JP4876997B2 - Manufacturing method of ceramic multilayer substrate - Google Patents

Description

  The present invention relates to a method for manufacturing a ceramic multilayer substrate. In particular, the present invention relates to a method for forming a conductor layer having a smooth surface.

  A conventional method for manufacturing a ceramic multilayer substrate is shown in FIG. In a first step shown in FIG. 8, a plurality of ceramic green sheets 3 having conductor patterns 1 and vias 2 formed therein are stacked and fired to obtain a sintered substrate 7. Next, in the second step shown in 16, the conductors 13 and 14 are printed at desired positions on the surface layers 11 and 12 on both surfaces of the sintered substrate 7 to obtain the ceramic multilayer substrate 15. Thereafter, in a third step shown at 20, conductors 21 and 22 are further printed on the conductors 13 and 14 to obtain the ceramic multilayer substrate 19. Thereafter, in the fourth step shown in 28, the ceramic multilayer substrate 19 obtained in the third step is fired at about 850 ° C. to obtain a finished ceramic multilayer substrate 27.

  In the conventional manufacturing method, a thick film material is used for the conductors 13 and 14 in the second step. However, when a thick film material is used, (1) the adhesion strength of the conductor (electronic components connected to the conductor and -This refers to the strength at which a lead terminal is broken by applying force in the vertical or horizontal direction.) (2) Resistance to solder erosion (when soldering an electronic component or lead terminal to a conductor. In addition, the film thickness must be increased in order to improve the conductor material (eg, Ag, Cu) diffused in the solder and eliminate the component land. This thickness is required to be 10 μm or more for Ag-based conductors, and more preferably 15 μm or more. For this reason, the conductors 21 and 22 are further printed on the conductors 13 and 14 by using the third step to ensure a necessary thickness. The conductors 21 and 22 are made of the same material as the conductors 13 and 14, and the conductors 13 and 14 and the conductors 21 and 22 were fired at the same time.

  Further improvement of solder erosion resistance and solder wettability (Generally, when a thick film material is used to form a conductor, several percent of glass is added to improve the adhesion strength between the sintered substrate and the conductor. In this case, Ni / Au plating 23 and 24 may be performed in the fifth step shown in FIG.

  However, in such a conventional method for manufacturing a ceramic substrate, many depressions are generated on the surfaces of the vias (2a, 2b) located on the surface layer. As the cause of the depression, (1) variation in the shrinkage ratio of the conductive paste occurs due to variation in the ratio of the inorganic components in the conductive paste forming the via. (2) The conductive paste is generally formed by a printing method, but the filling amount of the conductive paste into the through holes varies due to variations in printing conditions. The conductors 13 and 14 are printed and formed using conductive paste in the second step and the third step on the upper part of the via recess located on the surface layer generated due to the above-described causes, and further the conductor 21 as necessary. , 22 are printed and formed. Since the conductors 13 and 14 simultaneously print and form fine wiring on the surface layer, the viscosity of the conductive paste used is usually about 200 to 400 Pa · sec. However, since this conductive paste has a high viscosity, it is impossible to completely fill the via recess in the surface layer, and a space (via void) is generated between the surfaces of the vias 2 a and 2 b and the conductors 13 and 14. This via void cannot be filled even if the conductors 21 and 22 are stacked and printed. This via void causes indentations and cracks on the surface of the conductor layer from the via void between the surfaces of the vias 2a and 2b and the conductors 13 and 14 in the subsequent baking process of the conductive paste, thereby lowering the substrate quality. was there.

  In order to improve solder erosion resistance and solder wettability, electroless Ni / Au platings 23 and 24 may be formed on the surfaces of the conductors 21 and 22, but the surfaces of the vias 2a and 2b and the conductors 13 and 22 may be formed. When the Ni plating solution enters and remains in via voids between 14 and depressions and cracks generated on the surface of the conductor on the surface layer portion, a state where no Au plating is formed (no plating) occurs. In the non-plated portion, since Ni is exposed on the surface layer portion, corrosion occurs and solder wettability is deteriorated. In addition, plating liquid, cleaning liquid, etc. accumulate in via voids between the surfaces of the vias 2a and 2b and the conductors 13 and 14 and indentations and cracks generated on the conductor surface of the surface layer portion. During the reflow process such as solder mounting, the plating solution and the cleaning solution are vaporized to cause a defect (solder void) that forms a void inside the solder.

