Current Carrying Capabilities

Current carrying capability is a critical design consideration for rigidflex printed circuit boards, directly affecting safety, reliability, and performance. Because rigidflex PCBs combine rigid and flexible materials, designers must account for electrical, thermal, and environmental factors when establishing current ratings. Understanding how trace geometry, materials, and operating conditions interact helps ensure the circuit can safely handle required current levels.

At a Glance: Current Carrying Capabilities

• Current carrying capability is a critical design consideration for rigidflex printed circuit boards.
• Rigidflex constructions require careful evaluation of electrical, thermal, and environmental factors when establishing current ratings.
• Understanding trace geometry, materials, and operating conditions helps ensure safe and reliable current handling.

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Overview of Current Carrying Capabilities in RigidFlex PCBs

Rigidflex printed circuit boards are widely used for their ability to combine flexibility with structural stability. Their hybrid construction enables complex geometries while continuing to support electronic components reliably. As these designs become more compact and electrically demanding, understanding current carrying capabilities becomes increasingly important.

During design, considering current carrying capacity and current rating helps ensure the PCB can safely handle required electrical loads. Proper evaluation of these factors reduces the risk of excessive heating, performance degradation, and longterm reliability issues in rigidflex circuits.

Factors Influencing Current Carrying Capacity

Several design and environmental factors directly affect how much current a rigidflex PCB trace can carry. Each factor contributes to resistance, heat generation, or heat dissipation, which together determines overall current capacity.

Trace Width and Thickness

Wider and thicker conductive traces reduce electrical resistance. Lower resistance allows higher current flow while limiting temperature rise. Increasing trace crosssection is one of the most direct ways to improve current handling capability in rigidflex designs.

Copper Weight

Thicker copper layers, often referred to as heavier copper weight, offer reduced resistance compared to thinner layers. This allows them to carry higher currents more effectively while minimizing excess heat generation.

Temperature Rise

Electrical current generates heat within PCB traces. The ability of the rigidflex PCB to dissipate this heat plays a key role in current capacity. Excessive temperature rise can reduce reliability and negatively affect performance over time.

Copper Foil Type

Higher quality copper foils with better electrical conductivity improve current handling performance. The characteristics of the copper foil directly influence resistance and heating behavior during operation.

Circuit Board Material

Materials such as polyimide or FR4 affect thermal performance. Materials with higher thermal conductivity dissipate heat more efficiently, increasing current carrying capacity. Longer trace lengths increase resistance and heat generation, which reduces capacity, making shorter traces preferable where possible.

Operating Environment

Ambient temperature and airflow significantly influence heat dissipation. Higher surrounding temperatures reduce the PCBs ability to shed heat, lowering its current carrying capability.

Number of Parallel Traces

Using multiple traces in parallel increases total current capacity. This approach distributes current across conductors and helps prevent individual traces from overheating.

Manufacturing Process

Manufacturing precision affects trace width, thickness, and copper uniformity. Consistent fabrication improves current carrying performance by ensuring design parameters are accurately maintained.

Determining Current Carrying Capacity

Engineers commonly use a current rating nomograph to estimate the current carrying capability of rigidflex PCB traces. This graphical tool evaluates capacity based on trace width, copper thickness, temperature rise, and ambient temperature.

The nomograph provides an estimated current rating and is intended as a starting point. Designers should also consider parallel traces, the operating environment, and required reliability levels. Manufacturer datasheets and applicable industry references are used to further refine final design decisions.

Example Design Parameters Used in Estimation

Parameter	Value	Units
Trace width (example)	0.25	mm
Copper thickness (example)	35	µm

These values are used within the nomograph to estimate current capacity under selected temperature rise and ambient conditions.

Consider These Factors When Using Nomographs

• Use the nomograph as an estimation tool rather than a final limit
• Account for operating environment conditions
• Consider using parallel traces for higher currents
• Factor in reliability expectations and longterm performance requirements

For example, to find the current rating for a PCB with a 0.25mm trace width and 35µm copper thickness:

• Locate the 0.25mm value on the trace width axis.
• Find the 35µm value on the copper thickness axis.
• Draw a straight line connecting these points.
• Identify the desired temperature rise value on its axis.
• Trace a line from the temperature rise axis through the intersection point of the previous lines.
• The intersection with the current axis gives the current rating estimate.

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Frequently Asked Questions

Quick Links

• What determines current carrying capability in a rigidflex PCB?
• Why does trace width affect current carrying capacity?
• How does temperature rise impact current rating?
• What is a current rating nomograph used for?
• Are nomograph results exact limits?
• How can parallel traces increase current capacity?

What determines current carrying capability in a rigidflex PCB?

Current capacity depends on trace width and thickness, copper weight and quality, temperature rise, materials, operating environment, and manufacturing precision.

Why does trace width affect current carrying capacity?

Wider traces have lower resistance, allowing higher current flow without excessive heating.

How does temperature rise impact current rating?

Higher temperatures reduce reliability and performance, limiting how much current a trace can safely carry.

What is a current rating nomograph used for?

A nomograph provides a graphical estimate of current carrying capacity based on trace and environmental parameters.

Are nomograph results exact limits?

No. Nomograph values are estimates and should be used as a starting point alongside other design considerations.

How can parallel traces increase current capacity?

Parallel traces divide the current load, increasing total capacity and reducing the risk of overheating individual traces.

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Looking for More Information on Current Carrying Capabilities?

As electronic devices continue to shrink while increasing in functionality, accurately estimating current carrying capabilities remains a key design challenge. Applying nomographs and carefully evaluating design parameters helps ensure rigidflex PCBs perform safely and reliably across applications.

Expert guidance can support trace design decisions that balance electrical performance with manufacturability and longterm durability. Contact us now for help with your next flexible circuit project with reliable and safe designs.

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