an interconnecting post for mounting a microelectronic device such as an integral circuit chip is fabricated with generally uniform cross - section , by forming a first layer of positive photoresist on a substrate , soft - baking that first layer and exposing it for a short time with a wide - apertured mask or simply a uv blank flood exposure . without developing the first layer , a second layer of positive resist is then applied over the first layer , soft - baked , and then exposed with a narrow - apertured mask . during the soft - baking of the second layer , some of its activator in the photoresist compound diffuses into the exposed portion of the first layer and modifies its solubility in such a way that , when the layers are subsequently developed , the developer partially undercuts the unexposed portion of the first layer to form in the photoresist an opening of generally uniform cross - section . this opening can then be filled by plating to produce a strong , integral interconnect post .