JP2015201514A - Wiring board and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce both interfacial peelings between a ceramic substrate and a base electrode and between the base electrode and a surface electrode when an outer electrode that is formed on the ceramic substrate is constituted by the base electrode made of a conductive paste and the surface electrode formed by plating.SOLUTION: A method of manufacturing a wiring board 2a includes steps of: preparing an unbaked ceramic substrate 4; forming a base electrode 5a having an exposed surface exposed from one principal surface of the ceramic substrate 4 by printing a conductive pase containing a material constituting the ceramic substrate 4 and a metal on one principal surface of the unbaked ceramic substrate 4; baking the unbaked ceramic substrate 4 with the base electrode 5a; forming a surface electrode 5b on the base electrode 5a by plating treatment; and baking a metal of the base electrode 5a and a metal of the surface electrode 5b at a metal-sintering temperature thereby metal-sintering both the metals at an interface between the base electrode 5a and the surface electrode 5b.

Description

The present invention relates to a wiring board in which an external electrode composed of a base electrode and a surface electrode is formed on a main surface of a ceramic substrate, and a manufacturing method thereof.

  Conventionally, as shown in FIG. 4, a module in which components are mounted on a wiring board is known (see Patent Document 1). The module 100 includes a wiring board 101 and a plurality of components 102 mounted on the upper surface of the wiring board 101. The wiring substrate 101 includes a ceramic substrate 103 as a core substrate formed of, for example, a low-temperature co-fired ceramic, a plurality of internal electrodes 104 and via conductors 105 formed inside the ceramic substrate 103, and a plurality of built-in ceramic substrates. Chip component 106. Further, a plurality of external electrodes 107 for external connection are formed on the upper and lower surfaces of the ceramic substrate 103, and each external electrode 107 on the upper surface side is used as a mounting electrode for mounting each component 102. Yes.

JP 2007-53328 A (see paragraphs 0022 to 0028, FIG. 1 and the like)

  Each external electrode 107 of the conventional module 100 described above is formed by applying a conductive paste containing a metal such as Cu to the main surface of the ceramic substrate 103 by using a screen printing technique. However, since the metal contained in the conductive paste and the ceramic substrate 103 have low adhesion, when the wiring substrate 101 is connected to the outside, the interface between the external electrode 107 and the ceramic substrate 103 may be peeled off. As a measure for solving this problem, the conductive paste for forming the external electrode 107 is made to contain the material constituting the ceramic substrate 103 (for example, glass component), and then the conductive paste is combined with the ceramic substrate 103. It is conceivable to fire. In this case, the glass component functions as an adhesive that bonds the metal contained in the conductive paste and the ceramic substrate 103, so that interface peeling between the external electrode 107 and the ceramic substrate 103 can be reduced.

  On the other hand, when the external electrode is formed of a conductive paste containing a glass component, the wettability of solder and the like deteriorates, so that the connectivity with the outside deteriorates. Therefore, the external electrode is formed by screen-printing again the base electrode formed using the conductive paste containing the glass component as described above and the conductive paste not containing the glass component on the surface of the base electrode. A structure having a two-layer structure with the surface electrode formed has been developed.

  However, when external electrodes are formed by a plurality of printings in this way, a design space that takes into account printing accuracy, bleeding of conductive paste, and the like is necessary, which becomes an obstacle when arranging external electrodes at a narrow pitch. Further, in the printing method, the thickness of the external electrode is increased and it is difficult to reduce the thickness of the wiring board. Here, it is conceivable to form a surface electrode by plating using the metal of the base electrode as a plating nucleus. In this way, it is easy to reduce the pitch and thickness of the external electrode by the amount that the surface electrode is not formed by the printing method. However, since the glass component exists on the surface of the base electrode, There is an adverse effect that the adhesion strength is lowered. Therefore, in improving the adhesion strength between the ceramic substrate and the external electrode, the adhesion strength between the ceramic substrate and the base electrode formed of the conductive paste and the adhesion strength between the base electrode and the surface electrode formed by plating are improved. There is a demand for technology that can achieve both of these.

