Patent Description:
The present disclosure generally relates to materials for potting and encapsulating electronic components, and more particularly, relates to a multi-function and highly adaptable epoxy casting resin system designed for various applications in both indoor and outdoor environments.

A wide range of materials have been developed for potting and encapsulating electronic components. For example, materials made of epoxy resin are commonly used as potting compound in printed circuit board applications. While there is a variety of commercially available potting and encapsulation systems, there are drawbacks associated with each. For example, many currently used epoxies do not have sufficient thermal conductivity for use with electrical components which achieve high temperatures. Further, the epoxies that do achieve high thermal conductivity do so at the expense of other properties, such as strength, toughness, or electrical permittivity. Accordingly, there is a need for an improved epoxy casting resin system with desired properties.

<CIT> discloses curable epoxy resin compositions, cured epoxy resin compositions, and processes of forming the same, including at least one epoxy resin, at least one sterically hindered amine curing agent and at least one non-sterically hindered amine curing agent which provides toughness properties to the curable composition and resultant cured product made from the curable composition.

<CIT> discloses a curable epoxy resin formulation composition useful as insulation for an electrical apparatus including at least one liquid epoxy resin; at least one liquid cyclic anhydride hardener; at least one thermally conducting and electrically insulating filler, wherein the filler includes an epoxy-silane treated filler; and at least one cure catalyst with no amine hydrogens; wherein the epoxy resin formulation composition upon curing provides a cured product with a requisite balance of electrical, mechanical, thermal properties and volume resistivity such that the cured product can be used in applications operated at a temperature of greater than or equal to <NUM>.

Disclosed herein is an uncured epoxy resin according to claim <NUM> of the appended claims.

The bisphenol F epoxy resin can have a purity of at least <NUM>%. The bisphenol F epoxy resin can have a purity of at least <NUM>%.

Also disclosed herein is a method of producing a casting epoxy according to claim <NUM> of the appended claims.

Embodiments of the present invention provide a multi-function, highly adaptable material that can be used in various potting and encapsulation applications for both indoor and outdoor environments. In various embodiments, the material is an epoxy resin, cured epoxy, and/or epoxy casting resin system/epoxy resin system. The epoxy resin system can describe both the epoxy resin and/or the cured epoxy. The composition of the epoxy casting resin system can be formulated to achieve a combination of different desired properties without adversely affecting material performance. Specifically, embodiments of the disclosed epoxy resin system can have a high quantity of thermal conductive filler such as aluminum oxide and yet, still exhibit low mix viscosity and good physical strength. In certain embodiments, the epoxy resin system can provide a filled, medium viscosity, self-extinguishing flame retardant, low stress, thermally conductive material.

Embodiments of the disclosed epoxy resin system can be advantageous over other currently commercially available epoxies. For example, currently used epoxies can have insufficient thermal conductivity, electrical performance, and physical performance. If one of these properties were improved to sufficient levels, the other properties tend to decrease, thus making the commonly used epoxies not as desirable. However, as further described below, embodiments of the disclosed material can have about <NUM>% better thermal conductivity than current aluminum oxide based epoxies on the market. Further, embodiments of the disclosed cured epoxy can have about <NUM>% better electrical conductivity than current aluminum oxide based epoxies on the market. In addition, embodiments of the disclosed cured epoxy can have about <NUM>-<NUM>% better physical performance than current aluminum oxide based epoxies on the market.

While advantageous properties, such as thermal conductivity, achieved by the disclosed material can be obtained through the use of non-aluminum oxide filled epoxies, such as through the use of boron nitride, these are significantly more expensive. Accordingly, the disclosed material is a cost effective approach that has improved properties advantageous over other epoxies in its class.

The disclosed material may be an epoxy resin and/or cured epoxy with a full balance of enhanced material properties while maintaining adequate viscosity, thereby avoiding sacrificing ease of application which can happen to other resins on the market. For example, the disclosed material can have a low mixed viscosity, and is among the lowest commercially available for such a heavily thermally filled epoxy. Further, as discussed in detail below, embodiments of the disclosed material can have high thermal conductivity, increased strength (adhesive, physical, tensile, compressive, cohesive, etc.), low stress, and long pot life. In addition, embodiments of the disclosed material can have flexible ambient and thermal cure schedules. Further, embodiments of the disclosed material can have adjustable physical properties. Many of the current epoxies on the market cannot produce an cured epoxy and/or epoxy resin with the same properties as embodiments of the disclosed material.

