AD common knowledge points

• 	extension name
  Project Files	.Prjpcb
  Schematic Library File	.SchLib
  Schematic file	.SchDoc
  PCB library file	.PcbLib
  PCB file	.PcbDoc
  Netlist file	.NET

hot key:

T+A+U	Quickly modify all tag numbers
Q	Switch unit (metric (mm) unit and imperial (mil) unit) mil is 1/1000 of an inch, equal to 0.0254mm Most PCB design textbooks use imperial system and metric system, which can easily cause confusion. Why is there such a situation, can you just use one? This problem is indeed a problem that has plagued many engineers for many years. This involves the evolution of modern electronic technology. Modern electronic technology first emerged from imperial countries, so the early products were mostly in imperial units. Up to the early days of SMT technology, the unit is still in British system. For example, the commonly used SO-xxx series has a pin pitch of 50 mils, and a BGA ball pitch is also 50 mils. However, with the development of technology in other countries and regions and the increasing miniaturization of components, most of the new devices now use mm as the unit. In order to facilitate the alignment processing in the design, only the metric and imperial systems can be mixed. However, many high-density devices are basically designed in metric units, and high-precision placement machines are basically designed in metric systems. It is recommended that you use metric wiring for new learning. If you need to align with the British system, temporarily switch to the British system. After all, the current trend is that metric devices dominate, and other CAD software also use metric systems. In addition, there is no need to pursue complete accuracy when converting between metric and imperial systems. For example, when the rules are set, the error between 8mil and 0.2mm is less than 1.5%, and there is no need to pursue it in many cases.
G	Adjust grid
Shift+H	Used to display coordinates, grids, layers and other information in the PCB file (usually located in the upper left corner of the drawing)
D+R	rule
L	In the PCB file, the extra layers can be turned off
E + O + S	Set origin coordinates
P+L	Place the line (there is no network name on the line) (in the PCB file)
P+T	Wiring (network name on the line) (in the PCB file)
Ctrl+W	Place the line (in the schematic file)
J	Open the coordinate information of the line placement
P+A+N	Place an arc of any angle
D+S+D	Define according to the selected object (used to display the board frame when drawing the board frame in the PCB file)
P+P	Place the pad
P + V	Place via
I+L	Select all components and arrange them in a rectangular area
P+D+D	measure size
3	Switch to 3D view
A	Align view
Ctrl+Shift+wheel	Switch layer
T+D	Design rule check
E+W	Cutting and routing

• Designator：位号，一般用于标记元器件的种类与序号，例如U1代表芯片1，R2代表电阻2，C5代表电容5，问号代表还没有修改序号。其中元器件种类与字母有约定俗成的对应关系，以后会详细介绍。序号可以手动修改，也可以设置自动编号。
• Comment：翻译过来是“注释”，其实含义更像是参数，用于描述器件的基本特征，比如电阻的阻值、精度、电容的容值与耐压。
• Description：描述信息，通常用语用于方便采购，可以不填写。
• FootPrint：封装。

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• 设计规则检查（Design Rule Check，简称DRC）

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  后缀	英文	含义	密度	使用领域
  M	most	最大值	低密度	最大焊盘伸出，适用于手工焊接
  N	normal	标称值	中密度	中等焊盘伸出，比较适合机器贴
  L	least	最小值	高密度	最小焊盘伸出，只能机器SMT