Patent Description:
There has been known a wiring substrate in which an Al-based wiring conductor is disposed on an Si substrate with an insulating film and a titanium-based metal film in between. (See, for example, <CIT>). <CIT> discloses another conventional metal-ceramic circuit board.

A wiring substrate according to the present disclosure includes:.

An electronic device according to the present disclosure includes:.

An electronic module according to the present disclosure includes:.

Hereinafter, one or more embodiments of the present disclosure will be described in detail with reference to the drawings.

<FIG> each show part of a wiring substrate of an embodiment, wherein <FIG> is a vertical sectional view thereof, <FIG> is a plan view thereof, and <FIG> is a plan view thereof with an Ni (nickel) film removed. <FIG> is a plan view of the entire wiring substrate of the embodiment. In this description, explanation is made with a direction from a second surface <NUM> to a first surface <NUM> of an insulating substrate <NUM> regarded as upward. However, directions described in this description may be different from directions of a wiring substrate <NUM> when it is mounted or used.

The wiring substrate <NUM> of this embodiment is, for example, a submount that is, for mounting an electronic component on a module board or in a package, interposed between the electronic component and the mounting destination. The wiring substrate <NUM> includes the insulating substrate <NUM> made of a ceramic material containing AlN (aluminum nitride), a wiring conductor <NUM> formed on the insulating substrate <NUM>, and an Ni film <NUM> covering the upper surface and the side surface of the wiring conductor <NUM>. The wiring conductor <NUM> corresponds to an example of a conductor according to the present disclosure.

The insulating substrate <NUM> is made of a ceramic material containing AlN as a constituent element. The insulating substrate <NUM> has a first surface (first main surface) <NUM> and a second surface (second main surface) <NUM> on the opposite side. The wiring conductor <NUM> is formed on the first surface <NUM>. The wiring conductor <NUM> may be formed on each of the first surface <NUM> and the second surface <NUM> of the insulating substrate <NUM>. In a case where the wiring conductor <NUM> on the second surface <NUM> is regarded as the conductor according to the present disclosure, the second surface <NUM> corresponds to the first surface according to the present disclosure, and the first surface <NUM> corresponds to the second surface according to the present disclosure.

On the first surface <NUM> of the insulating substrate <NUM>, as shown in <FIG>, a plurality of Ti oxides <NUM> is scattered. In other words, Ti oxide <NUM> is scattered all over the first surface <NUM> in the plane direction thereof so as to be present at various points thereon. The Ti oxides <NUM> may each be, for example, TiO<NUM> (titanium oxide). The Ti oxides <NUM> may be disposed in recesses 11D of the first surface <NUM> described below.

The insulating substrate <NUM> has minute recesses 11D on the first surface <NUM>. The recesses 11D may each have an opening having a maximum width of, for example, <NUM> to <NUM>. On the first surface <NUM>, the recesses 11D may be provided at an area ratio of <NUM>% to <NUM>%. The recesses 11D are formed all over the first surface <NUM>, but may be formed only at a part(s) that the Ni film <NUM> contacts. Hereinafter, explanation is made with the recesses 11D regarded as points where the Ti oxides <NUM> are present on the first surface <NUM>.

The recesses 11D include compound recesses 11DW (shown in <FIG>) each having a shape of two or more recesses overlapped if the plane shape of each recess 11D is regarded as granular.

The wiring conductor <NUM> is a conductor made of Cu (copper) as a main component, and is formed on the insulating substrate <NUM> having a layer of the Ti oxides <NUM> in between. In a sintering step described below, the Ti oxides <NUM> may gather in the recesses 11D, and the interface between the insulating substrate <NUM> and the wiring conductor <NUM> may include parts where the layer of the Ti oxides <NUM> remains and parts where the layer of the Ti oxides <NUM> has disappeared. At parts where the Ti oxides <NUM> gather in the recesses 11D under the wiring conductor <NUM>, an interlayer 16a (<FIG>) where atoms other than the Ti oxides <NUM> interdiffuse is formed. Further, in the recesses 11D that the Ni film <NUM> contacts, a similar interlayer 16b (<FIG>) may remain.