  Further, when a via void is generated between the surface of the vias 2a and 2b and the conductors 13 and 14, the connection strength between the vias 2a and 2b and the conductors 13 and 14 is lowered. Therefore, the connection reliability between the vias 2a and 2b and the conductors 13 and 14 is reduced. Sex is reduced.

As a solution to this problem, a polyimide resin film is formed on the void generated in the conductor filling portion of the via hole of the ceramic multilayer substrate, dry etching with oxygen plasma is performed, and the polyimide resin film other than the inside of the void is removed, A method for flattening the substrate surface is disclosed (for example, see Patent Document 1). In addition, in a ceramic substrate having a via conductor or electrode conductor formed on the surface layer, there is a method for preventing the ingress of plating solution by covering at least a part of the via conductor or electrode conductor with a metal foil (see, for example, Patent Document 2). ).
Japanese Patent Application Laid-Open No. 7-307566 JP 2004-241432 A

  However, in the method of Patent Document 1, since the material for flattening the surface of the void generated in the conductor filling portion of the via hole is polyimide resin, Ag is sintered on the surface of the ceramic multilayer substrate at a high temperature, for example, 850 ° C. A conductor cannot be formed. In addition, the construction method of Patent Document 2 has a structure in which a via conductor and a metal foil are bonded, but the via conductor is usually a sintered body using metal powder and has a space inside, but the metal foil is dense. Even if the same metal is used between the via conductor and the metal foil, a difference in coefficient of linear expansion occurs. In the case of a ceramic multilayer substrate, there is usually a step of firing at a high temperature of about 850 ° C. such as printing resistance, overcoat glass, etc. after forming the electrode conductor on the surface, so that the linear expansion between the via conductor and the metal foil Due to the difference in the coefficients, peeling occurs between the via conductor and the metal foil, which causes a problem of reducing connection reliability. Also, the process of affixing a metal foil and a photosensitive film to a base film, the process of masking the base with a glass original plate, exposing and developing, the process of etching the metal foil, Compared with the step of roughening, the step of transferring the metal foil, and the print forming method, there is a problem of having many steps.

  In order to solve the above-mentioned conventional problems, the present invention aims to provide a method of manufacturing a ceramic substrate that can suppress a depression of a via on the surface of a ceramic multilayer substrate and create a smooth conductor layer even with a simple process. is there.

In order to solve the above-described conventional problems, a method for manufacturing a ceramic substrate of the present invention includes a through-hole forming step of forming a through-hole in a ceramic green sheet, and a via that forms a via using a conductive paste in the through-hole. A filling step, a conductive pattern forming step of forming a predetermined conductive pattern on the ceramic green sheet using a first conductive paste, and a laminate forming step of creating a laminate by laminating a plurality of the ceramic green sheets And a first firing step of firing the laminated body to obtain a sintered substrate, and first printing for printing a second conductor on the via surface of the sintered substrate using a second conductive paste And a second firing step of firing the sintered substrate on which the second conductor is printed,
Characterized in that comprising a second printing step of the third conductor formed by printing using a third conductive paste on the surface of the second conductor.

Furthermore, the method for manufacturing a ceramic substrate of the present invention includes a through hole forming step of forming a through hole in the ceramic green sheet, a via filling step of forming a via using a conductive paste in the through hole, and the ceramic green sheet. A conductive pattern forming step of forming a predetermined conductive pattern using a first conductive paste, a first laminate creating step of creating a laminate by laminating a plurality of ceramic green sheets, and the laminate A second laminate forming step of forming a second laminate by disposing a constraining sheet mainly composed of an inorganic composition that does not sinter and shrink at the sintering temperature of the ceramic green sheet on both sides of the ceramic green sheet; After firing the laminate of 2 at the sintering temperature of the ceramic green sheet, the first sintered substrate forming step of removing the restraining sheet and obtaining a ceramic sintered substrate, and the ceramic Tsu firing a first printing step of the second conductive layer formed by printing with a second conductive paste via the surface of the click sintered substrate, the sintered ceramic substrate having the second conductors are printed A second sintered substrate forming step and a second printing step of printing and forming the third conductor on the surface of the second conductor using a third conductive paste. It is.