Embodiments of the disclosed material can also have advantageous electrical properties, such as a low dielectric constant for such a heavily filled thermal management epoxy resin system, a high dielectric strength especially for a heavily filled thermal management epoxy resin system, and great electrical resistance.

Epoxide functional groups, or epoxy resins, can be cured to form epoxies or cured epoxies. These epoxy resins, or polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. Typically, these epoxy resins react, thereby forming cross links, through a number of different processes. For example, catalytic homopolymerization can be used to react an epoxy resin with itself. Further, co-reactants (known as hardeners or curatives), such as polyfunctional amines, acids, acid anhydrides, phenols, alcohols, and thiols can all be used to react epoxy resins.

The reaction that takes place in an epoxy resin can form cross-links, thereby solidifying the epoxy resin into a final product, known as an epoxy or cured epoxy. The cross-linking reaction can also be known as curing. In some embodiments, the final epoxy can have improved physical properties, such as high temperature and chemical resistance.

In the invention, the composition of an epoxy casting resin system includes many different components.

In the invention, the epoxy resin contains <NUM>%-<NUM>% by weight of bisphenol F epoxy resin as an epoxy resin base reactive constituent. In one embodiment, the bisphenol F epoxy resin can be high performance/high purity grade. In some implementations, the bisphenol F epoxy can have a dimer content of greater than about <NUM>%, <NUM>%, or <NUM>%.

In the invention, a diluent is also used in the epoxy resin. The diluent acts a diluting agent, which can decrease the viscosity of the substance, such as fluid, that the diluent is incorporated into. In some embodiments, the diluent can also be used in the process of solvent extraction. In the invention, <NUM>%-<NUM>% by weight of diluent is used. In the invention, the diluent is butyl glycidyl ether.

The disclosed epoxy resin is also colored. In the invention, color pigments are added into the resin to change or modify the color of the resin. In some embodiments, the color pigment does not affect the physical properties of the resin or final cured epoxy. In some embodiments, the color pigment can affect the physical properties of the resin or final cured epoxy. In the invention, <NUM>%-<NUM>% by weight of color pigments is used. In the invention, an epoxy carbon black dispersion is used. However, other types of coloring can be used, such as liquid dyes, and the type of coloring is not limiting. Further, other colors can be used, and the type of color used is not limiting.

The disclosed epoxy resin also contains thermally conductive filler. In the invention <NUM>%-<NUM>% by weight of aluminum oxide is used as the thermally conductive filler. In some embodiments, the aluminum oxide can have a purity of at least about <NUM>%, <NUM>%, or <NUM>%. In some embodiments, the aluminum oxide can have an average particle size of less than about <NUM> (<NUM> Mesh), <NUM> (<NUM> Mesh), <NUM> (<NUM> Mesh) or <NUM> (<NUM> Mesh). Typically, the use of such a high percentage of thermally conductive filler can lead to an epoxy resin that is so thick that it cannot be used. Advantageously, embodiments of the disclosed epoxy resin can be well filled with the thermally conductive filler, thereby maintaining high thermal conductance, while still having acceptable viscosity levels, as further discussed below.

In the invention, <NUM>%-<NUM>% by weight of a reactive constituent is also used. The reactive constituent is a phosphorous salt. An organophosphorous salt can be used as the phosphorous salt. The phosphorous salt can be used as a flame retardant, which can allow the resin to have self-extinguishing characteristics. Further, the use of the salt can lend to thermal conductivity and structural integrity of the cured resin.

In the invention, <NUM>%-<NUM>% by weight of flame retardant is used as well. Alumina trihydrate and ammonium polyphosphate are used in combination. In some embodiments, the alumina trihydrate can have a purity of at least about <NUM>%, <NUM>%, or <NUM>%. In some embodiments, the ammonium polyphosphate can have a purity of at least about <NUM>%, <NUM>%, or <NUM>%. However, other flame retardants can be used and the type of flame retardant is not limiting. In the invention, <NUM>-<NUM> wt. % alumina trihydrate is used, and <NUM>-<NUM> wt. % ammonium polyphosphate is used. In some embodiments, the alumina trihydrate and ammonium polyphosphate can have low particle size and low viscosity.

