GB1375381A - - Google Patents

Abstract

1375381 Thermoelectric devices ATOMIC ENERGY OF CANADA Ltd 30 Nov 1971 [16 Dec 1970] 55522/71 Heading H1K Limbs of thermoelectric semi-conductor material individually coated with uncured polyimide are assembled in superposed rows and with strips of cured polyimide film disposed between adjacent limbs in a row and between adjacent rows, the assembly slowly compressed to expel excess uncured resin which is then wiped off, and the assembly baked while compressed to cure the polyimide and baked again after removal of the compressing force. As described alternate limbs are bismuth telluride of P- and N-type respectively. The limbs are coated with a solution of partially cross-linked polymide in N-methyl pyrrolidone and xylene and assembled with the cured strips in a PTFE jig, which is placed successively in ovens at 80‹, 100‹ and 150‹ C. for periods of 24, ¢ and 1 hours respectively. After removal from the jig the assembly is heated at 350‹ C. for an hour. A pattern of contacts connecting the limbs in series, parallel, or series-parallel arrangement is provided on the ends of the assembly, e.g. by masked vapour deposition, electroplating through a mask, or by electroplating overall followed by pattern etching. However the contacts preferably consist of strips cut from lead coated nickel foil which are soldered on electroless nickel plated end. faces of the assembly. After soldering the contacts on one face excess lead is trimmed away with a knife, any residual lead, flux and electroless nickel between contacts removed by a jet of abrasive powder, the assembly washed in a flux solvent and the face polished. Then the process is repeated on the other face. Fired metal coatings on beryllia plates are photo-etched to provide metal areas matching the contact patterns, coated with zinc chloride flux and dipped in solder, suitable solders being lead and 2À5 wt. per cent silver for the plate on the hot side of the assembly and tin or tin and 38À1% lead for the cold side plate. The solder is reduced in thickness by mounting the plates in a jig (Fig. 4, not shown), and abrading with 600 grit silicon carbide. The assembly is then mounted on one of the plates with the corresponding metal and contact patterns aligned with the aid of adhesive marker strips on the assembly and plate, placed on a heated platform and heated to melt the solder for 30 seconds. After cooling the other plate is attached to the opposite face of the assembly.