After the PCB design is completed, the surface treatment process of the circuit board must be selected. The commonly used surface treatment methods for circuit boards include HASL (Hot Air Solder Leveling), ENIG (Electroless Nickel Immersion Gold), OSP (Organic Solderability Preservative), among others. How should we make the choice? Different PCB surface treatment processes have different costs, and the final results will also vary accordingly.
Let’s examine the advantages and disadvantages of the three most common surface treatment methods: HASL, ENIG, and OSP.
1. **HASL (Hot Air Solder Leveling)**
The HASL process is divided into lead-based and lead-free versions. This tinning process was the dominant surface treatment method during the 1980s. However, it is now less commonly used, as PCB technology is moving toward “smaller and more precise” designs. The HASL process can cause issues such as tin beads being formed around fine components during soldering, and poor production quality due to spherical tin dots. As a result, PCB manufacturers aiming for higher process standards and better production quality typically opt for ENIG or OSP surface treatments.
**Advantages of lead-based HASL:** Lower cost, excellent soldering performance, and better mechanical strength and gloss compared to lead-free HASL.
**Disadvantages of lead-based HASL:** Contains lead, a heavy metal, which is harmful to the environment during production and does not comply with RoHS and other environmental regulations.
**Advantages of lead-free tin spray**: It is cost-effective, offers excellent soldering performance, and is relatively environmentally friendly, meeting environmental protection standards such as ROHS.
**Disadvantages of lead-free tin spray**: The mechanical strength and gloss are not as high as those of lead-based tin spray.
**Common drawback of HASL PCB**: It is unsuitable for soldering fine-pitch pins or small components due to poor surface flatness of the PCB’s tin-plated surface. In PCBA processing, tin beads can form easily, which may cause short circuits, particularly with fine-pitch pin components.
### 2. ENIG (Immersion Gold Technology)
The immersion gold process is an advanced surface treatment, typically used for circuit boards requiring functional connections and long shelf life.
**Advantages of ENIG**: The surface is highly resistant to oxidation, has a long shelf life, and remains flat. It is ideal for soldering small-pitch pins and components with tiny solder joints. Reflow soldering can be repeated multiple times without compromising solderability. It also serves as an excellent substrate for COB wire bonding.
**Disadvantages of ENIG**: The cost is relatively high, and the welding strength is weaker compared to other methods due to the electroless nickel process. This can lead to issues such as “black pad,” as the nickel layer may oxidize over time, affecting long-term reliability.
### 3. OSP (Anti-Oxidation Process)
The OSP process involves chemically forming an organic film on the surface of bare copper. This film offers protection against oxidation, thermal shock, and moisture, preventing the copper from rusting or oxidizing in normal environments. However, it must be removed by flux during soldering, exposing a clean copper surface that bonds easily with molten solder to form strong solder joints in a short amount of time. The OSP process is becoming increasingly popular for both low-tech and high-tech circuit boards. If there are no specific requirements for surface functionality or storage duration, OSP is often the ideal surface treatment.
**Advantages of OSP**: It provides the same benefits as bare copper soldering. Even boards that have been stored for up to three months can be resurfaced, though typically only once.
**Disadvantages of OSP**: It is sensitive to acid and humidity. If secondary reflow soldering is required, it must be completed within a certain timeframe, as the performance typically decreases with each additional reflow. If the storage time exceeds three months, the board must be resurfaced. After opening, the OSP must be used within 24 hours. Since OSP acts as an insulating layer, solder paste must be applied to the test points to remove the original OSP layer before electrical testing. Significant changes to the PCB assembly process may be needed. If unprocessed copper is detected, it can negatively affect ICT testing. Over-pointed ICT probes can damage the PCB, requiring additional manual precautions, which limits ICT testing and reduces test repeatability.
The above analysis compares the surface treatment processes of HASL, ENIG, and OSP circuit boards. The selection of a surface treatment process depends on the specific requirements of the PCB’s intended application.
If you have any PCB manufacturing needs, please do not hesitate to contact me.Contact me
Let’s examine the advantages and disadvantages of the three most common surface treatment methods: HASL, ENIG, and OSP.
1. **HASL (Hot Air Solder Leveling)**
The HASL process is divided into lead-based and lead-free versions. This tinning process was the dominant surface treatment method during the 1980s. However, it is now less commonly used, as PCB technology is moving toward “smaller and more precise” designs. The HASL process can cause issues such as tin beads being formed around fine components during soldering, and poor production quality due to spherical tin dots. As a result, PCB manufacturers aiming for higher process standards and better production quality typically opt for ENIG or OSP surface treatments.
**Advantages of lead-based HASL:** Lower cost, excellent soldering performance, and better mechanical strength and gloss compared to lead-free HASL.
**Disadvantages of lead-based HASL:** Contains lead, a heavy metal, which is harmful to the environment during production and does not comply with RoHS and other environmental regulations.
**Advantages of lead-free tin spray**: It is cost-effective, offers excellent soldering performance, and is relatively environmentally friendly, meeting environmental protection standards such as ROHS.
**Disadvantages of lead-free tin spray**: The mechanical strength and gloss are not as high as those of lead-based tin spray.
**Common drawback of HASL PCB**: It is unsuitable for soldering fine-pitch pins or small components due to poor surface flatness of the PCB’s tin-plated surface. In PCBA processing, tin beads can form easily, which may cause short circuits, particularly with fine-pitch pin components.
### 2. ENIG (Immersion Gold Technology)
The immersion gold process is an advanced surface treatment, typically used for circuit boards requiring functional connections and long shelf life.
**Advantages of ENIG**: The surface is highly resistant to oxidation, has a long shelf life, and remains flat. It is ideal for soldering small-pitch pins and components with tiny solder joints. Reflow soldering can be repeated multiple times without compromising solderability. It also serves as an excellent substrate for COB wire bonding.
**Disadvantages of ENIG**: The cost is relatively high, and the welding strength is weaker compared to other methods due to the electroless nickel process. This can lead to issues such as “black pad,” as the nickel layer may oxidize over time, affecting long-term reliability.
### 3. OSP (Anti-Oxidation Process)
The OSP process involves chemically forming an organic film on the surface of bare copper. This film offers protection against oxidation, thermal shock, and moisture, preventing the copper from rusting or oxidizing in normal environments. However, it must be removed by flux during soldering, exposing a clean copper surface that bonds easily with molten solder to form strong solder joints in a short amount of time. The OSP process is becoming increasingly popular for both low-tech and high-tech circuit boards. If there are no specific requirements for surface functionality or storage duration, OSP is often the ideal surface treatment.
**Advantages of OSP**: It provides the same benefits as bare copper soldering. Even boards that have been stored for up to three months can be resurfaced, though typically only once.
**Disadvantages of OSP**: It is sensitive to acid and humidity. If secondary reflow soldering is required, it must be completed within a certain timeframe, as the performance typically decreases with each additional reflow. If the storage time exceeds three months, the board must be resurfaced. After opening, the OSP must be used within 24 hours. Since OSP acts as an insulating layer, solder paste must be applied to the test points to remove the original OSP layer before electrical testing. Significant changes to the PCB assembly process may be needed. If unprocessed copper is detected, it can negatively affect ICT testing. Over-pointed ICT probes can damage the PCB, requiring additional manual precautions, which limits ICT testing and reduces test repeatability.
The above analysis compares the surface treatment processes of HASL, ENIG, and OSP circuit boards. The selection of a surface treatment process depends on the specific requirements of the PCB’s intended application.
If you have any PCB manufacturing needs, please do not hesitate to contact me.Contact me
