A hole wall metallization paste and a method for preparing the same

Abstract

The application provides a hole wall metallization paste, which comprises tungsten powder, an organic medium, a second solvent and a thixotropic agent, the organic medium comprises a first solvent and a binder, and a preparation method of the hole wall metallization paste is provided. The hole wall metallization paste provided by the application has good printing performance, after printing, the metal paste on the hole wall is continuous and complete, the film thickness is uniform, the paste overflow on the hole surface is uniform, the film layer thickness is less than 10 um, the overflow is less than 110 um, the paste volatilization speed is moderate during the printing process, the screen plate is not blocked, batch printing can be carried out, the storage stability is good, the hole wall metal layer obtained after hole wall metallization has uniform film thickness and good continuity, and good interconnection and conduction effect is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of hole wall metallization slurry and its preparation method. BACKGROUND

[0002] SMD ceramic package base is a kind of three-dimensional interconnection structure formed by the ceramic green sheet printed with conductive pattern and punched with conductive via in a certain order and processed through atmosphere protection sintering process.In the manufacturing process of multilayer ceramic substrate (such as low temperature co-fired ceramic LTCC or high temperature co-fired ceramic HTCC), the hole wall of unsintered ceramic substrate (green ceramic) needs to be metallized, that is, a layer of metal conductive layer is formed on the hole wall.This process is crucial for realizing the electrical connection between different layers inside the substrate.

[0003] Hole wall metallization is generally carried out by screen printing the metallization slurry onto the hole wall of the green ceramic, then drying to remove the solvent in the slurry, curing to form a stable metal layer, and then high-temperature sintering.In the sintering process, the organic carrier in the slurry is burned off, and the metal particles are fused to form a continuous metal layer.

[0004] In the process of hole wall metallization, the metallization slurry flows from the conductive hole wall of the green ceramic during screen printing, and under the action of negative pressure, a uniform, delicate, continuous and complete metal slurry layer is formed on the conductive hole wall.However, the metallization slurry in the prior art has the following problems:

[0005] 1. Slurry clogging the via: During printing, if the flowability of the slurry is not properly controlled, the via may be completely clogged, affecting the effect of hole wall metallization.

[0006] 2. Uneven slurry hanging: Hole wall metallization requires uniform coating of slurry on the hole wall.If the viscosity of the slurry or the printing parameters are not properly set, the slurry hanging thickness may not be consistent, affecting the stability and reliability of electrical connection.

[0007] 3. Incomplete hole wall coverage: In some cases, the slurry may not be able to completely cover the hole wall, especially in some corners or edges of the hole wall, the metal slurry on the hole wall is not continuous and complete, which affects the continuity of the subsequent metal layer.

[0008] 4. Uniformity of slurry composition: If the uniformity of the slurry is not good, it may cause the slurry to be layered, resulting in uneven film thickness, and the film thickness of the upper and lower parts of the hole is not consistent.

[0009] 5. Hole surface paste overflow: During printing, the paste will overflow from the hole edge to the substrate surface outside the hole, which will affect the appearance quality of the substrate, cause material waste, increase the subsequent cleaning workload, contaminate the next printed pattern, and thus may affect the performance and reliability of the circuit board. Generally speaking, reducing the fluidity of the paste can reduce this overflow, but reducing the fluidity may cause the hole to be blocked or the screen to be blocked, and the film thickness on the hole wall is uneven.

[0010] 6. Storage stability: During long-term printing, the organic solvent may volatilize, causing changes in viscosity and fluidity, which may block the printing screen.

[0011] Therefore, it is necessary to develop and improve the hole wall metallization paste, and to provide a hole wall metallization paste with continuous and complete paste on the hole wall, uniform film thickness, uniform hole surface paste overflow, and good storage stability. SUMMARY

[0012] The purpose of the present application is to provide a hole wall metallization paste with good printing performance, which can achieve good interconnection and conduction effect.

[0013] The technical solution adopted by the present application is:

[0014] A hole wall metallization paste, comprising tungsten powder, an organic medium, a second solvent and a thixotropic agent, the organic medium comprising a first solvent and a binder, the first solvent or the second solvent being independently one or more of dibutyl phthalate, alcohol ester twelve, propylene glycol butyl ether, butyl carbitol acetate, polyol acetate, and solvent oil;

[0015] The binder is one or more of nitrocellulose, ethyl cellulose, and acrylic resin;

[0016] The thixotropic agent is tridecanol or polydiethylene glycol.

