Low modulus epoxy underfill adhesive, method of making and use thereof

Abstract

This invention discloses a low-modulus epoxy-based underfill adhesive, its preparation method, and its application, belonging to the field of electronic packaging materials technology. The low-modulus epoxy-based underfill adhesive comprises the following raw materials in parts by weight: 20-50 parts epoxy resin, 5-30 parts epoxy diluent, 30-50 parts curing agent, 0.1-2 parts curing accelerator, 5-15 parts toughening agent, 2-5 parts inorganic filler, 0.1-1 parts silane coupling agent, and 0.1-1 parts pigment. By introducing a toughening agent and controlling the content of low-content inorganic filler, this invention effectively reduces the storage modulus of the underfill adhesive without significantly increasing viscosity. This reduces thermal stress caused by the difference in thermal expansion coefficients between the chip and the substrate during thermal cycling, while maintaining a high glass transition temperature and good flowability. This underfill adhesive is particularly suitable for high-density, narrow-gap flip-chip packaging.

Description

Technical Field

[0001] This invention relates to the field of electronic packaging materials technology, specifically a low-modulus epoxy-based underfill adhesive, its preparation method, and its application. Background Technology

[0002] In flip-chip architectures, solder joints serve as the bridge connecting the chip and the substrate. However, the difference in thermal expansion coefficients between the chip and the substrate causes the solder joints to be subjected to repeated stress and tension during temperature changes, which can easily lead to fatigue cracks over time. Underfill adhesive fills the gaps between the chip, solder joints, and substrate, and after curing, it bonds the three together as a whole, dispersing thermal stress from the localized solder joints to a larger area.

[0003] As electronic components continue to evolve towards miniaturization and high density, the gap between flip chips and substrates is decreasing, while the distribution of solder joints is becoming increasingly dense. This trend places higher demands on the flow properties of underfill adhesives. In the dispensing process, the underfill adhesive needs to be able to quickly penetrate the narrow gap between the chip and substrate, spread evenly, and completely fill the entire space, while avoiding the formation of air bubbles or voids, thereby ensuring the overall reliability of the device. Generally, a viscosity between 100-1000 mPa·s is required. Within this range, the adhesive can quickly fill the gap between the chip and substrate through capillary action, while avoiding incomplete filling or voids due to excessively high viscosity, or overflow due to excessively low viscosity. In addition to flowability, the glass transition temperature (Tg) of the underfill adhesive should be significantly higher than the maximum operating temperature, maintaining rigidity even when the device is generating heat normally, effectively dispersing thermal stress, and extending the fatigue life of the solder joints.

[0004] Existing patent CN117801745A discloses an underfill adhesive with a low coefficient of thermal expansion, comprising the following components: 24%-33% epoxy resin, 58%-69% silica, 8%-19% curing agent, 0.1%-0.3% coloring agent, and 0.2%-0.4% adhesion promoter. Existing patent CN116063968A discloses an underfill adhesive for chip encapsulation, comprising 10wt%-25wt% silicone hybrid epoxy resin, 10wt%-25wt% curing agent, 50wt%-70wt% inorganic filler, 0.1wt%-2wt% curing accelerator, and 0.1wt%-2wt% coupling agent.

[0005] As mentioned above, existing technologies primarily reduce the coefficient of thermal expansion of the underfill adhesive by adding a large amount of filler (such as silica), thereby reducing thermal stress between the chip, solder joint, and substrate. However, adding a large amount of filler to the underfill adhesive can, on the one hand, increase its viscosity, severely affecting its flowability and the filling effect after curing; on the other hand, it can excessively increase the modulus of the underfill adhesive, increasing the thermal stress between the adhesive and the solder joint. Summary of the Invention

[0006] The purpose of this invention is to provide a low-modulus epoxy-based underfill adhesive, its preparation method, and its application, in order to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A low-modulus epoxy-based underfill adhesive comprises the following raw materials in parts by weight: 20-50 parts epoxy resin, 5-30 parts epoxy diluent, 30-50 parts curing agent, 0.1-2 parts curing accelerator, 5-15 parts toughening agent, 2-5 parts inorganic filler, 0.1-1 part silane coupling agent, and 0.1-1 part pigment.

