The invention relates to an electrical component, especially an NTC component, and also to its fabrication.
Conventional electroceramic components normally have contact bodies on the surface of the ceramic base body which are used for making electrical contacts to the components and which, among other things, guarantee the SMD (surface mounted device) capability of the component. These electrically conductive contact bodies or terminations are usually composed of a material that is different from that of the ceramic base body, with the result that problems arise concerning the adhesion of the contact bodies to the base body.
From U.S. Pat. No. 5,245,309, ceramic NTC components are known in which the ceramic base body is fabricated using multilayer technology and is composed of ceramic layers with internal electrodes arranged in these layers. These internal electrodes each contact an outer contact body and form an electrode terminal. Furthermore, an outer passivation layer, e.g., glass, can be applied on the surface of the component. With this technology, it is possible to realize different electrical resistances by varying the arrangement of the internal electrodes for components with the same component standard.
From DE 10159451 A1, an NTC component with a base body is known, which is composed of at least a first and a second spatially formed ceramic area part made from different NTC materials, wherein at least one first and one second contact layer are provided on the surface of the base body. Likewise, by varying both the relative arrangement and the relative portions of the two ceramic area parts in the base body and also through suitable material combinations for equal dimensions of the base body, NTC components with different electrical characteristics are fabricated.
From DE 4207915, it is known that the resistance value of a thermistor element can be changed by varying the distance between the ends of the internal electrodes. In this way, the production low-resistance NTC components that are particularly thin, and therefore susceptible to damage through fractures or cracks, can be avoided.
At the base of the present invention lies the problem of proposing an electrical component resistant to aggressive environmental conditions.
The problem is solved in terms of an electrical component and in terms of its fabrication by the features of the respective independent claim.
Advantageous embodiments of the invention follow from the dependent claims.
An electrical component is proposed, comprising:
the surface of the base body is provided with a bonding layer having a composition selected such that its bonding strength decreases when heated at the ends of the electrodes.
According to one embodiment of the invention, the electrical component has at least one electrical contact body applied to the surface of the base body and connected to the ends of the electrodes in an electrically conductive way. Here, the surface of the base body is provided with a bonding layer for at least partial connection of the contact body to the ceramic part of the surface of the base body.
An electrical component constructed in this way has the advantage that the bonding layer is run off/purged by itself when it is heated by the electrode ends and the area exposed in this way allows contacts to be made with the contact bodies to the electrode ends. This is done without a bonding layer remaining between the electrode ends and the contact body to a significant extent that changes the resistance value of the electrical component.
Thus, advantageously, the maximum surface area of the ceramic surface of the base body is used for bonding with the contact body. Simultaneously, the ceramic base body is provided with a bonding layer that protects against aggressive environmental conditions in the area where the contact body is not arranged on the substrate.
The contact bodies can as a matter of course also be realized as contact layers or also as ends of contact wires that create a connection to an external current and voltage source.
Advantageously, the contact bodies are connected to the ceramic areas of the ceramic surface due to the special characteristic of the bonding layer, even though at the same time they are through-contacted with the electrode ends arranged in the same area.
Another advantage is to be seen in that the contact bodies bond more strongly with the ceramic substrate and therefore exhibit a high pull-off resistance.
Until now, during a thermal fixing phase, the contact bodies could only be burned in on the ceramic substrate with simultaneous and considerable change to the basic resistance value of the electrical component. With one of the electrical components proposed here, it is particularly favorable that the effect of the burning in of the contact bodies on the resistance value of the electrical component is reduced by the coating of the ceramic substrate. This is because bonding and decoupling layers no longer have to be bonded to the electrode ends and the through-contact of the electrodes to the contact body is particularly clean. In addition, the ceramic substrate is electrically insulated from the contact bodies so that a reduced change in the basic resistance value of the electrical component can also be achieved here. For this purpose, it is preferred that the bonding layer is electrically insulating and is thus also a decoupling layer.
