US20130062045A1

US20130062045A1 - Heat-conductive dielectric polymer material and heat dissipation substrate containing the same

Info

Publication number: US20130062045A1
Application number: US13/232,515
Authority: US
Inventors: Fu Hua Chu; David Shau Chew Wang; Yi An Sha; Kuo Hsun Chen
Original assignee: Polytronics Technology Corp
Current assignee: Polytronics Technology Corp
Priority date: 2011-09-14
Filing date: 2011-09-14
Publication date: 2013-03-14

Abstract

A heat-conductive dielectric polymer material includes a thermosetting epoxy resin, a nonwoven fiber component, a curing agent and a heat-conductive filler. The thermosetting epoxy resin is selected from the group consisting of end-epoxy-function group epoxy resin, side chain epoxy function group epoxy resin, multi-functional epoxy resin or the mixture thereof. The thermosetting epoxy resin comprises 4%-60% by volume of the heat-conductive dielectric polymer material. The curing agent is configured to cure the thermosetting epoxy resin at a curing temperature. The heat-conductive filler comprises 40%-70% by volume of the heat-conductive dielectric polymer material. The nonwoven fiber component comprises 1%-35% by volume of the heat-conductive dielectric polymer material. The heat-conductive dielectric polymer material has a thermal conductivity greater than 0.5 W/mK.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not applicable.

INCORPORATION-BY-REFERENCE OF MATERIALS SUBMITTED ON A COMPACT DISC

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present application relates to a heat-conductive dielectric polymer material and a heat dissipation substrate containing the same, and more particularly to a heat-conductive dielectric polymer material having fiber component and a heat dissipation substrate containing the same.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
In recent years, the white light emitting diode (LED) has gained considerable attention worldwide as an important new technology with broad applications and numerous benefits. LED technology offers the advantages of having a small volume, low power consumption, long lifetime, a favorable reaction speed, and overcomes many of the problems of incandescent lamps. LED technology is used in many applications, including backlights for the LCD displays, mini-projectors, illuminators and light sources for vehicles, attracting increasing attention.
However, in high-power LEDs used for illumination, only about 15%-20% of the power inputted into the LED is converted into light, while the remaining 80%-85% is converted into heat, and the heat cannot be dissipated to the environment at the appropriate time. Thus, the interfacial temperature of the LED component is excessively high, thereby affecting the intensity of the emitted lights and the lifetime. Therefore, heat management of LED components becomes increasingly important.
FIG. 1 is a schematic view of a heat dissipation substrate 10 conventionally applied in an electronic component (e.g., an LED component, not shown). The heat dissipation substrate 10 includes a heat-conductive dielectric material layer 12 and two metal foils 11 respectively stacked on the upper and lower surfaces of the heat-conductive dielectric material layer 12. The electronic component is disposed above the upper metal foil 11. The conventional process for forming the heat dissipation substrate 10 includes the following steps. First, a liquid epoxy resin and a heat-conductive filler (e.g., aluminum oxide particles) are mixed, and then a curing agent is added, so as to form a slurry. Gas contained in the slurry is then removed through a vacuum process and the slurry is coated on the lower metal foil 11. The upper metal foil 11 is then disposed on the surface of the slurry to form a composite structure of metal foil/slurry/metal foil. Next, the composite structure is hot-pressed and cured to form the heat dissipation substrate 10, in which the slurry is formed into the heat-conductive dielectric material layer 12 upon being hot-pressed and cured.
However, the conventional art is limited by the property of the slurry and has the following disadvantages: (1) the conventional art must be finished within a specific time; otherwise, the slurry will cure and cannot be coated on the metal foil, causing a waste of the slurry; and (2) when the hot-press step is conducted in the conventional art, a quantity of slurry flows out of the two metal foils 11, and a separation between solid and liquid occurs upon reaching the hot-press temperature, thus, the heat-conductive filler is non-uniformly distributed in the heat-conductive dielectric material layer 12, thereby affecting the heat dissipation efficiency of the heat dissipation substrate 10. Furthermore, the slurry is difficult to be stored and the flexibility of the process for forming the heat dissipation substrate is limited by the viscosity of the slurry (e.g., heat dissipation substrates with different shapes cannot be fabricated efficiently).
In other words, the slurry of the mixture of the liquid epoxy resin, the heat-conductive filler and the curing agent is coated on a metal substrate, and is heated to B-stage and hot-pressed to form a circuit board. Likewise, as to a FR4 circuit board, epoxy resin is coated on a glass fiber cloth and then is heated to B-stage, and then it undergoes hot-press to form a glass fiber circuit board.
The above process uses slurry with low viscosity in which solid-liquid separation occurs due to the precipitation of heat-conductive filler. Consequently, the slurry is not evenly mixed and the efficiency of heat dissipation is decreased. Moreover, the slurry is not easily stored. Because the thermal conductivity of the glass fiber cloth is low, for example, approximately 0.36 W/mK, the circuit board using the glass fiber cloth performs poor heat dissipation efficiency.
In summary, known heat-conductive circuit board uses slurry with low viscosity, and thus solid-liquid separation will occur easily. Moreover, the circuit board having glass fiber cloth performs poor heat dissipation behavior due to the low thermal conductivity of glass fiber cloth. Therefore, it is desirable to develop a heat-conductive dielectric material serving as high efficient heat dissipation medium for circuit boards.