[0009] Furthermore, the epoxy resin is one or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin, naphthalene type epoxy resin, 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexylcarboxylate and bis(7-oxabicyclo[4.1.0]3-heptylmethyl)adipate.

[0010] Furthermore, the epoxy diluent is one or more of 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, and polypropylene glycol diglycidyl ether.

[0011] Furthermore, the curing agent is one or more of tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, and methyltetrahydrophthalic anhydride.

[0012] Furthermore, the curing accelerator is one or more of 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole and 1-cyano-2-ethyl-4-methylimidazole.

[0013] Furthermore, the toughening agent is one or more of the following: polyurethane modified epoxy resin, carboxyl-terminated liquid nitrile rubber, hydroxyl-terminated polybutadiene rubber, and epoxy-terminated polybutadiene rubber.

[0014] Furthermore, the inorganic filler is spherical silica powder with a D50 particle size of 0.1-10 μm.

[0015] Furthermore, the silane coupling agent is one or more selected from 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-methacryloyloxypropyltrimethoxysilane.

[0016] Another object of the present invention is to provide a method for preparing the above-mentioned low-modulus epoxy-based underfill adhesive, specifically including the following steps:

[0017] Epoxy resin, epoxy diluent, toughening agent, and silane coupling agent are mixed, then vacuumed and heated to 60-80℃ while stirring to obtain mixture A;

[0018] The temperature of mixture A is lowered to 20-30℃, then a curing agent and a curing accelerator are added, vacuum is applied, and the mixture is stirred to obtain mixture B;

[0019] Inorganic fillers and pigments are added to mixture B, vacuum is applied, and the mixture is stirred. After depressurization, the bottom filler adhesive is obtained.

[0020] Another object of the present invention is to provide an application of the above-mentioned low-modulus epoxy-based underfill adhesive in flip chip packaging, wherein the flip chip includes a chip, solder joints and a substrate; the gap between the chip, solder joints and the substrate is filled with the low-modulus epoxy-based underfill adhesive.

[0021] This invention provides a low-modulus epoxy-based underfill adhesive. By introducing a toughening agent and controlling the content of inorganic fillers, the storage modulus of the underfill adhesive is effectively reduced without significantly increasing viscosity. This reduces thermal stress caused by the difference in thermal expansion coefficients between the chip and the substrate during thermal cycling, while maintaining a high glass transition temperature and good flowability. This underfill adhesive is particularly suitable for high-density, narrow-gap flip-chip packaging, enabling rapid gap filling, reducing voids and other abnormalities after curing, and improving the long-term reliability of the package. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] In one embodiment of the present invention, a low-modulus epoxy-based underfill adhesive is provided, the preparation method of which includes the following steps:

[0024] S1. According to the mass fraction, mix 20-50 parts of epoxy resin, 5-30 parts of epoxy diluent, 5-15 parts of toughening agent and 0.1-1 parts of silane coupling agent, then vacuum, heat to 60-80℃, and stir at a speed of 200-400 rpm to obtain mixture A.

[0025] S2. Reduce the temperature of the above mixture A to 20-30℃, then add 30-50 parts of curing agent and 0.1-2 parts of curing accelerator, vacuum the mixture, and stir at a speed of 400-600 rpm to obtain mixture B.

[0026] S3. Add 2-5 parts of inorganic filler and 0.1-1 parts of pigment to the above mixture B, evacuate the vacuum, stir at a speed of 500-700 rpm, and after depressurization, obtain the bottom filler adhesive.

[0027] The epoxy resin is one or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin, naphthalene type epoxy resin, 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexylcarboxylate, and bis(7-oxabicyclo[4.1.0]3-heptylmethyl)adipate. Combining different epoxy resins can balance the tensile strength and glass transition temperature (Tg) of the underfill adhesive.

[0028] The epoxy diluent is one or more of 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, and polypropylene glycol diglycidyl ether. Adding an epoxy diluent not only reduces the viscosity of the underfill adhesive and increases its flowability, but also reduces its modulus.

[0029] The curing agent is one or more of tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, and methyltetrahydrophthalic anhydride. Choosing different curing agents can meet the requirements of the adhesive application process for curing speed and temperature.

