Electrical insulation of connection wires with residual elasticity on contact pads

Abstract

The invention describes a fixing bead for insulating connection wires on passive components, in particular sensors, preferably temperature sensors, on an inorganic substrate, in particular a metal-oxide, semiconductor and / or glass substrate, the fixing bead comprising a hydrophobic polymer composition, a passive component, a method for producing a passive component, a passive component obtainable by this method, and the use of such fixing beads for insulating connection wires on passive components.

Description

[0001] DESCRIPTION

[0002] Electrical insulation of connecting wires with residual elasticity at contact pads

[0003] The present invention relates to electrically insulating fixing drops, a passive component, a method for producing a passive component, a passive component obtainable by this method, and the use of such fixing drops for the electrical insulation of connecting wires on passive components.

[0004] Passive components are generally understood to be those components that, unlike active components, do not exhibit an amplifying effect or have a control function. Examples of passive components include resistors, capacitors, sensors, and heaters.

[0005] For the purposes of the invention, a passive component preferably comprises a substrate, a multilayer structure located on the substrate, at least one connecting wire, and a fixing drop for insulation, for fixing, and, in low-temperature applications, only to a limited extent for strain relief of the at least one connecting wire. A stranded wire or compacted stranded wire is also possible as the connecting wire. The multilayer structure, in turn, preferably comprises at least one contact pad to which the at least one connecting wire is fixed, at least one electrical conductor track, and at least one dielectric layer, for example a screen-printed glass layer or a polymer layer, which covers the conductor track but leaves the contact pad essentially exposed.

[0006] Fixing drops primarily serve to provide strain relief for at least one connecting wire. For sensors designed for operating temperatures above 200°C, the fixing drops are preferably made of glass or glass ceramic. This allows for reliable measurements at lower temperatures. Furthermore, the fixing drop protects the area it covers from possible external influences such as condensed air humidity. At operating temperatures below 300°C and thus a lower absolute expansion distance, mechanical strain relief of the connecting wires becomes less important during measurement.

[0007] Glass fixative drops are generally understood to be those based on a mineral glass composition. Such glass compositions according to the state of the art contain, for example, SiCh, Al2O3, B2O3, and ZnO and contain only small amounts of carbon. In particular, glass fixative drops are not based on polymeric compounds, especially not on organic polymers.

[0008] For the mass production of passive components, several structures are arranged on a common substrate, with at least one lead wire mechanically fixed to the respective structure. By applying a continuous fixation droplet, which runs as a continuous layer over several structures and at least partially covers them, the at least one lead wire is insulated and, in many cases, also relieved of strain. The subsequent separation of the components then involves severing the substrate and the fixation droplet.

[0009] There are various options available for singulating the passive components, with the passive components usually being singulated by sawing, laser singulation, or laser scribing and breaking. According to the invention, singulation should take place after the fixation has been applied. In a preferred application, singulation is possible using the fixation drop that has already been applied and thermally processed. Alternatively, it is also possible for each component to be singulated later to have a separate fixation drop, and singulation to take place between these. Although this procedure of sawing or laser singulation is associated with additional effort, particularly when the passive components comprise a hard substrate, e.g. based on Al2O3, it can be used independently of the fixation drop and its shape and is associated with low failure rates.Alternatively, separation by breaking is significantly less labor-intensive and therefore more cost-effective. However, this method is associated with the challenge that breaking glass fixative drops is often associated with higher failure rates.

[0010] Since most fixation drops do not break in a defined manner, glasses that have not been optimized for this type of separation have crooked fracture surfaces or break at the wrong location, i.e. not through the predetermined breaking point in the substrate. A fixation drop that can withstand the tensile stresses acting on the fixation during breakage or compensate for them through elastic deformation long enough that the predetermined breaking point in the substrate breaks first, thus determining the fracture position in the fixation drop would be advantageous. The fracture surface is understood to be the newly created surface of a passive component as a result of the separation. In this context, microcracks or spalling at the fracture surface of glass fixation drops are examples of risks. Furthermore, the microcracks can also propagate into the interior of the fixation drops, although these are difficult to detect.Passive components with such poorly broken fixation beads are often unsuitable for further use. Even more serious are the damages (likely microcracks) inside the glass fixation beads, which are caused by the mechanical stress during breakage above the wires, where the fixation beads are at their thinnest. These damages are not visually detectable and only propagate through the glass volume when the component is subjected to thermal stress. Fine hairline cracks then appear above the connecting wires.

[0011] State-of-the-art breakable glass fixation drops for sensors with operating temperatures up to 180°C and beyond are porous and therefore only partially waterproof. Furthermore, in humid atmospheres, water can leach mineral ions from the glass fixation drops, distorting the measured values.

[0012] A further disadvantage of using glass fixative drops is that the firing of glass fixative drops is extremely energy-intensive, as they are fired at 600 to 700 °C for approximately 15 minutes. These high temperatures are also disadvantageous because, when using inexpensive nickel wires as connecting wires, the firing of glass fixative drops can only be achieved under protective gas / forming gas, and adjusting the furnace temperatures requires longer purging and setup times. The direct use of plastic-coated connecting wires is also not possible at such high temperatures.

[0013] Likewise, the glass fixation droplet can bleed during firing, increasing the covered area during heat treatment. However, since a minimum fixation height of the glass fixation droplet above the lead wires must be achieved to ensure complete encapsulation of the front areas of the lead wires, a correspondingly larger amount of glass must be applied. The front area of ​​the lead wire is defined as the area where the lead wire is in contact with the substrate.

