Underfill adhesive for eliminating flow marks and preparation method therefor, and flip chip

Abstract

Provided in the present invention are an underfill adhesive for eliminating flow marks and a preparation method therefor and a flip chip. The underfill adhesive comprises the following components in percentages by mass: 16-24% of a polyurethane-modified epoxy resin, 52-64% of a filling agent, 19-23% of a curing agent, 0.2-0.6% of an accelerant and 0.1-0.2% of a coloring agent. The underfill adhesive for eliminating flow marks of the present application is prepared from the polyurethane-modified epoxy resin, the filling agent, the curing agent, the accelerant and the coloring agent according to a specific proportion. The good compatibility between the polyurethane-modified epoxy resin and the filling agent is utilized, the curing agent is added to change a reaction system into a solid state from a flowing state, and the reaction rate is increased by means of the accelerant, thereby improving the curing rate of the underfill adhesive, and thus improving the manufacturing efficiency of a flip chip.

Description

Bottom filling glue for eliminating flow marks, preparation method thereof and flip chip Technical Field

[0001] The invention belongs to the technical field of chip bottom filling glue, and in particular relates to a bottom filling glue for eliminating flow marks, a preparation method thereof and a flip chip. Background Art

[0002] To meet the reliability requirements of electronic devices, flip-chips generally use underfill technology. Underfill is a material suitable for flip-chip underfill technology. It typically penetrates the gap between the chip and substrate through capillary action, then gradually solidifies and fills the gap between the chip and substrate through thermal curing, protecting the high-density solder bumps between the chip and substrate and the chip. As shown in Figure 1, a number of contact pads 3 are spaced apart at the upper end of the substrate 1. A matching number of underfill metal 4 is provided at the lower end of the chip 2. A solder bump 5 is provided between each contact pad and the corresponding underfill metal. A solder mask 6 is provided between two adjacent contact pads, and a passivation layer 7 is provided between two adjacent underfill metals. The gaps formed between the chip, substrate, and solder bumps are filled with underfill material 8, thereby protecting the chip, substrate, and solder bumps. It can also disperse the stress borne on the chip surface and relieve the internal stress caused by the mismatch in thermal expansion coefficients of the chip, substrate, and solder bumps. This protects the chip from damage caused by physical, chemical, and other environmental factors, thereby increasing the processability, reliability, and service life of the chip and packaged device.

[0003] However, the existing underfill material formed after curing often cracks and can no longer protect the chip; at the same time, when the underfill flows in the gaps formed between the chip, substrate, and solder bumps, it also produces flow marks, which is not conducive to protecting the chip.

[0004] Therefore, how to provide an underfill glue to suppress the generation of flow marks and enhance the protection effect on the chip is a technical problem that needs to be solved urgently by those skilled in the art.

[0005] Summary of the Invention

[0006] The object of the present invention is to provide an underfill for eliminating flow marks, a preparation method thereof, and a flip chip, so as to solve at least one of the above-mentioned technical problems.

[0007] To achieve the above-mentioned objectives, the first aspect of the present invention provides a bottom filling glue for eliminating flow marks, wherein the bottom filling glue comprises the following components by mass percentage: 16%-24% of polyurethane modified epoxy resin, 52%-64% of filler, 19%-23% of curing agent, 0.2%-0.6% of accelerator and 0.1%-0.2% of colorant.

[0008] In the first aspect, the filler comprises silicon dioxide, and the average particle size of the silicon dioxide is 0.6-5 μm.

[0009] In the first aspect, the curing agent includes an amine curing agent.

[0010] In the first aspect, the accelerator includes an imidazole accelerator.

[0011] In the first aspect, the colorant includes carbon black.

[0012] A second aspect of the present invention provides an underfill adhesive, which is composed of an epoxy resin, a filler, a curing agent, an accelerator, and a colorant; wherein the epoxy resin includes a polyurethane-modified epoxy resin.

[0013] In the second aspect, the filler comprises silica; the average particle size of the silica is 0.6-5 μm; and / or the curing agent comprises an amine curing agent; and / or the accelerator comprises an imidazole accelerator; and / or the colorant comprises carbon black.