  The present invention has been made in view of the above-described problems, and includes an external electrode composed of a base electrode formed of a conductive paste on a main surface of a ceramic substrate and a surface electrode formed by plating on the surface of the base electrode. An object of the present invention is to provide a technique for reducing both interface peeling between a ceramic substrate and a base electrode and interface peeling between a base electrode and a surface electrode in a wiring board including electrodes.

  In order to achieve the above-described object, a method of manufacturing a wiring board according to the present invention includes a preparation step of preparing an unfired ceramic substrate, and a conductive paste containing a material and a metal constituting the ceramic substrate. A base electrode forming step of forming a base electrode for an external electrode having an exposed surface exposed from one main surface of the ceramic substrate by printing on one main surface of the ceramic substrate in a fired state; and the base electrode together with the base electrode A first firing step of firing the ceramic substrate in an unfired state, a surface electrode forming step of forming a surface electrode for an external electrode on the exposed surface of the ground electrode by plating, a metal of the ground electrode and the surface A second firing process in which the two metals are sintered at the boundary surface between the base electrode and the surface electrode by firing at a temperature at which the metal of the electrode is sintered. It is characterized in that it comprises and.

  In this case, in the first firing step, the base electrode for the external electrode formed of the conductive paste containing the material constituting the ceramic substrate is fired together with the ceramic substrate. In this way, since the material constituting the ceramic substrate contained in the conductive paste of the base electrode can function as an adhesive for bonding the ceramic substrate and the metal of the base electrode, the base for the ceramic substrate and the external electrode can be used. The adhesion strength with the electrode is improved.

  In addition, since the ceramic substrate and the external electrode have different sintering timings during firing, the ceramic substrate warps when the thickness of the external electrode formed on the ceramic substrate increases. However, in the present invention, since the thickness of the external electrode before firing can be reduced by forming the surface electrode for the external electrode after firing the ceramic substrate, warpage of the ceramic substrate after firing is reduced. In addition, since the conductive paste for forming the base electrode contains the material constituting the ceramic substrate, the sintering timing at the time of firing the base electrode can be brought close to the ceramic substrate.

  In addition, when the surface electrode is formed by screen printing on the exposed surface of the base electrode, the surface electrode for the external electrode is formed on the exposed surface of the base electrode by using the metal of the base electrode as a plating nucleus in the surface electrode forming step. Compared to the above, it is not necessary to secure a design space in consideration of printing accuracy, paste bleeding, etc., and external electrodes can be formed on the ceramic substrate at a narrow pitch.

  In addition, if a surface electrode is formed by plating on the surface (exposed surface) of a base electrode made of a conductive paste containing a material that constitutes a ceramic substrate, the adhesion strength of both electrodes may be reduced and interface peeling may occur. There is. However, in the present invention, after the surface electrode is formed, the metal of both electrodes is sintered at the boundary surface between the base electrode and the surface electrode by the second firing step, so that the adhesion strength between the base electrode and the surface electrode is improved. . As described above, in a wiring board including an external electrode composed of a base electrode formed of a conductive paste on a main surface of a ceramic substrate and a surface electrode formed by plating on the surface of the base electrode, the ceramic substrate and the base It is possible to manufacture a wiring board that can reduce both the interface peeling of the electrode and the interface peeling between the base electrode and the surface electrode.

  The wiring board of the present invention includes a ceramic substrate, a metal and a material constituting the ceramic substrate as a constituent material thereof, and an exposed surface exposed from one main surface of the ceramic substrate. A base electrode for the formed external electrode; and a surface electrode for the external electrode plated on the exposed surface of the base electrode, wherein the base electrode and the surface electrode include the metal of the base electrode and the surface electrode. It is characterized by being joined by metal sintering with the metal of the surface electrode.

  According to this configuration, since the base electrode for the external electrode contains the material constituting the ceramic substrate, the adhesion strength between the ceramic substrate and the base electrode is improved as compared with the case where the base electrode is made of only metal. To do. In addition, since the base electrode and the surface electrode for the external electrode are joined by metal sintering between the metal of the base electrode and the metal of the surface electrode, between the metal of the surface electrode and the metal of the base electrode Compared to the case without metal sintering, the adhesion strength between the base electrode and the surface electrode is improved.

