A system and method for a patch-like, self-contained substance infusion device which provides one or more substantially hidden patient needles which can be placed in fluid communication with a fluid reservoir subassembly that includes a rigid bladder portion used in conjunction with a non-distensible bladder film, such as a metallized film. Simple removal of an interlock allows a disk, or Belleville spring assembly to apply an essentially even and constant pressure to the contents of the fluid reservoir assembly, and allows the device to then be attached to a skin surface via an adhesive contact surface. A push button activation assembly is provided which can then be used to release and seat one or more spring-loaded patient needles into the skin surface, and establish a fluid communication path between the patient needles and the pressurized fluid reservoir contents thereby delivering an infusion into the skin.