BRIEF SUMMARY OF THE INVENTION

An aspect of the present application is to provide a heat-conductive dielectric polymer material, which contains nonwoven fiber component and thus is rubbery, thereby enhancing its processibility and heat dissipation property.
In another aspect, the present application provides a heat dissipation substrate containing the heat-conductive dielectric polymer material, which has a preferable heat dissipation property and a high voltage resistant dielectric property.
The present application discloses a heat-conductive dielectric polymer material having a fiber component. The heat-conductive dielectric polymer material includes a polymer component, a nonwoven fiber component, a curing agent and a heat-conductive filler. The polymer component includes a thermosetting epoxy resin. The curing agent is configured to cure the thermosetting epoxy resin at a curing temperature. The nonwoven fiber component and the heat-conductive filler are uniformly dispersed in the polymer component. In an embodiment, the heat-conductive filler comprises 40%-70% by volume of the heat-conductive dielectric polymer material, whereas the nonwoven fiber component comprises 1%-35% by volume of the heat-conductive dielectric polymer material. The heat-conductivity of the heat-conductive dielectric polymer material is larger than 0.5 W/mK.
In an embodiment, the thermosetting epoxy resin of the polymer component may be end-epoxy-function group epoxy resin, side chain epoxy function group epoxy resin, multi-functional epoxy resin or the mixture thereof. The thermosetting epoxy resin comprises 4%-60% by volume of the heat-conductive dielectric polymer material.
In an embodiment, the nonwoven fiber component may include inorganic ceramic fiber, organic polymer fiber or the mixture thereof. For example, glass fiber, aluminum oxide fiber, carbon fiber, polypropylene fiber, polyester fiber, or the mixture thereof. In terms of shapes, the nonwoven fiber component may include a chopped strand fiber.
In an embodiment, the polymer component may further include thermoplastic. In other words, thermoplastic is added to the thermosetting epoxy resin, and they are mutually soluble and form a homogeneous mixture before curing. Thus, the heat-conductive filler can be uniformly dispersed in the mixture to obtain optimal heat-conductive efficiency. Due to the properties of the thermoplastic and the fiber component, the heat-conductive dielectric polymer material can be molded by a thermoplastic process such as extrusion, calendaring or injection molding. Furthermore, the thermosetting epoxy resin can be cured and cross-linked at a high temperature, so that the thermoplastic and the thermosetting epoxy resin form an inter-penetrating network (IPN) structure, which not only has the thermosetting plastic properties of good high temperature deformation resistance and the thermoplastic properties of tenacious and non-brittle characteristics, but also can be strongly adhered to metal electrodes or a substrate.
The present application further discloses a heat dissipation substrate, which comprises a first metal layer, a second metal layer and a layer containing the aforementioned heat-conductive dielectric polymer material. The heat-conductive dielectric polymer material layer is sandwiched between and in physical contact with the first metal layer and the second metal layer. The metal layers and the thermosetting plastic are combined by hydrogen bonding or Van der Waals force, and the metal layers subjected to chemical surface treatment can be used to form more stable chemical bonding with the thermosetting plastic. The heat-conductive dielectric polymer material layer can withstand a voltage larger than 2000 volts in the case that the heat-conductive dielectric polymer material layer has a thickness of 0.1 mm.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The present application will be described according to the appended drawings in which:

FIG. 1 shows a known heat dissipation substrate for electronic device applications; and

FIG. 2 shows a heat dissipation substrate in accordance with an embodiment of the present application.

DETAILED DESCRIPTION OF THE INVENTION

The heat-conductive dielectric polymer material of the present application includes a polymer component, a nonwoven fiber component, a curing agent and a heat-conductive filler. The polymer component includes a thermosetting epoxy resin, which comprises 4% to 60%, preferably 6% to 50%, and especially preferably 8% to 40% by volume of the heat-conductive dielectric polymer material. The curing agent is used to cure the thermosetting epoxy resin at a curing temperature. The heat-conductive filler is uniformly dispersed in the polymer component, and comprises 35% to 75%, preferably 40% to 70%, and most preferably 45% to 65%, by volume of the heat-conductive dielectric polymer material. The nonwoven fiber component comprises 1%-35%, preferably 2%-30% and most preferably 3%-25% by volume of the heat-conductive dielectric polymer material. The thermal conductivity of the heat-conductive dielectric polymer material is greater than 0.5 W/mK, preferably greater than 1.0 W/mK, and most preferably greater than 1.5 W/mK.
FIG. 2 is a schematic view of a heat dissipation substrate 20 of the present application. The heat dissipation substrate 20 includes a first metal layer 21, a second metal layer 22, and a heat-conductive dielectric polymer material layer 23 having a nonwoven fiber component 24. The heat-conductive dielectric polymer material layer 23 is in physical contact with the first metal layer 21 and the second metal layer 22, and in an embodiment at least one of the interfaces is a micro rough surface 25 that includes a plurality of nodular protrusions 26 with the diameters mainly distributed between 0.1 μm and 100 μm, so as to enhance the tensile strength therebetween. The nodular protrusions 26 may include copper, nickel, zinc or arsenic plated layer, or organic silicon, organic titanium coatings.
The methods for fabricating the heat-conductive dielectric polymer material layer 23 and the heat dissipation substrate 20 are described as follows. First, the thermosetting epoxy resin and the fiber component are mixed while being heated at 170° C. for 30 minutes, so as to form a uniform mixture. The heat-conductive filler is then added into the uniform mixture, and they are mixed evenly to form a uniform rubbery material. The curing agent and an accelerating agent are then added into the uniform rubbery material having the fiber component at a temperature of 80° C. A hot-press process is then used to dispose the uniform rubbery material between two release films at 100° C., which is then leveled under a pressure of 30 kg/cm², so as to form the heat-conductive dielectric polymer material layer 23, which is a lamella-shaped heat-conductive dielectric composite material. In order to fabricate the heat dissipation substrate 20, the two release films are stripped off from the upper and lower surfaces of the heat-conductive dielectric polymer material layer 23. Next, the heat-conductive dielectric polymer material layer 23 is melt extruded at the temperature at least 30° C. below the curing temperature of the curing agent, and is sandwiched between the first metal layer 21 and the second metal layer 22, and after being hot-pressed for 30 minutes at 160° C. to crosslink the heat-conductive dielectric polymer layer to form a crosslinked heat dissipation substrate 20 with a thickness of, for example, 0.2 mm. The lamella-shaped heat-conductive dielectric composite material has the nonwoven fiber component, thereby enhancing the rigidity thereof and preventing the substrate from bending that may be caused by hot-press. Because the polymer component has a relatively high viscosity (about 10⁵to 10⁷poise), solid-liquid separation will not occur. The material of the first metal layer 21 and the second metal layer 22 may be selected from copper, nickel, or another metal processed by means of electroplating or other physical coating methods. The appearance of the lamella-shaped heat-conductive dielectric composite material is rubbery (not slurry); thus, it is easily stored and processed. Moreover, the heat-conductive dielectric composite material can be processed by a method commonly used for processing thermoplastic, thereby enhancing its processibility.
Table 1 shows the composition of the heat-conductive dielectric polymer material layer used in the heat dissipation substrate in accordance with the four embodiments (Em 1 to Em 4) of the present application and a comparative example (Comp). Table 2 shows appearance, thermal conductivity of the heat-conductive dielectric polymer material layer, and the corresponding voltage resistance according to Em 1 to Em 4 and Comp. The thickness of the heat-conductive dielectric polymer material layer in each embodiment and comparative example is approximately 0.2 mm.