[0014] The third aspect of the present invention provides a method for preparing a bottom filling glue for eliminating bottom flow marks as described in the first aspect, the preparation method comprising: stirring and mixing the components according to a certain ratio to obtain a preliminary mixed slurry, wherein the components include the following components by mass percentage: 16%-24% of polyurethane modified epoxy resin, 52%-64% of filler, 19%-23% of curing agent, 0.2%-0.6% of accelerator and 0.1%-0.2% of colorant; transferring the preliminary mixed slurry to a three-roll grinder for dispersion treatment to obtain a uniformly dispersed slurry; and vacuum degassing the uniformly dispersed slurry to obtain a bottom filling glue.

[0015] The fourth aspect of the present invention provides a flip chip, comprising a substrate, a chip arranged on a surface of 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, the gap between the substrate and the chip being filled with a bottom filling material, the bottom filling material being formed by curing the bottom filling glue for eliminating bottom flow marks described in the first aspect, the size of the chip being greater than 10 mm × 25 mm, and the gap between the chip and the substrate being less than 30 μm.

[0016] The fifth aspect of the present invention provides a method for preparing a flip chip, the preparation method comprising: obtaining a flip chip body, the flip chip body comprising a substrate, a chip arranged on a surface of 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, wherein a gap is formed between the substrate and the chip; the bottom filling glue for eliminating bottom flow marks described in the first aspect is arranged on the edge of the flip chip, 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; heating to solidify the bottom filling glue in the gap to obtain a flip chip. Beneficial effects:

[0017] The bottom filling glue for eliminating flow marks provided by the present invention comprises the following components by mass percentage: 16%-24% of polyurethane modified epoxy resin, 52%-64% of filler, 19%-23% of curing agent, 0.2%-0.6% of accelerator and 0.1%-0.2% of colorant. The polyurethane modified epoxy resin has an interpenetrating network structure and contains a large number of carbonyl groups, alcohol groups and amino groups, which enhances the polarity of the epoxy resin, thereby having a stronger force on the filler, effectively increasing the surface performance of the filler, and improving the polyurethane modified epoxy resin and the filler. The compatibility between the two makes the bottom filling glue have a certain fluidity, and it is not easy to produce agglomerates when the bottom filling glue liquid is cast to fill the gap, thereby suppressing the generation of flow marks; at the same time, the bottom filling glue of the present application is prepared by using polyurethane modified epoxy resin, filler, curing agent, accelerator and colorant in a specific proportion, utilizing the good compatibility between polyurethane epoxy resin and filler, adding curing agent changes the reaction system from a fluid state to a solid state, and accelerates the reaction rate through the accelerator, thereby improving the curing rate of the bottom filling glue, thereby improving the production efficiency of flip chips. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] 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.

[0019] FIG1 is a schematic diagram of the structure of a flip chip in the prior art;

[0020] FIG2 is a flow chart of a method for preparing a bottom filling adhesive for eliminating bottom flow marks according to the present application.

[0021] Reference numerals: 1. substrate; 2. chip; 3. contact pad; 4. bottom touch metal; 5. solder bump; 6. solder mask; 7. passivation; 8. underfill material. DETAILED DESCRIPTION

[0022] 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.

[0023] 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.

[0024] 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.

[0025] The present application provides a bottom filling glue for eliminating flow marks, which includes the following components by mass percentage: 16%-24% polyurethane modified epoxy resin, 52%-64% filler, 19%-23% curing agent, 0.2%-0.6% accelerator and 0.1%-0.2% colorant.

[0026] The bottom filling glue for eliminating flow marks provided by the present invention comprises the following components by mass percentage: 16%-24% of polyurethane modified epoxy resin, 52%-64% of filler, 19%-23% of curing agent, 0.2%-0.6% of accelerator and 0.1%-0.2% of colorant. The polyurethane modified epoxy resin has an interpenetrating network structure and contains a large number of carbonyl groups, alcohol groups and amino groups, which enhances the polarity of the epoxy resin, thereby having a stronger force on the filler, effectively increasing the surface performance of the filler, and improving the polyurethane modified epoxy resin and the filler. The compatibility between the two makes the bottom filling glue have a certain fluidity, and it is not easy to produce agglomerates when the bottom filling glue liquid is cast to fill the gap, thereby suppressing the generation of flow marks; at the same time, the bottom filling glue of the present application is prepared by using polyurethane modified epoxy resin, filler, curing agent, accelerator and colorant in a specific proportion, utilizing the good compatibility between polyurethane epoxy resin and filler, adding curing agent changes the reaction system from a fluid state to a solid state, and accelerates the reaction rate through the accelerator, thereby improving the curing rate of the bottom filling glue, thereby improving the production efficiency of flip chips.

