Low-volatile acrylic conductive adhesive for chip bonding, and preparation method and application thereof

Abstract

The application provides a low-volatility acrylic conductive adhesive for chip bonding as well as a preparation method and application thereof. The conductive adhesive comprises polybutadiene or its derivative with an acrylate end group, an acrylate monomer containing an imide structure, a multifunctional acrylate crosslinking monomer and a conductive filler. The application replaces a conventional volatile diluent with a non-volatile acrylate monomer containing an imide structure, and combines with low-viscosity polybutadiene or its derivative with an acrylate end group, so that the weight loss rate of the conductive adhesive is less than or equal to 0.3% during 80-120 DEG C heat curing, the voids in the adhesive layer (void area ratio is 0%) are fundamentally eliminated, excellent conductive performance (volume resistivity) and high bonding strength (19.3-21.2 MPa) are realized. The conductive adhesive is particularly suitable for advanced packaging applications such as back-silver chips which are sensitive to voids, and can significantly improve the long-term reliability of chip packaging.

Description

Technical Field

[0001] This invention relates to the field of semiconductor packaging materials technology. Specifically, it relates to an acrylic conductive adhesive for chip bonding, its preparation method, and its application. This acrylic conductive adhesive for chip bonding achieves ultra-low volatility during the curing process by using non-volatile acrylate monomers containing imide structures and low-viscosity polybutadiene acrylic resin, fundamentally eliminating voids in the adhesive layer. It also possesses excellent conductivity, high bonding strength, and good process adaptability, making it particularly suitable for advanced packaging applications sensitive to voids, such as back-silvered chips, and can significantly improve the long-term reliability of chip packaging. Background Technology

[0002] Chip adhesives are key materials in semiconductor packaging, primarily functioning to fix chips to substrates and provide electrical, thermal, and mechanical support. Currently, chip adhesives are mainly divided into two categories: epoxy and acrylic. Acrylic conductive adhesives exhibit superior resistance to moisture and heat compared to epoxy adhesives, and possess advantages such as fast curing speed and stable electrical properties. However, acrylic adhesives face a long-standing technical challenge in practical applications: due to the excessively rapid free radical curing speed and the high volatility of commonly used acrylate monomer diluents, voids frequently form in the adhesive layer during thermal curing. Even using high-boiling-point acrylate monomers as diluents does not fundamentally solve this problem—high-boiling-point monomers still volatilize to varying degrees during thermal curing, leading to the formation of microvoids within the adhesive layer.

[0003] This problem is particularly pronounced in back-silver chip bonding applications. Microscopic unevenness on the surface of the back-silver chip and voids in the adhesive layer further exacerbate localized stress concentration, severely impacting the long-term reliability of the chip package. The presence of voids not only reduces bond strength but can also disrupt conductive paths, increasing contact resistance and ultimately leading to device failure. Traditional acrylic conductive adhesives typically exhibit a curing weight loss rate exceeding 5%, with severe cases reaching 7%–15%, resulting in void areas accounting for as much as 5%–15%.

[0004] To address the aforementioned issues, the industry has primarily adopted the following improvement measures: first, optimizing the curing process curve and employing a stepped heating method; second, increasing the adhesive layer thickness to buffer the impact of voids; and third, adding nanofillers to fill the gaps. However, these methods are all passive remedial measures and fail to solve the volatilization problem at the source of material design.

[0005] Therefore, developing a conductive adhesive that fundamentally avoids the release of volatile raw materials during the thermosetting process and achieves ultra-low weight loss (≤0.3%) during curing is of great significance for improving the reliability of chip packaging.

[0006] The information disclosed in this background section is only for enhancing the understanding of the background technology of the present invention, and therefore may include information that does not constitute prior art. Summary of the Invention

[0007] To overcome the technical problems of reduced bonding strength, increased resistance, and poor durability caused by voids in the adhesive layer of existing acrylic conductive adhesives for chip bonding, this invention provides a low-volatile acrylic conductive adhesive for chip bonding, comprising polybutadiene or its derivatives with acrylate end groups, acrylate monomers containing imide structures, multifunctional acrylate crosslinking monomers, and conductive fillers. By using non-volatile acrylate monomers with imide structures to replace traditional volatile diluents, and combining them with low-viscosity polybutadiene or its derivatives with acrylate end groups, the weight loss rate of the conductive adhesive during thermosetting is extremely small, fundamentally eliminating voids in the adhesive layer, while simultaneously achieving excellent conductivity and high bonding strength. This conductive adhesive is particularly suitable for advanced packaging applications sensitive to voids, such as back-silver chips, and can significantly improve the long-term reliability of chip packaging.

