PCB Edge Plating

What is PCB Edge Plating?

PCB edge plating is a process in which the sides of a printed circuit board (PCB) are coated or plated with a conductive material, typically copper, across its height.PCB Edge plating is a technique of PCB manufacturing where the top and bottom side of the PCB is plated along the side walls. This plating can be applied to just one edge of the board or to all sides, depending on the specific requirements of the PCB design.

The purpose of edge plating is twofold. Firstly, it provides a reliable electrical connection along the edges of the PCB. This can be useful when the edge of the PCB needs to make electrical contact with another component or when the edge serves as a connection point for external devices or connectors. The edge plating ensures a consistent and reliable electrical pathway for these connections.

Secondly, edge plating enhances the rigidity and durability of the PCB. By plating the edges with a conductive material, the PCB becomes more structurally sound and less prone to failure in various aspects. It helps prevent delamination or separation of the PCB layers, provides additional mechanical support, and improves the overall strength of the board.

Edge plating is commonly used in applications where the PCB requires robust and reliable connections along its edges, such as in high-speed communication systems, connectors, or devices that undergo frequent handling or insertion/removal.

The process of PCB edge plating involves several steps. It typically begins with the preparation of the PCB edges by cleaning, etching, and applying a thin layer of seed material, such as copper. The seed layer acts as a base for subsequent electroplating. Then, an electroplating process is employed, where the PCB edges are immersed in an electrolyte bath, and a direct current is applied to deposit a layer of copper onto the exposed edges. Finally, additional finishing processes, such as surface treatment or solder mask application, may be performed to complete the edge plating.

In summary, PCB edge plating involves coating or plating the sides of a PCB with a conductive material to provide reliable electrical connections and improve the structural integrity of the board. It is a valuable technique for applications that require robust edge connections and enhanced durability.

How is the Edge Plating Process Handled?

The edge plating process requires careful handling and attention to detail to ensure successful plating and avoid potential issues. Here are some key aspects of how the edge plating process is handled:

Special Equipment and Skills: Proper execution of the edge plating process requires specialized equipment, such as plating tanks or machines, and skilled operators who are familiar with the plating techniques involved.

Handling and Preparation: Before the PCB edge can be plated, it needs to undergo proper handling and preparation. This includes cleaning the edge to remove any contaminants or residues that could interfere with the plating process. The edge also needs to be properly masked or protected to ensure that only the intended areas are plated.

Cohesion with Plating: The edge of the PCB needs to have good adhesion with the plating material to ensure that it remains securely attached for the lifespan of the board. Adhesion-promoting techniques, such as surface roughening or the application of adhesion-promoting chemicals, may be used to enhance the bond between the edge and the plating material.

Controlled Soldering Process: In some cases, soldering may be involved in the edge plating process. It is important to control the soldering process carefully to prevent damage to the interlayer through-hole connections. Excessive heat or improper soldering techniques can lead to solder wicking and potential damage to the internal layers of the PCB.

Prevention of Burrs: One of the major concerns during edge plating is the formation of burrs. Burrs are undesirable metal protrusions that can occur during the plating process and can lead to shorts or other electrical issues. Proper process control, including the selection of appropriate plating parameters and the use of deburring techniques, is essential to prevent the formation of burrs and ensure the reliability of the PCB.

By paying close attention to these considerations and implementing appropriate measures, the edge plating process can be successfully carried out, resulting in reliable and durable edge plating that meets the requirements of the PCB design. Careful handling, preparation, and process control help ensure the quality and integrity of the plated edges, minimizing the risk of issues and failures.

PCB Edge Plating Process Steps

In the intricate realm of printed circuit board (PCB) fabrication, the PCB edge plating process stands as a pivotal technique, particularly prized in applications demanding unwavering edge connections, unyielding conductivity, and steadfast protection for the exposed board edges. This meticulous procedure unfolds through a sequence of exacting steps, each playing a distinct role in achieving excellence in electrical connectivity, mechanical fortitude, and corrosion resistance. Let us embark on a comprehensive exploration of this process:

1. Drilling Holes: Commencing with precision, holes are meticulously drilled along the PCB’s edge to accommodate the forthcoming edge contacts or connectors.

