The manufacture of heavy copper PCBs requires specialized processes and equipment. These PCBs are defined as those with copper foil thicknesses greater than 3oz, which makes them ideal for high power and high-reliability electronic devices. In this article, we will discuss the manufacturing process of heavy copper PCBs in detail.
Heavy Copper PCB Manufacturing Process Step by Step
Step 1: Substrate Preparation
The first step in manufacturing heavy copper PCBs is substrate preparation. The substrate is typically made of a fiberglass-reinforced epoxy material. The substrate is cleaned and inspected for any defects or damage that may affect the final product’s quality. The substrate is then coated with a layer of copper foil.
Step 2: Imaging
The next step is imaging, where the desired circuit pattern is printed onto the copper foil using a photolithographic process. A photosensitive resist is applied to the copper foil, and then the resist is exposed to UV light through a mask that defines the desired circuit pattern.
Step 3: Etching
After imaging, the substrate is etched to remove unwanted copper from the circuit pattern. The substrate is immersed in an etching solution that dissolves the copper, leaving only the desired circuit pattern. The resist is then stripped away, leaving behind the copper traces and pads.
Step 4: Drilling
The substrate is then drilled to create holes for component placement and interconnection. High-speed drills with carbide or diamond tips are used to create precise holes. These holes are then plated with copper to create vias that connect the layers of the PCB.
Step 5: Electroplating
The heavy copper PCBs require thicker copper layers than standard PCBs. Therefore, an electroplating process is used to deposit additional copper onto the circuit pattern. The substrate is immersed in an electrolyte solution, and an electric current is applied to the copper layer. This causes copper ions to be deposited onto the substrate, resulting in a thicker copper layer.
Step 6: Lamination
After electroplating, the layers of the PCB are laminated together using heat and pressure. The layers are stacked and pressed together, with an adhesive layer between each layer. This creates a single, solid board with multiple copper layers.
Step 7: Soldermask and Silk Screening
The PCB is then coated with a soldermask layer, which protects the copper traces and pads from oxidation and contamination. The soldermask is applied using a screen printing process. The board is also silk screened with component identifiers, logos, and other markings.
Step 8: Surface Finish
Finally, the PCB is coated with a surface finish to protect the copper and ensure good solderability. The most common surface finishes for heavy copper PCBs are ENIG (Electroless Nickel Immersion Gold), OSP (Organic Solderability Preservative), and HASL (Hot Air Solder Leveling).
Heavy Copper PCB Manufacturing Process Notes and Tips
Specialized Manufacturing Process: The manufacture of heavy copper PCBs requires specialized processes and equipment. These processes include higher copper foil pressure and longer electrolyte deposition times to ensure a strong bond between the copper foil and the substrate.
- Multiple Copper Layers: Heavy copper PCBs often have multiple copper layers, with each layer requiring its own deposition process. This can increase the complexity and time required for manufacture.
- Thicker Substrates: Heavy copper PCBs require thicker substrates to support the weight of the copper layers. This can also affect the routing and drilling of the PCB.
- Controlled Impedance: Heavy copper PCBs often require controlled impedance for high-speed signal transmission. This requires precise control of the copper thickness and layer spacing.
Common Issues:
- Uneven Electrodeposition: Heavy copper PCBs require a longer electrodeposition time, which can result in uneven copper thickness across the board.
- Warping: The high copper weight can cause the board to warp during the manufacturing process, resulting in uneven board thickness and difficulties in assembly.
- Internal Connectivity: Heavy copper PCBs often require plated through-holes (PTHs) for internal connectivity. These PTHs can be difficult to manufacture and may result in reliability issues.
- Delamination: The increased weight and thickness of heavy copper PCBs can lead to delamination between the copper layers and substrate.
In conclusion, the manufacturing process of heavy copper PCBs requires specialized processes and equipment due to the thicker copper layers and the need for precise control of copper thickness and layer spacing. The process includes substrate preparation, imaging, etching, drilling, electroplating, lamination, soldermask, silk screening, and surface finishing. Heavy copper PCBs are ideal for high power and high-reliability electronic devices and are increasingly popular in industries such as automotive, medical, and industrial automation.
