A new low-cost, high volume technology for hermetically sealing large electronic packages

Early semiconductor manufacture frequently relied on resistance/projection welding for hermetic sealing of semiconductor devices, where the entire device perimeter is welded with a single current pulse lasting a few milliseconds. In the early days, the diameter of device seals was in the order of ¼ inch (6.3 mm) to about ½ inch (12.mm) diameter. These welds could be made using conventional moderately powered resistance welding equipment. As package sizes increased, larger welding equipment was developed to handle the longer package weld perimeters. Unfortunately, current projection welding machines may not reliably seal packages with weld perimeters exceeding 7.6 cm (3.0 in). This is due to the significant weld current required for longer package perimeters, the inadequate impedance match between the weld equipment and the weld; and the welding process may expel metallic particles into the package. Internal particle expulsion may be mitigated by the addition of particle getters described in JEDEC (Joint Electron Device Engineering Council) documents such as JESD72. However the welding process would be more useful if these particles could be avoided. While newer technologies have been developed to seal larger electronic packages - parallel seam, TIG, and laser welding - the original single shot welding technology remains the fastest, lowest cost sealing process ever developed. If one could reliably weld large packages, this technology would have significant advantages in high-throughput manufacturing. This paper addresses this need by describing a novel low-impedance projection welding device that can reliably weld large packages with up to 25.4 cm (10.0 in) weld perimeters with zero weld expulsion and zero weld defects, using half the energy required by traditional machines. This new welding machine uses a high magnetic flux density transformer to deliver ≫120kA of weld current while operating from a standard 110V, 15A electrical outlet, which eliminates the infrastructure costs of traditional external bus bars and cooling. In addition, the design can detect when the machine & weld electrical impedances are sufficiently matched to permit defect-free welding. A commercial version of this device has welded more than 1 million medical, communications, and military electronic packages with zero customer returns. Data is presented showing the weld parameters for a variety of commercial and military hermetic electronic packages.