When manufacturing high quality PCBs, different PCB surface treatment processes have different impacts on PCB performance and reliability.
Today, we will introduce several common surface treatment processes, including antioxidant, tin spraying, lead-free tin spraying, immersion gold, immersion tin, immersion silver, hard gold plating, full-board gold plating, gold finger, nickel-palladium-gold, and OSP, and discuss their characteristics and choices for different applications.
Antioxidant treatment is a process that protects the surface of a PCB from oxidation. It usually uses gold or tin plating to cover the surface of the PCB with a metal layer to prevent oxygen and moisture from eroding the PCB.
This process is low cost and has good solderability, but requires harsh storage conditions for a short period of time and is not suitable for long term storage. Antioxidant treatment is an environmentally friendly process with good solderability and flat surface.
Tin spray treatment
Tin spray treatment is commonly used for multi-layer high precision PCB prototypes, especially for boards with 4 to 46 layers. This process involves spraying tin onto the surface of the PCB to form a uniform layer of tin. Tin-sprayed boards are widely used in telecommunications, computers, medical devices and aerospace.
One such application is the gold finger, which is a connecting component on memory sticks to memory slots for signal transmission. Gold fingers consist of electrically conductive contacts that are usually gold plated to ensure good electrical conductivity. However, due to the high price of gold, some devices have started to use tin plating instead of gold plating, especially for price-sensitive devices.
Gold plating is a common surface treatment process, especially for high-density PCBs, which solves some of the problems of spray tin treatment, such as pad flatness and shorter life expectancy.
For surface mount processes, especially for ultra-small surface mount, such as 0603 and 0402, pad flatness is directly related to the quality of the solder paste printing process, so the whole board gold plating is very common in high-density and ultra-small surface mount processes. In addition, gold-plated boards have a much longer life expectancy than tin-sprayed boards, so they are often preferred at the pilot stage.
Immersion Gold Finish
Immersion gold is a high-quality surface treatment that offers several advantages. Firstly, immersion gold has a different crystalline structure to that of gold plating, and is a golden color, which is more pleasing to the customer. Secondly, immersion gold is easier to solder than gold plating and does not cause soldering problems or poor sold
ering.
In addition, immersed gold boards only have nickel gold on the pads, and the skin effect has less impact on signal quality. The crystal structure of immersed gold is denser than gold plating, which is less prone to oxidation, and the bonding between the solder resist and copper layer on the line is more solid.
Immersion Gold VS Gold Plating
While the gold plating process is still an effective surface treatment, the immersion gold process has significant advantages in a number of areas. It is more suitable for high-density PCBs, especially for ultra-small surface mount processes. The golden color of the immersion gold plate is more popular, and the soldering effect is better and less likely to cause soldering problems.
In addition, the crystal structure of the immersion gold plate is different, the skin effect has less influence, so it is suitable for high-frequency signal transmission. Although immersion gold is slightly higher than gold-plated boards in terms of cost, immersion gold is a better choice for some products that require high performance and reliability.
When selecting a PCB surface treatment process, several factors need to be considered, including cost, application, performance and reliability. Different processes are suitable for different situations.
Antioxidant treatment is suitable for some simple applications, while spray tin treatment is suitable for high precision PCBs. gold plating process is still a valid choice in many cases, but immersion gold process has obvious advantages in some aspects, especially suitable for high-density and high-performance applications.
Therefore, when manufacturing PCBs, it is vital to choose the most suitable surface treatment process to ensure product performance and reliability.
Answers to Frequently Asked Questions
1. Why should we choose immersion gold over gold-plated PCBs?
Immersion gold board has obvious advantages in high-density PCB and ultra-small surface mount process. Its golden color is more preferred for better soldering and less prone to soldering problems. In addition, the crystal structure of gold-immersed board is different, the skin effect has less influence, and it is suitable for high-frequency signal transmission.
2. Is anti-oxidation treatment environmentally friendly?
Yes, antioxidant treatment is an environmentally friendly process that protects the PCB surface from oxidization and prolongs the service life of the PCB.
3. What is the active life of an immersion plate?
Immersion tin plates typically have a longer shelf life than gold plated plates and can be kept for months or longer.
4. What applications are tin-sprayed boards used for?
Tin sprayed boards are typically used for multi-layer high precision PCB prototypes, especially for boards with 4 to 46 layers. It is used in a wide range of applications such as communications, computers, medical devices and aerospace, including connecting parts such as gold fingers.
5. What is the difference between immersion gold and immersion silver boards?
Immersion Gold and Immersion Silver are both high quality finishes, but they have different metals. Immersion gold is metallic gold, while immersion silver is metallic silver. Both have slightly different properties and applications, and the exact choice depends on the requirements.
These FAQs will hopefully help you better understand the different surface treatment processes and their applicability. If you have any additional questions or need further information, please feel free to ask our Hitech Circuits team.
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