Printed circuit boards (PCBs) are the most common chip carriers of modern electrical systems. Compared with integrated circuits, it is more straightforward to apply attacks such as reverse engineering, unauthorized access and tampering on PCBs. Among these attacks, tampering is a serious threat to modern electronic devices such as smart meters, digital media players, and video game consoles. By tampering a PCB, an attacker can eavesdrop and/or manipulate critical inter-component communications. In the case of home electronics, this is often done to bypass the device's copyright protection mechanisms. In this paper, a model-assisted attestation framework, MPA, is presented to mitigate these concerns. This framework exploits JTAG ports to create board-level ring oscillators which monitor critical PCB traces. The impact of temperature on the framework is also analyzed, and modeling is used to compensate for this effect. Besides the methodology, we also present the detailed hardware implementation and enrollment-detection flow in this paper. Finally, the performance of our proposed framework is validated with commercial SoCs and custom PCBs. A high detection accuracy (> 99.7%) is achieved across various testing corners.