[0030] The curing accelerator is one or more of 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole and 1-cyano-2-ethyl-4-methylimidazole.

[0031] The toughening agent is one or more of the following: polyurethane-modified epoxy resin, carboxyl-terminated liquid nitrile rubber, hydroxyl-terminated polybutadiene rubber, and epoxy-terminated polybutadiene rubber. The toughening agent can significantly reduce the modulus of the underfill and reduce the thermal stress generated in the underfill during thermal cycling.

[0032] The inorganic filler is spherical silicon micropowder with a D50 particle size of 0.1-10 μm, preferably 0.38-8.69 μm. With the same inorganic filler content, spherical silicon micropowder exhibits better flowability; adding a small amount of spherical silicon micropowder can result in a lower coefficient of thermal expansion (CTE) for the chip-level underfill adhesive, thus ensuring the reliability of chip integration and packaging.

[0033] The silane coupling agent is one or more selected from 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-methacryloyloxypropyltrimethoxysilane. Silane coupling agents can improve the compatibility between inorganic fillers and adhesives, enhance the wettability of the underfill adhesive on the substrate, and thus increase bond strength.

[0034] Pigments can be selected, but are not limited to, carbon black. Carbon black can cover up discoloration phenomena such as yellowing that occur in the underfill adhesive during high-temperature cycling.

[0035] In another embodiment of the present invention, the application of the aforementioned low-modulus epoxy-based underfill adhesive in flip-chip packaging is also provided, wherein the flip-chip includes a chip, solder joints, and a substrate; the gap between the chip, solder joints, and substrate is filled with the aforementioned low-modulus epoxy-based underfill adhesive. Specifically, the underfill adhesive filling method for flip-chip packaging is as follows: the underfill adhesive is applied to the edge between the chip and the substrate by dispensing, the gap is filled by capillary action, and then it is cured by heating.

[0036] In this embodiment of the invention, the thermal stress δH is calculated using the following formula: δH = (Ar - Am) × (Tp - Tr) × Er; where Er is the modulus of the underfill adhesive, Am is the coefficient of thermal expansion of the component, Ar is the coefficient of thermal expansion of the underfill adhesive, Tp is the highest temperature of the underfill adhesive during operation, and Tr is room temperature. According to the above formula, traditional underfill adhesives can reduce thermal stress by lowering the coefficient of thermal expansion, but this increases the viscosity of the underfill adhesive, affecting the filling effect. Therefore, this embodiment of the invention reduces the thermal stress of the chip during operation by lowering the modulus of the underfill adhesive, while also maintaining its low viscosity to improve the fluidity of the underfill adhesive. This allows for rapid filling of gaps, reducing abnormal phenomena such as voids after curing, and thus not affecting the filling effect.

[0037] The following embodiments are examples of the present invention in practical applications, and are only illustrative examples, not limited thereto. It should be noted that the raw materials used in the following embodiments are all commercially available products unless otherwise specified.

[0038] Example 1: This example provides a low-modulus epoxy-based underfill adhesive, the preparation method of which includes the following steps:

[0039] S1. Add 18g of bisphenol A type epoxy resin, 15g of bis(7-oxabicyclo[4.1.0]3-heptylmethyl) adipate, 10g of 1,4-butanediol diglycidyl ether, 10g of polyurethane modified epoxy resin NPER-133L (purchased from Nan Ya Plastics), and 0.5g of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane to a double planetary mixer and mix. Then, vacuum the mixture, heat it to 70°C, and stir it at 300 rpm for 30 minutes to obtain mixture A.

[0040] S2. The temperature of the above mixture A was lowered to 25°C, and then 42g of methyltetrahydrophthalic anhydride and 1.3g of 1-cyano-2-ethyl-4-methylimidazolium were added. The mixture was then vacuumed and stirred at 500 rpm for 40 minutes to obtain mixture B.

[0041] S3. Add 3g of spherical silica powder S31080XF (D50=8.69μm, D100=31μm; purchased from Lianrui New Materials) and 0.2g of carbon black MA100R (purchased from Mitsubishi) to the above mixture B, evacuate, stir at 600rpm for 60min, and after depressurization, obtain the bottom filler adhesive.

