Underfill adhesive having low coefficient of thermal expansion and preparation method therefor, and chip packaging structure

Abstract

An underfill adhesive having a low coefficient of thermal expansion and a preparation method therefor, and a chip packaging structure. The underfill adhesive comprises the following components in percentages by mass: 24-33% of epoxy resin, 58-69% of silicon dioxide, 8-19% of a curing agent, 0.1-0.3% of a coloring agent, and 0.2-0.4% of an adhesion promoter, wherein the epoxy resin is formed by compounding a trifunctional epoxy resin, a polyether-modified epoxy resin, and a naphthalene-type epoxy resin. The three compounded resins, i.e., the trifunctional epoxy resin, the polyether-modified epoxy resin, and the naphthalene-type epoxy resin, are cured by the curing agent, to provide basic performance for the underfill adhesive; the silicon dioxide is used as a filler to enhance the performance of the underfill adhesive; the adhesion between the underfill adhesive and a substrate is improved by means of the adhesion promoter. Thus, the reliability and service life of chip packaging are improved.

Description

Bottom filling glue with low thermal expansion coefficient, preparation method thereof and chip packaging structure Technical Field

[0001] The present invention belongs to the technical field of bottom filling glue packaging, and in particular relates to a bottom filling glue with a low thermal expansion coefficient, a preparation method thereof and a chip packaging structure. Background Art

[0002] Bottom filler is a key material in electronic device packaging technology. It is mainly used to fill the narrow gap between the chip and the substrate, disperse the stress borne on the chip surface, and at the same time relieve the internal stress caused by the mismatch of thermal expansion coefficients between the chip, solder and substrate. It reduces the stress impact caused by the difference in thermal expansion coefficients between the chip and the substrate, improves the structural strength and reliability of electronic devices, and enhances the drop resistance between the chip and the substrate.

[0003] The effectiveness of underfill is related to the difference in thermal expansion coefficients between the chip and substrate. The lower the underfill's thermal expansion coefficient, the better its adhesion to the chip surface and the longer the chip's lifespan. Furthermore, chips often face various temperature and humidity conditions in actual use, which will also affect the chip's reliability and service life. Therefore, underfill must not only have a low thermal expansion coefficient but also high moisture and heat resistance.

[0004] It can be seen that how to provide a bottom filling glue with a low thermal expansion coefficient to have high moisture and heat resistance and good silicon adhesion to improve the reliability and life of chip packaging is a technical problem that technical personnel in this field urgently need to solve.

[0005] Summary of the Invention

[0006] The object of the present invention is to provide an underfill with a low thermal expansion coefficient, a preparation method thereof, and a chip packaging structure, so as to solve at least one of the above-mentioned technical problems.

[0007] To achieve the above objectives, the first aspect of the present invention provides a bottom filling glue with a low thermal expansion coefficient, which includes the following components by mass percentage: 24% to 33% epoxy resin, 58% to 69% silicon dioxide, 8% to 19% curing agent, 0.1% to 0.3% dye and 0.2% to 0.4% adhesion promoter; the epoxy resin is compounded by trifunctional epoxy resin, polyether-modified epoxy resin and naphthalene-type epoxy resin.

[0008] In the first aspect, the mass percentage of the trifunctional epoxy resin is 4%-20%, the mass percentage of the polyether-modified epoxy resin is 4%-20%, and the mass percentage of the naphthalene-type epoxy resin is 4%-20%.

[0009] In the first aspect, the curing agent is Ancamine 2264.

[0010] In the first aspect, the structural formula of the polyether-modified epoxy resin is:

[0011] In the first aspect, the trifunctional epoxy resin includes at least one of MF-3285 and TPNE5501.

[0012] In the first aspect, the naphthalene-based epoxy resin includes at least one of SE-165 and EBA-65.

[0013] In the first aspect, the colorant comprises carbon black.

[0014] A second aspect of the present invention provides a method for preparing the underfill with a low thermal expansion coefficient as described in the first aspect, the preparation method comprising:

[0015] S1: Stirring and mixing the components according to their respective mass percentages to obtain a first slurry, wherein the mass percentages of the components specifically include: 24% to 33% epoxy resin, 58% to 69% silicon dioxide, 8% to 19% curing agent, 0.1% to 0.3% coloring agent, and 0.2% to 0.4% adhesion promoter;

[0016] S2: transferring the first slurry to a three-roll mill for dispersion to obtain a uniformly dispersed second slurry;

[0017] S3: vacuum degassing the second slurry to obtain an underfill adhesive.

