Wiring Board

Abstract

To provide a wiring board improved in junction reliability.SOLUTION: A wiring board comprises an insulation substrate and a conductor layer lamination part which is disposed on the insulation substrate and in which a plurality of conductor layers is laminated. The conductor layer lamination part includes a first conductor layer disposed in an outermost layer of the conductor layer lamination part, and a second conductor layer which is disposed between the first conductor layer and the insulation substrate and of which the hardness is equal to or lower than that of the first conductor layer.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a wiring board. [Background technology]

[0002] Conventionally, wiring boards have been proposed in which a plurality of conductive layers made of different materials are laminated on an insulating substrate (see, for example, Patent Document 1). Patent Document 1 discloses a wiring board in which a titanium (Ti) layer is formed on the surface of a ceramic substrate, and a copper (Cu) layer and a gold (Au) layer are laminated on the titanium (Ti) layer in this order. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-109858 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the wiring board described in Patent Document 1, copper used as an intermediate layer is harder (has higher hardness) than gold. Therefore, for example, when an electronic component is bonded to a gold layer using a gold bump, the gold layer on the outermost layer is less likely to deform due to the influence of the copper layer in the intermediate layer, and voids (vacancies) may occur at the gold-gold bonding interface, resulting in a decrease in bonding reliability. Note that this problem is not limited to gold-gold bonding, but is a common problem in bonding between various metals, such as when electronic components are bonded to a conductor layer using metal bumps of tin, copper, nickel, alloys thereof, etc.

[0005] The present invention has been made in order to solve the above-mentioned problems, and has an object to provide a wiring board having high bonding reliability. [Means for solving the problem]

[0006] The present invention has been made to solve at least part of the above-mentioned problems, and can be realized in the following forms.

[0007] (1) According to one aspect of the present invention, there is provided a wiring board comprising an insulating substrate and a conductor layer laminate section disposed on the insulating substrate and including a plurality of conductor layers laminated thereon, the conductor layer laminate section including a first conductor layer disposed on the outermost layer of the conductor layer laminate section and a second conductor layer disposed between the first conductor layer and the insulating substrate and having a hardness equal to or less than that of the first conductor layer.

[0008] According to this configuration, since the second conductor layer, which has a hardness equal to or less than that of the first conductor layer arranged on the outermost layer, is arranged between the first conductor layer and the insulating substrate, the conductor layer laminate portion is more likely to deform than when a conductor layer having a hardness higher than that of the first conductor layer is arranged between the first conductor layer and the insulating substrate. Therefore, when an electronic component is bonded to the first conductor layer using a metal bump or the like, the conductor layer laminate portion is deformed to reduce voids, and deterioration of bonding reliability can be suppressed. In other words, according to this configuration, a wiring board with high bonding reliability can be provided.

[0009] (2) In the wiring board of the above embodiment, the second conductor layer may be thicker than the first conductor layer. In this way, the hardness of the second conductor layer is equal to or less than the hardness of the first conductor layer, and the second conductor layer is thicker than the first conductor layer. This makes it possible to suppress a decrease in flexibility of the conductor layer laminated portion and a decrease in bonding reliability, compared to when the thickness of the second conductor layer is equal to or less than the thickness of the first conductor layer.

[0010] (3) In the wiring board of the above embodiment, the first conductor layer may be mainly composed of gold (Au). In this way, when an electronic component is bonded to the first conductor layer of the conductor laminated portion using a bump mainly composed of gold, it is possible to suppress the generation of voids at the gold-gold bonding interface and suppress a decrease in bonding reliability. In addition, since gold has low resistance, it is possible to reduce the resistance of the bonding points between the wiring board and the electronic component.

[0011] (4) In the wiring board of the above embodiment, the second conductor layer may be mainly composed of silver (Ag). Since silver has high flexibility, it is possible to suppress a decrease in flexibility of the conductor layer laminated portion, and therefore a decrease in joint reliability can be suppressed. Furthermore, since silver has low resistance, it is possible to reduce the resistance of the joint between the wiring board and the electronic component. Furthermore, by forming the conductor layer by laminating a first conductor layer mainly composed of gold and a second conductor layer mainly composed of silver, it is possible to reduce costs while maintaining the same flexibility and resistance, for example, compared to a case in which the conductor layer is composed only of a layer mainly composed of gold.

