Contact system for electrically conductive ceramic-like material

Abstract

Abstract AN IMPROVED CONTACT SYSTEM IS PROVIDED FOR CERAMIC OR CERAMIC-LIKE MATERIAL. PILLS OF ELECTRICALLY CONDUCTIVE OR SEMICONDUCTIVE CERAMIC MATERIAL SUCH AS A BARIUM TITANATE DOPED WITH A RARE EARTH ARE PLACED IN A HOLDER SO THAT THE OUTER PERIPHERY OF THE PILL IS MASKED AND FLAME SPRAYED WITH A METAL WHICH GIVES A GOOD PHYSICAL BOND AND AN OHMIC CONTACT HAVING A LOW ELECTRICAL RESISTANCE. ALTHOUGH SEVERAL METALS CAN BE EMPLOYED FOR THIS COATING, ALUMINUM IS PREFERRED. THE PILL IS PREHEATED TO MITIGATE THERMAL SHOCK PROBLEMS. WHEN ALUMINUM IS EMPLOYED, PREHEATING OF THE PILL IS ALSO FOUND TO SIGNIFICANTLY ENHANCE THE BOND STRENGTH BETWEEN THE CERAMIC AND THE ALUMINUM. THE END USE OF THE PILL AFFECTS THE CHOICE OF THE METALLIC LAYER APPLIED TO THE CERAMIC. FOR CERTAIN APPLICATIONS, FOR INSTANCE, ONE LAYER MAY SUFFICE, SUCH AS WHEN PRESSURE LEADS ARE EMPLOYED. FOR SUCH APPLICATIONS AN OHMIC CONTACT HAVING A GOOD PHYSICAL BOND IS ALL THAT IS REQUIRED; HOWEVER, IN MANY OTHER APPLICATIONS, IT IS DESIRED TO SOLDER LEADS TO THE CONTACT LAYER. IN SUCH CASES, THE CERAMIC PILL MUST HAVE A FIRST COATING OF ALUMINUM TO PROVIDE THE NECESSARY PHYSICAL BOND; HOWEVER, SINCE ALUMINUM CANNOT BE SOLDERED, ANOTHER LAYER OF MATERIAL IS REQUIRED. THIS SECOND LAYER OF SOLDERABLE MATERIAL, SUCH AS COOPER, IS APPLIED, PREFERABLY BY FLAME SPRAYING ONTO THE UNMASKED SURFACE OF THE PILLS. THE PILLS ARE REMOVED AND THE PERIPHERY IS ABRASIVELY CLEANED TO ENSURE REMOVAL OF ANY CONDUCTIVE MATERIAL WHICH MAY HAVE GOTTEN BEYOND THE MASK. THE PILLS ARE THEN PLACED BETWEEN THE ENDS OF A GENERALLY U-SHAPED SPRINGLY LEAD SO THAT THE ENDS ARE BIASED INTO ENGAGEMENT WITH THE OPPOSITE FACES OF THE PILL. THE PILLS ARE PASSED THROUGH A FOAM FLUX, THEN INTO A SOLDER BATH. FOR MANY APPLICATIONS, WHEN ELECTRICAL INSULATION IS NOT REQUIRED, THE PILLS ARE THEN READY FOR USE UPON CUTTING OFF OF THE BIGHT PORTION OF THE U-SHAPED LEAD. WHERE ELECTRICAL INSULATION IS REQUIRED, THE PILLS ARE COATED WITH A CONVENTIONAL ENCAPSULATING MATERIAL. IN EITHER CASE, THE LEADS MAY BE DEFORMED TO PROVIDE STOPS USEFUL TO LIMIT INSERTION OF THE SWITCH INTO ITS MOUNT AND FINALLY, IF THE BRIGHT PORTION OF THE LEAD IS STILL ATTACHED, IT IS CUT OFF.

Inventors

• 👤 John G Kourtesis
• 👤 Leo Marcoux

Bibliographic Details