JPH0653655A - Manufacture of circuit board with bump - Google Patents

Abstract

PURPOSE:To realize a method of manufacturing a circuit board with a bump which does not show any fluctuation in the shape, thickness and pitch of bumps. CONSTITUTION:Green sheets 210, 220, 230 to form ceramics substrate and an unsintered sheet 12 which is not sintered at the sintering temperature of the green sheet are prepared. A hole 10 is made on the unsintered sheet 12 and the hole 10 to form bumps is filled with a conductor 5. The green sheets 210, 220, 230 and an unsintered sheet 12 are laminated and thermally pressed to form a laminated plate. The laminated plate is heated and baked at the temperature for sintering the green sheet to obtain ceramics plates 21, 22, 23 and the conductor 5 is transferred and joined on the ceramics substrate to form a bump. Thereafter, the unsintered sheet is removed from the ceramics substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a circuit board with bumps, which has bumps for connecting to electronic parts and the like.

[0002]

2. Description of the Related Art Conventionally, a wire bonding method or a QFP surface mounting method has been mainly used for mounting an integrated circuit on a circuit board. However, due to the recent demand for smaller size and higher density, the flip-chip mounting method has attracted attention. In order to support flip chip mounting, it is necessary to form highly accurate electrodes (bumps) on the circuit board.

On the other hand, in order to mount the circuit board on another board (motherboard), conventionally, the DIP method or the PGA method has been adopted. However, due to the demand for smaller size, higher density, and lighter weight, there is a strong demand for a shift to the bump method that enables surface mounting. Here again, it is necessary to form highly accurate bumps on the circuit board. High-precision bumps mean bumps with small variations in diameter, thickness, and pitch.

The bump method is, as shown in FIGS. 7 and 8, in which convex bumps 57 are formed on the surface of the circuit board 9.
The bumps 57 and the pads 77 (FIG. 7) of the electronic component 7 or the bumps 57 and the pads 67 (FIG. 8) of the mother board 6 are connected and fixed by the solder 4. As a result, electrical connection between the circuit board 9 and the electronic component 7, or between the circuit board 9 and the motherboard 6 is achieved.

As a circuit board using the bump method,
For example, as shown in FIG. 9D, ceramic substrates 93, 92, 91 laminated in order from the bottom, through holes 90 formed in the ceramic substrates 91, 92, and formed on the through holes 90. Some have bumps 57. The conductor 5 is filled in the through hole 90. A wiring pattern 59 is formed on the ceramic substrates 92, 93.

Next, a method of manufacturing the circuit board with bumps will be described. First, as shown in FIG. 9A, green sheets 910, 920 and 930 for forming ceramic substrates 91, 92 and 93 are prepared, and through holes 915 and 925 are formed in the green sheets 910 and 920.
Next, the conductor 5 is filled in the through hole. Next, the wiring pattern 59 is formed on the green sheets 920 and 930.

Next, as shown in FIG. 9B, the green sheets 930, 920, and 910 are laminated in order from the bottom, these are aligned and thermocompression bonded to obtain a laminated plate. Next, as shown in FIG. 9C, the bumps 57 are formed by the conductor 5 on the green sheet 910. Next, the laminated plate is heated at the sintering temperature. As a result, the green sheets 930, 920 and 910 are sintered into the ceramic substrates 93, 92 and 91, and the bumped circuit board 9 as shown in FIG. 9D is obtained.

As a method of forming the bumps, there is a printing method of printing the conductor 5 on the green sheet 910.
Further, when the conductor 5 is filled in the silicone resin having the recessed portion is placed on the green sheet 910, and the conductor 5 is heated when the laminated plate is heated thereafter.
There is a resin transfer method for transferring to the 10 side.

[0009]

[Problems to be Solved] However, in forming bumps, in any of the above forming methods,
There are various problems described below. That is, in the above-described printing method, since the printing thickness varies, the bumps 57 have uneven thicknesses, and thin bumps 571 and thick bumps 572 and 573 are formed, as shown in the lower part of FIG.

Therefore, as shown in FIG. 10, the circuit board 9 having these bumps is attached to the pad 6 of the mother board 6.
When attempting to mount on 71, 672, 673, the gap 8 is generated between the thin bump 571 and the pad 671, so that they cannot be connected. Further, when mounting the electronic component 7 (FIG. 7), the same problem as described above occurs.

Therefore, it is necessary to make the bumps uniform in thickness. As a method for this, it is conceivable to polish the thick bumps with a surface grinder to make the thickness of the thin bumps uniform. However, carrying out this polishing work increases the number of manufacturing steps, and thus wastes both time and labor. Furthermore, due to variations in firing shrinkage of the laminated plate, as shown in FIG.
The pitch of the bumps 574, 575, 576 may not match the pitch of the motherboard pads 674, 675, 676.

Next, in the above resin transfer method, the silicone resin is deformed when the bump is transferred to the ceramic substrate side. Therefore, the bump formation position may deviate from the through hole position. Therefore, a method of brazing a metal solid after sintering the green sheet into a ceramics substrate can be considered. According to this method, it is possible to reduce variations in the shape of the bump and the thickness and pitch thereof.

However, in this method, the brazing jig to be used is expensive, and cracks may occur due to the difference in coefficient of thermal expansion. In view of such problems, the present invention aims to provide a method for manufacturing a circuit board with bumps, which does not cause variations in the shape, thickness and pitch of the bumps.

[0014]

According to the present invention, there is provided a green substrate for forming a ceramic substrate and a green sheet for forming the ceramic substrate, in a method of manufacturing a circuit board with bumps, which comprises a ceramic substrate and bumps protruding from the surface of the ceramic substrate. A preparatory step of preparing an unsintered sheet for bump formation that does not sinter at a sintering temperature, and a conductor filling step of forming a hole in the unsintered sheet and filling the hole with a conductor for bump formation A circuit forming step of arranging a wiring pattern on the surface of the green sheet, a laminating step of laminating the unsintered sheet on the green sheet, and thermocompression-bonding the laminated sheet; A ceramic substrate is obtained by heating at a temperature at which sinters, and the above conductor is transferred and bonded onto the ceramic substrate to form bumps. Extent and, in the production method of the bumps circuit board, comprising the removal to obtain a circuit board with the bump by removing a green sheet from the ceramic substrate.

What is most noticeable in the present invention is that the conductor for bump formation is filled in the hole of the unsintered sheet, the unsintered sheet is laminated on a green sheet, and the conductor is heated. Bonding to the green sheet and firing the green sheet to form a ceramic substrate, and then removing the unsintered sheet.

The unsintered sheet does not sinter due to thermocompression bonding in the laminating step and heating in the heating step, and does not undergo deformation such as expansion and contraction. The unsintered sheet does not prevent evaporation of the binder contained in the green sheet when laminated on the green sheet. The green sheet preferably has a thickness of 0.1 to 1.0 mm. Thickness 0.1
If it is less than mm, the green sheet may peel off during firing. Further, when the thickness exceeds 1.0 mm, there is a problem of insufficient binder removal.

As the unsintered sheet, a sheet material such as alumina, zirconia, or mullite and a binder are mixed. Alumina is the most preferable sheet material. The green sheet is preferably a material for a low temperature firing substrate that can be sintered at 1000 ° C or lower.

The conductor does not adhere to the green sheet when heated. As the conductor, a paste prepared by mixing silver, copper or the like with a binder is used. Further, it is preferable that the conductor does not contain frit. Since the conductor without frit does not adhere to the unsintered sheet, it is easy to separate the unsintered sheet and the bump in the removing process.

In the circuit forming process, a conductor is used to form a wiring pattern on the surface of the green sheet,
Get the circuit board. If necessary, a through hole is provided in the green sheet, and the through hole is filled with a conductor. As a result, the wiring pattern of each ceramic substrate can be electrically connected. In the removing step, the unsintered sheet is removed by hitting the circuit board or rubbing the unsintered sheet.

[0020]

In the present invention, a hole for forming a bump is formed in an unsintered sheet that does not sinter at the sintering temperature of the green sheet, and a conductor is filled in the hole.
The conductor adheres to the green sheet when the green sheet is heated. Therefore, the conductors filled in the holes of the green sheet are formed as bumps on the ceramic substrate.

The unsintered sheet is heated by the above-mentioned heating.
The binder in the unsintered sheet is thermally decomposed and becomes very brittle and easily peeled off. Therefore, in the removing step, the green sheet can be easily removed from the circuit board and the bumps by an extremely simple operation such as lightly tapping the circuit board and rubbing with a brush.

Further, the unsintered sheet for forming bumps is not deformed during thermocompression bonding and heating with the green sheet. Therefore, it is possible to manufacture a circuit board with bumps that does not have variations in the shape of the bumps and in the thickness and pitch thereof. Therefore, according to the present invention, it is possible to provide a method for manufacturing a circuit board with bumps, which does not cause variations in the shape, thickness and pitch of the bumps.

[0023]

EXAMPLES Example 1 An example according to the present invention will be described with reference to FIGS. The circuit board 2 manufactured according to this example has the structure shown in FIG.
As shown in (b), convex bumps 50 are formed on the ceramic substrate 21. The circuit board 2 includes ceramic boards 23, 22, 21 that are stacked in order from the bottom.
And a through hole 20.

The through hole 20 is formed on the ceramic substrate 2
The through holes 215 and 225 are formed in the holes 1 and 22. The conductor 5 made of silver paste is filled in the through hole 20. The bump 50 is formed right above the through hole 20. A wiring pattern 59 is formed on the ceramic substrates 22 and 23.

A method of manufacturing the circuit board with bumps will be described. First, in a preparatory step, as shown in FIG. 1A, green sheets 210, 220, 230 for forming ceramic substrates 21, 22, 23, and an unsintered sheet 11 that does not sinter at the sintering temperature of the green sheets 11 , 1
Prepare 2 and 13. As will be described later, among these, the unsintered sheet 12 is a bump-forming unsintered sheet.
The green sheet is a material for low temperature firing substrate that is sintered at 1000 ° C. or lower.

In producing the above green sheet, first, 60% by weight of CaO--Al ₂ O ₃ --SiO ₂ --B ₂ O ₃ system glass (hereinafter referred to as "%") and 40% of alumina.
The mixed powder of ceramic substrate material consisting of
Add a binder and a plasticizer and knead to make a slurry. Then, using a conventional doctor blade method, a green sheet having a thickness of 0.3 mm is prepared using the above slurry.

In producing the green sheet, alumina powder is mixed with a binder to form a paste. Next, a 0.2 mm-thick unsintered sheet is prepared using the above-mentioned paste by using a conventional doctor blade method. The unsintered sheet does not undergo deformation such as expansion and contraction due to thermocompression bonding in the laminating process and heating in the heating process. The unsintered sheet does not prevent evaporation of the binder contained in the green sheet when laminated on the green sheet.

Next, in the conductor filling step, as shown in FIG.
As shown in (b), the green sheets 210, 220 and the green sheet 12 for forming bumps are provided with through holes 215,
225 and hole 10 are drilled. Then, FIG. 2 (a)
As shown in FIG. 5, the conductor 5 is filled in the through holes 215 and 225 and the hole 10.

The conductor 5 does not adhere to the green sheet when the green sheet is heated. As the conductor 5,
A silver-based conductor containing no frit and a binder are mixed to form a paste. Next, in the circuit forming step, as shown in FIG. 2B, the wiring pattern 59 is formed on the green sheets 220 and 230.

Next, in the laminating step, as shown in FIG. 3A, the green sheet 2 for pressing and the green sheet 2 for pressing are pressed.
30, 220, 210, unsintered sheet 1 for bump formation
2. The green sheets 11 for pressing are laminated in order from the bottom, aligned, and thermocompression bonded to obtain a laminated plate. The pressing non-sintered sheets 11 and 13 are the same as the bump non-sintered sheet 12 except that the conductor 5 is not filled. The conditions for thermocompression bonding are a temperature of 100 ° C and a pressing force of the laminate of 50 kg / c
m ² and run for 20 seconds.

Next, in the heating step, the laminated plate is heated at a temperature at which the green sheet is sintered under conditions of a maximum temperature of 900 ° C. and a holding time of 20 minutes. As a result, the green sheets 230, 220, 210 are sintered to obtain the ceramic substrates 23, 22, 21. Further, the conductor 5 of the unsintered sheet 12 is transfer-bonded onto the ceramic substrate 21 to form the bump 50 on the ceramic substrate 91.

Next, in the removing step, the unsintered sheet 1
1, 12, 13 are peeled off and removed with a brush. Further, the alumina powder remaining on the ceramic substrate is removed by ultrasonic cleaning. As a result,
The circuit board 2 shown in FIG. 3B is obtained.

Next, the function and effect of this example will be described. In the manufacturing method of the present example, bumps are formed with holes 10 in the green sheet 12 that does not sinter at the sintering temperature of the green sheet, and the conductors 5 are filled in the holes 10. The conductor 5 is bonded to the softened ceramic substrate 21 without adhering to the green sheet 12 during the heating process. Therefore, the conductor 5 can form the bump 50 on the ceramic substrate 21.

Further, the unsintered sheets 11, 12, 1 of this example
In No. 3, the binder in the unsintered sheet is thermally decomposed by the above heating, and becomes very brittle and easily peeled off. Therefore, in the removing step, the green sheet can be easily removed from the circuit board and the bumps by an extremely simple operation such as tapping the circuit board with light and rubbing with a brush. Further, since the unsintered sheet 12 for bump formation does not deform during thermocompression bonding and heating of the green sheet, variations in the shape of the bump 50 and its thickness and pitch do not occur.

Example 2 In this example, as shown in FIG.
Only the unsintered sheet 12 for forming bumps is laminated on the sheet 10. Others are the same as in the first embodiment. Also in this example, the same effect as that of the first embodiment can be obtained.

Example 3 In the circuit board with bumps of this example, the bump 500 is larger than the diameter of the through hole 20, as shown in FIG. 5 (b). In forming the bump 500,
As shown in FIG. 5A, a hole 10 having a diameter larger than that of the through hole 20 is formed in the green sheet 12.
Others are the same as in the first embodiment. Also in this example, the same effect as that of the first embodiment can be obtained.

Embodiment 4 In the circuit board with bumps of this embodiment, as shown in FIG. 6B, bumps 51 are formed not only on the through holes 20 but also on the wiring patterns 59. ing. The circuit board 2 is composed of a single-layer ceramic substrate 24, and a wiring pattern 59 is formed on the ceramic substrate 24. The through hole 245 is the through hole 20. Others are the same as in the first embodiment.

In manufacturing the above-mentioned circuit board, as shown in FIG. 6A, in the preparation step, the green sheet 240 and the unsintered sheets 11, 12, 13 are prepared. Next, in the conductor filling process, the green sheet 2
40 through holes 245 and green sheet 12 through holes 10,
100 is bored, and the conductor 5 is filled in the through hole and the hole. Next, in the circuit forming step, the wiring pattern 59 is formed on the green sheet 240.

Next, in the laminating step, as shown in FIG. 6A, the unsintered sheet 13 for pressing, the green sheet 240, the unsintered sheet 12 for bump formation, and the unsintered sheet 11 for pressing. Are laminated in order from the bottom. Hereinafter, Example 1
A circuit board is manufactured by a method similar to. Also in this example, the same effect as that of the first embodiment can be obtained.

Example 5 With respect to the circuit boards with bumps (Examples 1 to 3), the bump thickness, pitch, and connection reliability when the bumps were connected to the pads of the mounted body via solder were evaluated. As a comparative example, the green sheets 210 and 22
Through holes 215, 225, and 235 were bored at 0 and 230, respectively, the conductor 5 was filled in the through holes, and then these were thermocompression bonded to obtain a laminated plate. Then, the conductor 5 was repeatedly printed 5 times on the laminated plate to form bumps 50 (see FIG. 9C).

Others are the same as in the first embodiment. The evaluation results are shown in Table 1. In the table, the variation in bump height means the absolute value of the difference between the maximum bump heights. Bump pitch variation is (maximum value-minimum value) x 1
It is calculated by 00 / (2 × average value). Bad soldering means bad connection between bumps and pads.

As can be seen from Table 1, Examples 1-3
, The bump height variation was 21 μm or less, the bump pitch variation was 0.11% or less, and no soldering failure occurred. In the above-mentioned evaluation, the comparative example has remarkably large variations as compared with Examples 1 to 3, and defective soldering also occurred.

[0043]

[Table 1]

[Brief description of drawings]

FIG. 1 is a manufacturing process explanatory view showing the manufacturing method of Example 1.

FIG. 2 is an explanatory view of the manufacturing process subsequent to FIG.

FIG. 3 is an explanatory view of the manufacturing process subsequent to FIG.

FIG. 4 is a manufacturing process explanatory view showing the manufacturing method of the second embodiment.

FIG. 5 is a manufacturing process explanatory view showing the manufacturing method of Example 3;

FIG. 6 is a manufacturing process explanatory view showing the manufacturing method of Example 4;

FIG. 7 is an explanatory diagram showing a state in which electronic components are mounted on a circuit board with bumps.

FIG. 8 is an explanatory diagram showing a state in which a circuit board with bumps is mounted on a motherboard.

FIG. 9 is a manufacturing process explanatory view showing a manufacturing method of a conventional example.

FIG. 10 is an explanatory view showing a defective state in which a circuit board with bumps on which bumps are formed by a printing method according to a conventional example is mounted on a motherboard.

FIG. 11 is an explanatory view showing another defective state in which the circuit board with bumps on which the bumps are formed by the printing method according to the conventional example is mounted on the motherboard.

[Explanation of symbols]

10. ． ． Hall, 12. ． ． Unsintered sheet for bump formation, 11, 13. ． ． Unsintered sheet for pressing, 1. ． ． Circuit board with bumps, 20. ． ． Through holes, 21, 22, 23, 24. ． ． Ceramic substrate, 210, 220, 230, 240. ． ． Green sheet, 215, 225, 235, 245. ． ． Through hole, 5. ． ． Conductor, 50, 500, 51. ． ． Bump, 59. ． ． Wiring pattern,

Claims (4)

[Claims] 1. A method of manufacturing a circuit board with bumps, comprising: a ceramic substrate; and bumps protruding from the surface of the ceramic substrate, wherein a green sheet for forming the ceramic substrate and a sintering temperature of the green sheet are used for firing. A preparatory step of preparing an unsintered bump-forming green sheet, a conductor filling step of forming a hole in the green sheet, and filling the hole with a bump-forming conductor; A circuit forming step of arranging a wiring pattern on the surface; a laminating step of laminating the green sheet on the green sheet to obtain a laminated sheet by thermocompression bonding; and a temperature at which the green sheet sinters the laminated sheet. A heating step for obtaining a ceramics substrate by heating at the same time and transferring and bonding the conductor onto the ceramics substrate to form bumps; A method of manufacturing a circuit board with bumps, comprising: a step of removing the unsintered sheet from the ceramic substrate to obtain the circuit board with bumps. 2. The method for manufacturing a circuit board with bumps according to claim 1, wherein the green sheet is a material for a low temperature firing substrate that can be sintered at 1000 ° C. or lower. 3. The method for manufacturing a circuit board with bumps according to claim 1, wherein the unsintered sheet is an alumina sheet made of alumina powder and an organic binder. 4. The method for manufacturing a circuit board with bumps according to claim 1, wherein the conductor does not contain frit.