[0017] Further, the first solvent is preferably dibutyl phthalate and alcohol ester twelve; the second solvent is preferably alcohol ester twelve;

[0018] The binder is preferably nitrocellulose.

[0019] The thixotropic agent is preferably tridecanol.

[0020] Further, the mass ratio of the tungsten powder, the organic medium, the second solvent, and the thixotropic agent is 1000:100~150:50~60:8~15, and more preferably 1000:120:55:10.

[0021] In the organic medium, the mass ratio of the first solvent and the binder is 80~90:10~20, and preferably 90:10.

[0022] The first solvent is preferably a mixture of dibutyl phthalate and alcohol ester dodecyl in a mass ratio of 1:0.8-1.

[0023] The tungsten powder in the hole wall metallization slurry is preferably uniformly dispersed by using a dispersant and a third solvent.

[0024] The dispersant is preferably a phosphate surfactant.

[0025] The third solvent is acetone or anhydrous alcohol.

[0026] The mass ratio of the tungsten powder, the dispersant and the third solvent is 1000:5-10:450-600, preferably 1000:5:500. The particle size of the tungsten powder is not required, and is adapted to the particle size of the ceramic green body. For example, when the particle size of the ceramic green body is small, the particle size of the tungsten powder is also small, and when the particle size of the ceramic green body is large, the particle size of the tungsten powder is also large.

[0027] The hole wall metallization slurry can be prepared by the following method:

[0028] (1) The first solvent and the binder are mixed uniformly in a certain proportion to obtain an organic medium;

[0029] (2) The tungsten powder, the dispersant and the third solvent are ball milled to obtain a mixed solution, and the mixed solution, the organic medium, the second solvent and the thixotropic agent are stirred and mixed uniformly to obtain a mixed slurry.

[0030] The application further provides a preparation method of the hole wall metallization slurry.

[0031] (1) The first solvent and the binder are mixed uniformly in a certain proportion to obtain an organic medium;

[0032] (2) The tungsten powder, the dispersant and the third solvent are ball milled to obtain a mixed solution, and the mixed solution, the organic medium, the second solvent and the thixotropic agent are stirred and mixed uniformly to obtain a mixed slurry.

[0033] The dispersant is a phosphate surfactant, and the third solvent is acetone or anhydrous alcohol.

[0034] The mass ratio of the tungsten powder, the dispersant and the third solvent is 1000:5-10:450-600.

[0035] In step (2), the vacuum is preferably performed at a vacuum degree of -0.04 to -0.095 MPa, so that the third solvent is completely volatilized, the viscosity of the mixed slurry is increased, and the hole wall metallization slurry is formed.

[0036] The time of general vacuumizing is 0.5-1 hour.

[0037] In the step (2), the filtration is generally performed by using a 500-mesh filter screen to obtain the hole wall metallization slurry.

[0038] In the step (1), the ball milling generally needs 20-30 hours.

[0039] In the formula of the present application, the binder has a great influence on the effect of the hole wall metallization slurry after sintering, and a plurality of experiments show that the nitrocellulose has the best effect as the binder. The thixotropic agent and the solvent can affect the printing effect, such as the continuity, integrity, uniformity and overflow performance of the slurry. Therefore, the raw materials of the formula are screened in a large amount in the present application. The preparation process of the slurry can also affect the performance of the slurry. In the present application, the third solvent is first added to uniformly disperse the tungsten powder, and then the third solvent is completely volatilized by vacuumizing after the mixed solution is uniformly mixed with other solvents and organic medium, so that a uniform and stable slurry is formed. The tungsten powder is dispersed in advance by using the third solvent and the dispersant, which is beneficial to improve the storage stability of the slurry.

[0040] The hole wall metallization slurry provided by the present application has good printing performance. After printing, the metal slurry on the hole wall is continuous and complete, the film thickness is uniform, the slurry overflow on the hole surface is uniform, the film layer thickness is less than 10 um, the overflow is less than 110 um, the slurry volatilization speed is moderate during the printing process, the screen plate is not blocked, the slurry can be batch printed, the storage stability is good, the film thickness of the hole wall metal layer obtained after the hole wall is metallized is uniform, the continuity is good, and good interconnection and conduction effect is achieved. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 The overflow situation of the hole wall metallization slurry prepared for Example 1 after printing.