	TABLE 1

	Component (volume %)

Heat-	Liquid epoxy
conductive	resin	Curing agent	Glass	Polyester
filler Al₂O₃	DER331	100S/UR500	fiber	fiber (PET)

Em 1	40	28	1.6/0.4	30	0
Em 2	55	28	1.6/0.4	15	0
Em 3	55	28	1.6/0.4	7	8
Em 4	70	25.1	1.5/0.4	3	0
Comp	60	37.3	2.2/0.5	0	0

TABLE 2

		Melt		Break-
		extrusion	Thermal	down
Uncured	Separation	to lamella-	conductivity	Voltage
appearance	(100° C.)	shaped film	(W/mK)	(KV)

Em 1	Rubbery	No	Yes	0.51	9.6
Em 2	Rubbery	No	Yes	1.46	8.5
Em 3	Rubbery	No	Yes	1.48	8.6
Em 4	Rubbery	No	Yes	2.83	6.9
Comp	Slurry	Yes	No	1.98	7.9

Table 3 shows the composition of the heat-conductive dielectric polymer material layer used in the heat dissipation substrate in accordance with five embodiments (Em 5 to Em 9) of the present application, in which thermoplastic is further added to increase impact resistance and strength of the material. Table 4 shows appearance, thermal conductivity of the heat-conductive dielectric polymer material layer, and the corresponding voltage resistance according to Em 5 to Em 9. The thickness of the heat-conductive dielectric polymer material layer in each embodiment is approximately 0.2 mm.

	TABLE 3

	Component (volume %)

Heat-	Liquid		Curing
conductive	epoxy	Thermo-	agent		Polyester
filler	resin	plastic	100S/	Glass	fiber
Al₂O₃	DER331	Phenoxy	UR500	fiber	(PET)

Em 5	40	23.4	10	1.3/0.3	25	0
Em 6	40	16.9	30	0.9/0.2	12	0
Em 7	55	21.5	7	1.2/0.3	8	7
Em 8	55	12.2	17	0.6/0.2	8	7
Em 9	70	21.5	5	1.2/0.3	2	0

TABLE 4

		Melt
		extrusion
		to lamella-	Thermal	Breakdown
Uncured	Separation	shaped	conductivity	Voltage
appearance	(100° C.)	film	(W/mK)	(KV)

Em 5	Rubbery	No	Yes	0.51	9.2
Em 6	Rubbery	No	Yes	0.52	9.0
Em 7	Rubbery	No	Yes	1.49	8.5
Em 8	Rubbery	No	Yes	1.47	8.8
Em 9	Rubbery	No	Yes	2.91	7.2

