Method for manufacturing polyimide molded articles

Abstract

This invention provides a manufacturing method for easily molding polyimide resin to obtain a polyimide molded product. [Solution] The present invention provides a method for producing a polyimide molded article, characterized by molding a molding raw material containing polyimide precursor powder and having an imidization rate of 40% or less by a transfer molding method.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a polyimide molded body.

Background Art

[0002] In recent years, there has been an increasing demand for semiconductor packages in terms of moisture resistance, heat resistance, dimensional stability, and low dielectric constant. In current epoxy resin encapsulation, although measures such as increasing the amount of inorganic filler and changing the resin composition are being taken, it is becoming difficult to meet higher requirements.

[0003] Polyimide resin is cited as a resin with excellent heat resistance, but polyimide resin does not exhibit fluidity even at high temperatures. In semiconductor packaging, a method using a polyimide film has been proposed (for example, see Patent Document 1). Also, to manufacture a polyimide molded body with a relatively large shape, first, a film-like product is formed from a polyamic acid solution, then it is pulverized into powder, and finally, it is sintered at a high temperature to produce a block-shaped molded body. Generally, the thus obtained block-shaped molded body is cut into a desired shape.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Conventional methods for manufacturing polyimide molded bodies are extremely inefficient from the perspectives of labor and energy. Therefore, there is a need for a method that can easily perform molding processing of polyimide resin to manufacture a polyimide molded body.

[0006] Therefore, the present invention aims to provide a manufacturing method that allows for easy molding of polyimide resin to obtain a polyimide molded article. [Means for solving the problem]

[0007] To achieve the above objectives, the inventors conducted extensive research and found that by using a molding raw material containing a polyimide precursor powder with an imidization rate below a predetermined value, fluidity can be ensured even at high temperatures, making it possible to easily manufacture polyimide molded articles.

[0008] In other words, the present invention is a method for producing a polyimide molded article, characterized by molding a molding raw material containing polyimide precursor powder and having an imidization rate of 40% or less by a transfer molding method. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a manufacturing method that allows for easy molding of polyimide resin to obtain a polyimide molded article. [Brief explanation of the drawing]

[0010] [Figure 1] This diagram illustrates the tabletization of polyamic acid powder; Figure 1(a) shows the state before pressurization, and Figure 1(b) shows the state after pressurization. [Figure 2] This diagram illustrates the molding flow using the transfer molding method. [Figure 3] This diagram illustrates the molding flow using the transfer molding method. [Figure 4] This diagram illustrates the molding flow using the transfer molding method. [Figure 5] This diagram illustrates the molding flow using the transfer molding method. [Figure 6] This diagram illustrates the molding flow using the transfer molding method. [Figure 7]It is a view showing an upper mold for a spiral flow test. Fig. 7(a) shows the upper surface, Fig. 7(b) shows the Y-Y cross section in Fig. 7(a), and Fig. 7(c) shows the Z-Z cross section in Fig. 7(a). [Figure 8] It is a graph showing the relationship between the imidization rate of polyamic acid and the resin weight by a spiral flow test. [Figure 9] It is a view showing an upper mold for a transfer molding test. Fig. 9(a) shows the upper surface, and Fig. 9(b) shows the Y-Y cross section in Fig. 9(a).

Embodiments for Carrying Out the Invention

[0011] Hereinafter, the method for producing the polyimide molded body of the present invention will be described in detail. In the method for producing a polyimide molded body of the present invention, molding is performed by a transfer molding method using a molding material containing powder of a predetermined polyimide precursor. The polyimide precursor is defined such that the imidization rate is 40% or less. Since the imidization rate is 40% or less, good fluidity is exhibited even in a high temperature range, and it has become possible to easily obtain a molded body. The imidization rate of the polyimide precursor is preferably 30% or less, and more preferably 10% or less.

[0012] Examples of the polyimide precursor include polyamic acid. Polyamic acid is, for example, a polycondensate of a diamine and an acid anhydride as shown in the following chemical formula.

[0013]

Chemical formula

[0014] The powder of the polyimide precursor can be prepared by dropping a diluted solution of polyamic acid in an aprotic polar solvent (hereinafter also referred to as "polyamic acid varnish") into an excessive amount of a poor solvent to precipitate spherical solids of polyamic acid having a size on the micrometer order. For the method of manufacturing such fine spherical polyamic acid, known dropping methods or atomization techniques of liquids such as ultrasonic atomization separation or two-fluid type (liquid mixing type) atomization separation can be used. The manufacturing method of polyamic acid using these atomization techniques will be described below.