[0008] Preferably, the conductive filler has a mass percentage content of 60% to 75% in the conductive adhesive.

[0009] Preferably, the polybutadiene or its derivative with acrylate end groups has a polybutadiene main chain, which imparts good flexibility and low shrinkage to the adhesive layer. At the same time, its low viscosity is beneficial to increasing the filler loading, including but not limited to BAC-45, Nisso-PB series TE-2000, CN301, CN9014NS and CN307, etc. More preferably, the viscosity of the polybutadiene or its derivative with acrylate end groups is 2000 to 10000 mPa·s (25°C), and most preferably 4000 to 8000 mPa·s (25°C).

[0010] Preferably, the acrylate monomer containing an imide structure is an acrylate monomer containing an imide ring, including but not limited to 2-(1,2-cyclohexanedicarboxyimide)ethyl acrylate or its derivatives; more preferably, one or a combination of 2-(1,2-cyclohexanedicarboxyimide)ethyl acrylate and 2-(1,2-cyclohexanedicarboxyimide)ethyl methacrylate; this type of monomer contains an alicyclic imide structure, has an extremely high boiling point (>300℃) and an extremely low vapor pressure, and is almost non-volatile under curing conditions of 80-120℃; at the same time, the imide structure has good affinity for metal substrates (especially silver and copper surfaces), which can significantly improve the bonding strength.

[0011] Preferably, the multifunctional acrylate crosslinking monomer is one or more of tricyclodecanediethanol diacrylate (DCPDA) or its analogues, bisphenol A diacrylate ethoxylate, and bisphenol A diacrylate propionate; more preferably, tricyclodecanediethanol diacrylate (DCPDA) or its analogues, specifically tricyclodecanediethanol diacrylate or tricyclodecanediethanol dimethacrylate, wherein the tricyclodecanediethanol diacrylate (DCPDA) or its analogues have a rigid tricyclodecane backbone and bifunctionality, for moderate crosslinking, improving the heat resistance and dimensional stability of the adhesive layer, while maintaining moderate flexibility.

[0012] Preferably, the thermal initiator is one or more of tert-amyl peroxide-2-ethylhexyl carbonate, tert-butyl peroxide, dicumyl peroxide, and tert-butyl peroxide-2-ethylhexyl carbonate; more preferably, it is tert-amyl peroxide-2-ethylhexyl carbonate (P16), which has a suitable decomposition half-life (decomposition rate > 90% in 1 hour) in the range of 80 to 120°C, and can achieve mild and controllable free radical polymerization, avoiding internal stress and voids caused by excessively rapid curing.

[0013] Preferably, the polymerization inhibitor is one or more of 2,5-dichloro-1,4-benzoquinone, 1,4-naphthoquinone, and p-tert-butylcatechol; more preferably, it is 2,5-dichloro-1,4-benzoquinone, used to improve storage stability and prevent premature gelation at room temperature.

[0014] Preferably, the antioxidant is one or more of 2,6-di-tert-butyl-4-methylphenol, dithioethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1035), or hindered phenolic antioxidants; used to inhibit oxidative degradation at high temperatures and improve the thermal aging stability of the adhesive layer.

[0015] Preferably, the silane coupling agent is γ-methacryloyloxypropyltrimethoxysilane (KH570), such as Dow Corning Z-6030, Shin-Etsu KBM-503, etc. Vinyltrimethoxysilane or vinyltriethoxysilane, etc., can also be selected as alternatives as needed to improve the interfacial bonding between the resin and conductive filler, chip and substrate. At the same time, the alkenyl groups contained therein can participate in free radical polymerization to form chemical bonds.

[0016] Preferably, the thixotropic agent is fumed silica (such as TS720, Aerosil R974, etc.) used to adjust thixotropy and prevent the sedimentation of conductive fillers.

[0017] Preferably, the conductive filler is silver powder, more preferably flake silver powder with an average particle size of 1-10 μm; alternative materials such as silver-plated copper powder or silver-plated nickel powder may also be selected as needed to balance conductivity and cost.