The particle sizes of the heat-conductive filler Al₂O₃in Tables 1 and 3 are between 5 and 45 μm, which is produced by Denki Kagaku Kogyo Kabushiki Kaiya Company. The liquid epoxy resin adopts the DER331™ of Dow Chemical Company, which is a thermosetting epoxy resin. The curing agent adopts a dicyandiamide (Dyhard 100S™) of Degussa Fine Chemicals Company, and accelerating agent is UR-500. The thermoplastic is an ultra-high molecular phenoxy resin PKHH™ from the Phenoxy Associates with a weight average Mw of larger than 30000.
It can be known from Tables 1 and 2 that, in Em 1-4 of the present application, after the curing agent is added, the thermosetting epoxy resin (liquid epoxy resin is used in the Em 1-4 and Comp in Table 1) is reacted with the nonwoven fiber component such as glass fiber and polyester fiber to form a fiber-reinforced structure, thus, the obtained heat-conductive dielectric polymer material layer has a rubbery appearance and is suitable for melt extrusion, and solid-liquid separation will not occur during the hot-press at 100° C. Moreover, according to the thermal conductivity and breakdown voltage shown in Table 2, the four embodiments of the present application can indeed meet the requirements for the heat dissipation conditions of electronic components. However, the comparative example (Comp) without adding fiber component shows slurry appearance before curing, and solid-liquid separation occurs during hot-press process. In addition, the heat-conductive dielectric polymer material of the comparative example cannot be melt-extruded to a lamella-shaped film, and thus it is not easily processed.
It can be known from Tables 3 and 4 that, in Em 5-9 of the present application, in addition to the thermosetting epoxy resin and the nonwoven fiber component, the thermoplastic is further introduced. After the curing agent is added, the thermosetting epoxy resin is reacted with the thermoplastic to form an IPN structure. Thus, the obtained heat-conductive dielectric polymer material layer exhibits reinforced rubbery behavior and is suitable for melt extrusion process, and solid-liquid separation will not occur during hot-press process. According to the thermal conductivity and breakdown voltage shown in Table 4, the embodiments of the present application can indeed satisfy the requirements for the heat dissipation conditions of electronic components.
According to Tables 1-4, the thermal conductivities are greater than 0.5 W/mK, preferably greater than 1.0 W/mK, most preferably greater than 1.5 W/mK, and voltage endurance characteristics are greater than 500V/0.1 mm, preferably 2000V/0.1 mm, and most preferably 3000V/0.1 mm.
According to the aforementioned embodiments, the heat-conductive dielectric polymer material uses nonwoven fiber component to significantly enhance rigidity and support behavior thereof. Moreover, the IPN structure may be further introduced, in which the thermoplastic and the thermosetting epoxy resin in the heat-conductive dielectric polymer material are substantially mutually soluble. The term “substantially mutually soluble” means that the thermoplastic and the thermosetting epoxy resin are mixed to form a solution having a single glass transition temperature. The thermoplastic and the thermosetting epoxy resin are mutually soluble; thus, when mixed together, the thermoplastic is dissolved into the thermosetting epoxy resin, so that the glass transition temperature of the thermoplastic is substantially reduced, and the mixing process is allowed to be conducted under a temperature lower than the normal softening temperature of the thermoplastic. The formed mixture (i.e., the polymer component) is rubbery (or solid) at room temperature and thus is easily weighted and stored. For example, even if the thermosetting epoxy resin is a liquid epoxy resin, the mixture formed by mixing with the thermoplastic can be fabricated into a tough leathery film. At 25° C., the mixture has a relatively high viscosity (about 10⁵to 10⁷poise), which is sufficient to prevent filler from settling or redistribution in the polymer matrix. However, the mixture has a sufficiently low viscosity (about 10⁴to 10⁵poise at 60° C.) at common mixing temperatures (about 40° C. to 100° C.) to allow the added curing agent and heat-conductive filler to be uniformly distributed in the mixture and be reacted. Many examples of the mixture can be obtained with reference to U.S. patent application Ser. No. 07/609,682 (filed on 6 Nov. 1990 and abandoned now) and PCT Patent Publication No. WO92/08073 (published on 14 May 1992), which are both incorporated herein by reference.
The curing temperature T_cureof the curing agent in the heat-conductive dielectric polymer material of the present application is higher than 80° C. or preferably higher than 100° C., which is used to cure (i.e., crosslink or catalytic-polymerize) the thermosetting epoxy resin. The curing agent is used to quickly cure the thermosetting epoxy resin under a temperature higher than the mixing temperature T_mix, in which the mixing temperature T_mixrefers to the temperature at which the thermoplastic, the thermosetting epoxy resin, and the curing agent are mixed together, and the mixing temperature T_mixis usually about 25° C. to 100° C. When the curing agent is mixed at the mixing temperature T_mix, a substantial curing will not be induced. The amount of the curing agent in the present application causes the thermosetting epoxy resin to be cured at a temperature higher than the mixing temperature T_mix. Preferably, the curing agent will not induce a substantial curing at a temperature of lower than about 80° C. or 100° C., and accordingly, the heat-conductive dielectric polymer material remains substantially uncured at 25° C. for at least half a year.
The aforementioned thermosetting epoxy resin may be an uncured liquid epoxy resin, a polymerized epoxy resin, a phenolic epoxy resin or a bisphenol A epoxy resin. The thermosetting epoxy resin may be a mixture of a plurality of epoxy resins, and may include end-epoxy-function group epoxy resin, side chain epoxy function group epoxy resin, multi-functional epoxy resin or the mixture thereof. Also, the thermosetting epoxy resin may comprise mono-functional group, bi-functional group, tri-functional group, multi-functional group or the mixture thereof. In an embodiment, side chain epoxy function group epoxy resin may use NAN YA Plastic corporation NPCN series, e.g., NPCN-703, or Chang Chun Group BNE-200.
