Thursday, 29 November 2018

pcie - What is the usable area (for connectors) of a PCI Express card bracket?



I have a number of awkwardly shaped connectors that I need to cram into a single PCI Express slot metal bracket without any of them colliding with the host PC case's metalwork. The connectors are a mixture of proprietary and standard.


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My connectors will obviously need to be arranged so that they do not interfere with the PC case's metalwork so this means they they must fit within some sub-set area of the metal bracket (the red box).


Where can I find the official dimensions of the red box? (specifically the maximal area that I'm allowed to use while still being "compliant" with the physical spec of PCIe).


The specs that I have seen give details on the spatial relationship between the metal bracket and the add-in card PCB, but they do not seem to give details of the space that may be used for connectors to pass through.


PC cases vary so much from one brand to another (high-end versus low-end particularly) that I'm worried that if I don't get this right early on in the design then I'll have to re-spin all my PCBs and metalwork later on when someone finds a case that this device won't fit into.



Answer



According to the PCIe Card Electromechanical Specifications (CEM), we have the following specification for connector openings:


CEM Spec Connector Openings


Image Source - CEM Spec rev 1.1, Section 6, Figure 6-2, page 73



So your magic numbers are 89.9mm x 12.06mm.


That diagram also shows you how the space positions relative to the PCB.


If you follow that spec and it doesn't fit into a given case, it is not your problem as you've conformed to the specification that the case designer should also have conformed to.


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