Preferably, the reduced adhesion of the bonding layer to the ends of the electrodes lies in a temperature range between 50 to 200 K below the burn-in temperature of the contact body. This results in the advantage that during the burn-in of the contact body on the ceramic substrate, sufficient softening of the bonding layer takes place so that the bonding layer is by itself purgeable/runs off from the ends of the electrodes. For this purpose, the bonding layer preferably comprises a lead-borosilicate mixture so that it is thoroughly purgeable from the ends of the electrodes during softening.
For fabricating an electrical component, a method is proposed in which
Poor bonding is also understood to mean that the bonding layer no longer adheres to the ends of the electrodes in the heated state.
The fabrication process is preferably extended in such a manner that a contact body is applied to the base body, whereby the electrical component is heated during a thermal fixing phase so that the bonding layer is run off/purged from the parts of the surface of the base body formed with electrodes and a through-contact of the contact body to the ends of the electrodes is achieved.
The term “thermal fixing phase” is understood to be a thermal phase in which the contact bodies are burned in on the ceramic base body—the burn-in of the contact bodies is thus a part of the thermal fixing phase.
The invention is explained in more detail with reference to the following embodiments and figures, wherein:
The electrodes preferably comprise a silver-palladium (Ag—Pd) alloy. The contact bodies comprise a base metallization made from silver (Ag) that preferably is reinforced galvanically with a nickel and a tin layer.
Such an electrical NTC component is preferably fabricated in the following way: a glass layer 5 is applied to the sintered ceramic base body 2. This is performed preferably by a method for depositing thin layers, e.g., through immersion in a glass slurry, spraying of a glass slurry and subsequent or accompanying drying. The glass slurry is advantageously provided with a bonding agent, thereby improving the adhesion of the dried layer. Typical layer thicknesses, dried green, lie in the range between 1 and 20 μm. An exemplary glass slurry consists of 100 g of glass powder, 3-20 g of bonding agent and 500-1000 g of water. As a bonding agent, cellulose derivatives, for example carboxymethyl cellulose, hydroxypropylmethyl cellulose, polyvinyl alcohol, polyethylene glycol and silicone resins may be used.
The composition of the glass is tailored to the wetting in particular of the ceramic body, i.e., the ceramic surface of the ceramic substrate. A typical composition of the glass can stem from the systems B—Si (borosilicate), in particular lead-borosilicate (Pb—B—Si), or Zn—B—Si (tin borosilicate), optionally with other additives, for example Ba, Al, Cu, Fe, Cr, Mg. The coated ceramic base body 2 obtained in this way is now provided with the contact bodies or the terminations 4 in a known way through immersion and drying. After the contact bodies are applied to the ceramic substrate for the first time with this step, the bonding layer already bonds to the surface of the contact body since its surface comprises a surface composition resulting in the bonding layer penetrating between the particles of the contact body surface.
A permanent bond between the contact body and the bonding layer is therefore also guaranteed in the later thermal fixing phase. The thermal fixing, typically in the range between 650° C. and 850° C., follows thereafter.
The glass is selected so that its softening point lies ca. 50-200 K below the burn-in temperature of the contact body or the termination. In this thermal fixing phase, the bonding layer is heated to a temperature at which it begins to soften and is finally run-off/purged from the ends of the electrodes. Thus, the bonding layer remains bonded to the ceramic surface of the ceramic base body but not to the ends of the electrodes, thereby allowing the formation of a through-contact from the termination or the contact body to the ends of the electrodes. The through-contacts of the contact bodies to the electrode ends are realized since the contact body partially softens during the thermal fixing phase and thus flows onto the electrode ends. This liquefied contact body material may then harden and thus forms a solid electrical contact to the electrodes.
The composition of the bonding layer is to be selected such that the general interaction between the glass and the electrode material is considered insofar as the removal of the softened glass layer in the thermal fixing phase is simplified. In general, care is to be taken that the electrode ends are composed of a different material than the contact bodies to the extent that the bonding layer forms a significantly poorer bond to the electrode ends than to the contact bodies.
