- The solderability and cleanliness of an inter-metallic joint are determined by the surface finish, which affects the reliability of the connection between the PCB and its components.
- Rework (or touch-up) and associated scrap rate are kept minimum with the use of surface finish. This makes the process simple and minimizes waste while increasing productivity.
- It helps PCB for detailed diagnostics and functional validation.
- The choice of surface finish affects the PCB processing expenses. Thus, the cost of the manufacturing process changes according to it.
The selection of surface finish is one of the most important decisions to be made when it comes to printed circuit board (PCB) design. It greatly affects the performance, reliability, and manufacturability of the final product. The surface finish acts as a guard that covers copper traces to prevent oxidation and allow solderability with components. The purpose of this blog is to discuss the different PCB surface finishes and the impact they have on the performance of PCB.
Types of PCB Surface Finishes
PCB surface finishes are of great importance to PCB manufacturing. Each surface finish has some properties that serve specific applications. Below is an overview of the leading types of surface finish for PCBs.
Hot Air Solder Level (HAL)
Hot Air Solder Level (HAL) is one of the most common finishes with a 60/40 tin-to-lead mixture and is suitable for through-hole technology. On the other hand, it is unsuitable for Surface Mount Devices (SMD) technology because of its nonuniform finish. This surface finish is cheap and rugged but can cause defects due to the heating process involved in its application.
Lead-Free HAL
Lead-free HAL has similarities with traditional HAL except that the lead is replaced by a combination of tin and copper to improve the surface finish. It is durable, exhibits a strong solderability, is less adaptable with small boards, and has a much-increased application temperature.
Immersion Silver (Au)
Good at providing flat surface finishes and excellent conductivity, immersion silver is ideally suited for SMD (Surface Mount Device) assembly. Although it is an affordable environmental option, immersion silver is highly tarnished and has relatively low durability.
Immersion Tin (Sn)
Immersion Tin, or White Tin, gives a flat, bright surface. This thin finish is especially appropriate for SMD assembly and press-fit pin insertion. Immersion tin is prone to tin whiskers and more susceptible to corrosion than others.
Electroless Nickel Immersion Gold (ENIG)
ENIG consists of a layer of nickel to prevent gold migration, with an outer layer of gold for excellent solderability and conductivity. ENIG is long-lasting and durable. This surface finish is used for many purposes though it is much more expensive and subject to complicated application processes.
Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG)
ENEPIG has layers of nickel, palladium, and gold, which provide reliable quality, solderability and corrosion resistance. It was developed for mixed assembly technology and multiple cyclic assembly. ENEPIC are expensive and have a process-intensive mechanism compared to others.
Electrolytic Wire Bondable Gold
Electrolytic Wire Bondable Gold is also referred to as soft gold. This high bond quality and excellent connection strength are due to its almost pure 24-carat gold composition. Usually applied prior to the solder mask, it offers a long shelf life.
Electrolytic Hard Gold
Electrolytic Hard Gold, although much tougher than Wire Bondable Gold, is also suitable for repeated applications. This gives good durability and long shelf life, but it is costly and needs additional processing stages like bus bars and active fluxes.
Impact of a PCB Surface Finish on Your PCB
A PCB surface finish plays an important part in making sure that printed circuit boards are fully operative and dependable. The surface finish has a significant impact on a number of critical operational metrics, including the following.
Conclusion
Choosing the proper PCB surface finish is key to the optimal performance and reliability of electronic devices. Each finish type has unique parameters that must be adequately considered for PCB fabrication. Understanding the different characteristics of surface finishes helps designers and engineers decide which variants will increase functionality while meeting industry standards.
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