[0042] Figure 2 The overflow situation of the hole wall metallization slurry prepared for Comparative Example 2 after printing. DETAILED DESCRIPTION

[0043] The technical solutions of the present application will be further described below with specific examples, but the protection scope of the present application is not limited thereto.

[0044] Example 1

[0045] Dibutyl phthalate 50 g and alcohol ester twelve 40 g were mixed according to the proportion, then nitrocellulose 10 g was added, and stirring was performed at room temperature for 20 min to obtain a transparent and clear organic medium.

[0046] Tungsten powder 1000 g, phosphate surfactant 5 g and acetone 500 g were sequentially added to a roller ball mill tank according to the proportion, and the slurry was taken out after ball milling for 24 hours at a frequency of 20 HZ. The mixed solution was poured into a planetary stirrer.

[0047] Add 120g of the prepared organic medium, 55g of dodecayl alcohol ester, and 10g of tridecaol to a planetary mixer, stir, and evacuate the mixture for 0.5 hours at a vacuum degree of -0.04 to -0.095 MPa to remove acetone.

[0048] The slurry after vacuuming is filtered through a 500-mesh filter to obtain the pore wall metallized slurry.

[0049] The SMD ceramic package substrate product is metallized using screen printing. The ceramic strip is 0.254mm thick, and the hole diameter is 0.48mm. The specific process flow is as follows:

[0050] 1. Punch holes that require metallization on the ceramic green body.

[0051] 2. Holes corresponding to the ceramic green body are machined on the mask.

[0052] 3. Place the photomask on the printing platform.

[0053] 4. The paste is applied to the printing screen, printed, and dried. The drying process is: 70℃, 40 minutes.

[0054] The obtained metal layer on the pore wall has a uniform thickness of 6 μm, and the slurry overflow on the pore surface is as follows. Figure 1 As shown, the overflow is 80µm, the amount of overflow is very small and uniform, and the metal paste layer on the hole wall is continuous and intact.

[0055] Comparative Example 1:

[0056] 50g of dibutyl phthalate and 40g of dodecyl alcohol ester were mixed in a certain proportion, and then 10g of ethyl cellulose was added. The mixture was stirred evenly to obtain a transparent and clear organic medium.

[0057] Add 1000g of tungsten powder, 5g of phosphate surfactant, and 500g of acetone to a drum ball mill in the following proportions. After ball milling at 20Hz for 24 hours, the slurry is discharged and the mixed solution is poured into a planetary mixer.

[0058] Add 120g of the prepared organic medium, 55g of dodecayl alcohol ester, and 10g of tridecaol to a planetary mixer, stir, and evacuate the mixture under a vacuum of -0.04 to -0.095 MPa.

[0059] The slurry after vacuuming is filtered through a 500-mesh filter to obtain the pore wall metallized slurry.

[0060] The above hole wall metallization paste is printed on the SMD ceramic packaging base product, the process is the same as in Example 1, the film layer thickness of the obtained hole wall metal layer is 8um, the paste overflow on the hole surface is 130um, the paste dries slowly, which affects the printing of the next process. And ethyl cellulose as the binder, after sintering in a hydrogen atmosphere, carbon residue is left after sintering, which is not conducive to electrical conduction.

[0061] Comparative Example 2:

[0062] Dibutyl phthalate 50g, alcohol ester twelve 40g are mixed in proportion, then acrylic resin 10g is added, and stirring is uniform, to obtain transparent and clear organic medium.

[0063] Tungsten powder 1000g, phosphate surfactant 5g, and acetone 500g are sequentially added in proportion in a drum ball mill tank, the slurry is discharged after ball milling for 24 hours at a frequency of 20HZ, and the mixed solution is poured into a planetary stirrer.

[0064] The prepared organic medium 120g, alcohol ester twelve 55g, and tridecanol 10g are added to the planetary stirrer, stirring is performed, and the mixed solution is vacuumed under a vacuum degree of -0.04 — -0.095Mpa.

[0065] The vacuumed slurry is filtered with a 500-mesh filter screen to obtain the hole wall metallization paste.

