An injection moldable, thermally conductive polymer composition that has ultra low CTE properties is provided. The composition is suitable both for substrate applications in high precision electronics assemblies as well as over molding applications in conjunction with ceramic substrates. The composition includes a base polymer matrix material loaded with thermally conductive filler, which imparts thermal conductivity to the polymer matrix while also maintaining or enhancing the dielectric properties of the base polymer. The resultant composition exhibits CTE properties in the range of between 9 ppm/° C. and 2 ppm/° C., exhibits an optical anisotropy of below 1.5, and a thermal conductivity of greater than 2W/m° K. The composition is suitable for use in over molding applications in conjunction with virtually any suitable electronics substrate material without the introduction of mechanical stresses produced by large CTE differentials.