JP7527583B2 - Resin composition for protective film for electronic components and protective film for electronic components using the resin composition - Google Patents

Description

The present invention relates to a resin composition for a protective film for electronic components and a protective film for electronic components using the resin composition.

In recent years, the number of electronically controlled automobiles such as electric vehicles (EVs) and hybrid vehicles (HVs) has increased, and the electronic control units (ECUs) installed in these vehicles are likely to be exposed to more severe temperature environments due to direct mounting on the engine and electromechanical integration of electronic components in the engine. In the future, it is expected that ECUs will be mounted on the same substrate as SiC semiconductors and GaN semiconductors that operate at 250°C, and resistors, which are passive components, will also be required to have the same level of heat resistance.
For example, Patent Document 1 listed below discloses a chip resistor having an electrode structure in which the electrodes do not deteriorate even when operated for a long period of time in a high-temperature environment of about 250 to 350° C.

JP 2015-119125 A

The resistor described in Patent Document 1 has a pair of electrodes formed on an insulating substrate such as alumina, and a resistor formed to straddle the pair of electrodes.

The resistor is further covered with a glass protective film, the upper surface of which is covered with a protective film made of glass or resin and serving as the outermost layer, and end electrodes are formed on the end surfaces of the substrate.
The outermost protective layer is made of glass or epoxy resin.

However, glass protective films need to be fired at high temperatures, which can lead to problems such as the effect on resistance values due to diffusion between materials. In addition, if epoxy resin is used as a protective film, it is difficult to achieve the required heat resistance due to its chemical structure.

The present invention aims to provide a new protective film for electronic components that has excellent heat resistance. It also aims to provide a protective film for electronic components that can be cured at low temperatures and in a short time.

According to one aspect of the present invention, there is provided a resin composition for producing an allylphenol-maleimide copolymer for use in a protective film for electronic components, the resin composition containing (A) an allyl group-containing phenol compound having a rigid structure, (B) an N-aromatic maleimide group-containing compound having a rigid structure, (C) an N-aliphatic maleimide group-containing compound having a flexible structure, and (D) silicone particles.

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（式中、ｎは０～２である。）

It is preferable that the compound (A) is represented by the following formula 1, the compound (B) is represented by the following formula 2, and the compound (C) is represented by the following formula 3.

(In the formula, n is 0 to 2.)

(In the formula, n is 0 to 2.)

The silicone particles are preferably either silicone rubber particles or silicone resin particles.

The content of the silicone particles is preferably 10 to 25% by weight based on the total amount of the resin composition.
The silicone particles preferably have an average particle size of 1 to 10 μm.

The present invention is a method for producing an allylphenol-maleimide copolymer for use in a protective film for electronic components, comprising a step of curing the resin composition described in any one of the above by heating.

The present invention is a protective film for electronic components that contains an allylphenol-maleimide copolymer, which is a heat-cured product of the resin composition described in any one of the above.

The present invention further provides the use of the allylphenol-maleimide copolymer described above in the second protective film of an electronic component having an insulating substrate, a pair of electrodes formed opposite to each other on at least one surface of the insulating substrate, a resistor electrically connecting the pair of electrodes, a first protective film covering the resistor, and a second protective film covering the first protective film.

The present invention provides a novel protective film for electronic components that has excellent heat resistance and oxidation resistance.

FIG. 1 is a diagram showing an example of a process for producing a resin composition for producing an allylphenol-maleimide copolymer for electronic component protective films ("cured resin for electronic component protective films") according to the inventors' earlier application listed below. FIG. 2 is a diagram showing the principle of measuring the tensile shear adhesive strength of a cured resin for protective films for electronic components according to the previous application. FIG. 2 is a diagram showing the principle of measuring the fracture toughness of a cured resin for protective films for electronic components according to the previous application. FIG. 13 is a diagram showing the results (n=5) of a tensile shear adhesive strength test of the optimized cured resin for protective films for electronic components before and after 100 hours of heat resistance and humidity resistance testing. FIG. 13 is a diagram showing the thermal properties of an optimized cured resin for use in a protective film for electronic components, and is a diagram showing the results of DMA measurement. FIG. 1 is a diagram showing the thermal properties of an optimized cured resin for use in a protective film for electronic components, and is a diagram showing the results of TG-DTA measurement. FIG. 1 is a graph showing the residual weight fraction (n=3) of MP1 (sample 11), MP3 (sample 12), and the resin component from which the inorganic filler component in an epoxy resin-based cured material has been removed when heated at 250° C. FIG. 1 shows the results of EGA-MS analysis, specifically, the results of analysis of an allylphenol-maleimide copolymer. FIG. 1 shows the results of EGA-MS analysis, specifically, the results of analysis of an abnormal product (one with a changed solvent composition). 1 is a cross-sectional view showing an example of the configuration of a thick-film chip resistor, which is an example of an electronic component to which the cured resin for electronic component protective film according to the previous application can be applied as a final protective film. 11 is a flow chart showing an example of a manufacturing process for the thick film chip resistor shown in FIG. 10. FIG. 13 is a diagram showing the evaluation results of the product state in the high temperature storage test (H250), the change in insulation resistance before and after 1000 hours (n=5). FIG. 13 is a diagram showing the change in ΔR of a thick-film chip resistor when a high-temperature storage test (H250, 250° C. storage test) is performed. FIG. 13 is a graph showing the change over time in ΔR (n=20) during a humidity load life test (MR85, 85° C., 85% RH, with a load of an applied voltage of 75 V). FIG. 13 is a graph showing the change in ΔR over time (n=20) during a humidity load life test (MR60, 60° C., 95% RH, with a load of an applied voltage of 75 V). FIG. 13 is a graph showing the change in ΔR over time (n=20) during a humidity resistance life test (M60, 60° C., 95% RH, no load). FIG. 13 is a graph showing the change in ΔR over time (n=20) during a temperature cycle test (−55/155° C.). FIG. 1 is a diagram showing an example of a configuration of a maleimide resin composition according to an embodiment of the present invention. This is a diagram showing the appearance of the surface of a thick-film chip resistor (2 A, 1 MΩ) after a long-term (1000 h) heat resistance test at 230° C., 240° C., and 250° C. FIG. 1 is a diagram showing a cross-sectional SEM image of a protective film of a thick-film chip resistor before a H250 high-temperature storage test (immediately after curing) and the distribution of Al and Si. FIG. 13 is a diagram showing the results of Fourier transform infrared spectroscopy (FT-IR) measurement of a thick film chip resistor protective film before an H250 high temperature storage test (immediately after curing). FIG. 13 is a diagram showing the measurement results of Fourier transform infrared spectroscopy (FT-IR) after a high temperature storage test at 250° C./1000 h of a thick film chip resistor protective film. FIG. 1 shows a cross-sectional SEM image of a protective film of a thick-film chip resistor after a high-temperature storage test at 250° C./1000 h and the distribution of Al and Si.

