This article discusses the concept of characteristic impedance in PCBs and how to address impedance-related issues.
With the advancement of consumer products towards greater intelligence, the demands for PCB impedance have become increasingly stringent. This trend has also driven the continual refinement of impedance design technologies. In this article, we summarize methods for impedance application and control for collective discussion and knowledge sharing.
What is characteristic impedance?
1. The resistance encountered by alternating current in components is influenced by capacitance and inductance. When an electronic signal waveform propagates through a conductor, the resistance experienced is referred to as impedance.
2. Resistance refers to the opposition encountered by direct current in components, which depends on voltage, resistivity, and current.
Application of characteristic impedance
Here’s a refined version of your article, keeping the original meaning, clarity, and technical accuracy intact:
1. In high-speed signal transmission and high-frequency circuits, the electrical performance of the printed circuit board (PCB) must effectively prevent signal reflection, maintain signal integrity, minimize transmission loss, and facilitate impedance matching. This ensures complete, reliable, accurate, and noise-free signal transmission.
2. Impedance size cannot be oversimplified as merely “larger is better” or “smaller is better”; the critical factor is matching.
**Control Parameters for Characteristic Impedance:**
The dielectric constant of the substrate, the thickness of the dielectric layer, line width, copper thickness, and solder mask thickness.
**Influence and Control of Solder Mask:**
1. The thickness of the PCB solder mask has minimal impact on impedance. An increase of 10µm in solder mask thickness typically results in an impedance change of only 1-2 ohms.
2. There is a significant difference in performance between boards with and without solder mask coverage, showing variations of 2-3 ohms for single-ended and 8-10 ohms for differential signals.
3. In manufacturing impedance-controlled boards, solder mask thickness is usually regulated based on production requirements. The fundamental method for testing impedance is the Time Domain Reflectometry (TDR) technique. This involves emitting a pulse signal that reflects back from the test PCB, allowing measurement of changes in characteristic impedance, which are then analyzed by a computer to determine the output characteristic impedance.
**Addressing Impedance Issues:**
1. To control impedance parameters, adjustments can be made during production to meet specifications.
2. After lamination, boards are sliced and analyzed. If the dielectric thickness is reduced, the line width can be decreased to satisfy requirements; conversely, if the thickness is excessive, increasing copper thickness can help lower the impedance.
3. In testing, significant discrepancies between theoretical and actual values often indicate issues with engineering design or test strip design.
This overview addresses what characteristic impedance is in PCBs and outlines methods to resolve impedance-related issues.
With the advancement of consumer products towards greater intelligence, the demands for PCB impedance have become increasingly stringent. This trend has also driven the continual refinement of impedance design technologies. In this article, we summarize methods for impedance application and control for collective discussion and knowledge sharing.
What is characteristic impedance?
1. The resistance encountered by alternating current in components is influenced by capacitance and inductance. When an electronic signal waveform propagates through a conductor, the resistance experienced is referred to as impedance.
2. Resistance refers to the opposition encountered by direct current in components, which depends on voltage, resistivity, and current.
Application of characteristic impedance
Here’s a refined version of your article, keeping the original meaning, clarity, and technical accuracy intact:
1. In high-speed signal transmission and high-frequency circuits, the electrical performance of the printed circuit board (PCB) must effectively prevent signal reflection, maintain signal integrity, minimize transmission loss, and facilitate impedance matching. This ensures complete, reliable, accurate, and noise-free signal transmission.
2. Impedance size cannot be oversimplified as merely “larger is better” or “smaller is better”; the critical factor is matching.
**Control Parameters for Characteristic Impedance:**
The dielectric constant of the substrate, the thickness of the dielectric layer, line width, copper thickness, and solder mask thickness.
**Influence and Control of Solder Mask:**
1. The thickness of the PCB solder mask has minimal impact on impedance. An increase of 10µm in solder mask thickness typically results in an impedance change of only 1-2 ohms.
2. There is a significant difference in performance between boards with and without solder mask coverage, showing variations of 2-3 ohms for single-ended and 8-10 ohms for differential signals.
3. In manufacturing impedance-controlled boards, solder mask thickness is usually regulated based on production requirements. The fundamental method for testing impedance is the Time Domain Reflectometry (TDR) technique. This involves emitting a pulse signal that reflects back from the test PCB, allowing measurement of changes in characteristic impedance, which are then analyzed by a computer to determine the output characteristic impedance.
**Addressing Impedance Issues:**
1. To control impedance parameters, adjustments can be made during production to meet specifications.
2. After lamination, boards are sliced and analyzed. If the dielectric thickness is reduced, the line width can be decreased to satisfy requirements; conversely, if the thickness is excessive, increasing copper thickness can help lower the impedance.
3. In testing, significant discrepancies between theoretical and actual values often indicate issues with engineering design or test strip design.
This overview addresses what characteristic impedance is in PCBs and outlines methods to resolve impedance-related issues.