[0042] Example 2: This example provides a low-modulus epoxy-based underfill adhesive, the preparation method of which includes the following steps:

[0043] S1. Add 23g of bisphenol F type epoxy resin, 10g of 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexyl carboxylate, 10g of 1,4-butanediol diglycidyl ether, 10g of polyurethane modified epoxy resin NPER-133L (purchased from Nan Ya Plastics), and 0.5g of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane to a double planetary mixer and mix. Then, evacuate the mixture, heat it to 70°C, and stir it at 300 rpm for 30 minutes to obtain mixture A.

[0044] S2. The temperature of the above mixture A was lowered to 25°C, and then 42g of tetrahydrophthalic anhydride and 1.3g of 1-cyano-2-ethyl-4-methylimidazolium were added. The mixture was then vacuumed and stirred at 500 rpm for 40 min to obtain mixture B.

[0045] S3. Add 3g of spherical silica powder S31080XF (D50=8.69μm, D100=31μm; purchased from Lianrui New Materials) and 0.2g of carbon black MA100R (purchased from Mitsubishi) to the above mixture B, evacuate, stir at 600rpm for 60min, and after depressurization, obtain the bottom filler adhesive.

[0046] Example 3: This example provides a low-modulus epoxy-based underfill adhesive, the preparation method of which includes the following steps:

[0047] S1. 18g of bisphenol A type epoxy resin, 15g of bis(7-oxabicyclo[4.1.0]3-heptylmethyl) adipate, 10g of 1,4-butanediol diglycidyl ether, 10g of carboxyl-terminated liquid nitrile rubber HYPOX® RA 1340CI (purchased from Huntsman) and 0.5g of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane were added to a double planetary mixer and mixed. Then, the mixture was vacuumed, heated to 70°C, and stirred at 300 rpm for 30 min to obtain mixture A.

[0048] S2. The temperature of the above mixture A was lowered to 25°C, and then 42g of methyltetrahydrophthalic anhydride and 1.3g of 1-cyano-2-ethyl-4-methylimidazolium were added. The mixture was then vacuumed and stirred at 500 rpm for 40 minutes to obtain mixture B.

[0049] S3. Add 3g of spherical silica powder S31080XF (D50=8.69μm, D100=31μm; purchased from Lianrui New Materials) and 0.2g of carbon black MA100R (purchased from Mitsubishi) to the above mixture B, evacuate, stir at 600rpm for 60min, and after depressurization, obtain the bottom filler adhesive.

[0050] Example 4: This example provides a low-modulus epoxy-based underfill adhesive, the preparation method of which includes the following steps:

[0051] S1. Add 18g of bisphenol A type epoxy resin, 15g of bis(7-oxabicyclo[4.1.0]3-heptylmethyl) adipate, 10g of 1,4-butanediol diglycidyl ether, 10g of polyurethane modified epoxy resin NPER-133L (purchased from Nan Ya Plastics), and 0.5g of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane to a double planetary mixer and mix. Then, vacuum the mixture, heat it to 70°C, and stir it at 300 rpm for 30 minutes to obtain mixture A.

[0052] S2. The temperature of the above mixture A was lowered to 25°C, and then 42g of methyltetrahydrophthalic anhydride and 1.3g of 1-cyano-2-ethyl-4-methylimidazolium were added. The mixture was then vacuumed and stirred at 500 rpm for 40 minutes to obtain mixture B.

[0053] S3. Add 3g of spherical silica powder NQS002 (D50=0.38μm, D100=0.87μm; purchased from Lianrui New Materials) and 0.2g of carbon black MA100R (purchased from Mitsubishi) to the above mixture B, evacuate, stir at 600rpm for 60min, and after depressurization, obtain the bottom filler adhesive.

[0054] Example 5: This example provides a low-modulus epoxy-based underfill adhesive, the preparation method of which includes the following steps:

[0055] S1. Add 10g of bisphenol A type epoxy resin, 10g of naphthalene type epoxy resin, 2g of 1,6-hexanediol diglycidyl ether, 3g of polyethylene glycol diglycidyl ether, 5g of terminal epoxy-terminated polybutadiene rubber (CAS: 2915-90-4), and 0.1g of 3-aminopropyltriethoxysilane to a double planetary mixer and mix. Then, evacuate the mixture, heat it to 60°C, and stir it at 200 rpm for 30 minutes to obtain mixture A.