In the invention, <NUM>%-<NUM>% by weight of a reactive agent is used. Polyglycol diamine is used as the reactive agent. In some embodiment, the polyglycol diamine can be high performance/high purity grade. For example, in some embodiments the polyglycol diamine can have a purity of greater than <NUM>%, <NUM>%, or <NUM>%. In some embodiments, the polyglycol diamine can have low viscosity. The polyglycol diamine can be used as a curative agent (reactant) so as to bring about the reactive process which can result in the curing and cross-linking of the epoxy resin.

In the invention, <NUM>%-<NUM>% by weight of a reactive agent/catalyst is used. A polyamine blend is used. The polyamine blend can be used as a curative agent (reactant) so as to bring about the reactive process which can result in the curing and cross-linking of the epoxy resin. Specifically, the polyamine blend can be a reactive agent utilized primarily as a catalyst to initiate and promote the curing of the epoxy resin. Further, the polyamine blend can allow for the resin to be cured at room temperature and can improve short thermal cure cycles.

An embodiment of a composition of the disclosed epoxy resin and/or cured epoxy is listed below in table <NUM>.

In the invention, as described below, the final cured resin is formed by the mixing of two parts including different materials. These parts are a resin part (Part A) and a hardener part (Part B). These parts are mixed together to begin the reaction process. In the invention, the bisphenol F epoxy resin, butyl glycidyl ether, epoxy carbon black dispersion, aluminum oxide, phosphorous salt, alumina trihydrate, and ammonium poly phosphate are Part A, and polyglycol diamine and polyamine blend are Part B.

The disclosed epoxy resin system can have numerous advantageous properties. For example, embodiments of the disclosed epoxy resin system can be a medium viscosity, self-extinguishing flame retardant, low stress, thermally conductive epoxy resin system.

Further, embodiments of the disclosed epoxy resin system can be RoHS compliant. In addition, embodiments of the disclosed epoxy resin system can be UL 94V0 rated, and can meet the physical security requirements of FIPS <NUM>-<NUM>, and FIPS <NUM>-<NUM> for encapsulating material.

In some embodiments, the disclosed epoxy resin system can provide for good whisker, such as tin-whisker, mitigation properties. In some embodiments, the disclosed epoxy resin system can have good resistance to water, salt spray, inorganic acids, bases, and most organic solvents. Accordingly, embodiments of the epoxy resin system can be used both indoors and outdoors.

In some embodiments, the resin can exhibit good wetting and adhesion to most surfaces. Further, the resin can be free flowing to penetrate voids and provide good air release.

In some embodiments, the resin can contain a flame retardant package and thermal conductive fillers which can settle over time. In some embodiments, the resin has good resistance to hard settling.

Further described are some properties of embodiments of the resin system. All properties are at <NUM> unless noted otherwise. Table <NUM> illustrates some of the physical properties of the uncured resin. Table <NUM> illustrates some of the physical properties of embodiments of the cured resin. Table <NUM> illustrates some of the thermal properties of embodiments of the cured resin. Table <NUM> illustrates some of the electrical properties of embodiments of the cured resin. In all of the below tables, the numeric values should be understood to include the term about or approximately.

As embodiments of the disclosed epoxy resin system can be considered heavily filled (e.g. having high amounts of thermal fillers), it is unexpected that the disclosed resin achieves lower permittivity than comparably filled resins. Typically, adding thermal fillers into an epoxy resin system causes the electrical permittivity to increase, sometimes drastically. Advantageously, the disclosed cured epoxy does not have this negative effect.

Further, embodiments of the disclosed resin may impact strength, and electrical RTIs of <NUM>. The RTI temperature indicates the maximum service temperature for a material where specific properties are not unacceptably compromised, generally defined as having greater than <NUM>% of its typical properties. Most epoxies currently in use have a RTI of <NUM>. Accordingly, embodiments of the disclosed resin have an advantageously high RTI, which allows the resin to hold its properties for longer at higher temperatures.

In some embodiments, the disclosed epoxy resin system can have a flammability of V-<NUM> (BK) under IEC <NUM>-<NUM>-<NUM>. Further, the resin can have a high-voltage arc tracking rate of <NUM> and a dimension stability % of <NUM>. The <NUM> results indicate that the material passed the tests at the top level.

In the invention, Part A and Part B of the disclosed epoxy resin are formed separately. <FIG> illustrates an embodiment of a method for making a cured epoxy.