The disclosure of the inventors' previous application (Patent Application No. 2018-208444) is as follows. The disclosure of the previous application forms the basis of the present invention, and the embodiments of the present invention described below will be explained with reference to this disclosure.

(Disclosure of earlier application)
The resin composition for producing the allylphenol-maleimide copolymer for use in a protective film for electronic components according to the invention of the previous application is a three-component allylphenol-maleimide resin composition (sometimes simply referred to as a maleimide resin composition in the present invention) using an allylphenol group compound having a rigid molecular structure and two types of maleimide group compounds having a rigid molecular structure and a flexible molecular structure, respectively. The copolymer produced from this resin composition can provide a protective film for electronic components that is endowed with high heat resistance due to its rigid structure and high toughness due to its flexible structure.

Furthermore, by using one type of resin with a flexible structure, the internal stress of the protective film for electronic components is reduced, the adhesive strength to the electrodes and substrate is increased, and it is possible to prevent moisture from penetrating through the interface of the protective film, thereby achieving high moisture resistance.

(1) Composition according to an embodiment of the prior application The resin composition according to the prior application uses a bismaleimide resin which has higher heat resistance than conventional epoxy resins and overcomes the drawback of bismaleimide resins, that is, their brittleness.

Specifically, heat resistance is imparted by introducing rigid structures such as phenol rings, maleimide rings, and benzene rings.

In addition, the introduction of a linear saturated hydrocarbon chain structure imparts toughness (flexibility), thereby relieving internal stress and increasing adhesive strength.

As described above, the resin composition for producing the allylphenol-maleimide copolymer for protective films for electronic components according to the present invention can increase the adhesion between the resistor and the protective film, and improve the moisture resistance.

The procedure for optimizing the resin composition is as follows.
a) First stage: Selection of resin materials that have the potential to have both high heat resistance and high moisture resistance
b) Second stage: Optimization stage of resin composition having both high heat resistance and high moisture resistance c) Third stage: Optimization stage of resin composition using the determined resin composition

The raw material composition of the resin composition is, for example, as follows.
(as a vehicle)
Resin raw material, curing catalyst, solvent, additives: 1) rheology control agent, 2) dispersant, 3) defoamer These additives are appropriately selected and added depending on the required properties of the resin composition (resin paste). In addition, a surface conditioner, etc. may be added.

(as a filler)
Among alumina, magnesium oxide, silica, etc., alumina is preferable from the viewpoint of cost and chemical stability. The filler is preferably spherical in shape, and the particle size can be about 0.1 to about 10 μm. For example, more preferable spherical alumina particles have a particle size in the range of about 0.1 to about 10 μm, and for example, two types of particles having a particle size in the range of about 0.1 to about 0.5 μm (e.g., average particle size of about 0.3 μm) and a particle size in the range of about 1 to about 10 μm (e.g., average particle size of about 4 μm) can be used.

(Inorganic filler)
The effects of including the inorganic filler are as follows.
- By containing inorganic filler (spherical alumina particles) with a low linear expansion coefficient, the linear expansion coefficient can be reduced.
In particular, when it is contained at 75 wt % in the resin composition (resin paste), it can be adjusted to have a linear expansion coefficient equivalent to that of solder (about 20) and closer to that of alumina substrates (about 7) and glass (3 to 10) (17).
It is possible to form a protective film that is not only heat resistant, but also resistant to temperature cycles (-55°C⇔155°C, etc.) and has high thermal shock resistance.

An example of a resin composition is described below. The resin composition according to this embodiment contains the following raw materials 1) to 3). These resin raw materials were selected as they have the potential to have both high heat resistance and high moisture resistance.

1) Raw Material A: Allyl Group-Containing Phenol Compound (Allyl Novolak)
For example, the allyl group-containing phenol compound (allylated novolak) shown below is a diallylphenol compound having a rigid structure, and may be composed of two or more allylphenol structures and a linking group therebetween that is a linear carbon chain of C1 or more (e.g., C1 to C6, preferably C1).

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(In the formula, n is 0 to 2.)

The above chemical structure is less rigid than N-aromatic maleimide, so it can impart toughness to the resin while maintaining heat resistance.

Examples of substitutes for raw material A include the following:
Allylphenol novolac
2,2'-Diallylbisphenol A

2) Raw material B: N-aromatic maleimide group-containing compound ((polymer type) phenylmethanemaleimide)
For example, the N-aromatic maleimide group-containing compound ((polymer type) phenylmethanemaleimide) shown below may be composed of two or more rigid N-aromatic maleimide structures and a carbon chain with a -CH ₂ - linking group therebetween.

（式中、ｎは０～２である。）

(In the formula, n is 0 to 2.)

The above chemical structure is due to the rigid structure of the N-aromatic maleimide, which can increase the heat resistance of the resin, but on the other hand makes the cured product brittle.

Examples of substitutes for raw material B include the following:
4,4'-Diphenylmethane bismaleimide
m-Phenylene bismaleimide Bisphenol A diphenyl ether bismaleimide
3,3'-Dimethyl-5,5'-diethyl-4,4'-diphenylmethane bismaleimide
4-Methyl-1,3-phenylenebismaleimide
4,4'-Diphenyl ether bismaleimide
4,4'-Diphenylsulfone bismaleimide
1,3-Bis(3-maleimidophenoxy)benzene
1,3-Bis(4-maleimidophenoxy)benzene

3) Raw material C: N-aliphatic maleimide group-containing compound (1,6-bismaleimide-(2,2,4-trimethyl)hexane)
For example, the N-aliphatic maleimide group-containing compound (1,6-bismaleimide-(2,2,4-trimethyl)hexane) shown below may be composed of two maleimide structures and a linking group therebetween that is a linear carbon chain of C1 or more (e.g., C1 to C10, preferably C6).

The above chemical structure, due to the flexible structure of N-aliphatic maleimide, reduces heat resistance but increases toughness.

Examples of substitutes for raw material C include the following:
1,6-Bismaleimido-(2,2,4-trimethyl)hexane
1,6-Bismaleimide-(2,4,4-trimethyl)hexane N,N'-Decamethylenebismaleimide N,N'-Octamethylenebismaleimide N,N'-Hexamethylenebismaleimide N,N'-Trimethylenebismaleimide N,N'-Ethylenebismaleimide

Table 1 shows an example of the composition ratio of the resin raw materials. Samples 1 to 12 are shown as examples in Table 1.

Below is an example of a paste raw material composition and curing conditions optimized for the resin raw material composition shown in Table 1.

