An embodiment of a method of attaching a semiconductor die to a substrate includes placing a bottom surface of the die over a top surface of the substrate with an intervening die attach material. The method further includes contacting a top surface of the semiconductor die and the top surface of the substrate with a conformal structure that includes a non-solid, pressure transmissive material, and applying a pressure to the conformal structure. The pressure is transmitted by the non-solid, pressure transmissive material to the top surface of the semiconductor die. The method further includes, while applying the pressure, exposing the assembly to a temperature that is sufficient to cause the die attach material to sinter. Before placing the die over the substrate, conductive mechanical lock features may be formed on the top surface of the substrate, and/or on the bottom surface of the semiconductor die.