MULTIFUNCTIONAL PROTECTIVE COMPONENT

Abstract: Subject of the present invention is multifunctional protective component. This new component provides simultaneous protection against voltage strokes and against both high and low frequency disturbances. It is composed of two discrete chip components, namely of multilayer ZnO polycrystalline diode and multilayer ceramic condenser or multilayer self-limiting condenser and multilayer ceramic condenser, which are mutually mechanically connected with non-conductive low-temperature glass (frite), parallel electrical connection between both chips being created with second metallisation, and common outer electrodes of newly formed chip. This new component is suitable for surface mounting as well as in terminal leads form.

Description: MULTIFUNCTIONAL PROTECTIVE COMPONENT Field of invention Subject of the present invention belongs to the field of protective electronic elements, used in safeguarding of other electronic elements and devices against voltage and current strokes, and against high and low-frequency disturbances. Technical problem Miniaturisation and increase of complexity of contemporary electronic elements and systems, as well as their increasingly wider application simultaneously increase their sensitivity to electronic discharge (ESD), voltage excess and strokes and frequency disturbances. These phenomena may disable normal functioning of separate components, decrease their stability and reliability and may even destroy them. In this way above phenomena jeopardise normal functioning of very complex and expensive electronic systems Sources of these phenomena may be various. For instance the largest source of electrostatic discharge is man itself in the process of manipulation with electronic devices. Most typical source of voltage strokes is lightning, which induces charge in electrical and telecommunication lines, this charge being transferred through the lines to electronic elements. And some of electronic elements themselves (e.g. electromotor, relay) induce disturbances of various frequencies and emit them in their closest surrounding. Thus each separate electronic component and its part shall be protected with special components that provide such protection. On the other hand this means that disturbance emission shall be prevented at the source. Only use of components, with following properties may provide protection against ESD and voltage strokes: non-linear I-U characteristic, short response time and ability to absorb larger amounts of energy. Such characteristics are available in some elements, like Zener diode, multilayer ZnO polycrystalline diode (Varicon), varistor, and condensers with varistor characteristic or self-limited breakthrough. The simplest elements for protection against frequency disturbances are condensers with capacitance up to do 100 nF for high frequencies and in case of lower or radio frequencies with capacitance up to 2000 nF. Consequently it is clear that in order to protect against all mentioned undesired phenomena, such protective component shall have all required properties: non-linear I-U characteristic, short response time, ability to absorb larger amount of energy, and adjustable capacitance in range from 10 to 2000 nF. Beside that it must be smaller than any existing solutions and shall offer surface mounting option with terminal leads. Subject of this invention, multifunctional component has exactly such properties. State of art Beside the most expensive solution, namely use of two discrete elements in parallel electrical connection e.g. combinations Zener diode - condenser or varistor-condenser, there are some other contemporary solutions one of which is condenser with varistor properties as described in European Patent 418394A. Mentioned condenser is based on SrTiO 3 , which provides high value of dielectric constant (ε > 20000). Multilayer manufacturing technology provides wide scope of capacitance (10 - 2000 nF) at relatively small dimensions. However its worst side is, bad varistor characteristic and low value of non-linearity coefficient, soft knee and also high leakage current, high value of breakthrough voltage temperature coefficient and very narrow range of operating voltage. Further more materials for manufacturing such elements and production technology are very expensive. In USA patent US 5,146,200 hybrid bond between multilayer chip varistor and multilayer chip condenser is disclosed. Physical bond of these two elements is achieved with gluing and parallel electrical connection is achieved with soldering. Components as self-limiting multilayer condenser as shown in USA Patent No 4,729,058 and multilayer ZnO polycrystalline diode (Varicon diode) have very non-linear I-U characteristic and high self capacitance, which may within real dimensions reach up to 100 nF. In that way these two mentioned components provide protection against ESD and voltage strokes and effectively filter high frequency disturbances, but not low frequency disturbances. Description of invention New multifunctional component is based on the following facts: self-limiting multilayer condenser and Varicon diode have such properties, which provide effective protection against ESD and voltage strokes in voltage range from 4 to 150 V contemporary commercially available chip condensers have very high capacitance while dimensions are small both components have similar shape and similar dimensions. Present invention proves that low temperature scorching provides possibility to create monolith element from two discrete elements, this newly created element preserving all unchanged functions of both discrete elements, which are mutually electrically parallel connected in new element. As mentioned above, two discrete components are used to produce this new component. One of them must provide good ESD protection and good protection against voltage strokes. To meet these demands self-limiting condenser or Varicon diode may be used, both have excellent properties of protective component. Second component only completes already high self capacitance of Varicon diode or self-limiting condenser up to preferred value, which is necessary for successful protection against high or low frequency disturbances. For this purposes use of multilayer ceramic condenser is preferred. Ceramic condenser provides desired capacitance, even up to 2000 nF and is manufactured in similar shapes and dimensions as Varicon diode or self-limiting condenser. Both elements to bond shall have equal planar dimensions (wideness and length) and their largest sides must be even. Figure 1 shows Varicon diode chip (1) and condenser chip (2), each separately. As shown in figure 1, both components have same shape, equal planar dimensions, and on their shortest sides outer silver electrodes (3) in (4), which are already formed to allow electrical checking of both discrete components. Physical bond between two chips is made in such manner, that thin layer of suspension is brought on only one of two largest area of Varicon diode or condenser, in such way to cover whole area of the chip between two electrodes (5). Suspension is composed from dust of low temperature high resistant glass (frite), with temperature of glassification between 500° and 800 °C, binder and solvent, which allow glass (frite) to be placed to the chip surface with printing, brash or in some other manner. Thickness of the suspension layer brought to the chip surface is between 10 and 500 μm. Immediately after suspension is placed, second unplastered chip is placed with its larger side on the plastered side of the first chip in such manner that all edges are even, and their outer electrodes (3) in (4) fall in, and lay one upon another on both sides of the chips, as shown in figure 2. Both chips with glass inter layer form sandwich structure. So placed chips are than scorched at temperature between 500° in 800 °C. Binder and solvent evaporate at lower temperatures so only glass remains between chips (1) in (2). At certain temperature glass liquefies and diffuses in bodies of both components. Depth of diffusion may be controlled via glassification parameters (time and temperature) to ensure that glass will not diffuse to inner electrodes depth. In certain temperature range glass turns into thin amorphous layer with good mechanical, heat and insulating properties, after cooling. Glass layer is very good bound with both chips, due diffusion into both chip bodies. In that way, with glass layer, very good mechanical bond between both elements is achieved, and the surface between both elements has no porosity. Therefore we may say, that with glass, one monolith element composed of two discrete elements is created from two discrete elements. Regardless to the fact that outer electrodes of both chips are in physical contact, we may still not claim that reliable electric connection between them is achieved. Therefore so formed composition - monolith is repeatedly metallised with Ag or AgPd paste in such manner, that both smaller sides are plunged to certain depth into Ag or AgPd paste, and uninterrupted outer electrodes (6) of new component are created, both being at the same time in contact with both outer electrodes of both chips on the inner side. After this paste is scorched at the temperature from 550° to 850 °C, reliable electric contact, and parallel electrical connection between Varicon diode and ceramic condenser. When AgPd is used as second electrode paste, new chip (e.g. protective multifunctional protective component) is suitable for surface mounting. If component with terminal leads is desired, second metallisation will be performed with Ag paste. So achieved component is placed between terminal leads, which will be finally metallurgical and electrical connected with outer electrodes in soldering process. Additional moulding into epoxy resins provides standard shapes of components with terminal leads. Example Using self-limiting condensers and Varicon diodes on one side and multilayer condenser on other side, varieties of multifunction protective components were made, using above described technique. Some of results are shown in table 1. Table 1 Un - breakdown voltage 1 mA α - non-linearity coefficient Imax - Higher impulse current, without consequences for component C - capacitance measured at value of 1 kHz

