For the electronics on PCB’s,dielectric materials provide not only material and media support for the high-speed digital and RF systems,but also electrical performance. Impedance control and signal integrity have become increasingly important in high frequency applications,while trends in electronic industry continue to drive high-speed digital,RF and microwave systems for high-density integration,high system performance and high power operations over a wide range of operating temperatures. Microstrip and stripline are widely used in the high data rate and high frequency circuitry designs because they can be easily and cost-effectively fabricated with high performance,planar PCB laminates for various applications. To obtain optimal signal/power transmission,signal integrity and low signal distortion,certain controlled impedance (typically 50O) is very important to minimize impedance mismatching and power reflection. In practical designs,characteristic impedance of transmission lines is a complex function of substrate dielectric properties and physical structures,such as dielectric constant (er),trace width (W) and substrate thickness (h or b),or even metal strip thickness (t). However,when designers come to selecting the proper PCB laminates for their designs,there is lack of design tools for them to quantitatively evaluate the target board materials in terms of impedance control to effectively compare their temperature performance in terms of key PCB material properties,such as dielectric constant thermal stability and substrate thermal expansion. In this paper,based on the practical design equations for microstrip and stripline circuitry and using the Taylor series expansion (e.g. ?Z=dZ/dk*?k+dZ/dW*?W+dZ/dh*?h+dZ/dt*?t) for linear approximation of multiple-variable functions (e.g. Z0=Z(k,W,h,t)),analytic design equations for evaluating the transmission line impedance variations from its board dielectric and dimensional change have been developed. Additionally,these analytic design tools can also be readily applied to evaluate the variations of planar transmission lines for practical design and PCB fabrication impedance control with the board material’s dielectric constant and dimensional stability resulting from substrate tolerances (i.e. laminate DK and thickness tolerance) and PCB processing (such as trace etching resolution,multilayer thickness and etc.).