[0056] S2. The temperature of the above mixture A was lowered to 20°C, and then 30g of hexahydrophthalic anhydride and 0.1g of 2-methylimidazole were added. The mixture was then vacuumed and stirred at 400 rpm for 40 minutes to obtain mixture B.

[0057] S3. Add 2g of spherical silica powder S31080XF (D50=8.69μm, D100=31μm; purchased from Lianrui New Materials) and 0.1g of carbon black MA100R (purchased from Mitsubishi) to the above mixture B, evacuate, stir at 500rpm for 60min, and after depressurization, obtain the bottom filler adhesive.

[0058] Example 6: This example provides a low-modulus epoxy-based underfill adhesive, the preparation method of which includes the following steps:

[0059] S1. Add 30g of bisphenol A type epoxy resin, 10g of 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexylcarboxylate, 10g of bis(7-oxabicyclo[4.1.0]3-heptylmethyl) adipate, 15g of polyethylene glycol diglycidyl ether, 15g of polypropylene glycol diglycidyl ether, 10g of polyurethane modified epoxy resin NPER-133L (purchased from Nan Ya Plastics), 5g of hydroxyl-terminated polybutadiene rubber (CAS: 69102-90-5), 0.5g of γ-glycidyl etheroxypropyltrimethoxysilane, and 0.5g of γ-methacryloyloxypropyltrimethoxysilane to a double planetary mixer and mix. Then, vacuum the mixture, heat it to 80°C, and stir it at 500 rpm for 30 minutes to obtain mixture A.

[0060] S2. The temperature of the above mixture A is lowered to 30°C, and then 50g of methylhexahydrophthalic anhydride and 2g of 2-ethyl-4-methylimidazolium are added. Vacuum is drawn and the mixture is stirred at 600rpm for 40min to obtain mixture B.

[0061] S3. Add 5g of spherical silica powder S31080XF (D50=8.69μm, D100=31μm; purchased from Lianrui New Materials) and 1g of carbon black MA100R (purchased from Mitsubishi) to the above mixture B, vacuum, stir at 700rpm for 60min, and after depressurization, the bottom filler is obtained.

[0062] Comparative Example 1: This comparative example provides a low-modulus epoxy-based underfill adhesive, the preparation method of which includes the following steps:

[0063] S1. Add 18g of bisphenol A type epoxy resin, 15g of bis(7-oxabicyclo[4.1.0]3-heptylmethyl) adipate, 10g of 1,4-butanediol diglycidyl ether, 10g of polyurethane modified epoxy resin NPER-133L (purchased from Nan Ya Plastics), and 0.5g of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane to a double planetary mixer and mix. Then, vacuum the mixture, heat it to 70°C, and stir it at 300 rpm for 30 minutes to obtain mixture A.

[0064] S2. The temperature of the above mixture A was lowered to 25°C, and then 42g of methyltetrahydrophthalic anhydride and 1.3g of 1-cyano-2-ethyl-4-methylimidazolium were added. The mixture was then vacuumed and stirred at 500 rpm for 40 minutes to obtain mixture B.

[0065] S3. Add 65g of spherical silica powder S31080XF (D50=8.69μm, D100=31μm; purchased from Lianrui New Materials) and 0.2g of carbon black MA100R (purchased from Mitsubishi) to the above mixture B, vacuum, stir at 600rpm for 60min, and after depressurization, the bottom filler is obtained.

[0066] Comparative Example 2: This comparative example provides a low-modulus epoxy-based underfill adhesive, the preparation method of which includes the following steps:

[0067] S1. Add 18g of bisphenol A type epoxy resin, 15g of bis(7-oxabicyclo[4.1.0]3-heptylmethyl) adipate, 10g of 1,4-butanediol diglycidyl ether, 10g of polyurethane modified epoxy resin NPER-133L (purchased from Nan Ya Plastics), and 0.5g of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane to a double planetary mixer and mix. Then, vacuum the mixture, heat it to 70°C, and stir it at 300 rpm for 30 minutes to obtain mixture A.