  Moreover, the metal of the said base electrode and the metal of the said surface electrode may be formed with the same metal. This is practical because a metal bond between both electrodes can be smoothly formed, for example, the sintering temperature of the base electrode metal and the surface electrode metal can be lowered.

  Further, the surface electrode may not contain a material constituting the ceramic substrate. In this case, since the metal density of the portion directly connected to the outside of the external electrode can be increased, the wiring board having the external electrode having excellent connectivity with the outside while improving the adhesion strength with the ceramic substrate Can be provided.

  According to the present invention, in the first firing step, the unfired ceramic substrate is fired together with the base electrode formed of the conductive paste containing the material constituting the ceramic substrate. Then, after the surface electrode is formed on the exposed surface of the base electrode by plating, the metal between the metal of the base electrode and the metal of the surface electrode is sintered in the second firing step. In this case, when the external electrode is constituted by the base electrode formed of the conductive paste and the surface electrode formed by plating on the surface of the base electrode, interface peeling between the ceramic substrate and the base electrode and the base electrode and the surface Both interfacial delamination of electrodes can be reduced.

It is sectional drawing of the module with which the wiring board concerning 1st Embodiment of this invention is applied. It is sectional drawing of the external electrode of FIG. It is sectional drawing of the external electrode of the wiring board concerning 2nd Embodiment of this invention. It is sectional drawing of the module to which the conventional wiring board was applied.

<First Embodiment>
A wiring board 2a according to a first embodiment of the present invention will be described with reference to FIGS. 1 is a cross-sectional view of the wiring board 1a, and FIG. 2 is a partial enlarged view of FIG. 1, showing a cross-sectional view of the external electrode.

  As shown in FIG. 1, a module 1 to which a wiring board 2a according to this embodiment is applied includes a wiring board 2a and a plurality of electronic components 3 mounted on one main surface of the wiring board 2a. Used as a high frequency module.

  Each electronic component 3 includes a semiconductor element formed of Si, GaAs, or the like, or a chip component such as a chip inductor, a chip capacitor, or a chip resistor. Mounted on the surface (upper surface).

  The wiring substrate 2a includes a ceramic substrate 4 as a core substrate formed by laminating a plurality (three layers in this embodiment) of ceramic layers 4a, a plurality of external electrodes 5 formed on both main surfaces of the ceramic substrate 4, and A plurality of internal electrodes 6 and a plurality of via conductors 7 formed inside the ceramic substrate 4 are provided.

  Each ceramic layer 4a of the ceramic substrate 4 is made of, for example, a low-temperature co-fired ceramic (LTCC) mainly composed of borosilicate glass (glass component), alumina, silica, or the like. The ceramic substrate 4 may be a single layer.

  Each internal electrode 6 is formed of a metal used for a general wiring electrode such as Cu or Ag, and is formed on the main surface of a predetermined ceramic layer 4a by screen printing or the like. Each via conductor 7 is made of a metal such as Cu or Ag, and is formed on each ceramic layer 4a by a known method. Here, each via conductor 7 is used as an interlayer connection conductor for connecting predetermined external electrodes 5 and internal electrodes 6 to each other or connecting predetermined internal electrodes 6 to each other.

As shown in FIG. 2, each external electrode 5 has a base electrode 5a formed on the ceramic substrate 5 so as to have an exposed surface exposed from the main surface of the ceramic substrate 4, and plating is formed on the exposed surface of the base electrode 5a. The surface electrode 5b is connected to a predetermined via conductor 7 respectively.
Here, each base electrode 5 a is not necessarily connected to the via conductor 7, and may be connected to a wiring electrode formed on the main surface of the ceramic substrate 4. In this embodiment, each external electrode 5 formed on the upper surface of the ceramic substrate 4 is used as a mounting electrode for mounting each electronic component 3.