[0066] The above hole wall metallization paste is printed on the product, the process is the same as in Example 1, the film layer thickness of the obtained hole wall metal layer is 12um, the overflow of the paste on the hole surface is as shown in Figure 2 It can be seen that the overflow is 140um, the overflow is uneven, and the hole wall and the hole surface metal layer have a wire drawing phenomenon, which is easy to contaminate the product, and the printing performance is poor.

[0067] Comparative Example 3:

[0068] Dibutyl phthalate 50g, alcohol ester twelve 40g are mixed in proportion, then nitrocellulose 10g is added, stirring is performed at room temperature for 20min, and transparent and clear organic medium is obtained.

[0069] Tungsten powder 1000g, phosphate surfactant 5g, and acetone 500g are sequentially added in proportion in a drum ball mill tank, the slurry is discharged after ball milling for 24 hours at a frequency of 20HZ, and the mixed solution is poured into a planetary stirrer.

[0070] The prepared organic medium 120g, alcohol ester twelve 55g, and polydiethylene glycol 400# 10g are added to the planetary stirrer, stirring is performed, and the mixed solution is vacuumed under a vacuum degree of -0.04 — -0.095Mpa.

[0071] The slurry after vacuumizing is filtered with a 500-mesh filter screen to obtain the hole-wall metallization slurry.

[0072] The hole-wall metallization slurry is printed on the product, and the process is the same as in Example 1. The film layer thickness of the obtained hole-wall metal layer is 15 um, and the overflow is 75 um, but the metal slurry is not printed on 1 / 3 of the hole-wall depth, and the product cannot realize interconnection conduction.

[0073] Comparative Example 4:

[0074] Dibutyl phthalate 50 g, propylene glycol butyl ether 40 g are mixed in a certain proportion, and then nitrocellulose 10 g is added. Stirring is carried out at room temperature for 20 min to obtain a transparent and clear organic medium.

[0075] Tungsten powder 1000 g, phosphate surfactant 5 g, and acetone 500 g are sequentially added in a certain proportion in a drum ball mill. After ball milling for 24 hours at a frequency of 20 HZ, the slurry is discharged, and the mixed solution is poured into a planetary stirrer.

[0076] The prepared organic medium 120 g, propylene glycol butyl ether 55 g, and tridecanol 10 g are added to the planetary stirrer, and the mixed solution is stirred and vacuumized at a vacuum degree of -0.04 to -0.095 Mpa.

[0077] The slurry after vacuumizing is filtered with a 500-mesh filter screen to obtain the hole-wall metallization slurry.

[0078] The hole-wall metallization slurry is printed on the product, and the slurry volatilizes quickly, blocking the screen plate, and batch printing cannot be carried out.

[0079] Comparative Example 5:

[0080] Dibutyl phthalate 50 g, butyl carbitol acetate 40 g are mixed in a certain proportion, and then nitrocellulose 10 g is added. Stirring is carried out at room temperature for 20 min to obtain a transparent and clear organic medium.

[0081] Tungsten powder 1000 g, phosphate surfactant 5 g, and acetone 500 g are sequentially added in a certain proportion in a drum ball mill. After ball milling for 24 hours at a frequency of 20 HZ, the slurry is discharged, and the mixed solution is poured into a planetary stirrer.

[0082] The prepared organic medium 120 g, propylene glycol butyl ether 55 g, and tridecanol 10 g are added to the planetary stirrer, and the mixed solution is stirred and vacuumized at a vacuum degree of -0.04 to -0.095 Mpa.

[0083] The slurry after vacuumizing is filtered with a 500-mesh filter screen to obtain the hole-wall metallization slurry.

[0084] The above hole wall metallization slurry is printed on the product, the process is the same as in Example 1, the film layer thickness of the obtained hole wall metal layer is 10 um, and the slurry overflow on the hole surface is 220 um, which is too large and pollutes the next printing pattern.

[0085] Comparative Example 6:

[0086] Dibutyl phthalate 50 g, polyol acetate 40 g are mixed in a certain ratio, and then nitrocellulose 10 g is added, stirred at room temperature for 20 min, and a transparent and clear organic medium is obtained.

