Question

How to consider impedance control and Stackup design during PCB design process Qui

Answer 1

During the PCB design process, it is very important to consider impedance control and stackup design, especially in terms of high-speed circuits and signal integrity. Here are some considerations:

Impedance Control: Impedance is a key parameter in the transmission characteristics of a circuit. In PCB design, impedance can be controlled through several aspects:

Material selection: Select the appropriate dielectric material and copper layer thickness to achieve the desired impedance value.

Trace Width and Spacing: Determine the appropriate trace width and trace spacing based on the desired impedance value.

Dielectric layer thickness: Adjusting the thickness of the Dielectric layer can have an impact on the impedance. Thinner Dielectric layers will produce lower impedance, while thicker layers will produce higher impedance.

Stackup design: Stackup design refers to arranging different signal layers, ground layers and power layers in the appropriate position and order in the PCB stacking hierarchy. Here are some suggestions:

Distinguish high-speed and low-speed signal layers: Separate high-speed signal layers from low-speed signal layers to reduce the possibility of mutual interference.

Ground plane layer: Use a ground plane layer to provide a good ground reference and reduce coupling between signal layers.

Power plane layers: Arrange appropriate power plane layers in Stackup to provide power supply stability and reduce power supply noise.

Signal layering: Grouping related signals on the same layer to reduce signal coupling and cross-interference.

In addition to the above suggestions, you should also consider following PCB design specifications and standards and using appropriate PCB design tools to simulate and verify the impedance control and Stackup solutions in the design. Additionally, working with PCB manufacturers and suppliers to understand their manufacturing capabilities and recommendations can help optimize impedance control and stackup design.

Answer 2

In the PCB design process, impedance control and Stackup design are important considerations.

Impedance control:

The characteristic impedance of the wires on the printed circuit board is an important indicator of circuit board design. Especially in the PCB design of high-frequency circuits, it must be considered whether the characteristic impedance of the wires is consistent and matched with the characteristic impedance required by the device or signal. Because various signals are transmitted through the conductors in the circuit board, the frequency must be increased in order to increase the transmission rate. The line itself will cause changes in impedance due to different factors such as etching, lamination thickness, wire width, etc., causing Signal distortion. Therefore, the impedance value of conductors on high-speed circuit boards should be controlled within a certain range, which is called "impedance control".

In actual situations, impedance control is generally required when the digital signal edge is lower than 1ns or the analog frequency exceeds 300MHz. The impedance of a PCB trace will be determined by its inductive and capacitive inductance, resistance, and conductance coefficients. The main factors that affect the impedance of PCB traces are: the width of the copper wire, the thickness of the copper wire, the dielectric constant of the medium, the thickness of the medium, the thickness of the pad, the path of the ground wire, the wiring around the wire, etc.

Stackup design:

Stackup means PCB board stacking, which is an important factor affecting signal transmission speed and signal integrity. The principles of stacked design include prioritizing the TOP layer for key signals, because below the TOP layer is the GND layer. For RF and high-speed signals, the wiring needs to be 50ohm, so the lamination thickness needs to be considered for impedance control. GND and PWR layers generally use core boards to make them thinner to ensure the decoupling effect of planar capacitors. The purpose of option 2 is to provide better shielding, so the GND layer and PWR layer are placed on the outermost layer. But the ideal is full and the reality is skinny. In order to obtain a good shielding effect under this lamination condition, there are strict requirements for the design using it. It is suitable for the situation where the main components are laid out on the BOTTOM, and the key signals are routed on the BOTTOM layer. If necessary, it is recommended that you consult a PCB design professional.

Answer 3

When designing BGA via window, there are several considerations to consider:

Pin location and layout: Ensure the accurate location and layout of pins in the package. Crossing and overlapping of pins should be avoided to ensure proper connection and layout specifications.

Via window location and size: Make sure the via window is accurately positioned to match the corresponding pins and has careful sizing design. Accuracy of size and location is critical for correct inter-layer connections.

via Window Management: Be careful with via apertures and layout created through packaged areas. Make sure they do not conflict with other signal lines or power planes and that the shape and size match the package specifications.

Interlayer connection and impedance control: Ensure that the interlayer connection through the via window has correct impedance control and meets the design requirements. Use proper interlayer spacing and ground plane guides to reduce signal crosstalk and power/supply noise issues.

Rule verification and simulation: Perform rigorous rule verification and simulation to ensure that the interlayer connections and via windows in the design do not cause signal integrity, timing or power interference issues. Use PCB design tools for layout and signal integrity analysis.

Manufacturing feasibility: Communicate with the PCB manufacturer and ensure the design is manufacturable. Pay attention to the manufacturer's minimum line width/space requirements, interlayer via requirements, and material requirements.

Thermal management: In BGA via window design, thermal management is also an important factor. Ensure that the heat from the BGA package is controlled and dissipated through appropriate thermal design and high thermal conductivity materials.

By following these considerations, you can ensure that your BGA via window design is properly laid out on the board and able to provide good signal connections and electrical performance. At the same time, it is recommended to work with a professional PCB design team to ensure proper guidance and support during the design process.