JP2013045957A - Wiring board and electronic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wiring board in which conductivity of a small diameter through hole having a high aspect ratio is enhanced, and to provide an electronic device.SOLUTION: A wiring board 5 includes an insulation substrate 1 having a through hole 1a and containing aluminum nitride as a main component, an aluminum layer 2 provided from the upper end to the lower end of the inner surface of the through hole 1a, a thin film layer 3 provided on the surface of the aluminum layer 2, and a metal layer 4 provided on the surface of the thin film layer 3. Since the wiring board 5 includes such a configuration, a sufficient electric path can be provided from the upper end to the lower end of the through hole 1a by the aluminum layer 2, even if the thin film layer 3 is not provided in the center of the through hole 1a due to high aspect ratio thereof, and thereby the conductivity of a small diameter through hole 1a having a high aspect ratio is enhanced.

Description

  The present invention relates to a wiring board and an electronic device.

  For example, in the illumination field, as high-power light-emitting diode elements have been developed in recent years, light-emitting diode devices have been used as illumination light sources due to their long life and low power consumption. In such a light emitting diode device, a wiring substrate having a wiring conductor formed on the surface of a ceramic substrate or a through conductor formed therein is used.

  For example, as a light-emitting device is required to have a smaller size, a higher density, or a higher output, a demand for a wiring board is increasing due to the utilization of ceramic substrate characteristics such as high heat dissipation and heat resistance. As a method for reducing the size of a light emitting device, there is a method in which through holes are formed in a wiring substrate at a high density and LED elements are mounted at a high density.

  As one of the methods, when a metal layer is provided in the through hole after the through hole is formed in the insulating substrate mainly composed of aluminum nitride, the metal layer is used to improve the adhesion between the insulating substrate and the metal layer. Before providing, a thin film layer may be formed by thin film formation techniques, such as a vapor deposition method, an ion plating method, and a sputtering method (for example, refer patent document 1).

JP 2005-101178 A

  However, according to Patent Document 1, although a small-diameter through hole can be formed with high dimensional accuracy, a thin film layer is not provided in the central portion of the through hole as the through hole has a higher aspect ratio. was there. Therefore, the thin film layer is not continuously provided from the upper end portion to the lower end portion of the through hole, and it may be impossible to provide a sufficient electrical path. Therefore, it is necessary to improve the through hole with a small diameter and a high aspect ratio in order to conduct stably.

  A wiring board according to one aspect of the present invention includes an insulating substrate having a through hole and containing aluminum nitride as a main component, and an aluminum layer provided from the upper end portion to the lower end portion of the inner surface of the through hole. And a thin film layer provided on the surface of the aluminum layer, and a metal layer provided on the surface of the thin film layer.

  An electronic device according to another aspect of the present invention includes a wiring board and an electronic component mounted on the wiring board.

A wiring substrate according to one aspect of the present invention has a through hole, an insulating substrate containing aluminum nitride as a main component, an aluminum layer provided from the upper end to the lower end of the inner surface of the through hole, A thin film layer provided on the surface of the aluminum layer and a metal layer provided on the surface of the thin film layer are provided. Since the wiring board according to one aspect of the present invention includes such a configuration, even if a high aspect ratio of the through-hole is advanced and a thin film layer is not provided in the central portion of the through-hole, aluminum is used. The layer can provide a sufficient electrical path from the upper end to the lower end of the through hole.

  The electronic device according to another aspect of the present invention includes the wiring board having the above-described configuration, whereby the electrical conductivity of the small-diameter through hole 1a having a high aspect ratio is improved.

(A) is a top view which shows the electronic device in one Embodiment of this invention, (b) is a longitudinal cross-sectional view in the AA line of the electronic device shown by (a). (A) is a top view which shows one Embodiment of the wiring board (mother wiring board) used for the electronic apparatus shown by FIG. 1, (b) is an enlarged view of the B section of (a). (C) is a longitudinal cross-sectional view in CC line of (b). It is sectional drawing which expands and shows the principal part of the wiring board shown by FIG.2 (c). It is an enlarged view of the principal part of the wiring board in other embodiment of this invention. It is an enlarged view of the principal part of the wiring board in other embodiment of this invention.

