Printed Circuit Boards (PCBs) are easy target for reverse engineering and counterfeiting attacks due to the distributed supply chain. The integrated circuits (ICs) authentication techniques such as Physically Unclonable Function (PUF) are not easily extendible to PCBs. In this paper, we analyze various sources of variations in PCB and qualitatively study the quality metrics that can be used to quantify the PCB PUFs. We propose several flavors of PCB PUFs by exploiting the manufacture process variations. We also propose a multi-stage arbiter PUF with exponential challenge response pairs. Our preliminary simulations revealed an average 50.4% inter-PCB hamming distance.