The Ni film <NUM> is a film made of Ni as a main component, and covers the upper surface <NUM> and the side surface <NUM> of the wiring conductor <NUM> until it reaches a part of the first surface <NUM> of the insulating substrate <NUM>. The Ni film <NUM> has, at its foot near the first surface <NUM> of the insulating substrate <NUM>, a protrusion <NUM> that protrudes to the side opposite the wiring conductor <NUM>. The outer edge of the protrusion <NUM> has a plurality of hills h1 to h4 and a plurality of valleys c1 to c3 as viewed in a direction perpendicular to the first surface <NUM> of the insulating substrate <NUM> (<FIG>).

The Ni film <NUM> is in contact with some of the recesses 11D on the first surface <NUM> of the insulating substrate <NUM> with the Ti oxides <NUM> in between. Hereinafter, contact of the Ni film <NUM> and the recesses 11D with the Ti oxides <NUM> in between may be simply referred to as contact of the Ni film <NUM> and the recesses 11D. Hereinafter, of the recesses 11D, those with which the Ni film <NUM> is in contact may be referred to as contact recesses 11Da. The contact recesses 11D may include the compound recesses 11DW.

As shown in <FIG>, the contact recesses 11Da align along the side surface <NUM> (lower side 22e of the side surface <NUM>, to be specific) of the wiring conductor <NUM>. Further, as shown in <FIG>, the protrusion <NUM> of each Ni film <NUM>, the protrusion <NUM> being in contact with the insulating substrate <NUM>, is present around the entire perimeter of the wiring conductor <NUM>, and the contact recesses 11Da are present around the entire perimeter under the protrusion <NUM> as shown in <FIG>. Thus, the contact recesses 11Da surround the wiring conductor <NUM> and are present at least in four directions around the wiring conductor <NUM>. The contact recesses 11Da include those partly uncovered with the Ni film <NUM> and exposed and those fully covered with the Ni film <NUM> and not exposed. The contact recesses 11Da fully covered with the Ni film <NUM> mean that the protrusion <NUM> protrudes to positions beyond the contact recesses 11Da.

In a section perpendicular to the first surface <NUM> and the side surface <NUM> of the wiring conductor <NUM>, the wiring substrate <NUM> may include a point where two or more contact recesses 11Da are present under the Ni film <NUM>. Presence of the protrusion <NUM> of the Ni film <NUM> increases the contact area between the Ni film <NUM> and the insulating substrate <NUM>, and enables the Ni film <NUM> to contact more recesses 11D.

<FIG> shows concentration distributions of constituent elements in the interlayer between the wiring conductor and the insulating substrate. <FIG> shows concentration distributions of the constituent elements in the interlayer under the Ni film. The constituent elements and the concentration distributions in the interlayers 16a, 16b described hereinafter are results of measurement with electron energy loss spectroscopy (TEM-EELS). The concentrations are expressed with at% (atomic percent).

The interlayer 16a present at the interface between the wiring conductor <NUM> and the recesses 11D has a thickness of, for example, <NUM> to <NUM>, and as shown in <FIG>, contains Al (aluminum), N (nitrogen), Cu (copper), Ti (titanium) and O (oxygen). The interlayer 16a has concentration gradients in which Al, N and Cu concentrations gradually change. Al and N concentration gradients are each a gradient in which the closer the position in the interlayer 16a is to the wiring conductor, the lower the concentration is, and Cu concentration gradient is a gradient in which the closer the position in the interlayer 16a is to the wiring conductor <NUM>, the higher the concentration is. These concentration gradients may exist from the wiring conductor <NUM> side to the insulating substrate <NUM> side of the interlayer 16a.

The interlayer 16b present at the interface between the Ni film <NUM> and the contact recesses 11Da has a thickness of, for example, <NUM> to <NUM>, and as shown in <FIG>, contains Al, N, Cu, Ti and O. The interlayer 16b has concentration gradients in which Al, N and Cu concentrations gradually change. Al and N concentration gradients are each a gradient in which the closer the position in the interlayer 16b is to the Ni film <NUM>, the lower the concentration is, and Cu centration gradient is a gradient in which the closer the position in the interlayer 16b is to the Ni film <NUM>, the higher the concentration is. These concentration gradients may exist from the Ni film <NUM> side to the insulating substrate <NUM> side of the interlayer 16b.

The interlayers 16a, 16b may contain <NUM> at% or less of C (carbon). C concentration of <NUM> at% or less may be approximately the same as C concentration in the wiring conductor <NUM>.