[0018] In the second aspect, the epoxy resin is compounded by a trifunctional epoxy resin, a polyether-modified epoxy resin and a naphthalene-type epoxy resin; the mass percentage of the trifunctional epoxy resin is 4%-20%, the mass percentage of the polyether-modified epoxy resin is 4%-20%, and the mass percentage of the naphthalene-type epoxy resin is 4%-20%.

[0019] The third aspect of the present invention provides a chip packaging structure, comprising a substrate, a chip arranged on the substrate, and a plurality of spaced solder bumps arranged between the substrate and the chip and electrically connected to the substrate and the chip, a gap being formed between the substrate and the chip, the bottom filling glue with a low thermal expansion coefficient described in the first aspect being arranged at the edge of the substrate so that the bottom filling glue flows from one end of the gap to the other end of the gap by capillary action to fill the gap; the bottom filling glue is cured; after the curing is completed, a chip packaging structure is obtained. Beneficial effects:

[0020] The present invention provides a bottom filling glue with a low thermal expansion coefficient, which comprises the following components by mass percentage: 24% to 33% epoxy resin, 58% to 69% silicon dioxide, 8% to 19% curing agent, 0.1% to 0.3% dye and 0.2% to 0.4% adhesion promoter; the epoxy resin is compounded by trifunctional epoxy resin, polyether modified epoxy resin and naphthalene epoxy resin; the trifunctional epoxy resin has the dual characteristics of alicyclic epoxy resin and glycidyl ester, and has high reactivity and high adhesion; the polyether modified epoxy resin has low viscosity and a large number of flexible groups, which can increase the fluidity of the bottom filling glue, reduce hardness, and improve curing shrinkage and flexibility; the naphthalene epoxy resin contains a highly hydrophobic and rigid naphthalene ring structure, which can still maintain good performance under high temperature environment and has high Yang The modulus, in-plane orientation and stacking coefficient of the bottom filler are small, the free volume in which the molecular chain can move is small, the expansion in the direction of the molecular chain is small, and as the temperature rises, the thermal expansion perpendicular to the direction of the molecular chain will be suppressed, which can effectively reduce the thermal expansion coefficient of the bottom filler. The three resins of trifunctional epoxy resin, polyether modified epoxy resin and naphthalene epoxy resin are cured by a curing agent to form a whole, providing basic performance for the bottom filler, and silica is used as a filler to enhance the performance of the bottom filler. At the same time, the adhesion promoter is used to improve the adhesion of the bottom filler to the substrate, and a dye is used for dyeing and marking. The bottom filler prepared by the specific formula ratio of this application has good fluidity, low thermal expansion coefficient and moisture and heat resistance, and at the same time has good adhesion to silicon wafers, thereby improving the reliability and life of chip packaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of this specification or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] FIG1 is a flow chart of a method for preparing an underfill adhesive with a low thermal expansion coefficient according to the present application. DETAILED DESCRIPTION

[0023] The present invention will be described in detail below in conjunction with specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly presented. It should be understood by those skilled in the art that these specific embodiments and examples are for illustrating the present invention, rather than for limiting the present invention.

[0024] Throughout this specification, unless otherwise specified, the terms used herein should be understood as having the same meaning as commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In the event of any conflict, the present specification shall take precedence.

[0025] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or obtained through existing methods.

[0026] The present application provides a bottom filling glue with a low thermal expansion coefficient, which includes the following components by mass percentage: 24% to 33% epoxy resin, 58% to 69% silicon dioxide, 8% to 19% curing agent, 0.1% to 0.3% dye and 0.2% to 0.4% adhesion promoter; the epoxy resin is compounded by trifunctional epoxy resin, polyether-modified epoxy resin and naphthalene-type epoxy resin.

[0027] Specifically, the present invention provides a bottom filling glue with a low thermal expansion coefficient, which includes the following components by mass percentage: 24% to 33% epoxy resin, 58% to 69% silicon dioxide, 8% to 19% curing agent, 0.1% to 0.3% dye and 0.2% to 0.4% adhesion promoter; the epoxy resin is compounded by trifunctional epoxy resin, polyether modified epoxy resin and naphthalene epoxy resin; the trifunctional epoxy resin has the dual characteristics of alicyclic epoxy resin and glycidyl ester, and has high reactivity and high adhesion; the polyether modified epoxy resin has low viscosity and a large number of flexible groups, which can increase the fluidity of the bottom filling glue, reduce hardness, and improve curing shrinkage and flexibility; the naphthalene epoxy resin contains a highly hydrophobic and rigid naphthalene ring structure, which can still maintain good performance under high temperature environment, and has high Young's modulus, in-plane orientation and stacking coefficient, the free volume in which the molecular chain can move is small, the expansion in the direction of the molecular chain is small, and as the temperature rises, the thermal expansion perpendicular to the direction of the molecular chain will be suppressed, which can effectively reduce the thermal expansion coefficient of the bottom filling glue. The three resins of trifunctional epoxy resin, polyether modified epoxy resin and naphthalene epoxy resin are cured by a curing agent to form a whole, providing basic performance for the bottom filling glue, and using silica as a filler to enhance the performance of the bottom filling glue. At the same time, the adhesion promoter is used to improve the adhesion of the bottom filling glue to the substrate, and a dye is used for dyeing and marking. The bottom filling glue prepared by the specific formula ratio of this application has good fluidity, low thermal expansion coefficient and moisture and heat resistance, and at the same time has good adhesion to silicon wafers, thereby improving the reliability and life of chip packaging.