Claims: CLAIMS 1. Multifunctional protective component, characterised in that, that provides simultaneously protection against voltage strokes and frequency disturbances, and that the component is composed of two chip components as multilayer ZnO polycrystalline diode and multilayer ceramic condenser or multilayer self-limiting condenser and multilayer ceramic condenser, mutually connected with thin layer of non-conductible glass, where the parallel electric connection between both chips is achieved with second metallisation, and with common outer electrodes of new composed chip, respectively. 2. Multifunctional protective component according to claim 1, composed of two different chip components, characterised in that, that both chips have equal shape and equal planar dimensions, and lay one on top of another in such manner, that their outer electrodes fall in touching one another, while thin layer of glass is present between larger sides, where the chips interact, where glass layer in the process of glassification diffused into bodies of both chips and created mechanical connection between both chips. 3. Multifunctional protective component according to claim 1, characterised in that, that parallel electric connection between both mechanically connected chips is made with greasing and scorching of common Ag or AgPd outer electrodes of new formed chip. 4. Multifunctional protective component according to claim 1, characterised in that, that it is made in accordance with the process, which consists from following important process steps: a) bringing suspension of high-resistant low-temperature glass onto the largest surface of one of the components b) forming sandwich structure and evening the chips c) low-temperature scorching in the temperature range between 500° and 850 °C d) forming of outer electrodes with Ag or AgPd paste and scorching 5. Process according to claim 4, characterised in that, that 10 - 500 μm thick layer of high- resistance low-temperature glass frite in form of suspension is brought onto only one large area of only one chip of the pair with printing, brush or in some other manner, to cover the whole area of the chip between both outer electrodes. 6. Process according to claim 4, characterised in that, that second chip is laid upon the greased one in such manner, to create sandwich, where the glass layer lies between them, all their edges are mutually even, and their outer electrodes fall in one another and touch one another. 7. Process according to claim 4, characterised in that, that created sandwich, composed from two chips and thin glass layer between them, after removal of solvent and binder from brought layer, is scorched at the temperature in range from 500° and 850 °C. 8. Process according to claim 4, characterised in that, that both smaller sides of new formed monolith chip, composed of two elements, are metallized with Ag or AgPd paste to create common outer electrodes of new chip, and that in the course of scorching at the temperature between 550° and 850° C common electrodes provide parallel electric connection between both chips, that are basic elements of new chip.

Inventors: ZIVIC ZORAN, ZIVIC, ZORAN
Applicants: ZIVIC ZORAN, ZIVIC, ZORAN
Application year: 1997
Main classification: H01G4
IPC codes: H01C7, H01G4