Conductive adhesive and in-vehicle electronic control device using same

Abstract

Provided are: a conductive adhesive which has suppressed characteristic variations even for a temperature cycle in a wide temperature range such as a use environment of an automobile; and an in-vehicle electronic control device using the same. This conductive adhesive is characterized in that: conductive filler particles are dispersed in a matrix of a silicone resin; the conductive filler particles have a core-shell structure in which a core composed of a metal material is coated with a shell composed of a metal material; said conductive adhesive has a Young's modulus E (-40ºC) at -40ºC of at most 50 MPa and a Young's modulus E (25ºC) at 25ºC of at most 10 MPa; and the ratio [E (-40ºC) / E (25ºC)] of these Young's moduli is at most 5.

Description

Conductive adhesive and on-board electronic control device using the same

[0001] The present invention relates to technology for electronic control devices, and more particularly to a conductive adhesive and an on-vehicle electronic control device using the same.

[0002] The technologies of advanced driver assistance systems (ADAS) and autonomous driving (AD) for automobiles and other vehicles have made great progress in recent years, and further development is expected in the future. In ADAS and AD, electronic control units (ECUs) play a very important role, and many ECUs are installed for various applications and purposes. In this specification, the various ECUs installed in automobiles and other vehicles are collectively referred to as automotive ECUs.

[0003] Automotive ECUs perform various calculations in their internal electronic circuits, and advances in ADAS and AD have created a demand for faster calculations. High-speed data transmission is essential to achieve high-speed calculations. Furthermore, reducing and shielding electromagnetic noise is important for high-speed data transmission, and it is common for electronic circuits to be covered with an electromagnetic shielding case. Conductive adhesives are often used to fill gaps in such electromagnetic shielding cases.

[0004] For example, Patent Document 1 (JP 2007-027111 A) teaches a conductive polymer composition containing a particulate conductive composite filler in a polymer matrix, the particulate conductive composite filler comprising a central carbon-based core having a size of at least about 350 microns based on the 50th percentile and a conductive metal coating or composite metal coating on the central carbon-based core, wherein the particulate conductive filler constitutes about 25 to 35 volume percent of the conductive polymer composition.

[0005] According to Patent Document 1, when a particulate filler is mixed with a polymer matrix to form a conductive polymer composition, improved process rheology, greater flexibility in filler formulation, improved conductivity, improved electrical stability, and lower density can be obtained compared to the prior art.

[0006] Japanese Patent Application Laid-Open No. 2007-027111

[0007] The conductive polymer composition described in Patent Document 1 is believed to contribute to improving the shielding effectiveness of electromagnetic shielding products. However, unfortunately, in Patent Document 1, the properties were measured and verified only in a room temperature environment.

[0008] On the other hand, automotive ECUs must be able to withstand a wide temperature range (for example, -40 to 105°C) to adapt to the vehicle's operating environment, and must also be able to operate reliably even when the temperature fluctuates within that range (temperature cycles occur).

[0009] However, temperature cycling is a harsh environment for composite materials such as conductive polymer compositions and conductive adhesives because it subjects each component material of the composite to repeated thermal stresses.

[0010] For example, in the conductive polymer composition described in Patent Document 1, the resin material constituting the matrix is ​​usually 10 -4 The carbon-based material that forms the core of the conductive filler has a linear expansion coefficient of the order of 10 -6 / °C, and the metal material covering the core usually has a linear expansion coefficient of 10 -5 / °C. In other words, the linear expansion coefficients of the materials that make up the conductive polymer composition differ by one to two orders of magnitude, which causes large thermal stresses to occur between the materials due to temperature fluctuations. Graphite, a type of carbon-based material, is unique in that its crystalline structure results in large differences in the linear expansion coefficients in the a-axis and c-axis directions (particularly in the a-axis direction, it exhibits a negative linear expansion coefficient depending on the temperature range).

[0011] The present invention has been made to address the above-mentioned problems. A primary object of the present invention is to provide a conductive adhesive that suppresses fluctuations in characteristics even during temperature cycles over a wide temperature range, such as those found in automotive operating environments. A secondary object of the present invention is to provide an on-board electronic control device that uses the conductive adhesive and can operate reliably even during temperature cycles over a wide temperature range.

[0012] (I) One aspect of the present invention provides a conductive adhesive in which conductive filler particles are dispersed in a silicone resin matrix, the conductive filler particles having a core-shell structure in which a core made of a metal material is covered with a shell made of a metal material, the conductive adhesive having a Young's modulus E(-40°C) of 50 MPa or less at -40°C, a Young's modulus E(25°C) of 10 MPa or less at 25°C, and a ratio of these Young's moduli "E(-40°C) / E(25°C)" of 5 or less. Note that in the present invention, the Young's modulus is a value measured with a dynamic viscoelasticity measuring device.

