Metal fusion bonding – Process – Preplacing solid filler
Reexamination Certificate
1999-07-12
2001-06-05
Ryan, Patrick (Department: 1725)
Metal fusion bonding
Process
Preplacing solid filler
C228S245000, C228S232000, C029S612000, C029S620000
Reexamination Certificate
active
06241146
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns a process for manufacturing a sensor arrangement for temperature measurement comprising a temperature-sensitive measuring resistance which has a thin metal film as a resistance layer and contact surfaces on a ceramic substrate, wherein the resistance layer is covered by an electrically insulating protective layer. The contact surfaces are, however, electrically conductive and are directly and firmly connected with conductor paths, which are electrically insulated from one another, on a high temperature-resistant carrier element, wherein the measuring resistance is bonded on one end of the carrier element, and on the end of the carrier element facing away from the measuring resistance, contact surfaces are arranged for connecting a contact clip, plug or cable.
A process for bonding electrical conductors in the form of fine wires or bands with electrical conductor paths is known from German published patent application DE 34 24 387 A1. According to this publication, Pt wires with a diameter of about 0.1 to 0.5 mm are connected electrically and mechanically fixed on a ceramic substrate, in which a thick layer paste is applied to the conductor paths on the ceramic substrate. The wires are laid into this paste and run through a firing process together with the paste.
Furthermore, printed circuit boards are adequately known as carrier elements for passive or active components, for example from German patent DE 39 39 165 C1 or German utility model DG 87 16 103 U1. Since most of these components find applications in the temperature range up to a maximum of 150° C., the board material is also usually designed only for this temperature range. As a rule, these materials are plastics, which are often reinforced with inorganic materials. To the extent that a wireless bonding of the components is provided, as is typical, for example, also with temperature measurement resistances for application as calorimetric sensors (see German patent DE 44 24 630 C1), this takes place with soft solder and/or by means of conductive glue. These connection techniques to plastic boards are, however, completely unsuited for temperatures above 300° C.
A sensor arrangement, likewise for calorimetry, is known from German utility model DE 295 04 105 U1, in which a short (15 mm long) ceramic layer is used as a carrier element. Since use as a calorimetric sensor is indicated here as well, one must assume that the bonding is provided by soft solder, which likewise only permits a maximum operating temperature of 300° C.
Further procedures for producing sensor arrangements with temperature measuring resistances for high temperature applications according to the state of the art (described, for example, in German utility models DGm 1,784,455 and DGm 1,855,262) are so designed that first the connection wires of the measuring resistance are lengthened by electrically insulated connection wires of the connection circuit. The connection from the rather thin connection wire of the measuring resistance to the considerably thicker connection wire of the supply circuit is produced by welding or hard soldering. If a fiber glass-jacketed supply lead is used, it must first be stripped. In order to rule out a short circuit during operating conditions, an electrical insulation for the connection wires of the measuring resistance and for the area of the weld or hard solder joint must be provided in some form. Moreover, the connection wires must be relieved from traction either by cast masses or special ceramic molded parts (see DGm 1,855,262).
The electrical insulation of the connection circuit for high temperature use is accomplished either with ceramic capillary tubes, which, however, constitute a large proportion of the overall material costs and often stand in the way of miniaturization due to their geometrical dimensions, or is ensured by fiberglass casings, which are stiffened by an organic impregnation for production reasons. This impregnation must be removed in an extra firing process. For fixing the position of the measuring resistance, it is furthermore customary to introduce a ceramic adhesive into the tip of the measuring unit protective tube. According to the prior art, a high temperature measuring unit is thus produced with a great number of individual parts and process steps, which either cannot be automated at all, or are automatable only at great expense.
SUMMARY OF THE INVENTION
Against this background, underlying the present invention is the object of creating an economical process for manufacturing a sensor arrangement, the process comprising a few standardized individual parts and being on the basis of easily automatable process steps from SMD (surface mounted device) technology. This sensor arrangement should be suitable for temperature measurement above about 400° C.
The object is accomplished according to the invention for the process of manufacturing a sensor arrangement for temperature measurement, in that at least one thick film conducting paste is applied to the contact surface of the carrier element and/or the measuring resistance before the measuring resistance is laid on the high temperature-resistant carrier element provided for it. The measuring resistance with its contact surfaces is then set upon the carrier element and then fired in a temperature range between 1000° C. and 1350° C. and thereby bonded and attached.
Applying the paste can take place by screen printing, dispensers or brushing, for example. Subsequently, the measuring resistance is bonded by the so called flip chip technique. That is, it is set down with its contact surfaces (“face down”) on the corresponding contact surfaces of the carrier element which have been pre-prepared with thick film conductive paste, and then fired at temperatures between 1000° C. and 1350° C. Additional aids for fixing the position are not necessary with the process of the invention, since the thick film conducting paste pressed on in the screen printing process has an approximately rectangular profile so that, in contrast with the spherical surface of solder pads, the flat measuring resistance remains in its position after being applied. This process requires fewer individual operations and can be easily automated.
Thick film conducting pastes of PtPd, PtRh or Pt have proven themselves as a contact-forming layer for the contact surfaces for bonding the measuring resistance. In order to improve the adhesion between the contact surfaces and the carrier element or the ceramic substrate of the measuring resistance, it has proven advantageous to construct the contact surfaces in several layers, as a so-called thick film system, in which preferably two thick film conducting pastes are applied one after the other to the contact surfaces, wherein the thick film conducting paste for the first application to the contact surfaces contains in addition to Pt, PtPd or PtRh a fritted glass component which improves the adhesion to the base, while the paste for the repeated application must contain no fritted glass in addition to Pt, PtPd or PtRh and organic binding agent. The fritted glass component in the first thick film conducting paste amounts to about 0.5 to 20% by weight. Since the measuring resistance as a standard component is frequently equipped with platinum contact surfaces, the use of a platinum paste or a paste containing a platinum alloy is an expedient choice.
Preferably, a firing temperature of 1200° C. is selected for attaching and bonding the measuring resistance to the carrier element, for which 15 minutes is expedient as a period for holding at peak temperature.
Setting the measuring resistance on the contact surfaces of the carrier element can take place directly on the still wet thick film conducting paste or, alternatively, only after pre-drying at temperatures between 50° C. and 400° C., and optionally after a pre-sintering of the thick film conducting paste at a temperature between 1000° C. and 1350° C., preferably about 1200° C., subsequent to the pre-drying.
Outfitting the preferably ceramic ca
Dietmann Stefan
Sander Margit
Wienand Karlheinz
Akin Gump Strauss Hauer & Feld L.L.P.
Herarus Electro-Nite International N.V.
Johnson Jonathan
Ryan Patrick
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