PCB Technical - Detailed explanation of PCB surface coating

Detailed explanation of PCB surface coating

Many newcomers often ask what is the surface coating of PCB? What problems should be paid attention to to ensure the reliability of the surface coating process? Next, the "senior" editor of PCB proofing manufacturers will come to analyze some knowledge points about PCB coating with you, and hope to help you.

The coating is used to protect the surface of the circuit copper foil. Copper is a good surface for soldering components, but it is easily oxidized; copper oxide hinders the wetting of solder. Although gold is now used to cover copper, because gold will not oxidize; gold and copper will quickly diffuse and penetrate each other. Any exposed copper will quickly form unsoldered copper oxide. One method is to use a "barrier layer" of nickel, which prevents the transfer of gold and copper and provides a durable, conductive surface for component assembly.

At present, in terms of PCB surface coating process, almost all manufacturers operate in accordance with the international standard IPC-A-610 acceptance standard for electronic components. Generally speaking, the IPC standard is that the surface coating is transparent and uniformly covering the circuit boards and components, and the coverage of the coating depends on the coating method. But be aware that most surface coatings now contain optical brighteners, which fluoresce when exposed to ultraviolet light. In turn, this makes it easier to inspect surface coatings. However, some defects in the coating will not be visible under ultraviolet light and may need to be inspected under white light. Due to the nature of the material, some coatings have weak UV fluorescence. This situation can be seen in many silicon surface coatings and may make inspection more difficult.

For OSP coating, it is an organic soldering protection film on Cu surface that appeared in the 1990s. Certain cyclic nitrogen compounds, such as aqueous solutions containing benzotriazole (BTA), imidazole, alkylimidazole, benzoimidazole, etc., can easily react with clean copper surfaces. The nitrogen heterocycles in these compounds form the surface of Cu Complex, this protective film prevents the Cu surface from being oxidized.

In addition, I would like to add that non-electrolytic nickel and gold have only recently become a common final PCB surface coating, so industrial procedures may not be suitable. The above are some instructions on PCB surface coating. If you think it is useful, please hurry up and collect it. iPCB is a high-tech manufacturing enterprise focusing on the development and production of high-precision PCBs. iPCB is happy to be your business partner. Our business goal is to become the most professional prototyping PCB manufacturer in the world. Mainly focus on microwave high frequency PCB, high frequency mixed pressure, ultra-high multi-layer IC testing, from 1+ to 6+ HDI, Anylayer HDI, IC Substrate, IC test board,rigid flexible PCB, ordinary multi-layer FR4 PCB, etc. Products are widely used in industry 4.0, communications, industrial control, digital, power, computers, automobiles, medical, aerospace, instrumentation, Internet of Things and other fields.