[0015] As the polyamic acid varnish, for example, commercially available products obtained by diluting polyamic acid with N-methyl-2-pyrrolidone (NMP) such as PAA-1 (manufactured by T&K TOKA Co., Ltd.) may be used as they are. Alternatively, if necessary, commercially available polyamic acid varnish can be further diluted with a small amount of NMP or an aprotic polar solvent other than NMP, such as N,N'-dimethylformamide (DMF) and N,N'-dimethylacetamide (DMAC), and then used.

[0016] Next, a poor solvent such as water, alcohol, ketone, ether, or aromatic solvent is mixed with the polyamic acid varnish. Examples of alcohol include methanol, ethanol, and isopropanol (IPA). Examples of ketone include acetone, methyl ethyl ketone (MEK), and methyl isobutyl ketone. Examples of ether include tetrahydrofuran (THF), 1,4-dioxane, and butyl cellosolve. Examples of aromatic solvent include benzene and toluene. The addition amount of the poor solvent is in the range where the polyamic acid does not precipitate and atomization does not become difficult. For example, when adding IPA to polyamic acid varnish diluted with NMP, it is 0.5 to 2 weight times based on the polyamic acid varnish.

[0017] After mixing the poor solvent with the polyamic acid varnish, atomization separation is performed. When using ultrasonic atomization separation, atomization is performed by the tip amplitude by an ultrasonic vibrator. When using two-fluid type atomization separation, spraying introduction by gas-liquid two-fluid is performed at a spray pressure of 0.03 to 0.15 Pa. By performing such atomization separation, micrometer-sized droplets are formed.

[0018] Typically, polyamic acid varnish mixed with a poor solvent is introduced into the poor solvent simultaneously with the atomization process. The poor solvent used here is the same as that described above. When the polyamic acid varnish, which has formed droplets by atomization separation, is introduced into the poor solvent, the good solvent in the polyamic acid varnish diffuses into the poor solvent, forming fibrous spherical particles of polyamic acid. When the poor solvent becomes a non-flowing phase, the polyamic acid particles, which have a high specific gravity, settle by their own weight without agglomerating.

[0019] By filtering and drying solid polyamic acid particles formed in a poor solvent using a known method, spherical solids of polyamic acid having a particle size on the order of micrometers can be obtained.

[0020] As described above, the imidation rate of the polyamic acid used in the present invention is 40% or less. The imidation rate can be determined by measuring the IR spectrum of both the polyimide and its precursor using Fourier transform infrared spectroscopy (FT-IR) and observing the change in peak intensity. For example, in aromatic polyimides, the peak derived from the aromatic ring does not change before and after heating, so the peak derived from the imide group (1775 cm⁻¹) is obtained. -1 ) and the peak derived from the aromatic ring (1519cm) -1 It is determined from the peak intensity ratio of ).

[0021] Since imidation proceeds by heating the polyamic acid, the imidation rate can be controlled by adjusting the heating temperature. The imidation temperature is usually 100 to 400°C, with 140 to 350°C being preferred. Heating is carried out at a predetermined temperature while removing the water produced by the imidation reaction from the reaction system. This heating may be carried out under reduced pressure of 0.7 to 0.01 atmospheres to the extent that water can be efficiently removed.

[0022] The particle size of the spherical solid polyamic acid can be adjusted by changing the spray pressure and nozzle diameter of the two-fluid atomizing spray nozzle device. Furthermore, when polyamic acid varnish is diluted with a small amount of poor solvent and then dispensed dropwise using a Pasteur pipette, spherical solid polyamic acid with a particle size of approximately 3000 μm can be obtained. The 50% diameter (D50) of the spherical solid polyamic acid is between 10 and 3000 μm.

[0023] Polyamic acid powder, as a molding material, may be used as a raw material in its powder form to produce polyimide molded articles by the transfer molding method. However, using it as polyamic acid tablets molded into tablet form offers advantages in that it enables mass production of polyimide molded articles. The term "powder" may include powder, granules, and other forms. The term "tablet" may refer to solid objects of cylindrical, rectangular prism, disc, or irregular shape.

