Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
1997-08-07
2001-12-04
Zimmerman, John J. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S627000, C428S629000, C428S666000, C428S645000, C428S646000, C228S056300, C228S194000, C228S246000, C228S249000
Reexamination Certificate
active
06326088
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a diffusion-soldered joint and to a method for making diffusion-soldered joints.
BACKGROUND INFORMATION
Diffusion-soldering is based on the fact that two base materials present in solid phases can diffuse into one another even at a temperature well below the melting point of a joint component. A suitable solder is placed between the soldering surfaces of the base materials, and the joint components are pressed together and heated for a long period. The result is a vacuum-tight, nondetachable joint. It is also known, instead of a separate solder, to produce diffusion-promoting layers, partially or over the entire surface, on the base materials by galvanic deposition, metallization, or vacuum sputtering, or by plasma spraying. The base materials are then pressed together and heated. Layers of pure tin, pure indium, or pure bismuth are known as diffusion-promoting layers of this kind. Solder joints made in this fashion have, however, only limited mechanical and thermal strength.
A method for joining planar workpieces, in which the workpieces participate in a direct joint by means of soldering or diffusion joining under vacuum, is already known from German Unexamined Patent Application No. 44 12 792. For this purpose, the workpieces are held in a sealed vacuum chamber, a melting intermediate layer being applied between the workpieces being joined. The intermediate layers are comprised of solders known in the art, which are introduced in the form of foils, powders, or granules.
Conventional joining methods such as soft soldering, brazing, and welding are used to produce joints which disadvantageously either have insufficient strength or require excessive joining temperatures. Such methods are therefore unsuitable when requirements exist for high thermal and mechanical strength over large areas (e.g., wafers) and for the lowest possible joining temperature in order to retain the original strength of the base materials of the joint components while maintaining very close dimensional tolerances.
SUMMARY OF THE INVENTION
The diffusion-soldered joint according to the present invention has the advantage that at a comparatively low joining temperature, at which the original strength of the joined materials is maintained, high thermal and mechanical strength of the components being joined (joint components) is achieved. The strength attained in the diffusion-soldered joint according to the present invention is comparable to that of brazed joints; the joining temperature (e.g., 250° C. to 450° C.) is considerably lower than in the case of brazed joints, so that, for example, the work-hardening produced by rolling, and the spring properties of the toughened joined materials are retained. As a consequence, very close dimensional tolerances for the joint components can be maintained.
With the solder carrier introduced between two joint components, it is possible in a simple manner to apply particularly actively diffusing, low-melting-point intermediate layers, applied in the molten state, to specific areas of the components being joined. The solder carriers allow very reliable, uncomplicated, and precisely targeted application of the aforesaid intermediate layers. Particularly advantageous in this context is the possibility of also applying a solder carrier of this kind to soldered parts that cannot be immersed in solder.
It is particularly advantageous to solder-coat a thin metal foil in a solder bath, using a passthrough method, in order to obtain a suitable solder carrier. Low-melting-point soft-solder alloys are suitable in this context as solder layers. The low-melting-point coating alloys can also, advantageously, be applied as multilayers in the form of their respective individual constituents, galvanically or by vacuum metallization, layer thicknesses of 1 to 10 micrometers in each case being preferred.
The method according to the present invention for making diffusion-soldered joints has the advantage of being applicable very reliably and precisely to produce high-strength joints in the case of joint components having relatively large areas. When large-area components are being joined, for example onto a wafer, it is advantageous to arrange an expendable, plastically deformable, solder-rejecting, and thermally conductive insert foil between a ram of the diffusion-soldering tool and the joint components. The insert foil allows compensation for dimensional tolerances in the height of the individual parts being joined, and thus approximately uniform distribution of the ram pressure. Lastly, joints of approximately uniform strength over a large area are obtained in this fashion. The aluminum or chromium layers of the insert foils guarantee good thermal conduction and distribution, and solder rejection.
REFERENCES:
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Semalloy Solder Alloys, Semi-Alloys Technical Bulletin No. SA-64, five pages, Jul. 1968.*
PREFORM, Alloys Unlimited, Inc. brochure, p. 5, 1959, (No month).*
A. D. Merriman, “A Dictionary of Metallurgy”, 1958 (no month), “Solder”, “Soldering”, p. 328.*
Howard H. Manko, “Solders and Soldering”, 1964 (no month), p. 109, 1958.*
W. Krause, “Konstruktionselemente der Feinmechanik”, pp. 196-201 (No date provided).
Engelhart Rolf
Mayer Rolf
Reschnar Wilfried
Schmitz Godehard
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