[0027] In some possible embodiments, the filler includes silicon dioxide, and the average particle size of the silicon dioxide is 0.6-5 μm.

[0028] The filler includes silicon dioxide, which is used to reduce the thermal expansion coefficient of the bottom filling glue, and the average particle size of the silicon dioxide is 0.6-5μm. By controlling the average particle size of the silicon dioxide, the rate of the bottom filling glue flowing in the gap can be controlled and the generation of agglomerates can be suppressed.

[0029] In some possible embodiments, the curing agent includes an amine curing agent. Preferably, the amine curing agent can be diethyltoluenediamine, ethylenediamine, etc., which can react with the epoxy resin under the action of a certain temperature and an accelerator, and the system changes from a fluid state to a solid state.

[0030] In some possible embodiments, the accelerator includes an imidazole accelerator. Preferably, the imidazole accelerator can be 1-cyanoethyl-2-ethyl-4-methylimidazole, N-methylimidazole, etc., which are inactive at room temperature but can promote the reaction at a certain temperature. In other words, the imidazole accelerator can extend the shelf life of the underfill.

[0031] In some possible embodiments, the colorant includes carbon black and is used to dye the underfill glue for easy identification.

[0032] Based on a general inventive concept, the present application also provides a bottom filling glue, which is composed of an epoxy resin, a filler, a curing agent, an accelerator and a colorant; wherein the epoxy resin includes a polyurethane-modified epoxy resin, and the filler includes silica; the average particle size of the silica is 0.6-5 μm.

[0033] As another optional embodiment, the curing agent may be selected from amine curing agents; as another optional embodiment, the accelerator may be selected from imidazole accelerators; as another optional embodiment, the colorant may be selected from carbon black.

[0034] Based on a general inventive concept, the present application further provides a method for preparing the underfill adhesive for eliminating bottom flow marks as described above, the preparation method comprising:

[0035] S1: Stirring and mixing the components in a certain ratio to obtain a preliminary mixed slurry, wherein the components include the following components by mass percentage: 16%-24% of polyurethane-modified epoxy resin, 52%-64% of filler, 19%-23% of curing agent, 0.2%-0.6% of accelerator, and 0.1%-0.2% of colorant; wherein the stirring and mixing time is 85-255s, the rotation is 950r / min, and the revolution is 1050r / min;

[0036] S2: transferring the preliminary mixed slurry to a three-roll mill for dispersion treatment to obtain a uniformly dispersed slurry; wherein the feed gap in the three-roll mill is 15-50 μm and the discharge gap is 5-25 μm;

[0037] S3: vacuum degassing the uniformly dispersed slurry to obtain an underfill glue; wherein, the vacuum degassing is performed in a centrifugal mixer, the vacuum degassing time is 30-60s, the rotation is 950r / min, and the revolution is 1050r / min.

[0038] Based on a general inventive concept, the present application also provides a flip chip, comprising a substrate, a chip arranged on a surface of 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. The gap between the substrate and the chip is filled with a bottom filling material, and the bottom filling material is formed by curing the bottom filling glue for eliminating bottom flow marks described in the first aspect. The size of the chip is greater than 10 mm × 25 mm, and the gap between the chip and the substrate is less than 30 μm.

[0039] Based on a general inventive concept, the present application also provides a method for preparing a flip chip, the preparation method comprising: obtaining a flip chip body, the flip chip body comprising a substrate, a chip arranged on a surface of 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, wherein a gap is formed between the substrate and the chip; the bottom filling glue for eliminating bottom flow marks described in the first aspect is arranged on the edge of the flip chip, 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; heating is applied to solidify the bottom filling glue in the gap to obtain a flip chip.

[0040] 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.

[0041] The weight percentages of the components of the underfill glue in Examples 1-3 and Comparative Examples 1-6 are shown in the following table:

[0042] The underfills provided in Examples 1-3 and Comparative Examples 1-6 were tested for fluidity, storage modulus, glass transition temperature, thermal expansion coefficient, and adhesion. The specific testing process is as follows:

[0043] 1. Fluidity test method: Place a 20mm×20mm, 0.5mm thick square glass sheet on a glass slide with 30um thick double-sided tape at the four corners. Place the sheet on a 90°C hot plate and preheat for three minutes. Use a fine steel needle to apply the underfill glue to be tested horizontally along one edge of the square glass sheet. Start timing at the same time. Under the action of capillary force, the underfill glue will flow along the bottom of the glass sheet. Note the time it takes to flow to half the length of the side and the time it takes to fully flow. Visually observe whether there are any flow marks.