<FIG> each show an electron microscope image of a lower end part of the wiring conductor in the wiring substrate of the embodiment. As shown in <FIG>, although in practice, an inwardly curved shape (undercut) is generated at a lower end corner E1/E2/E3 of the wiring conductor <NUM>, the Ni film <NUM> extends along the side surface of the wiring conductor <NUM> to the lower end corner E1/E2/E3 of the wiring conductor <NUM>. The Ni film <NUM> partly protrudes from the lower end corner E1/E2/E3 of the wiring conductor <NUM> to the side opposite the wiring conductor <NUM> along the first surface <NUM> of the insulating substrate <NUM>, thereby forming the protrusion <NUM>. The border between the Ni film <NUM> including the protrusion <NUM> and the insulating substrate <NUM> includes the contact recesses 11Da. If the interface in the contact recesses 11Da is measured with energy dispersive X-ray spectroscopy (EDS) or electron energy loss spectroscopy, Ti and O are observed.

<FIG> shows a diagram to explain a manufacturing method of the wiring substrate of the embodiment.

The manufacturing method of the wiring substrate <NUM> of the embodiment includes, in chronological order, a pretreatment step J1, a Ti film forming step J2, an electroless plating and sintering step J3, a resist processing step J4, an electroplating step J5, a resist removal and etching step J6, and a plating step J7.

In the pretreatment step J1, a ceramic green sheet(s) <NUM> of pre-sintered ceramic is molded into the shape of a substrate by punching, die machining or the like. The ceramic green sheet <NUM> may be provided with vias v for electrical conduction into the substrate. In order to form the insulating substrate <NUM>, the ceramic green sheet <NUM> is sintered. In the pretreatment step J1, a pre-sintered or sintered ceramic green sheet(s) <NUM> may be anisotropically etched by using a chemical(s) or reactive ions. This anisotropic etching can control the size and density of the recesses 11D on the first surface <NUM> and the second surface <NUM> of the insulating substrate <NUM>.

The Ti film forming step J2 is a step of applying an organic Ti solution to a pre-sintered or sintered ceramic green sheet(s) <NUM> and sintering these. This sintering may be performed under conditions of <NUM> or higher and <NUM> minutes or longer, for example. This sintering transforms the organic Ti solution <NUM> into a solidified titanium oxide layer 71A. The sintering for the titanium oxide layer 71A and the sintering on the ceramic green sheet <NUM> may be performed in parallel.

In the electroless plating and sintering step J3, after electroless Cu plating is performed on the insulating substrate <NUM> having the titanium oxide layer 71A, sintering is performed thereon to diffuse elements at the interface. Conditions for this sintering may be <NUM> or higher and <NUM> minutes or longer in an atmosphere of an inert gas. The electroless Cu plating forms a Cu plating layer <NUM>, and the sintering forms the interlayers 16a, 16b described above. The titanium oxide layer 71A and the Cu plating layer <NUM> that have undergone this sintering function as a seed layer. Since the seed layer is formed by wet process, manufacturing cost is reduced.

In the resist processing step J4, a pattern for the wiring conductors <NUM> (shown in <FIG>) is formed on the Cu plating layer <NUM> with a DFR (Dry Film Resist) <NUM>, for example. In the Cu electroplating step J5, Cu electroplating is performed on the Cu plating layer <NUM> in accordance with the pattern of the DFR <NUM> to form Cu conductors <NUM> having a predetermined thickness. If the vias v have been formed in the insulating substrate <NUM>, the vias v are filled with the Cu conductors <NUM> in the Cu electroplating step J5.

In the resist removal and etching step J6, first, the DFR <NUM> is removed. Removal of the DFR exposes the seed layer (Cu plating layer <NUM> and titanium oxide layer 71A). Thereafter, the exposed seed layer is etched by using a chemical(s). The amount of etching is controlled such that the components of the titanium oxide layer 71A remain in the recesses 11D of the insulating substrate <NUM>. In the steps J6 and J7, although it is depicted in a simplified form in <FIG>, the titanium oxide layer 71A is not in the shape of a layer but scattered so as to be present in the recesses 11D.

In the plating step J7, electroless Ni plating is performed on a side where the Cu conductors <NUM> are formed, so that the Ni films <NUM> cover the Cu conductors <NUM> and the peripheries of residues 74a of the Cu plating layer <NUM> under the Cu conductors <NUM>. Further, since the components of the titanium oxide layer 71A remain in the recesses 11D on the insulating substrate <NUM>, the Ni films <NUM> are formed so as to slightly extend on the insulating substrate <NUM> to contact the recesses 11D near the Cu conductors <NUM> and the residues 74a. In the plating step J7, in addition to the Ni films <NUM> being formed, the Ni films <NUM> may be plated with other metals (e.g. Pd (palladium) and Au (gold)).