[0087] In a drum ball mill, tungsten powder 1000 g, phosphate surfactant 5 g, and acetone 500 g are sequentially added in a certain ratio, and the slurry is discharged after ball milling for 24 hours at a frequency of 20 HZ. The mixed solution is poured into a planetary mixer.

[0088] In the planetary mixer, the prepared organic medium 120 g, polyol acetate 55 g, and tridecanol 10 g are added, stirred, and the mixed solution is vacuumed under a vacuum degree of -0.04 to -0.095 Mpa.

[0089] The vacuumed slurry is filtered with a 500-mesh filter screen to obtain the hole wall metallization slurry.

[0090] The above hole wall metallization slurry is printed on the product, the process is the same as in Example 1, the film layer thickness of the obtained hole wall metal layer is 10 um, and the slurry overflow on the hole surface is 220 um, which is too large and pollutes the next printing pattern.

[0091] Comparative Example 7:

[0092] Dibutyl phthalate 50 g, solvent oil 200# 40 g are mixed in a certain ratio, and then nitrocellulose 10 g is added, stirred at room temperature for 20 min, and a transparent and clear organic medium is obtained.

[0093] In a drum ball mill, tungsten powder 1000 g, phosphate surfactant 5 g, and acetone 500 g are sequentially added in a certain ratio, and the slurry is discharged after ball milling for 24 hours at a frequency of 20 HZ. The mixed solution is poured into a planetary mixer.

[0094] In the planetary mixer, the prepared organic medium 120 g, polyol acetate 55 g, and tridecanol 10 g are added, stirred, and the mixed solution is vacuumed under a vacuum degree of -0.04 to -0.095 Mpa.

[0095] The vacuumed slurry is filtered with a 500-mesh filter screen to obtain the hole wall metallization slurry,

[0096] The above hole wall metallization paste was printed on the product, the process was the same as in Example 1. The paste was easily delaminated, resulting in uneven film thickness, with the upper part of the hole having a film thickness of 15 um and the lower part having a film thickness of 5 um, and the paste overflowing the surface of the hole by 150 um.

Claims

1. A via wall metallization paste, characterized in that, The hole wall metallization slurry comprises tungsten powder, organic medium, second solvent and thixotropic agent, the organic medium comprises first solvent and binder; The first solvent is dibutyl phthalate and alcohol ester twelve; the second solvent is alcohol ester twelve; The binder is nitrocellulose; The thixotropic agent is tridecanol; The hole wall metallization slurry is prepared by the following method: (1) the first solvent and the binder are mixed uniformly according to the proportion to obtain the organic medium; (2) the tungsten powder, dispersant and third solvent are ball milled to obtain a mixed solution, the mixed solution, the organic medium, the second solvent and the thixotropic agent are stirred and mixed uniformly to obtain a mixed slurry, the third solvent is removed by vacuum extraction, and the hole wall metallization slurry is prepared by filtration.

2. The via wall metallization paste of claim 1, wherein, The mass ratio of the tungsten powder, the organic medium, the second solvent and the thixotropic agent is 1000:100-150:50-60:8-15.

3. The via wall metallization paste of claim 1, wherein, In the organic medium, the mass ratio of the first solvent and the binder is 80-90:10-20.

4. The via wall metallization paste of claim 1, wherein, The first solvent is a mixture of dibutyl phthalate and alcohol ester twelve according to the mass ratio of 1:0.8-1.

5. The via wall metallization paste of claim 1, wherein, The dispersant is a phosphate surfactant; the third solvent is acetone or anhydrous alcohol.

6. The hole wall metallization paste of claim 1, wherein, The mass ratio of the tungsten powder, the dispersant and the third solvent is 1000:5-10:450-600.

7. A method of preparing a via wall metallization paste according to any one of claims 1 to 6, wherein The method is: (1) the first solvent and the binder are mixed uniformly according to the proportion to obtain the organic medium; (2) the tungsten powder, dispersant and third solvent are ball milled to obtain a mixed solution, the mixed solution, the organic medium, the second solvent and the thixotropic agent are stirred and mixed uniformly to obtain a mixed slurry, the third solvent is removed by vacuum extraction, and the hole wall metallization slurry is prepared by filtration; The dispersant is a phosphate surfactant; the third solvent is acetone or anhydrous alcohol. The mass ratio of the tungsten powder, the dispersant and the third solvent is 1000:5-10:450-600.

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