TW202020100A - Potting composition, method for the electrical insulation of an electrical or electronic component, and electrically insulated component - Google Patents

Abstract

The invention relates to a potting composition. This comprises 5.0 - 30.0% by weight of reactive particles selected from magnesium oxide particles with particle size at most 5.0 μm, porous magnesium oxide particle agglomerates, silicon oxide particles with particle size at most 0.5 μm, silica particles with particle size at most 0.5 μm and mixtures thereof, 45.0 - 90.0% by weight of filler particles with particle size above 1 μm and/or filler fibres, and 5.0 - 20.0% by weight of water. In a method for the electrical insulation of an electrical or electronic component, this is potted (11) with the potting composition. It is then heat treated (12) at a temperature in the range 50℃ to 95℃ in a water-saturated atmosphere, and dried. An electrically insulated component can thus be produced.

Description

Potting composition to electrically insulate electrical or electronic components and electrical insulating components

The present invention relates to potting compositions. It further relates to a method of electrically insulating electrical or electronic components in the case of using potting compositions, and to electrically insulating components that can be produced by this method.

The standard method of encapsulating and protecting electronic components and also from their effective heat dissipation losses uses organically-bonded potting compositions, which have been mixed with ceramic fillers to increase the thermal conductivity of these organic-bonding potting compositions. This type of potting composition is known for example from DE 10 2008 045 424 A1. However, the organic matrix limits the heat resistance of the potting composition by virtue of the selected polymer. The requirement for sufficient fluidity during potting limits the amount of thermally conductive solids that can be used, because even before cross-linking, the inherent viscosity of the polymer is still significantly higher than that of water, and is generally between 50% and 60% by volume The volumetric filler content reaches the upper limit of treatability. The thermal conductivity that can be achieved with polysiloxane-elastomer-based potting compositions that can withstand temperatures up to 200°C is 2.5 to 3.0 W/mK.

The polymer bonding potting composition mixed with the ceramic filler also has a thermal expansion coefficient higher than that of the electronic component. Although elastic formulations can dissipate mechanical stress caused by differences in expansion, at use temperatures above 200°C, formulations may experience shrinkage and embrittlement. Accordingly, mechanical loads in the form of shear forces can act on the components.

By using potting compositions based on aluminum cements or phosphate cements, the heat resistance limit can be increased to at least 300°C and the thermal conductivity can be increased to well above 3.0 W/mK. Such potting compositions based on aluminum cements or phosphate cements are known, for example, from WO 2015/067441 A1. The liquid phase used in this article, namely water, has a very low viscosity; it permits high-filling thermally conductive ceramic particles above 70% by volume. Part of the water herein is bound to the cement to obtain a hydrate phase, which then acts as a binder matrix for encapsulating filler particles and thus causes thermal conductivity better than that of organic polymers. The thermal expansion coefficient of this article is also significantly lower than that of the polymer binding composition. However, after reaching the required maximum service temperature of 300°C, the formed hydrate phase is completely dehydrated. The result is a significant shrinkage of 0.4% to 0.6% and sometimes internal micro-cracking within the structure. Therefore, high shear forces are generated at the interface with the potted element. The thermal conductivity value is very high at first, and in addition it is greatly reduced. This is due to the loss of additional pore volume and the formation of microcracks due to water loss.

It is proposed to comprise as ingredients at least 5.0% by weight to 30.0% by weight, preferably 5.0% by weight to 20.0% by weight, particularly preferably 5.0% by weight to 15.0% by weight reactive particles, 45.0% by weight to 90.0% by weight filler particles and/or Or a potting composition of filler fiber and 5.0 wt% to 20.0 wt% water. These weight percentage data and all these data below are always based on 100% by weight of the overall potting composition.

The reactive particles are selected from magnesium oxide particles with a particle size of at most 5.0 μm, cohesive polymers of porous magnesium oxide particles (with a particle size of at most 75 μm), and silicon oxide particles with a particle size of at most 0.5 μm (amorphous oxidation of particles Silicon particles), silicon dioxide particles with a particle size of at most 0.5 μm and mixtures thereof. It permits hardening of the potting composition by reacting the reactive particles with water to form a thermally stable magnesium hydroxide hydrate phase, silicate hydrate phase and/or magnesium silicate hydrate phase.

The porous magnesia particle cohesive polymer can be produced by calcination. Magnesium oxide particles without pores can be produced by the fusion process.

The particle size of all particles can be determined by using a laser particle measuring instrument for grain size measurement and using a scanning electron microscope (SEM) for initial particle size measurement.