[0018] Preferably, the viscosity of component A after mixing is controlled at 800–1500 mPa·s (25°C). By adjusting the amount of acrylate monomer containing the imide structure, the viscosity of component A can be precisely controlled: increasing the amount of this monomer decreases the viscosity of component A, which is beneficial for filling more conductive filler; decreasing the amount of this monomer increases the viscosity of component A, and the amount of conductive filler filled is correspondingly reduced.

[0019] Another aspect of the present invention provides a method for preparing the above-mentioned conductive adhesive, comprising the following steps: (1) Polybutadiene or its derivatives with acrylate end groups, acrylate monomers with imide structures, and multifunctional acrylate crosslinking monomers are mixed evenly at 20-35°C to obtain a resin mixture. (2) Add antioxidant, silane coupling agent, polymerization inhibitor and thixotropic agent to the resin mixture in sequence, stir and disperse for 30 to 60 minutes to obtain a premix; (3) Add a thermal initiator to the premix under light-protected conditions, stir evenly and test the viscosity. Adjust the viscosity of component A to 800-1500 mPa·s by adding acrylate monomers containing imide structure to obtain component A base material. (4) The conductive filler is added to the A component base material in batches at a final content of 60% to 75 wt%, and the mixture is stirred and degassed under vacuum to obtain the conductive adhesive.

[0020] Another aspect of the present invention provides an application of the above-mentioned conductive adhesive for chip bonding, wherein the chip includes a back-silver chip; the conductive adhesive for chip bonding is cured by constant temperature curing at 80-120℃ for 30-60 minutes, for example: 80℃ / 60min, 100℃ / 40min, and 120℃ / 30min can all achieve good curing effect without the need for stepped temperature increase. This curing process is simple and adaptable to the needs of different production lines. During the curing process, due to the use of non-volatile monomers, the system weight loss rate is ≤0.3%, and the cured adhesive layer is dense and uniform, which can completely eliminate voids in the adhesive layer.

[0021] Compared with the prior art, the beneficial effects of the present invention may include: 1. Ultra-low volatility and no voids: It uses acrylate monomers with imide structure as the main diluent monomers, combined with low viscosity polybutadiene or its derivatives with acrylate end groups, so that the curing weight loss rate is ≤0.3% (comparative example >10%), eliminating voids in the adhesive layer from the source. The void area ratio is 0%, which is particularly suitable for void-sensitive packaging applications such as back-silver chips.

[0022] 2. Excellent electrical conductivity: By controlling the viscosity of component A within the range of 800–1500 mPa·s, high filling density (60%–75%) of the conductive filler can be achieved, with a volume resistivity reaching [missing value]. The scale is sufficient to meet the conductivity requirements of high-power chips.

[0023] 3. Good process adaptability: Component A has a moderate viscosity, which is suitable for processes such as dispensing and printing; the curing temperature range is wide (80~120℃), which can match the temperature resistance requirements of different chips and substrates.

[0024] Excellent overall mechanical properties: The imide structure gives the adhesive layer good heat resistance and adhesion, the polybutadiene segments with acrylate end groups or their derivatives provide flexibility, the crosslinking monomers ensure dimensional stability, and the bonding strength can reach more than 20MPa.

[0025] The effects of this invention are not limited to those mentioned herein, and those skilled in the art will clearly understand other effects from the description of the claims. Detailed Implementation

[0026] Embodiments of the invention will be described in more detail below. However, the invention may be embodied in various different forms and should not be construed as being limited to the embodiments described herein. Rather, these embodiments are provided as examples so that the invention will be thorough and complete, and will fully convey aspects and features of the invention to those skilled in the art. Therefore, unnecessary processes, steps, and techniques that would allow those skilled in the art to fully understand aspects and features of the invention are not described. The terms or words used in this specification and claims should not be construed as limited to their ordinary or dictionary meaning, but should be interpreted as meaning and concept consistent with the technical concept of the invention, based on the principle that the inventors can appropriately define the concepts of the terms to best describe the invention.

[0027] It is understood that the present invention can be modified in many alternative forms. It should be understood that the present invention is not limited to the specific forms disclosed, but is intended to cover all modifications, equivalents, and alternatives falling within the scope of the present invention.

