How Printed Circuit Boards work?

I was reading an article where I came to know that FR4 being the most common/popular type of PCB out there. What are the other levels of FR(Flame Retardant) PCBs? Is there an FR3 , 2 and 1?

Yes, PCBs are comprise of different materials such as: FR1,FR2, FR3, FR4. Which article you are referring? Generally, use of flame retardants depends upon what you are trying to make.

Ahh… I see. Thanks. I also read somewhere on the internet about different FRs. FYI: Here when you scroll down to bottom of the page Construction of the Printed Circuit Board you will see they mentioned about FR4 .

Thanks for your response!