## Calculating Hole and Pad size for the JTAG Connector

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I'm laying out a board that will have a MegaAvr1281 and an Atmel ICE connector.  I'm stumped trying to get the proper hole size and pad diameter for this .05 pitch connector.  The Samtec connector I've choosen (ESHF series) has a square .016" pin.  Using the information from this page http://www.pcb-3d.com/knowledge-... I came up with the following:

Pin diameter = .0226  (hypotenuse of the square)

Level C hole size = .028527

Level C pad dia = .048

So the absolute minimum pad diameter is almost the distance between pins!  What did I do wrong here?

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Last Edited: Wed. Mar 23, 2016 - 09:48 PM

For 10 thou clearance, you'd use a 40thou pad. 20+20+10 = 50.
At 40thou, that's near enough to 1mm

Using Eagle I manually assigned a 40mil pad, but with a hole size greater then 25mil or so, it will fail DRC.

Change the design rule constraint. You either fall foul of pad to pad clearance or minimum annular size. You probably don't want to go below 8thou pad to pad unless you pay premium for your pcb. So that's a 42 thou pad - 28 = 14 thou which is a 7thou annulus.

Last Edited: Wed. Mar 23, 2016 - 07:02 AM

You could think about fitting it sideways on the edge of the PCB... i.e. have 'fingers' top and bottom. You'd have to bend out the legs a bit...

I was hoping to get the math down before I go to my board vendor, but I think the next step is to verify my DRC rules with what my vendor can make.  And like you say I figure it's the annular size that's biting me.

As far as an edge mount, I would probably go with the SMD version of this connector before trying that.  I'd rather use the through-hole to get some robustness on this connector since it is the debug connector and will probably see a lot of insertions/removals with the ICE module.

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Ok I found the problem.  I was unaware the the Eagle DRC settings can change your pad sizes, I though it was a check and report function only.  So after reducing the minimum RestRing I have everything behaving.

dksmall wrote:

I'm laying out a board that will have a MegaAvr1281 and an Atmel ICE connector.

I'm stumped trying to get the proper hole size and pad diameter for this .05 pitch connector.

dksmall wrote:

I'd rather use the through-hole to get some robustness on this connector since it is the debug connector and will probably see a lot of insertions/removals with the ICE module.

My JTAGICE cable is new but probably has an MTBF of 50 uses.

alank2 designed a pcb that plugs into the Atmel ICE and allows regular ribbon cables with 0.1" connectors to plug into the target board to be debugged: