JP2004221238A - Circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a high quality circuit board by stabilizing connection resistance of a double-sided circuit board and a multilayer substrate when a low compressibility prepreg sheet is employed. <P>SOLUTION: After circuit patterns formed on the opposite sides of a compressive prepreg sheet having a conduction hole and the conduction hole filled with conductive paste are compressed while sustaining a relatively low temperature condition, it is hot pressed by raising the temperature while sustaining the pressed state, thus obtaining a conduction connected circuit board. Consequently, the connection resistance is stabilized and a high quality circuit board is attained. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board formed by conductively connecting a plurality of circuit patterns on a surface layer of a double-sided circuit board or a multilayer circuit board.
[0002]
[Prior art]
2. Description of the Related Art In recent years, with the miniaturization and high density of electronic devices, there has been a strong demand for multilayered circuit boards not only for industrial use but also for consumer use.
[0003]
In such a circuit board, it is indispensable to newly develop a connection method for connecting inner circuit holes between a plurality of layers of circuit patterns and a highly reliable structure. A method for manufacturing a circuit board having a high density has been proposed. A method for manufacturing this circuit board will be described below.
[0004]
Hereinafter, a conventional method for manufacturing a double-sided circuit board and a multilayer circuit board, here, a four-layer circuit board will be described with reference to FIGS.
[0005]
First, a method for manufacturing a double-sided circuit board serving as a base of a multilayer circuit board will be described.
[0006]
3 (a) to 3 (g) are process sectional views of a conventional method for manufacturing a double-sided circuit board.
[0007]
Reference numeral 1 denotes a prepreg sheet, for example, a base material made of a composite material obtained by impregnating a thermosetting epoxy resin into an aromatic polyamide fiber of a nonwoven fabric having a thickness t1 (150 μm) and a compressibility of about 35%. The prepreg sheet 1 is made of a porous material having holes to obtain compressibility.
[0008]
Reference numerals 2a and 2b denote releasable films each having a Si-based release agent applied to one surface, and for example, polyethylene terephthalate is used. Reference numeral 3 denotes a through hole, which is filled with a conductive paste 4 that is electrically connected to metal foils 5a and 5b, such as Cu, to be attached to both surfaces of the prepreg sheet 1.
[0009]
First, as shown in FIG. 3 (b), through holes 3 are formed at predetermined positions of prepreg sheet 1 (FIG. 3 (a)) having release films 2a and 2b adhered to both sides by using a laser processing method or the like. Is formed. Next, as shown in FIG. 3C, the conductive paste 4 is filled in the through holes 3 by using a printing method or the like.
[0010]
Next, as shown in FIG. 3D, the release films 2a and 2b are peeled from both surfaces of the prepreg sheet 1.
[0011]
Then, as shown in FIG. 3E, the metal foils 5a and 5b are overlaid on both surfaces of the prepreg sheet 1. By heating and pressing in this state with a hot press, as shown in FIG. 3F, the thickness of the prepreg sheet 1 is compressed (t2 = about 100 μm) and the prepreg sheet 1 and the metal foils 5a and 5b are Are adhered, and the metal foils 5 on both sides are electrically connected by the conductive paste 4 filled in the through holes 3 provided at predetermined positions, that is, through holes.
[0012]
Then, as shown in FIG. 3 (g), the metal foils 5a, 5b on both sides are selectively etched to form circuit patterns 6a, 6b, thereby obtaining a double-sided circuit board.
[0013]
4A to 4D are process cross-sectional views showing a conventional method for manufacturing a multilayer substrate, and show a four-layer substrate as an example.
[0014]
First, as shown in FIG. 4 (a), the double-sided circuit board 10 having the circuit patterns 6a and 6b manufactured according to FIGS. 3 (a) to 3 (g) and the double-sided circuit board 10 manufactured according to FIGS. 3 (a) to 3 (d). Prepreg sheets 1a and 1b having through holes 3 with conductive holes filled with conductive paste 4 are prepared.
[0015]
Next, as shown in FIG. 4B, the metal foil 5b, the prepreg sheet 1b, the double-sided circuit board 10, the prepreg sheet 1a, and the metal foil 5a are positioned and stacked on the laminated plate in this order.
[0016]
Next, while the product is placed on a laminated plate (not shown), the thickness of the prepreg sheets 1a and 1b is compressed (t2) as shown in FIG. The double-sided circuit board 10 is bonded to the metal foils 5a and 5b, and the circuit patterns 6a and 6b are connected to the metal foils 5a and 5b by the conductive paste 4 in the inner via holes.
[0017]
Then, as shown in FIG. 4D, by selectively etching the metal foils 5a and 5b on both surfaces to form circuit patterns 6c and 6d, a four-layer substrate is obtained.
[0018]
Here, a four-layered multilayer board has been described. However, for a four- or more-layered multilayer board, for example, a six-layer board, a four-layer board obtained by a manufacturing method is used instead of a double-sided circuit board. 3 (a) to 3 (g)｝ may be repeated.
[0019]
Although the temperature profile of the hot press is not described, generally, in consideration of the number of stacking stages and quality, etc., a two-stage pressurization in which the pressure is low until the temperature is raised and then high as shown in FIG. In general, a two-stage heating method is used in which the temperature is maintained at about 130 ° C., at which the melt viscosity of the resin component of the prepreg sheet becomes near the lowest point, the temperature variation within the number of stacked sheets is absorbed and molded, and then the curing temperature is raised. Has been adopted.
[0020]
That is, emphasis is placed on setting and maintaining the temperature at which the thermosetting resin component in the prepreg starts curing (molding), that is, the temperature at which the viscosity of the thermosetting resin due to melting becomes minimum.
[0021]
As prior art document information related to the invention of this application, for example, Patent Document 1 is known.
[0022]
[Patent Document 1]
JP-A-6-268345
[Problems to be solved by the invention]
However, in the above-described conventional method for manufacturing a circuit board, the following problem occurs when the diameter of the through hole is reduced and the pitch of the through holes is narrowed in order to cope with finer circuit boards.
[0024]
That is, the prepreg sheet as a porous material has pores for obtaining compressibility, but when the proportion of the pores is high, a part of the conductive paste enters the pores. This is not preferable in terms of the resistance value of the conduction hole and the insulating property with the adjacent conduction hole. Therefore, although it is preferable to use a material having a low porosity, a material having a low porosity is a material having low compressibility.
[0025]
As shown in FIG. 6 (a), when the prepreg sheet 1 having a compression ratio of 35% is used, the conductive paste 4 is required to be sufficiently compressed before the resin component in the prepreg sheet flows in the surface direction. There is no outflow of the conductive paste 4 from the through hole, and a stable connection resistance value can be obtained.
[0026]
However, in the case of using a prepreg sheet having a low porosity and a low compression rate, that is, in the case of a prepreg sheet 1 having a compression rate of less than 10% as shown in FIG. The compressibility of the conductive paste decreases, and the pressing force between the conductive particles in the conductive paste also decreases.
[0027]
From this, when the resin component in the prepreg sheet 1 is melted by heating and pressing and flows in the plane direction, the conductive paste 4 flows out from the through-hole {the conductive paste flow 15 in FIG. 6B}. In some cases, the connection resistance value of the conduction hole is increased, and the quality of the circuit board is lowered.
