We hand-solder a magnetic connector (see example drawing) to a FlexPCB. The FlexPCB is cut with a 30um wide laser, so rectangular holes are possible. How can I plate this rectangle from top to bottom layer, like a regular PTH?
Second image shows the footprint done with edge cuts and regular pads. I believe rectangular PTH were not possible before KicCad v6 and KiCad 6.0.0 rc1 seems to offer only circular and oval for hole shapes. So guess I need to communicate it with text to my fab?
The problem here is that there are a lot of different Gerber dialects around. The latest X3 version probably has clear and precise functions to implement this, but KiCad does not implement some of the more obscure gerber features, and most manufacturers don’t understand them either. Apparently there is a strong tendency to “keep what works” (for 30+ years).
The final result is the only way to make sure such things are implemented in the way you want them, is to communicate with your PCB manufacturer.
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Well, I wouldn’t call them “dialects” (which assumes parallel forks) but rather “versions” (X1, X2, X3). Gerber file spec is open and clear but indeed it depends on the CAD/CAM software to actually implement them.
The only way to make a truly rectangular hole is by punching. Non circular holes are usually made with a router bit, which means a minimum corner radius of 1~2 mm
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Per OP they seem to use laser for cutting the flexboard material.
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I was told by our local PCB manufacturer that I can define openings in my PCB by just using Edge.Cut lines. Till now I was defining such openings only with rounded corners.
I don’t expect any problem to define that way a rectangular opening if I will know they are able to do it.
Even if you can create (almost) perfect sharp corners with your laser, it probably is not good to do so.
Sharp corners create concentrations of stresses in the base material, and this is especially important with flex PCB’s.
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right, we have done this many times with FlexPCB=FPC. The reason for the question was whether there is a common way to communicate a rectangular PTH in the gerber files (and not tell the fab in prose). paulvdh gave a great answer.
I agree, it’s typically a bad idea to have sharp corners in FlexPCB.
I’am only aware of 2 potential issues with sharp corners:
- mechanical stress: when the FlexPCB is subject to a mechanical force, sharp edge tend to break. A rectangular PTH for a connector that is filled with solder is probably not an issue as mechanical forces are distributed with the solder. Tough that’s only an assumption from my side.
- when not powered correctly, the laser stresses thermally the material. No idea whether this could happen with FlexPCB laser machines but it certainly happens in metal laser cutting.
Do you know more issues or is one above incomplete?
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