2. Copper Electroless and Electrolytic Plating: The PCB embarks on a two-fold plating journey. First, an electroless copper plating bath meticulously deposits a fine copper layer uniformly across the entire PCB, extending to the edges. This initial layer serves as a conductive foundation for subsequent plating endeavors. Subsequently, the PCB enters the realm of electrolytic copper plating, where a thicker copper layer is meticulously built up along the edges. This stage is instrumental in securing both conductivity and durability.

3. Etching: Following the plating process, the PCB undertakes an etching ritual, designed to remove any surplus copper and delineate isolated traces. This crucial step ultimately defines the precise shape and configuration of the edge contacts.

4. Surface Preparation: The edges of the PCB undergo meticulous surface preparation techniques, including microetching. This methodical preparation eradicates any surface oxides or contaminants, thereby enhancing adhesion and ensuring comprehensive plating coverage.

5. Immersion Plating: The prepared edges are immersed in a plating bath, typically containing a noble metal such as gold or another metal renowned for its excellent conductivity and corrosion resistance. The immersion plating process meticulously deposits a delicate layer of the chosen metal onto the exposed copper surfaces, encompassing the edges.

6. Cleaning and Drying: Post-plating, the PCB is subjected to rigorous cleaning procedures to eradicate any lingering residues or contaminants. This stringent cleansing regimen safeguards the integrity of the plated edges. Subsequently, the board undergoes a thorough drying process, priming it for subsequent manufacturing phases.

7. Quality Inspection: The edge-plated PCB then undergoes a meticulous quality inspection. This comprehensive assessment encompasses various critical parameters, including plating thickness, the uninterrupted continuity of the edge contacts, and the discernment of any anomalies or defects. This meticulous scrutiny ensures that the edge plating precisely aligns with the designated specifications and rigorous quality standards.

8. Electrical Testing (If Needed): Depending on the specific requisites of the PCB and the application at hand, an optional electrical testing phase may ensue. This test aims to validate the functionality and performance of the edge contacts and overall electrical connectivity, leaving no room for uncertainty.

The PCB edge plating process, while firmly rooted in conventional PCB manufacturing methods, carves a distinctive path by adding these specialized steps dedicated to edge plating. These meticulous measures serve to fortify the reliability of edge contacts, secure an adequate plating thickness, and uphold the overarching quality of the edge plating.

Edge Plating Quality Control

Edge plating quality control is crucial in the manufacturing of printed circuit boards (PCBs) to ensure the reliability and performance of edge connectors. Here are key process controls, reliability considerations, and inspection guidelines related to edge plating quality control:

Key Process Controls:

1. Plating Thickness: It is essential to confirm that the minimum plating thickness is met. This can be done through microscopic examination or X-ray fluorescence analysis. Insufficient plating thickness can lead to wear or corrosion issues over time.
2. Continuity: Verify the electrical connectivity from the inner layers of the PCB through the plated edge contacts. Ensuring that electrical signals can pass through the edge contacts is critical for functionality.
3. Plating Coverage: Inspect the plating for voids or thin areas around traces. Inconsistent plating coverage can lead to electrical or mechanical problems.
4. Overplating: Ensure that the plating does not excessively build up on the glass weave of the PCB. Excessive plating can interfere with the mating of connectors.
5. Trace Geometry: Confirm that the dimensions of the traces on the edge contacts match the specified design. Deviations from the design can affect electrical performance.