[0028] Embodiments of the invention are described in more detail below. However, these embodiments are merely examples, and the invention is not limited thereto; rather, it is defined by the scope of the claims. The terminology used herein is for descriptive purposes only and is not intended to limit the invention.

[0029] As used herein, the terms “substantially,” “about,” and similar terms are used as approximate terms rather than as terms of degree, and are intended to take into account the inherent biases of measurements or calculations that would be recognized by one of ordinary skill in the art.

[0030] Furthermore, any numerical range described herein is intended to include all subranges containing the same numerical precision within the described range. For example, the range "1.0 to 10.0" is intended to include all subranges between the described minimum value of 1.0 and the described maximum value of 10.0 (and includes both the described minimum value of 1.0 and the described maximum value of 10.0), i.e., having a minimum value equal to or greater than 1.0 and a maximum value equal to or less than 10.0, such as 2.4 to 7.6. Any maximum numerical limit described herein is intended to include all lower numerical limits contained therein, while any minimum numerical limit described in this specification is intended to include all higher numerical limits contained therein. Therefore, the applicant reserves the right to amend this specification (including the claims) to expressly describe any subranges contained within the scope expressly described herein.

[0031] The following section will describe in detail the acrylic conductive adhesive for chip bonding of the present invention, its preparation method, and its application.

[0032] A low-volatile acrylic conductive adhesive for chip bonding includes component A and component B, wherein component A comprises the following raw materials in parts by weight: 100 parts of polybutadiene or its derivatives with acrylate end groups 30-60 parts of acrylate monomers containing imide structure 5-15 parts of multifunctional acrylate crosslinking monomer 1-3 parts of thermal initiator Polymerization inhibitor 0.05–0.2 parts Antioxidant 0.1 to 0.5 parts 0.5 to 2 parts of silane coupling agent Thixotropic agent 1-4 parts; Component B is a conductive filler, and the amount of conductive filler added makes the mass percentage of conductive filler in the conductive adhesive 60% to 75%. The end group is polybutadiene or its derivative with acrylate, and its main chain is a polybutadiene structure, which gives the adhesive layer good flexibility and low shrinkage. At the same time, its low viscosity is conducive to increasing the filler loading, including but not limited to BAC-45, Nisso-PB series TE-2000, CN301, CN9014NS and CN307, etc. Further, the viscosity of the end group of polybutadiene or its derivative with acrylate is 2000 to 10000 mPa·s (25°C), preferably 4000 to 8000 mPa·s (25°C), preferably BAC-45, CN301 and CN307, and more preferably BAC-45.

[0033] In embodiments of the present invention, the acrylate monomer containing an imide structure is an acrylate monomer containing an imide ring, including but not limited to 2-(1,2-cyclohexanedicarboxyimide)ethyl acrylate or its derivatives, preferably one or a combination of 2-(1,2-cyclohexanedicarboxyimide)ethyl acrylate and 2-(1,2-cyclohexanedicarboxyimide)ethyl methacrylate; this type of monomer contains an alicyclic imide structure, has an extremely high boiling point (>300℃) and an extremely low vapor pressure, and is almost non-volatile under curing conditions of 80-120℃; at the same time, the imide structure has good affinity for metal substrates (especially silver and copper surfaces), which can significantly improve the bonding strength.

[0034] In embodiments of the present invention, the multifunctional acrylate crosslinking monomer is one or more of tricyclodecanediethanol diacrylate (DCPDA) or its analogues, bisphenol A diacrylate ethoxylate, and bisphenol A diacrylate propionate; preferably tricyclodecanediethanol diacrylate (DCPDA) or its analogues, specifically tricyclodecanediethanol diacrylate or tricyclodecanediethanol dimethacrylate, which has a rigid tricyclodecane backbone and bifunctionality for moderate crosslinking, improving the heat resistance and dimensional stability of the adhesive layer, while maintaining moderate flexibility.

[0035] In embodiments of the present invention, the thermal initiator is one or more of tert-amyl peroxide-2-ethylhexyl carbonate, tert-butyl peroxide, dicumyl peroxide, and tert-butyl peroxide-2-ethylhexyl carbonate; preferably tert-amyl peroxide-2-ethylhexyl carbonate (P16), which has a suitable decomposition half-life (decomposition rate > 90% in 1 hour) in the range of 80 to 120°C, and can achieve mild and controllable free radical polymerization, avoiding internal stress and voids caused by excessively rapid curing.