  As described above, according to the present invention, even when the surfaces of the vias 2a and 2b are rough and have recesses, the via voids at the connection portions between the surfaces of the vias 2a and 2b and the conductors 13 and 14 and the recesses in the conductor surface of the surface layer portion. And a ceramic substrate free from cracks can be provided. Furthermore, in the present invention, since the conductors 13 and 14 in contact with the surfaces of the vias 2a and 2b can be formed by the conductive paste printing process, no extra process is required.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, about the same thing as the past, description is simplified using the same code | symbol.

(Embodiment 1)
FIG. 1 shows a method for manufacturing a ceramic substrate according to the present invention. The first step 8 is a step of obtaining a sintered body 7 by laminating and firing green sheets. Specifically, a plurality of green sheets 3 having conductor patterns 1 and vias 2 formed therein are stacked and fired to obtain a sintered body 7. The conductor pattern 1 and the via 2 are mainly composed of Ag. The green sheet 3 was formed by a doctor blade method using a slurry obtained by adding an organic binder and a solvent to a powder obtained by mixing alumina powder at a ratio of approximately 50 wt% and glass powder at a ratio of approximately 50 wt%. The firing temperature for obtaining the sintered body 7 was about 900 ° C.

  The second step 16 is a step of printing the second conductors 13 and 14 on the outermost layers 11 and 12 of the sintered body 7. The main component of the second conductors 13 and 14 is Ag, and the conductive paste viscosity is 100 Pa · sec.

  The third step 18 is a step of firing the second conductors 13 and 14, and the firing temperature is about 850 ° C. In this example, the fired film thickness of the second conductors 13 and 14 after firing was 8 μm.

  The fourth step 26 is a step of printing and forming the third conductors 21 and 22 on the second conductors 13 and 14. The components of the third conductors 21 and 22 were the same as those of the second conductors 13 and 14, but the conductive paste viscosity was 300 Pa · sec. The effect of this conductive paste due to the difference in viscosity will be described later with reference to Table 1.

  The fifth step 30 is a step of firing the third conductors 21 and 22. The firing temperature was about 850 ° C., and the total fired film thickness of the second conductors 13 and 14 and the third conductors 21 and 22 after firing was 17 μm.

  The sixth step 34 is a step of forming plated layers 23 and 24 on the surfaces of the third conductors 21 and 22. This time, Ni / Au electroless plating was performed.

  The effect of the viscosity of the conductive paste differs depending on the difference. That is, if the viscosity of the conductive paste is high, bleeding at the time of printing the wiring is small, which is advantageous for forming the wiring, but it is not suitable for the depression generated in the via. On the other hand, if the viscosity of the conductive paste is low, printing blur increases, which is unsuitable for wiring formation, but has the effect of being well adapted to via depression. Table 1 shows the results of evaluating the printability, the non-plating occurrence rate, and the solder void occurrence rate by varying the viscosities of the second and third conductive pastes.

  The viscosity and film thickness of the conductive paste for forming the second conductors 13 and 14 and the viscosity of the conductive paste for forming the third conductor were determined from the experimental data shown in Table 1. The sample preparation conditions of Embodiment 1 were selected from the experimental data shown in Table 1.

  From the results in Table 1, when the conductive paste viscosity of the second conductors 13 and 14 is in the range of 50 to 250 Pa · sec, there is no blur and good printability is shown. When the viscosity of the conductive paste was lower than 50 Pa · sec, for example, 30 Pa · sec, the result of the experiment was that bleeding was large and conductor formation was not achieved. However, when the conductive paste viscosity is 250 Pa · sec, no plating and solder voids are observed. Due to the high viscosity of the conductive paste, the indentation of the vias 2a and 2b in the surface layer portion is poor, and there are via voids between the vias 2a and 2b and the first conductors 13 and 14, and indentations and cracks on the surface of the conductor in the surface layer portion. It appears that no plating or solder voids occurred. Therefore, the range of the conductive paste viscosity of the second conductors 13 and 14 is appropriately 50 to 200 Pa · sec.

