Ask about copper plating and splitting power planes

RobertLiang

Ask about copper plating and splitting power planes [Copy link]

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Dear Expert:

I am a novice and encountered a problem when drawing PCB for the first time:

I need to cut out a small piece of copper in the center of a 3.3V power plane to connect to the 2.5V power supply.

I used Allegro 17.4 anti-etch - split plane method, and the results are as follows:

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Figure 1a. The lines (white) in the anti-etch are connected to each other

Figure 1b. Copper plating is normal: purple 2.5V orange 3.3V

Figure 2a. The anti-etch lines are not connected together (hopefully a copper strip is cut out of the center of the 3.3V plane)

Figure 2b. Copper effect (purple and yellow copper overlap!)

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I believe this is not a bug in Allegro, but a problem in my own understanding, so I would like to ask:

1. I heard that there should be no "islands" in PCB. Is this the reason why my plane segmentation is abnormal? (I understand that an island is a suspended plane, but my plane is connected to 2.5V)

2. If Allegro does not want users to cut out a piece of copper in the center of the plane, what is the reason? (My immature guess is that it is to avoid the loop and antenna effect of the power plane, but the copper I cut out in the center is very small and should not cause any impact; on the other hand, sometimes we need to cut out an outer ring ground at the edge of the PCB to enhance EMC, but I did not encounter any abnormality when splitting the plane in this case)

3. I discovered this problem accidentally. DRC did not report any errors. Is there something wrong with my constraint settings?

4. If I need to manually cut out a part from the Shape, is it feasible and how should I do it?

Thank you very much!

RichSJ

I think anti-etch was still done, but the line width of this piece changed. The line width on the lower left is still correct. DRC is related to your settings. If you turn it off, DRC will of course not appear.

Can it be segmented using 2D lines?

RobertLiang

RichSJ posted on 2022-6-2 12:45 I think anti-etch is still done, but the line width of this block has changed. The line width of the lower left is still correct. DRC and...

Thank you~

I checked the line width of the anti-etch, and it was 0.5mm, no problem;

If the line-width is really 0mm, the shape of VCC_3.3V should not overlap with 2.5V, but should be separated, but the boundary is very small. However, the two shapes overlap;

Now that I understand the DRC issue, I will study it further;

I don't quite understand 2D line, does it mean add -> line? This is what I use.

RichSJ

I remember there is a 2D line, can you use help to check it. I hope I am not confused.

RichSJ

It should belong to the label, without electrical characteristics, and can be split when used in that layer, but DRC cannot find it, so after anti-etching is completed, use it to widen it.

qwqwqw2088

Need to manually cut out a part from the Shape

What is artificial

After the PCB is made, is it engraved with a knife?

qwqwqw2088

There is no error in drc, it may be that the drc rule is accidentally set to be ignored

RobertLiang

qwqwqw2088 posted on 2022-6-2 13:46 It is necessary to manually cut out a part from the Shape. What is manual PCB? After it is made, use a knife to carve it?

Ah this

What I mean is that if I use Polygon to draw a filled shape, is there a way to cut out a piece from this shape in some way, similar to the effect of the AntiPad pad in the negative layer?

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Of course you can use Anti Etch, but testing has found that it is not feasible.

RobertLiang

RichSJ posted on 2022-6-2 13:21 It should belong to the label, without electrical characteristics, and can be split when used in that layer, but DRC cannot find it, so after anti-etch is completed...

Thanks! I will learn

RichSJ

The "manual" method you mentioned is to escape the constraints of the allegro netlist and make some special line shapes. These are very dangerous and will not give you error prompts. You must be extremely careful. Of course, only in this way can you sometimes do things that others cannot do. Good luck!