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Copper PCB Boards

Table of Contents

Introduction to Copper PCB Boards

Copper has become the standard base material for printed circuit boards due to its high conductivity and elasticity. The copper layer forms the conductive pathways, or traces, that connect electronic components. Printed circuit boards (PCBs) form the backbone of electronics. Without PCBs, electronic components and circuits would have no structural base on which to shape and connect. When designed and manufactured correctly, PCBs provide a solid foundation for any electronic device or system. Let’s explore the role of copper in PCB boards and how it enables functional, long-lasting, and efficient circuits.

Before diving into the specifics of copper PCBs, let’s briefly overview the PCB fabrication process:
● PCB design – all trace routing and board dimensions are virtually designed.
● Copper lamination – a layer of copper foil is laminated onto the raw PCB substrate, usually FR-4 fiberglass.
● Photolithography – the copper layer is coated with a photosensitive chemical and exposed to UV light through a mask. This transfers the trace pattern onto the copper.
● Etching – unwanted copper is removed, leaving only the desired traces protected by the photochemical.
● Component assembly and soldering – electronic components are placed and fused onto the PCB pads and traces.
Copper plays a fundamental role in Printed circuit board design and manufacturing process. It forms the conductive network that electronically connects all components.

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Figure1: Copper PCB

Copper PCB Design Considerations

When planning new PCB designs, engineers must make informed choices about copper weight, trace geometries, and layout to achieve design goals and board performance targets.
Copper Thickness:
Copper thickness greatly influences conductivity and thermal performance. Thicker copper provides lower electrical resistance and better heat dissipation. Key factors to consider.
● Current levels – the higher current ratings of PCB components may require thicker copper to avoid overheating.
● Routing density – tight pad/trace spacing limits how much copper can be added.
● Layer count – thermal loads can be distributed across layers.
● Frequency – thicker copper maintains signal integrity at high frequencies.

Trace Spacing and Width:
Narrower PCB traces result in a higher resistance, impacting voltage drop across the board. Wider traces reduce resistance.
However, wide traces consume more space, limiting routing density. Careful width selection balances conduction needs with board space limitations.
Spacing between traces is another key factor – tighter spacing increases board area utilization but can increase parasitic capacitance and exchange, impacting high-speed signals.
Current Density:
The amount of current flowing through a given cross-sectional area of copper has a significant impact on printed circuit board performance.
● The current density within the copper traces affects conduction efficiency and heat generation. Higher current density leads to more resistive losses and heating.
● When routing high-current PCB traces, the width and thickness can be increased to reduce current density and avoid excessive heating.
● For signal traces, a lower current density is desirable to minimize capacitive coupling.
● Complex board designs require calculating and analyzing current densities across different trace sizes to optimize the setup
Trace Routing:
How PCB traces are scattered can impact both performance and manufacturing ability.
● Right-angle trace turns should be avoided where possible. Gradual curved turns help maintain signal integrity.
● Grouping associated signals together minimizes noise pickup and cross-talk.
● Current loops should be minimized to reduce electromagnetic emissions.
● Thermal gradients guide routing away from hot components to prevent localized copper heating.
● Clearance rules for high voltage traces prevent arcing or insulation breakdown.
● Test points incorporated along trace routes enable signal inspection during debugging.
Pad and Via Design:
The size, shape, and design of component contact pads and vias affect the soldering process and reliability:
● Printed circuit board Pad size should match component lead dimensions, with adequate space for solder.
● Thermal relief breaks in pads reduce heat conduction away from a solder joint.
● Through pad diameters and hole sizes should allow for misalignment tolerances.
● Pad and via geometries affect solder paste deposit volumes and wetting.
● Non-circular pad shapes provide orientation and polarization.

Panel Utilization:
To maximize manufacturing efficiency and board supplies:

● PCB structures should make use of as much panel area as possible when fabricated in panels.
● Critical traces should be routed away from panel edges.
● Allow adequate tooling and break-off tab space around panel edges.
● Panelize boards to balance stress and avoid “potato-chipping.”
● Precut V-scores make separating boards easier and prevent copper tearing.