[0044] 2. Storage modulus: Reference standard: ASTM E2254-2018, take a sample cured at 150°C for 2h, the size of the test sample is 55mm×10mm×2mm, and the measurement is performed using DMA, measurement mode: dual cantilever mode, vibration frequency: 1Hz, amplitude: 10μm, heating rate: 3°C / min; the storage modulus is taken as the value between 25°C and 260°C.

[0045] 3. Glass transition temperature (Tg): Prepare a sample 5 mm × 5 mm × 2 mm in size after curing at 150°C for 2 hours. Measure the glass transition temperature using a TMA (compression mode). TMA parameters include: preload force: 0.05 N; first scan: room temperature to 250°C (heating rate: 10°C / min); second scan: room temperature to 250°C (heating rate: 10°C / min), and collect the curve data for the second heating period.

[0046] 4. Coefficient of thermal expansion: Reference standard: ASTM E831-2019, take a sample that is fully cured at 150°C for 2h, and prepare a test sample with a size of 5mm×5mm×2mm. Use TMA (compression mode) to test the thermal expansion coefficient of the sample. TMA parameter settings: preload force: 0.05N, first scan: room temperature to 250°C (heating rate 10°C / min); second scan: room temperature to 250°C (heating rate 10°C / min), take the curve data of the second heating section; the thermal expansion coefficient CTE1 / 2 takes the values ​​of the temperature at 40°C-100°C and 150°C-200°C respectively.

[0047] 5. Adhesion test method: Cast the sample into a pudding mold with a diameter of 3 mm and a height of 2 mm. Place one end of the cast sample in contact with a copper or silicon wafer. Secure the copper or silicon wafer to the pudding mold. After curing at 150°C for 2 hours, remove the pudding mold and take out the sample. Test the sample using a thrust machine at a thrust speed of 50 μm / s and a contact height of 20 μm. Record the adhesion of the silicon wafer and the copper sheet during the test.

[0048] 6. High-temperature and high-pressure cooking (PCT) test: The samples were cured at 150°C for 2 hours. After curing, the samples were placed at 120°C for 20 hours for PCT test. The samples were then measured according to the above test method, and the storage modulus, glass transition temperature Tg, thermal expansion coefficient CTE1 / 2, silicon wafer adhesion, and copper sheet adhesion were recorded.

[0049] The liquidity test results are shown in the following table:

[0050] As can be seen from the table above, the epoxy resins used in Comparative Examples 1 and 2 are unmodified bisphenol A and bisphenol F epoxy resins, respectively. When the gap is 60 μm, no flow marks appear, but when the gap is reduced to 40 μm and 30 μm, flow marks appear. However, the polyurethane-modified epoxy resin used in Example 1 does not appear at 40 μm and 30 μm, indicating that the polyurethane-modified epoxy resin has better compatibility with silica. Although polyurethane-modified epoxy resins are also used in Comparative Examples 3 and 4, flow marks also appear when the gap is reduced to 40 μm and 30 μm, indicating that the polyurethane-modified epoxy resin Only when the grease is formulated in a specific ratio can flow marks be controlled. In Comparative Example 5, the lower solid content results in lower viscosity and better fluidity, which increases the pressure differential during flow. Although no flow marks occur when the gap is 40μm and 60μm, flow marks appear when the gap is further reduced to 30μm. In Comparative Example 6, the higher solid content results in higher viscosity and poorer fluidity, which results in lower pressure differential during flow. Therefore, flow marks appear at 30μm, 40μm, and 60μm. Therefore, only when the components in the underfill are formulated in a specific ratio can the formation of flow marks be suppressed. From this, we can know that its possible mechanism of action is:

[0051] The driving force for the colloid to flow in the chip gap mainly comes from the pressure difference. In the gap at the bottom of the chip, due to the pressure difference, the colloid will flow from one end of the gap to the other end. When the gap is too small, the friction increases, and the friction causes the loss of the kinetic energy of the colloid flow, making the flow speed slower and slower. When the gap is too large, the leakage increases, and the colloid will overflow from the other end. In actual applications, the gap of the chip is generally between 30-60um, and the length and width are 10-25mm square. The filler selected is silica with an average particle size of 0.6-5um. During the flow process, the closer the glue is to the other end, the smaller the flow kinetic energy. A small part of the silica will agglomerate and stop flowing. The agglomerates hinder the continued flow of the colloid, and the formation of multiple agglomerates will produce dendritic flow marks. Glue materials that produce flow marks are unqualified products.