(Regarding the vehicle)
・Optimum resin raw material composition: A/B/C=1/1/0.6 (equivalent ratio)
・Resin raw material composition range:
A/(B+C) = Allylphenol compound: Bismaleimide compound = 1:1 to 1:3
B:C=1:0.6~1:1.6
Curing catalyst: None Composition ratio of resin raw materials (A+B+C) and solvent: 75/25 (weight ratio)
Solvent composition:
BCA (butyl carbitol acetate, bp: about 250°C)/EC (ethyl carbitol, bp: about 200°C) = 25/75 (weight ratio)
Additives: 1) Rheology control agents (e.g., organic materials), 2) Dispersants (e.g., urethane-based), 3) Defoamers (e.g., polymer-based)

(About fillers)
Fused spherical alumina particles (combination of average particle sizes 4 μm and 0.3 μm)

(Vehicle and filler composition)
1) MP1 is 50/50 (weight ratio)
2) MP3: 25/75 (weight ratio)

The curing conditions are as follows:
A short two-step cure was performed, such as 200°C/10min + 250°C 10min.
In order to reduce production costs, it is preferable to carry out the curing treatment at 250° C. or less for 30 minutes or less.

Next, a method for producing a resin paste will be described with reference to FIG.
Vehicle manufacturing process: Predetermined amounts of resin raw material B and resin raw material C are heated to 150°C and melted (step S1). A predetermined amount of resin raw material A is added to the molten resin mixture and mixed uniformly while stirring at 100 to 150°C, and then a mixed solvent (BCA (butyl carbitol acetate, bp: about 250°C)/EC (ethyl carbitol, bp: about 200°C) = 25/75) is added (step S2), and after uniformly stirring and mixing at 100 to 150°C (step S3), it is slowly cooled naturally to room temperature to obtain a uniform resin raw material liquid (steps S4 and S5).
Resin paste manufacturing process 1: A total of 10 g or 30 g of alumina filler (DENKA: molten spherical alumina DAW-03 (d50 = 4 μm), ASFP-20 (d50 = 0.3 μm)) is added to 10 g of the obtained resin raw material liquid (step S6), and kneaded using a revolving mixer and a three-roll mill (step S7) to prepare a paste-like resin composition (mixture). At this time, 0.5 to 1.5 g of a wetting dispersant may be added.
Resin paste production process 2: A wetting and dispersing agent, a rheology control agent, and an antifoaming agent are added to the obtained paste-like resin composition (mixture) (step S8), and the mixture is kneaded using a revolution mixer (step S9) to produce a resin composition (paste for protective films for electronic components) (step S10).
Protective film manufacturing process: A resin composition is screen-printed and cured so as to cover the upper part of the resistor and a part of the electrode formed on an insulating substrate such as alumina. The curing conditions for the protective film paste were 200° C./10 min+250° C./10 min.

In this manner, the resin cured product for the electronic component protective film according to the previous application can be manufactured. The thickness of the electronic component protective film as the resin cured product is preferably about 10 to about 15 μm, for example about 12 μm.

The following describes the method for evaluating the properties of the cured resin for protective films for electronic components, which is related to the previous application.

1) Method for Measuring Tensile Shear Adhesive Strength FIG. 2 is a diagram simply illustrating the principle for measuring the tensile shear adhesive strength of the cured resin for protective films for electronic components according to the previous application.
In accordance with JIS K6850, test pieces of the resin according to the present embodiment were prepared and measurements were carried out.

First, as a preliminary step, a test piece of cold-rolled steel plate (JIS G3141 SPCC-SB) measuring 100 mm in length, 25 mm in width, and 1.6 mm in thickness was degreased with IPA (isopropyl alcohol), polished with No. 240 SiC abrasive paper, and then ultrasonically cleaned in IPA and dried.

Next, a solution was prepared based on the resin composition, and a certain amount of this was applied to a portion of each of the two steel plates (application area: approximately 25 mm x 12.5 mm). The two steel plates were clamped with a paper clip so that the applied portions overlapped, and pressed together. The excess resin solution was removed, and the plates were cured under the specified curing conditions. The prepared specimens were then exposed to H175, H200, H250, M85, and M60 test tanks for 100 hours each. The tensile shear adhesive strength was measured using an Autograph AGS-X 10kN (Shimadzu Corporation), with the test specimens (n=5) set in the device as shown in Figure 2, and the maximum stress at break was measured under conditions of an environmental temperature of 23°C and a loading speed of 5 mm/min.

2) Method for Measuring Fracture Toughness FIG. 3 is a diagram showing the principle for measuring the fracture toughness of the cured resin for protective films for electronic components according to the previous application.
As shown in FIG. 3, a test piece (length 40 mm×width 5 mm×thickness 3 mm) was cut out from the prepared cured product using a diamond cutter, and the surface of the sample was polished with SiC polishing paper (No. 240).

Thereafter, the sample was left to stand in a thermostatic chamber (23° C.) for one day. In FIG.
A test piece X for fracture toughness measurement (see FIG. 3) was cut out from the prepared cured product using a microcutting machine, and the surface of the sample was polished with SiC abrasive paper (No. 240). Next, a notch (0.45-0.55 mm) was made using a microtome blade. Then, the sample was left to stand in a thermostatic chamber (23°C) for one day. The fracture toughness value was measured in compression mode using an autograph (Shimadzu AL5-X) and a three-point bending jig. Next, the fracture toughness value was calculated by introducing the obtained fracture load value into a specified formula of ASTM D5045-93.

Table 2 shows the results of the tensile shear adhesion test of each sample before and after 100 hours of heat and moisture resistance testing. An epoxy resin-based sample was used as the comparison sample.

The criteria for selecting the most suitable sample are as follows:
Index 1: Glass transition temperature ⇒ Target: 250°C or higher Index 2: Initial tensile shear adhesive strength ⇒ Equivalent level to epoxy resin (10 Pa) Index 3-1: (H175), H200, H250, target rate of change in adhesive strength before and after 100 hours of testing: -50% or higher Index 3-2: M60, M85 target rate of change in adhesive strength before and after 100 hours of testing: -20% or higher

From the above results, it can be determined that the resin raw material composition of sample 10, A/B1/B2 = 1/1/0.6, is close to optimal because it cleared the target values for the above three indicators.

Figure 4 shows the results (n=5) of tensile shear adhesive strength tests of the cured resin for protective films for electronic components optimized above before and after 100 hours of heat and moisture resistance testing.

The rate of change in adhesive strength before and after 100 hours of the H200 test was small at -5.5%, but the rate of change in adhesive strength before and after 100 hours of the H250 test was large at -42.9%.

The rate of change in adhesive strength before and after 100 hours of testing for M60 and M85 was relatively small at -9.8% and -16.8%, respectively.