[0014] The disadvantages described above are even more serious for glass fixation drops optimized for separation by breaking, since the firing of such breakable glass fixation drops is usually carried out at high temperatures, and breakable glass fixation drops have a larger pore volume than conventional glass fixation drops. In this context, it should be noted that with porous glass fixation drops, it is difficult to form a closed porosity and thus a closed surface during sintering. This can lead to open or broken pores at the exit points of the lead wires of the glass fixation drops, and the ingress of vapor and / or condensate from the environment can lead to electrochemical processes during the measurement.

[0015] One possibility to at least circumvent the requirement for breakability would be, as described above, to attach the fixation drops only at specific points to the connecting wires, so that breaking through the fixation drops would be eliminated.

[0016] The object of the present invention is to provide a fixing drop that, after application to a substrate and commissioning of the component, possesses residual elasticity and is preferably pore-free. In particular, the object of the present invention is to provide a fixing drop for electrically insulating connecting wires on passive components on an inorganic substrate, wherein the heat treatment can be carried out at lower temperatures, thus making a wider selection of materials available for the connecting wires and their optional sheathing.

[0017] This object was surprisingly achieved by a fixing drop according to claim 1, namely a fixing drop for the electrical insulation of contact pads and the connecting wires contacted thereon on passive components, in particular sensors, preferably temperature sensors, on an inorganic substrate, in particular metal oxide, semiconductor, metal and / or glass substrate, characterized in that the fixing drop comprises a hydrophobic polymer composition.

[0018] Hydrophobic or water-repellent polymer compositions are polymer compositions predominantly composed of at least one hydrophobic polymer that is insoluble or only nearly insoluble in water or other polar solvents. Examples of hydrophobic polymers include acrylates, epoxies, polyethylene, polyimides, polystyrene, polyvinyl chloride, polytetrafluoroethylene, siloxanes such as polydimethylsiloxane, polyesters, and polyurethanes. For the purposes of the present invention, a hydrophobic polymer composition is understood to mean a polymer composition that has a contact angle with water of at least 80°, measured according to DIN EN ISO 19403.

[0019] Preferably, the hydrophobic polymer composition with diiodomethane as test reagent has a contact angle of less than 48° measured according to DIN EN ISO 19403.

[0020] Preferably, the hydrophobic polymer composition has a surface tension measured according to DIN EN ISO 19403 of more than 20 mN / m, preferably more than 27 mN / m, even more preferably more than 33 mN / m.

[0021] Preferably, the hydrophobic polymer composition has a disperse fraction measured according to DIN EN ISO 19403 of more than 20 mN / m, preferably more than 27 mN / m, even more preferably more than 32 mN / m.

[0022] Preferably, the hydrophobic polymer composition has a polar content measured according to DIN EN ISO 19403 of less than 3 mN / m.

[0023] The fixation drop according to the invention offers numerous advantages. For example, this fixation drop is at least water-repellent and exhibits minimal cracking or cracking that is not optically detectable when the passive components are separated by breaking, thus enabling further assembly immediately afterward. In particular, the production of passive components can be carried out more energy-efficiently, and the connecting wires and their optional sheathing can be freely selected. This is due to the fact that the fixation drop according to the invention can be heat-treated at significantly lower temperatures than corresponding glass fixation drops. Furthermore, the use of media such as process or inert gas is not necessary at such low temperatures.

[0024] A further advantage of polymer-based fixer drops is the formation of an interface between the cover layer of the thermosensitive element, e.g., the cover layer of the meander, and the polymer. After the fixer firing, glass fixer drops generally adhere very well to the underlying glass layers. In contrast, the polymer-glass interface remains discrete. There is no mixing of the polymer with the adjacent glass layer. This discrete boundary region acts as a crack brake. As a result, cracks occurring in the fixer drop cannot penetrate beyond the interface into the cover layer. Stresses arising during the breaking process or other production steps, or during subsequent application, can be dissipated in the residually elastic fixer drop.

[0025] Due to the residual elasticity of the fixation and the firing at a lower temperature than glass, more precise target resistances with less scatter can be achieved in larger production runs. The elasticity also allows the fixation drop to be broken and easily machined or installed under slight compressive stress. At the same time, the fixation drop has a low volume fraction of pores.

[0026] Passive components whose connecting wires have been provided with the fixing drop according to the invention also have the advantage that the self-heating of the passive components is lower, which enables temperature measurements with lower systematic errors.

[0027] Another advantage is that the fixation drop according to the invention exhibits greater residual elasticity than conventional glass fixation drops, allowing it to act as a type of expansion joint. When temperatures change in a passive component, the connecting wires cool down first and shrink, while the fixation drop retains the heat longer and therefore contracts more slowly. Due to its residual elasticity, the fixation drop according to the invention can better follow these movements, thus minimizing critical crack formation at the points where the connecting wires exit the fixation drop.

[0028] A further advantage of the fixation drop according to the invention is the improved thermal conductivity of the compact material compared to porous glass. This also minimizes thermal stresses that occur in the sensor and at its contact surfaces with the environment during rapid or severe temperature changes.

[0029] Numerous specific details are discussed below to provide a thorough understanding of the subject matter. However, it will be apparent to one skilled in the art that the subject matter can be practiced and recreated without these specific details.

[0030] All features of one embodiment can be combined with features of another embodiment if the features of the various embodiments are compatible. The terminology used in the description of the present disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of the subject matter. As used in the present description and claims, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly dictates otherwise. The reverse is also true, meaning that the plural forms also include the singular forms. It is also understood that the term "and / or," as used herein, refers to and includes all possible combinations of one or more of the associated listed elements.It is further understood that the terms "includes," "including," "comprises," and / or "comprising," when used in the present description and claims, specify the presence of the stated features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0031] It is particularly advantageous to apply the fixative drop according to the invention over part of the surface of the cover layer. Although small pockets may form at the edge of the interface when voltages occur, the live parts, i.e., the lead wires and the contact pads, remain completely electrically insulated and protected from atmospheric moisture.