[0028]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a circuit pattern formed on both sides of a prepreg sheet configured by impregnating a base material with a thermosetting resin, and a thermosetting resin formed in a through hole provided in the prepreg sheet. A conductive hole filled with a conductive paste containing a resin is a circuit board that is conductively connected by being heated and pressurized, and a softening point of the thermosetting resin in the conductive paste is: A circuit board characterized by being lower than the softening point of the thermosetting resin in the prepreg sheet, or a circuit pattern formed on both sides of a prepreg sheet formed by impregnating a thermosetting resin into a base material, A conduction hole formed by filling a conductive paste containing a thermosetting resin into a through-hole provided in the prepreg sheet is close to a softening point of the thermosetting resin in the prepreg sheet. The circuit board or the base material which is electrically connected by being heated and pressurized at a first heating temperature set at a predetermined temperature for a predetermined time and then heated and pressed at a second heating temperature higher than the heating temperature for a predetermined time. A circuit pattern formed on both sides of a prepreg sheet formed by impregnating a thermosetting resin, and a conductive paste containing a thermosetting resin filled in through holes provided in the prepreg sheet. The heating hole is heated and pressurized at a first heating temperature for a certain time, and heated and pressed at a second heating temperature higher than the first heating temperature for a certain time, and then heated to a temperature higher than the second heating temperature. Providing a circuit board which is conductively connected by being heated and pressurized at a third heating temperature for a certain period of time, whereby the through-hole is filled with the conductive paste even when a prepreg sheet having low compressibility is used. To stabilize the connection resistance was introducing hole, it is that it is possible to improve the quality of the circuit board.
[0029]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention relates to a first heating temperature set at a relatively low temperature, a second heating temperature higher than the first heating temperature, and a third heating temperature set at a curing temperature of the resin in the prepreg sheet. By increasing the temperature and applying heat and pressure, the adhesiveness between the outermost layer and the interlayer can be improved, and in the case of a circuit board having a conductive hole using a conductive paste, the connection resistance value is stabilized. It is possible to provide a high quality circuit board.
[0030]
The present invention also provides a prepreg sheet that is heated and pressurized at a predetermined pressure for a predetermined time while maintaining a first heating temperature set at a temperature (range) near the softening point of the impregnating resin constituting the prepreg sheet. Resin flow can be suppressed, and this is particularly effective when a prepreg sheet having a low vertical compression ratio is used.
[0031]
The present invention also relates to a double-sided circuit board in which metal foils are arranged on both sides of a prepreg sheet, or a multilayer in which metal foils are arranged on outermost sides after positioning and stacking the prepreg sheets on both sides of a circuit board having two or more layers. It is effective for a circuit board, and is heated and pressurized at a predetermined pressure for a certain period of time while maintaining a first heating temperature set at a temperature (range) near the softening point of the impregnating resin constituting the prepreg sheet. It has the effect of increasing the adhesion between the metal foil or a different material such as a prepreg sheet and a conductor circuit on a circuit board.
[0032]
In addition, the present invention is particularly effective in adopting a prepreg sheet having conductive holes filled with a conductive paste, so that only the conductive paste is intensively pressed and the contact with the metal foil is reduced. As the resin component in the conductive paste diffuses to the surface of the metal foil, the pressure contact force between the conductive particles increases and the conductive paste hardly flows out of the resin in the prepreg sheet, thereby stabilizing the connection resistance value. It has the action of:
[0033]
The present invention, the softening point of the thermosetting resin in the conductive paste, by employing a lower than the softening point of the resin in the prepreg sheet, the region where the melt viscosity of the resin component of the prepreg sheet is high, that is, the resin The prepreg sheet is easy to compress by making it a soft but hard to flow area, and the pressing force between the conductive particles in the conductive paste can be increased, and the deformation of the prepreg sheet decreases due to the melting of the resin of the prepreg sheet. Thus, the resin flow can be reduced, and the conductive paste is less likely to flow out.
[0034]
Further, at the first heating temperature, the softening of the resin in the conductive paste is promoted, and the viscosity of the conductive paste is set near the lowest point, so that the resin component in the conductive paste easily diffuses to the surface of the metal foil. In other words, it has an effect that the pressure contact force between the conductive particles can be increased.
[0035]
Further, the present invention has an effect that by using a prepreg sheet in a B-stage state having compressibility, it is possible to improve the interlayer adhesion of a double-sided or multilayer circuit board as a copper-clad laminate.
[0036]
Further, the present invention can realize the mechanical strength and the weight reduction of the circuit board by using the prepreg sheet using the nonwoven fabric of the aromatic polyamide fiber as the base material, and particularly, the diameter of the through hole can be reduced. In this case, the connection resistance of the conduction hole using the conductive paste is stabilized, and a high-quality circuit board can be provided.
[0037]
In addition, the present invention can improve the mechanical physicochemical strength of the circuit board by using a prepreg sheet employing a woven or nonwoven fabric of glass fiber as a base material to be formed, and in particular, a relatively vertical compression. Even when a prepreg sheet made of a material having a low rate is used and a through hole is provided in the prepreg sheet, the connection resistance of the conduction hole using a conductive paste can be stabilized and a high-quality circuit board can be provided. is there.
[0038]
(Embodiment)
Hereinafter, a circuit board according to an embodiment of the present invention will be described in terms of its manufacturing process.
[0039]
First, the method for manufacturing a double-sided circuit board in the embodiment of the present invention shown in FIGS. 1A to 1E is the same as the conventional method, and a multilayer circuit using the double-sided circuit board as a circuit board for an inner layer. Since the method of manufacturing the substrate is also substantially the same as the conventional method, the description is omitted here.
[0040]
Therefore, the process of heating and pressing by the hot press shown in FIG. 1F, which is a feature of the method of manufacturing a circuit board of the present invention, will be described in detail below.
[0041]
First, as a prepreg sheet 1, a 250 mm square, about 110 μm thick non-woven aromatic polyamide fiber was impregnated with a thermosetting epoxy resin having a softening point of about 70 ° C. at a temperature rise of 3 ° C./min. A material which is later compressed to about 100 μm and in a B stage (semi-cured) state was used.
[0042]
The conductive paste 4 filled in the through holes 3 is mainly composed of a conductive filler and a thermosetting epoxy resin (solvent-free type), and contains an acid anhydride-based curing agent. 12.5% by weight and 2.5% by weight were sufficiently kneaded with three rolls.
[0043]
As the conductive filler, Cu powder having an average particle size of 2 μm is used, but powder such as Au, Ag, or an alloy thereof may be used.
[0044]
In particular, a thermosetting epoxy resin (solvent-free type) having a lowest viscosity at 70 ° C. or lower due to softening and melting was selected.
[0045]
It is desirable that the softening point of the thermosetting epoxy resin (solvent-free type) contained in the conductive paste 4 be lower than the softening point of the thermosetting epoxy resin impregnated in the prepreg sheet 1.
[0046]
FIG. 2 is a diagram showing a press profile in the embodiment of the present invention, and relates to a temperature and pressure profile of a hot press.
[0047]
The number of sheets stacked in the hot press apparatus was set at 10 sheets / stage through a mirror plate made of stainless steel or the like having a thickness of about 1 mm (not shown). In the press profile, only the press temperature, the press pressure, and the prepreg sheet temperature are shown, and the vacuum pressure and the like are omitted for convenience of description.
[0048]
As shown in FIG. 2, the press profile of the present invention includes a first heating temperature (a temperature corresponding to the compression zone of the conductive paste in the figure) and a second heating temperature (the resin component in the prepreg sheet in the figure). ), And a third heating temperature (a temperature corresponding to the resin component curing zone in the prepreg sheet in the figure).
[0049]
In the temperature profile in the press profile, the zone of the first heating temperature was steeply raised from room temperature to 70 ° C., held for 30 minutes, and the pressure was set to 5 MPa when the temperature reached 70 ° C.
[0050]
In the zone of the first heating temperature, the prepreg sheet temperature gradually rises, converges to a temperature slightly lower than 70 ° C., and is maintained for about 10 minutes.
[0051]
In the zone of the first heating temperature, the thermosetting epoxy resin (solventless) component in the conductive paste starts to soften, and its viscosity reaches the lowest point. As a result, the conductive paste 4 is easily deformed by pressure and is slowly compressed. Therefore, the thermosetting epoxy resin (solvent-free type) is diffused from the through hole 3 into the metal foil, and at the same time, the pressing force between the Cu powders in the conductive paste can be increased.
[0052]
By the way, the prepreg sheet after 30 minutes at 70 ° C. at the stage of forming the circuit board was taken out, and the metal foil on both sides was peeled off and observed. It was found that the resin in the conductive paste had diffused into the metal foil, It was also confirmed that the product was slightly molded and the thickness was reduced.
[0053]
Here, the resin in the prepreg sheet whose softening point at a temperature rise of 3 ° C./min was about 70 ° C. was heated to 70 ° C., but the first heating temperature of the press profile of the present invention is the temperature of the prepreg sheet. May be set near the softening point of the resin, and even at a temperature of 70 ° C. or higher, the heating method may be changed to set the temperature near the softening point of the resin. Although the temperature in the low temperature range is set to 70 ° C. here, the temperature may be set according to the softening temperature of the resin component in the prepreg sheet.
[0054]
Next, in the temperature profile in the press profile, the zone of the second heating temperature is raised at a rate of 3 ° C./min to around 130 ° C., which is the resin component molding start temperature in the prepreg sheet, while maintaining the pressure. The temperature was maintained for about 20 minutes in order to reduce the temperature variation during the process and to form the material uniformly.
[0055]
Further, in the temperature profile in the press profile, in the zone of the third heating temperature, the temperature is raised at a rate of 3 ° C./min to 200 ° C., which is the curing temperature of the resin in the prepreg sheet, and after being held for about 60 minutes and cured. And cooling (not shown).
[0056]
The pressure profile was 5 MPa from when the temperature began to rise in the compression zone of the conductive paste to when it was being cooled.
[0057]
When using this press profile, the temperature of the prepreg sheet itself is maintained at a certain time while the temperature of each prepreg sheet converges around 70 ° C. of the first heating temperature, and then the second heating is performed. After maintaining the temperature for a certain time while slightly converging at around 130 ° C. of the temperature, the third heating temperature of 200 ° C. is maintained.
[0058]
Through the above manufacturing process, a circuit board of the present invention as shown in FIG. 1 (g) is obtained.
[0059]
Conducting holes (formed by filling conductive paste 4 into through-holes 3) of a double-sided circuit board {FIG. 1 (g)} and a four-layered multilayer circuit board (not shown) produced by the press profile of the present invention. The connection resistance value was improved by about 20% with respect to the circuit board manufactured by the conventional press profile.
[0060]
In addition, even when the area around the through-hole 3 was checked, it was visually confirmed that there was no outflow of the conductive paste.
[0061]
In the embodiment, the base material of the composite material in which the thermosetting epoxy resin is impregnated into the base material of the nonwoven fabric made of the aromatic polyamide fiber is used for the prepreg sheet. The prepreg may be a B-stage prepreg impregnated with a resin material mainly composed of a conductive resin.
[0062]
Alternatively, a prepreg obtained by impregnating a resin material mainly composed of a thermosetting resin into a woven or non-woven fabric mainly composed of glass fiber and forming a B-stage prepreg may be used. For example, in the case of using a prepreg having a compression ratio of less than 10% obtained by impregnating a thermosetting resin into a woven cloth mainly composed of glass fiber and forming a B-stage, the connection resistance value of the conduction hole is improved by about 30%. confirmed.
[0063]
In the embodiment, a four-layer circuit board has been described as a multilayer circuit board. However, a similar effect can be obtained with a circuit board having four or more layers.
[0064]
【The invention's effect】
As described above, the present invention provides a circuit pattern formed on both sides of a prepreg sheet and a conductive connection between a conductive hole provided in the prepreg sheet and a softening point of a thermosetting resin in a conductive paste. In a conductive connection between a circuit board selected from those having a softening point lower than the softening point of the thermosetting resin in the prepreg sheet, or a circuit pattern formed on both sides of the prepreg sheet and a conductive hole provided in the prepreg sheet, After maintaining the sheet at a relatively low temperature and compressing it under pressure, the temperature of the sheet is increased while maintaining the pressure, and the resin of the prepreg sheet is melted and cured to provide a circuit board formed. This stabilizes the connection resistance value with the pattern and improves the quality of the circuit board.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a method for manufacturing a circuit board according to an embodiment of the present invention. FIG. 2 is a view illustrating a press profile according to an embodiment of the present invention. FIG. 3 illustrates a conventional method for manufacturing a double-sided circuit board. FIG. 4 is a cross-sectional view showing a conventional method for manufacturing a four-layer multilayer circuit board. FIG. 5 is a view showing a conventional press profile. FIG. 6 is a view showing a problem in the conventional circuit board manufacturing method. Description]
1, 1a, 1b Pre-preg sheet 2a, 2b Release film 3 Through hole 4 Conductive paste 5a, 5b Metal foil 6a, 6b, 6c, 6d Circuit pattern 10 Double-sided circuit board

Claims (12)

A circuit pattern formed on both sides of a prepreg sheet formed by impregnating a base material with a thermosetting resin, and a conductive paste containing a thermosetting resin filled in through holes provided in the prepreg sheet. The formed conductive hole is a circuit board that is conductively connected by being heated and pressurized, and the softening point of the thermosetting resin in the conductive paste is the softening point of the thermosetting resin in the prepreg sheet. A circuit board characterized by being lower than the point. A circuit pattern formed on both sides of a prepreg sheet formed by impregnating a base material with a thermosetting resin, and a conductive paste containing a thermosetting resin filled in through holes provided in the prepreg sheet. After the formed conduction hole is heated and pressurized at a first heating temperature set to a temperature near the softening point of the thermosetting resin in the prepreg sheet for a certain time, a second heating temperature higher than the heating temperature The circuit board is electrically connected by heating and pressurizing for a certain time. A circuit pattern formed on both sides of a prepreg sheet formed by impregnating a base material with a thermosetting resin, and a conductive paste containing a thermosetting resin filled in through holes provided in the prepreg sheet. After the formed conduction hole is heated and pressurized at a first heating temperature for a certain time, and then heated and pressurized at a second heating temperature higher than the first heating temperature for a certain time, the second heating is performed. A circuit board electrically connected by being heated and pressurized at a third heating temperature higher than the temperature for a certain time; The circuit board according to claim 1, wherein the prepreg sheet is in a B-stage state having compressibility. The circuit board according to claim 4, wherein the base material constituting the prepreg sheet is a nonwoven fabric of an aromatic polyamide fiber. The circuit board according to claim 4, wherein the base material constituting the prepreg sheet is a woven or nonwoven fabric of glass fiber. A circuit board, wherein the prepreg sheet according to claim 6 has a lower compression ratio than the prepreg sheet according to claim 5. 4. The circuit board according to claim 1, wherein the conductive paste is mainly composed of a conductive filler and a non-solvent type thermosetting resin. 5. The heating and pressing lamination is performed by heating and pressing at a first heating temperature for a certain time while pressing at a predetermined pressure, and after heating and pressing for a certain time at a second heating temperature higher than the first heating temperature, 2. The circuit board according to claim 1, wherein the circuit board is heated and pressed at a third heating temperature higher than the second heating temperature for a predetermined time. 10. The circuit board according to claim 3, wherein the first heating temperature is set to a temperature near a softening point of the resin in the prepreg sheet. The circuit board according to claim 3 or 9, wherein the third heating temperature is a curing temperature of a resin in the prepreg sheet. 4. The circuit board according to claim 2, wherein the softening point of the thermosetting resin in the conductive paste is lower than the softening point of the thermosetting resin in the prepreg sheet.

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