This shows that the allylphenol-maleimide copolymer optimized above has both high heat resistance of 200°C or higher and moisture resistance.

Figures 5 and 6 show the thermal properties of the optimized cured resin for protective films for electronic components. Figure 5 shows the results of DMA measurements, and Figure 6 shows the results of TG-DTA measurements.

As shown in Figure 5, the DMA measurement results show that the Tg (glass transition temperature) of the optimized allylphenol-maleimide copolymer is 300°C or higher, indicating high physical heat resistance.

8, the TG-DTA measurement results show that T _d5 (5% thermal weight loss temperature) is 424° C. This result indicates that the chemical heat resistance is high.

The fracture toughness measurement results are shown in Table 3. _KIC was 0.960, which was confirmed to be at the same level as epoxy resin.

Figure 7 shows the remaining weight fraction (n=3) of MP1, MP3, and the resin component from which the inorganic filler in the epoxy resin-based cured material has been removed when heated to 250°C.

The developed products MP1 and MP3 (allylphenol-maleimide resin system) lost weight by about 40% at H250/1000 hours, but the weight loss was almost saturated.
In the comparative example, epoxy resin system 1, the resin content continues to decrease even at H250/1500 hours, with almost no resin remaining.

Therefore, it can be said that the optimized allylphenol-maleimide copolymer is less susceptible to thermal degradation of the resin than epoxy resin system 1.

Figures 8 and 9 show the results of EGA-MS analysis. Figure 8 shows the analysis results of an allylphenol-maleimide copolymer, and Figure 9 shows the analysis results of an abnormal product (one with a changed solvent composition).

Evolved gas analysis (EGA-MS) was used to evaluate the cured state of the copolymer. Conventionally, FT-IR, thermal analysis, HPLC, or Py-GC/MS are used for simple evaluation of the cured state of resin. However, the allylphenol-maleimide copolymer of this embodiment has a complex curing reaction mechanism and products, so satisfactory data could not be obtained using conventional methods.

EGA-MS is one of the components of pyrolysis mass spectrometry, in which a heating furnace for sample introduction and a mass spectrometer are connected with a straight stainless steel tube to detect the total amount of evolved gas without separation. The mass spectrum obtained is complex because it is mixture data, but by comparing it with the analysis results of the raw materials and the analysis results from pyrolysis GC/MS (Py-GC/MS), it is possible to analyze the state of the resin. In addition, since the results can be obtained in about an hour without pretreatment such as extraction, it is an effective analysis method when examining a large number of conditions.

- EGA-MS measurement method: Take an appropriate amount of the hardened sample and crush it in a mortar or similar. After crushing, weigh out about 1 mg of the sample and place it in a sample cup for measurement. The sample is set in the device and placed in a furnace preheated to 200°C, and held for 20 minutes to remove low-boiling volatiles such as solvents. The furnace is then heated to 600°C (10°C/min), and the pyrolysis gas generated during heating is detected by mass spectrometry.

In Figure 8, the peak temperature is 470°C. In Figure 9, a peak at 550°C can be seen along with a peak at 470°C. The peak at 550°C coincides with the peak of the hardened material when the raw material is used alone.

・Analysis results The state of the resin is analyzed from the position of the peak temperature that appears in the thermogram showing the relationship between the obtained strength and temperature (time) and the detected mass number data at each point. For the allylphenol-maleimide copolymer resin targeted in this study, prior analysis has revealed that if the resin is in a normal state after curing, one peak appears at 470°C (Figure 8).

Additionally, the peak positions and masses detected when analyzing the raw materials and their individual cured products were also analyzed in advance to confirm. Based on this information, the analysis results of resin copolymers with various conditions or compositions changed were checked to see if the peak positions and mass numbers matched the data in Figure 8. Furthermore, when differences in the data were found, it was possible to identify anomalies by comparing them with the analysis results of the raw materials. Figure 9 shows an example of an analysis of a blend with a different solvent composition. It can be seen that some of the raw materials precipitated before curing, and an individual cured product was produced. In such cases, there is a possibility that variations in strength and adhesive power may occur, and it was determined that these conditions were unsuitable for producing copolymers.

It is also possible to check for residual raw materials in the same way. In this way, analysis using EGA-MS makes it possible to visualize the structure of the resin in terms of the relationship between the decomposition temperature and the strength of the pyrolysis products that are generated.

The above analysis confirmed that the optimized allylphenol-maleimide copolymer can be cured at low temperatures in a short time and is a candidate for a protective film for electronic components with excellent heat resistance.

Next, we will explain the results of applying the optimized allylphenol-maleimide copolymer described above to a resistor as an example of an electronic component.

Figure 10 shows an example of the configuration of a thick-film chip resistor, which is an example of an electronic component to which the cured resin for electronic component protective film according to this embodiment can be applied as a final protective film.

The thick film chip resistor A shown in FIG. 10 has a resistor 3 formed on an insulating substrate 1. The resistor 3 has a trimming groove 3a formed by a trimming process for adjusting the resistance value, for example, by a laser. Before the trimming process, a first protective film 11 is formed to protect the resistor 3, and after the trimming process, a protective film (second protective film) 17 made of the above-mentioned optimized allylphenol-maleimide copolymer is formed to protect the resistor 3 and the electrodes 5a, 5b from the external environment and to cover the resistor 3 and the electrodes 5a, 5b. The second protective film 17 is sometimes called an overcoat film.

In addition, end electrodes (Ni/Cr, etc.) 9a, 9b and back electrodes (Ag, Cu, or conductive adhesive) 7a, 7b are formed on the end and back surfaces of the insulating substrate 1, respectively. In addition, plating layers 13a, 13b of Ni, Sn, etc. are formed to cover these electrodes.

FIG. 11 is a flow chart showing an example of a manufacturing process for the thick film chip resistor shown in FIG.
First, in step S11, an alumina substrate with a purity of, for example, 96% is prepared as a large-sized insulating substrate for multiple production. In step S12, for example, an Ag/Ag-Pd electrode paste material is prepared. In step S13, the Ag/Ag-Pd electrode paste material is printed and fired, for example, by a screen printing method, on one side of the insulating substrate 1 as the back electrodes 7a, 7b. Next, in step S15, the Ag/Ag-Pd electrode paste material prepared in step S14 is used to print and fire, for example, by a screen printing method, the front electrodes 5a, 5b on the surface opposite to the surface of the insulating substrate 1 on which the back electrodes 7a, 7b are formed in step S14.

Next, in step S16, for example, _RuO2 resistor paste is prepared, and in step S17, resistor 3, one end of which is connected to surface electrodes 5a, 5b, is printed and fired, for example, by screen printing.

