EA035216B1 - Method for connecting piezoceramic substances with various materials - Google Patents

Abstract

The invention relates to the field of piezoelectronics, in particular to methods for connecting piezoceramic materials using reactive multilayer foils, and can find application in the manufacture of piezoceramic composite materials and multilayer ceramics, wiring of microwave devices, printed circuit boards and electronic components. The method of connecting piezoceramic materials involves the use of a reactive foil, 40-150 m thick, its layers made of 2-20 nm thick metals and/or non-metals selected from the group including nickel, aluminium, copper, niobium, cobalt, titanium, molybdenum, tantalum, carbon, silicon, boron; before applying the solder, an adhesive coating of 30 to 120 nm thickness is applied to the foil, after which a 2-15 m thick solder is applied, and the surfaces are pressed together at a pressure of 0.7-2.2 kg/cm(Fig. 1). In individual embodiments of the invention, before pressing surfaces together, the surfaces to be joined are preliminarily heated, in particular to a temperature not higher than the Curie temperature of the piezoceramic material and the melting temperature of the solder; the solder is applied galvanically, chemically or by spraying.

Description

The invention relates to the field of piezoelectronics, and in particular to methods of joining piezoceramic materials using a reaction multilayer foil, and can find application in the production of piezoceramic composite materials and multilayer ceramics, during the installation of microwave devices, printed circuit boards and electronic components.

It is known in the prior art to use piezoelectric materials, in particular piezoelectric materials, in the production of various elements, assemblies and devices: generators, sensors (sensors), actuators (piezoelectric drives), transducers and combined systems. Among the piezoceramic materials, several types are distinguished, characterized by various physical properties, which, in turn, determine the features of the manufacture of elements of technology from them (especially the connection of piezoceramic materials), as well as the features of the use of such elements.

Currently, there are several ways to connect piezoceramic materials to obtain structural elements of devices: soldering and connection by means of electrically conductive glue. However, none of the above methods does not guarantee the absence of damage to the sensitive piezoelectric element upon receipt of such an element of the device.

So, from the prior art there is a known method of connecting piezoceramic materials with various materials by soldering (patent RU 2041776 for the invention. Method of brazing ceramics with metal, date prior. 04/27/1992, publ. 08/20/1995, B23K 1/00). To connect the materials, the solder is melted; the liquid state of the solder is achieved by a relatively long and high-temperature impact on it (for example, a soldering iron tip). This, in turn, leads to heating of the materials being joined, damage to the crystal structure of the piezoelectric ceramic part and, as a result, loss of its electrophysical properties (depolarization of the piezoceramic material). In practice, in order to avoid undesirable heating of the surfaces to be joined during the brazing process, the brazing area is additionally cooled between the repeated steps of the solder heating, which significantly increases the time of joining of materials. In addition, the strength of the connection of materials and the quality of the resulting product (the performance of the piezoceramic product) depend, in particular, on the amount of material connecting them (solder): the lack of solder reduces the strength of the connection, and excess - the quality of the assembled product. The bonding strength of materials is also determined by the force of their clamping during bonding: a small clamping force reduces the bonding strength, and excessive clamping force increases the risk of fracture of the parts being joined, the risk of their displacement relative to each other and leakage of solder. With traditional soldering, measuring the exact amount of solder is very difficult, and varying the clamping force with a suboptimal amount of solder is inefficient. In addition to the above, the disadvantages also include the need for auxiliary operations, such as preliminary cleaning of the surfaces to be joined from the film formed due to the reaction of silver on the surface of piezoceramics and sulfur in atmospheric air, and post-cleaning of used fluxes (this increases the time of joining of materials).

A known method of connecting piezoceramic materials with various materials using electrically conductive glue (patent RU 2491684 for the invention of a multilayer ceramic heterostructure with a magnetoelectric effect and method for its preparation, date prior. 04/27/1992, publ. 08/20/1995, B23K 1/00).

However, this method does not provide sufficient electrical conductivity of the assembled product as a whole. In addition, the difference in the coefficients of thermal expansion of the piezoelectric element itself, the fastening layer (glue) and the reciprocal base leads to destruction (cracking) of the assembled product during operation, which limits the possibility of its use in special cases.

An alternative way to connect piezoceramic materials is a method using reaction foil materials in which fast self-propagating high-temperature synthesis is possible (hereinafter referred to as SHS reaction), which allows them to be used as a source of controlled heat.

