A system and method for a patch-like, self-contained substance infusion device (700) which can be attached to a skin surface via an adhesive contact surface. A push button (780) activation assembly can then be used to remove an interlock (730), allowing a disk or Belleville spring (735) assembly to apply an essentially even and constant pressure to the contents of a fluid reservoir assembly (710). This allows the release of one or more spring-loaded patient needles (760) into the skin surface, and establishes a fluid communication path between the patient needles (760) and the pressurized fluid reservoir contents thereby delivering an infusion into the skin. The push button (780) activation assembly further allows the release of one or more improved safety mechanisms (794) after use.