A modular heat exchanger suitable for automotive applications, and methods for forming the modular heat exchanger. The modular heat exchanger construction incorporates a monolithic brazed core assembly composed of flat-type cooling tubes and sinusoidal centers. The required positional tolerances of the tubes for mating with the remainder of the heat exchanger are maintained within the brazed core assembly by minimizing core shrinkage resulting from the brazing operation during which the tubes are brazed to the centers.