Besides the materials listed in Tables 1 and 3, the thermosetting epoxy resin in the heat-conductive dielectric polymer material of the present application also can be selected from the thermosetting resin defined in “Saechtling International Plastic Handbook for the Technology, Engineer and User, 2nd (1987), pp. 1-2, Hanser Publishers, Munich.” In an embodiment, the thermosetting epoxy resin usually comprises 4% to 60%, preferably 6% to 50%, and especially preferably 8% to 40% by volume of the heat-conductive dielectric polymer material. The thermosetting epoxy resin preferably has a functionality of larger than 2. At room temperature, the thermosetting epoxy resin is liquid or solid. If cured without adding thermoplastic, the thermosetting epoxy resin is rigid or rubbery. The thermosetting epoxy resin is preferably uncured epoxy resin, and especially uncured epoxy resin defined by ASTM D 1763. The liquid epoxy resin can be further understood with reference to the description in “Volume 2 of Engineered Materials Handbook, Engineering Plastics, Publisher: ASM International, Pages 240-241.” The term “epoxy resin” refers to a conventional dimeric epoxy resin having at least two epoxy functional groups, an oligomeric resin, or a polymeric resin. The epoxy resin is a reaction product of bisphenol A with epichlorohydrin, a reaction product (novolac resin) of phenol with formaldehyde, a reaction product of epichlorohydrin, cycloaliphatics, peracid epoxy resin with glyceryl ether, a reaction product of epichlorohydrin with p-amino phenol, a reaction product of epichlorohydrin with glyoxal tetraphenol, phenolic epoxy resin or bisphenol A epoxy resin. Commercially available epoxide ester is preferably 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane formate (e.g., ERL 4221 of Union Carbide Company or CY-179 of Ciba Geigy Company) or bis(3,4-epoxycyclohexylmethyl) adipate (e.g., ERL 4299 of the Union Carbide Company). Commercially available diglycidyl ether of bisphenol A (DGEBA) may be selected from Araldite 6010 of Ciba Geigy Company, DER 331 of Dow Chemical Company, and Epon 825, 828, 826, 830, 834, 836, 1001, 1004, or 1007 of Shell Chemical Company. Moreover, the polyepoxidized phenol formaldehyde novolac prepolymer may be selected form DEN 431 or 438 of Dow Chemical Company and CY-281 of Ciba Geigy Company. The polyepoxidized cersol formaldehyde novolac prepolymer may be selected from ENC 1285, 1280, or 1299 of Ciba Geigy Company. The poly polyol glycidyl ether is selected from Araldite RD-2 (based on butyl-1,4-diol) of the Ciba Geigy Company or Epon 812 (based on glycerol) of Shell Chemical Company. A suitable diepoxide of alkylcycloalkyl hydrocarbon is vinyl cyclohexane dioxide, e.g., ERL 4206 of Union Carbide Company. Moreover, a suitable diepoxide of cycloalkyl ether is bis(2,3-diepoxycyclopentyl)-ether, e.g., ERL 0400 of Union Carbide Company. Moreover, the commercially available flexible epoxy resin includes polyglycol diepoxy (e.g., DER 732 and 736 of the Dow Chemical Company), diglycidyl ether of linoleic dimer acid (e.g., Epon 871 and 872 of Shell Chemical Company), and diglycidyl ether of bisphenol, wherein the aromatic ring is connected by a long aliphatic chain (e.g., Lekutherm X-80 of the Mobay Chemical Company).
Moreover, the thermosetting epoxy resin having multi-functional group may be selected from DEN 4875 (solid novolac epoxy resin) of Dow Chemical Company, Epon 1031 (tetra-functional solid epoxy resin) of Shell Chemical Company and Araldite MY 720 (N,N,N′,N′-tetraglycidyl-4,4′-methylene dianiline) of Ciba-Geigy Company. Moreover, the difunctional epoxy resin (dicyclic oxide) may be selected from HPT 1071 (solid resin, N,N,N′,N′-tetraglycidyl-a,a′-bis(4-aminophenyl)P-Di-Isopropylbenzene), HPT 1079 of Shell Chemical Company (solid diglycidyl ether of bisphenol-9-fluorene) or Araldite 0500/0510 (triglycidyl ether of para-aminophenol) of Ciba-Geigy Company.
The curing agent used in the present application may be selected from isophthaloyl dihydrazide, benzophenone tetracarboxylic dianhydride, diethyltoluene diamine, 3,5-dimethylthio-2,4-toluene diamine, dicyandiamide (obtained from Curazol 2PHZ of the American Cyanamid Company) or DDS (diaminodiphenyl sulfone, obtained from Calcure of Ciba-Geigy Company). Moreover, the curing agent may be selected from substituted dicyandiamide (e.g., 2,6-xylylbiguanide), solid polyamide (e.g., HT-939 of Ciba-Geigy Company or Ancamine 2014AS of Pacific Anchor Company), solid aromatic amine (e.g., HPT 1061 and 1062 of Shell Chemical Company), solid anhydride hardener (e.g., pyromellitic dianhydride (PMDA)), phenolic resin hardener (e.g., poly(p-hydroxy styrene), imidazole, the adduct of 2-phenyl-2,4-dihydroxymethylimizole and 2,4-diamino-6[2′-methylimizole(1)]ethyl-s-triazinylisocyanate), boron trifluoride, and amine complex (e.g., Anchor 1222 and 1907 of Pacific Anchor Company), and trimethylol propane triacrylate.
For the thermosetting epoxy resin, the curing agent is preferably dicyandiamide and is used together with an accelerating agent. The commonly used accelerating agent for curing includes urea or urea compounds; for example, 3-phenyl-1,1-dimethylurea, 3-(4-chlorophenyl)-1,1-dimethylurea, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, 3-(3-chloro-4-methylphenyl)-1,1-dimethylurea and imidazole (e.g., 2-heptadecylimidazole, 1-cyanoethyl-2-phenylimidazole-trimellitate, or 2-[.beta.-{2′-methylimidazol-(1′)}]-ethyl-4,6-diamino-s-triazine).
If the thermosetting epoxy resin is urethane, then the curing agent can use blocked isocyanate, (e.g., alkyl phenol blocked isocyanate selected from Desmocap 11A of Mobay Corporation) or phenol blocked polyisocyanate adduct (e.g., Mondur S of Mobay Corporation). If the thermosetting epoxy resin is unsaturated polyester resin, then the curing agent can use peroxide or other free radical catalysts, such as dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, t-butyl cumyl peroxide, and 2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexyne. Moreover, the unsaturated polyester resin may be crosslinked through irradiation (e.g., an ultraviolet radiation, a high-power electron beam, or γ radiation).
Some thermosetting epoxy resin can be cured without using a curing agent. For example, if the thermosetting epoxy resin is a bismaleimide (BMI), the BMI are cross-linked under a high temperature, and a co-curing agent (e.g., O,O′-diallyl bisphenol A) may be added together to make the cured BMI tougher.
The above epoxy resin cross-linked by using a peroxide crosslink agent, high-power electron beam, or γ radiation is preferably added with an unsaturated cross-linking aid, e.g., triallyl isocyanurate (TAIC), triallyl cyanurate (TAC) or trimethylol propane triacrylate (TMPTA).
The nonwoven fiber component may be ceramic fiber or organic polymer fiber. For example, glass fiber, aluminum oxide fiber, carbon fiber, polypropylene fiber, polyester fiber or the mixture thereof. The nonwoven fiber component comprises 1%-35%, preferably 2%-30% and most preferably 3-25% by volume of the heat-conductive dielectric polymer material.