By the above manufacturing method, the wiring substrate <NUM> of the embodiment can be manufactured.

<FIG> is a sectional view of an electronic device and an electronic module according to an embodiment of the present disclosure.

An electronic device <NUM> of this embodiment is configured by mounting an electronic component <NUM> on the wiring substrate <NUM>. The electronic component <NUM> may be joined to the wiring conductor(s) <NUM> and the Ni film(s) <NUM> with a joining material. Electrodes of the electronic component <NUM> may be connected to the wiring conductor <NUM> and the Ni film <NUM> through bonding wires. On the Ni film <NUM>, other metal films, such as a Pd film and an Au film, may be formed. The electronic device <NUM> may have a package that houses the wiring substrate <NUM> and the electronic component <NUM>.

As the electronic component <NUM>, various electronic components are applicable, which include: optical elements, such as an LD (Laser Diode), a PD (Photo Diode) and an LED (Light Emitting Diode); imagers, such as a CCD (Charge Coupled Device) image sensor and a CMOS (Complementary Metal Oxide Semiconductor) image sensor; piezoelectric vibrators, such as a crystal oscillator; surface acoustic wave devices; semiconductor devices, such as a semiconductor integrated circuit (IC) device; electric capacitors; inductors; and resistors.

An electronic module <NUM> of this embodiment is configured by mounting the electronic device <NUM> on a module board <NUM>. On the module board <NUM>, in addition to the electronic device <NUM>, other electronic device(s), electronic element(s), electric element(s) and/or the like may be mounted. The module board <NUM> may be provided with an electrode pad <NUM>, and the electronic device <NUM> may be joined to the electrode pad <NUM> with a joining material <NUM>, such as solder. At a part of the electronic device <NUM> to which the joining material <NUM> is joined, the wiring conductor <NUM> and the Ni film <NUM> may be provided. If the electronic device <NUM> has a package, a wiring conductor of the package may be joined to the electrode pad <NUM> of the module board <NUM>.

As described above, according to the wiring substrate <NUM> of an embodiment, the Ni film <NUM> covers the upper surface and the side surface of the wiring conductor <NUM> having Cu as a constituent element. Further, the foot of the Ni film <NUM> reaches the insulating substrate <NUM> and is in contact with the Ti oxides <NUM>. Thus, the foot of the Ni film <NUM> adheres to the insulating substrate <NUM> with the Ti oxides <NUM> in between with high strength, which can suppress separation of the Ni film <NUM> from the foot. This can suppress inconvenience, such as the following: the wiring conductor <NUM> is partly exposed due to the separation of the Ni <NUM>, and consequently corrosion occurs at the exposed part or ion migration occurs from the exposed part onto the insulating substrate <NUM>.

Further, according to the wiring substrate <NUM> of the embodiment, the Ni film <NUM> has the protrusion <NUM> that protrudes to the side opposite the wiring conductor <NUM> along the first surface <NUM> of the insulating substrate <NUM>. The protrusion <NUM> increases the contact area between the Ni film <NUM> and the insulating substrate <NUM>, and increases the number of contact recesses 11Da, which the Ni film <NUM> contacts. This can further increase adhesion strength of the foot of the Ni film <NUM> to the insulating substrate <NUM>, and accordingly further suppress the separation of the Ni film <NUM>.

Further, the protrusion <NUM> protrudes beyond at least one of the contact recesses 11Da. Hence, at least at this part, contact of the Ni film <NUM> and the contact recess 11Da with the Ti oxide <NUM> in between is obtained, and high adhesion strength of the Ni film <NUM> to the insulating substrate <NUM> is obtained.

Further, according to the wiring substrate <NUM> of the embodiment, the edge on the protruding side of the protrusion <NUM> has a shape in which the hills h1 to h4 and the valleys c1 to c3 are included as viewed in the direction perpendicular to the first surface <NUM> of the insulating substrate <NUM> (<FIG>). Hence, on the insulating substrate <NUM> where the recesses 11D are randomly arranged, the Ni film <NUM> contacts many recesses 11D at the hills h1 to h4 of the protrusion <NUM> to increase the adhesion strength. On the other hand, at a part(s) where a small number of recesses 11D are present, the valleys c1 to c3 are arranged to shorten a part(s) having low adhesion strength. In the case where the recesses 11D are randomly arranged, the hills/valleys of the protrusion <NUM> are arranged in such a manner in many areas. The work of these further increases the adhesion strength of the protrusion <NUM> to the insulating substrate <NUM>, and can provide a characteristic of the separation being more unlikely to occur.