[0068] S2. The temperature of the above mixture A was lowered to 25°C, and then 42g of methyltetrahydrophthalic anhydride and 1.3g of 1-cyano-2-ethyl-4-methylimidazolium were added. The mixture was then vacuumed and stirred at 500 rpm for 40 minutes to obtain mixture B.

[0069] S3. Add 10g of spherical silica powder S31080XF (D50=8.69μm, D100=31μm; purchased from Lianrui New Materials) and 0.2g of carbon black MA100R (purchased from Mitsubishi) to the above mixture B, vacuum, stir at 600rpm for 60min, and after depressurization, the bottom filler is obtained.

[0070] Comparative Example 3: This comparative example provides a low-modulus epoxy-based underfill adhesive, the preparation method of which includes the following steps:

[0071] S1. Add 18g of bisphenol A type epoxy resin, 15g of bis(7-oxabicyclo[4.1.0]3-heptylmethyl) adipate, 10g of 1,4-butanediol diglycidyl ether, 20g of polyurethane modified epoxy resin NPER-133L (purchased from Nan Ya Plastics), and 0.5g of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane to a double planetary mixer and mix. Then, vacuum the mixture, heat it to 70°C, and stir it at 300 rpm for 30 minutes to obtain mixture A.

[0072] S2. The temperature of the above mixture A was lowered to 25°C, and then 42g of methyltetrahydrophthalic anhydride and 1.3g of 1-cyano-2-ethyl-4-methylimidazolium were added. The mixture was then vacuumed and stirred at 500 rpm for 40 minutes to obtain mixture B.

[0073] S3. Add 3g of spherical silica powder S31080XF (D50=8.69μm, D100=31μm; purchased from Lianrui New Materials) and 0.2g of carbon black MA100R (purchased from Mitsubishi) to the above mixture B, evacuate, stir at 600rpm for 60min, and after depressurization, obtain the bottom filler adhesive.

[0074] Comparative Example 4: This comparative example provides a low-modulus epoxy-based underfill adhesive, the preparation method of which includes the following steps:

[0075] S1. Add 18g of bisphenol A type epoxy resin, 15g of bis(7-oxabicyclo[4.1.0]3-heptylmethyl) adipate, 10g of 1,4-butanediol diglycidyl ether, 40g of polyurethane modified epoxy resin NPER-133L (purchased from Nan Ya Plastics), and 0.5g of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane to a double planetary mixer and mix. Then, vacuum the mixture, heat it to 70°C, and stir it at 300 rpm for 30 minutes to obtain mixture A.

[0076] S2. The temperature of the above mixture A was lowered to 25°C, and then 42g of methyltetrahydrophthalic anhydride and 1.3g of 1-cyano-2-ethyl-4-methylimidazolium were added. The mixture was then vacuumed and stirred at 500 rpm for 40 minutes to obtain mixture B.

[0077] S3. Add 3g of spherical silica powder S31080XF (D50=8.69μm, D100=31μm; purchased from Lianrui New Materials) and 0.2g of carbon black MA100R (purchased from Mitsubishi) to the above mixture B, evacuate, stir at 600rpm for 60min, and after depressurization, obtain the bottom filler adhesive.

[0078] Performance Testing: 1. Viscosity test of the underfill adhesive: According to the ASTM D 2393 test standard, a Brookfield DV2T rotational viscometer was used at a temperature of 25°C and a 52# rotor at a rotation speed of 50 rpm to test the viscosity.

[0079] II. Storage modulus test of bottom filler: According to the ISO11359 test standard, thermomechanical analysis (DMA) test was conducted from 20-230℃, with a heating rate of 5℃ / min and a frequency of 1HZ. The test mode was single cantilever mode.

[0080] III. Glass transition temperature (Tg) test of the bottom filler: According to the ASTM D696 test standard, thermomechanical analysis (TMA) was used for the test, from -40℃ to 230℃, with a heating rate of 10℃ / min, and the test mode was compression mode.