[0032] In a special embodiment, at least 80% of the sensor surface or the entire sensor surface can be covered by the fixing drop according to the invention.

[0033] In a further specific embodiment, the fixing drop according to the invention protrudes less than 10%, preferably less than 5%, particularly preferably less than 3%, of the sensor length beyond the substrate surface.

[0034] In another common design, the second side of the substrate remains essentially free of the fixation drop material. This facilitates the automated production of entire sensor arrays before the separation process into individual elements.

[0035] Specifically, the inventive design consists of a sensor element with a fixation droplet that is not yet fitted or secured in an additional casing. Therefore, the inventive sensor element is not primarily housed. However, subsequent attachment of an additional housing is possible. Furthermore, installation in a housing is also possible without first dismantling the fixation droplet.

[0036] The fixing drop according to the invention for electrically insulating connecting wires is preferably located on the structure in such a way that the contact pads for the connecting wires are covered.

[0037] Furthermore, it is advantageous that the meander surface is covered by 10 to 80%, preferably 10 to 60%, particularly preferably 20 to 50% with the fixing drop according to the invention.

[0038] The fixative drop according to the invention is at least water-repellent and provides a certain degree of protection against moisture. Fixative drops based on, for example, silicones or polyimides are also hydrophobic, which can increase resistance to water penetration or dissolution in water. Furthermore, the leaching of minerals, such as boron in glass fixative drops, can be prevented.

[0039] The fixing drop according to the invention is therefore preferably characterized in that the polymer composition comprises at least one silicone, preferably liquid silicone plastic or polyimides, in particular one-component polymers.

[0040] Preferably, the hydrophobic polymer composition of the fixing drop according to the invention is substantially free of fluorine compounds and thus complies with EU Regulation 2021 / 1297 regarding PFAS concentrations.

[0041] A further advantage of the preferred use of silicone as a polymer composition is that shrinkage during the manufacturing process is generally lower than with a comparably sized glass fixation drop. This allows for better encapsulation of the connecting wires in the shaft area of ​​a passive component.

[0042] However, the shrinkage of glass and polymer fixation drops is based on different processes. Glass fixation drops and glass-ceramic fixation drops shrink due to the loss of water or solvent from the applied fixation paste, as well as the sintering of the individual glass particles during the firing process. Silicone materials shrink primarily due to the chemical polymerization reaction and the removal of liquid components from the fixation paste. Shrinkage is accompanied by a reduction in volume.

[0043] Fixing beads filled with fillers whose coefficient of thermal expansion is lower than the thermal expansion coefficient of the substrate are particularly advantageous, as such filled fixation beads remain crack-free even during rapid temperature changes. The use of mineral, glass, or plastic fibers is also conceivable.

[0044] A further advantage of the filled polymer composition, especially a polymer composition filled with inorganic fillers, is the low shrinkage during application and curing of the fixative drop. The filled polymer compositions exhibit lower shrinkage even during curing, which minimizes stresses occurring at the interface between the cover layer and the fixative drop.

[0045] In principle, for substrates with low expansion coefficients, especially those lower than the expansion coefficient of the fixative drop, the shrinkage stresses from curing and the thermal stresses from temperature changes can add up. This applies especially to substrates with an expansion coefficient of less than 16 x 10' 6 K' 1 , measured over a temperature range of 0 to 100°C.

[0046] It is also advantageous to fill the fixation drop, whereby the difference in the expansion coefficients between the filling of the fixation drop and the polymer matrix of the fixation drop is less than 100 x 10' 6 K' 1 , preferably smaller than 30 x 10' 6 K' 1 , preferably smaller than 6 x 10' 6 K' 1 , particularly preferably smaller than 4 x 10' 6 K -1In this case, the risk of the droplet breaking open due to internal stresses during temperature changes is lower. Metal oxides with high expansion coefficients are also described in EP1072569B1.

[0047] Possible impurities, trace elements, water-soluble components or the occurrence of polarization effects in the minerals do not significantly impair the function of the filler and the fixing drop, since the filler is surrounded by the matrix of the fixing drop according to the invention. The fixing drop according to the invention is preferably characterized in that the polymer composition comprises at least one particulate filler selected from the group consisting of oxide ceramics, nitrides and carbides, particularly preferably SiO2, Al2O3, SiN, SiC, TiO2, MgO, ZrO2, or mixed oxides thereof or other metal nitrides, or glasses, and / or the filler has a particle size distribution with a D50 of less than 50 pm, in particular with a D50 of less than 5 pm, preferably from 0.4 pm to 3.7 pm, particularly preferably from 0.8 pm to 1.3 pm or 2.1 to 3.7 pm, determined by laser diffraction.

[0048] The glass is preferably a Si-Al-Ba glass, in particular a high-temperature-resistant Si-Al-Ba glass with boron contents below 0.5%, and very particularly preferably a Si-Al-Ba glass, wherein SiO2, Al2O3 and BaO make up a proportion of at least 70 wt.%, preferably at least 80 wt.% and more preferably at least 90 wt.%.

[0049] In an alternative embodiment, the at least one particulate filler selected from glass is coated glass, preferably glass coated with vinyl silane.

[0050] Preferably, the at least one particulate filler is a spherical glass bead, preferably with diameters in the sub-micron range, coated with a vinylsilane coating. Without being bound to any particular theory, it is believed that a vinylsilane coating improves the wettability of the filler with the hydrophobic polymer composition. Furthermore, the round shape of the filler facilitates the application of the paste produced therefrom in a pipe system or through a cannula.

[0051] The at least one particulate filler may also comprise mixtures of different fillers or fillers with different particle size distributions.

[0052] Surprisingly, it has been shown that, despite the addition of the particulate filler as defined above, the hydrophobic properties of the fixing drop according to the invention are retained or even improved. Preferably, the fixing drop according to the invention, comprising a particulate filler as defined above, has a contact angle with water of more than 80°, preferably more than 85°, particularly preferably more than 88°, measured according to DIN EN ISO 19403.

