Author Topic: Slots in PCBs  (Read 1075 times)

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Offline NivagSwerdnaTopic starter

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Slots in PCBs
« on: November 17, 2019, 12:13:51 pm »
I would like to cut a slot in my PCB through which another PCB will slot at 90 degrees.... Which got me to wondering...

What constraints exist in practice when making slots?

Can they really have square edges or should they be rounded?

I looked on the JLPCB web site but couldn't find any guidance.

In my example I need a slot through which a PCB would fit... The PCB being 37mm wide and 1.6mm thick.

I presume I would need to allow wiggle room too.

Does anyone have any wisdom they could share please.

Thanks
Nivag

 

Online Jeroen3

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Re: Slots in PCBs
« Reply #1 on: November 17, 2019, 12:16:24 pm »
Usually the milling tool is 2mm. So the minimum width is 2mm. Square corners will also be at 2mm radius.
Less is possible, but requires an extra step at higher price.
And you have to keep enough rigidity in the board to be able to mill and pick&place. This depends on the design.
 
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Offline Miti

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Re: Slots in PCBs
« Reply #2 on: November 17, 2019, 12:38:37 pm »
They use router bits for slots and those are, obviously, round. So you can have square outer corners but rounded inner corners but that’s ok as long as the flat part of the slot has the same length as the board you put through. As for the wiggle room, the board thickness may vary a bit, mainly with the finish. Immersion gold is more consistent, hasl is bumpy, for example. For my  projects I make it tight and, if needed, a small file does wonders.
Fear does not stop death, it stops life.
 
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Offline NivagSwerdnaTopic starter

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Re: Slots in PCBs
« Reply #3 on: November 17, 2019, 02:01:13 pm »
So say I just went for a 2mm wide slot... It would have semi circles at both ends .. should I submit a board outline layer which has the arcs?

(Currently I have a 1.6mm X 37mm rectangle with no wiggle room)
 

Offline T3sl4co1l

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Re: Slots in PCBs
« Reply #4 on: November 17, 2019, 07:00:41 pm »
You can make a dogbone shape so the board registers against a flat end stop in the slot.

They'll rout smaller slots too, but there may be added cost; 2mm is just the most common end mill.

mikeselectricstuff also did a video about doing this at minimum cost, where you make a somewhat zig-zag pattern so the board is sprung between faces with the correct spacing, without requiring a smaller end mill.

Tim
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Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 
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Offline IanJ

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Re: Slots in PCBs
« Reply #5 on: November 17, 2019, 07:29:35 pm »
So say I just went for a 2mm wide slot... It would have semi circles at both ends .. should I submit a board outline layer which has the arcs?

(Currently I have a 1.6mm X 37mm rectangle with no wiggle room)

My 2mm slots are drawn rectangular, but as the fab uses 2mm bits the holes come out perfectly rounded at the ends.....so in reality there is a tiny bit of the pcb left on the board at each corner of the slot. They don't go over the line.

Note: Pcbway will do down to 0.8mm as a special.

Ian.
« Last Edit: November 17, 2019, 07:31:36 pm by IanJ »
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Offline Miti

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Re: Slots in PCBs
« Reply #6 on: November 17, 2019, 11:13:27 pm »
So say I just went for a 2mm wide slot... It would have semi circles at both ends .. should I submit a board outline layer which has the arcs?

(Currently I have a 1.6mm X 37mm rectangle with no wiggle room)

Make it 1.6mm and submit. If they want more money or reject it, they'll let you know. Your mechanical strength is reduced with a wider slot the assembly relies only on the pads/solder.
Fear does not stop death, it stops life.
 


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