[0012] The present invention can be realized in various forms, for example, in the form of a product including a wiring board, a manufacturing method for a product including a wiring board, and the like. [Brief description of the drawings]

[0013] [Figure 1] FIG. 2 is an explanatory diagram illustrating a schematic cross-sectional configuration of the wiring board according to the first embodiment. [Diagram 2] FIG. 4 is an explanatory diagram of a method for measuring the hardness of a conductor layer. [Diagram 3] 1A to 1C are process diagrams illustrating an example of a method for manufacturing a wiring board. [Figure 4] FIG. 2 is an explanatory diagram illustrating a schematic cross-sectional configuration of the wiring board according to the first embodiment. [Diagram 5] 1A to 1C are process diagrams illustrating an example of a method for manufacturing a wiring board. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] First Embodiment 1 is an explanatory diagram illustrating a schematic cross-sectional configuration of a wiring board 10 according to a first embodiment of the present invention. The wiring board 10 includes an insulating substrate 2 and a conductor layer laminate portion 4.

[0015] The insulating substrate 2 is an insulating flat plate. In this embodiment, an aluminum nitride (AlN) ceramic substrate is used. Aluminum nitride has high heat dissipation and high strength, so it can be suitably used for components that generate a large amount of heat, such as power semiconductor modules. The material for forming the insulating substrate 2 is not limited to this embodiment, and may be ceramics such as alumina (Al2O3), alumina zirconia (Al2O3 / ZrO2), silicon nitride (Si3N4), silicon carbide (SiC), or may be resins such as glass, glass epoxy, thermoplastic resins and thermosetting resins, paper phenol, paper epoxy, glass composite, low temperature co-fired ceramics (LTCC), or metal members having these insulating members formed on the surface.

[0016] The conductor layer laminated portion 4 is a layer that is mainly composed of metal and has conductivity, and constitutes a wiring layer (including electrodes). The conductor layer laminated portion 4 has a first conductor layer 41 that is disposed on the outermost layer of the conductor layer laminated portion 4, a second conductor layer 42 that is disposed between the first conductor layer 41 and the insulating substrate 2 and has a hardness equal to or lower than that of the first conductor layer, and a third conductor layer 43 that is disposed between the first conductor layer 41 and the insulating substrate 2 and has a hardness higher than that of the first conductor layer 41. The conductor layer laminated portion 4 may contain resin and the like in addition to metal.

[0017] The wiring board 10 of the present embodiment includes a first layer 431, a second layer 432, and a third layer 433 as the third conductor layer 43. In the wiring board 10, the conductor layers are stacked on the insulating substrate 2 in the following order: the first layer 431, the second conductor layer 42, the second layer 432, the third layer 433, and the first conductor layer 41.

[0018] In this embodiment, the first conductor layer 41 is mainly composed of gold (Au). Since the first conductor layer 41 is mainly composed of gold, it is flexible and has a smooth surface. The first conductor layer 41 can be formed using gold or a gold alloy (for example, an Au-Sn (gold-tin) alloy, an Au-Co (gold-cobalt) alloy, etc.).

[0019] In this embodiment, the second conductor layer 42 is mainly composed of silver (Ag). The hardness of the second conductor layer 42 is equal to or lower than that of the first conductor layer 41, and the second conductor layer 42 has the same flexibility as the first conductor layer 41. In addition, since the second conductor layer 42 is mainly composed of silver, it has a lower resistance than the first conductor layer 41. The second conductor layer 42 can be formed using silver or a silver alloy (for example, an Ag-Ge-Pd alloy, an Ag-Ge-Sc alloy, etc.).

[0020] In this embodiment, the first layer 431 and the second layer 432 are mainly composed of titanium (Ti). The first layer 431 and the second layer 432 can be formed using titanium, titanium nitride (TiN), or a titanium alloy (for example, a Ti-Zr (titanium zirconium) alloy, a Ti-Hf (titanium hafnium) alloy, or the like). The third layer 433 is mainly composed of platinum (Pt). The third layer 433 can be formed using platinum or a platinum alloy (for example, a Pt-Hf (platinum hafnium) alloy, or the like).

[0021] The first layer 431, the second layer 432, and the third layer 433 each have a higher hardness and a lower flexibility than the first conductor layer 41. In addition, the first layer 431, the second layer 432, and the third layer 433 each have a smaller thickness than the second conductor layer .