Preferably, the reactive particles are a mixture of magnesium oxide particles as first particles and silicon oxide particles and/or silicon dioxide particles as second particles. The weight ratio of the first particles to the second particles herein is in the range of 99:1 to 40:60. The weight ratio is particularly preferably between 90:10 and 70:30. Therefore, it is possible to produce a magnesium silicate hydrate phase with specific thermal stability.

The expression filler particles (filler particles) mean particles with a particle size (the initial particle size in more detail) higher than 1 μm. In detail, the materials suitable as filler particles are magnesium oxide, aluminum oxide, silicon, aluminosilicate, silicon carbide and boron nitride. In detail, other materials suitable as filler particles are kyanite, rutile, quartz and fluorite. Other materials suitable as filler particles are inorganic silicates, metal oxides, mixed oxides, spinels, nitrides, carbides and borides. In addition, in detail, it is also possible to use the following as filler particles: surface-oxidized silicon powder and surface-oxidized metal powder such as copper powder or aluminum powder.

Carbon can be used as filler particles, specifically in the form of diamonds.

Particularly preferred are alumina, kyanite, quartz, fluorspar, aluminosilicate, surface oxidized silicon powder, surface oxidized silicon carbide powder, and mixed oxides (detailed ferrite iron).

In detail, the filler fiber may be carbon fiber or carbon nanotube. Other organic or inorganic fibers are also suitable as filler fibers, or specific examples are amide fibers or glass fibers.

During hardening of the potting composition, the filler particles and filler fibers do not react with the water of the potting composition or at most react with the water surface of the potting composition. When magnesium oxide particles without pores with a particle size higher than 5.0 μm are used as filler particles, the hardening process is interrupted, after which any other hydroxide is formed to cause the hardened composition to swell.

The high proportion of filler particles that can be present in the potting composition permits extremely high thermal conductivity.

Some ratios of reactive particles, filler particles and water can give the potting composition thixotropy to a paste-like consistency, reducing its fluidity. Therefore, preferably, the potting composition further comprises 0.5% to 5.0% by weight of at least one plasticizer. In particular, suitable plasticizers are polycarboxylate ethers (PCE), polycondensates, polymer-based defoamers and wetting agents, and polycarboxylate ethers are preferred herein.

In addition, preferably, the potting composition further comprises 1.0 wt% to 15.0 wt% of at least one cross-linkable resin. The synthetic resin is particularly preferably polysiloxane. If a pore volume is formed during dehydration of the potting composition, its pore channel can be sealed by a synthetic resin, and its pore wall can be covered by a synthetic resin and thus hydrophobic by the synthetic resin.

It has been found that during an extended period of time under humid conditions, 5 mol% or less of silicon oxide or silicon dioxide and magnesium oxide (corresponding to 7.4% by weight relative to 100% by weight of the overall reactive particles) are used Silica or silica) and alumina fillers cause the formation of permeable bauxite as a new undesirable phase, which increases the volume and therefore causes structural expansion. Therefore, preferably, for the potting composition containing alumina, the proportion of silicon oxide and the proportion of silicon dioxide in the reactive particles is at least 8% by weight, specifically at least 14% by weight.

The potting composition can be used in a method of electrically insulating electrical or electronic components. The term component in this document is also intended to mean a module component. In detail, the electronic component may be a circuit having a high-power semiconductor such as a WBG semiconductor (wide-band gap semiconductor) on a direct-bonded copper (DBC) substrate. In addition, in detail, the element may be a passive element, such as an inductor coil or a transformer coil in a metal casing (for example, in a pot transformer, in a radiator with a current interrupter, or in a frame module). This method can also be used to electrically insulate battery cells. In addition to electrical insulation, improved heat loss dissipation is also achieved.

The method begins by using the potting composition to pot the element. Subsequently, the potted element is heat-treated in a water-saturated atmosphere at a temperature ranging from 50°C to 95°C. This article requires a minimum temperature in order to initiate the reaction between reactive particles and water in the potting composition. The highest temperature ensures an accelerated set response, and a water-saturated atmosphere is used to suppress evaporation. The duration of the heat treatment is preferably 30 minutes to 10 hours. After the heat treatment, the potted element is dehydrated at a temperature of preferably at most 40°C, preferably in the range of 30°C to 40°C. If dehydration occurs at a pressure below 100 kPa, it can also be carried out particularly at a temperature below 30°C. When magnesium oxide is used as a filler, this dehydration method prevents the formation of undesirable magnesium hydroxide from continuing, causing expansion of the hardened potting composition. When the potting composition does not contain magnesium oxide as a filler, it is also possible to perform accelerated dehydration at a higher temperature (for example, at 80°C).

