| 摘要 |
A ceramic substrate includes a multiplicity of alternately screened and fired conductor and dielectric levels, with interconnections between levels through small via holes in the dielectric layers or alternately by means of crossovers. Thick film resistors are incorporated throughout the ceramic substrate, wherever needed, and the thick film resistors are printed and trimmed through windows which extend through any upper layers. In addition, resistors may be printed directly on top of the dielectric layers where necessary. Selective area hermetic sealing is utilized only for those chips and wire bonds which require environmental protection by placement of a ring frame seal encircling the selected area and over insulation on substrate conductors which are routed directly beneath the sealing area. A lid is directly soldered to the frame and, before final sealing, a proper environment is created within a sealed area. Where equivalent chip versions of electronic components are not available, discrete components are soldered directly to the ceramic substrate outside of the sealed area. Necessary thermal dissipation can be afforded by direct mounting of the multilevel substrate on a heat sink.
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