Understanding PCB Resistance: Key Factors, Testing Methods, and Design Best Practices

How easily current flows through a circuit board is determined by its resistance. Although some resistance is provided by each trace and component on the board, the objective is to reduce it. When the material that electrons pass through blocks or slows down their flow, resistance results. Energy is lost as a result of this obstruction, frequently as heat. Trace resistance is a crucial factor in determining the circuit's operational current in power-related circuits, such as amplifier units. To guarantee smooth current flow, printed circuit boards (PCBs) should have traces and channels with low resistance.

Resistors, on the other hand, are purposefully included in circuits to regulate the current flow. All of the parts need to be energized and connected for proper functioning of the circuit. Any damage to these connections could cause issues by obstructing the current flow. Trace width, thickness, length, material type, and ambient temperature are some of the variables that affect it.

Difference Between PCB Resistance and Impedance:

PCB Resistance:

PCB resistance is the term used to describe the components' and traces' impedance to the direct current (DC) flow. Trace width, thickness, length, substance, and temperature all have an impact. Frequency may not directly affect the resistance, but if there is change in voltage or current then the value of resistance can also be affected.

PCB Impedance:

Impedance can be determined as the resistance to the flow of alternating current (AC). Why AC? Because in the calculation of impedance we have a combination of resistance, inductance, and capacitance. Trace width, dielectric material, , and signal behavior all play a role in deciding this impedance. There is a noticeable variation in the signal's impedance as the frequency changes. It is essential for preserving signal integrity in RF and high-speed designs.

In general, impedance concentrates on dynamic signals and frequency-specific behavior, whereas resistance handles static current and power control. Although they pertain to separate facets of circuit design, both are necessary for PCB performance.

Factors Affecting PCB Resistance:

1. Trace Material: Because copper has such good conductivity, it is used for traces on the majority of PCBs. The physical characteristics and purity of copper traces determine their resistance.

2. Trace Dimensions: Resistance is reduced by thicker and wider traces. Because there is a longer path for current to travel, longer traces result in higher resistance.

3. Temperature: As the temperature rises, resistance rises and copper's overall conductivity reduces in case of metal core and carbon core resistors.

4. Substrate Material: By influencing signal integrity and thermal performance, the dielectric material (such as FR-4 or PTFE) indirectly affects resistance.

What is Open Circuit and Short Circuit Resistance?

When there is no current flowing between two sites because of a severed channel or excessive resistance, this is known as an open circuit. A voltmeter can be used to measure the potential difference, or "open circuit voltage," in this case. Very high resistance results in the circuit's disruption, which stops current flow.

Conversely, a short circuit occurs when current goes directly through a low-resistance route, bypassing the load and producing a high current. When conductive materials or wires inadvertently join the circuit, this can happen.

How to Check Resistors on a Circuit Board?

Resistance value calculation and testing guarantees that the PCB satisfies design requirements. Important techniques consist of: Four-point probes are used for high-precision resistance measurements, while ohmmeters are used for direct trace resistance measurement.

Step 1: Power Off the Circuit: To prevent damage or inaccurate readings, make sure the circuit board is unplugged from any power sources.

Step 2: Locate the Resistor: Find the Resistor Use the circuit diagram or color code to identify the resistor on which is placed on the PCB board.

Step 3: Set the Multimeter: Switch the multimeter to the resistance (Ω) mode.

Step 4: Measure Resistance:

• Place the probes on both ends of the resistor.
• Read the value on the multimeter display.
• Compare the measured resistance with the resistor's specified value.

Step 5: In-Circuit Testing: The reading may be impacted by other components if the resistor is soldered into the board. Before testing, desolder one resistor leg for accuracy.

Step 6: Check for Damage: A defective resistor may be indicated by a reading that is infinite or wrong.

How Are Circuit Boards Grounded?

The ground plane, which is frequently a thick sheet of copper, is connected to a grounding point (common to all the connected circuits). But some of the circuit board's grounding modes are based on the applications. They primarily consist of floating ground, virtual ground and multi-point grounding.

Single-Point Grounding

This technique minimizes impedance coupling and ground loop interference by connecting all ground points to a single reference point, making it appropriate for low-frequency circuits (<1 MHz).

Multi-Point Grounding

Each ground point connects to the closest ground plane, minimizing parasitic effects. which also reduce the impedance interference, making them perfect for high-frequency circuits (>10 MHz). Specially in video signal amplifiers circuits.

Floating Ground

By doing this, electromagnetic interference is avoided by isolating the circuit ground. It is susceptible to parasitic capacitance, which can change ground potential and increase noise in analog circuits.

What is the Rule for Resistance in a Circuit?

Ohm's Law, which states that voltage (V) is equal to current (I) times resistance (R), governs the fundamental law of resistance. This demonstrates that the amount of current flowing at a given voltage is directly influenced by the resistance.

The value of resistance is based on the voltage drop and current flowing through it. Higher resistance, for instance, reduces the passage of current, whereas lower resistance permits greater current to flow.

Conclusion

For reliable and effective electrical designs, it is important to understand and control the resistance of PCBs. Engineers can reduce resistance and enhance overall device performance by optimizing materials, dimensions, and design layouts. Resistance regulation is important because:

• Signal Integrity
• Power Delivery
• Thermal Management

Expert solutions for a range of applications are offered by manufacturers such as JLCPCB for high-quality, low-resistance PCBs. To make sure your designs satisfy industry requirements, always give careful testing top priority!