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I want to design a MOD PCB (daughter board,) to transform from QNF package to QFP package to use it on a existing/mother-board (just a reminder of the packages):

qfn qfp

Picture taken from here.

My MOD PCB uses half plated through holes (PTH) on the edge of the board:

mod PCB

This is how it will look like on the mother-PCB:

mother PCB

Eurocircuits will not let me make such a board because the drill holes are too close to each other (I cannot make the drill holes less than 0.5 mm since they are on the edge of the PCB.)

With those limitations, the only thing left to do, is to use pads on the bottom of the mod PCB instead of drill holes/PTH.

The MOD PCB will be transformed into a SMD-QNF-style package. This is the new design:

new design pcb

Do you think that the solder paste will short circuits under the mod PCB?

Is there any rule of thumb to consider when designing the pads so that they won't short themselves?

Additional info:

Eurocircuits lets me make either 130 μm or 100 μm stencil height/depth (I will go with the 100μm one for the mother-PCB.)

MOD PCB: Copper clearance between the pads is 0.295 mm.

MOD PCB: Mask layer between the pads is 0.150 mm

MOD PCB: Each pad is 0.5 mm width

My question is kind of similar to this one but I am more worried about shorting the bottom pads, not the techniques used for daughter/motherboards.

JRE
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Christianidis Vasileios
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    _"Each pad is 500 mm width"_ I suppose you mean 0.5 mm? Have you tried other PCB manufactures? – winny Jun 17 '21 at 13:12
  • You are right, let me fix that typo! My company always orders from this manufacturer. Lets say this is not an option for now. – Christianidis Vasileios Jun 17 '21 at 13:15
  • What's their capability on non-plated holes? Same? Can't you make the board larger and V-score them at the end? – winny Jun 17 '21 at 13:27
  • But with non-plated holes I wont be able to solder the MOD pcb on the mother-board. Non plated holes have no copper on/in them so how could they help? – Christianidis Vasileios Jun 17 '21 at 13:31
  • Copper on bottom side only. Not a good solution for ease of solder but if it’s a one off or very small series you may get away with it. How about V-scoring? – winny Jun 17 '21 at 14:35
  • Regarding the V-scoring, I cannot use it when I have PTH on the edge, Eurocircuits wont let you select it. (And its not physically possible, obviously). Also, you asked me if I could make the board larger and use V-scoring, This would destroy the plating on the board edge, So I would not have any plating, since V-scoring 'scratches' the pcb outline – Christianidis Vasileios Jun 17 '21 at 14:43
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    I still think you should talk to another supplier. Make a board large enough to accommodate your plated holes, THEN V-score the board across the holes. – winny Jun 17 '21 at 14:45
  • Is this a one-off part or something you need to make a lot of? For a single unit I think pads on the button might be a little annoying, but you could go easy on the paste (to make bridging less likely) and then touch up as needed after reflow. – user1850479 Jun 17 '21 at 15:06
  • We need to make alot of these MOD pcbs, and we will also have them assembled (both the motherboard, the daughter board and the MOD on the motherboard) – Christianidis Vasileios Jun 17 '21 at 15:35
  • JLC? PCB cart? PCBway? – winny Jun 17 '21 at 15:40

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