For Part A, the bisphenol F resin, the butyl glycidyl ether diluent, and the carbon black dispersion pigment can be blended together at low and high speeds to shear. This blending can be done for high speeds of shear. The high blending speed of this step may be approximately <NUM>% faster than the high blending speed of the first step. This blending can be done for approximately <NUM> minutes. After blending, the aluminum trihydrate flame retardant can be added to the mixture. This can then be blended together at low and high speeds of shear. This blending can be done for approximately <NUM> minutes. Following, the ammonium poly phosphate flame retardant can be added to the mixture. This can then be blended together at low and high speeds of shear. This blending can be done for approximately <NUM> minutes. After blending, portions of the aluminium oxide thermal filler can be added. In some embodiments, only a portion of the thermal filler may be added, then blended, and then another portion of thermal filler is added, and then blended, until all thermal filler is added. For example, the portions can be about <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>% of the thermal filler. This can then be blended together at low and high speeds of shear. This blending can be done for approximately <NUM> minutes. Afterwards, the entire mixture can be blended under low and high speed shear under vacuum. This vacuum blending can be done for approximately <NUM> minutes. A machine used for blending can be cleaned after each step. A person having skill in the art would understand that other basic methods of producing the resin could be used, and the method is not limiting.

In some embodiments, a different method for forming Part A can be used. Instead of waiting until the end to add the thermal filler, a portion of the thermal filler can be blended along with the resin, diluent, and pigment in the first step. For example, approximately <NUM>, <NUM>, or <NUM>% of the total thermal filler can be added. The remaining thermal filler is added at the end as describe above. This method can be advantageous as it can provide for better dispersion and wetting of the thermal filler in the epoxy resin. Further, it can reduce the likelihood of soft settling. In addition, this method can use less diluent (a solvent), thus allowing for a greener material.

In the invention, Part B is formed by mixing together the polyglycol diamine reactive agent and the polyamine blend catalyst. These reactive agents and catalysts can be in liquid form. In some embodiments, the reactive agents and catalysts can be blended at medium speeds for about <NUM> minutes.

To begin the curing process, in invention, Part A and Part B are mixed together. In some embodiments, mix ratio of Part A to B can be, by weight, <NUM> to <NUM> (variable up to <NUM>:<NUM>). In some embodiments, mix ratio of Part A to B can be, by volume, <NUM> to <NUM> (variable up to <NUM>:<NUM>).

In some embodiments, the resin can reach a state of "cure-to-handle" at room temperature within about <NUM> hours. However, the time can change depending on mass and ambient temperature. Embodiments of the resin can cure within about <NUM> to <NUM> hours, though this can be accelerated by the application of heat. Times and temperatures from <NUM> hours at <NUM> to <NUM> minutes at <NUM> can be achieved. In some embodiments, the resin can cure at room temperature. Upon curing, embodiments of the resin can form a tough, semirigid polymer that exhibits good wetting and adhesion to most surfaces. Further, the resin can be free flowing to penetrate voids and provide good air release, while offering good resistance to hard settling. Table <NUM> illustrates some of the cure schedule of embodiments of the resin.

An epoxy resin was prepared by mixing together <NUM> wt. % bisphenol F epoxy resin, <NUM> wt. % butyl glycidyl ether, <NUM> wt. % epoxy carbon black dispersion, <NUM> wt. % aluminum oxide, <NUM> wt. % phosphorous salt, <NUM> wt. % alumina trihydrate, and <NUM> wt. % ammonium poly phosphate. A curative/hardener was prepared by mixing together <NUM> wt. % polyglycol diamine and <NUM> wt. % polyamine blend. The epoxy resin and the hardener were then mixed together at a <NUM> to <NUM> weight mix ratio (or a <NUM>:<NUM> to <NUM> volume mix ratio) to form a resin which was poured in a container for curing. The mixed resin was then cured for <NUM> hours at <NUM>. The cured epoxy had physical properties of a tensile strength of <NUM> MPa (<NUM> psi), a tensile modulus of <NUM> MPa (<NUM> psi), a compressive strength of <NUM> MPa (<NUM> psi), a shear strength of <NUM> MPa (<NUM> psi), an Izod impact of <NUM> J/m (<NUM> ft. /in), a relative temperature index for both impact and strength of <NUM>. Further, the cured epoxy had thermal properties of a thermal conductivity of <NUM> W/(m·K) at <NUM> and an extrapolated coefficient of thermal expansion of <NUM> in/in/°C × <NUM>-<NUM> (below Tg). In addition, the cured epoxy had electrical properties of a volume resistivity of <NUM> × <NUM><NUM> ohm·m (<NUM> × <NUM><NUM> ohm·cm), a relative temperature index for electrical of <NUM>, a dielectric constant of <NUM> at <NUM> and <NUM> at <NUM>, and a dissipation factor of <NUM> at <NUM> and <NUM> at <NUM>. The properties achieved by an embodiment of the disclosed resin indicates that the disclosed resin has improved and advantageous physical, thermal, and electrical properties over other epoxies in the same class.

