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- October 20, 2022
- PCB knowledge
- (0)
- 06 mins
A guide to PCB plating for beginners
The PCBs help keep electronic equipment running smoothly. It is, therefore, necessary to protect them against oxidation. The PCB plating method protects these PCBs against oxidation and corrosion by metal deposition. Additionally, PCB plating offers a precise soldering surface and clear surface finishing for mounting components. There are various plating techniques used in PCB production and PCBA production.
Do you want to learn more about them? If so, this post will introduce you to PCB plating and its significance.
What is PCB plating?
PCB plating is depositing a layer or layers of copper or another conductive material on a printed circuit board (PCB).
The thickness of the finished plated layer will depend on the type of plating solution used, but it is usually between 0.001″ (0.025mm) and 0.005″ (0.13mm).
PCB plating aims to improve electrical properties such as solderability, electrical resistance, and durability by increasing the thickness and amount of metal in certain areas of the PCB.
What is the purpose of plating?
The following are reasons why plating a printed circuit board is advantageous.
- The plating enhances the PCB’s aesthetic attractiveness.
- This shield protects the board from contamination, moisture, and oxidation.
- The PCB platingsaves downtime and lowers the overall cost of printed circuit boards.
- Soldering looks neat and appealing after plating.
What is the PCB plating process?
The PCB plating process begins with PCB cleaning. The main purpose is to remove oils or contaminants from the board’s surface. One can clean this by immersing in water or using chemicals.
Following that, a metal layer is deposited on top of the board. This layer, called the solder mask, prevents the solder from “wicking” up through the holes in your circuit board. The solder mask is created by applying either a photoresist or positive-tone lacquer to the surface of the circuit board.
The next step is to apply a photoresist or positive tone lacquer to the circuit board. It protects copper traces from etching. An etching process removes any unwanted copper from the design, leaving only the areas that need copper (the traces).
Finally (and optionally), designers can add an anti-green coating to prevent corrosion inside the computer case and help keep it looking good for years to come!
What are the types of PCB plating?
The following is a list of the most common types of PCB plating:
Through-hole plating
Through-hole plating is used to plate through-holes. The holes are masked (preventing the copper from being plated), and the rest of the area is plated.
Finger-plated plating
Finger-plated plating uses a mask on one side of the board to prevent copper from being plated while allowing it to be deposited on the other side. This allows for selective plating of smaller areas than can be achieved with wire bonder plating or brush plating/selective plating.
Reel linkage selective plating
Reel linkage selective plating is similar to finger-plated plating in that it uses a mask on one side of the board to prevent copper from being plated while allowing it to be deposited on the other side. It differs because it can be used with reeled boards instead of single ones.
Brush plating/selective plating
It involves coating parts with an even layer of thin metal (usually aluminum). The parts are placed in a “bath” that contains a combination of chemicals and electrolytes. Applying an electric current to the bath makes ions in the solution migrate to your part. The result is an electroplated coating that has excellent adhesion and conforms well to the contours of your design.
What are the PCB plating materials?
In the PCB industry, 3 types of materials are used for the plating process:
- Copper: This is one of the most commonly used materials for PCB plating. It is used for both via and surface finishing. Copper is usually applied as electroless nickel immersion or electroplated copper.
- Gold: Gold is used as an alternative to copper in high-end applications where greater durability and higher performance are required. It can be applied as a thin layer of electroless nickel immersion gold (ENIG) or electroplated gold (EP).
- Tin: Tin can be used to plate through hole pads that require high thermal conductivity, such as heat sinks or other circuitry. Tin is typically applied as a thin layer of electroless nickel immersion tin (ENIT).
How to choose PCB plating material and thickness?
Choosing PCB plating material
When it comes to PCBs plating materials, there are plenty of options available. There’s no right or wrong way to decide on a specific material, but users should make sure that the type they choose has the following characteristics:
Rhythmic performance: For an even finish and resist corrosion, the material should also withstand high temperatures without becoming brittle or deforming.
High conductivity: Materials should transfer heat efficiently from one place to another. This is especially important for boards with significant components like CPUs and GPUs, where heat needs to be dissipated quickly.
High dielectric strength: Dielectric materials help insulate electrical currents from external sources so that they don’t interfere. This is especially important in high-voltage circuits like power supplies, where the electricity could cause damage if it leaks through the board’s insulation layer.
Low thickness: Thicknesses between 0.8mm and 1mm are typical for standard 0201-sized boards, while larger ones require a thicker layer to support more significant components.
Choosing PCB plating thickness
The average PCB plating thickness is in the range of 100 micro-inches. The normal thickness might be as little as 10 micro-inches for immersion silver and OSP. Specifying the kind and thickness of PCB plating is simple: just write it down in the fabrication notes.
Manufacturers offer a standard quote form that users can use to specify the plating type when generating prototypes. Once the fabricator has been supplied with the required plating value, it is his responsibility to ensure that it can be reliably applied to the requisite thickness.
Considerations when doing PCB plating
Here are some considerations when doing PCB plating:
Trace widths – The thickness of the copper layer increases as the trace width increases. A narrow trace on PCB means there is less surface area to carry current. To increase current carrying capacity without increasing size, use wider traces.
Spacing between traces – If there is too much space between traces, it will result in high resistance and poor conductivity. Too little space between traces leads to failure during soldering.
Tolerances for electrical factors that may influence board functionality – Electrical connections are made between components on a board by creating contact points called pads or lands on each component lead and routing a trace between them on the PCB layout.
Clearance of traces and components to board edge– Another thing that must be considered when doing PCB plating is whether there are any parts on your board that have close clearance with its edges or not.
Challenges in printed circuit board plating
PCB plating can be challenging, especially when your design is complex. Here are some of the biggest challenges that manufacturers face when plating:
Poor solder joints and bridging
One of the most common problems with PCB plating is poor solder joints and bridging due to poor surface preparation before deposition. Improperly cleaned surfaces can cause solder deposits to form over large areas instead of just at the desired contact points. The result is weak electrical connections that lead to short circuits or other electrical failures.Smutches and voids
The most common defects in solder masks are smutches or voids. The solder mask does not adhere to the PCB surface, resulting in smutches. Voids occur when there is insufficient solder mask layer thickness or an excess amount of solder mask layer thickness.Contamination
Contamination of copper connections with other metals can also lead to failure in the printed circuit board plating process. It can cause short circuits in electronic systems that use these boards as an integral part of their functionality.Conclusion
In summary, PCB plating is a vital part of the manufacturing process for PCBs. This process ensures that the final products are aesthetically pleasing and corrosion resistant, which makes them ideal for integration into electronic circuit boards and other pieces of hardware.