  The base electrode 5 a is formed of a conductive paste containing a metal such as Cu or Ag and a glass component that is one of the materials constituting the ceramic substrate 4. Screen printing or the like is performed on the main surface of the ceramic substrate 4. After being applied by the above, it is obtained by firing together with the ceramic substrate 4. In the conductive paste in this embodiment, the metal component is formed of Cu.

  The surface electrode 5b is formed by plating with a metal such as Cu on the exposed surface of the base electrode 5a using the metal of the base electrode 5a as a nucleus. By doing in this way, the film | membrane (surface electrode 5b) with a high metal density which does not contain a glass component is formed in the exposed surface of a base electrode. Each external electrode 5 is joined by metal sintering between the metal of the base electrode 5a and the metal of the surface electrode 5b at the boundary surface between the base electrode 5a and the surface electrode 5b.

(Method for manufacturing a wiring board)
Next, a method for manufacturing the wiring board 2a will be described. First, a plurality of ceramic green sheets for forming each ceramic layer 4a are prepared, and the internal electrode 6 and the via conductor 7 are formed on each ceramic green sheet. At this time, each via conductor 7 is formed by forming a through hole at a predetermined position of the ceramic green sheet with a laser or the like and filling the through hole with a conductive paste containing a metal such as Cu by a printing method. can do. The internal electrodes 6 can be formed by applying a conductive paste containing a metal such as Cu to the main surface of the ceramic green sheet by screen printing or the like. Each ceramic green sheet in this embodiment is formed of a low-temperature cofired ceramic containing alumina, a glass component, or the like.

  Next, the ceramic green sheets on which the internal electrodes 6 and the via conductors 7 are formed are stacked, and an unfired ceramic substrate 4 formed by stacking the ceramic green sheets is prepared (preparation step).

  Next, base electrodes 5a for external electrodes each having an exposed surface exposed from the main surface of the ceramic substrate 4 are formed on both main surfaces of the unfired ceramic substrate 4 by screen printing using a conductive paste. (Underlying electrode forming step). At this time, a conductive paste containing Cu particles and a glass component which is one of the materials constituting the ceramic substrate 4 in an organic solvent is used.

  Next, the laminated body (ceramic substrate 4) of each ceramic green sheet in an unfired state, together with each paste-like base electrode 5a, is fired at a temperature of about 800 ° C. to 1000 ° C., for example (first firing step). In this case, the glass component in the conductive paste contributes to the sintering of the ceramic substrate 4, so that the glass component functions as an adhesive that bonds the metal (Cu) of the conductive paste and the ceramic substrate 4. Therefore, the adhesion strength between the ceramic substrate 4 and the base electrode 5a for the external electrode is improved.

  Next, each surface electrode 5b for an external electrode is formed on the exposed surface of each base electrode 5a by similarly plating a metal such as Cu using the metal (Cu) of the base electrode 5a as a plating nucleus (surface) Electrode forming step). If it does in this way, a film | membrane (surface electrode 5b) with a high metal density will be supplied to the said exposed surface of the base electrode 5a in which the metal density became low by containing a glass component. In addition, any of electrolytic plating and electroless plating may be used for the plating treatment. Further, the metal of the base electrode 5a and the metal of the surface electrode 5b may be different.

  Next, the base electrode 5a is fired at a temperature (for example, 800 to 1000 ° C.) at which the metal (Cu) of the base electrode 5a and the metal (Cu) of the surface electrode 5b of each external electrode 5 are sintered. The two metals are sintered at the interface between the surface electrode 5b and the surface electrode 5b (second firing step) to complete the wiring board 2a. When the second firing step is not provided, the boundary between the base electrode 5a and the surface electrode 5b becomes a porous state (so-called porous) due to the influence of the glass component present on the exposed surface of the base electrode 5a. In this respect, in this embodiment, since the holes generated at the boundary between the electrodes 5a and 5b can be reduced by firing in the second firing step, the adhesion strength between the electrodes 5a and 5b can be improved. it can.