In an embodiment, the thermoplastic comprises 1%-40%, or preferably 2%-30%, by volume of the heat-conductive dielectric polymer material. The thermoplastic may include a hydroxy-phenoxyether polymer structure. The hydroxy-phenoxyether may be formed by a polymerization reaction of the stoichiometric mixture including diepoxide and difunctional species. The diepoxide is an epoxy resin with an epoxy equivalent weight of about 100 to 10000, such as diglycidyl ether of bisphenol A, diglycidyl ether of 4,4′-sulfonylbisphenol, diglycidyl ether of 4,4′-oxybisphenol, diglycidyl ether of 4,4′-dihydroxybenzophenone, diglycidyl ether of hydroquinone, and diglycidyl ether of 9,9-(4-hydroxyphenyl)fluorine. The difunctional species is dihydric phenol, dicarboxylic acid, primary amine, dithiol, disulfonamide, or bis-secondary amine. The dihydric phenol may be selected from the group consisting essentially of 4,4′-isopropylidene bisphenol (bisphenol A), 4,4′-sulfonylbisphenol, 4,4′-oxybisphenol, 4,4′-dihydroxybenzophenone, and 9,9-bis(-hydroxyphenyl)carbazole. The dicarboxylic acid may be selected from the group consisting essentially of isophthalic acid, terephthalamic acid, 4,4′-biphenylenedicarboxylic acid, and 2,6-naphthalenedicarboxylic acid. The bis-secondary amine may be selected from the group consisting essentially of piperazine, dimethyl piperazine, and 1,2-bis(N-aminomethyl)ethane. The primary amine may be selected from the group consisting essentially of 4-methoxyaniline and 2-aminoethanol. The dithiol may be 4,4′-dimercaptodiphenyl ether. The disulfonamide may be selected from the group consisting essentially of N,N′-dimethyl-1,3-benzenedisulfonamide, and N,N′-bis(2-hydroxyethyl)-4,4-biphenyldisulfonamide. Moreover, the difunctional species may be a mixture comprising two different functional groups for being reacted with the epoxide group, for example, salicylic acid and 4-hydroxybenzoic acid.
Moreover, the thermoplastic in the heat-conductive dielectric polymer material of the present application may be selected from the group essentially consisting of a reaction product of liquid epoxy resin with bisphenol A, bisphenol F, or bisphenol S, a reaction product of liquid epoxy resin with a diacid, and a reaction product of liquid epoxy resin with amines.
In an embodiment, the thermoplastic in the heat-conductive dielectric polymer material of the present application may be selected from the substantially amorphous thermoplastic resin, and its definition can be obtained with reference to Page 1 of “Saechtling International Plastic Handbook for the Technology Engineer and User, Second Edition, 1987, Hanser Publishers, Munich.” The term “substantially amorphous” means that the proportion of the part of “crystallinity” in the resin is at most 15%, and preferably 10%, and especially preferably 5%, for example, a crystallinity of 0% to 5%. The substantially amorphous thermoplastic resin is a high-molecular polymer, which is rigid or rubbery at room temperature, and the thermoplastic resin is used for providing the properties of strength and high viscosity when the above polymer component is substantially uncured. The substantially amorphous thermoplastic may be selected from the group consisting essentially of polysulfone, polyethersulfone, polystyrene, polyphenylene oxide, polyphenylene sulfide, polyamide, phenoxy resin, polyimide, polyetherimide, polyetherimide/silicone block copolymer, polyurethane, polyester, polycarbonate, and acrylic resin (e.g., polymethyl methacrylate, styrene/acrylonitrile, and styrene block copolymers).
In an embodiment, the aforementioned thermoplastic may include an ultra-high molecular phenoxy resin that may have a molecular weight of greater than 10000. The thermoplastic may include hydroxy phenoxy ether polymer. In an embodiment, diepoxide is polymerized with difunctional species to yield the hydroxy phenoxy ether polymer. The thermoplastic can be generated by reacting the liquid epoxy resin with the bisphenol A, the liquid epoxy resin with a divalent acid, or the liquid epoxy resin with amines.
The heat-conductive filler may include one or more kinds of ceramic powders, and may be nitride, oxide, or a mixture thereof. The nitride may be selected from the group consisting essentially of zirconium nitride, boron nitride, aluminum nitride, and silicon nitride. The oxide may be selected from the group consisting essentially of aluminum oxide, magnesium oxide, zinc oxide, silicon oxide or titanium oxide. As usual, the oxide has low thermal conductivity, whereas the nitride cannot be filled with a large amount. Therefore, the mixture of oxide and nitride can overcome the shortcomings.
The heat-conductive dielectric polymer material may be made by the following method. The fiber component, the thermosetting epoxy resin and the thermoplastic (optionally) are blended and heated at around 200° C. for 30 minutes to form a uniform glue. The heat-conductive filler is added to the uniform glue to form a uniform rubbery material, and then a curing agent (Dicy) and an accelerating agent are added to the uniform rubbery material at a temperature higher than 80° C. to form the cured heat-conductive dielectric polymer material having an IPN structure. Because the thermoplastic and the thermosetting epoxy resin are mutually soluble and homogeneous, the heat-conductive filler is uniformly distributed in the IPN structure to achieve optimal heat conductive efficiency.
The nonwoven fiber component can provide stable structure so that the heat-conductive dielectric material is tenacious and non-brittle. The heat-conductive dielectric polymer material including the thermoplastic can be processed by thermoplastic methods because it performs like a thermoplastic polymer. Moreover, the heat-conductive dielectric polymer material also includes a thermosetting plastic so that the thermoplastic and thermosetting epoxy resin can be cross-linked at a high temperature to form an IPN structure. This structure has the characteristics of a thermosetting plastic of good high temperature deformation resistance, and has tenacious, non-brittle characteristics similar to those of a thermoplastic, and can easily and firmly adhere to metal electrodes or a substrate.
Table 5 shows the heat-conductive dielectric polymer material in accordance with other examples of the present application. The nonwoven fiber component uses glass fiber, polyester fiber or the mixture thereof, and comprises 1%-35%, preferably 2%-30%, and most preferably 3%-25% by volume of the heat-conductive dielectric polymer material. The thermosetting epoxy resin may include bisphenol A epoxy resin and multi-functional epoxy resin. The multi-functional epoxy resin may be side chain epoxy group epoxy resin or tetra-functional epoxy resin. The thermoplastic may be phenoxy resin and comprises 1%-40% and preferably 2%-30% by volume of the heat-conductive dielectric polymer material. The heat-conductive filler includes aluminum oxide, and may further include boron nitride or aluminum nitride. The heat-conductive filler comprises 35%-75%, preferably 40%-70% and most preferably 45%-65% by volume of the heat-conductive dielectric polymer material. It can be known from Table 5 that all embodiments have high thermal conductivities, which are equal to or greater than 1.5 W/mK, the peeling strengths are equal to or greater than 0.8 kg/cm (the peeling strengths of the examples except “Example 7” are greater than 1.5 kg/cm), and all examples have superior voltage endurance characteristics those are greater than 2000V/0.1 mm, and preferably 3000V/0.1 mm.