  Several exemplary embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIGS. 2A and 2B are plan views showing one embodiment of a wiring board (mother wiring board) used in the electronic device shown in FIGS. The electronic device according to the first embodiment of the present invention will be described with reference to FIG. 3 which is an enlarged cross-sectional view of the main part of the wiring board 5 shown in (c) and FIG. 2 (c). As shown in FIGS. 1A and 1B, the electronic device according to the present embodiment includes a wiring board 5 and an electronic component 6 mounted on the wiring board 5.

  Also, as shown in FIGS. 1A, 1B, 2A, 2B, 3C and 3, the wiring board 5 has a through hole 1a. Insulating substrate 1 containing aluminum nitride as a main component, aluminum layer 2 provided from the upper end portion to the lower end portion of the inner surface of through-hole 1a, thin film layer 3 provided on the surface of aluminum layer 2, and thin film layer 3 and a metal layer 4 provided on the surface of 3.

  Further, since the wiring board 5 is often small in product size, as shown in FIGS. 2A, 2B, and 2C, the mother wiring board 5 in which a large number of wiring boards 5 are formed. In some cases, the mother wiring board is also included in the wiring board.

A method of creating the wiring board 5 that is obtained by dividing the mother wiring board 5 ′ and the mother wiring board 5 ′ in the present embodiment shown in FIG. 2 will be described below. The mother insulating substrate 1 ′ containing aluminum nitride as a main component is made into a slurry by adding and mixing yttria, calcia, a suitable organic solvent, and a solvent as a sintering aid to aluminum nitride as a main raw material. A green sheet (raw sheet) is formed by adopting a conventionally known doctor blade method or calendar roll method, and then the green sheet is fired at a high temperature (about 1800 ° C.). In order to increase productivity, the insulating substrate 1 is usually formed in a state of a mother insulating substrate in which a large number of insulating substrates 1 are assembled, and is divided when the mother wiring substrate 5 'is completed or the electronic device is completed. In many cases, the production process is mainly the production process of the mother wiring board 5 ′. However, the wiring board 5 can also be produced directly without dividing the mother wiring board 5 ′. The phrase “containing aluminum nitride as a main component” means that the insulating substrate 1 contains 80% by mass or more of aluminum nitride. If the aluminum nitride contained in the insulating substrate 1 is less than 80% by mass, it is difficult to stably form the aluminum layer 2 on the surface of the through hole 1a. Preferably, the aluminum nitride in the insulating substrate 1 is contained at 95% by mass or more. It is preferable that 95% by mass or more of aluminum nitride is included because the thermal conductivity of the insulator is easily set to 170 W / mK or more, and the wiring board 5 is excellent in heat dissipation.

A through hole 1a is formed in a predetermined portion of the mother insulating substrate 1 'made of aluminum nitride by laser processing. If a YAG laser or excimer laser with a short wavelength is used, the aluminum nitride is instantly evaporated, and the aluminum layer 2 is not easily formed on the inner surface of the through hole 1a. If a CO ₂ laser is used, the surface of the aluminum nitride is stable. Since the aluminum layer 2 is easily formed, it is preferable to use a CO ₂ laser. For example, an insulating substrate having an aluminum nitride content of 95% by mass, a thermal conductivity of 170 W / mK, a plate thickness of 0.38 mm, an output of 20 W, and a focal point diameter of 0.1 mm CO ₂ laser (wavelength 10.6 μm) ) Is used to form a through hole 1a having an incident side diameter of 0.13 mm and an exit side diameter of 0.06 mm, and aluminum is formed on the surface of the through hole 1a. . The thickness of the aluminum layer 2 at this time was 1 to 16 μm.

  The aluminum layer 2 is formed by reducing the aluminum nitride by the laser processing described above when the through-hole 1a is formed in the mother insulating substrate 1 ′ made of aluminum nitride. 2 is provided from the upper end to the lower end of the inner surface of the through hole 1a.

