PCIe Design Rules

[JohnsonMiller]

Hi Guys,

Design and ordering a PCIe card I qot some questions which need your comments, thanks in advance:
- The board thickness is 1.6mm, but how far we make board thicker?
- Gold finishing on edge fingers and board area looks to be different, method used for board inside is ENIG but edge finger is Electrolytic gold, what is difference? What is minimum gold thickness?
- In some PCI card there is trace extension to both side of finger, attached is a sample. Little trace extension to outside is my question, what is reason for?

[robertferanec]

- board thickness: see PCIE connector datasheet, but it looks like specification says 1.57mm (62mil)

- I do not remember the exact thickness, but maybe this can help a little bit (from the specification): "To be sure that the environmental tests measure the stability of the connector, the add-in cards used shall have edge finger tabs with a minimum plating thickness of 30 microinches of gold over 50 microinches of nickel for the environmental test purpose only. "

- I think, the little trace is used to put gold on the fingers. I may be wrong, but the technology of putting gold on the fingers may require electrically connect all the fingers together ... so during PCB manufacturing they may need to add a little bit of PCB, which is then removed, but you still can see the small tracks on the end of the fingers connected to this small PCB. However, this is my theory

This may help PCI Expres Card Electromechanical Specification: http://read.pudn.com/downloads166/eb...ss_CEM_1.1.pdf