[0013] The present invention allows the following improvements and modifications to be freely combined with the conductive adhesive (I) of the present invention. (i) The metallic material of the core of the conductive filler particle has an electrical resistivity of 1 μΩ / m or less, the metallic material of the shell has an electrical resistivity of 1 μΩ / m or less, and the absolute value of the difference in linear expansion coefficient between the metallic material of the core and the metallic material of the shell is within 20 ppm / °C. In the present invention, the electrical resistivity and linear expansion coefficient are values ​​at 20°C. (ii) The conductive filler particles have a median diameter D50 of 30 μm or more and 150 μm or less. In the present invention, the particle size of the conductive filler particles is measured using a laser diffraction particle size analyzer. (iii) The content of the conductive filler particles in the conductive adhesive is 40% by mass or more and 99% by mass or less. (iv) The conductive adhesive has a Young's modulus E(105°C) at 105°C of less than 10 MPa. (v) The conductive filler particles have an aluminum core and a nickel shell.

[0014] (II) Another aspect of the present invention provides an in-vehicle electronic control device having a conductive housing base and a conductive housing cover that accommodate a circuit board on which electronic components are mounted, wherein any of the above-mentioned conductive adhesives is disposed between the circuit board and the conductive housing base and / or between the circuit board and the conductive housing cover so as to cover the outer peripheral region of the circuit board.

[0015] According to the present invention, it is possible to provide a conductive adhesive that suppresses fluctuations in characteristics even when subjected to temperature cycles over a wide temperature range, such as those found in automobile operating environments. Furthermore, by using this conductive adhesive, it is possible to provide an on-board electronic control unit that can operate reliably even when subjected to temperature cycles over a wide temperature range.

[0016] Problems, configurations, and effects other than those described above will become clear from the description of the embodiments below.

[0017] 1 is a schematic cross-sectional view showing an example of the structure of a conductive adhesive according to the present invention; 2 is an exploded perspective view showing an example of an on-vehicle electronic control device according to the present invention;

[0018] [Basic Concept of the Present Invention] The inventors investigated the changes over time that occur in conventional conductive adhesives due to temperature cycles over a wide temperature range, such as those found in automotive operating environments, and found that electrical resistance increases as the temperature cycle progresses. Further investigation of the microstructure and other aspects revealed that conductive adhesives with increased electrical resistance exhibited cracks in the conductive filler particles, which have a core-shell structure with a carbon core and a metal shell, and peeling between the conductive filler particles and the matrix. The present inventors believed that this was due to differences in the linear expansion coefficients of the materials that make up the conductive adhesive and the resulting thermal stress.

[0019] Therefore, we conducted extensive research into a structure for obtaining a conductive adhesive that exhibits minimal change in electrical resistance over time even under such temperature cycles. As a result, we found a possible solution by controlling the temperature change in the Young's modulus of the adhesive to fall within a specified range. The present invention was completed based on this finding.

[0020] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the specific embodiments described, and can be appropriately combined with known technologies or improved based on known technologies within the scope of the technical concept of the invention. Furthermore, substantially equivalent configurations will be assigned the same reference numerals, and redundant explanations may be omitted.

[0021] [Conductive adhesive according to the present invention] Figure 1 is a schematic cross-sectional view showing an example of the structure of a conductive adhesive according to the present invention. As shown in Figure 1, a conductive adhesive 40 according to the present invention has conductive filler particles 42 dispersed in a silicone resin matrix 41. The conductive filler particles 42 have a core-shell structure in which a core 43 made of a metal material is covered with a shell 44 made of a metal material.

[0022] Furthermore, it is preferable that the Young's modulus E(-40°C) of the conductive adhesive 40 is 50 MPa or less at -40°C, that the Young's modulus E(25°C) is 10 MPa or less at 25°C, and that the ratio of these Young's moduli "E(-40°C) / E(25°C)" is 5 or less. It is preferable that the Young's modulus E(105°C) of the conductive adhesive 40 at 105°C is less than 10 MPa.

[0023] The configuration of the conductive adhesive 40 will be described in more detail below.

[0024] The silicone resin that constitutes the matrix 41 of the conductive adhesive 40 is not particularly limited as long as it can be used in a temperature range of -40 to 105°C (as long as it maintains its shape and elasticity) and the conductive adhesive 40 satisfies the above-mentioned Young's modulus (also known as tensile modulus). For example, silicone resins with a main skeleton of dimethylsiloxane or diphenylsiloxane can be suitably used. Furthermore, additives such as coupling agents and adhesive aids may be mixed into the matrix 41 to improve adhesion and wettability with the adherend and the conductive filler particles 42.

