Pads and flash symbols in cadence

from http://blog.csdn.net/gtkknd/article/details/49102253

Soldermask_TOP
Soldermask _BOTTOM
It refers to the green oil layer of the solder mask （ But the color of the solder mask , Not just green , And red 、 Blue 、 Black and white and so on ）, It is the non wiring layer of the circuit board , Used for making screen printing plate , Apply solder resist to areas that do not need welding . Due to the fluidity of solder at high temperature when welding circuit boards , Therefore, it is necessary to apply a layer of welding resistance material where welding is not required , Prevent solder from flowing 、 Overflow causes a short circuit . The size of the pad reserved on the solder mask , Larger than the actual pad , The difference is generally 10～20mil, stay Pad_Design It can be set in the tool .

Pastemask_TOP
Pastemask _BOTTOM
Solder paste protective layer （Paste Mask）:
Non wiring layer , This layer is used to make steel film （ slice ）, And the holes in the steel film correspond to those on the circuit board SMD Solder joints of devices . Surface mount （SMD） When the device is welded , First cover the circuit board with the steel film （ Corresponding to the actual pad ）, Then apply the solder paste , Scrape off the excess solder paste with a spatula , Remove the steel film , such SMD The pad of the device is pasted , After the SMD Attach the device to the solder paste （ Manual or Mounter ）, Finally, it is completed by reflow welding machine SMD Welding of devices .
Usually, the size of the aperture on the steel film is smaller than the actual solder joint on the circuit board , The difference is in Pad_Design It can be set in the tool .

Thermal relief
Thermal relief( Flower pad / Hot air pad )： Also called hot air pad , Anti heat dissipation heat release pad . The hot air pad has the following two functions ：
（1） Prevent heat dissipation . Because the power and ground on the circuit board are provided by large pieces of copper foil , Therefore, in order to prevent false soldering caused by too fast heat dissipation , Therefore, the power supply and grounding via are in the form of hot air pad ;
（2） Prevent large pieces of copper foil from extruding the through hole and hole wall due to thermal expansion and cold contraction , Cause hole wall deformation .

Anti pad, Isolation PAD： Act as an insulator , An electrical isolation is formed between the pad and the copper layer , At the same time, prove the electrical space occupied by the pad in the circuit board .

Positive and negative The concept of ： Positive and negative are just two different display effects of one layer . Whether your layer is positive or negative , Made PCB The plates are the same . It's just cadence In the process of handling , Data volume ,DRC testing , And the processing process of the software is just different . He is two ways of expressing one thing . The positive is , What do you see , That's what , You see wiring is wiring , It really exists . Negative is , What do you see , There is nothing , What you see , It's the copper that needs to be corroded . Positive and negative films , How to use and set up （Regular pad,thermal relief,anti pad） These three types of pads
We're making pad when , It's better to flash do , Set all three parameters , Whether you do positive or negative , Once and for all . If you don't use negatives , that , congratulations , You can and flash Say goodbye . If you're making pads , You don't make flower pads in the inner layer , So in multilayer boards , If the power layer is negative, there will be no flower pads , We have to do it in the early stage . If I go the other way , I did , But when drawing, you don't want to spend pads , Can be directly in art work The negative is set to remove the flower pad . Of course, you can also use the positive layer of copper directly , When paving holes, set parameters such as the connecting mode of holes , It can also achieve the effect of flower pad , In this way, when making a pad, you can also achieve the effect of a flower pad by setting the connection mode of holes without making a flower pad .（ mean , If your power Layers are positive , Then you don't have to do it flash Pad ） Setup method ：shape—global dynamic parameter－Thermal relief connects Set it up in . Each pin can have all types of pad（Regular, thermal relief, anti-pad and custom shapes）, these pad It will be applied to each routing layer in the design . about artwork The negatives in the layers ,allegro Will use thermal relief and anti-pad. And for positive films ,allegro Use only Regular pad. These jobs are allegro When generating photo files , Automatically selected . It is possible to specify... In each layer Regular Thermal relief And Anti-pad Because of the following considerations ： When you light up a file , When the layer is connected with the pad is the general routing , that , In the positive wiring layer ,Allegro Will decide to use Regular Pad . If it's copper , Then use Thermal relief Pad , If you can't connect to it , Then use Anti-pad. The specific use is decided by Allegro decision .（ Because when you are making pads , It is impossible to judge whether your pad is used for positive or negative film , So when making pads , Add all three types of pads as much as possible ）.
About making pads , Attention should be paid to the following points ：
First , For the naming of pads , It should be noted that normally, the standard names are underlined _, Instead of a minus sign -.
1： Usually the pad is larger than the pin 0.3mm.
2： Usually regular pad Size and paste mask Equal in size , and sold mask The size is larger than regular pad It's big 0.1mm.
3： Custom pad making , Do it first shape symbol（ Make two , One is regular Of , One is sold mask Of ）, Then I do pad.
4： Through hole pads , The aperture is made larger than the actual size 12mil that will do , In the inner electric layer flash The inner diameter is larger than the hole diameter 8mil that will do . and anti-pad than regular pad Big 0.1mm.
5：slot Pad making , Make a rectangle first flash, Then make a pad , Of course , Among them anti pad than regular pad Big size 0.1mm.
notes ： For drill holes without electrical characteristics , The pad is made in plating Time selection Non-plated, And only do begin layer and end layer,internal layer and paste mask And sold mask All choose null.