Manufacturing circuit boards is a costly process, and PCB manufacturers aim to protect their components from various factors such as corrosion, stress, and environmental conditions. Plating the circuit boards can help extend their lifespan. There are different plating options available, and various methods can be used to plate the PCB.
Electroless plating is a chemical process used to apply a thin layer of copper to the outer layers of the PCB, including the inner surfaces of holes and vias, and the surface of the circuit board. This method creates a metal matrix that serves as a foundation for subsequent electroplating. The holes are cleaned, prepared with microetches, covered with photoresist material, exposed to UV light, and then the photoresist cover is removed before electroplating can take place.
The electroplating process involves dipping the circuit board into a plating solution, which is a liquid containing dissolved metal ions. An electrical charge is then passed through the solution in which the board is immersed, resulting in the application of a coating.
After the plating process is complete, the manufacturer can proceed with the soldering step or release the assembly. By plating their PCBs, manufacturers can ensure that their electronic components are better protected and last longer.
In PCB manufacturing, plating is a critical process that protects components from corrosion, stress, and environmental factors to extend the lifespan of the electronics. There are two subtypes of electroplating, including through-hole plating and surface treatment, each requiring different materials. Surface PCB plating can be done using various methods, including Hot Air Solder Leveling (HASL), Electroless Nickel Immersion Gold (ENIG), Electroless Nickel Electroless Palladium Immersion Gold (ENEPIG), immersion silver, immersion tin, and Organic Solderability Preservatives (OSP).
HASL is a low-cost method that provides good shelf life but can result in an uneven surface and is not suitable for through-hole plating. ENIG is a popular premium finish that is RoHS compliant and supports through-hole plating, but it is expensive and prone to signal loss and black pads. ENEPIG is a three-step coating that provides excellent finish quality, is wire-bondable, and has the best corrosion resistance but is the most expensive method and has processing limitations. Immersion silver is a relatively inexpensive and environmentally friendly method that results in a more even surface but can easily oxidize and is less durable than other plating methods. Immersion tin is a low-cost plating method that is reworkable but can create tin whiskers and is prone to handling damage. OSP is the most environmentally friendly method that provides a flat surface and is reworkable but has an average shelf life and is sensitive to handling.
Finger Plating
Finger plating involves the use of gold to provide lower contact resistance and higher wear resistance. The previous tin coating is removed, and the PCB is dipped in sulfuric acid, followed by plating with nickel and then gold solution treatment and electroplating. This process provides the best contact plating available at a lower cost compared to ENIG and ENEPIG.
Through Hole Plating
This is a coating applied to the inner surface of the PCB after drilling. Copper foil and synthetic resin are damaged and melted during the drilling process, which can affect the board's performance. To alleviate this problem, the inner surface is coated with a conductive film, and the components are heat-cured to fully harden. This process is a one-step and relatively inexpensive solution.
Reel Linkage Selective Plating
This process involves the selective plating of certain components such as connectors, integrated circuits, and transistors. The method is similar to finger plating, and manual or automatic methods can be used. The process involves flattening the ends of the foil, die cutting, cleaning, and plating. The area is coated with a resist film and then electroplated on the copper foil.
Brush Plating
This is a type of selective plating used when only a limited area needs to be plated, and not all parts are immersed in the electrolyte. This technique is typically used on board edge connectors and is a quick rework method used in repair shops. The anode is encased in an absorbent material, and the plating solution is brought to the parts of the PCB to be plated.
In conclusion, these plating methods are essential in PCB surface treatments, and each method has its advantages and disadvantages. Choosing the right method depends on the specific requirements of the PCB design.