[0028] In some possible embodiments, the mass percentage of the trifunctional epoxy resin is 4%-20%, the mass percentage of the polyether-modified epoxy resin is 4%-20%, and the mass percentage of the naphthalene-type epoxy resin is 4%-20%.

[0029] Those skilled in the art will understand that the epoxy resin of the present application is a compound of a trifunctional epoxy resin, a polyether-modified epoxy resin and a naphthalene-type epoxy resin. Each epoxy resin has its own specific properties and functions. By compounding the three and adjusting the ratio between the three, the thermal expansion coefficient, fluidity and moisture and heat resistance of the bottom filling glue can be controlled.

[0030] In some possible embodiments, the curing agent is Ancamine 2264.

[0031] This is because Ancamine 2264 is an epoxy curing agent with both alicyclic and aromatic properties. It has a high glass transition temperature and reacts with epoxy resin at a certain temperature to form a thermosetting compound with a three-dimensional network structure. In this application, the curing agent connects the trifunctional epoxy resin, polyether-modified epoxy resin, and naphthalene-based epoxy resin into a single integrated structure, further enhancing the performance of the underfill.

[0032] In some possible embodiments, the structural formula of the polyether-modified epoxy resin is:

[0033] The polyether-modified epoxy resin, as a material matrix, can provide adhesive and mechanical properties to the underfill adhesive and improve the fluidity of the underfill adhesive. The polyether-modified epoxy resin can be SE-4125P.

[0034] In some possible embodiments, the trifunctional epoxy resin includes at least one of MF-3285 and TPNE5501.

[0035] The trifunctional epoxy resin contains a large number of highly reactive groups, which can provide cross-linking fulcrums for the curing reaction of the bottom filling glue, further improving the compatibility of the polyether epoxy resin and the naphthalene epoxy resin.

[0036] In some possible embodiments, the naphthalene-based epoxy resin includes at least one of SE-165 and EBA-65.

[0037] Naphthalene-based epoxy resin can maintain good performance even at temperatures up to 150°C, and its molecular structure contains a rigid molecular structure that can reduce the thermal expansion coefficient of the underfill. Furthermore, the addition of silica further reduces the thermal expansion coefficient of the underfill, while also improving the compatibility of silica with the underfill.

[0038] In some possible embodiments, the colorant includes carbon black.

[0039] Those skilled in the art will understand that the dye is used to color the bottom filling glue to facilitate chip identification. In this application, the dye may be carbon black.

[0040] Based on a general inventive concept, referring to FIG1 , the present application further provides a method for preparing an underfill having a low thermal expansion coefficient as described in the first aspect, the method comprising:

[0041] S1: Stirring and mixing the components according to their respective mass percentages to obtain a first slurry, wherein the mass percentages of the components specifically include: 24% to 33% epoxy resin, 58% to 69% silicon dioxide, 8% to 19% curing agent, 0.1% to 0.3% coloring agent, and 0.2% to 0.4% adhesion promoter; wherein the stirring and mixing is performed by a centrifugal mixer, and the stirring and mixing time of the centrifugal mixer is set to 115 to 155 seconds, the rotation is 1050 r / min, and the revolution is 1320 r / min;

[0042] S2: transferring the first slurry to a three-roll mill for dispersion treatment to obtain a uniformly dispersed second slurry; wherein the feed gap of the three-roll mill is 10-40 μm and the discharge gap is 10-20 μm;

[0043] S3: vacuum degassing the second slurry to obtain an underfill adhesive. The vacuum degassing is performed in a centrifugal mixer with a vacuum degassing time of 65 to 95 seconds, a rotation speed of 1050 rpm, and a revolution speed of 1320 rpm.

