spray tin board” refers to silver boards that have a layer of tin sprayed onto the outer layer of the copper circuit, aiding soldering. However, it does not provide long-term contact reliability like gold does. This type is mainly used in small digital products, primarily because of its low cost.
**Advantages:** It offers a lower price and good soldering performance.
**Disadvantages:** Spray tin is not suitable for soldering pins with fine gaps or very small components, as its surface flatness is inferior. Tin beads can easily form during PCB processing, increasing the risk of short circuits in components with closely spaced pins.