Due to the running off/purging of the bonding layer from the electrode ends during the thermal fixing phase, the previously common processing step in which the bonding layer parts still bonded to the ends of the electrodes must be ablated, is eliminated. As a matter of course, the thickness of the bonding layer applied to the surface of the ceramic substrate is selected so that a complete softening of the bonding layer at the ends of the electrodes can be achieved during the thermal fixing phase.
The bonding layer remaining between the contact bodies and the ceramic surface of the ceramic base body produces a reinforced pull-off resistance of the contact body, so that a pull-off resistance of the contact body of up to 50 N can be achieved. In contrast, reference components without a bonding layer between the contact bodies and the ceramic surface can have a defect percentage of typically 10-20% during a peel-off test, while the component proposed according to the invention passes this test with 100%.
The change in the basic resistance value of the electrical component through the burning-in of the contact body can be reduced from ca. 12% to below 4% with an electrical component according to the invention. The change in the resistance of the ceramic base body during the galvanic reinforcement of the contact body, caused by the ceramic removal at the exposed surface of the ceramic substrate in acid galvanic baths, is reduced from 2% to below 0.5% (see
It is preferred that the ceramic base body is fabricated using known multilayer technology.
The bonding layer applied to the areas of the base body not lying between the contact body and the base body is used as a protective layer that is resistant to aggressive environmental conditions in other processing steps, for example during the galvanic reinforcement of the termination with nickel-tin layers or during the onset of flux material during soldering.
The left group of bars shows the case when the ceramic base body is provided with a bonding layer according to the invention, whereby:
1. The left bar B1 shows a small change in the resistance value ΔW1 of the ceramic base body in a period of 10 min before and after the galvanic reinforcement of the termination at 25° C.
2. The central bar B2 shows a minor change in the resistance value of the base body in a period of 10 min before and after the galvanic reinforcement of the termination at temperatures between 25 and 100° C.
3. The right bar B3 shows the negative change in the resistance value of the ceramic base body during the thermal fixing phase.
The central group of bars shows the case when the ceramic base body is also provided with a bonding layer according to the invention; this time with a thicker layer deposit, whereby a waiting time of 20 min after the above delineated time points 1 to 3, until the resistance value is measured, was included here. As in the left group of bars, a high stability of the resistance value of the ceramic base body is also to be seen here.
The right group of bars shows the reference case in which there is no bonding and decoupling layer according to the state of the art between the contact body or the termination and the ceramic substrate. In this case, the changes in the resistance values of the ceramic substrate in the above delineated cases 1 to 3 are much higher.
This patent application relates to an electrical component, such as an NTC component, and also to fabrication of the electrical component.
An electroceramic component includes electrically conductive contact bodies on a ceramic base body surface, which are used for making electrical contacts and which, among other things, enable SMD (surface mounted device) mounting. These electrically conductive contact bodies, or terminations, are usually comprised of a material that is different from that of the ceramic base body. As a result, problems arise with adhering the contact bodies to the base body.
U.S. Pat. No. 5,245,309 describes a ceramic NTC component in which a ceramic base body is fabricated using multilayer technology and is comprised of ceramic layers with internal electrodes arranged in these layers. These internal electrodes each contact an outer contact body and form an electrode terminal. Furthermore, an outer passivation layer, e.g., glass, can be applied on a surface of the component. With this technology, it is possible to obtain different electrical resistances by varying the arrangement of the internal electrodes for components with a same component standard.
DE 10159451 A1 describes an NTC component with a base body, which is comprised of at least first and second spatially formed ceramic area parts made from different NTC materials. At least one first and one second contact layer are on a surface of the base body. It is possible to fabricate NTC components with different electrical characteristics by varying both the arrangement and the relative portions of the two ceramic area parts in the base body, and also by varying material combinations without changing the dimensions of the base body.
DE 4207915 describes that a resistance value of a thermistor element can be changed by varying a distance between ends of its internal electrodes. In this way, it is possible to avoid production of low-resistance NTC components that are particularly thin, and therefore susceptible to damage through fractures or cracks.