The closest in technical essence to the claimed solution is a method of joining various materials, including components of microelectronic devices, which use a multilayer reaction foil (application US 2002182436 for the invention of stand-alone reaction multilayer foils, prior. 04/18/2002, publ. 05.12.2002, C23C 14/34). The method includes placing a multilayer reaction foil with a thickness of 50 μm to 1 cm with pre-applied solder between the surfaces to be joined, clamping said surfaces and initiating a reaction in the foil by applying a short-term energy pulse to the foil. The foil layers are made of metals or metal alloys selected from the group of aluminum, nickel, copper, titanium, zirconium, hafnium.

However, the known technical solution, selected as a prototype for the claimed method, does not provide a durable connection of piezoceramic materials with various materials while maintaining their functional properties for the following reasons. The indicated thickness and chemical composition of the multilayer reaction foil used determine the presence of a significant amount of stored energy in it and, accordingly, the release of a large amount of heat upon initiation of the SHS reaction in it. The process of joining piezoceramic materials, which are known to be extremely sensitive to heat, with various materials, requires controlling the amount of heat generated, taking into account the type of piezoceramic material, its thickness and the required operational characteristics of the finished product (connected materials). However, the qualitative composition of the foil in the prototype method does not allow to reduce the amount of heat generated to an acceptable value. For example, a foil with a thickness of 80 μm, consisting of 2,000 alternating layers of aluminum and nickel, each of which has a thickness of 2 nm, with the addition of 1% molybdenum, 0.5% silver, 1.5% indium, gives a very large energy yield, which is unacceptable for joining thin piezoceramic materials (they are destroyed). On the other hand, the use of foils of less energy-intensive materials, for example foil, consisting of 900 alternating layers of aluminum and iron oxide, where the thickness of each layer of aluminum is 1.5 nm and the thickness of each layer of iron oxide is 2.5 nm, with the addition of 1 % molybdenum, 0.7% silver, 1% indium, does not provide sufficient melting of the solder and, therefore, obtain a strong connection. In addition, the lack of consistency in the pressing force, the characteristics of the foil and solder used does not allow one to obtain a strong joint capable of soldering (disconnecting) without breaking piezoceramic materials (without losing their functional properties).

The objective of the invention is to provide a method that provides a quick and durable connection of piezoceramic materials while maintaining their functional properties, if possible, their desoldering, if necessary, without destroying the piezoceramic materials.

The objective is achieved by the fact that in the method of connecting piezoceramic materials with various materials, in which a multilayer reaction foil 3 with a pre-solder is placed between the joined surfaces 1 and 2, these surfaces are pressed and a short-term energy pulse is applied to the foil, according to the invention, a foil with a thickness of 30-100 μm, the layers of which are made 2-20 nm thick from metals and / or non-metals selected from the group nickel, aluminum, copper, niobium, cobalt, titanium, molybdenum, tantalum, carbon, silicon, boron, before applying solder to the foil apply an adhesive coating with a thickness of 30 to 120 nm, after which a solder of 2-15 μm thickness is applied, and the surfaces are pressed with a pressure of 0.7-2.2 kg / cm ² .

In private embodiments of the invention, prior to pressing, the surfaces to be joined are preheated, in particular, to a temperature not higher than the Curie temperature of the piezoceramic material and the melting temperature of the foil solder; solder is applied by a galvanic method, chemical deposition or by spraying.

The authors experimentally established that the claimed ranges of characteristics of the foil used and the modes of the method are optimal for obtaining a solid connection of piezoceramic materials with various materials without loss of functional properties, if possible, their desoldering if necessary without destroying the piezoceramic materials.

The achievement of the technical result provided by the implementation of the claimed method is due to the following.

The use of a multilayer reaction foil of the claimed composition and thickness and when activated by an energy pulse ensures the rapid release of stored energy in a volume that provides a sufficient degree of melting of solder of various thickness in the shortest possible time, which eliminates excessive heating of piezoceramic materials. This, combined with the clamping force, makes it possible to obtain the process parameters most suitable for joining piezoceramic materials, the variation of which, in turn, determines the fast and durable joining of piezoceramic materials of various thicknesses while maintaining their functional properties. Applying an adhesive coating of a given thickness on the foil provides strong adhesion of the solder of various thicknesses to the foil, which eliminates its sticking from the foil and, therefore, helps to obtain a high-quality material connection. And the claimed thickness of the solder provides the ability to unsolder the connection if necessary without destroying the piezoceramic materials.

Preheating the surfaces to be joined, in particular, to a temperature not higher than the Curie temperature of the piezoceramic material and the melting temperature of the foil solder, makes it possible to reduce the temperature gradient at the foil-joined element interface, which significantly reduces the amount of mechanical stress in the materials being joined and, therefore, leads to a significant improving the quality of the resulting compound. The application of solder by the galvanic method, chemical deposition or by spraying allows you to get a thin uniform layer, which also contributes to a durable connection of materials while maintaining their functional properties, if possible, their desoldering, if necessary, without breaking the piezoceramic materials.