Next, in step S18, a glass paste is prepared, and in step S19, the first protective film 11 is printed and fired on the resistor 3, for example, by screen printing.

In this state, the resistance value is measured, and in step S20, the resistance value is adjusted to the desired resistance value by forming trimming grooves 3a by laser trimming.

Next, in step S21, the optimized allylphenol-maleimide resin composition according to this embodiment is screen-printed on the resistor 3 and the first protective film 11 so as to cover at least the trimming groove 3a, and the optimized allylphenol-maleimide resin raw material composition is heated and cured at, for example, about 200°C to form the second protective film 17.

In step S23, the substrate 1 is divided into rectangular pieces, in step S24, the end electrodes 9a, 9b are formed, and in step S25, the rectangular pieces are divided to separate the resistors. In step S26, the external electrodes 13a, 13b are formed by a plating process or the like.
Through the above steps, the resistor according to this embodiment is completed.

The resistor 3, rear electrodes 7a, 7b, front electrodes 5a, 5b, and first and second protective films 11, 17 can all be formed by screen printing. The first protective film 11 can be omitted.

The front electrodes 5a, 5b and the back electrodes 7a, 7b may be formed in the same process, or the order of the processes may be changed. The order of the resistor formation process and the front electrode formation process may also be changed.

The end electrodes 9a and 9b can be formed, for example, by dividing the insulating substrate 1 into strips and then using a sputtering method or the like.

In the previous application, the protective film was described as having two layers, but the first protective film 11 does not need to be formed, and the protective film can be a single layer.

The following describes the evaluation results of thick-film chip resistors manufactured in the manner described above, in which the optimized allylphenol-maleimide copolymer according to this embodiment is used as the second protective film.

(Evaluation of insulation resistance of thick film chip resistors)
FIG. 12 is a diagram showing the evaluation results of the product state in terms of the change in insulation resistance before and after 1000 hours (n=5) in the high temperature storage test (H250).

The optimized allylphenol-maleimide copolymers MP1 and MP3 (see Table 1) of the previous application showed that even after 1000 hours at 250°C, the insulation resistance only decreased from 74 TΩ to 14 TΩ for MP1 and from 69 TΩ to 31 TΩ for MP3, and both showed high insulation resistance of about 10 TΩ. This shows that the degree of decrease in insulation resistance due to heating is smaller than when general epoxy resin systems 1 and 2 are used as protective films. This confirmed that good insulation resistance was obtained when applied to products as a protective film paste.

It was confirmed that the insulation resistance of epoxy resin systems 1 and 2 had dropped significantly after 1,000 hours at 250°C, from 75 TΩ to 0.28 TΩ for epoxy resin system 1, and from 112 TΩ to 1.9 TΩ for the finished product.

(Results of long-term insulation resistance test of thick film chip resistors)
Next, the results of a long-term storage test at 250° C. including the optimized allylphenol-maleimide copolymers MP1 and MP3 (see Table 1) according to the previous application will be described. The results of epoxy resins (normal and heat-resistant products) are also shown as comparative examples.

Figure 13 shows the change in ΔR of a thick-film chip resistor when a high-temperature storage test (H250, 250°C storage test) is performed.

As shown in Figure 13, the resistance change ΔR of conventional epoxy resin system 1 after 3,000 hours of H250 testing was +0.8% or more.

On the other hand, for allylphenol-maleimide copolymers MP1 and MP3 and epoxy resin system 2, ΔR was less than ±0.5% after 3,000 hours of H250 testing.

This shows that, compared to conventional epoxy resin 1, the change in resistance value is small when using the optimized allylphenol-maleimide copolymers MP1 and MP3 according to this embodiment.

The reason why the resistance change ΔR is high in the initial stage is due to the recovery of the effects of the distortion that occurred in the resistor when it was trimmed with a laser, and it is believed that the effect of the protective film is small.

(Results of humidity load life test for thick film chip resistors)
The humidity load life test was performed under the following temperature and relative humidity conditions in a thermo-hygrostat (ESPEC PL-3J), with the voltage applied being switched on for 1.5 hours and off for 0.5 hours, and the resistivity was measured for 3000 hours. The voltage applied to the resistor was 75V.

Figure 14 shows the change in ΔR over time (n=20) during a humidity load life test (MR85, 85°C, 85% RH, with load). The samples used are the same as those in Figure 13.

As shown in Figure 14, after 3,000 hours of MR85 testing, almost no difference was observed among all samples, with ΔR being less than ±0.1%, a favorable result.

Figure 15 shows the change in ΔR over time (n=20) during a humidity load life test (MR60, 65°C, 95% RH, with load).

As shown in Figure 15, after 3,000 hours of MR60 testing, almost no difference was observed among all samples, with ΔR being less than ±0.2%, a favorable result.

(Humidity life test results for thick film chip resistors)
FIG. 16 is a diagram showing the change in ΔR over time (n=20) during a humidity resistance life test (M60, 60° C., 95% RH, no load).

As shown in Figure 16, after 3,000 hours of M60 testing, almost no difference was observed among all samples, with ΔR less than ±0.1%, a favorable result.

In this way, when the optimized allylphenol-maleimide copolymers MP1 and MP3 of the previous application are used, the results of the humidity load life test and humidity life test show that the resistance value changes very little over time, which is favorable. This is thought to be because the allylphenol-maleimide copolymer of the present invention used in the protective film is a resin with a flexible structure, which reduces the internal stress of the protective film, increases the adhesion of the first protective film to the surfaces of other materials of the resistor, such as the glass and electrodes, and prevents moisture from penetrating from the interface, improving moisture resistance.

(Results of temperature cycle testing of thick film chip resistors)
FIG. 17 is a diagram showing the change over time in ΔR (n=20) during a temperature cycle test (−55/155° C.).
As shown in FIG. 17, after 1500 cycles of the temperature cycle test, almost no difference was observed among all the samples, and ΔR was good at about +0.1%.

Tables 4 and 5 summarize the changes in the resistance values over time.
Tables 4 and 5 show the change in ΔR after 1000 hours of MR60 (60°C, 95% RH, with load) and MR85 (85°C, 85% RH, with load) tests when applied to thick-film chip resistors (2A, 1MΩ). It was confirmed that the developed allylphenol-maleimide resin product (without silicone particles) had a smaller ΔR (rate of change in resistance value) before and after 1000 hours of exposure in both the MR60 and MR85 tests compared to epoxy resin. Therefore, it was confirmed that the developed product has higher long-term moisture resistance when applied to thick-film chip resistors compared to epoxy resin.

As explained above, by using the allylphenol-maleimide resin composition according to the previous application, it is possible to provide a new protective film for electronic components that has excellent heat resistance and moisture resistance. It is also possible to provide a protective film for electronic components that can be cured at low temperatures and in a short time.

