A pattern matched pair of a front metal interconnect layer and a back metal interconnect layer having matched thermal expansion coefficients are provided for a reduced warp packaging substrate. Metal interconnect layers containing a high density of wiring and complex patterns are first developed so that interconnect structures for signal transmission are optimized for electrical performance. Metal interconnect layers containing a low density wiring and relatively simple patterns are then modified to match the pattern of a mirror image metal interconnect layer located on the opposite side of the core and the same number of metal interconnect layer away from the core. During this pattern-matching process, the contiguity of electrical connection in the metal layers with a low density wiring may become disrupted. The disruption is healed by an additional design step in which the contiguity of the electrical connection in the low density is reestablished.