Advantages and Manufacturing Process of Heavy Copper PCB

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PCBs are indispensable components in modern electronic devices. Among them, heavy copper PCBs, a specialized type of circuit board, boast unique performance characteristics and application scenarios. This article provides an in-depth exploration of the definition, advantages, manufacturing process, and challenges of heavy copper PCBs.

What is a Heavy Copper PCB?

A heavy copper PCB refers to a printed circuit board that features a significantly thicker copper layer as its conductive layer during production. Typically, the copper layer in standard PCBs ranges from 1 oz (approximately 35 microns) to 2 oz (approximately 70 microns). In contrast, heavy copper PCBs feature copper layers far exceeding this range, often reaching 4 oz (approximately 140 microns) or more. This design enhances the PCB’s conductivity, current-carrying capacity, and thermal performance.

Advantages of Heavy Copper PCB

  • Excellent Thermal Conductivity
    The thicker copper layer effectively dissipates heat, improving thermal performance. This reduces temperature-induced PCB expansion, enhancing the board’s reliability.

  • Enhanced Component Reliability
    Heavy copper PCBs offer superior current-carrying capacity, minimizing the risk of burnout or localized heat concentration. This significantly improves the reliability of electronic components.

  • Increased Mechanical Strength
    The greater thickness of the copper layer imparts higher mechanical strength. In demanding environments, such as those involving high vibration or impact, heavy copper PCBs provide improved resistance to mechanical stress, protecting electronic components from damage.

  • Improved Signal Transmission Performance
    The thick copper layer reduces signal transmission loss and crosstalk. For high-frequency and microwave circuits, heavy copper PCBs offer low impedance and low loss, enhancing signal transmission quality and extending transmission distances.

How to Estimate the Required Copper Thickness for PCBs

The IPC-2152 Conservative Chart provides a reliable reference for determining PCB design parameters. Its significance lies in its ability to account for various factors, including internal and external conductors, PCB materials, board thickness, and environmental conditions such as air (excluding vacuum scenarios). The values derived from this chart are highly dependable, ensuring applicability in all non-vacuum environments without considering additional variables.

When engineers design PCBs using the Conservative Chart, the resulting designs may not always optimize cost or area but will reliably meet current-carrying and temperature rise requirements.

IPC-2152 Conservative Chart

Using the IPC-2152 Conservative Chart

Engineers can consult the IPC-2152 Conservative Chart to calculate trace width and determine the appropriate copper thickness.

  1. Example with a Trace Width of 140 mil:

    • Following the red arrow, for a trace width of 140 mil and a copper thickness of 1 oz, vertically locate the temperature rise requirement of 10°C.
    • From there, trace back to the y-axis to find the corresponding maximum allowable current of 2.75A.

  2. Example for Conducting 1A Current:

    • Using the orange arrow, if the PCB conductor needs to carry 1A of current with a target temperature rise of 30°C, locate the trace width required for different copper thicknesses.
    • For a copper thickness of 0.5 oz, the required trace width is 40 mil.

By following these guidelines, engineers can accurately estimate the copper thickness and trace width needed for specific current and thermal requirements.

Manufacturing Process of Heavy Copper PCBs

  • Material Preparation
    This includes essential materials such as PCB substrates, copper foil, copper-clad film, and printing ink.

  • Shaping
    The substrate is machined or stamped to meet the required dimensions and shapes of the product.

  • Drilling
    Tools like drilling machines are used to create holes on the PCB for component mounting and circuit connections.

  • Coating
    A layer of copper-clad film is applied to the PCB surface to protect the copper foil and pads.

  • Chemical Copper Plating
    Chemical plating increases the thickness of the copper foil, enhancing the board’s conductivity.

  • Pattern Imaging
    Patterns and text are printed on the PCB using techniques like ink printing or thermal transfer.

  • Surface Treatment
    The surface is treated to improve solderability and resistance to corrosion.

  • Cutting
    The board is cut into individual units of specified dimensions for assembly and use.

How to Address the Challenges of Heavy Copper PCB Production

Due to the thickness of the copper, manufacturing heavy copper PCBs involves significant challenges. LSTPCB has developed a dedicated production line to systematically tackle these issues.

1. Etching

  • Thick copper increases the difficulty of chemical exchange and side etching.
  • The solution involves multiple rapid etching processes and higher etching compensation factors to mitigate side etching issues.
  • LSTPCB has customized a DES etching line designed for thick copper, enabling one-pass etching of up to 6 oz copper.

Thick copper dedicated DES line

2. Lamination

  • Deep gaps between circuits necessitate using multiple prepreg sheets with excellent flow characteristics to ensure sufficient resin filling.
  • Rivets are added to enhance the fixation of core boards, reducing slippage risks.
  • Thicker copper slows heating rates during lamination, requiring extended high-temperature phases for effective curing.
  • LSTPCB employs Burkle’s fully automated multilayer lamination lines and specialized brown oxidation solutions. Their Mass LAM and Pin LAM integration supports the production of heavy copper PCBs with up to 50 layers.

Burkle Press

3. Drilling

  • For boards thicker than 2.0 mm, segmented drilling is used to ease the process.
  • Parameters like feed and retract speeds are adjusted to optimize drill quality and avoid pad cracking caused by excessive impact.

4. Solder Mask Printing

  • Deep gaps and height differences between copper and the substrate can lead to issues such as ink flow, insufficient coating thickness, red circuit lines, pinholes, and bubbles.
  • These problems are resolved by thinning the ink viscosity and applying multiple printing passes.
  • LSTPCB uses an automated solder mask spray line with pre-treatment, double-sided spraying, pre-baking, and full automatic inline technology. Their high-pressure nozzles and high-viscosity brand inks enable single-pass spraying for up to 4 oz copper, ensuring uniform coating thickness and excellent solderability.

Fully automatic solder mask spraying line

Conclusion

Heavy copper PCBs, as a specialized type of printed circuit board, stand out with superior conductivity, high current-carrying capacity, and exceptional thermal performance. They are widely used in high-power electronics, industrial control, and renewable energy fields. With advancements in technology and industry growth, heavy copper PCBs are expected to find even broader applications, playing a pivotal role in the development of modern electronic devices.