[0036] In embodiments of the present invention, the polymerization inhibitor is one or more of 2,5-dichloro-1,4-benzoquinone, 1,4-naphthoquinone, and p-tert-butylcatechol; preferably 2,5-dichloro-1,4-benzoquinone, used to improve storage stability and prevent premature gelation at room temperature.

[0037] In embodiments of the present invention, the antioxidant is one or more of 2,6-di-tert-butyl-4-methylphenol, dithioethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1035), or hindered phenolic antioxidants; used to inhibit oxidative degradation at high temperatures and improve the thermal aging stability of the adhesive layer.

[0038] In embodiments of the present invention, the silane coupling agent is γ-methacryloyloxypropyltrimethoxysilane (KH570), such as Dow Corning Z-6030, Shin-Etsu KBM-503, etc. Vinyltrimethoxysilane or vinyltriethoxysilane, etc., can also be selected as alternatives as needed to improve the interfacial bonding between the resin and conductive filler, chip and substrate. At the same time, the alkenyl groups contained therein can participate in free radical polymerization to form chemical bonds.

[0039] In embodiments of the present invention, the thixotropic agent is fumed silica (such as TS720, Aerosil R974, etc.), used to adjust thixotropy and prevent the sedimentation of conductive fillers.

[0040] In embodiments of the present invention, the conductive filler is silver powder, preferably flake silver powder with an average particle size of 1 to 10 μm; alternative materials such as silver-plated copper powder or silver-plated nickel powder may also be selected as needed to balance conductivity and cost.

[0041] In this invention, the viscosity of component A after mixing is controlled at 800–1500 mPa·s (25°C). By adjusting the amount of acrylate monomer containing an imide structure, the viscosity of component A can be precisely controlled: increasing the amount of this monomer decreases the viscosity of component A, which is beneficial for filling more conductive filler; decreasing the amount of this monomer increases the viscosity of component A, and the amount of conductive filler filled is correspondingly reduced.

[0042] Another aspect of the present invention provides a method for preparing the above-mentioned conductive adhesive, comprising the following steps: (1) Polybutadiene or its derivatives with acrylate end groups, acrylate monomers with imide structures, and multifunctional acrylate crosslinking monomers are mixed evenly at 20-35°C to obtain a resin mixture; (2) Antioxidant, silane coupling agent, polymerization inhibitor and thixotropic agent are added to the resin mixture in sequence, and stirred and dispersed for 30-60 minutes to obtain a premix; (3) Thermal initiator is added to the premix under light-protected conditions, and the viscosity is measured after stirring evenly. The viscosity of component A is adjusted to 800-1500 mPa·s by adding acrylate monomers with imide structures to obtain component A base material; (4) Conductive filler is added to component A base material in batches at a final content of 60%-75wt%, and stirred and degassed under vacuum conditions to obtain the conductive adhesive.

[0043] Another aspect of the present invention provides an application of the above-mentioned conductive adhesive for chip bonding, wherein the chip includes a back-silver chip; the conductive adhesive for chip bonding is cured by constant temperature curing at 80-120℃ for 30-60 minutes, for example: 80℃ / 60min, 100℃ / 40min, and 120℃ / 30min can all achieve good curing effect without the need for stepped temperature increase. This curing process is simple and adaptable to the needs of different production lines. During the curing process, due to the use of non-volatile monomers, the system weight loss rate is ≤0.3%, and the cured adhesive layer is dense and uniform, which can completely eliminate voids in the adhesive layer.

[0044] To better understand the technical content of this invention, the following embodiments are provided for detailed explanation. Unless otherwise specified, the experimental methods in the following embodiments are conventional methods. Unless otherwise specified, the raw materials involved in the following embodiments are all commercially available products, which can be obtained through market purchase or prepared using existing methods. Information on some of the raw materials used in the embodiments of this invention is as follows: Polybutadiene with acrylate end groups: Acrylic polybutadiene resin, viscosity 4000~8000mPa·s (25℃), Osaka Organic Chemicals, brand name BAC-45; 2-(1,2-cyclohexanedicarboxyimide)ethyl acrylate: Industrial grade, Sartoma Chemicals; Tricyclodecanediethanol diacrylate: Industrial grade, Sartoma Chemicals, brand name SR833S; P16 initiator: 2-ethylhexyl carbonate tert-amyl peroxide, AkzoNobel; 2,5-Dichloro-1,4-benzoquinone: Analytical grade, Sinopharm Group; BHT: 2,6-di-tert-butyl-4-methylphenol, industrial grade, BASF; or antioxidant 1035; KH570: γ-methacryloyloxypropyltrimethoxysilane, industrial grade, Nanjing Liangui Chemical; or Dow Corning Z-6030; TS720: Fumed silica, Cabot Corporation; EA0295 silver powder: flakes, average particle size 2-5μm, produced by Guizhou Platinum Industry. Examples 1-4

