Take the Bluetooth speaker as an example to integrate the basic knowledge of PCB design into a practical case, and explain the function and practical experience and skills of PCB design software through the operation process. This course will learn the related knowledge of PCB wiring by explaining the overview and principles of wiring design.

Key points of this study:

1. Wiring overview and principles

2.PCB wiring basic requirements

3. Impedance control of PCB wiring

Learning difficulties in this period:

1. Wiring overview and principles

2. Impedance control of PCB wiring

1. Wiring overview and principles

In traditional PCB design, the wiring on the board only serves as the carrier of signal connectivity, and the PCB design engineer does not need to consider the wiring distribution parameters.

With the rapid development of the electronic industry, data swallowing from a few megabytes per unit time, tens of megabytes to the rate of 10Gbit/s has brought about the rapid development of high-speed theory, PCB wiring is no longer a simple interconnection carrier, but from the transmission line theory to analyze the impact of various distribution parameters

At the same time, the complexity and density of PCB is increasing at the same time, from the common hole design to micro hole design to multistage blind hole design, there are still buried resistance, buried container, a design of high density PCB wiring to bring huge difficulties at the same time, also need PCB design engineer more in-depth understanding of the process parameters of the PCB production and processing process.

With the development of high speed and high density PCB, PCB design engineers are becoming more and more important in hardware design, while the corresponding PCB design challenges are becoming more and more, and design engineers need to know more and more knowledge points.

Two, PCB wiring type

The wiring types on PCB board mainly include signal cable, power supply and ground wire. Among them signal line is the most common wiring, the type is more. Still have mono line according to wiring form, difference line.

According to the physical structure of wiring, it can also be divided into ribbon line and microstrip line.

Iii. Basic knowledge of PCB wiring

General PCB wiring has the following basic requirements:

(1) QFP, SOP and other packaged rectangular pads should be led out from the PIN center (generally using pave shape).

(2) Cloth (1) QFP, SOP and other packages of rectangular pads out of the wire, from the PIN center (generally using shape. The distance from the line to the edge of the plate shall not be less than 20MIL.

Note: in the figure above, the red is the OUTLINE of the outer frame of the board, and the green is the routkeepin of the entire board wiring area (the Routkeepin is more than 20mil indented relative to the OUTLINE).

Note: This board edge also includes window opening, milling groove, ladder, milling thin area by milling cutter processing graphics edge.

(3) Under metal shell devices, other network holes are not allowed, and surface wiring (common metal shells include crystal oscillator, battery, etc.)

(4) Wiring shall not have DRC errors, including the same name network DRC errors, except for compatible design, except DRC errors caused by packaging itself.)

(5) There is no unconnected network after PCB design, and the PCB network should be consistent with the circuit diagram.

He is not allowed to attend the Dangline.

(7) If it is clear that non-functional pads do not need to be retained, they must be removed from the light drawing file.

(8) It is recommended not to first half of the distance from the big fish 2MM

(9) It is recommended to use inner wiring for signal cables

(10) It is recommended that the corresponding power plane or ground plane of the high-speed signal area be kept intact as far as possible

(11) It is recommended that the wiring be evenly distributed. Copper should be laid in large areas without wiring, but the impedance control should not be affected

(12) It is recommended that all wiring should be chamfered, and the chamfering Angle is 45°

(13) It is suggested to prevent signal lines from forming self-loops with side length over 200ML in adjacent layers

(14) It is recommended that the wiring direction of adjacent layers be orthogonal structure

Note: The wiring of adjacent layers should be avoided in the same direction to reduce cross-talk between layers. If it is unavoidable, especially when the signal rate is high, the floor plane should be considered to isolate each wiring layer, and the land signal should isolate each signal line.

4. Impedance control of PCB wiring

Description: Line width in PCB processing is divided into two parts, the width of the upper surface and the width of the lower surface.

Schematic diagram of impedance calculation of single-ended signal microstrip line:

Schematic diagram of impedance calculation of differential signal microstrip line:

Schematic diagram of impedance calculation of strip line of single-ended signal:

Schematic diagram of band line impedance calculation of differential signal:

Schematic diagram of impedance calculation of single-ended signal microstrip line (with coplanar ground wire) :

Schematic diagram of impedance calculation of differential signal microstrip line (with coplanar ground wire) :

This is the wiring overview and principles of ALLEgro for PCB design software.