PCB edge plating in assembly process

Edge Plating:

In the PCB industry, edge plating is also referred to as metalized edge plating, border plating, plated contour, side plating, and castellation. The PCB board’s edges are encapsulated by the electroplating coating, which extends from the top to the bottom surface. PCBs can have their single-axis or multi-axis edges plated. Frequently used to enhance chassis grounding for signals and EMI shielding for high-frequency designs.

Purpose of Edge Plating:

Using PCB plating, printed circuit boards can be better protected against a number of vulnerabilities. The edge plating can assist in the following four primary areas:

1. Signal and power integrity:

The board’s power and signal integrity will both be enhanced by EMI reduction. High-speed electronics will benefit from extra shielding and better current-carrying capabilities due to the expanded grounding provided by the edge plating.

2. Electromagnetic adaptability:

The current flowing between the ground and power planes on multilayer circuit boards may cause electromagnetic interference (EMI) at their edges. The circuit board may surpass the EMC criteria it is designed to fulfill as a result of this interference’s potential to radiate outside of the system. The metal plating barrier that surrounds the board’s edges stops the electromagnetic interference (EMI) from radiating.

3. Thermal dissipation:

As signal rates rise, circuit boards have the potential to produce significant amounts of heat. In order to transfer this heat uniformly throughout the board, thermal vias are usually used to route it into an internal ground plane. Heat can easily escape the board through the metal edge since the ground plane is attached to the edge plating.

4. Structural reliability:

A circuit board’s strength and stiffness are reinforced by the addition of metal on its sides. Regular use reduces the likelihood of physical damage to the boards. Additionally, the PCB’s metal sides offer superior support when sliding the board into the intended electronic systems’ metal frames and casings. Additionally, edge plating will shield the PCB from unintentional physical harm while handling or use.

PCB edge plating in assembly process

PCB Edge Plating Layout Guidelines

A few factors the designer should be aware of. A metal strip on the surface layers is first needed for the plating to bond with. In order to leave the metal strips exposed for plating, the designer must not only mention them in the layout data but also remove the solder mask from that region. Arranging the internal plane layers’ configuration is a crucial aspect of design.

It is necessary to move the power plane’s boundary away from the board’s edge, even though the ground plane is often attached to the edge plating. Any possibility that the power plane will make contact with the PCB edge plating during manufacturing and result in a direct power-to-ground short will be eliminated by pulling back the power plane boundaries.

The manufacturing drawings are the means by which PCB designers convey their intention for the edge plating. The sides of the board that must be plated, how the edge plating overlaps with the metal strips on the surface layers and the kind of plating and surface finishes needed must all be specified in the documents. A reputable PCB manufacturer can assist you in making these choices. 

PCB Edge Plating DFM Guidelines

Alongside the common board plating procedures, edge plating—also referred to as rout plating—occurs to denote the partial or total depanelization that takes place prior to the metallization process. This is less of an issue in single-edge plating, although partially routed boards may still include tabs in the panel that serves as just fasteners connecting the routed edges to the panel as a whole. Depending on when depanelization is to take place, these tabs must strike a compromise between ease of removal and durability because they are only meant to be temporary throughout production operations.

The following are some main points that should be kept in consideration while doing DFM of plating

  • The thickest point of the tabs between the board and panel should be about 2.5 mm or 100 mils. For better adhesion, the tabs on the substrate will be thicker.
  • To avoid exposure during de-tabbing, artwork surrounding the tabs on both the outer and inner layers should be free of metal. Set a minimum as your goal. There is a 25mm/10 mil gap between the copper layer features and the tabs.
  • Tabs may be solid for removal after manufacturing, or they may have mouse bites for a less rigorous breakup after assembly.
  • Generally, tabs are placed every 50 mm or 2 inches along routed edges; however, more frequent placement may be necessary for extremely thick or thin panels or those with less mechanically robust substrates.
  • The edge plating will wrap around the routed edge to the other side of the board for optimal adhesion. The edge plating needs to be at least 0.4 mm/15 mils beyond the edge, with a gap of 2.5 mm/100 mils between it and any other plated edges and a clearance of 0.25 mm/10 mil to any other net copper features.
  • Although edge plating is usually continuous, it can be purposefully interrupted using tabs or by routing off plating. For connectivity with any exterior pours or same-net plane layers, the plating needs lastly be assigned to a net, usually ground.

Read More: Soldering Techniques for PCB – A Beginner’s Guide

Key points to handle the process of Edge Plating:

To guarantee successful plating and prevent possible problems, the edge plating procedure requires cautious handling and close attention to detail. The following are a few key components of the procedure:

1. Managing and Handling:

The PCB edge must be handled and prepared properly before it can be plated. Cleaning the edge to get rid of any impurities or residues that can impede the plating process is part of this. To guarantee that only the designated regions are plated, the edge must also be appropriately coated or protected.

2. Specialized Tools and Capabilities:

Specialized tools, including plating tanks or machines, along with experienced operators who are familiar with the relevant plating processes, are needed for the plating process to be carried out correctly.

3. Precautionary measures for Burrs:

The formation of burrs during plating is one of the main issues. Unwanted metal bulges called burrs can happen during the plating process and cause short circuits or other electrical problems. In order to avoid burrs and guarantee the PCB’s dependability, proper process control is necessary. This includes choosing the right plating parameters and applying deburring methods.

4. Adhesion with Plating:

For the PCB to be firmly attached for the lifetime of the board, the edge must have high adhesion with the plating material. The bond between the edge and the plating material can be strengthened by adhesion-promoting methods such surface roughening or the use of adhesion-promoting chemicals.

5. Controlled Soldering:

Soldering may occasionally be required during the plating procedure. The interlayer through-hole connections must be carefully controlled during the soldering process to avoid damage. The inside layers of the PCB may sustain damage from solder wicking, which can be caused by overheating or using incorrect soldering procedures.

The edge plating process can be effectively completed, producing dependable and long-lasting edge plating that satisfies PCB design criteria by closely monitoring these factors and putting the right safeguards in place. The danger of problems and failures is reduced by careful handling, preparation, and process control, which assist in guaranteeing the quality and integrity of the plated edges.