Embodiments of the disclosed epoxy resin system can have many different uses. For example, the disclosed epoxy resin system can be used in:.

The disclosed uses are not limiting, and the disclosed epoxy resin system can have other uses.

In some embodiments, the disclosed epoxy resin system can be used in:.

In some embodiments, the disclosed resin can be used with electronics and other electric systems. For example, the resin can be incorporated into motors, generators, transformers, switchgears, bushings, and insulators. As embodiments of the disclosed epoxy resin system can have excellent electrical resistance, the resin can be advantageous for covering electrical components to prevent shorting, and to keep particles like dust and moisture, out of the electrical components. Further, embodiments of the epoxy resin system can be used in the overmolding of integrated circuits, transistors, and hybrid circuits.

The disclosed resin can be used in the potting and or encapsulation of electronics. In the potting process, the resin can fill an electronic component or assembly, thus reducing shock and vibration. The potted resin can also prevent moisture, dust, particles, and other corrosive elements from entering the electronic assembly. Embodiments of the disclosed resin can also have a high thermal conduction, and can have a higher thermal conduction than air. Accordingly, embodiments of the disclosed resin can be used for potting transformers and inductors, thereby reducing and/or eliminating hot spots, giving the transformers and inductors a stable and longer life than unspotted components. In some embodiments, the disclosed resin can be used for potting or encapsulating electronic components in a printed circuit board, such as shown in <FIG>. The potted or encapsulated electrical components on the printed circuit board can withstand both indoor and outdoor environments without degradation.

In some embodiments, the resin can be used for casting. For example, the resin can be used for filling, sealing, covering, or soaking technical parts. In some embodiments, the resin can be used in casting electronic components, for example transformers and liquid crystal displays.

Embodiments of the disclosed resin can be used in many fields of interest. For example, embodiments of the disclosed epoxy resin system can be used in the fields of:.

The disclosed fields are not limiting, and the disclosed epoxy resin system can be used in other fields as well.

Conditional language, such as "can," "could," "might," or "may," unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include or do not include certain features, elements, and/or steps. Thus, such conditional language is not generally intended to imply that features, elements, and/or steps are in any way required for one or more embodiments.

For example, the terms "approximately", "about", "generally," and "substantially" may refer to an amount that is within less than or equal to <NUM>% of, within less than or equal to <NUM>% of, within less than or equal to <NUM>% of, within less than or equal to <NUM>% of, and within less than or equal to <NUM>% of the stated amount.

Claim 1:
An uncured epoxy resin comprising:
<NUM>-<NUM> wt. % of at least one epoxy resin base reactive constituent, wherein the at least one epoxy resin base reactive constituent comprises bisphenol F epoxy resin;
<NUM>-<NUM> wt. % of diluent, wherein the diluent comprises butyl glycidyl ether;
<NUM>-<NUM> wt. % of at least one color pigment, wherein the at least one color pigment comprises epoxy carbon black dispersion;
<NUM>-<NUM> wt. % of at least one thermally conductive filler, wherein the at least one thermally conductive filler comprises aluminum oxide;
<NUM>-<NUM> wt. % of at least one reactive constituent, wherein the at least one reactive constituent comprises phosphorous salt;
<NUM>-<NUM> wt. % of at least one flame retardant, wherein the at least one flame retardant comprises <NUM>-<NUM>% alumina trihydrate and <NUM>-<NUM>% ammonium poly phosphate;
<NUM>-<NUM> wt. % of at least one reactive agent, wherein the at least one reactive agent comprises polyglycol diamine; and
<NUM>-<NUM> wt. % catalyst, wherein the at least one catalyst comprises polyamine blend.