(Embodiments of the present invention)
1) Based on the disclosure of the above-mentioned prior application, the present invention will be described in detail below. Note that the method of using the resin composition according to the present embodiment for a protective film of a resistor in an electronic component is the same as that in the prior application, and therefore a detailed description thereof will be omitted.

2) Background and Problems of the Invention In recent years, the number of electronically controlled automobiles such as EVs and HVs has been increasing. The electronic control units (ECUs) installed in these automobiles are likely to be exposed to more severe temperature environments in the future due to direct mounting on the engine and electromechanical integration of electronic components in the engine. Therefore, in the future, in-vehicle mounting materials installed in ECUs will also be required to have long-term heat resistance that can withstand high temperatures of 200°C or higher. In addition, since it is expected that electronic components will be mounted on the same substrate as SiC semiconductors and GaN semiconductors that operate at 250°C in the future, it is highly likely that resistors, which are passive components, will also be required to have the same level of heat resistance.

In view of this situation, there are growing expectations for the use of maleimide resins, which have high heat resistance, since it is difficult, due to their chemical structure, to meet the required long-term heat resistance of 200°C or higher with epoxy resins, which are primarily used as resins for mounting materials.
The background of the invention of the previous application is that the high heat resistance of conventional maleimide resins is due to their rigid molecular structure and high crosslink density after curing, but on the other hand, they also have the drawback of being brittle. Therefore, there is a demand for improving the toughness of maleimide resins. In addition, because of the rigid structure, internal stress is likely to be high, which leads to a decrease in adhesive strength to the adherend, which makes it easier for water to penetrate through the adhesive interface, resulting in a problem of low moisture resistance.
In the previous application, the above problem was solved by using a resin composition to produce an allylphenol-maleimide copolymer.

Conventional maleimide resins are resistant to thermal degradation but susceptible to thermal oxidative degradation. Therefore, if voids or the like are present on the surface of the protective film or on the interface between the protective film and the adherend surface, the presence of oxygen in the air contained in the voids on the surface of the protective film and at the adhesive interface can cause thermal oxidative degradation even at temperatures lower than the physical heat resistance temperature (glass transition point).
Therefore, the present invention provides a resin composition for producing an allylphenol-maleimide copolymer for use in a protective film for electronic components, which has improved heat resistance compared to the resin composition of the previous application.

The resin composition and cured product for producing the allylphenol-maleimide copolymer according to this embodiment are based on the resin raw material composition ratio of sample 11 (MP1) (A/B1/B2 = 1/1/0.6) in Table 1, and further contain silicone particles. The filler used was molten spherical alumina particles (a combination of particles with an average particle size of 4 μm and 0.3 μm).

FIG. 18 is a diagram showing an example of the configuration of the allylphenol-maleimide resin composition according to this embodiment.
As shown in FIG. 18, the allylphenol-maleimide resin composition according to the present embodiment contains the following resin raw materials.
(A) an allyl group-containing phenol compound having a rigid structure; (B) an aromatic maleimide group-containing compound having a rigid structure; (C) an aliphatic maleimide group-containing compound having a flexible structure; and (D) silicone particles. However, a curing catalyst is not required.
In addition to the above (A) to (D), alumina particles were used as an inorganic filler. For example, a combination of alumina particles with an average particle size of 4 μm and an average particle size of 0.3 μm was added to adjust the viscosity of the paste during screen printing.

Thus, the present embodiment is characterized in that silicone particles are added to the allylphenol-maleimide resin composition of the previous application. The silicone particles are at least either silicone rubber particles or silicone resin particles. The silicone particles have an average particle size of 1 to 10 μm.
The content of the silicone particles is 10 to 25% by weight based on the total weight of the resin composition.

The following describes the results of applying a protective film made of a resin composition for producing an allylphenol-maleimide copolymer for protective films for electronic components according to this embodiment to a thick-film chip resistor and conducting long-term heat resistance/oxidation resistance tests in an oxygen-containing atmosphere.

Figure 19 shows the surface appearance of a thick-film chip resistor (2A (2.0 x 1.25 mm), 1 MΩ) after a long-term (1000-hour) heat resistance test at 230°C, 240°C, and 250°C.

Five types of samples were prepared for the resin composition MP1 of the previous application: sample MP31 with no silicone particles added, MP32 with 25% by weight of silicone rubber particles with an average particle size of 5 μm added to the total amount of the resin composition, and MP33 to MP35 with 25% by weight of silicone resin particles with different average particle sizes added to the total amount of the resin composition, and a long-term heat resistance test (evaluation of long-term thermal and thermal oxidative degradation) was conducted. Figure 19 shows the results of a long-term heat resistance test of thick-film chip resistors using protective films with parameters of silicone type and average particle size for MP31 to MP35 (n=20 each).

In MP31, which does not contain silicone particles in the allylphenol-maleimide resin composition, cracks (areas surrounded by white frames in Figure 19) occurred on the surface of the protective film after 250°C/1000h, and the protective film also peeled off from the resistor and surface electrode. On the other hand, in samples (MP32, MP33) in which a protective film made of a resin composition in which silicone rubber particles (average particle size 5 μm) or silicone resin particles (average particle size 5 μm) were added to an allylphenol-maleimide resin composition was applied to a thick-film chip resistor, neither cracks nor peeling occurred even after 250°C/1000h. However, in samples (MP34, MP35) in which the average particle size of the silicone resin particles was reduced, peeling did not occur, but in MP34, which had an average particle size of 2 μm, slight cracks occurred in the protective film of the thick-film chip resistor, and in MP35, which had an average particle size of 0.7 μm, numerous cracks occurred.

One of the reasons for the above results is that when the average particle size of the silicone particles is about 5 μm, the elastic modulus of the silicone particles is low, so the silicone particles contribute to stress relaxation of the protective film, making it difficult for cracks to occur due to thermal stress. On the other hand, when the particle size of the silicone particles is small, the surface area of the silicone particles increases even with the same content, and the force that binds the matrix resin becomes stronger, so the elastic modulus of the paste made of the allylphenol-maleimide resin composition increases, cracks occur, and as a result, it is assumed that it becomes easier to induce cracks in the protective film (resin cured product) (see MP35 in Figure 19). Furthermore, maleimide has a high elastic modulus, while silicone has a low elastic modulus, and the elastic modulus of the maleimide resin paste as a whole is reduced by adding silicone particles, and the thermal stress associated with the difference in linear expansion coefficient during and after curing is relaxed, making it difficult for cracks to occur. If many cracks occur at the adhesive interface of the protective film, it is predicted that air containing oxygen will easily enter, which will lead to peeling. That is, in this embodiment, the elastic modulus of the protective film is reduced, making it less likely to crack, and therefore preventing the protective film from peeling off.