[0045] Conductive adhesives were prepared according to the proportions (parts by weight) of Group A shown in Table 1, with the final silver powder content in the conductive adhesives set to 75%, 70%, 65%, and 60%, respectively. The preparation process is as follows: (1) Add acrylic polybutadiene resin, 2-(1,2-cyclohexanedicarboxyimide) ethyl acrylate and tricyclodecanediethanol diacrylate to a reaction vessel and stir and mix at 30°C for 30 minutes to obtain a resin mixture. (2) Add BHT, KH570, 2,5-dichloro-1,4-benzoquinone and TS720 to the resin mixture in sequence, and continue stirring for 45 minutes to obtain the premix; (3) Add P16 initiator under light-protected conditions, stir for 15 minutes, take a sample to test the viscosity, and adjust the viscosity of component A to the target range (800-1500 mPa·s) by adding 2-(1,2-cyclohexanedicarboxyimide)ethyl acrylate to obtain component A base material; (4) Add EA0295 silver powder to the A component base material in three portions according to the final silver content in the conductive adhesive shown in Table 1. Stir and degas for 20 minutes using a planetary vacuum mixer under a vacuum of -0.095MPa to obtain the finished conductive adhesive. The viscosity of the A component was tested using a Brookfield DV3T viscometer at 25°C with a CP51 rotor and a rotation speed of 5 rpm.

[0046] Table 1. Distribution ratios and performance of Group A in Examples 1-4 Comparative Example 1 Comparative Example 1 used a traditional acrylic conductive adhesive formulation, specifically composed of: 100 parts of acrylic polyurethane oligomer (CN8887), 40 parts of hydroxyethyl acrylate (boiling point ~202℃), 10 parts of trimethylolpropane triacrylate, 2 parts of BPO initiator, 1 part of KH570, 2 parts of TS720, and silver powder added to a final silver content of 65%. The preparation method was the same as in Examples 1-4.

[0047] Performance testing The conductive adhesives prepared in Examples 1-4 and Comparative Example 1 were subjected to the following performance tests, and the test results are listed in Table 2.

[0048] 1. Curing weight loss rate: Take about 2g of conductive adhesive sample, weigh it accurately (W1), cure it according to the curing program (100℃ / 60min), weigh it again after curing (W2), and calculate the weight loss rate = (W1-W2) / W1×100%.

[0049] 2. Volume resistivity: Conductive adhesive is coated onto a glass plate to prepare a film strip with dimensions of 100mm×10mm×0.1mm. After curing, the resistance is tested using the four-probe method, and the volume resistivity is calculated.

[0050] 3. Void rate observation: Apply conductive adhesive to the center of the back silver chip (5mm×5mm), mount it on the BT substrate, and after curing, use an ultrasonic scanning microscope to observe the voids in the adhesive layer and calculate the void area ratio.

[0051] 4. Bonding strength: A 2mm×2mm silicon chip is mounted on a silver-plated copper frame. After curing, a shear test is performed using a Dage series shear force tester. The maximum shear force is recorded, and the bonding strength (MPa) is calculated.