[0052] Agglomerates are formed due to the poor compatibility and weak bonding between silica and resin. Using a resin with good compatibility with silica can effectively eliminate flow marks. This application uses a polyurethane-modified epoxy resin. Polyurethane-modified epoxy resins contain a large number of carbonyl, alcohol, and amine groups, which enhance the polarity of the resin and thus exert a stronger force on silica. The interaction between the two is greater, the compatibility is better, and agglomerates are less likely to form, resulting in no flow marks.

[0053] The DMA and TMA test results of the bottom filler of this application after curing at 150°C for 2 hours are shown in the following table:

[0054] The DMA and TMA test results of the bottom filler of this application after curing at 150°C for 2 hours and then undergoing the PCT high temperature and high pressure cooking test (test conditions: test temperature of 120°C and test time of 20 hours) are shown in the following table:

[0055] As shown in the table above, a comparison of Comparative Examples 1 and 2 with Example 1 shows that, given the same filler, the storage modulus of the polyurethane-modified epoxy resin is greater than that of bisphenol A and bisphenol F epoxy resins, and the expansion coefficient of the polyurethane-modified epoxy resin is less than that of bisphenol A and F epoxy resins. A comparison of the examples with the comparative examples shows that adding an appropriate amount of polyurethane-modified epoxy resin to the underfill in the examples can improve the adhesion of silicon wafers and copper sheets, but the adhesion of silicon wafers and copper sheets is also related to the solid content of the system.

[0056] After high-temperature and high-pressure cooking at 120°C for 20 hours, within the ratio range of the components provided in this application, the bottom filling glue still has a high storage modulus after curing and PCT test, and the adhesion of silicon wafers and copper sheets decreases slightly. However, when the ratio is not within the range provided in this application or when bisphenol A epoxy resin or bisphenol F epoxy resin is used, the adhesion decreases significantly.

[0057] 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.

[0058] 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.

[0059] 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 filling glue for eliminating flow marks, characterized in that: The bottom filling glue is composed of the following components by mass percentage: 16%-24% of polyurethane modified epoxy resin, 52%-64% of filler, 19%-23% of curing agent, 0.2%-0.6% of accelerator and 0.1%-0.2% of colorant; The filler is silicon dioxide, and the average particle size of the silicon dioxide is 0.6-5 μm; The polyurethane modified epoxy resin is EPU300A.

2. The bottom filling glue for eliminating flow marks according to claim 1, characterized in that: The curing agent includes an amine curing agent.

3. The bottom filling glue for eliminating flow marks according to claim 2, characterized in that: The accelerator includes an imidazole accelerator.

4. The bottom filling glue for eliminating flow marks according to claim 3, characterized in that: The colorant includes carbon black.

5. A method for preparing a bottom filling adhesive for eliminating bottom flow marks according to any one of claims 1 to 4, characterized in that: The preparation method comprises: The components are stirred and mixed according to a certain ratio to obtain a preliminary mixed slurry, wherein the components include the following components by mass percentage: 16%-24% of polyurethane modified epoxy resin, 52%-64% of filler, 19%-23% of curing agent, 0.2%-0.6% of accelerator and 0.1%-0.2% of colorant; Transferring the preliminarily mixed slurry to a three-roll mill for dispersion treatment to obtain a uniformly dispersed slurry; The uniformly dispersed slurry is subjected to vacuum degassing to obtain the bottom filling adhesive.

6. A flip chip, comprising a substrate, a chip disposed on a surface of 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 the gap between the substrate and the chip is filled with an underfill material, characterized in that: The bottom filling material is formed by curing the bottom filling glue for eliminating bottom flow marks according to any one of claims 1 to 4, the size of the chip is greater than 10 mm×25 mm, and the gap between the chip and the substrate is less than 30 μm.

7. A method for preparing a flip chip, characterized in that: The preparation method comprises: Obtaining a flip chip body, the flip chip body comprising a substrate, a chip disposed on a surface of 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; Disposing the bottom filling glue for eliminating bottom flow marks according to any one of claims 1 to 4 at the edge of the flip chip, 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 by heating in the gap to obtain a flip chip.

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