The cover and case of fusible material forming the enclosure for a semiconductor chip are provided with a hermetically sealed joint in the form of a "stitch" weld along the marginal edge of the cover by multiple impulse, overlapped spot welding, with the heat of the welding current confined to a zone spanning the distance between a pair of pressure-imparting electrodes and transmitted transversely of the side wall of the case, thereby avoiding heat transfer across the case with consequent damage to the circuitry, electrical devices, semiconductor material and other contents of the case. A special carrier provides a mount for the case and, through use of a template on the carrier and a drive associated with the template, the case and cover are advanced or indexed in small increments after each resistance weld cycle, relocating the package in readiness for the next succeeding welding step.