I found a translation as "cartelă fiică" or "placă fiică" on a few sites (example), but I don't know how much they use these terms, in *these* forms precisely. It is definitely less known than the related "placă de bază" (motherboard) and Romanians do tend to use the English term in every day conversation, a lot of times, when it comes to technical things.
PS. To the moderators: Is it OK to reply in English? I know it's the Romanian forum, but I usually reply in the language of the OP.