[0024] Polyamic acid tablets are obtained by pressing polyamic acid powder into a tablet shape using a tablet molding die. The tableting of polyamic acid powder will be explained with reference to Figure 1.

[0025] As shown in Figure 1(a), the tablet molding die 10 consists of a first wall die 12, a second wall die 13, a third wall die 14, a first air vent die 15, a pressure die 16, and a second air vent die 17. The upper part 15a of the first air vent die 15 and the lower part 17a of the second air vent die 17, which come into contact with the polyamic acid powder 20, are made of porous material. Specifically, the porous material is porous cemented carbide. By using porous material, it is possible to improve air venting when the tablet is pressurized. Specifically, voids inside the tablet are improved.

[0026] Using a press device, the pressure die 16 is pressurized as shown in Figure 1(b). For example, by applying pressure with a press load of 5 to 15 kN for about 1 to 10 seconds, polyamic acid tablets 20a can be obtained. The polyamic acid tablets 20a can be, for example, about 10 to 20 mm in diameter and 5 to 30 mm in height. The dimensions of the polyamic acid tablets 20a can be adjusted as appropriate by changing the die diameter and the amount of polyamic acid powder.

[0027] When tableting polyamic acid powder, at least one additive selected from the group consisting of curing agents, fillers, flame retardants, diluents, hygroscopic agents, mold release agents, coupling agents, colorants, and carbon components may be incorporated. For example, if silica powder is incorporated as a filler at a concentration of 10 to 90% by volume, the shrinkage of the final polyimide molded product can be suppressed, thereby reducing the occurrence of cracks. Examples of silica powder include molten spherical silica. The particle size of the silica powder can be appropriately selected within the range of 5 to 30 μm.

[0028] Referring to Figures 2-6, a molding method using polyamic acid tablets 20a via the transfer molding method will be described. First, as shown in Figure 2, the upper mold 30 and the lower mold 32 are positioned spaced apart. The upper mold 30 is provided with a predetermined shaped space 30a into which molten polyamic acid is filled. In the lower mold 32, polyamic acid tablets 20a are placed on a descending transfer 34. The upper mold 30 and the lower mold 32 can be heated in the range of 180 to 280°C.

[0029] In the upper mold 30, a combination of laminate film and porous cemented carbide may be used, as described in Japanese Patent Publication No. 2022-129893. By using porous cemented carbide, permeability of compressed gas during transfer and outgassing during molding is ensured.

[0030] As the lower mold 32 rises, the top surface of the upper mold 30 comes into contact with the bottom surface of the lower mold 32, as shown in Figure 3, and the two molds clamp together. The clamping force can be set appropriately within the range of 170 to 210 kN, but is not limited to this range.

[0031] After the upper and lower molds are clamped, the transfer 34 rises after approximately 5 to 10 seconds, as shown in Figure 4. The rising speed of the transfer 34 can be set appropriately within the range of 0.5 to 3.0 mm / sec, but is not limited to this range. The polyamic acid tablet 20a heats up, and the molten polyamic acid 20b begins to flow into the space 30a of the upper mold 30.

[0032] Next, as shown in Figure 5, the transfer 34 is raised further. This fills the entire space 30a in the upper mold 30 with molten polyamic acid 20b. After filling, the transfer 34 is raised further to apply pressure to the polyamic acid 20b in space 30a. The transfer thrust can be appropriately selected within the range of 1.806 to 3.284 kN, but is not limited to this range.

[0033] After a curing time of 40 to 3600 seconds, the polyamic acid in space 30a undergoes imidization through a condensation reaction. Subsequently, as shown in Figure 6, the lower mold 32 is lowered, opening the upper and lower molds 30 and 32. The cured polyimide molded body 24 is then placed on the top surface of the lower mold 32.

[0034] The imidization rate of the polyimide molded body 24 can be increased by subjecting it to an after-baking treatment. The after-baking treatment is a process (after-baking process) performed after the molding process in which the polyimide molded body 24 is molded by the transfer molding method. In the after-baking process, the polyimide molded body 24 is reheated at a temperature higher than the heating temperature in the molding process (reheating temperature).

[0035] In the after-bake process, the polyimide molded body 24 is placed in a separate reheating furnace (bake furnace) and reheated in that furnace. This makes it possible to achieve a 100% imidization rate. In the after-bake process, the molded body may be heated in the bake furnace or similar location at 200-350°C for 1-8 hours, for example, at 280°C for 2 hours, but is not limited to this range.