[0025] The conductive filler particles 42 have a core 43 and a shell 44 each having an electrical resistivity of 1×10 at 20° C. -6It is preferable that the metal material has an electrical resistivity of 5×10 Ω / m or less. -7 Ω / m or less is more preferable, and 1×10 -7 Preferably, the core 43 and the shell 44 are combined such that the absolute value of the difference in the linear expansion coefficient at 20°C is within 20 ppm / °C. More preferably, the absolute value of the difference in the linear expansion coefficient is within 18 ppm / °C, and even more preferably, within 15 ppm / °C.

[0026] There are no particular limitations on the metallic materials constituting the core 43 and the shell 44 as long as they satisfy the above-mentioned requirements for electrical resistivity and linear expansion coefficient. For example, copper, iron, aluminum, nickel, chromium, and alloys based on one of these metals are suitable. From the viewpoint of suppressing changes in electrical resistivity over time due to oxidation, it is preferable to select a metallic material constituting the shell 44 that is resistant to oxidation (i.e., that is resistant to forming an oxide film).

[0027] The shape of the conductive filler particles 42 is not particularly limited. For example, as shown in FIG. 1, they may be spherical, oval-spherical, plate-like, needle-like, irregular, or a mixture thereof. The size of the conductive filler particles 42 is preferably 30 μm or more and 150 μm or less, more preferably 50 μm or more and 130 μm or less, in terms of median diameter D50 measured by a laser diffraction particle size distribution analyzer. If the size of the conductive filler particles 42 is too small, they tend to aggregate, reducing their dispersibility in the matrix 41. If the size of the conductive filler particles 42 is too large, it becomes difficult to control the thickness of the adhesive layer when bonded.

[0028] The content of the conductive filler particles 42 in the conductive adhesive 40 is preferably 40% by mass or more in order to ensure desirable conductivity, and is preferably 99% by mass or less in order to ensure adhesiveness, and more preferably 60% by mass or more and 90% by mass or less.

[0029] By controlling the temperature change of the Young's modulus of the conductive adhesive 40 to be within a specified range and controlling the difference in the linear expansion coefficient between the core 43 and shell 44 of the conductive filler particle 42 to be within a specified range, it is possible to suppress thermal stress between the materials that make up the conductive adhesive 40 even when placed in an environment with a wide range of temperature cycles, and to obtain a conductive adhesive with little change in electrical resistance over time.

[0030] [On-vehicle electronic control device according to the present invention] As described above, an on-vehicle ECU is a type of computer that electronically controls various uses / purposes (e.g., engine, transmission, steering, airbags, etc.) in driving an automobile, etc., and has internal electronic circuits. Fig. 2 is an exploded perspective schematic diagram showing an example of an on-vehicle electronic control device (on-vehicle ECU) according to the present invention.

[0031] 2, the in-vehicle ECU 10 has a housing formed by a conductive housing base 11, a conductive housing cover 15, and fasteners 20, and accommodates a circuit board 30 on which electronic components are mounted to form an electronic circuit inside the housing. In Fig. 2, the electronic components are mounted on the conductive housing base 11 side of the circuit board 30 (the side not visible in the drawing).

[0032] The on-vehicle ECU 10 in Fig. 2 is an example in which a conductive housing base 11 also functions as a heat dissipation member. A heat dissipation seat 12 is formed on the conductive housing base 11 at a location facing an electronic component from which heat is to be dissipated, and a thermal interface material 50 (TIM, also sometimes referred to as a thermal conductive material or heat dissipation member) is disposed between the heat dissipation seat 12 and the electronic component. The heat dissipation seat 12 and the TIM 50 are not essential components in the present invention, but are preferably formed and disposed from the viewpoint of heat dissipation.

[0033] The circuit board 30 is structured to be fixed to the conductive housing base 11 by fasteners 20. Furthermore, in the present invention, a conductive adhesive 40 is disposed between the circuit board 30 and the conductive housing base 11 in the peripheral region of the circuit board 30 (particularly in the peripheral region of the surface on which electronic components are mounted). This makes it possible to more effectively shield electromagnetic noise emitted by the electronic components and electromagnetic noise attempting to intrude from outside the on-vehicle ECU 10, contributing to improved reliability of high-speed calculations and high-speed data transmission.