[0053] Preferably, fixing drops according to the invention comprising a particulate filler as defined above have a contact angle with diiodomethane of less than 48°, preferably less than 46°, particularly preferably less than 44°, measured according to DIN EN ISO 19403.

[0054] Preferably, the fixing drop according to the invention, comprising a particulate filler as defined above, has a surface tension of more than

[0055] 20 mN / m, preferably more than 27 mN / m, even more preferably more than 33 mN / m, most preferably greater than 37 mN / m, measured according to DIN ISO19403.

[0056] Preferably, the fixing drop according to the invention, comprising a particulate filler as defined above, has a disperse fraction of more than 20 mN / m, preferably more than 27 mN / m, even more preferably 32 mN / m, preferably more than 34 mN / m, particularly preferably more than 36 mN / m, measured according to DIN EN ISO 19403.

[0057] Preferably, the fixing drop according to the invention, comprising a particulate filler as defined above, has a polar fraction of less than 3 mN / m, preferably less than 2 mN / m, particularly preferably less than 1 mN / m, measured according to DIN EN ISO 19403.

[0058] The expansion coefficient of the polymer composition and, preferably, also the thermal conductivity of the polymer composition can be adapted to the environment or the nearest parts of the passive component. The filling can also be selected so that the expansion coefficient is correspondingly larger than the expansion coefficient of the substrate.

[0059] The fixing drop according to the invention is therefore preferably characterized in this embodiment in that the expansion coefficient of the polymer composition is greater than the expansion coefficient of the substrate and / or the connecting wires and / or the contact pads. This property is particularly advantageous in the preferred use as a fixing drop on a passive component, since the fixing drop according to the invention is preferably applied in rows to passive components, which are then separated by breaking. Thermal annealing of the fixing drop according to the invention is not necessary after breaking, since no critical, transport-shock-sensitive cracks remain in the silicone material.

[0060] The fixing drop according to the invention is further preferably characterized in that the at least one filler is present in an amount of 3 to 60 wt.%, preferably 5 to 30 wt.%, more preferably 5 to 13 wt.%, particularly preferably 7 to 11 wt.%, based on the total mass of the fixing drop.

[0061] Since the fixing drop according to the invention may be an inhomogeneous mixture, the stated wt. % refers to the average content in the fixing drop. Local deviations in the wt. % in the fixing drop are possible, but they balance out to the stated wt. %.

[0062] The filler in the fixation drop according to the invention is preferably selected from MgO and Al2O3, as these fillers exhibit a low expansion mismatch with the substrate. The difference in the thermal expansion coefficient between filler and substrate is preferably between +30% and -20%, more preferably between +15% and -5%, and even more preferably between 10% and 0%. The mismatch should be measured, in particular, from 20°C to the operating temperature of the sensor. For silicone-based fixation drops, the recommended temperature range is generally from -50°C to 150°C.

[0063] In particular, AI2O3 is preferred since this filler can be incorporated into the fixing drop according to the invention in particularly high amounts of up to 60 wt.%, based on the total mass of the fixing drop.

[0064] In contrast to glass fixation drops, the fixation drop according to the invention preferably has a small pore volume or exhibits no open porosity, thus largely preventing water penetration. This prevents water from penetrating the connecting wires, even in the presence of surface cracks. Furthermore, the transport of any ions present is prevented, thus preventing the generation of undesirable offset voltage.

[0065] The fixing drop according to the invention is further preferably characterized in that the fixing drop has less than 35 vol.%, preferably less than 25 vol.%, preferably less than 15% of pores, and / or shows no open porosity.

[0066] The fixing drop according to the invention preferably has a hardness of 75 to 95 Shore A, preferably 80 to 95 Shore A, measured with a Shore A hardness tester handheld device.

[0067] The present invention further relates to a passive component, in particular a sensor, preferably a temperature sensor.

[0068] The present invention further relates to a passive component, in particular a sensor, preferably a temperature sensor, or heater, comprising connecting wires and an inorganic substrate, in particular a metal oxide, semiconductor and / or glass substrate or a metal substrate, in particular a steel substrate, with at least one insulation layer or intrinsic insulation layer.

[0069] The present invention further relates to a passive component, in particular a sensor, preferably a temperature sensor, comprising connecting wires and an inorganic substrate, in particular a metal oxide, semiconductor and / or glass substrate, or polymer substrate, characterized in that the connecting wires are electrically insulated by the applied fixing drop according to the invention.

[0070] Furthermore, it is preferred that the inorganic substrate is selected such that it is adapted to the expansion coefficient of the fixing drop according to the invention.

[0071] In a preferred embodiment of the passive component according to the invention, the substrate is a multilayer substrate comprising several layers arranged one above the other, wherein the layers comprise inorganic substances and / or plastics.

[0072] Furthermore, it is preferred that the expansion of the polymer fixation drop is adapted to the expansion coefficient of the uppermost layer of the contact pads and the connecting wires used. A further advantage of using the fixation drop according to the invention for electrically insulating the connecting wires of a passive component is the low material requirement and thus the possibility of producing flatter passive components with the same thickness of the connecting wires and the substrate. Breakable glass fixation drops can generally only be produced within a narrow thickness range. Glass fixation drops should have a relatively large height above the connecting wires so that the glass fixation drop breaks at the correct location during separation. As an upper limit, breakable passive components with glass fixation drops can reach a thickness of up to 1.2 mm; beyond this, breakability with a satisfactory yield is usually no longer possible.In contrast to passive components that have been strain-relieved and electrically insulated with a glass fixation drop, which often have a raised portion between the connecting wires, passive components that have been electrically insulated at the contact point with the fixation drop according to the invention can have a recess between the connecting wires.