The invention is illustrated by drawings, where in FIG. 1 shows a schematic diagram of the connection of piezoceramic materials with metallic materials according to the claimed method, FIG. 2 is a structural diagram of one embodiment of a multilayer reaction foil used; FIG. 3 - micrographs of plate multilayer reaction foils obtained by various methods: (a) and (b) - 2 035216 magnetron deposition; (c) the initial stack of foil before cold rolling, (d) after cold rolling; (e) and (f) a high-energy ball mill and cold rolling; (a), (b), (f) were obtained using a TEM tunneling electron microscope (light Al phase, dark Ni phase); (c) - (e) were obtained on an SEM atomic force electron microscope (dark Ni phase, light Al phase).

The invention is illustrated by the following examples presented in tables 1, 2, in which the connection of piezoceramic materials with various materials was carried out according to the scheme described above (taking into account the polarity of piezoceramics) on a mechanical installation, including a base with appropriate marking and accessories for positioning piezoceramic elements, clamping cargo and means of launching the SHS reaction. Metallic materials (e.g., aluminum base, nickel body, brass body, copper base, treacherous body) and non-metallic materials (e.g. piezoceramics, germanium, sapphire, polycor, silicon, textolite, lavsan) were used to connect with piezoceramic materials.

A spark generated by a direct current source and passed through a small portion of the foil (voltage 6-12 V) was used as a means of triggering the SHS reaction;

soldering iron tip, providing short-term point contact of the small tip of the foil (tip temperature 350-600 ° C);

a laser that briefly and precisely acts on the foil section (wavelength 0.3–10 μm, power 1–100 W / min).

Piezoceramic elements manufactured by Morgan Matroc Ltd (Electro Ceramic Division, USA) and Aurora-Elma (RF, Volgograd), of the following sizes, were used as piezoelectric ceramic materials to be joined:

disk, thickness 0.2 mm, diameter 4 mm;

disk, thickness 0.5 mm, diameter 7 mm;

cylinder, height 5 mm, diameter 8 mm;

cylinder, height 15 mm, diameter 25 mm.

Given in the examples of sizes of piezoceramic materials do not limit the possibility of applying the claimed method for materials of other sizes.

The foil samples were coated with an adhesive coating with high functional characteristics (well adhesive during application and subsequent soldering), with a thickness of 30 to 120 nm based on silver, gold and copper.

Solder based on tin and bismuth was applied over the adhesive coating by electroplating, chemical deposition, or by spraying.

When using foil samples Nos. 4, 6, before pressing the joined surfaces, they were heated to a temperature not higher than the Curie temperature of the corresponding piezoceramic materials and not higher than the melting temperature of the solder in order to reduce the temperature gradient during the SHS reaction and, as a result, soften the thermal shock accompanying SHS -reaction. So, for sample No. 4, the preheating temperature was 100 ° C, and for sample No. 6 124 ° C.

The clamping of the joined surfaces was carried out by installing the clamping weights of the corresponding mass on the package of connected elements (duration not more than 1 min).

The parameters of the materials used and the modes of the method are presented in table. 1. The thickness of the layers of each metal or non-metal in one foil sample varied in the ranges indicated in the table. So, in sample No. 1, the layers of Ni and Al had a thickness of 7 to 20 nm each, with the same number of layers, the total thickness of the foil was different, and, as a result, the amount of energy released when the SHS reaction was started was different. Depending on the amount of energy released, the clamping pressure necessary to obtain the optimal connection parameters was determined.

Table 1

Used materials and modes

Sample No. Qualitative composition of the reaction foil The number of layers, pcs Thickness ranges of alternating layers, min -max nm Ranges of the total thickness of the foil, min - max microns Solder Thickness, microns The melting temperature of the upper layer Tm, ° C The temperature of the front of the SHS reaction, Tad, ° C The speed of the reaction front, m / s The specific amount of energy released during the reaction, j / g The specific heat of the weld C, J / (kg * K) The range of acceptable pressure clamps, kg / cm ² 1 Ni + Al 4000 7-20 28-80 ten 182 1450 12 1050-1250 670 1.1-4.0 2 Cu + Al 4500 4-15 18-68 ten 170 1340 nine 1000-1240 564 1.2-3.2 3 Nb + c 6000 5-12 30-72 ten 180 1015 15 970 - 1000 720 1.0-3.8 4 Co + A1 5000 3-10 15-50 8 170 1350 24 975 - 1245 685 1,5-4,2 five Ti + Si 3000 9-18 27-54 3 185 1820 26 980-1540 540 1.9-3.2 6 Ti + Al 3000 8-20 24-60 five 179 1780 18 990 - 1400 613 1.8-2.9 7 Mo + 2Si 2500 10-20 25-50 five 182 1610 13 950 - 1450 640 1.7-3.5 8 Mo + B 6000 4-10 24-60 12 171 1220 20 980 - 1230 532 1.4-5 nine Ti + C 5000 5-8 25-40 8 170 1310 21 1010-1200 751 1.2-4.9 ten 2Ta + C 1500 12-20 18-30 five 186 1112 nineteen 800-1100 650 1.0-1.4

