Metal fusion bonding – Process – Metal to nonmetal with separate metallic filler
Reexamination Certificate
2000-12-29
2002-12-03
Dunn, Tom (Department: 1725)
Metal fusion bonding
Process
Metal to nonmetal with separate metallic filler
C228S248100
Reexamination Certificate
active
06488199
ABSTRACT:
FIELD OF THE INVENTION
Using the method according to the present invention for increasing the manufacturing certainty of soldered connections, the quality of the soldered connections can be better monitored by fully automatic soldering-point control systems.
BACKGROUND INFORMATION
In a method for the throughplating using silver conductive paste of printed-circuit boards that are coated on two sides, a printing screen is used that has openings that are assigned to the throughplating holes of the printed-circuit board. In this method, the printing screen, furnished with a silver conductive paste layer, is placed onto the printed-circuit board and the lower side of the printed-circuit board is exposed to an atmospheric partial vacuum, as a result of which the silver conductive paste forms hollow-cylindrical, electrical conductors that contact the walls of the throughplating holes.
Furthermore, it is known from the related art to furnish throughplating holes with a tin-plating to improve the bonding of the solder. However, tin cannot be used in ceramic carriers; sensors arranged on the ceramic carrier could be impaired by the tin-plating applied.
SUMMARY OF THE INVENTION
The method according to the present invention for increasing the manufacturing certainty of soldered connections makes it possible to use fully automatic optical soldering-point control systems having low error rates. In contrast to the known methods for creating throughplatings in printed-circuit boards, the wetting capacity for the solder is significantly improved by applying a second metallizing layer onto a preceding first metallizing layer, which can be composed, for example, of an AgPd thick film paste, so that it is possible to achieve an improved solder rise especially on endplatings on ceramic carriers. The resulting increase in the overall metallizing layer thickness increases the resistance against the decomposition of the metallization in response to soldering, the “leaching” effect.
In ceramic carriers, printed-circuit boards, or the like, throughplatings are produced by a sucking or pressing of conductive materials; endplatings can be produced by separating throughplatings along their lines of symmetry. In producing throughplatings in ceramic carriers or circuit boards, a first metallizing layer is initially applied, onto which, in a second method step, a second metallizing layer is imprinted. In an advantageous manner, a first metallizing layer is made of a corrosion-resistant material, such as AgPd thick film metal. To increase the overall metallizing layer and to improve the wetting capacity of the second metallizing layer, the first metallizing layer is provided with a further metallizing layer. The latter contributes appreciably to an improved wetting capacity of the first metallizing layer as a result of the solder. The second metallizing layer is preferably made of a rare metal layer, such as Au, which has better wetting capacities and whose wetting angle is <60°.
Using the method according to the present invention, it is possible in the edge area of the metallizing layer to achieve a sufficient layer thickness, dimensioned such that there is still material even in the outflow area of the metallizing layer. If there is sufficient metallizing material on hand at that location, the wetting capacity there can be maintained at a high level, in the edge area of the metallizing layer a rise of the solder is assured by the good wetting capacity. This in turn supports the use of fully automatic soldering-point control systems because a solder rise can be achieved in this way which can be reliably detected by a fully automatic soldering-point control system.
Using the application of the second metallizing layer, as called for in the present invention, the overall metallizing layer thickness in the edge area is increased, and the wetting capacity is improved so that the solder rises sufficiently. Since a second metallizing layer, for example of Au, can be affected by the disadvantage of decomposition, this disadvantage is removed by using AgPd as the first metallizing layer. The combination of the two metallizing layers in the production of throughplatings in the ceramic carrier lays the foundation for improving the endplatings generated after the separation of the throughplatings, such that fully automatic soldering-point control systems can be used which check the dimensions of the soldering points, assuring the prerequisite for meaningful fully-automatic measurements, namely a sufficient solder rise.
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Masatoshi, Satou. 12-96. Translation to JP 08-330173. pp. 1-9.
Becker Rolf
Schwaiger Jürgen
Dunn Tom
Johnson Jonathan
Kenyon & Kenyon
Robert & Bosch GmbH
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