Described herein is an electrical component that comprises a ceramic base body with a partially ceramic surface, and a plurality of electrodes arranged in the ceramic base body. The ends of the electrodes form a part of the surface of the base body. The surface of the base body includes a bonding layer having a composition with a bonding strength that decreases when heated at ends of the electrodes.
According to one embodiment, the electrical component has at least one electrical contact body applied to a surface of the base body and connected to ends of the electrodes in an electrically conductive way. The surface of the base body includes a bonding layer for at least partly connecting the contact body to the ceramic part of the surface of the base body.
In the foregoing electrical component, only the bonding layer is run off/purged when it is heated by the electrode ends. The resulting exposed area allows contacts to be made between the contact bodies and the electrode ends. This is done without a bonding layer remaining between the electrode ends and the contact body which, to a significant extent, changes the resistance value of the electrical component.
Thus a maximum surface area of the ceramic surface of the base body can be used for bonding with the contact body. The ceramic base body also includes a bonding layer that protects against adverse environmental conditions in an area where the contact body is not on the substrate.
The contact bodies can be implemented as contact layers or as ends of contact wires that create a connection to an external current and voltage source.
Advantageously, the contact bodies are connected to ceramic areas of the ceramic surface due to a special characteristic of the bonding layer, even though they are also through-contacted with electrode ends arranged in the same area.
Another advantage is that the contact bodies bond more strongly with the ceramic substrate and, therefore, have a high pull-off resistance.
Heretofore, during a thermal fixing phase, contact bodies could only be burned in on the ceramic substrate with simultaneous and considerable change to the basic resistance value of the electrical component. In the electrical components described herein, an effect of burning-in the contact bodies on resistance value of the electrical component is reduced by virtue of the coating on the ceramic substrate. This is because bonding and decoupling layers no longer have to be bonded to the electrode ends and the through-contact of the electrodes to the contact body is particularly clean. In addition, the ceramic substrate is electrically insulated from the contact bodies so that a reduced change in the basic resistance value of the electrical component can also be achieved. For this purpose, the bonding layer is electrically insulating and is thus also a decoupling layer.
The reduced adhesion of the bonding layer to the ends of the electrodes may be in a temperature range between 50 to 200 K below the burn-in temperature of the contact body. As a result, during burn-in of the contact body on the ceramic substrate, sufficient softening of the bonding layer takes place so that only the bonding layer is purgeable/runs off from the ends of the electrodes. The bonding layer may comprise a lead-borosilicate mixture so that it is thoroughly purgeable from the ends of the electrodes during softening.
Also described herein is a method for fabricating an electrical component. According to the method, a ceramic base body is generated with a partially ceramic surface. A plurality of electrodes are formed in an interior of the ceramic base body in such a manner that the ends of the electrodes form a part of the surface. The surface of the base body is wetted with a bonding layer that bonds poorly to the ends of the electrodes at a given temperature. Poor bonding is understood to mean that the bonding layer no longer adheres to the ends of the electrodes when heated.
The fabrication process may be extended so that a contact body is applied to the base body. The electrical component is heated during a thermal fixing phase so that the bonding layer is run off/purged from the parts of the surface of the base body formed with electrodes, and a through-contact of the contact body to the ends of the electrodes is formed.
The term “thermal fixing phase” is understood to be a thermal phase in which the contact bodies are burned-in on the ceramic base body—the burn-in of the contact bodies is thus a part of the thermal fixing phase.
Embodiments are explained in more detail with reference to the following figures.
The electrodes may comprise a silver-palladium (Ag—Pd) alloy. The contact bodies comprise a base metallization made from silver (Ag) that may be reinforced galvanically with a nickel and a tin layer.
