Setting of the Allegro medium pad

When using Cadence Pad designer to make a pad, you will encounter the thermal relief and anti pad design size problems

Thermal Relief: Regular Chinese translation should be called anti-thermal pad. It mainly from a welding pad to prevent the heat too fast welding effect, in the non-full layer is the case of copper it can be made into a ring, the size of the same as anti pad. When in the power layer or GND layer, it is also to reduce the role of thermal shock, to prevent the pad and the copper layer is connected to a complete area is too large, due to the difference between the expansion coefficient between the plate and copper, resulting in plate warping, floating, or foaming and other problems. This time if you have to make that kind of hollow.

Anti pad: An insulating effect, so that the pad and the layer of copper between the formation of an electrical isolation, while in the circuit board to prove the electrical space occupied by the pad. When this value is less than the size of the pad, the solder pads cannot avoid copper when the negative static copper is laid, and a short circuit is formed.

1.regular Pad,themal Relief,anti pad Concept and how to use it

A: regular pad (regular pad) is mainly connected with top Layer,bottom layer,intemal layer and so on all the positive (including wiring and copper cladding). Generally used in the top, bottom, and signal layers, because these layers are more positive.

Themal Relief (anti-thermal pad), anti pad (isolated pad), mainly connected with the negative and isolated insulation. Generally used in the inner layer of VCC or GND, because these layers are more negative. But we also set the Themal relief (hot-air pad) in the begin layer and end layer, and the parameters of the anti pad (disk), because the begin layer and end layer are also possible to do the inner layers, or the negative.

In summary, that is, for a fixed pad connection, if you this layer is positive, then you set the regular pad with this pad connection, themal Relief (hot air pad), anti pad (isolation disk) in this layer does not have any effect.

If this layer is negative, is through the themal relief (anti-thermal pad), anti pad (isolation pad) to connect or isolate, regular pad in this layer does not have any effect.

Of course, a pad can also be used regular pad with the top layer of the positive network connection, at the same time, with the Themal relief (hot air pad) and gnd inside the negative of the layer connected to the network.


2. The concept of positive and negative

A: positive and negative only refer to the two different display effects of a single layer. Whether you are setting a positive or negative layer, the PCB board is the same. Only in the course of cadence processing, the data volume, the DRC detection, and the software processing process are different.

It's just two ways of expressing a thing.

Negative is, you see what, there is nothing, you see, is precisely the need to corrode the copper skin.

3. How to use and set (regular pad,themal relief,anti pad) These three kinds of pads when positive and negative

When we make a pad, it is best to do the flash well, the three parameters are all set up, whether you do a positive or negative, are once and for all. If, you must say I will never use negative, then, congratulations, you can say goodbye to flash.

4. Set regular pad,themal Relief,anti pad pads when they are in relation to the dimensions or formulas

A: Different companies, different habits, standards will be different, but the absolute difference is not small.

Experience value (for reference only)

Anti pad diameter =regular pad diameter +10mil

Soldermask diameter =regular pad diameter +6~8mil

Flash ID =drill diameter+16mil

Flash od =drill diameter+30mil

As for the opening width of the flash, it is calculated according to Pi, to ensure that the width of the connection is not less than 10mil.

Setting of the Allegro medium pad