Assessment of the preservation of functional properties connected using the presented samples

- 3 035216 foils of piezoceramic materials with various materials, was produced on equipment for monitoring the parameters of piezoelectric elements and Censourk-M transducers by measuring the parameters of the electromechanical oscillating system: dielectric loss tangent tg5,%, resonant frequency f _p , kHz, antiresonance frequency f _a , kHz resonance gap Af, kHz.

Evaluation of the strength characteristics of the samples of compounds was carried out on a tensile testing machine WPM Masch 2168, type FM-250, by measuring several key strength indicators: temporary tensile strength σ _Β , kgf / mm ² (tests for 50 hours); tensile strength of a soldered seam a _p , MPa; elastic modulus E, GPa; tensile strength of a brazed joint at shear m _cf , MPa, shear modulus G (GPa), Poisson's ratio μ.

Parameters of the characteristics of the finished products are presented in table. 2.

table 2

Characteristics of the resulting compounds

No. image of tsa The tensile strength of a brazed joint for tensile σ _Β , MPa Elastic modulus E, GPa The tensile strength of the solder joint to the cut Тср, MPa Modulo shift aG, GPa Poisson's ratio μ Dielectric loss tangent tg5,% Resonance frequency fp max | Y |, kHz Resonant frequency f _a min | Y |, kHz Resonance gap ok fa - fa, kHz. 1 48 18 45 4.6 0.32 0.0075 17.27 18.15 0.87 2 42 10,2 38 2.6 0.34 0.008 17.23 18.10 0.87 3 55 3.6 56 1.4 0.25 0.0065 17.27 18.15 0.88 4 70 7.4 65 2.2 0.35 0.0075 17.30 18.17 0.88 five 62 10.6 68 4.1 0.32 0.005 17.26 18.15 0.87 6 65 10,2 69 3.9 0.31 0.005 17,20 18.10 0.87 7 41 of 39 3.8 0.29 0.0065 17.24 18.15 0.88 8 thirty 11.1 32 3.91 0.29 0.004 17.30 18.17 0.88 nine 24 10.3 21 4.3 0.32 0.009 17.24 18.15 0.88 ten thirty 10.8 23 2.1 0.35 0.0085 17.19 18.17 0.88

Given in the table. 1, 2, the data confirm that the claimed method allows to obtain a solid connection of piezoceramic materials in the shortest possible time (1-2 ms) without losing the functional properties of such materials (the measured parameters of the electromechanical oscillatory system correspond to GOST 12370-80, GOST R 57438-2017 and GOST R 8.945-2018, as well as the regulatory documentation of most consumers).

All samples of the compounds were tested for the possibility of desoldering them without destroying the piezoceramic materials. For this, each soldered joint was heated to a temperature above the temperature of the onset of melting of the solder. Piezoceramic materials thus separated do not damage, do not lose their functional properties and can be reused.

Thus, the claimed method of joining piezoceramic materials provides a quick and durable connection with maintaining the functional properties of piezoceramics, if possible, desoldering the connection, if necessary, without destroying the piezoceramics.

Claims (4)

1. A method of connecting piezoceramic materials with various materials, in which a multilayer reaction foil with pre-applied solder is placed between the surfaces to be joined, these surfaces are pressed and a short-term energy pulse is applied to the foil, characterized in that 30-100 microns thick foil is used, layers which are made 2-20 nm thick from metals and / or non-metals selected from the group nickel, aluminum, copper, niobium, cobalt, titanium, molybdenum, tantalum, carbon, silicon, boron, before applying solder to the foil, an adhesive coating with a thickness of 30 up to 120 nm, after which a solder 2-15 microns thick is applied, and the surfaces are pressed with a pressure of 0.7-2.2 kg / cm ² . 2. The method according to claim 1, characterized in that before pressing the surfaces, the surfaces to be connected are preheated. 3. The method according to claim 2, characterized in that, the heating is carried out to a temperature not higher than the Curie temperature of the piezoceramic material and the melting temperature of the solder foil. 4. The method according to claim 1, characterized in that the solder is applied in a galvanic manner, by chemical deposition or by spraying.