What we are sharing today is: PCB side electroplating, PCB side electroplating types, and how to design PCB side electroplating?
What is PCB side electroplating?
PCB side plating, also known as edge plating, is a copper plating layer that runs from the top to the bottom of the board and along at least one peripheral edge. PCB side electroplating reduces the possibility of device failure through the firm connection of the PCB, especially for small PCBs and motherboards. Examples of this electroplating are common in Wi Fi and Bluetooth modules.
During the manufacturing process, the edges to be metallized should be milled before the copper plating process. After copper deposition, perform appropriate surface treatment on the edges of the PCB.
When will PCB side electroplating be used?
Under what circumstances is edge electroplating implemented:
- Need to improve the conductivity of PCB
- The connection needs to be at the edge of the PCB
- PCB needs to prevent lateral impact
- The secondary PCB is connected to the motherboard through edges
- Need to weld edges to improve assembly
PCB side electroplating type
- Circumferential edge electroplating
Surrounding electroplating is used to wire the metal edges along the side after drilling. The wiring process exposes the PCB sidewall to the chemical plating base copper, so that it can be applied simultaneously when drilling.
In the following case, the substrate creates a conductive surface on which you can electroplate a thicker and more durable copper layer (for better adhesion).
- Copper plate edge
To avoid damaging copper, we usually require a minimum distance between the copper feature and the edge of the PCB. This distance is:
Outer layer 0.25mm with open circuit
Inner layer 0.40 mm with open circuit
0.45mm on all layers with V-shaped cutting marks.
The distance from copper to the edge of the board should only be used for flat and large copper areas, where any slight damage to copper will not affect the performance of the board. The track should not be located within the minimum distance of the board edge to avoid damage.
If pads are found within the minimum distance of the plate edge, they will be cut back to restore the minimum copper free space, unless:
A pad is a part of an edge connector (usually with beveled edges)
The solder pad is marked as “up to the edge of the circuit board” in a separate mechanical layer
Cutting beyond 25% of the pad surface is actually quite abnormal in this case.
- Plate edge PTH
Board edge PTH is an electroplated hole cut at the edge of a circuit board, also known as a butterfly hole, used for direct welding or through connectors between two PCBs. Used to connect two circuit boards directly by soldering or through connectors. The edges of the PCB must have sufficient free space to secure the circuit board in the production panel during the manufacturing process.
The top and bottom layers must have solder pads to firmly secure the plating to the circuit board. For smaller sizes, a golden surface treatment is preferred.
Here are some points to note:
- The edges of the PCB must have sufficient free space for us to fix the PCB in the production panel during the manufacturing process.
- Pads must be placed on the top and bottom layers (as well as possible inner layers) to firmly secure the plating to the PCB.
- As a general rule, holes should be as large as possible to ensure good welding with the parent PCB, and it is recommended to have a diameter of 0.80 millimeters or more.
- All surface treatments are acceptable, but I prefer to choose gold over nickel in smaller sizes.
- Circular edge electroplating
Circular edge electroplating means that most or part of a PCB or cut is electroplated from top to bottom. The main purpose is to establish a good grounding for the purpose of metal casing or shielding. In order to produce this type of electroplated circuit board, the contour of the circuit board is milled before the through hole electroplating process.
Due to the need for electroplating to be fixed in the production panel during the processing, 100% edge electroplating is not feasible. Placing routing tabs must have some issues, and for circular edge electroplating, choosing chemical nickel gold is the ideal surface treatment.
Here are some points to note:
- Each side requires a copper strip for electroplating connection.
- Due to the need to fix the circuit inside the production panel during the processing, it is not possible to perform 100% electroplating on the edges.
- Clearly indicate in the mechanical layer that requires circular edge electroplating.
- Selective chemical nickel gold is the only surface treatment suitable for circular edge electroplating.
How to design PCB edge electroplating?
- PCB Edge Plating Guidelines
In the design/layout file, overlapping copper is used to define the copper plating area, and this additional copper deposition can be copper pads, surfaces, or traces.
To ensure the producibility of the side panels, overlapping copper (copper surface, solder pad, or rail) must be used in the CAD layout to define the metallization area.
Minimum overlap: 500 μ M.
On the connection layer, the minimum value. A connection copper wire of 300 µ m must be defined.
On non connecting layers, copper should have a minimum gap of 800 from the outer contour μ M.
- Metallization electroplating process
During this process, only four steps need to be performed in the following order: drilling ->milling metal grooves ->removing dirt ->chemical copper plating
The external contour that needs to be metallized must be milled before the through-hole electroplating process, as the metallization of the edges is carried out during this manufacturing step. After copper deposition, the expected surface finish is ultimately applied to the edges.
- Manufacturing issues
- Copper peeling – on large substrates
Electroplating on the surface may cause copper plating to peel off due to a lack of adhesion. Firstly, it is necessary to solve this problem by combining chemical and other proprietary methods to roughen the surface. Next, direct metallization with higher copper bonding strength is used to prepare the electroplated surface.
- Burr edge electroplating
In some electroplating processes, burrs may occur during the final machining process. A proprietary process that requires modification to polish the burrs to the edges of the features.
- Wafer Factory Precautions
The position of the gold pad antenna is too large, which affects welding or signal transmission.
Connecting the inner edge pad to the wires on the board may cause a short circuit.
The design of the stamp hole at the edge grinding groove must be processed in the second drilling process.
By using each PCB as a panel for process related manufacturing, it is impossible to achieve continuous metallization of the outer edges. Metallization cannot be applied at the location where the small panel bridge is located. A solder mask layer can be used to cover the sliding electroplating metallization layer.
When purchasing edge banding boards, it is necessary to confirm with the PCB supplier the possibility of using electroplating technology to manufacture the PCB and the extent to which the manufacturer can edge seal the PCB. Gerber files or factory drawings should indicate in the mechanical layer where they require sliding plating and the surface finish they require.
The benefits of PCB edge electroplating
- Enhanced current conduction
Improving current carrying capacity can improve the reliability and quality of circuit boards. In addition, the correct conduction level is an ideal choice for components to operate according to requirements, and it can also protect vulnerable edge connections.
- Signal integrity
Edge electroplating enhances signal integrity by preventing interference from entering the internal electrical pulse transmission.
- Heat distribution
Due to the metallic nature of the plated edges, they generate additional cooling surface area to dissipate heat into the surrounding air. The metal surface improves the reliability of the circuit board, especially when components are sensitive to heat.
- Better EMC/EMI performance
The metallized edges allow stray currents to escape, preventing the generation of sporadic electric and magnetic fields.
- Improving electromagnetic compatibility
Edge electroplating enhances the electromagnetic compatibility of multi-layer boards.
- Preventing static damage
When handling circuit boards, static electricity can hit sensitive components, and the metal surface helps absorb static electricity.
Application of PCB Side Electroplating
Improving EMC performance by shielding multiple layers of internal areas (such as high-frequency circuit boards)
The edge serves as an additional cooling surface for cooling, allowing for active heat dissipation
Shell connection
Plate to plate connection (see electroplating half hole)
The above is the knowledge about PCB side copper plating.