  When the range of the conductive paste viscosity of the second conductors 13 and 14 was 50 to 200 Pa · sec, the conductor film thickness after firing of the second conductor was 5 to 15 μm. When the conductor film thickness of the second conductors 13 and 14 was 5 to 15 μm, the printability was good when the conductive paste viscosity of the third conductors 21 and 22 was 200 to 500 Pa · sec. When the conductor film thickness of the second conductors 13 and 14 was 18 μm, blurring and faint printing defects occurred in the entire range of the conductive paste viscosity of the third conductors 21 and 22 in the range of 150 to 600 Pa · sec. The third conductors 21 and 22 are printed on the upper portions of the second conductors 13 and 14, but may also be disposed in adjacent portions of the second conductors 13 and 14. For example, when the third conductors 21 and 22 are arranged above the second conductors 13 and 14, if the thickness of the conductors of the second conductors 13 and 14 is thick, edge breakage failure occurs. In addition, when the third conductors 21 and 22 are arranged adjacent to the second conductors 13 and 14, if the conductor thickness of the second conductors 13 and 14 is thick, a step is generated around the conductors 13 and 14. In the printing method using the conductive paste, adhesion between the plate making and the surface of the ceramic substrate becomes unstable, and blurring occurs.

  When the viscosity of the conductive paste of the third conductors 21 and 22 was lower than 200 Pa · sec, for example, 150 Pa · sec, the result of the experiment was that bleeding occurred in the wiring formation portion. For example, when a wiring having a line width / line spacing of about 100 μm / 100 μm is formed, when the viscosity of the conductive paste is 150 Pa · sec, the paste has a small shape retention force and is easy to flow, so the line width / line spacing is 150 μm. / 50 μm. If the wiring portion has a blur of 50 μm, it is defective as a fine wiring.

  Further, in the case of higher than 500 Pa · sec, for example, in the case of 600 Pa · sec, as a result of the experiment, fading occurred in the wiring formation portion. When fine wiring is formed by a printing method, generally, high-mesh plate making is used, but high-mesh plate making has a narrow mesh opening. When printing is performed using a high-mesh plate making with a conductive paste of 600 Pa · sec, insufficient transfer occurs due to poor fluidity of the conductive paste, and blurring occurs. Therefore, the range of the conductive paste viscosity of the third conductors 21 and 22 is appropriately 200 to 500 Pa · sec.

(Embodiment 2)
FIG. 2 shows Embodiment 2 of the method for producing a ceramic substrate of the present invention. The first step 6 is a step of obtaining a sintered body 5 by laminating and firing green sheets. Specifically, a plurality of green sheets 3 having conductor patterns 1 and vias 2 formed therein are stacked, and a restraining sheet 4 that is not sintered at the green sheet sintering temperature is stacked and fired. A sintered body 5 is obtained. The conductor pattern 1 and the via 2 are mainly composed of Ag. The green sheet 3 was formed by a doctor blade method using a slurry obtained by adding an organic binder and a solvent to a powder obtained by mixing alumina powder at a ratio of approximately 50 wt% and glass powder at a ratio of approximately 50 wt%. The restraining sheet 4 was formed by a doctor blade method using a slurry obtained by adding an organic binder and a solvent to alumina powder. The firing temperature for obtaining the sintered body 5 was about 900 ° C.

  The second step 52 is a step of obtaining the ceramic multilayer substrate 51 by removing the restraining sheet 4 on the surface of the sintered body 5. Generally, it is a non-shrinkable ceramic multilayer substrate that does not shrink in the plane direction.

  The third step 54 is a step of printing the second conductors 13 and 14 on the outermost layers 11 and 12 of the sintered body 51. The main component of the second conductors 13 and 14 is Ag, and the conductive paste viscosity is 100 Pa · sec.

  The fourth step 56 is a step of firing the second conductors 13 and 14, and the firing temperature is about 850 ° C. In this example, the fired film thickness of the second conductors 13 and 14 after firing was 8 μm.

  The fifth step 58 is a step of printing and forming the third conductors 21 and 22 on the second conductors 13 and 14. The components of the third conductors 21 and 22 were the same as those of the second conductors 13 and 14, but the conductive paste viscosity was 300 Pa · sec.