The adhesion metal layer constituting the thin film layer 3 is planarized by removing the projections formed by laser processing around the through-holes 1a on the front and back surfaces of the mother insulating substrate 1 'by polishing or the like as necessary. It is formed near the front and back surfaces and the upper and lower surfaces of the through hole 1a. The adhesion metal layer is made of, for example, tantalum nitride, nickel-chromium, nickel-chromium-silicon, tungsten-silicon, molybdenum-silicon, tungsten, molybdenum, titanium, chromium, etc., and thin films such as vapor deposition, ion plating, and sputtering. By adopting the formation technique, it is deposited on the aluminum layer 2 and the insulating substrate 1 in the through hole 1a. For example, when forming using a vacuum evaporation method, the mother insulating substrate 1 'is installed in a film forming chamber of a vacuum evaporation apparatus, and a metal piece serving as an adhesion metal layer is disposed in a vapor deposition source in the film forming chamber, and then The inside of the film forming chamber is evacuated (pressure of 10 ⁻² Pa or less), the metal piece arranged in the vapor deposition source is heated and vapor-deposited, and the molecules of the vapor-deposited metal piece are deposited on the insulating substrate 1. As a result, a thin film metal layer to be an adhesion metal layer is formed. Then, after a resist pattern is formed on the insulating substrate 1 on which the thin film metal layer is formed by using a photolithography method, an extra thin film metal layer is removed by etching, thereby forming an adhesion metal layer. A barrier layer constituting the thin film layer 3 is deposited on the upper surface of the adhesion metal layer. The barrier layer has good adhesion and wettability with the adhesion metal layer and the main conductor layer, and the adhesion metal layer and the main conductor layer are firmly bonded. It serves to prevent the mutual diffusion between the adhesion metal layer and the main conductor layer as well as joining. The barrier layer is made of, for example, nickel-chromium, platinum, palladium, nickel, cobalt or the like, and is deposited on the upper surface of the adhesion metal layer by a thin film forming technique such as a vapor deposition method, an ion plating method, or a sputtering method.

The thickness of the adhesion metal layer is preferably about 0.01 to 0.5 μm. If it is less than 0.01 μm, it tends to be difficult to firmly adhere the adhesion metal layer on the insulating substrate 1 and the aluminum layer 2. When the thickness exceeds 0.5 μm, peeling of the adhesion metal layer is likely to occur due to internal stress during the formation of the adhesion metal layer.

  The thickness of the barrier layer is preferably about 0.05 to 1 μm. If the thickness is less than 0.05 μm, defects such as pinholes tend to occur, and the function as a barrier layer tends not to be achieved. When the thickness exceeds 1 μm, the barrier layer is easily peeled off due to internal stress during film formation.

The metal layer 4 is formed by forming a resist film (not shown) on the front and back surfaces of the insulating substrate 1 on portions where the surface wiring 7 is not formed, and forming copper on the surfaces of the thin film layer 3 and the aluminum layer 2 by electrolytic plating. By this formation method, the metal layer 4 is filled in the through hole 1a and a thick conductor layer is formed in a portion to be the surface wiring 7.

  When titanium (Ti) is used as the adhesion metal layer and copper (Cu) is sputtered in this order, a titanium / copper barrier layer is formed at the junction between titanium and copper, and is formed on the surface. Since a copper conductor layer is formed, if copper is formed on the surface by electrolytic plating, the metal layer 4 is entirely formed of copper, so that the electrical resistance and thermal resistance are lowered and a large current is passed. Since it becomes easy, it is preferable.

  The thickness of the surface wiring layer 7 is preferably about 2 to 200 μm. If the thickness is less than 2 μm, there is a tendency that current cannot sufficiently flow. If the thickness exceeds 200 μm, the temperature cycle reliability tends to be lowered. If the thickness of the surface wiring layer 7 is 50 μm or more, the difference in thermal expansion from the insulating substrate 1 cannot be ignored, but if the thickness difference between the upper and lower surface wiring layers 7 is 5 μm or less, the wiring substrate 5 is warped. Since it becomes difficult to do, it is preferable.