Another reason is presumably that the silicone particles, which are resistant to thermal and thermal oxidative degradation even at 250°C, cover the surface of the protective film and protect the maleimide resin, which is resistant to thermal degradation but vulnerable to thermal oxidative degradation, thereby suppressing the generation of gas associated with the thermal decomposition of the resin. The mechanism by which the addition of silicone particles to an allylphenol-maleimide resin composition suppresses deterioration of the protective film due to thermal oxidative degradation is summarized below.
Silicone has the property of being resistant to thermal and thermo-oxidative degradation.

On the other hand, maleimide resins are resistant to thermal degradation, but are not so resistant to thermal oxidative degradation. Degradation begins from oxygen in the air or voids in the cured resin (e.g., the protective film), causing cracks and peeling in the protective film.
Therefore, the inventors thought that if the surface of the maleimide resin was covered with silicone, it would be possible to suppress the thermal oxidative deterioration of the protective film, and so they mixed silicone particles into the allylphenol-maleimide resin composition described in the previous application.

The specific gravity of silicone (about 1) is similar to that of maleimide resin (about 1). The relatively light silicone and maleimide resin move to the top of the protective film (the side opposite to the resistor, surface electrode, and interface between the alumina substrate and the protective film), while the relatively heavy alumina (about 4) settles to the bottom of the protective film. Here, the allylphenol-maleimide resin composition of the present invention has a high curing temperature of about 200°C, so that when heated for curing, the viscosity of the resin decreases and the fluidity increases prior to the curing reaction, resulting in two resin layers in the protective film. In other words, by distributing silicone particles unevenly on the top of the continuous phase of the maleimide resin, it is possible to prevent the maleimide resin from coming into contact with oxygen in the air, and as a whole, thermal oxidative deterioration is suppressed.

Therefore, by covering the surface of the maleimide resin with silicone particles that are resistant to both thermal and thermal oxidative degradation, it is possible to suppress the thermal oxidative degradation of the maleimide resin even in an environment of 250°C. As a result, it is presumed that it has been possible to maintain the moisture resistance of the allylphenol-maleimide resin in the previous application while also improving its heat resistance up to 250°C.

Table 6 shows the experimental results of 250°C/1000h high temperature storage test (insulation resistance) of thick film chip resistors (MP31-MP34). The remaining insulation resistance rate is a relative value after long-term exposure at 250°C, with the initial insulation resistance set at 100. Maleimide resin protective films (MP32-MP34) with added silicone rubber particles (average particle size 5μm) and silicone resin particles (average particle sizes 5μm and 2μm), which showed almost no cracking or peeling, maintained 80% or more of their initial insulation resistance after 250°C/1000h, whereas the insulation resistance of the film without added silicone particles (MP31) dropped to 18%.

As described above, in MP32-34, silicone particles that are resistant to both thermal degradation and thermal oxidation in a 250°C environment spread near the surface of the protective film and cover the maleimide-based resin, suppressing the thermal oxidative degradation of the maleimide-based resin, which is resistant to thermal degradation but vulnerable to thermal oxidation in a 250°C environment.

Figure 20 shows cross-sectional SEM images of the protective film of thick film chip resistors (MP31 to MP33) before the H250 high temperature storage test (immediately after curing) and the distribution of Al and Si. MP31 is a sample without silicone particles, MP32 is a sample with silicone rubber particles added (average particle size 5 μm), and MP33 is a sample with silicone resin particles added (average particle size 5 μm). Figure 20 is an image of a rectangular solid-shaped portion of the surface layer of a sample (thick film chip resistor) cut out from diagonally above.

That is, each SEM image shown in Figure 20 shows, from the top, a surface portion of the protective film (the area surrounded by the dotted line), a cross-sectional portion of the protective film and resistor (dashed dotted line), and below that is the surface portion of the protective film (the same as the area surrounded by the dotted line).
In MP32 and MP33, which contain silicone particles, the distribution of Si (the white areas in the SEM images in the rightmost column) is more prevalent on the surface than in MP31. This indicates that the silicone particles are distributed in large amounts on the surface (top) of the protective film, covering the maleimide resin. In addition, because a small amount of hydrophobic nanosilica is added as a rheology control agent to both samples, the distribution of Si is also observed in MP31, which does not contain silicone particles.

In addition, it can be seen that particulate matter is distributed on the upper part of the protective film in MP33, which contains silicone resin particles (average particle size 5 μm). The specific gravity of the silicone resin particles is similar to that of the maleimide resin matrix, and is about 1/4 that of the alumina particles, so it is presumed that many of the silicone resin particles move to the upper part by 200°C, when hardening begins. On the other hand, it can be seen that in MP32, which contains silicone rubber particles (average particle size 5 μm), the silicone rubber has spread to the upper part without retaining its particle shape. It is presumed that the silicone rubber has melted and spread to the upper part. From Figure 20, it can be seen that the protective film is two layers, with the silicone covering the maleimide resin, in both the allylphenol-maleimide resin composition containing silicone rubber particles and the silicone resin particles.

FIG. 21 is a diagram showing the FT-IR spectrum of the protective film of a thick-film chip resistor (MP33 to MP35 with added silicone resin particles) before the H250 test.
As shown in FIG. 21, in MP31 (without silicone particles), peaks derived from the maleimide resin and the hydrophobic silica added as a rheology control agent were observed.

On the other hand, in MP33 to MP35, which contained silicone resin particles, a strong peak derived from silicone was observed, whereas a weak peak derived from maleimide resin was observed. Here, the peak derived from silicone included both the peak derived from silicone resin and the peak derived from hydrophobic nanosilica added as a rheology control agent.
FIG. 21 suggests that in MP33 to MP35, in which silicone resin particles were added, silicone was present in large amounts on the surface of the protective film of the resistor.

FIG. 22 is a diagram showing the measurement results of the protective film of a thick-film chip resistor (MP32 with added silicone rubber particles) by Fourier transform infrared spectroscopy (FT-IR) using the ATR method.
22, in the case of MP31 (without silicone particles), the peak intensity (height) derived from maleimide and the peak intensity derived from silicone were almost the same, and the intensity ratio was about 1. Here, the peak derived from silicone observed in MP31 is derived from the hydrophobic nanosilica added as a rheology control agent.

On the other hand, in the case of MP32 to which silicone rubber particles were added, a strong peak derived from silicone was observed, and the intensity ratio was about twice that of the peak derived from maleimide. The intensity ratio indicates the relative composition ratio, and it can be confirmed that the relative amount of silicone is high in MP32.
Here, the peaks derived from silicone include both the peaks derived from silicone rubber and the peaks derived from hydrophobic nano-silica added as a rheology control agent.