[0073] The passive component according to the invention is further preferably characterized in that the contact pads and the connecting wires contacted thereon are electrically insulated by a fixer drop, wherein preferably the complete component above the connecting wires, in particular over the entire height including substrate, connecting wires and fixer drops at the position of the connecting wires, has a height of less than 0.8 mm, preferably less than 0.75 mm, particularly preferably less than 0.7 mm.

[0074] The height is understood to mean the total height of the passive component according to the invention, including the substrate.

[0075] Breaking separation has established itself as a particularly cost-effective process for passive components whose connecting wires are strain-relieved with a glass fixation drop. This separation method has proven advantageous if predetermined breaking points are present in the substrate, thus allowing easy breaking, especially with hard substrates.

[0076] The passive component according to the invention is further preferably characterized in that the passive component was obtained by singulation, wherein the singulation preferably comprises breaking, in particular at at least one predetermined breaking point, and / or sawing. Even if, from a process-economic perspective, singulation by breaking is preferable to sawing, providing suitable fixation drops suitable for this method presents some challenges. In particular, the occurrence of critical cracking can be avoided with the fixation drop according to the invention.

[0077] The passive component according to the invention is further preferably characterized in that the fixing drop does not exhibit any critical crack formation during the separation of the passive components.

[0078] For the purposes of the present invention, crack formation is characterized based on the cutting angles. When separating the passive components, at least two passive components are separated from each other by breaking. The resulting fracture surface on one of the passive components is ideally perpendicular to the substrate plane, so that the four cutting angles between the fracture surface and the substrate plane are all 90°. Since secondary angles add up to 180°, it is not necessary to consider all angles; instead, the crack formation can be qualified by specifying the smallest cutting angle. Under real conditions, however, the passive components do not fracture ideally, but considerable deviations can occur. These deviations are tolerable as long as the dimensions of the passive component lie safely within the specified tolerances.

[0079] Critical crack formation is therefore understood to mean that the smallest intersection angle between the fracture surface and the substrate plane of the passive component is less than 45°.

[0080] It is therefore preferred that the smallest intersection angle between the fracture surface and the substrate plane of the passive component is more than 45°, more preferably 60°, further preferably more than 70°.

[0081] Microcracks are small, difficult-to-detect cracks in the fixation droplet. These microcracks can occur when the fixation droplets break and are detected, for example, by visual inspection after the completion of manufacturing and separation of the passive components.

[0082] The fixative drop according to the invention not only has a lower hardness than glass fixative drops, but also possesses residual elasticity. After polymerization, the polymer material alone, as well as a powder-filled material according to the invention, is still elastically deformable. This elasticity can decrease with storage time and aging due to repeated temperature changes. However, in components just a few weeks old and with a low number of temperature changes, residual elasticity is present.

[0083] A particular advantage of the residual elasticity of the slightly aged fixer drops is their ease of installation, especially in narrow housings or tubes. Crushing or abrading the edge of the fixer drop hardly contributes to further cracking after separation. In fact, it can even be used to remove excess molding from the fixer drop.

[0084] Post-processing involving material removal, cutting to a shape, and especially edge reworking of the fixation drop by pulling it through a caliber are possible both manually and automatically. Due to the expected very low failure rate of the robust fixation, even automatic post-processing is possible. Even installation in a confined space with abrasive scraping of the fixation drop is possible. In particular, installation and the intended temperature change do not trigger critical cracking, which could propagate through the entire fixation drop and, even worse, further into the covering layer of the meander.

[0085] Since these manipulations do not cause cracking in the fixation drop during post-processing or sensor installation, thermal annealing after the manipulation is not necessary.

[0086] Furthermore, it is possible, and not fundamentally disadvantageous, for the residually elastic fixation drop to be installed under compressive or tensile stress. This is an advantage if the passive component is to be installed in narrow tubes or near walls or adjacent to rugged surfaces.

[0087] Furthermore, the residual elasticity of the fixative droplet enables stress-free overmolding of the passive component. The electrical characteristics are changed only slightly, within the specifications. Particularly with platinum thin-film temperature sensors, the previously set tolerance values ​​of the temperature coefficient (TK) and the nominal resistance (Ro) are maintained within the quality class 1 / 3 DIN F 0.1. The passive component according to the invention is preferably characterized in that the passive component has a self-heating of less than 0.4 K / mW, preferably less than 0.35 K / mW, particularly preferably 0.3 K / mW.

[0088] Lower self-heating of the passive component has the advantage that measurements in the steady state can be carried out more precisely with a lower systematic error.

[0089] Lead wires made of nickel or more easily solderable silver-coated nickel, or any other common materials such as gold, platinum-coated nickel, or platinum wires can be used as connecting wires for the passive components. Unlike glass fixation drops, the fixation process according to the invention is compatible with various plastics, so plastic-coated connecting wires can also be used for the passive components. The coated connecting wires must be stripped in the contact area.

[0090] The passive component according to the invention is preferably characterized in that the connecting wires comprise nickel or copper wire, optionally with a plastic, silver or platinum sheath.

[0091] Instead of a sheath, the connecting wires can also be provided with a coating, as long as this is compatible with the fixing drop according to the invention.

[0092] Preferably, the fixing drop according to the invention is applied to the contact pads in such a way that the connecting wires are covered. Optionally, the fixing drop according to the invention can also partially cover the non-stripped area of ​​the sheathed connecting wires. Particularly with the preferred use of plastic as the sheath for the connecting wires, it is advantageous that the plastic can extend into the fixing drop according to the invention on the side facing the sensor.

