My costum board can not be detected as USB3.0. It fails to go through link training.
What could i do to solve it ?
I believe it is your custom board, and it is succesfully enumerating as a USB 2.0 device. Please ensure the guidelines are followed as in http://www.cypress.com/?rID=53203. If you want us to review your PCB layout, please create a tech support at www.cypress.com -> Support -> technical support. We can review it for you.
A quick thing you can do is check if a resistor has been populated on R_USB3 pin of FX3 chip.