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High Quality 4 OZ Copper PCB Manufacturer


4 Oz Copper PCB  Is a heavy copper PCB,  Only 2 layer , still many PCB manufacturer can handle it ,if multilayer PCB, inner layer is 4 oz, few PCB factory can fabricate it well . RayMing have rich experience manufacturing 4 oz PCB whatever double side or Multi-layer PCB .

4OZ heavy copper printed circuit PCB. Heavy Copper Board does not have a set of definition in IPC standard. However, peopel generally use this name to identify a printed circuit board with copper conductors 3 oz/square feet- 10 oz/square feet in inner and/or outer layers.

General Guideline for Min Spacing by Copper Weight

Cu Weight               Min Recommended Space   between Copper Feature

4 OZ                                     14 mil (0.355 mm)


Printed circuit boards (PCBs) are at the heart of electronics, providing the foundation for mounting and interconnecting components. For high power applications, 4 oz copper PCBs are increasingly preferred over standard 1-2 oz copper to provide lower electrical losses, handle higher currents, dissipate heat effectively, and improve reliability under thermal stresses.

However, not all PCB manufacturers can reliably produce quality 4 oz boards. In this article, we will examine what capabilities are required for a PCB fab house to deliver robust, high performance 4 oz copper multilayer boards suited to the demands of cutting-edge electronics designs.

What is a 4 oz Copper PCB?

PCB copper thickness is designated in terms of ounces per square foot (oz/ft2). This refers to the amount of copper foil weight present per square foot of board area, excluding the fiberglass substrate.

Some standard copper weights are:

  • 1 oz – 1 oz/ft2 (35 μm)
  • 2 oz – 2 oz/ft2 (70 μm)
  • 3 oz – 3 oz/ft2 (105 μm)
  • 4 oz – 4 oz/ft2 (140 μm)

So a 4 oz copper PCB has around 4 ounces copper foil weight per square foot on each conductive layer. In terms of thickness, 4 oz copper is approximately:

  • 140 μm (micrometers)
  • 5.5 mils
  • 0.14 mm (millimeters)

This heavy foil thickness provides the highest performance for the most demanding electronics applications.

Benefits of 4 oz Copper PCBs

heavy copper pcb circuit board

The key advantages of 4 oz copper PCBs over standard 1-2 oz material include:

  • Lower electrical resistance – Almost 4X less resistive than 1 oz copper due to thicker traces.
  • Higher current capacity – Ability to handle over 3X the current versus 1 oz copper without overheating.
  • Improved thermal management – The excellent conductivity of thick copper spreads heat over larger board area.
  • Greater power density – More power can be delivered through a given PCB footprint area.
  • Superior EMI shielding – 4 oz copper provides excellent shielding from electromagnetic interference.
  • Higher reliability – More resistant to thermal cycling, electromigration failures and physical damage over product lifetime.
  • Lower impedance planes – Power and ground planes have lower noise pickup and distribution issues.
  • High frequency performance – Thicker traces have less inductance and impedance mismatch.
  • Finer line/space capability – Very fine 1-2 mil traces and spacing can be achieved.

Capabilities Needed for High Quality 4 oz PCBs

Producing robust, high yield PCBs using ultra-thick 4 oz copper requires advanced capabilities from the manufacturer’s fabrication process:

1. Tight Registration and Layer-to-Layer Alignment

With over 5 mils thickness, 4 oz inner copper layers can potentially shift during lamination leading to misregistration. The PCB press cycles must tightly control temperatures, pressures and times to minimize any alignment issues.

2. Void-Free Filling of High Aspect Ratio Holes

The high via aspect ratio with 4 oz copper makes getting void-free plating difficult. Special plating chemistry and racking processes are needed to reliably copper fill vias across all layers without issues like voids or dimpling.

3. Excellent Etch Control and Capability

To hold the fine 1-2 mil lines and spaces possible with 4 oz material, the copper etch process must have excellent control across the entire panel. This requires high accuracy conveyorized equipment.

4. Strong Bonding Between Layers

Delamination or separation between layers is a reliability risk with thicker copper. The lamination process must create excellent adhesion between the prepregs and copper foils across the stackup.

5. Minimal Copper Surface Roughness

The matte side of copper foils can suffer from excessive surface roughness. This must be controlled to allow successful photolithography when using liquid resists.