[0022] The first layer 431 is mainly composed of titanium (Ti) and is disposed to ensure the bonding strength between the insulating substrate 2 and the conductor laminate portion 4. The second layer 432 is mainly composed of titanium (Ti), and since titanium has a high melting point, the second layer 432 functions as a so-called barrier metal layer. The third layer 433 is mainly composed of platinum (Pt). The first conductor layer 41 is well bonded to the second conductor layer 42 via the second layer 432 which is mainly composed of silver (Ag) and has good adhesion to the second conductor layer 42, the first conductor layer 41 which is mainly composed of gold (Au), and the third layer 433 which is mainly composed of gold (Au) and has good adhesion to the second layer 432.

[0023] The main components of each layer constituting the conductor layer laminated portion 4 can be identified by analyzing a cross section of the conductor layer laminated portion 4 with an electron probe micro analyzer (EPMA). In the EPM, an energy dispersive X-ray spectroscopy (EDS) is used as a spectrometer for characteristic X-rays.

[0024] As described above, according to the wiring board 10 of the present embodiment, the second conductor layer 42 having a hardness equal to or less than that of the first conductor layer 41 arranged on the outermost surface of the conductor layer laminated portion 4 is arranged between the first conductor layer 41 and the insulating substrate 2. Therefore, compared to the case where only a conductor layer having a hardness higher than that of the first conductor layer 41 is arranged between the first conductor layer 41 and the insulating substrate 2, the flexibility of the conductor layer laminated portion 4 can be improved, and the conductor layer laminated portion 4 is easily deformed. Therefore, when an electronic component is bonded to the first conductor layer 41 using a gold bump, the conductor layer laminated portion 4 is deformed, thereby reducing voids at the bonding interface between the gold bump and the conductor layer laminated portion 4, and suppressing a decrease in bonding reliability. That is, the wiring board 10 of the present embodiment can provide high bonding reliability.

[0025] Furthermore, the conductor layer laminated portion 4 includes the third conductor layer 43, which has a higher hardness than the first conductor layer 41, but the layer thickness thereof is thinner than the second conductor layer 42. Therefore, the flexibility of the conductor layer laminated portion 4 can be improved compared to a case in which the layer thickness of the second conductor layer 42 is equal to or less than the layer thickness of the third conductor layer 43.

[0026] In the case of forming a conductor layer (wiring layer) mainly made of gold in a wiring board, for example, it is possible to increase the layer thickness in order to reduce resistance. However, since gold is expensive, the cost of the wiring board increases. In contrast, according to the wiring board 10 of this embodiment, the conductor layer laminated part 4 is used as the conductor layer, and although the outermost layer is the first conductor layer 41 mainly made of gold, the other layers are mainly made of a material that is cheaper than gold, so that the cost can be reduced. Also, as described above, in the conductor layer laminated part 4 of the wiring board 10, since the outermost layer is the first conductor layer 41 mainly made of gold, the surface of the conductor layer laminated part 4 is soft and smooth, and since the conductor layer laminated part 4 has the second conductor layer 42, it is easy to deform, so that the bonding with a bonding member such as a metal bump can be improved. That is, according to the wiring board 10 of this embodiment, compared to a wiring board having a conductor layer mainly made of gold, the cost can be reduced while maintaining the same bonding reliability.

[0027] The wiring board 10 of this embodiment uses an aluminum nitride (AlN) ceramic substrate as the insulating substrate 2, and has high heat dissipation properties and high strength. Furthermore, as described above, the conductor layer laminated portion 4 has low resistance and high bonding reliability. Therefore, the wiring board 10 can be suitably used as a wiring board for mounting light-emitting elements and a wiring board for mounting power semiconductor elements.

[0028] Hardness measurement method: FIG. 2 is an explanatory diagram of a method for measuring the hardness of a conductor layer. The hardness of the conductor layer is measured by a nanoindentation method and evaluated by an indentation load at a depth of 1 / 10 of the film thickness. By using the nanoindentation method, the hardness of a thin film can be measured. Furthermore, by evaluating at a depth of 1 / 10 of the film thickness, the influence of the base can be reduced. FIG. 2(A) shows the measurement of the hardness of the first conductor layer 41, and FIG. 2(B) shows the measurement of the hardness of the second conductor layer 42. In measurement step 1 (FIG. 2(A)), the hardness of the first conductor layer 41 is measured. Thereafter, the first conductor layer 41, the third layer 433, and the second layer 432 are peeled off, and in measurement step 2 (FIG. 2(B)), the hardness of the second conductor layer 42 is measured. Similarly, the hardness of the first layer 431, the second layer 432, and the third layer 433 can also be measured. This makes it possible to know the magnitude relationship between the hardness of first conductor layer 41, second conductor layer 42, and third conductor layer 43.