Dehydration causes pore formation in the hardened potting composition. In order to prevent the subsequent absorption of water into these pores, it is preferable to use synthetic resin to seal the pores. Related to this, various specific examples of the method provide the possibility of introducing synthetic resins into the potting composition.

As for the potting composition itself does not contain a synthetic resin, in a specific example of the method, it is preferable to subject the potted element to pressure infiltration with a crosslinkable synthetic resin after dehydration.

In another specific example, pressure infiltration into the dehydrated potting composition structure is performed using a solid synthetic resin solution in an organic solvent such as ethanol or xylene.

If the potting composition itself already contains a synthetic resin, it is preferable to subject the potted element to another heat treatment at a temperature in the range of 150°C to 200°C after dehydration. The synthetic resin melts here, and the capillary force acting on the pore volume of the vacant residual water in the binder matrix draws the melt into the finest pores with a diameter in the submicron range. Therefore, the open pore structure becomes sealed, resulting in a substantially impermeable structure, or at least a hydrophobic layer covering the capillary surface is obtained. Therefore, capillary transport of polar fluids such as water or aqueous solutions is prevented in the resulting final product. If the crosslinkable resin is polysiloxane, then the polysiloxane is reacted at the stated temperature in the presence of an alkaline hydroxide with a crosslinked hardened potting composition to obtain Thermally stable thermosetting plastic with long-term temperature up to 350℃.

The sealing of the pore volume in the hardened potting composition in particular causes the water absorption of the potting composition to be reduced by at least 10 times during storage under water.

This method permits the production of electrically insulating elements, which in particular have insulation with a resistance higher than 10 ⁸ Ω×cm. Even after the hydrophobic pore filling, the potting composition based on magnesium oxide as a filler and exclusively based on magnesium hydroxide as a binder phase does not have a high temperature such as a temperature of at least 80°C and a high humidity such as 95% humidity Long-term stability at gas level. However, in order to ensure the dimensional stability of the electrical insulation, preferably, there is an airtight protective covering surrounding the electrical insulation element.

FIG. 1 is a flowchart of three specific examples of the method of the present invention. The procedure in this article begins with the provision of 10 potting compositions B1, B2 or B3. The composition of these potting compositions is stated in Table 1: Table 1

In Table 1 and the following table, d is the grain size range of the reactive particles and filler particles, and d50 is the median particle size.

Use the following components:

Magnesium oxide 2837 is produced by fusion process. Magnesium oxide 298 is composed of an open-pore magnesia particle agglomerate produced by calcination.

In step 11, the electronic components of the WBG semiconductor on the DBC substrate are encapsulated in a specific example of the present invention with individual potting compositions. The heat treatment in a water-saturated atmosphere takes place in step 12 in the curing oven. The treatment temperature is 80°C. The processing time of the potting composition B1 is one hour; the processing time of the potting compositions B2 and B3 is 10 hours. In step 13, the heat-treated potted elements are dehydrated. The dehydration temperature of the potting composition B1 is 35°C, and the dehydration temperature of the potting compositions B2 and B3 is 80°C. In this connection, the potted elements are placed in a convection oven in each case.

At this stage, the formation of brucite caused its instability when the hardened potting composition B1 was exposed to humid conditions for an extended period of time (longer than 5 days at 85°C and 100% relative humidity). Under these conditions, the formation of perensite makes the hardened potting composition B2 unstable. In contrast, the hardened potting composition B3 is dimensionally stable under these conditions.

Pressure infiltration with methyl polysiloxane resin (Wacker Chemie AG, MSE 100) occurred in step 14 at 200 bar pressure for one hour. This causes infiltration of the material with a thickness of 12 mm and absorption of 10% to 11% by mass. In this procedure, the pores formed in the hardened potting composition during the dehydration step, causing 20% by volume porosity, are completely sealed.

The thermal conductivity of the hardened potting composition thus treated is 5-10 W/mK.

In an alternative embodiment, the pressure infiltration of the solid methyl polysiloxane resin solution used in ethanol occurs in step 14. At the end of the pressure infiltration, the solvent is withdrawn, thus retaining the unfilled pore volume to some extent.

The method ends with the production of 16 electrically insulating elements 20. This situation is depicted in Figure 2. It consists of an electronic component 21 in the form of a WBG semiconductor on a substrate 22, which is in the form of a DBC substrate. The hardened potting composition 30 surrounds the element 21. An airtight protective cover 40 composed of silicone gel is also applied around the hardened potting composition 30. When the potting composition B3 is used, the airtight protective cover 40 can be omitted.