An electrical NTC component such as that of
The composition of the glass is tailored to the wetting of the ceramic body, i.e., the ceramic surface of the ceramic substrate. A typical composition of the glass can stem from the systems B—Si (borosilicate), in particular, lead-borosilicate (Pb—B—Si), or Zn—B—Si (tin borosilicate), optionally with other additives, for example Ba, Al, Cu, Fe, Cr, Mg. The coated ceramic base body 2 obtained in this way includes contact bodies or terminations 4 obtained through immersion and drying. After the contact bodies are applied to the ceramic substrate for the first time, the bonding layer bonds to the surface of the contact body, since its surface has a composition that causes the bonding layer to penetrate between particles of the contact body surface. A permanent bond between the contact body and the bonding layer is, therefore, also guaranteed in the later thermal fixing phase. Thermal fixing, typically in the range between 650° C. and 850° C., follows thereafter.
The glass is such that its softening point is ca. 50-200 K below the burn-in temperature of the contact body or the termination. In this thermal fixing phase, the bonding layer is heated to a temperature at which it begins to soften and is finally run-off/purged from the ends of the electrodes. Thus, the bonding layer remains bonded to the ceramic surface of the ceramic base body, but not to the ends of the electrodes, thereby enabling formation of a through-contact from the termination or the contact body to the ends of the electrodes. The through-contacts of the contact bodies to the electrode ends are obtained, since the contact body partially softens during the thermal fixing phase and thus flows onto the electrode ends. This liquefied contact body material may then harden and thus forms a solid electrical contact to the electrodes.
The composition of the bonding layer is such that the general interaction between the glass and the electrode material is considered insofar as removal of the softened glass layer in the thermal fixing phase is simplified. In general, care is to be taken that the electrode ends are comprised of a different material than the contact bodies to the extent that the bonding layer forms a significantly poorer bond to the electrode ends than to the contact bodies.
Due to the running off/purging of the bonding layer from the electrode ends during the thermal fixing phase, the previously common processing step in which the bonding layer parts still bonded to the ends of the electrodes must be ablated, is eliminated. The thickness of the bonding layer applied to the surface of the ceramic substrate is such that a complete softening of the bonding layer at the ends of the electrodes can be achieved during the thermal fixing phase.
The bonding layer remaining between the contact bodies and the ceramic surface of the ceramic base body produces a reinforced pull-off resistance of the contact body, resulting in a pull-off resistance of the contact body of up to 50 N. In contrast, reference components without a bonding layer between the contact bodies and the ceramic surface can have a defect percentage of typically 10-20% during a peel-off test. The component described herein passes this test with 100%.
The change in the basic resistance value of the electrical component through the burning-in of the contact body can be reduced from ca. 12% to below 4%. The change in the resistance of the ceramic base body during galvanic reinforcement of the contact body, caused by ceramic removal at the exposed surface of the ceramic substrate in acid galvanic baths, is reduced from 2% to below 0.5% (see
The ceramic base body may be fabricated using known multilayer technology.
The bonding layer applied to the areas of the base body that are not between the contact body and the base body is used as a protective layer that is resistant to adverse environmental conditions in other processing steps, for example, during galvanic reinforcement of the termination with nickel-tin layers or during onset of flux material during soldering.
The left group of bars shows the case when the ceramic base body has a bonding layer. More specifically:
1. The left bar B1 shows a small change in the resistance value, ΔW1, of the ceramic base body in a period of 10 min before and after the galvanic reinforcement of the termination at 25° C.
2. The central bar B2 shows a minor change in the resistance value of the base body in a period of 10 min before and after the galvanic reinforcement of the termination at temperatures between 25 and 100° C.
3. The right bar B3 shows the negative change in the resistance value of the ceramic base body during the thermal fixing phase.
The central group of bars shows the case when the ceramic base body has a bonding layer; this time with a thicker layer deposit, which includes a waiting time of 20 min after the above time points 1 to 3, until the resistance value is measured. As in the left group of bars, a high stability of the resistance value of the ceramic base body is also shown.
The right group of bars shows the reference case in which there is no bonding and decoupling layer according to the state of the art between the contact body or the termination and the ceramic substrate. In this case, the changes in the resistance values of the ceramic substrate in the above cases 1 to 3 are much higher.
Number | Date | Country | Kind |
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10 2004 037 588.7 | Aug 2004 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/DE05/01377 | 8/3/2005 | WO | 9/6/2007 |