ATR measurement in FT-IR is a method for analyzing the composition of the surface several microns deep. Based on this, Figure 22 suggests that MP32, which contains silicone rubber particles, has a large amount of silicone rubber present on the surface of the protective film.
From the above, it can be seen that the observation results in FIG. 20 and the measurement results in FIGS. 21 and 22 show good agreement.

Figure 23 shows cross-sectional SEM images of the protective film of thick-film chip resistors (MP31 to MP33) after a 250°C/1000h high-temperature storage test, as well as the distribution of Al and Si. In MP32, the silicone rubber particles have melted and spread further than before the high-temperature storage test. On the other hand, in MP33, the silicone resin particles are distributed in the upper part of the protective film, just as they were before the high-temperature storage test. Therefore, in the case of silicone resin particles (average particle size 5 μm), the silicone particles, which are resistant to both thermal degradation and thermal oxidation, cover the surface of the protective film without undergoing changes such as melting in a 250°C environment (Si spreads and particles are visible at the top), and it is presumed that this suppresses the thermal oxidation degradation of maleimide, which is resistant to thermal degradation but vulnerable to thermal oxidation in a 250°C environment. In both protective films to which silicone rubber particles (MP32) and silicone resin particles (MP33) were added, the silicone remained concentrated at the top of the maleimide resin, resulting in an excellent protective film for electronic components that had heat resistance of over 250°C while maintaining moisture resistance.

Maleimide resins are resistant to thermal degradation caused by heat alone, but are vulnerable to thermal oxidative degradation caused by the synergistic action of heat and oxygen. In contrast, silicones (including both silicone resins and silicone rubber) are resistant to both thermal and thermal oxidative degradation, but have the disadvantage of being weak in mechanical strength. In addition, maleimide resins and silicones fundamentally have low affinity, so when a silicone layer is layered on top of a maleimide resin layer, peeling is likely to occur at the interface, and two printing processes are required.

In the present invention, when silicone particles are dispersed in a maleimide resin, the movement of the silicone particles is suppressed at high viscosity, but in the process of raising the temperature to the curing temperature (200°C or higher), the viscosity of the maleimide resin decreases, and the silicone particles, which have a lower specific gravity than the alumina particles and a lower affinity with the maleimide resin, move to the upper layer. It is presumed that peeling is less likely to occur because the maleimide resin penetrates between the silicone particles. By distributing the silicone particles unevenly at the top of the continuous phase of the maleimide resin, it is possible to suppress the maleimide resin from coming into contact with oxygen in the air, and thermal oxidation deterioration is suppressed overall. In addition, the mechanical strength of the protective film is sufficient because the silicone is dispersed in the continuous phase of the maleimide resin, which has relatively good mechanical strength.

In the resin protective film of the thick film chip resistor according to this embodiment, in order for the surface of the resin protective film to be covered with silicone (the protective film will be two layers of silicone and maleimide resin), it is preferable to add 10% by weight or more to the total amount of the resin composition so that the number of silicone particles is not too small relative to the surface area.

Here, because maleimide resins have a low viscosity, the alumina particles give the paste viscosity. Increasing the amount of silicone reduces the amount of alumina, so it is not desirable to have too many silicone particles, so the amount of silicone particles is set to 25% by weight or less of the total amount of the resin composition.

The silicone particles may be a mixture of two types, silicone rubber particles and silicone resin particles, so that the total silicone particles content is in the range of 10% to 25% by weight based on the total amount of the resin backing composition.

In this embodiment, one type of allylphenol compound with a rigid molecular structure and two types of maleimide compounds with rigid and flexible molecular structures are used, and by mixing these in an appropriate composition, the hardened product can be given high heat resistance due to the rigid structure and high toughness due to the flexible structure. In contrast to the previous application, silicone resin particles or silicone rubber particles with an average particle size of several μm are added, and these cover the surface of the protective film based on the allylphenol-maleimide resin, making it possible to impart high heat resistance of 250°C or more.

Furthermore, by adding 10 to 25% by weight of silicone resin particles or silicone rubber particles with an average particle size of 1 to 10 μm to the protective film, before hardening begins at 200°C, the surface of the protective film is covered (distributed in large amounts on the surface) with silicone particles that are resistant to both thermal degradation and thermal oxidation and have a specific gravity similar to that of maleimide-based resin, making it possible to suppress the thermal oxidative degradation of maleimide-based resin, which is resistant to thermal degradation but vulnerable to thermal oxidation, in an environment of 250°C.

As described above, next-generation semiconductors are preferably designed to operate at 250°C, and electronic components are required to have a similar level of heat resistance, so the allylphenol-maleimide resin cured film according to this embodiment is extremely useful as a protective film for electronic components, including resistors.

The allylphenol-maleimide resin composition of the present invention can be used as a protective film for various electronic components. In addition to chip resistors, the electronic components can also include capacitors, chip fuses, varistors, etc.

The configurations shown in the figures in the above embodiments are not limited to these, and can be modified as appropriate within the scope of the effects of the present invention. In addition, the present invention can be modified as appropriate without departing from the scope of the purpose of the present invention.

Furthermore, each component of the present invention can be selected at will, and inventions that incorporate selected configurations are also included in the present invention.

This invention can be used for protective films for resistors.

A Thick film chip resistor 1 Insulating substrate 3 Resistor element 3a Trimming groove 5a, 5b Surface electrodes 7a, 7b Back electrodes 9a, 9b End electrodes 13a, 13b Plating layer (external electrodes)

Claims (4)

(A) an allyl group-containing phenol compound having a rigid structure;
(B) an aromatic maleimide group-containing compound having a rigid structure;
(C) an aliphatic maleimide group-containing compound having a flexible structure;
(D) silicone particles ,
The compound (A) is represented by the following formula 1, the compound (B) is represented by the following formula 2, and the compound (C) is represented by the following formula 3:
the silicone particles are particles made of either silicone rubber or silicone resin,
The content of the silicone particles is 10 to 25% by weight based on the total amount of the resin composition,
The silicone particles have an average particle size of 2 to 5 μm .

(In the formula, n is 0 to 2.)

(In the formula, n is 0 to 2.)

A method for producing an allylphenol-maleimide copolymer for use in a protective film for electronic components, comprising a step of curing the resin composition according to claim 1 by heating. A protective film for electronic parts, comprising an allylphenol-maleimide copolymer which is a heat-cured product of the resin composition according to claim 1 . 4. Use of the allylphenol-maleimide copolymer according to claim 3 in a second protective film of an electronic component having an insulating substrate, a pair of electrodes formed opposite to each other on at least one surface of the insulating substrate, a resistor electrically connecting the pair of electrodes, a first protective film covering the resistor, and a second protective film covering the first protective film.

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