TABLE 5

Example	1	2	3	4	5	6	7

Composition	bispheonol A		10	18	23	18	18	25	22
(vol %)	epoxy resin
	Multi-functional	7	8	13	12	12	10	10
	epoxy resin
	Glass fiber	6	5	5	10	3	10	7
	Polyester fiber	4	3	3	0	7	5	0
	phenoxy resin	23	8	6	2	2	8	7
	Aluminum oxide	50	58	50	53	53	0	0
	Boron nitride	0	0	0	0	5	0	54
	Aluminum nitride	0	0	0	5	0	42	0
	Curing agent	Dicy	Dicy	Dicy	Dicy	Dicy	Dicy	Dicy
Physical	Thermal	1.5	1.8	1.5	4.5	3.9	3.9	1.8
characteristics	conductivity
	(W/mK)
	Glass transition	105	130	140	150	150	130	130
	temperature (° C.)
	Peeling strength	1.85	1.82	1.86	1.61	1.52	1.81	0.8
	(kg/cm)
	Voltage endurance	52	48	51	50	55	50	48
	(KV/mm)

As shown in FIG. 2, the aforementioned heat-conductive dielectric polymer material can be fabricated to a heat dissipation substrate 20, in which the interfaces between the heat-conductive dielectric polymer material layer 23 and the first and second metal layers 21 and 22 may include a micro-rough surface 25 having nodular protrusions 26. According to Table 5, the heat-conductive dielectric polymer material layer 23 can withstand a voltage larger than 2000V, and preferably 3000V in the case that its thickness is 0.1 mm, and the thermal conductivities are greater than 1.5 W/mK.
According to the present application, the heat-conductive dielectric polymer material has IPN structure or nonwoven fiber component, so that solid-liquid separation issue will not occur when it is subjected to hot-press. The metal layers may use copper, aluminum, nickel, copper alloy, aluminum alloy, nickel alloy, copper-nickel alloy and aluminum-copper alloy. The heat-conductive dielectric polymer material is rubbery rather than slurry-like, and thus can be easily stored and processed. In the case of addition of thermoplastic, the heat-conductive dielectric polymer material can be made according to common thermoplastic processing methods, thereby enhancing the processibility.
Table 6 shows coefficient of thermal expansion (CTE) data in X-axis and Y-axis of examples in which the heat-conductive dielectric polymer material includes nonwoven fibers of different volume percentages. The polyester fiber uses polyethylene terephthalate (PET) fiber. Tg indicates the glass transition temperature of the polymer component. Example 1 uses glass fiber “A” only. Example 2 uses both glass fiber “A” and glass fiber “B”. Example 3 and Example 4 further add polyester fibers. Glass fiber “A” has a length of 12.7 mm and a diameter of 13 μm, and thus its aspect ratio of length to diameter is approximately 970. Glass fiber “B” has a length of 3.2 mm and a diameter of 10 μm, and thus its aspect ratio of length to diameter is approximately 320. In practice, the ratio of length to diameter is between 50 and 10000, and preferably between 150 and 5000, and most preferably between 250 and 1000.

TABLE 6

Example	1	2	3	4

Composition	Liquid epoxy resin DER331	42.8%	42.8%	43%	41.6%
(vol %)	Aluminum oxide	50%	50%	50%	50%
	Glass fiber A (12.7 mm/13 μm)	7.2%	3.2%	5.7%	5.5%
	Glass fiber B (3.2 mm/10 μm)	0	4%	0	0
	Polyester fiber	0	0	1.3%	2.9%

Physical	CTE	X-axis	22.46	20.05	18.2	13.87
Characteristics	(10⁻⁶/° C., <Tg)	Y-axis	29.47	25.86	22.82	16.58
		Y-axis/X-axis	1.31	1.29	1.25	1.2
	CTE	X-axis	47.76	41.78	42.14	64.41
	(10⁻⁶/° C., >Tg)	Y-axis	100.18	66.43	65.68	71.25
		Y-axis/X-axis	2.1	1.59	1.56	1.11