[0036] The molding raw material used in the method of the present invention exhibits excellent fluidity in the high-temperature range, making it possible to easily manufacture polyimide molded articles by the transfer molding method. This excellent fluidity is due to the imidization rate being 40% or less. [Examples]

[0037] The present invention will be specifically described below with reference to examples, but the scope of the present invention should not be interpreted as being limited by the specific examples shown below.

[0038] A polyamic acid powder with a predetermined imidization ratio is prepared as a polyimide precursor powder, and this is formed into tablets which are used as a molding raw material to produce a polyimide molded article by the transfer molding method.

[0039] <Preparation of polyamic acid powder> Using polyamic acid varnish (product name PAA-1, manufactured by T&KTOKA Co., Ltd.) as a raw material, the material was powdered based on the examples in Japanese Patent Publication No. 2022-134208. A 1:1 (mass ratio) mixed solution of N-methyl-2-pyrrolidone (NMP) and isopropanol (IPA) was prepared. A diluted polyamic acid varnish solution was prepared by mixing PAA-1 varnish with the mixed solution in a 1:2 (mass ratio).

[0040] The obtained polyamic acid varnish dilution was atomized and sprayed onto an IPA bath to precipitate the powder. Specifically, using a two-fluid atomizing spray nozzle device (product name SUJ22; manufactured by Spraying Japan Co., Ltd.), 750 g of the polyamic acid varnish dilution was atomized at a liquid pressure of 0.05 MPa and a spray pressure of 0.05 MPa. Approximately 1300 mL of IPA was contained in the IPA bath, and the spray was performed with a nozzle-to-liquid distance of 250 mm. The powder was repeatedly filtered and washed with IPA, and then dried under reduced pressure to prepare polyamic acid (PAA(1)) powder.

[0041] The imidization rate of polyamic acid (PAA(1)) was 0%. The imidization rate was determined using an infrared spectrometer (FT / IR-4200) manufactured by JASCO Corporation. Furthermore, the particle size distribution of PAA(1) powder was measured using the MT3300EXII particle size distribution analyzer manufactured by Microtrac-Bell Co., Ltd. The 50% diameter D of the PAA(1) powder was measured. 50 The size was 63-94 μm.

[0042] The above-mentioned PAA(1) was heat-treated to prepare polyamic acid powder with a predetermined imidization rate (21-92%). Specifically, about 20g of PAA(1) was spread in an aluminum rectangular container (15 x 25 cm) and heated in a heating device for a predetermined time at a predetermined temperature to obtain the following PAA(2) to PAA(8). The heating device used here was a constant-temperature dryer DY300 manufactured by Yamato Scientific Co., Ltd.

[0043] A polyamic acid (PAA(2)) with an imidization rate of 21% was obtained by heat treatment at 80°C for 30 minutes.

[0044] The mixture was heated at 80°C for 60 minutes, at 10°C for 30 minutes, and then at 120°C for 30 minutes to obtain polyamic acid (PAA(3)) with an imidization rate of 27%.

[0045] The mixture was heat-treated at 150°C for 15 minutes to obtain polyamic acid (PAA(4)) with an imidization rate of 49%.

[0046] A polyamic acid (PAA(5)) with an imidization rate of 42% was obtained by heat treatment at 130°C for 60 minutes.

[0047] The mixture was heated at 130°C for 60 minutes, 140°C for 15 minutes, and then at 150°C for another 15 minutes to obtain polyamic acid (PAA(6)) with an imidization rate of 54%.

[0048] The mixture was heat-treated at 150°C for 180 minutes to obtain polyamic acid (PAA(7)) with an imidization rate of 64%.

[0049] The mixture was heat-treated at 180°C for 15 minutes to obtain polyamic acid (PAA(8)) with an imidization rate of 92%.

[0050] <Tabletization of polyamic acid powder> As explained with reference to Figure 1, each polyamic acid powder was placed in a tablet molding die and molded into a tablet shape using a press device (owned by Kanak Co., Ltd.). As shown in Figure 1(b), the pressure die 16 was pressed with a press load of 7.5kN for 10 seconds to produce polyamic acid tablets 20a with a diameter of 13.8 mm and a height of 9 mm.