Reliability Considerations:

Several factors can impact the reliability and lifespan of edge connectors:

1. Plating Thickness: Thicker gold or tin plating tends to improve the cycle life and durability of edge connectors.
2. PCB Thickness: Boards that are thinner than 1 mm may bow or deform under mating stress, affecting the reliability of the connection.
3. Contact Geometry: Well-designed trace shapes on the edge contacts can tolerate repeated mating forces without damage.
4. Receptacle Contacts: Select robust and proven connector contact designs that match the specific application’s requirements.
5. Contamination: Prevent the introduction of dirt, oils, or particles during the handling and use of edge connectors, as these contaminants can affect performance.

Inspecting Assembled Connections:

Key checks to perform on completed connectors include:

1. Continuity: Spot-check the electrical conductivity through the mated connection to ensure that signals pass as intended.
2. Contact Engagement: Confirm full insertion of connectors through visual checks to avoid partial connections.
3. Marks/Damage: Inspect for signs of wear, scrapes, or damage after multiple assembly cycles, as these can affect reliability.
4. Contamination: Verify the absence of foreign particles or films resulting from handling, as these can disrupt the connection.

Edge Connector Standards:

Key specifications and standards that govern edge connectors include:

1. IPC-2223: Sectional requirements for PCB edge contacts.
2. IPC-6013: Qualification and performance standards for edge connections.
3. IPC/EIA J-STD-002: Solderability tests for component leads/terminations, which can impact the quality of edge connector solder joints.
4. IEC 60352-5: Reliability testing and requirements specific to connectors.

Compliance with these standards ensures that edge connectors meet the necessary quality and reliability criteria for their intended applications.

Tips for Designing PCB Gold Fingers

Creating engineering documents for metallized edging in PCB design is a critical aspect of ensuring proper manufacturing and functionality. Below is a structured summary of key points and precautions related to metallized edging:

1. Determining the Area for Metallization:

• Identify the specific areas of the PCB where metallization is required. This information can often be derived from Gerber files, PDFs, TXT, DWG, or other design sources.

2. Copper Stretch on Outer Edges:

• Be aware that in some cases, copper traces may extend to the outer edges of the board. This may necessitate considerations for hemming and the inclusion of metalized edging in the production process. Formal instructions from the customer are typically required in such cases.

3. Design and Precautions:

• Copy the outline layer from the design file to the pthrou layer to create a closed long slot for metallized edging.
• When creating the hemming shape, factor in compensation due to the specific copper thickness required for plating during encapsulation.

4. Electrical Connectivity for Edging:

• Determine the electrical connectivity for the edging. Follow these steps:

Identify the layers and areas specified by the customer for connectivity.
Clarify the connection requirements for each layer.

5. Production Precautions for Metallized Edging:

• To prevent film chipping, ensure that there is a 10MIL pad on one side of the edged board, whether inside, outside, or on the side.
• Maintain a minimum distance of 8MIL between pads near the edging and the edging disk.
• After hemming, check the connection between inner and outer layers to avoid electrical and ground short circuits.
• Special-shaped grooves in the edging should be filled and enlarged by 4mil, similar to PTH grooves.
• Solder mask design should fully window the edging groove, with a bounding solder mask opening equal to the bounding pad +0.16mm.

6. PCB Side Plating:

• For efficiency, use standard milling cutters (e.g., 0.8, 1.0, 1.6, 2.0, 2.4mm) for edging grooves. If not specified by the customer, 2.0mm or greater is recommended.

7. Panel Design and Surface Treatment:

• Ensure that the long direction of the edging slot is parallel to the long side of the rear panel, typically in line with the tin spray direction.
• For orders not meeting this requirement, consider non-sprayed surface processes such as gold or copper-nickel plating.

8. Additional Considerations:

• Beware of antenna positions that may interfere with welding or signal transmission.
• Pay attention to inner cladding pad connections to prevent short circuits.
• When designing stamp holes at the edging slot, consider using two drills to avoid plate breakage due to irregular forces during electroplating.
• Ensure a sufficient bridge width during tin spray to prevent plate breakage due to the force of the wind knife.

These comprehensive guidelines and precautions help ensure the successful integration of metallized edging in PCB design and manufacturing processes.