[0081] IV. Coefficient of Thermal Expansion (CTE) Test of Underfill Adhesive: According to ASTM D696 test standard, thermomechanical analysis (TMA) test is used, from -40℃ to 230℃, with a heating rate of 10℃ / min. The CTE value range is 0-50℃, and the test mode is compression mode.

[0082] V. Shear strength test of bottom filler: The shear strength of the PCB / PCB substrate is tested using a universal testing machine according to the ASTM D1002 test standard.

[0083] VI. Moisture and heat resistance test of the underfill adhesive: The sheared specimens were placed at 85℃ and 85%RH for 1000h, dried at 80℃, and the shear strength was retested. The degree of shear strength retention indicates the moisture and heat resistance of the underfill adhesive.

[0084] The test results are shown in Table 1:

[0085] Table 1 Performance comparison results of each embodiment and comparative example

[0086]

[0087] As can be seen from Table 1, by controlling the low amount of inorganic filler and introducing an appropriate amount of toughening agent, the underfill adhesive prepared in the embodiments of the present invention significantly reduces the room temperature viscosity and storage modulus while maintaining a high Tg, thereby taking into account both good flow filling ability and low thermal stress characteristics. At the same time, the shear strength and damp heat resistance of the underfill adhesive prepared in the embodiments of the present invention meet the requirements of encapsulation reliability, achieving a comprehensive performance balance of high Tg, low modulus and low viscosity.

[0088] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification.

Claims

1. A low-modulus epoxy-based underfill adhesive, characterized in that, It includes the following raw materials by weight: 20-50 parts epoxy resin, 5-30 parts epoxy diluent, 30-50 parts curing agent, 0.1-2 parts curing accelerator, 5-15 parts toughening agent, 2-5 parts inorganic filler, 0.1-1 part silane coupling agent, and 0.1-1 part pigment.

2. The low-modulus epoxy-based underfill adhesive according to claim 1, characterized in that, The epoxy resin is one or more of bisphenol A type epoxy resin, bisphenol F type epoxy resin, naphthalene type epoxy resin, 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexylcarboxylate and bis(7-oxabicyclo[4.1.0]3-heptylmethyl)adipate.

3. The low-modulus epoxy-based underfill adhesive according to claim 1, characterized in that, The epoxy diluent is one or more of 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, and polypropylene glycol diglycidyl ether.

4. The low-modulus epoxy-based underfill adhesive according to claim 1, characterized in that, The curing agent is one or more of tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, and methyltetrahydrophthalic anhydride.

5. The low-modulus epoxy-based underfill adhesive according to claim 1, characterized in that, The curing accelerator is one or more of 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole and 1-cyano-2-ethyl-4-methylimidazole.

6. The low-modulus epoxy-based underfill adhesive according to claim 1, characterized in that, The toughening agent is one or more of the following: polyurethane modified epoxy resin, carboxyl-terminated liquid nitrile rubber, hydroxyl-terminated polybutadiene rubber, and epoxy-terminated polybutadiene rubber.

7. The low-modulus epoxy-based underfill adhesive according to claim 1, characterized in that, The inorganic filler is spherical silica powder with a D50 particle size of 0.1-10 μm.

8. The low-modulus epoxy-based underfill adhesive according to claim 1, characterized in that, The silane coupling agent is one or more of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-methacryloyloxypropyltrimethoxysilane.

9. A method for preparing a low-modulus epoxy-based underfill adhesive as described in any one of claims 1-8, characterized in that, Includes the following steps: Epoxy resin, epoxy diluent, toughening agent, and silane coupling agent are mixed, then vacuumed and heated to 60-80℃ while stirring to obtain mixture A; The temperature of mixture A is lowered to 20-30℃, then a curing agent and a curing accelerator are added, vacuum is applied, and the mixture is stirred to obtain mixture B; Inorganic fillers and pigments are added to mixture B, vacuum is applied, and the mixture is stirred. After depressurization, the bottom filler adhesive is obtained.

10. The application of a low-modulus epoxy-based underfill adhesive as described in any one of claims 1-8 in flip-chip packaging, characterized in that, The flip chip includes a chip, solder joints, and a substrate; the gaps between the chip, solder joints, and substrate are filled with the low-modulus epoxy-based underfill adhesive.

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