  The sixth step 60 is a step of firing the third conductors 21 and 22. The firing temperature was about 850 ° C., and the fired film thickness of the third conductors 21 and 22 after firing was 17 μm.

  The seventh step 34 is a step of forming plated layers 23 and 24 on the surfaces of the third conductors 21 and 22. This time, Ni / Au electroless plating was performed.

  The viscosity and conductive film thickness of the conductive paste were determined in the same manner as in the first embodiment.

  The method for producing a ceramic substrate according to the present invention is useful for reducing cracks and voids on the surface of the outermost layer conductor by an inexpensive method, and reducing plating defects due to cracks and voids and defects of solder voids. The ceramic multilayer substrate obtained by the present invention is particularly useful for improving the secondary mounting reliability.

Manufacturing process diagram of ceramic substrate shown in Embodiment 1 of the present invention Manufacturing process diagram of ceramic substrate shown in Embodiment 2 of the present invention Manufacturing process diagram of conventional ceramic substrate

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Conductor pattern 2 Via 2a, 2b Surface layer via 3 Green sheet 4 Restraint sheet 5, 7 Sintered body 11, 12 Outermost layer 13, 14 Second conductor 21, 22 Third conductor 23, 24 plating layer

Claims (10)

A through hole forming step of forming a through hole in the ceramic green sheet;
A via filling step of forming a via using a conductive paste in the through hole;
A conductor pattern forming step of forming a predetermined conductor pattern using the first conductive paste on the ceramic green sheet;
A laminate creating step of creating a laminate by laminating a plurality of the ceramic green sheets;
A first firing step of firing the laminate to obtain a sintered substrate;
A first printing step of printing a second conductor on the via surface of the sintered substrate using a second conductive paste;
A second firing step of firing the sintered substrate on which the second conductor is printed;
Method of producing a ceramic multilayer substrate and a second printing step of the third conductor formed by printing using a third conductive paste on the surface of the second conductor. The method for producing a ceramic substrate according to claim 1 , wherein the viscosity of the second conductive paste is 50 to 200 Pa · sec, and the viscosity of the third conductive paste is 200 to 500 Pa · sec.   The method for manufacturing a ceramic substrate according to claim 1, wherein the temperature of the second firing step is a temperature at which the second conductive paste is fired. The method for producing a ceramic substrate according to claim 1, wherein after the second firing step, the thickness of the fired second conductor is 5 to 15 µm.   The method for manufacturing a ceramic substrate according to claim 1, wherein the second conductive paste and the third conductive paste are the same. A through hole forming step of forming a through hole in the ceramic green sheet;
A via filling step of forming a via using a conductive paste in the through hole;
A conductor pattern forming step of forming a predetermined conductor pattern using the first conductive paste on the ceramic green sheet;
A first laminate creating step of creating a laminate by laminating a plurality of the ceramic green sheets;
A second laminate creating step of creating a second laminate by disposing a constraining sheet mainly composed of an inorganic composition that does not shrink at the sintering temperature of the ceramic green sheet on both sides of the laminate; ,
After firing the second laminate at the sintering temperature of the ceramic green sheet, a first sintered substrate creating step of removing the restraining sheet and obtaining a ceramic sintered substrate;
A first printing step of printing a second conductor using a second conductive paste on the via surface of the ceramic sintered substrate;
A second sintered substrate creating step of firing the ceramic sintered substrate on which the second conductor is printed;
Method of producing a ceramic multilayer substrate and a second printing step of the third conductor formed by printing using a third conductive paste on the surface of the second conductor.   The method for producing a ceramic multilayer substrate according to claim 6, wherein the viscosity of the second conductive paste is 50 to 200 Pa · sec, and the viscosity of the third conductive paste is 200 to 500 Pa · sec.   The method for producing a ceramic substrate according to claim 6, wherein the temperature of the second sintered substrate creation step is a temperature at which the second conductive paste is fired. The method for producing a ceramic substrate according to claim 6, wherein after the second sintered substrate creation step, the thickness of the fired second conductor is 5 to 15 μm.   The method for manufacturing a ceramic substrate according to claim 6, wherein the second conductive paste and the third conductive paste are the same.

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