Abstract: An apparatus having and method of forming grooves in the surface of a substrate adjacent and parallel to sidewall locations for circuit chips or die mounted on the surface. The grooves have physical dimensions to retain fill material formed between the packages and the surface of the substrate so that the fill material does not bridge between chips, thus reducing warping of the substrate due to mismatches in coefficient of thermal expansion (CTE) between the fill material, the substrate, the chips, and mold material formed over the substrate, under fill, and chips.