[0052] Table 2. Performance Test Results As shown in Table 2, the weight loss rates of Examples 1-4 were all ≤0.3% (0.08%-0.18%), while the weight loss rate of Comparative Example 1 was as high as 10.6%. This indicates that hydroxyethyl acrylate in the traditional acrylic system volatilizes significantly during the thermosetting process, while the non-volatile imide-containing monomer system used in this invention effectively suppresses volatilization during thermosetting, achieving the goal of ultra-low weight loss. As the silver powder content increased from 60% to 75%, the volume resistivity decreased from... Reduce to The two parameters show a clear negative correlation, consistent with the conductivity percolation law. Example 1 (75% silver content) achieved a volume resistivity of [missing value]. It is superior to Comparative Example 1. This indicates that while achieving the advantage of ultra-low volatility, the conductivity was not compromised, but rather improved. The void area ratio of Examples 1-4 was 0%, while that of Comparative Example 1 was as high as 16.5%. Ultrasonic scanning microscopy showed that the adhesive layer of the Example samples was dense and uniform, without any void defects; while the Comparative Example 1 sample contained a large number of microvoids. This shows that the ultra-low volatility formulation design of the present invention has a significant effect on eliminating voids in the adhesive layer. The bond strength of Examples 1-4 was 19.3-21.2 MPa, all of which were better than the 15.8 MPa of Comparative Example 1, indicating that the good affinity of the imide monomer to the metal substrate and the complete adhesive layer structure resulting from the absence of void defects jointly improved the bond reliability.

[0053] The above-described technical features of the present invention and the technical features specifically described below (such as in the embodiments) can be combined with each other to form new or preferred technical solutions.

[0054] Finally, it should be emphasized that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-volatile acrylic conductive adhesive for chip bonding, characterized in that, It includes polybutadiene or its derivatives with acrylate end groups, acrylate monomers containing imide structures, multifunctional acrylate crosslinking monomers, and conductive fillers.

2. The low-volatile acrylic conductive adhesive for chip bonding according to claim 1, characterized in that, It also includes one or a combination of thermal initiators, polymerization inhibitors, antioxidants, silane coupling agents, and thixotropic agents.

3. The low-volatile acrylic conductive adhesive for chip bonding according to claim 1, characterized in that, The acrylate monomer containing the imide structure is an acrylate monomer containing an imide ring.

4. The low-volatile acrylic conductive adhesive for chip bonding according to claim 1, characterized in that, The multifunctional acrylate crosslinking monomer is one or more of tricyclodecanediethanol diacrylate, tricyclodecanediethanol dimethacrylate, bisphenol A diacrylate ethoxylate, and bisphenol A diacrylate propionoxylate.

5. The low-volatile acrylic conductive adhesive for chip bonding according to claim 2, characterized in that, The thermal initiator is one or more of tert-amyl peroxide-2-ethylhexyl carbonate, tert-butyl peroxide, dicumyl peroxide, and tert-butyl peroxide-2-ethylhexyl carbonate; and / or, the polymerization inhibitor is one or more of 2,5-dichloro-1,4-benzoquinone, 1,4-naphthoquinone, and p-tert-butylcatechol.

6. The low-volatile acrylic conductive adhesive for chip bonding according to claim 2, characterized in that, The antioxidant is one or more of 2,6-di-tert-butyl-4-methylphenol, dithioethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1035), or hindered phenolic antioxidants; and / or, the silane coupling agent is one or more of γ-methacryloyloxypropyltrimethoxysilane, γ-methacryloyloxypropyltriethoxysilane, vinyltrimethoxysilane, or vinyltriethoxysilane; and / or, the thixotropic agent is fumed silica.

7. The low-volatile acrylic conductive adhesive for chip bonding according to claim 1, characterized in that, The conductive filler is one or more of silver powder, silver-plated copper powder, or silver-plated nickel powder.

8. A method for preparing a low-volatile acrylic conductive adhesive for chip bonding according to any one of claims 1 to 7, characterized in that, Includes the following steps: (1) Polybutadiene or its derivatives with acrylate end groups, acrylate monomers with imide structures, and multifunctional acrylate crosslinking monomers are mixed evenly at 20-35°C to obtain a resin mixture. (2) Add antioxidant, silane coupling agent, polymerization inhibitor and thixotropic agent to the resin mixture in sequence, stir and disperse for 30 to 60 minutes to obtain a premix; (3) Add a thermal initiator to the premix under light-protected conditions, stir evenly, and then test the viscosity to obtain component A base material; (4) The conductive filler is added to the A component base material in batches at a final content of 60% to 75 wt%, and the mixture is stirred and degassed under vacuum to obtain the conductive adhesive.

9. An application of a low-volatile acrylic conductive adhesive for chip bonding according to any one of claims 1 to 7, characterized in that, The conductive adhesive is used for chip bonding.

10. The application of the low-volatile acrylic conductive adhesive for chip bonding according to claim 9, characterized in that, The chip includes a back-silver chip.

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