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  • R. Smith says:

    Active brazing using Cu-Ag-ti filler metals cannot be used since the brazing temperatures are over the melting temperature of aluminum and its alloys. This means active solders such as S-Bond must be used if a thermally and/or electrically condcutive metal bond are needed. When using active solders, the bonding temperature of 220 – 250C are required; therefore, the CTE mismatch when bonding to high CTE aluminum alloys, must accomodate the strain mismatch properly and not overstress the joint or lead to distortion that if manifesting itself as bending, can crack the ceramic.

    If the alumina parts are less that 25 mm (1 in. )in any direction it is likely that the CTE mismtach stresses will be low enough not to fracture the ceramic or the solder bond. If however the size is larger than 50 mm then both joint design and tiling (making smaller ceramic pieces to bond) will be required. Another option is to use lower temperature active S-Bond solders made from In-Sn or Bi-Sn. With lower bonding temperatures, there will be a lowering of the stresses from less strain at these lower temperatures.

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