[0029] Manufacturing method of wiring board 10: 3A to 3C are process diagrams showing an example of a method for manufacturing the wiring board 10. In Fig. 3, a cross section of the wiring board 10 (corresponding to the cross section shown in Fig. 1) is shown generally.

[0030] In step P102, an insulating substrate 2 is prepared and baked in a vacuum at, for example, 1000° C. or higher.

[0031] In step P104, a first thin film 11p containing titanium (Ti) as a main component is formed on the insulating substrate 2 by sputtering.

[0032] In process P106, a resist R is formed on the first thin film 11p by a known method such as photolithography, printing, etc. Thereafter, a second thin film 12 containing titanium (Ti) as a main component, a second conductor layer 42, a second layer 432, a third layer 433, and a first conductor layer 41 are formed in that order on the first thin film 11p by sputtering.

[0033] In process P108, after the resist R is removed, a portion of the first thin film 11p is removed by etching to form the first thin film 11. As shown in the figure, the first layer 431 is configured by the first thin film 11 and the second thin film 12. Through the above processes, the wiring board 10 of the present embodiment is manufactured.

[0034] <Second embodiment> 4 is an explanatory diagram illustrating a schematic cross-sectional configuration of a wiring board 10A of the second embodiment. The wiring board 10A of the present embodiment includes a conductor layer laminate portion 4A instead of the conductor layer laminate portion 4 of the wiring board 10 of the first embodiment. In the following description, the same components as those of the wiring board 10 of the first embodiment are denoted by the same reference numerals, and the preceding description is to be referred to.

[0035] The conductor layer laminate portion 4A is similar to the first embodiment in that it comprises a first conductor layer 41, a second conductor layer 42, and a third conductor layer 43; however, the main component of the third conductor layer 43 and the shapes of the first conductor layer 41 and the third conductor layer 43 differ from those of the conductor layer laminate portion 4 of the first embodiment.

[0036] The conductor layer lamination portion 4A includes a first layer 431, a fourth layer 434, and a fifth layer 435 as the third conductor layer 43. In the wiring board 10, the conductor layers are laminated on the insulating board 2 in the following order: the first layer 431, the second conductor layer 42, the fourth layer 434, the fifth layer 435, and the first conductor layer 41.

[0037] The fourth layer 434 is mainly composed of nickel (Ni). The fourth layer 434 can be formed using nickel or a nickel alloy (for example, a Ni-Cr (nickel chromium) alloy, etc.). The fifth layer 435 is mainly composed of palladium (Pd). The fifth layer 435 can be formed using palladium or a palladium alloy.

[0038] The first layer 431, the fourth layer 434, and the fifth layer 435 each have a higher hardness and a lower flexibility than the first conductor layer 41. In addition, the first layer 431, the fourth layer 434, and the fifth layer 435 each have a smaller thickness than the second conductor layer .

[0039] The fourth layer 434 is mainly composed of nickel (Ni) and has high corrosion resistance, so that by covering the surface of the second conductor layer 42 mainly composed of silver (Ag), it is possible to suppress corrosion of the second conductor layer 42. The fifth layer 435 is mainly composed of palladium (Pd) and has good adhesion to the fourth layer 434 mainly composed of nickel and the first conductor layer 41 mainly composed of gold, so that the first conductor layer 41 is well bonded to the fourth layer 434. Furthermore, since the surface (upper surface and side surface) of the conductor layer laminated portion 4A is formed by the first conductor layer 41 mainly composed of gold, which has high corrosion resistance, it is possible to improve the corrosion resistance of the conductor layer laminated portion 4A.

[0040] According to the wiring board 10A of the present embodiment, a wiring board with high joint reliability can be provided, similarly to the wiring board 10 of the first embodiment, and further, a wiring board with a conductor layer having high corrosion resistance can be provided.

[0041] 5A to 5C are process diagrams showing an example of a method for manufacturing wiring board 10A. In Fig. 5, a cross section (corresponding to the cross section shown in Fig. 4) of wiring board 10A is shown generally.