[0093] The passive component according to the invention is further preferably characterized in that the connecting wires comprise nickel wire with a plastic sheath, wherein the plastic is preferably selected from glass fiber, silicone, Teflon, PEEK, polyurethane, cresols, polyimide, polyesterimide, PMA, PMAA, or Viton or filled plastic, and the plastic sheath was attached to the connecting wire before the application of the fixing drop and / or protrudes into the fixing drop.

[0094] The passive component according to the invention is further preferably characterized in that the passive component is a temperature sensor which complies with the validity of the tolerance class F 0.3 (B) at a temperature of -20 to 130°C.

[0095] Further preferred embodiments of the passive component according to the invention meet the tolerance class F0.3 (B) at a temperature of -20 to 270°C.

[0096] Particularly preferably, the passive component according to the invention is a Pt temperature sensor that meets the quality class 1 / 3 DIN (F 0.1). This applies both to unused Pt temperature sensors and after an aging test at 85°C and 85% humidity for 1000 hours.

[0097] The present invention further relates to a method for producing passive components, in particular for producing the passive component according to the invention. The method comprises the following steps, whereby the order of the individual steps cited below is not mandatory.

[0098] - Providing an inorganic substrate, in particular a metal oxide or semiconductor substrate or a glass substrate, on which several structures are arranged, in particular in series,

[0099] - optionally forming predetermined breaking points in the inorganic substrate between the structures, in particular by means of a laser and / or by means of mechanical ablation,

[0100] - Attaching at least one connecting wire to each of the contact pads of the structures,

[0101] - covering the contact pads and the tips of the connecting wires by applying a polymer paste, in particular the polymer composition according to the invention, - heat-treating the polymer paste, in particular at a temperature of 120 to 375°C, preferably from 120°C to 300°C, more preferably from 140 to 220°C, in order to obtain a fixing drop, in particular the fixing drop according to the invention

[0102] - Cooling the fixative drop to a temperature at which the fixative drop is dimensionally stable, preferably to room temperature

[0103] - Separation of the passive components, in particular by breaking the inorganic substrate at the predetermined breaking points.

[0104] If necessary, the edges of the fixation drop must be mechanically reworked after the manufacturing process, which can lead to material loss.

[0105] The passive component produced in this way, in particular the passive component according to the invention, can be installed under mechanical stress, which already acts on the fixation drop at room temperature, and the electrical resistance can be measured, or it can be applied to rough surfaces. Fixation drops generally have a higher coefficient of expansion than the adjacent substrate or the platinum connecting wires. Therefore, the fixation drops are subjected to tensile stress even at room temperature and expand more rapidly when the temperature increases. This reduces the tensile stress on the fixation drop, making the passive component more stable. A further advantage is that the stress on the meander is lower at higher temperatures.

[0106] Since the method according to the invention provides for heat treatment at significantly lower temperatures than methods for producing passive components according to the prior art, which regularly require a temperature of up to 600 to 700°C or higher for the heat treatment, considerable amounts of energy can be saved.

[0107] Furthermore, such low temperatures prevent unwanted side reactions, so that, in addition to air ingress, no purging with process or forming gas is necessary. Consequently, long setup times or pre-purging times with process gas in the process furnace during the heat treatment of the fixation droplet are eliminated.

[0108] The material selection for the connecting wires and their optional sheathing is also significantly wider at such low temperatures; in particular, expensive platinum-coated connecting wires can be dispensed with. Since connecting wires made of nickel, for example, do not oxidize to nickel oxide, significantly cheaper pure nickel wires, optionally coated with plastic, can also be used.

[0109] Silver-coated nickel connecting wires can also be used, which are preferred due to their better solderability without the need for complex process control with narrow process windows under forming gas.

[0110] Preferred embodiments of the method described above include alternative temperature ranges for the heat treatment, depending on the composition of the polymer paste and the material used for the connecting wires and optional sheaths.

[0111] In a preferred embodiment of the method according to the invention, the steps are designed as follows:

[0112] - Providing an inorganic substrate, in particular a metal oxide or semiconductor substrate or a glass substrate, on which several structures are arranged, in particular in series,

[0113] - Forming predetermined breaking points in the inorganic substrate between the structures, in particular by means of a laser and / or by means of mechanical ablation,

[0114] - Attaching at least one connecting wire to each of the structures,

[0115] - covering the connecting wires by applying a polymer composition comprising a silicone, preferably liquid silicone plastic, in particular one-component polymers, over the plurality of structures,

[0116] - Heat treatment of the polymer composition at a temperature of 120 to 300 °C, preferably 120 °C to 220 °C, in order to obtain a preferred embodiment of the fixing drop according to the invention

[0117] - Cooling of the fixing drop to a temperature at which the fixing drop is dimensionally stable - Separation of the passive components by breaking the inorganic substrate and the continuous fixing drop at the predetermined breaking points.

[0118] Since the solderability of nickel connecting wires can be improved by a silver coating, this alternative embodiment is advantageous for certain applications. Advantageously, the addition of forming gas can be omitted in the subsequent process, preventing silver oxidation, thus preserving the solderability of the connecting wires.

[0119] In a further preferred embodiment of the method according to the invention, the steps are designed as follows:

[0120] - Providing an inorganic substrate, in particular a metal oxide or semiconductor substrate or a glass substrate, on which several structures are arranged, in particular in series,

[0121] - Forming predetermined breaking points in the inorganic substrate between the structures, in particular by means of a laser and / or by means of mechanical ablation,

[0122] - Attaching at least one connecting wire, the connecting wires comprising nickel wire with a silver sheath, to each of the structures,

[0123] - covering the connecting wires by applying a polymer composition comprising polyimides, in particular single-component polymers, over the plurality of structures,

[0124] - heat treatment of the polymer composition at a temperature of 325 to 400 °C, in particular 350 to 375 °C, in order to obtain a preferred embodiment of the fixing drop according to the invention,

[0125] - Cooling the fixative drop to a temperature at which the fixative drop is dimensionally stable, preferably to room temperature

[0126] - Separation of the passive components by breaking the inorganic substrate and the continuous fixative droplet at the predetermined breaking points. The sequence of steps for the processes listed above is not mandatory, but includes all technically reasonable sequences. For example, it would be possible to form the predetermined breaking points only after applying a continuous polymer paste.