[0044] As another optional embodiment, the epoxy resin is compounded by a trifunctional epoxy resin, a polyether-modified epoxy resin and a naphthalene-type epoxy resin; the mass percentage of the trifunctional epoxy resin is 4%-20%, the mass percentage of the polyether-modified epoxy resin is 4%-20%, and the mass percentage of the naphthalene-type epoxy resin is 4%-20%.

[0045] Based on a general inventive concept, the present application further provides a chip packaging structure, comprising a substrate, a chip disposed on the substrate, and a plurality of solder bumps disposed between the substrate and the chip and electrically connected to the substrate and the chip, wherein a gap is formed between the substrate and the chip.

[0046] Disposing the bottom filler glue with a low thermal expansion coefficient as described in the first aspect at the edge of the substrate, so that the bottom filler glue flows from one end of the gap to the other end of the gap by capillary action to fill the gap;

[0047] Curing the bottom filling glue;

[0048] After curing, a chip packaging structure is obtained.

[0049] The present application will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present application only and are not intended to limit the scope of the present application. The experimental methods in the following examples where specific conditions are not specified are usually measured in accordance with national standards. If there are no corresponding national standards, then the methods are carried out in accordance with general international standards, conventional conditions, or according to the conditions recommended by the manufacturer.

[0050] The components of the underfill glue in Comparative Examples 1-5 and Examples 1-4 are shown in Table 1 below in terms of mass percentage:

[0051] Table 1 Raw material components by mass percentage

[0052] The storage modulus, glass transition temperature, thermal expansion coefficient, elongation / tensile strength, and fluidity tests were performed on the underfills provided in Examples 1-4 and Comparative Examples 1-5. The specific testing process is as follows:

[0053] 1. Flowability test method: A rectangular Si wafer measuring 20mm x 40mm and 0.5mm thick is attached to a substrate with 50um thick double-sided tape at the four corners. A dispensing machine is used to dispense 30-35mg of the underfill glue to be tested laterally along one edge of the rectangular Si wafer. The wafer is then placed on a 90°C hot plate and timing is started. Under the action of capillary force, the underfill glue will flow to the bottom of the Si wafer. The time it takes for the glue to flow to half of the wafer and the time it takes for the glue to be fully filled are recorded.

[0054] 2. Thermal expansion coefficient: Reference standard: ASTM E831-2019, take a sample that is fully cured at 165°C for 2h, and prepare a test sample with a size of 5mm×5mm×10mm. Use TMA (compression mode) to test the thermal expansion coefficient of the sample. TMA parameter settings: preload force: 0.2N, first scan: room temperature-260°C (heating rate 20°C / min); second scan: 40-260°C (heating rate 5°C / min), take the curve data of the second heating section; the expansion coefficient CTE1 / 2 takes the values ​​of temperature at 50°C-90°C and 160°C-200°C respectively.

[0055] 3. Glass transition temperature Tg: Reference standard: ASTM E2254-2018, take a sample that is fully cured at 165°C for 2h, the size of the test sample is 55mm×10mm× / 3mm, and DMA is used for measurement, measurement mode: dual cantilever mode, vibration frequency: 1Hz, amplitude: 10μm, heating rate: 5°C / min.

[0056] 4. Storage modulus: Reference standard: ASTM E2254-2018, take a sample cured at 165°C for 2h, the size of the test sample is 55mm×10mm×3mm, and DMA is used for measurement. The measurement mode is dual cantilever mode, vibration frequency: 1Hz, amplitude: 10μm, and heating rate: 5°C / min; the storage modulus takes the value of 25°C-245°C.

[0057] 5. Reliability test: The sample was cast in a pudding mold with a diameter of 3mm and a height of 2mm. One end of the cast sample was in contact with the silicon wafer. The silicon wafer and the pudding mold were fixed. After curing at 165℃ / 2h, the pudding mold was removed and the sample was taken out and tested using a thrust machine. The sample was cooked in a high-temperature and high-pressure cooker (PCT) at a temperature of 120℃ and a humidity of 100% for 48h. After being taken out, it was tested using a thrust machine. The thrust machine test speed was 50μm / s and the contact height was 20μm.

[0058] The test results are shown in Table 2 below:

[0059] Table 2 Test results

[0060] From the above table we can see that:

[0061] (1) In Comparative Example 1, only polyether-modified epoxy resin and naphthalene-type epoxy resin were added without trifunctional epoxy resin. Although the material had good fluidity, its thermal expansion coefficient was high. During the curing reaction, the cross-linking points decreased and the proportion of flexible segments in the molecule increased, resulting in a smaller Tg of the material and weaker adhesion.

