Alternate SOB size case design

Standard PCB templates and project cases

Re: Alternate SOB size case design

Postby ian » Tue Mar 27, 2012 9:50 am

The Open Case design is very nice because you get almost 100% freedom to work with the top and bottom plates. It is simple to open, like scheme G.

The big problem I had was that most of our boards were too big, and pushed the edges of the case outwards so it could not close properly. Sjaak of course picked a perfect board the first time and asked me why I was having problems :)

I think we can safely assume all PCBs will be at or above (not below) the requested dimensions. Amateur home boards can be all over. I think that will need to be addressed for the open case, maybe with deeper ridges? I'd suggest holding bumps/fingers/brackets/etc, but that could interfere with the parts on the PCB.
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Re: Alternate SOB size case design

Postby Sjaak » Wed Mar 28, 2012 5:17 pm

ian wrote: The big problem I had was that most of our boards were too big, and pushed the edges of the case outwards so it could not close properly. Sjaak of course picked a perfect board the first time and asked me why I was having problems :)


Sorry man ;) station me over seeed and all you problem (regarding the cases and pcb sizes) are over :D

I'm just wondering if 'real' productions runs would be much better within certain tolerances then the 'prototype' runs?
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Re: Alternate SOB size case design

Postby ian » Thu Mar 29, 2012 12:30 am

Here's the info on board routing tolerance from Seeed. Not sure it is consistent with what we have found though:

Hi lan,
I have asked some PCB manufacturers, the tolerance of board dimension is
±0.2mm, and the minimum space from route to the edge is 10mil.
Any more confusion, please feel free to contact with us.
Regards,
Dwin
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Re: Alternate SOB size case design

Postby dsm » Sun Apr 01, 2012 8:03 pm

comments

ian,
ian wrote:I think we can safely assume all PCBs will be at or above (not below) the requested dimensions.

Sorry, but I tend to disagree that this result is inevitable.
If Seeed Studio's PCB vendor built your boards within the ±0.2mm board size tolerance they specify, there would be no problem.

dsm wrote:I don't think that Seeed Studio realizes that they may have a board size problem with their PCB vendors.
±0.2mm board size tolerance would be fine, but Seeed Studio's vendors appear to be consistently out of this tolerance range.
Sjaak makes an interesting point above in that the PCB vendors will only deliver correctly sized boards
if the PCB vendors understand that it matters to the customer and someone is watching (or inspecting the results).



ian wrote:Amateur home boards can be all over.

Amateur home boards can be sanded to bring them into compliance.
150 grit sandpaper with a palm sander works well and only takes a few seconds to take off enough PCB material.



ian wrote:I think that will need to be addressed for the open case, maybe with deeper ridges?

The walls of the open case and the modular open case designs are currently 2.0 mm thick with a 1.0 mm deep slots for the boards and the acrylic windows. Making these slots deeper is probably a bad idea in that changing this specification affects the width of the board edge component keepout which affects the layout of the boards you've just updated. In addition, making these slots deeper would cause the wall thickness to increase which drives up the cost of the case.

The open case design and the modular open case design are parameterized.
Increasing the board-to-case margin from 0.4 mm to 0.6 mm is fairly simple and might allow out-of-tolerance over-sized Dangerous Prototypes board to fit, but then the probably undersized laser-cut top and bottom acrylic windows might start to be loose. The top and bottom acrylic windows are designed to be the same size as the nominal size of the board
in order to make it simpler to laser-cut openings.

Overall, I believe the best solution is to try to get Seeed Studio's PCB vendor to fabricate the boards as specified.
Perhaps you might want to get Seeed Studio interested in the open case and the modular open case designs.
That way Seeed Studio's interests would be aligned with yours.
:)

Thanks for your time.

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