[0127] In a preferred embodiment of the method according to the invention, the method steps are carried out in the listed order.

[0128] All preferred embodiments and definitions for the passive components according to the invention apply analogously to the method according to the invention.

[0129] The present invention further relates to a passive component obtainable by the method described above.

[0130] The present invention also relates to the use of a fixing drop as described above for insulating contact pads and connecting wires on passive components, in particular as described above or obtainable by the methods described above.

[0131] In a preferred embodiment of the use according to the invention, the passive components were obtained by singulation, wherein the singulation comprises breaking, in particular at predetermined breaking points.

[0132] The preferred embodiments listed above for the fixing drop according to the invention and the passive component according to the invention also apply to the method according to the invention, the passive component obtained by this method and the use of the fixing drops.

[0133] The invention is explained in more detail below using non-limiting examples. Description of the figures

[0134] Figure 1 shows a comparative measurement of the self-heating of four passive components at the same applied voltage.

[0135] Figure 2: shows the results of an aging test for a series of 10 platinum temperature sensors with a nominal resistance of 1000 ohms (Pt1000 elements) according to the invention. The drift is plotted as the difference in the temperatures displayed in the same component at 0°C before and after the aging test.

[0136] Examples

[0137] Example 1 :

[0138] Four passive components were provided with the same Al2O3 substrates, glass cover layers, Pt lead wires, geometries, and resistors. Manufacturing took place in an identical production cycle. The lead wires of two passive components were coated with commercially available glass fixative drops, and the lead wires of the other two passive components were coated with the silicone fixative drops according to the invention, thus electrically insulating them.

[0139] The precursor dispersion for the silicone fixative drops was mixed from 71% Locktite SI 5091 LC from Henkel, 20% Al2O3 powder with a particle size of D50 = 0.8-1.3 μm, and 9% hydrolysis product of trimethoxyoctylsilane and silicon dioxide powder (silane, trimethoxyoctyl, hydrolysis products with silicon dioxide CAS 92797-60-9). The data are in weight percent. This dispersion was thinly applied to the prepared sensor rows using a syringe and cured for 1 minute under an Amba® UV curing lamp from Heraeus Noblelight. The rows were then divided into individual sensors.

[0140] The four passive components manufactured in this way were tested for their self-heating. The components were connected in parallel and subjected to increased voltage, resulting in a current higher than the usual measurement current and significant heating of all components, reaching over 55°C.

[0141] The measurements were carried out in air, at room temperature, with the same voltage applied to the passive components for all measurements.

[0142] The measurement results are shown in Figure 1.

[0143] It was found that the passive components, which were strain-relieved and electrically insulated with the glass fixative drop, exhibited a self-heating of 0.4 K / mW.

[0144] In contrast, the self-heating of the passive components coated with the inventive fixative drop was below 0.3 K / mW. Example 2:

[0145] Ten components with platinum connecting wires, electrically insulated with the silicone fixative drop, were fabricated and subjected to an aging test. These were Pt1000 temperature sensors.

[0146] The conditions for the aging test stipulated that the passive components were exposed to an ambient temperature of 85°C and 85% humidity for 1,000 hours. Before and after the test, the resistance of the components was measured at 0°C, and a temperature value was calculated from this. The difference between these measured temperature values ​​within the same component is the component's drift.

[0147] The measurement results are shown in Figure 2.

[0148] It was also found that all temperature sensors tested met the requirements for a sensor of quality class 1 / 3 DIN (F 0.1) even after the aging test.

[0149] Example 3:

[0150] A resistor pattern and two contact pads are screen-printed with silver paste onto a 50 μm-thick FeCrAl steel sheet, which has previously been coated with a dense insulating oxide layer. The resistor area is then passivated with a thin layer of glass, leaving the contact pads unaffected. Lead wires are attached to the contact pads. Silicone fixative drops are applied over the connection points and polymerized by UV radiation. After manufacturing, the component is separated from the metal panel by laser separation.

[0151] The heating element constructed in this way was resistively heated to 150°C 400 times and cooled back to room temperature. The required heating current did not change noticeably over the duration of the test. Example 4:

[0152] A series of heating elements identical to Example 3 was manufactured. The size of each heating element was 10 mm x 30 mm. The connecting wires were arranged parallel to the long side of the substrate. Twenty heating elements were manufactured on the same 25 cm x 3 cm sheet and were not separated from each other. The connecting wires of all heating elements were arranged parallel. The sheet was bent in a semicircle along the long side. Even when bent, the heating elements still functioned, and the electrical insulation of the connecting wires was maintained. Heating to 150°C in the bent state was possible. The strip remained resilient and could be flattened again after heating. Even in this case, all 20 heating elements were still functional.

[0153] Example 5:

[0154] Two fixative drops according to the invention were compared, differing only in the presence of filler. The material for fixative drop 1 corresponds to the composition of the fixative drop according to Example 1. The material for fixative drop 2 has the same composition as the material for fixative drop 1, but with less filler added. These two fixative drops were each applied to a glass substrate and then cured.

[0155] The surface topography and roughness were determined using an Olympus LEXT OLS4100 laser scanning microscope. The contact angles for each material were measured using the OCA200 contact angle measuring device according to DIN EN ISO 19403 from two directions (each parallel to the substrate edges) using five drops each of water and diiodomethane.

[0156] No directional dependence of the contact angle could be determined. The average values ​​of all 10 measurements are given.