Figure 3 depicts the relative length change DL of various materials when the temperature T increases to 300°C and decreases again. However, the length change of metals such as copper Cu is reversible, and other materials depicted shrink after expansion, causing irreversible length changes. However, for the hardened potting compositions B1, B2, B3 according to specific examples of the present invention, this change in length is only slight and less than 0.20%. For example, the expansion and contraction behavior of an alumina-aluminum cement encapsulation composition of the type known from WO 2015/067441 A1 is depicted as Comparative Example VB. It can be seen that the shear force acting on the thus encapsulated element when using the encapsulating composition of the present invention is much smaller than that when using the encapsulating composition according to Comparative Example VB Shear force.

Another specific example of the present invention uses potting compositions B4 and B5. The composition of these potting compositions is stated in Table 2: Table 2

"Siloxane" is a reactive polysiloxane (Wacker Chemie AG, Silres MK).

The use of potting compositions B4 and B5 in electrically insulating elements differs from the procedure described for potting compositions B1 and B3 in which the pressure infiltration step 14 is replaced by a second heat treatment step 15. This case uses heat treatment in a convection oven at a temperature of 175°C. The polysiloxane present in the hardened potting composition melts here and is drawn to the pore walls by capillary force, where it hardens and crosslinks.

For the purpose of the hydrolysis-resistant and air-impermeable protective covering 40, the behavior of the potting composition B4 is similar to that of the potting composition B1, and the behavior of the potting composition B5 is similar to that of the potting composition B3 behavior.

10: Provide 11: potting 12: Heat treatment 13: Dehydration 14: Pressure infiltration 15: Heat treatment 16: Production 20: Electrically insulating components 21: Electronic components 22: substrate 30: Hardened potting composition 40: Airtight protective covering B1: Potting composition B2: Potting composition B3: Potting composition VB: Comparative example

Specific examples of the invention are depicted in the drawings and explained in more detail in the embodiments below. FIG. 1 is a flowchart of a specific example of the method of the present invention. 2 is a cross-sectional view of an electrically insulating element according to a specific example of the present invention. 3 is a graph showing thermal expansion and contraction of electrical insulation according to the present invention and according to the prior art.

10: Provide

11: potting

12: Heat treatment

13: Dehydration

14: Pressure infiltration

15: Heat treatment

16: Production

Claims (12)

A potting composition comprising 5.0% by weight to 30.0% by weight selected from the group consisting of magnesium oxide particles with a particle size of at most 5.0 μm, porous magnesium oxide particle cohesion, silicon oxide particles with a particle size of at most 0.5 μm, silicon dioxide particles with a particle size of at most 0.5 μm and their Reactive particles of the mixture, 45.0 wt%-90.0 wt% filler particles and/or filler fibers with a particle size higher than 1 μm, 5.0 wt%-20.0 wt% water. The potting composition according to claim 1, wherein the reactive particles are a mixture of magnesium oxide particles as first particles and silicon oxide particles and/or silicon dioxide particles as second particles, wherein the first particles The weight ratio of one particle to the second particles ranges from 99:1 to 40:60. The potting composition according to claim 1 or 2, wherein the filler particles are selected from the group consisting of alumina, kyanite, quartz, fluorspar, aluminosilicate, surface oxidized silicon powder , Surface oxidized silicon carbide powder, mixed oxides and mixtures thereof. The potting composition according to any one of claims 1 to 3, wherein it contains alumina particles as filler particles, wherein the oxidation in the reactive particles is 100% by weight of the reactive particles The proportion of silicon particles and/or silicon dioxide particles is at least 8% by weight. The potting composition according to any one of claims 1 to 4, further comprising 0.5% by weight to 5.0% by weight of at least one plasticizer. The potting composition according to any one of claims 1 to 5, wherein it further comprises 1.0% by weight to 15.0% by weight of at least one cross-linkable resin. The potting composition according to claim 6, wherein the synthetic resin is polysiloxane. A method for electrically insulating (21) electrical or electronic components, which includes the following steps: The component (21) is potted (11) with the potting composition as described in any one of claims 1 to 7, Heat-treating (12) the potted element (21) in a water-saturated atmosphere at a temperature ranging from 50°C to 95°C, and Dehydrate (13) the potted element (21). The method according to claim 8, wherein the potting composition is the potting composition according to any one of claims 1 to 5, and the potted element (21) is subjected to use after dehydration The pressure infiltration of the synthetic resin solution with solid synthetic resin in organic solvent (14). The method according to claim 8, wherein the potting composition is the potting composition according to claim 6 or 7, and the potted element (21) is subjected to a temperature between 150°C after dehydration Another heat treatment (15) at a temperature in the range of up to 200°C. An electrically insulating element (20), which can be produced by the method described in any one of claims 8 to 10. The electrically insulating element (20) according to claim 11, wherein it is surrounded by a gas-impermeable protective covering (40).

Images