6. High Aspect Ratio Drilling

Mechanically drilling through over 5 mils of copper requires rigid machinery and specialized drill bits to achieve straight vertical holes without breakage or excessive taper.

7. Fine Line Photolithography Capability

To fully leverage the high density interconnect capability of 4 oz copper, the photolithography process must be capable of defining very fine 1-2 mil line/space geometries.

8. Robust Final Finish Plating

Thick gold or other metallic finishes prevent oxidation and ensure reliable soldering. The plating thickness uniformity across a large panel must be tightly controlled through optimized racks and solution maintenance.

9. Stackup Design Experience

Proper incorporation of 4 oz copper in the layer stackup is critical, accounting for factors like registration, aspect ratios, impedances and plane placement. Extensive modeling experience is invaluable.

10. Application-Specific Design Guidance

Experienced 4 oz PCB manufacturers provide guidance to designers on layout techniques optimized for the capabilities of ultra-thick copper to avoid issues and maximize performance.

Key Indicators of 4 oz PCB Manufacturing Quality

Certain metrics and process capability markers indicate whether a PCB manufacturer has the technical competence to reliably produce high quality 4 oz copper boards:

  • Tight laminate thickness variation (<5%)
  • Excellent foil-to-foil registration (<0.10mm)
  • Void-free hole fill down to 0.15mm vias
  • Fine line resolution down to 1 mil line/space
  • High peel strengths between layers (>9 N/mm) with 0% delamination
  • Minimal surface roughness (<2 μm Ra)
  • Very low impedance power/ground planes (<5 mΩ)
  • Well-controlled gold plating thickness (+/- 5%)
  • Rigorous incoming material QC and lot traceability
  • Extensive inspection and reliability testing capabilities
  • Stringent process controls and change management
  • Zero-defect quality culture at all organizational levels

Benefits of Partnering with a High Quality Manufacturer

Selecting a PCB manufacturer capable of flawless volume production with 4 oz copper provides significant advantages to electronics companies:

Faster Time-to-Market – Get advanced 4 oz designs to field faster by avoiding new process engineering efforts.

De-Risked Introduction – Minimize initial issues and ramp smoothly to volume production by leveraging proven 4 oz expertise.

Enhanced Performance – Achieve electrical, thermal and reliability goals through precision 4 oz fabrication.

Robust Quality – Ensure consistently defect-free boards and minimize fallout related delays or shortages.

Stable Long Term Supply – Maintain continuity of supply and performance improvements through strategic supplier relationships.

Cost Savings – Leverage economies of scale and receive cost transparency for informed tradeoff decisions.

On-Demand Flexibility – Meet changing requirements rapidly through responsive small batch builds.

For companies looking to utilize advanced 4 oz copper technology in new products, partnering with manufacturers that have perfected quality 4 oz PCB fabrication can provide substantial benefits in capabilities, performance and business success.

Frequently Asked Questions

Q1. Can 4 oz copper withstand multiple reflows?

Yes, the high melting point and thickness of copper makes it resistant to typical soldering heat allowing multiple passes through reflow ovens.

Q2. Does 4 oz copper cause registration issues in multilayer PCBs?

In high quality PCB production, 4 oz inner layers can be laminated without any registration problems between layers.

Q3. Are there limitations on minimum hole sizes with 4 oz copper?

With laser drilling, hole sizes down below 0.15mm diameter can reliably achieve high quality copper plating.

Q4. Can 4 oz copper be used for flex PCBs?

Yes, 4 oz copper can be used on flex PCBs. But thinner foils are more common to maintain flexibility.

Q5. Does solder mask adhesion change on 4 oz copper?

Standard liquid photoimageable solder mask formulations adhere very well to 4 oz copper without any decrease in bond strength versus thinner foils.


As electronics products push towards greater capabilities and miniaturization, partnering with an expert PCB manufacturer capable of flawless quality 4 oz copper multilayer boards enables designers to fully leverage the benefits of low loss, high current, enhanced thermal performance and layout density that this leading-edge thick copper technology provides. Careful qualification using key process indicators outlined above helps identify manufacturers with proven expertise in 4 oz copper fabrication. By selecting a precision high quality partner, engineers can mitigate risks, enhance final product performance, and achieve successful adoption of advanced 4 oz PCB technology.




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