[0157] The measurement results are listed in the following table:

[0158] Example 6

[0159] Two fixative drops according to the invention were compared, differing only in the type and amount of filler. Fixative drop 1 corresponds to the composition of the fixative drop according to Example 1. Fixative drop 3 has the same composition as fixative drop 1, but 23 wt.% glass powder was added as filler instead of AhOa powder. The glass powder is a high-temperature-resistant Si-Al-Ba glass with a boron content of less than 0.1%, which was adjusted to a grain size D 50 = 2.1 to 3.7 pm by grinding and sieving. These two fixative drops were each applied to prepared identical sensor rows by dispensing and cured. The sensor rows were each separated by breaking.

[0160] The two sensor types with the different fixing drops were tested for their resistance to changing temperatures. For this purpose, the sensors were subjected to a cycle test according to DIN IEC EN 60731, which involves ten temperature changes from 150 °C to -50 °C.

[0161] It was found that during the cycle test of the sensors, small cracks formed on fixer drop 1, while no cracks formed on fixer drop 3.

Claims

CLAIMS 1. Fixing drop for the electrical insulation of contact pads and the connecting wires contacted thereon on passive components, in particular sensors, preferably temperature sensors, on an inorganic substrate, in particular metal oxide, semiconductor, metal and / or glass substrate, characterized in that the fixing drop comprises a hydrophobic polymer composition.

2. Fixing drops according to claim 1, characterized in that the polymer composition comprises a silicone, preferably liquid silicone plastic or polyimides, in particular one-component polymers.

3. Fixing drops according to one of the preceding claims, characterized in that the polymer composition comprises at least one particulate filler selected from the group consisting of oxide ceramics, nitrides and carbides, particularly preferably SiO2, Al2O3, SiN, SiC, TiO2, MgO, ZrO2, or mixed oxides thereof or other metal nitrides, or glasses, and / or the filler has a particle size distribution with a D50 of less than 50 pm, in particular with a D50 of less than 5 pm, preferably from 0.4 pm to 3.7 pm or 2.1 to 3.7 pm, particularly preferably from 0.4 pm to 1.3 pm, determined by laser diffraction.

4. Fixing drop according to claim 3, characterized in that the fixing drop has a contact angle with water of more than 80°, preferably more than 85°, particularly preferably more than 88°, measured according to DIN EN ISO 19403.

5. Fixing drops according to one of the preceding claims, characterized in that the expansion coefficient of the polymer composition is greater than the expansion coefficient of the substrate and / or the connecting wires and / or the contact pads. 6 Fixing drops according to one of claims 3 to 5, characterized in that the at least one filler is present in an amount of 3 to 60 wt.%, preferably of 5 to 30 wt.%, more preferably from 5 to 13 wt.%, particularly preferably from 7 to 11 wt.%, based on the total mass of the fixing drop.

7. Fixing drop according to one of the preceding claims, characterized in that the fixing drop has less than 35 vol.%, preferably less than 25 vol.%, preferably less than 15% of pores, and / or shows no open porosity.

8. Passive component, in particular sensor, preferably temperature sensor, comprising connecting wires and an inorganic substrate, in particular metal oxide, semiconductor and / or glass substrate, characterized in that the contact pads and the connecting wires contacted thereon are electrically insulated by a fixing drop according to one of claims 1 to 7, wherein preferably the complete component above the connecting wires, in particular over the entire height including substrate, connecting wires and fixing drops at the position of the connecting wires, has a height of less than 0.8 mm, preferably less than 0.75 mm, particularly preferably less than 0.7 mm.

9. Passive component according to claim 8, characterized in that the passive component was obtained by singulation, wherein the singulation preferably comprises breaking, in particular at at least one predetermined breaking point, and / or sawing.

10. Passive component according to claim 8 or 9, characterized in that the passive component has a self-heating of less than 0.4 K / mW, preferably less than 0.35 K / mW, particularly preferably 0.3 K / mW.

11. Passive component according to one of claims 8 to 10, characterized in that the connecting wires comprise nickel or copper wire, optionally with a plastic, silver or platinum sheath.

12. Passive component according to one of claims 8 to 11, characterized in that the connecting wires comprise nickel wire with a sheath, wherein the sheath is preferably selected from glass fiber, silicone, Teflon, PEEK, polyurethane, cresols, polyimide, polyesterimide, PMA, PMAA, or Viton or filled plastic, and the sheath was attached to the connecting wire before the application of the fixing drop and / or protrudes into the fixing drop.

13. A method for producing passive components, in particular according to one of claims 8 to 12, comprising the steps: - Providing an inorganic substrate, in particular a metal oxide or semiconductor substrate or a glass substrate, on which several structures are arranged, in particular in series, - Attaching at least one connecting wire to each contact pad of the structures, - covering the contact pads and the tips of the connecting wires by continuously applying a polymer paste, in particular comprising a polymer composition according to one of claims 1 to 7, - heat treatment of the polymer paste, in particular at a temperature of 120 to 375 °C, preferably 120 °C to 300 °C, more preferably 140 to 220 °C, in order to obtain a fixing drop, in particular according to claims 1 to 8 - Cooling the fixative drop to a temperature at which the fixative drop is dimensionally stable and preferably still elastic, preferably to room temperature - Separation of the passive components, in particular by sawing or laser cutting the inorganic substrate and the continuous fixation drop.

14. The method according to claim 13, wherein the singulation is a breaking process which includes the introduction of predetermined breaking points in the inorganic substrate between the structures, in particular by means of a laser and / or by means of mechanical ablation.

15. Passive component obtainable by the method according to claim 13 or 14.

16. Use of a fixing drop according to one of claims 1 to 7 for electrical Insulation of the contact point of connecting wires and the contact pads on passive components, in particular according to one of claims 8 to 12 or claim 15.

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