  When the metal layer 4 and the surface wiring layer 7 are copper, it is preferable to form a nickel layer and a gold layer on the surface in this order for preventing corrosion of the surface.

  Next, the resist is peeled off, and the exposed thin film layer 3 is removed by etching with hydrofluoric acid, whereby the mother wiring board 5 'is obtained.

  Since the through-hole 1a is formed in the fired mother insulating substrate 1 'by laser processing and the surface wiring 7 is formed, the mother wiring substrate 5' having high dimensional accuracy can be obtained. Thus, the electronic component 6 such as a light emitting element can be easily arranged and the electrical connection by the bonding wire 8 can be performed.

  When the electronic device is assembled on the mother wiring board 5 ', the electronic device is divided into individual electronic devices by a method such as dicing or laser cleaving from the assembled state. Alternatively, after dividing the mother wiring board 5 ′ into individual wiring boards 5 by the same method, the electronic components 6 are arranged and connected in the same manner to obtain an electronic device.

  In the wiring substrate 5 of the present embodiment, the insulating substrate 1 having the through hole 1a and containing aluminum nitride as a main component, and the aluminum layer 2 provided from the upper end portion to the lower end portion of the inner surface of the through hole 1a. And the thin film layer 3 provided on the surface of the aluminum layer 2 and the metal layer 4 provided on the surface of the thin film layer 3, the aspect ratio of the through hole 1 a is increased and the through hole is temporarily provided. Even if the thin film layer 3 is not provided in the central portion of the la, the aluminum layer 2 can provide a sufficient electrical path from the upper end to the lower end of the through hole 1a, and the small diameter through hole 1a having a high aspect ratio. This improves the electrical conductivity.

  Moreover, in the electronic device of this embodiment, by providing the wiring substrate 5 having the above-described configuration, the electrical conductivity of the small-diameter through hole 1a having a high aspect ratio is improved.

(Second Embodiment)
An electronic device according to the second embodiment of the present invention will be described with reference to FIG. In the electronic device of the present embodiment, the difference from the first embodiment is the structure of the metal layer 4 in the through hole 1a. In the first embodiment, the inside of the through hole 1a is filled with the metal layer 4. However, in this embodiment, the through hole 1a is formed in layers on the inner surface, and one of the through holes is a surface wiring layer. 7 is closed, but the other is open. By adopting the structure of the second embodiment, it is difficult to apply stress due to the difference in thermal expansion between the insulating substrate 1 and the metal layer 4, so that even if the arrangement density of the through holes 1 a is increased, the insulating substrate 1 is preferable because cracks due to stress are less likely to occur.

(Third embodiment)
An electronic device according to a third embodiment of the present invention will be described with reference to FIG. In the electronic device of the present embodiment, the through hole 1a is filled with the metal layer 4 and then the front and back surfaces are polished, and then the surface wiring layer 7 is formed. In this way, the metal layer 4 in the through hole 1a is formed. When the surface wiring layer 7 is formed separately, the surface wiring layer 7 can be made of a metal different from the metal layer 4, so that a thick film layer is formed as the surface wiring layer 7 in addition to the layer using the thin film forming technique. In addition, even when the thin film forming technique is used, the insulating substrate 1 formed up to the through conductor is prepared, and various surface wiring layers 7 are formed on the front and back surfaces of the insulating substrate 1 as necessary. This is preferable because the delivery time can be shortened.

DESCRIPTION OF SYMBOLS 1 ... Insulating substrate 1a ... Through-hole 2 ... Aluminum layer 3 ... Thin film layer 4 ... Metal layer 5 ... Wiring board 6 .... ... Electronic components 7 ... Surface wiring layer 8 ... Bonding wire

Claims (2)

  An insulating substrate having a through hole and containing aluminum nitride as a main component, an aluminum layer provided from the upper end to the lower end of the inner surface of the through hole, and a thin film provided on the surface of the aluminum layer A wiring board comprising: a layer; and a metal layer provided on a surface of the thin film layer.   An electronic device comprising: the wiring board according to claim 1; and an electronic component mounted on the wiring board.

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