[0034] There are no particular limitations on the electronic components mounted on the circuit board 30 as long as they are for automotive use, and examples of such components include semiconductor elements such as a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), an SoC (System on a Chip), and a DDR SDRAM (Double-Data-Rate Synchronous Dynamic Random Access Memory). There are also no particular limitations on the connectors mounted on the circuit board 30, and conventional automotive connectors can be used as appropriate.

[0035] Metallic materials (e.g., aluminum alloys, magnesium alloys, and steel materials) that can ensure heat resistance, waterproofness, dustproofness, thermal conductivity, and electrical conductivity suitable for in-vehicle use can be used appropriately for the conductive housing base 11 and the conductive housing cover 15. The heat dissipation member is not limited to the conductive housing base 11, and the conductive housing cover 15 may also function as a heat dissipation member, or both the conductive housing base 11 and the conductive housing cover 15 may also function as a heat dissipation member.

[0036] The TIM 50 can also be a conventional in-vehicle material, and for example, a material with a silicone resin matrix can be suitably used.

[0037] The present invention will be explained in more detail below with reference to various experiments, but the present invention is not limited to the configurations and structures described in these experiments.

[0038] [Experiment 1] (Preparation of conductive adhesive samples 1 to 6) First, six types of silicone resin (commercially available, with dimethylsiloxane as the main skeleton) were prepared, each adjusted to have a different Young's modulus E(25°C) at 25°C when cured. Additionally, commercially available conductive filler particles were prepared, each with a core of pure aluminum and a shell of pure nickel (approximately 2 μm thick). The particle size of the conductive filler particles was measured using a laser diffraction particle size analyzer (Japan Laser Co., Ltd., model HELOS & RODOS), and the median diameter D50 was found to be 130 μm.

[0039] Next, conductive filler particles were added to each silicone resin at a mixing ratio of 70 mass % and mixed thoroughly so that the conductive filler particles were uniformly dispersed, thereby preparing conductive adhesive samples 1 to 6.

[0040] [Experiment 2] (Investigation of the properties of conductive adhesive samples 1 to 6) Samples 1 to 6 were cured under conditions appropriate for each silicone resin, and test specimens (20 mm x 4 mm x 1 mm) for measurement and evaluation were cut from the cured samples. The Young's modulus E (25°C) and E (-45°C) of each test specimen were measured using a dynamic viscoelasticity measuring device (IT Measurement & Control Co., Ltd., Model: DVA-200). The measurement conditions were a frequency of 10 Hz and a strain of 0.1%. The results are shown in Table 1 below.

[0041] The Young's modulus E (105°C) of each test piece was measured in the same manner as above, and it was confirmed that it was less than 10 MPa for all test pieces.

[0042] For each test piece whose Young's modulus E (25°C) and E (-45°C) were measured, the impedance at 1 GHz was measured using an impedance analyzer (Agilent Technologies, Model 4294A). As a result, it was confirmed that the impedance in the thickness direction was 500 mΩ or less and in the in-plane direction was 1 mΩ or less for all test pieces.

[0043] The cross-sectional microstructure of each test piece was observed using a scanning electron microscope (Hitachi High-Tech Corporation, Model S-4800), and no cracks in the conductive filler particles or delamination between the conductive filler particles and the matrix were observed before the temperature cycle test was performed.

[0044] Next, a temperature cycle test was performed on each test piece after measuring Young's modulus E (25°C) and E (-45°C). The test conditions were "hold at -40°C for 30 minutes → heat to 105°C in 5 minutes → hold at 105°C for 30 minutes → cool to -40°C in 5 minutes," and this cycle was repeated 1,000 times.

[0045] Next, the impedance at 1 GHz was measured for each test piece that had undergone the temperature cycle test in the same manner as above. A test piece that showed an increase of less than two times the measured value before the temperature cycle test was judged to be "pass," while a test piece that showed an increase of more than two times was judged to be "fail." The results are also shown in Table 1.

[0046] Next, the cross-sectional microstructure of each test piece that had undergone the temperature cycle test was observed in the same manner as above. If cracks in the conductive filler particles and / or peeling between the conductive filler particles and the matrix were not observed, the test piece was judged as "passed." If cracks in the conductive filler particles and / or peeling between the conductive filler particles and the matrix were observed, the test piece was judged as "failed." The results are also shown in Table 1.

[0047]

[0048] As shown in Table 1, samples 1 to 3, which meet the specifications of the present invention, showed little change in impedance even when subjected to a temperature cycle test, and no cracks in the conductive filler particles and / or delamination between the conductive filler particles and the matrix were observed in cross-sectional microstructure observation.