  Therefore, according to the above-described embodiment, each of the base electrodes 5a for the external electrodes formed of the conductive paste containing the material (glass component) constituting the ceramic substrate 4 is combined with the ceramic substrate 4 by the first firing step. Baked. In this way, the glass component contained in the conductive paste of the base electrode 5a can function as an adhesive for bonding the ceramic substrate 4 and the metal (for example, Cu) of the base electrode 5a. The adhesion strength with the base electrode 5a for external electrodes is improved.

  Moreover, since the ceramic substrate 4 and the external electrode 5 have different sintering timings during firing, the ceramic substrate 4 warps as the thickness of the external electrode 5 formed on the ceramic substrate 4 increases due to the difference in timing. growing. However, in this embodiment, the thickness of the external electrode 5 before firing can be reduced by forming the surface electrode 5b for the external electrode after firing the ceramic substrate 4, so that the warp of the ceramic substrate 4 after firing is made. Is reduced. In addition, since the conductive paste forming the base electrode 5 a contains the material (glass component) constituting the ceramic substrate 4, the sintering timing at the time of firing the base electrode 5 a can be brought close to the ceramic substrate 4.

  In addition, since the surface electrode 5b is formed on the exposed surface of the base electrode 5a by using the metal of the base electrode 5a as a plating nucleus in the surface electrode forming step, the surface of the base electrode 5a is exposed by screen printing or the like. Compared with the case where the electrode 5b is formed, it is not necessary to secure a design space in consideration of printing accuracy, paste bleeding, and the like, and the external electrode 5 can be formed on the ceramic substrate 4 at a narrow pitch.

  Further, when the surface electrode 5b is formed by plating on the surface (exposed surface) of the base electrode 5a formed of a conductive paste containing the material (glass component) constituting the ceramic substrate 4, the exposed surface of the base electrode 5a Since the adhesion strength between the electrodes 5a and 5b is reduced due to the influence of the glass component present in the electrode, there is a possibility that the interface peeling between the electrodes 5a and 5b occurs. However, in this embodiment, after the surface electrode 5b is formed, the metal of both the electrodes 5a and 5b is sintered at the boundary surface between the base electrode 5a and the surface electrode 5b by the second firing step. The adhesion strength of the surface electrode 5b is improved. As described above, when the external electrode 5 is constituted by the base electrode 5a formed of the conductive paste on the main surface of the ceramic substrate 4 and the surface electrode 5b formed by plating on the surface of the base electrode 5a, the ceramic substrate 4 and the base electrode 5a and the interfacial peeling between the base electrode 5a and the surface electrode 5b can be manufactured.

  In addition, by forming the metal contained in the base electrode 5a and the metal of the surface electrode 5b with the same metal (Cu in this embodiment), the second firing step is compared with the case where the types of these metals are different. This is practical because the metal sintering can be performed at a lower temperature.

  In addition, since the surface electrode 5b is formed on the exposed surface of the base electrode 5a by plating, the metal density of the portion directly connected to the outside of the external electrode 5 can be increased, so that the adhesion strength with the ceramic substrate 4 is increased. Thus, it is possible to provide the wiring substrate 2a including the external electrode 5 having excellent connectivity with the outside.

Second Embodiment
A wiring board 2b according to a second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a cross-sectional view of the external electrode 50 of the wiring board 2b and corresponds to FIG. 2 of the wiring board 2a of the first embodiment.

  The wiring board 2b according to this embodiment is different from the wiring board 2a of the first embodiment described with reference to FIGS. 1 and 2 except that the end surface 7a of the via conductor 7 is used as a base electrode and is formed on the base electrode. The external electrode 50 is formed by forming the surface electrode 5b by plating. Since other configurations are the same as those of the wiring substrate 2a of the first embodiment, the description thereof is omitted by giving the same reference numerals.