[0042] In step P202, an insulating substrate 2 is prepared and baked in a vacuum at, for example, 1000° C. or higher.

[0043] In process P204, a third thin film 431p containing titanium (Ti) as a main component and a fourth thin film 42p containing silver (Ag) as a main component are formed on the insulating substrate 2 by sputtering.

[0044] In process P206, a resist R is formed on the fourth thin film 42p by a known method such as photolithography or printing.

[0045] In process P208, the third thin film 431p and the fourth thin film 42p are partially removed by etching to form the first layer 431 and the second conductor layer 42. Thereafter, the resist R is removed.

[0046] In process P210, electroless plating is used to form fourth layer 434, fifth layer 435, and first conductor layer 41. Through the above processes, wiring board 10A of the present embodiment is manufactured.

[0047] <Modifications of this embodiment> The present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit and scope of the invention. For example, the following modifications are also possible.

[0048] In the above embodiment, the conductor layer laminated portion includes the first conductor layer, the second conductor layer, and the third conductor layer, but the third conductor layer may not be included. Even in this case, a highly flexible conductor layer can be provided.

[0049] In the above embodiment, the thickness of the second conductor layer is greater than that of the third conductor layer, but the thickness of the second conductor layer may be equal to or less than that of the third conductor layer. Even in this case, by disposing the second conductor layer between the first conductor layer and the insulating substrate, the flexibility of the conductor laminate portion can be improved and the joining reliability can be improved compared to when the second conductor layer is not provided.

[0050] The main components of the first conductor layer 41, the second conductor layer, and the third conductor layer are not limited to those in the above embodiment. For example, the first conductor layer 41 and the second conductor layer 42 may be mainly composed of a highly flexible metal such as tin or indium. In this way, a highly flexible conductor layer laminate can be formed.

[0051] In the above embodiment, an example is shown in which the second conductor layer has one layer and the third conductor layer has three layers, but the number of layers constituting the conductor laminate section is not limited to the above embodiment. For example, the second conductor layer may have two or more layers, and the third conductor layer may have two or less layers.

[0052] The arrangement of the second conductor layer and the third conductor layer is not limited to the above embodiment. For example, the third conductor layer may be arranged only between the first conductor layer and the second conductor layer, or the third conductor layer may be arranged only between the second conductor layer and the insulating substrate.

[0053] The method for manufacturing the wiring board is not limited to the above embodiment. For example, in step P204 of the method for manufacturing the wiring board of the second embodiment, after forming a layer mainly made of titanium and a layer mainly made of silver by sputtering, a layer mainly made of silver may be further formed by electroless plating. In this way, the time required for film formation can be shortened.

[0054] The wiring board of the above embodiment may be used to form, for example, a lighting device with LED elements mounted thereon, or a device with, for example, a power semiconductor that supplies and controls power, or an LSI (Large-Scale Integration) such as a microcomputer (CPU: central processing unit) or memory mounted thereon.

[0055] The present invention has been described above based on the embodiments and modifications, but the above-mentioned embodiments are intended to facilitate understanding of the present invention and do not limit the present invention. The present invention may be modified or improved without departing from the spirit and scope of the claims, and the present invention includes equivalents thereof. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate. [Explanation of symbols]

[0056] 2...Insulating substrate 4, 4A…Conductor layer laminate 10, 10A…wiring board 11, 11p...first thin film 12…Second thin film 41...First conductor layer 42...Second conductor layer 42p…4th thin film 43…Third conductor layer 431...1st layer 431p…Third thin film 432…Second layer 433...Third layer 434…4th layer 435...5th layer R…Resist

Claims

1. A wiring board, An insulating substrate; a conductor layer stacking section disposed on the insulating substrate and including a plurality of conductor layers stacked thereon; Equipped with The conductor layer laminate portion is A first conductor layer disposed on the outermost layer of the conductor layer laminated portion; a second conductor layer disposed between the first conductor layer and the insulating substrate, the second conductor layer having a hardness equal to or lower than that of the first conductor layer; Characterized in that it has Wiring board.

2. 2. The wiring board according to claim 1, The second conductor layer is The thickness of the first conductor layer is greater than that of the second conductor layer. Wiring board.

3. 3. The wiring board according to claim 1, The first conductor layer is Characterized in that gold (Au) is the main component. Wiring board.

4. 4. The wiring board according to claim 1, The second conductor layer is Characterized in that silver (Ag) is the main component. Wiring board.

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