[0049] In contrast, samples 4 to 6, which do not fall within the scope of the present invention, showed large changes in impedance due to the temperature cycle test, and cracks in the conductive filler particles and / or peeling between the conductive filler particles and the matrix were observed when the cross-sectional microstructure was observed.

[0050] The above-described embodiments and experiments are described to aid in understanding the present invention, and the present invention is not limited to the specific configurations described. For example, it is possible to replace part of the configuration of the embodiments with configurations within the technical common sense of those skilled in the art, or to add configurations within the technical common sense of those skilled in the art to the configuration of the embodiments. In other words, it is possible to delete, replace, or add part of the configuration of the embodiments and experiments described in this specification without departing from the technical spirit of the invention. For example, the conductive adhesive used in the present invention is not limited to use in automotive ECUs, but can also be used in inverters, converters, and other devices other than automotive ECUs.

[0051] 10...In-vehicle electronic control device, 11...Conductive housing base, 12...Heat dissipation base, 15...Conductive housing cover, 20...Fastener, 30...Circuit board, 40...Conductive adhesive, 41...Matrix, 42...Conductive filler particles, 43...Core, 44...Shell, 50...Thermal interface material.

Claims

1. A conductive adhesive in which conductive filler particles are dispersed in a silicone resin matrix, the conductive filler particles having a core-shell structure in which a core made of a metal material is covered with a shell made of a metal material, the conductive adhesive having a Young's modulus E(-40°C) of 50 MPa or less at -40°C, a Young's modulus E(25°C) of 10 MPa or less at 25°C, and a ratio of the Young's moduli "E(-40°C) / E(25°C)" of 5 or less.

2. A conductive adhesive according to claim 1, wherein the metallic material of the core of the conductive filler particle has an electrical resistivity of 1 μΩ / m or less, the metallic material of the shell has an electrical resistivity of 1 μΩ / m or less, and the absolute value of the difference in linear expansion coefficient between the metallic material of the core and the metallic material of the shell is within 20 ppm / °C.

3. The conductive adhesive according to claim 1, wherein the conductive filler particles have a median diameter D50 of 30 μm or more and 150 μm or less.

4. The conductive adhesive according to claim 2, wherein the conductive filler particles have a median diameter D50 of 30 μm or more and 150 μm or less.

5. The conductive adhesive according to claim 1, wherein the content of the conductive filler particles in the conductive adhesive is 40% by mass or more and 99% by mass or less.

6. The conductive adhesive according to claim 2, wherein the content of the conductive filler particles in the conductive adhesive is 40% by mass or more and 99% by mass or less.

7. The conductive adhesive according to claim 3, wherein the content of the conductive filler particles in the conductive adhesive is 40% by mass or more and 99% by mass or less.

8. The conductive adhesive according to claim 4, wherein the content of the conductive filler particles in the conductive adhesive is 40% by mass or more and 99% by mass or less.

9. The conductive adhesive according to any one of claims 1 to 8, wherein the conductive adhesive has a Young's modulus E(105°C) at 105°C of less than 10 MPa.

10. A conductive adhesive according to any one of claims 1 to 8, wherein the conductive filler particles have an aluminum core and a nickel shell.

11. The conductive adhesive according to claim 9, wherein the conductive filler particles have an aluminum core and a nickel shell.

12. An in-vehicle electronic control device having a conductive housing base and a conductive housing cover that accommodate a circuit board on which electronic components are mounted, characterized in that the conductive adhesive described in any one of claims 1 to 8 is arranged between the circuit board and the conductive housing base, or between the circuit board and the conductive housing cover, at least one of the two, so as to cover the outer periphery of the circuit board.

13. An in-vehicle electronic control device having a conductive housing base and a conductive housing cover that house a circuit board on which electronic components are mounted, wherein the conductive adhesive according to claim 9 is disposed between the circuit board and the conductive housing base, or between the circuit board and the conductive housing cover, at least one of them, so as to cover the outer peripheral region of the circuit board.

14. An in-vehicle electronic control device having a conductive housing base and a conductive housing cover that house a circuit board on which electronic components are mounted, characterized in that the conductive adhesive described in claim 10 is arranged so as to cover the outer peripheral region of the circuit board at least one of between the circuit board and the conductive housing base and between the circuit board and the conductive housing cover.

15. An in-vehicle electronic control device having a conductive housing base and a conductive housing cover that house a circuit board on which electronic components are mounted, wherein the conductive adhesive according to claim 11 is disposed between the circuit board and the conductive housing base, or between the circuit board and the conductive housing cover, at least one of them, so as to cover the outer peripheral region of the circuit board.

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