[0051] <Spiral Flow Test> The prepared polyamic acid tablets were used as the molding material, and a spiral flow test was performed using an ATOM-F1 press machine owned by M-Tex Matsumura Co., Ltd. Figure 7 shows the upper mold for the spiral flow test. As shown in Figure 7(a), the upper mold 40 for the spiral flow test is a mold in which the resin flows outward through a spiral-shaped channel 42. The dimensions of the channel 42 are 1.5 mm in width and 0.75 mm in depth, as shown in Figure 7(c). The filled portion within area A enclosed by the dashed line was extracted, and the weight of the molded body was measured to evaluate the fluidity. A higher weight of the filled portion indicates better fluidity.

[0052] The clamping force was set to 170 kN, the pressure to 10.8 MPa, and the curing time to 1800 s. The test conditions and resin flow weight are shown in the table below.

[0053] [Table 1]

[0054] It was confirmed that the resin was stable at approximately 42% or less in terms of imidation rate, and there were no problems with filling properties. At imidation rates of 49% and 54%, there were problems with filling properties, although the resin was fluid. Furthermore, at imidation rates of 64% or higher, there was almost no fluidity. Figure 8 shows the relationship between the imidation rate and the resin weight.

[0055] As shown in Figure 8, fluidity gradually deteriorates between an imidation rate of 42% and 49%. Fluidity deteriorates rapidly between an imidation rate of 54% and 64%, and the material becomes almost non-flowing. Based on these results, it was determined that an imidation rate of 40% or less is appropriate for molding using the transfer molding method, and the imidation rate of the polyimide precursor used in this invention was specified to be 40% or less.

[0056] <Transfer molding test> Polyamic acid (PAA(1)) tablets were used as the molding material, and tests were conducted using semiconductor molds owned by M-Tex Matsumura Co., Ltd. under the conditions shown in the table below. Figure 9 shows the upper mold for the transfer molding test. As shown in Figure 9, the upper mold 50 for the transfer molding test has a product section 52 and a cal section 54.

[0057] [Table 2]

[0058] The obtained molded bodies (test numbers 1-13) were evaluated by visual inspection of their appearance. If the molded body was completely filled to the corners, the appearance evaluation was marked "○"; if the corners were slightly incomplete, the appearance evaluation was marked "△". The results are summarized in the table above. In all cases, it was possible to obtain molded bodies.

[0059] In the following, transfer molding tests were conducted using polyamic acid tablets containing fillers. Polyamic acid tablets were prepared using the same method as described above, except that a predetermined amount of filler was added to the polyamic acid (PAA(1)) powder. Silica powder was used as the filler, and the amount added was 20 vol% or 80 vol% relative to the polyamic acid powder.

[0060] A transfer molding test was conducted using polyamic acid tablets containing a filler (silica) with the same mold as described above. The molding conditions are shown in the table below. In all cases, the mold temperature was set to 280°C. The obtained molded bodies were visually inspected and evaluated in the same manner as described above. The results are summarized below.

[0061] [Table 3]

[0062] Filling was confirmed with silica content of 80 vol% (test numbers 14, 15) and silica content of 20% or less (test number 16).

[0063] This invention makes it possible to easily mold polyimide resin and manufacture polyimide molded articles. [Explanation of symbols]

[0064] 10…Mold for tablet molding 12…First wall-side die 13…Second wall-side die 14...3 third wall-side die 15...1st air vent die 15a...First porous die 16...Pressure die 17...Second air vent die 17a...Second porous die 2 20...Polyamic acid powder 20a...Polyamic acid tablets 20b...Flowing polyamic acid 24...Polyimide molded body 30...Upper mold 30a...Space 32...Lower mold 34...Transfer 40...Upper mold for spiral flow testing 42...Flow channel 50…Upper mold for transfer molding 52…Product section 54…Cal

Claims

1. A method for producing a polyimide molded article, characterized by molding a molding raw material containing polyimide precursor powder and having an imidization rate of 40% or less by a transfer molding method.

2. The manufacturing method according to claim 1, further comprising the step of molding the polyimide precursor powder by pressing it with a porous body to obtain a tablet-shaped molding material.

3. The manufacturing method according to claim 2, wherein the polyimide precursor powder is pressed together with at least one selected from the group consisting of a curing agent, a filler, a flame retardant, a diluent, a hygroscopic agent, a mold release agent, a coupling agent, a coloring agent, and a carbon component.

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