OPA928: OPA928

1) How to select the best feedback RES.  Is 100 MΩ OK?

A 100 M Ω resistor may be suitable for your application, but it depends on the input bias current and noise characteristics of OPA928. Please take a try according to your application.

2) How to choose the material for PCB? Is FR4 four-layers PCB suitable?

FR4 four layer PCB is a reasonable choice, but please ensure that the PCB design meets the requirements for precise measurement of low current.

TI provided a EVM below, you can tale a look

https://www.ti.com/lit/ug/sbou282a/sbou282a.pdf?ts=1721353967149&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FOPA928

Thank you very much for your reply.

I have reviewed the document of EVM. But there is no information about the material of PCB.