[0062] (2) In Comparative Example 2, only naphthalene ring resin and trifunctional epoxy resin were added without polyether modified epoxy resin, resulting in poor fluidity and easy shrinkage after curing;

[0063] (3) In Comparative Example 3, only polyether-modified epoxy resin and trifunctional epoxy resin were added, without naphthalene ring resin. The glass transition temperature of the bottom filler was low, the thermal expansion coefficient was large, and the Si adhesion decreased significantly after PCT.

[0064] (4) Comparative Examples 4-5 added three resins in combination, but the added amounts were outside the percentage range specified in this application. The obtained underfill had average performance and low Si adhesion, which was not conducive to chip packaging.

[0065] (5) In Examples 1-4, the amount of silicon dioxide added is the same. Example 1 uses trifunctional epoxy resin as the main resin, and is compounded with polyether modified epoxy resin and naphthalene ring resin. The bottom filling glue has greater Si adhesion and higher Tg; Example 2 uses polyether modified epoxy resin as the main resin, and is compounded with trifunctional epoxy resin and naphthalene ring resin. The bottom filling glue has good fluidity; Example 3 uses naphthalene ring resin as the main resin, and is compounded with trifunctional epoxy resin and polyether modified epoxy resin. The bottom filling glue has a low thermal expansion coefficient and increased Si adhesion after PCT; In Example 4, the percentages of trifunctional epoxy resin as the main resin, polyether modified epoxy resin and naphthalene ring resin are the same. The bottom filling glue has good fluidity, higher Tg, and lower thermal expansion coefficient, and after the PCT test, the bottom filling glue still has strong Si adhesion, thereby improving the reliability and life of the chip package.

[0066] In summary, by using the bottom filling glue configured within the specified range of this application as the raw material components, and adjusting the ratio of polyether modified epoxy resin, naphthalene ring resin and trifunctional epoxy resin within a fixed range, a bottom filling glue with good fluidity, low thermal expansion coefficient and excellent moisture and heat resistance can be obtained. That is, this application provides a bottom filling glue with a low thermal expansion coefficient, high moisture and heat resistance and good silicon adhesion, thereby improving the reliability and life of chip packaging; in addition, the bottom filling glue of this application also has a high glass transition temperature and can be applied to more fields.

[0067] Finally, it should be noted that the terms "comprises," "includes," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements, but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0068] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0069] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A bottom filler with a low thermal expansion coefficient, characterized in that: The bottom filling glue is composed of the following components by mass percentage: 24% to 33% epoxy resin, 62% silicon dioxide, 8% to 19% curing agent, 0.2% dye and 0.3% adhesion promoter; the epoxy resin is compounded by trifunctional epoxy resin, polyether modified epoxy resin and naphthalene epoxy resin; The mass percentage of the trifunctional epoxy resin is 4%-20%, the mass percentage of the polyether-modified epoxy resin is 4%-20%, and the mass percentage of the naphthalene-type epoxy resin is 4%-20%; The curing agent is Ancamine 2264; The structural formula of the polyether modified epoxy resin is: The trifunctional epoxy resin includes at least one of MF-3285 and TPNE5501; The naphthalene-type epoxy resin includes at least one of SE-165 and EBA-65; The coloring agent includes carbon black; The adhesion promoter is NXH-635.

2. A method for preparing a bottom filler with a low thermal expansion coefficient as claimed in claim 1, characterized in that: The preparation method comprises: S1: Stirring and mixing the components according to their respective mass percentages to obtain a first slurry, wherein the mass percentages of the components specifically include: 24% to 33% epoxy resin, 62% silicon dioxide, 8% to 19% curing agent, 0.2% coloring agent, and 0.3% adhesion promoter; S2: transferring the first slurry to a three-roll mill for dispersion to obtain a uniformly dispersed second slurry; S3: vacuum degassing the second slurry to obtain an underfill glue; The epoxy resin is compounded by trifunctional epoxy resin, polyether modified epoxy resin and naphthalene epoxy resin; the mass percentage of the trifunctional epoxy resin is 4%-20%, the mass percentage of the polyether modified epoxy resin is 20%-30%, and the mass percentage of the polyether modified epoxy resin is 10%-20%. The mass percentage of epoxy resin is 4%-20%, and the mass percentage of naphthalene type epoxy resin is 4%-20%.

3. A chip packaging structure comprising a substrate, a chip disposed on the substrate, and a plurality of solder bumps disposed between the substrate and the chip and electrically connected to the substrate and the chip, wherein a gap is formed between the substrate and the chip, wherein: Disposing the bottom filler glue with a low thermal expansion coefficient according to claim 1 at the edge of the substrate, so that the bottom filler glue flows from one end of the gap to the other end of the gap by capillary action to fill the gap; Curing the bottom filling glue; After curing, a chip packaging structure is obtained.

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