What is the impedance control in PCB design and why is that important? PCB & MCPCB – Best Technology

In high -speed electronic systems, signal integrity is very important. One of the main factors that ensures clear and distortion -free signal transmission is impedance control. In this blog, we will explore what impedance control is, why important in PCB design, how to calculate, and what factors affect it. Whether you are a PCB designer or source board from producers, understanding impedance control is very important to ensure performance and reliability.

What is the impedance in the PCB?

Impedance refers to the resistance offered by the circuit for alternating current (AC), especially in the presence of inductors and capacitors. Simply put, that’s how many signals “battle back” when moving through traces on the PCB. The impedance unit is Ohm (î ©).

In the PCB, impedance is not only about resistance, including the effects of capacitance and inductance created by PCB structures and materials. That is why it needs to be strictly controlled, especially in high -speed signal circuits.

Why is the impedance match needed?

Matching impedance is very important to ensure efficient signal transmission in various parts of the electrical system. When the signal source impedance, the transmission pathway (such as PCB footprints), and the load does not match correctly, it causes signal reflection, power loss, and distortion, especially in high -speed design or RF.

The main reasons why impedance match is needed:

• Prevent signal reflection: Any incompatibility causes the part of the signal to rise back to the source, interfere with the original signal and create noise.
• Maintaining signal integrity: In order for data to achieve its goals accurately and consistently, impedance must be uniform along the transmission path.
• Reducing EMI (Electromagnetic Disorders): Inappropriate impedance can result in emitted emissions, which can interfere with the nearest circuit.
• Increasing power transfer: In the RF application, the maximum power is transferred only when the source and load impedance is the same.
• Activating high -speed communication: interfaces such as HDMI, USB, Ethernet, and LVD require strict impedance control for the right function.

In short, impedance matching is very important to achieve predictable and reliable performance in complex circuits and digital systems or high -speed RFs.

What is impedance control?

Control impedance is the process of designing a PCB trail so that their impedance remains in the specified tolerance, usually ± 10%. This ensures that the signal transmission remains clean, reduces signal reflection, and avoiding data loss or distortion ”is very important for USB, HDMI, high -speed memory, and RF circuit.

Why is an important impedance control?

Controlled impedance is important in high frequency applications such as:

• Communication equipment
• Medical devices
• Aerospace and Defense Electronics
• Consumer Electronics
• Automotive system

Signals that travel through unsuitable impedance can reflect back to the source, which leads to noise, jitter, and signal loss.

Types of Common PCB Impedance

Impedance is a one -size metric for all. There are various types, depending on the signal configuration:

1. Single impedance (single trail)

This refers to a single signal line impedance in connection with the reference plane (usually GND). This type is common in digital signals or basic analogs.

Example: 50î © Impedance, 5 million line width on L1 Reference L2.

2. Differential impedance

Used in a differential pair routing in which two lines carry the same and opposite signals (such as in USB, HDMI). Impedance is measured between two lines.

Example: 90î © Impedance, Line/Distance Width = 5/6 Million, referring to L2.

3. Coplanar impedance

Here, the signal line is flanked by the land or electricity plane to the same layer, adding a tighter protective and impedance control.

• Single coplanar impedance: signal lines with soil on both sides.
• Differential Coplanar Impedance: Differential pair is surrounded by soil in the same layer.

Example: 90î © Impedance, Line/distance width = 7.5/8/8 miles.

How is the impedance calculated?

Impedance is calculated using a simulation device that is a factor in geometry and material properties. The most commonly used tools include:

• Si8000 Pole
• Si9000 Polar

These tools allow engineers to model various piles and design constraints to meet the impedance targets.

• General input parameters include:
• Trace Width
• Distance traces (for differentials)
• Distance to the reference plane (dielectric thickness)
• Dielectric Constant (DK)
• Copper thickness

Factors that influence impedance in PCB design

Controlling impedance means adjusting several design parameters. This is the way they influence impedance:

In practice, designers will change the width of the line, distance, and thickness of dielectric to achieve the target value, because the thickness of the DK and copper is often limited by the availability or material costs.

Impedance control verification

Verification of impedance control is the measurement process and confirms that the actual impedance on the PCB produced according to the design specifications. This verification ensures that the council will carry out reliably in the intended high -speed application. Here are some of the verification impedance control methods:

1. Test Coupon:

• Special trail structure is added to the edge of the production panel.
• This is produced using a pile and the same process as the main board.

2. TDR (Time Domain Reflection):

• Signal pulses are sent via the test coupon trail.
• Equipment measures how the signal reflects along the trail to determine the actual impedance.
• This method is not destructive and is very appropriate.

3. Report & Tolerance of Inspection:

• The value measured compared to the target impedance (for example, 50î ​​©, 90î ©).
• Typical tolerance is ± 10%, depending on customer needs.
• Formal impedance test reports are provided.

4. Adjustment of the process (if necessary):

If the value falls beyond tolerance, producers can change the width of the line or thickness of the dielectric and re -test before the final production.

Verifying impedance is not just a formality ‘it guarantees that the council will function correctly in its application. Passing this step can result in field failure, EMI problems, or complete communication damage.

Why choose the best technology for PCB controlled by impedance?

In the best technology, we specialize in high -speed PCB and high reliability with appropriate impedance control. We use the industrial standard impedance calculation software and make a test coupon to verify each of the designs controlled by impedance. Do you need a simple PCB 2-Lather or a complex PCB HDI pile with a tight tolerance, we provide:

• Competitive price
• Tight quality control
• Technical Support for Stackup & Impedance Design
• Fast waiting time

FAQ About Impedance Control

1. What is typical tolerance for controlled impedance?

Most designs require a tolerance of ± 10% of the target impedance value.

2. Do all PCBs need impedance control?

No, only a high -speed board or RF that requires a trace that is controlled by impedance.

3. How do producers verify impedance control?

They use test coupons and tools such as TDR (Time Domain Reflection).

4. Can I use FR4 for the design controlled impedance?

Yes, but the dielectric constant must be taken into account in the calculation.

5. What happens if the impedance is not controlled?

This can cause signal reflection, data loss, and poor system performance.