  The manufacturing method of the wiring board 2b will be described. The via conductors 7 of the lowermost layer and the uppermost ceramic layer 4a of the ceramic substrate 4 are made of the material constituting the ceramic substrate 4 (as in the base electrode 5a of the first embodiment). It is formed by a conductive paste containing a glass component) and a metal (for example, Cu). Specifically, a through hole for the via conductor 7 is formed in each of the ceramic green sheets forming the uppermost layer and the lowermost ceramic layer 4a by a laser or the like, and the through hole is conductive using a screen printing technique or the like. A conductive paste (containing a glass component and a metal) (base electrode forming step). In addition, you may form another ceramic green sheet in the same way as the manufacturing method of the wiring board 2a of 1st Embodiment. The internal electrode 6 can be formed in the same manner as the wiring board 2a of the first embodiment.

  Next, the ceramic green sheets are laminated, and the laminate of the ceramic green sheets (the unfired ceramic substrate 4) is fired together with the via conductors 7 (first firing step). Next, the surface electrode 5b is formed in the same manner as the wiring substrate 2a of the first embodiment, using the end surfaces 7a of the via conductors 7 exposed from both main surfaces of the ceramic substrate 4 as base electrodes for external electrodes. The subsequent steps (second firing step) are performed in the same manner as the wiring substrate 2a of the first embodiment, thereby completing the wiring substrate 2b.

  According to this configuration, in addition to the same effects as those of the wiring substrate 2a of the first embodiment, the following effects can be obtained. That is, by substituting the base electrode 5a provided on the wiring board 2a of the first embodiment with the end face 7a of the via conductor 7, it is not necessary to secure a design space that takes into account the printing accuracy and bleeding of the conductive paste. Therefore, the pitch of the external electrodes 50 formed on the main surface of the ceramic substrate 4 can be further reduced. Further, since the thickness of the external electrode 50 can be reduced by the amount of the base electrode 5a (thick film) formed on the main surface of the ceramic substrate 4 by screen printing or the like, the wiring substrate 2b can be further reduced. it can. Moreover, since the thickness of the external electrode 50 before firing can be reduced compared with the wiring board 2a of the first embodiment by using the base electrode for the external electrode as the end surface 7a of the via conductor, The warp of the ceramic substrate 4 can be further reduced.

  The present invention is not limited to the above-described embodiments, and various modifications other than those described above can be made without departing from the spirit of the invention. For example, in each of the above-described embodiments, the case where the material constituting the ceramic substrate 4 contained in the conductive paste forming the base electrode 5a is a glass component has been described. However, other constituent materials containing the ceramic substrate 4 are contained. You may make it do.

  Further, the present invention provides various wiring boards in which the external electrode provided on the main surface of the ceramic substrate is composed of a base electrode formed of a conductive paste and a surface electrode formed by plating on the base electrode. Can be applied.

2a, 2b Wiring substrate 4 Ceramic substrate 5, 50 External electrode 5a Base electrode 5b Surface electrode 7a End surface of via conductor (base electrode)

Claims (4)

A preparation step of preparing an unfired ceramic substrate;
An exterior having an exposed surface exposed from one main surface of the ceramic substrate by printing a conductive paste containing a material constituting the ceramic substrate and a metal on the one main surface of the unfired ceramic substrate. A base electrode forming step of forming a base electrode for the electrode;
A first firing step of firing the unfired ceramic substrate together with the base electrode;
A surface electrode forming step of forming a surface electrode for an external electrode on the exposed surface of the base electrode by plating;
By firing at a temperature at which the metal of the base electrode and the metal of the surface electrode are sintered,
And a second firing step in which the two metals are sintered at the interface between the base electrode and the surface electrode. A ceramic substrate;
A base electrode for an external electrode formed on the ceramic substrate so as to have an exposed surface exposed from one main surface of the ceramic substrate, containing a metal and a material constituting the ceramic substrate in the constituent material;
A surface electrode for an external electrode plated on the exposed surface of the base electrode,
The wiring substrate, wherein the base electrode and the surface electrode are joined by metal sintering between the metal of the base electrode and the metal of the surface electrode.   The wiring board according to claim 2, wherein the metal of the base electrode and the metal of the surface electrode are formed of the same metal.   The wiring board according to claim 2, wherein the surface electrode does not contain a material constituting the ceramic substrate.

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