According to Table 6, Example 1 using glass fiber “A” only has CTE in Y-axis of approximately 100×10⁻⁶/° C., and the ratio of CTE in Y-axis to X-axis is approximately 2.1 at a temperature higher than Tg. If a material has a CTE and a ratio larger than these values, the heat dissipation substrate containing the material is easily bent. Therefore, it does not meet the requirement for processing. Example 2 uses two glass fibers of different length-to-diameter ratios to decrease the CTE to below 70×10⁻⁶/° C. and the ratio of CTE in Y-axis to CTE in X-axis is approximately 1.6 at a temperature higher than Tg. Specifically, the ratio of CTE in Y-axis to CTE in X-axis can be lower than 1.6 or preferably lower than 1.3 by adding polyester fiber with appropriate amount at a temperature higher than Tg. In summary, the ratio of CTE in two mutually perpendicular axes of the heat-conductive dielectric polymer material is less than 2.1, preferably 1.6 or most preferably 1.3, and the values of CTE in X-axis and CTE in Y-axis are less than 100×10⁻⁶/° C., thereby significantly preventing the substrate from bending to increase the processibility. Referring to the examples having both glass fiber and polyester fiber of Tables 5 and 6, the volume ratio of the glass fiber to the polyester fiber is between 0.3 and 5, or preferably between 0.5 and 4.5.
According to the present application, nonwoven fiber component is added to make the heat-conductive dielectric polymer material rubbery, and the ratio of CTE in different axes can be controlled to below an appropriate number by modifying the fiber component amount or fiber types, thereby significantly increasing the processibility.
The above-described embodiments of the present application are intended to be illustrative only. Numerous alternative embodiments may be devised by persons skilled in the art without departing from the scope of the following claims.

Claims

1. A heat-conductive dielectric polymer material, comprising:

a polymer component comprising a thermosetting epoxy resin, wherein the thermosetting epoxy resin comprises 4%-60% by volume of the heat-conductive dielectric polymer material;

a nonwoven fiber component uniformly dispersed in the polymer component, wherein the nonwoven fiber component comprises 1%-35% by volume of the heat-conductive dielectric polymer material;

a curing agent configured to cure the thermosetting epoxy resin at a curing temperature; and

a heat-conductive filler uniformly dispersed in the polymer component, wherein the heat-conductive filler comprises 40%-70% by volume of the heat-conductive dielectric polymer material;

wherein the heat-conductive dielectric polymer material has a thermal conductivity greater than 0.5 W/mK.

2. The heat-conductive dielectric polymer material of claim 1, wherein the thermosetting epoxy resin is selected from the group consisting of end-epoxy-function group epoxy resin, side chain epoxy function group epoxy resin, multi-functional epoxy resin or the mixture thereof.

3. The heat-conductive dielectric polymer material of claim 1, wherein the nonwoven fiber component is selected from the group consisting of ceramic fiber, organic polymer fiber and the mixture thereof.

4. The heat-conductive dielectric polymer material of claim 1, wherein the nonwoven fiber component is selected from the group consisting of glass fiber, aluminum oxide fiber, carbon fiber, polypropylene fiber, polyester fiber and the mixture thereof.

5. The heat-conductive dielectric polymer material of claim 1, wherein the nonwoven fiber component is a chopped strand fiber.

6. The heat-conductive dielectric polymer material of claim 1, wherein a ratio of CTE in two mutually perpendicular axes of the heat-conductive dielectric polymer material is less than 2.1 at a temperature higher than a glass transition temperature of the polymer component.

7. The heat-conductive dielectric polymer material of claim 1, wherein a ratio of CTE in two mutually perpendicular axes of the heat-conductive dielectric polymer material is less than 1.3 at a temperature higher than a glass transition temperature of the polymer component.

8. The heat-conductive dielectric polymer material of claim 1, wherein CTE of the heat-conductive dielectric polymer material is less than 100×10⁻⁶/° C. at a temperature higher than a glass transition temperature of the polymer component.

9. The heat-conductive dielectric polymer material of claim 1, wherein the nonwoven fiber component comprises glass fiber and polyester fiber, and a volume ratio of the glass fiber to the polyester fiber is in the range between 0.3 and 5.

10. The heat-conductive dielectric polymer material of claim 1, wherein the nonwoven fiber component comprises at least two glass fibers of different ratios of length to diameter.

11. The heat-conductive dielectric polymer material of claim 1, wherein the nonwoven fiber component comprises a glass fiber of a ratio of length to diameter ranging from 50 to 10000.

12. The heat-conductive dielectric polymer material of claim 1, wherein the thermosetting epoxy resin is uncured liquid epoxy resin or polymerized epoxy resin.

13. The heat-conductive dielectric polymer material of claim 1, wherein the thermosetting epoxy resin comprises mono-functional group, bi-functional group, tri-functional group, multi-functional group or the mixture thereof.

14. The heat-conductive dielectric polymer material of claim 1, wherein the thermosetting epoxy resin comprises phenolic epoxy resin or bisphenol A epoxy resin.

15. The heat-conductive dielectric polymer material of claim 1, wherein the curing agent has a curing temperature higher than 80° C.

16. The heat-conductive dielectric polymer material of claim 1, wherein the polymer component further comprises a thermoplastic, and the thermoplastic and the thermosetting epoxy resin are mutually soluble prior to curing and form an inter-penetrating network structure after curing.

17. The heat-conductive dielectric polymer material of claim 16, wherein the thermoplastic comprises 1% to 40% by volume of the heat-conductive dielectric polymer material.

18. The heat-conductive dielectric polymer material of claim 16, wherein the thermoplastic comprises bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin or the mixture thereof.

19. A heat dissipation substrate, comprising:

a first metal layer;

a second metal layer; and

a heat-conductive dielectric polymer material layer comprising the heat-conductive dielectric polymer material of claim 1, wherein the heat-conductive dielectric polymer material layer is sandwiched between and in physical contact with the first metal layer and the second metal layer;

wherein the heat-conductive dielectric polymer material layer can withstand a voltage greater than 2000V in the case that the heat-conductive dielectric polymer material layer has a thickness of 0.1 mm.

20. The heat dissipation substrate of claim 19, wherein interfaces between the heat-conductive dielectric polymer material layer and the first and second metal layers comprise at least one micro-rough surface having a plurality of nodular protrusions.

21. The heat dissipation substrate of claim 19, wherein peeling strength between the heat-conductive dielectric polymer material layer and the first or the second metal layer is greater than 0.8 kg/cm.