PCB After Removing Unwanted Copper from Copper Clad Laminate
Figure 2: Laminate Copper PCB

Copper PCB Manufacturing Process

Copper Printed Circuit Board manufacturing and assembling Process requires careful design techniques and procedures. Let’s look at some key steps in detail:
Copper Foil Selection:
Not all copper is created equal when it comes to PCB fabrication. Several types of copper foil are used in PCB production:
Rolled copper – thin copper sheets that are rolled to a final thickness. Low-cost but contains more impurities.
Electrolytic copper – very pure copper formed through electroplating. Higher cost but optimal purity and conductivity.
ED copper – a hybrid created by electrodepositing copper onto rolled foil. It combines cost-effectiveness with improved purity. The choice depends on printed circuit board performance requirements vs cost considerations. High-frequency or high-speed boards may utilize electrolytic copper for maximum conductivity.
Surface Treatment:
Micro-roughening copper foil before lamination enhances PCB integrity and copper adhesion to the substrate. Common surface treatments include:
Hot oil oxidation – oxidizing the foil surface with hot oil baths.
Plasma/corona etching – ionizes air to react with the copper surface.
Mechanical abrasion – physically roughens the foil through abrasives or scratches.
The roughened copper surface provides “anchors” for the laminate resin to grip, creating a stronger bond and preventing delamination issues.
Lamination
Lamination fuses the copper foil to the substrate resin through high heat and pressure. This bonds the foil tightly across the PCB blank. Lamination cycle parameters like temperature, pressure, and time must be involved to sufficiently bond the copper without over-stressing the substrate material.
Imaging and Etching:
Photolithographic patterning transfers the PCB design from a photomask to the copper layer. Photoresist chemicals and UV light impressions create a copy of the trace setup. Etching then removes all unprotected copper regions, isolating the traces and pads. Tight process controls prevent over- and under-etching and achieve trace precision down to ±0.1 mm.
Surface Finishes:
Post-etching, copper traces may receive a metal plating or organic coating to protect against oxidation and enhance solderability.
Common PCB surface finishes include:
● Organic solderability preservatives (OSPs) – provide temporary oxidation prevention during assembly.
● Immersion tin – tin-plated coating to prevent copper oxidation and improve solderability.
● Immersion silver – silver plating for maximum conductivity and solderability.
● Electroless nickel immersion gold (ENIG) – nickel barrier layer with gold outer coating for corrosion protection and conductivity.
Quality Assurance and Testing:
To analyze performance of electronic devices, manufactured printed circuit boards undergo extensive inspection and testing:
● Automated optical inspection (AOI) checks for physical defects, wrong components, alignment issues, etc.
● Netlist testing compares actual board connectivity against circuit graphic
● Flying probe testing checks shorts, opens, and impedance of traces/pads.
● Functional testing verifies boards operate properly within their electronic systems.
This comprehensive testing ensures copper PCB production quality and long-term reliability in the field.

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Figure 3: Copper PCB Manufacturing Layout

Applications of Copper PCBs

The unique benefits of copper make it an essential material across almost all types of electronic devices. Following are some common application of copper printed circuit boards.
Consumer Electronics:
From smartphones to tablets, TVs, gaming systems, and more, copper PCBs enable complex yet compact consumer electronic product designs. High trace densities, multi-layer boards, and fine geometries are achievable with copper PCBs.
Automotive Electronics:
Copper’s vibration resistance provides reliable interconnections over the lifetime of a vehicle. Safety systems, engine control modules, and sensors all utilize copper printed circuit boards.
Aerospace and Avionics:
Shaking vibration resistance and lightweight make copper PCBs well-suited for aerospace systems. Copper also withstands the extreme temperature swings experienced in space applications.
Industrial Electronics:
For process control systems, automation, robotics, and instrumentation, copper PCBs deliver proven healthiness and survival in harsh industrial settings
Medical Equipment:
Biocompatibility and sterilization resistance enable copper PCB usage in medical devices like imaging systems, heart monitors, and surgical equipment.

Future Development of Copper PCBs

Looking ahead, copper PCB technology and fabrication will continue advancing:
● Manufacturing equipment improvements allow smaller trace widths and spaces down to 25 μm or less. This expands routing densities.
● PCB laminates with higher glass transition temperatures, enabling lead-free solders.
● Direct imaging techniques replace photomasks with laser or inkjet copper patterning for faster prototyping.
● Multi-branched circuits built on flexible copper substrates enable roll-to-roll fabrication of IoT devices.
● Installed component technology incorporates capacitors/resistors within copper inner layers to save space.
● Thermally conductive dielectric and filling materials manage heat release as boards get more densely packed.

Conclusion

In summary, the unique material properties of copper make it the backbone of the electronics industry for manufacturing printed circuit boards. The incomparable electrical and thermal conductivity of copper enables efficient and reliable circuits for all classes of electronic products and applications. Ongoing PCB innovations will unlock even greater densities and performance capabilities to meet emerging needs. But the fundamental role of copper is certain to remain, carrying signals and power into the expected future.

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