Further, according to the wiring substrate <NUM> of the embodiment, the contact recesses 11Da, which contact the Ni film <NUM>, align along the edge of the wiring conductor <NUM>. In addition, the contact recesses 11Da, which contact the Ni film <NUM>, surround the wiring conductor <NUM>. Such configuration can suppress the separation of the Ni film <NUM> from the foot at many points around the wiring conductor <NUM>.

Further, according to the wiring substrate <NUM> of the embodiment, in a longitudinal section perpendicular to the first surface <NUM> of the insulating substrate <NUM> and the side surface <NUM> of the wiring conductor <NUM>, the Ni film <NUM> is in contact with two or more recesses 11D. The Ni film <NUM> being in contact with two or more recesses 11D can provide high adhesion strength of the Ni film <NUM> to the insulating substrate <NUM>, and accordingly further suppress the separation of the Ni film <NUM> from the foot.

Further, according to the wiring substrate <NUM> of the embodiment, the recesses 11D that are in contact with the Ni film <NUM> include the compound recesses 11DW each having a shape of two or more recesses 11D overlapped if the individual recesses 11D are regarded as granular. The compound recesses 11DW increase the contact area between the Ni film <NUM> and the compound recesses 11DW with the Ti oxides <NUM> in between. This can provide high adhesion strength of the Ni film <NUM> to the insulating substrate <NUM>, and accordingly further suppress the separation of the Ni film <NUM> from the foot.

Further, according to the wiring substrate <NUM> of the embodiment, the interface between the insulating substrate <NUM> and the wiring conductor <NUM> includes the interlayer 16a having Cu, Al and N concentration gradients. Presence of the interlayer 16a reduces stress at the interface caused by thermal expansion, and accordingly can suppress adhesion failure between the insulating substrate <NUM> and the wiring conductor <NUM> caused by thermal expansion.

Further, according to the wiring substrate <NUM> of the embodiment, the interface between the Ni film <NUM> and the recesses 11D includes the interlayer 16b having Cu, Al and N concentration gradients. Since coefficients of thermal expansion of Cu and Ni are close to one another, presence of the interlayer 16b reduces stress at the interface caused by thermal expansion, and accordingly can suppress adhesion failure between the insulating substrate <NUM> and the Ni film <NUM> caused by thermal expansion, and further suppress the separation of the Ni film <NUM> from the foot.

According to the electronic device <NUM> and the electronic module <NUM> of an embodiment, the wiring substrate <NUM> having the Ni film <NUM>, the separation of which has been suppressed, is mounted therein. This can enhance reliability thereof.

In the above, some embodiments of the present disclosure have been described. However, the present invention is not limited thereto. For example, in the above embodiments, examples of the size and the density of the recesses 11D on the insulating substrate <NUM> have been described, but the size and the density thereof are not limited thereto. Further, in the above embodiments, the Ni film <NUM> covers the entire upper surface and the entire side surface of the wiring conductor <NUM>, but may not cover part thereof. Still further, in the above embodiments, the Ni film <NUM> has the protrusion <NUM>, but may not have a shape corresponding to the protrusion <NUM>. Yet further, in the above embodiments, an example of the manufacturing method of the wiring substrate <NUM> has been described, but the wiring substrate <NUM> may be manufactured by another manufacturing method. The details described in the embodiments can be appropriately modified within a range not departing from the scope of the invention.

Claim 1:
A wiring substrate (<NUM>) comprising:
an insulating substrate (<NUM>) having a first surface (<NUM>) and a second surface (<NUM>) on a side opposite the first surface (<NUM>), and containing AlN;
a conductor (<NUM>) disposed on the first surface (<NUM>) and containing Cu; and
an Ni film (<NUM>) disposed so as to extend across an upper surface (<NUM>) and a side surface (<NUM>) of the conductor (<NUM>) to the first surface (<NUM>),
characterized in that Ti oxide (<NUM>) is scattered so as to be at a plurality of points on the first surface (<NUM>).