JPH11265899A - Printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printed wiring board that is capable of withstanding the brazing temperature of wax with a high melting point and has a unwetting brazing layer which is efficiently formed in state of substrate aggregate (large size) prior to Au plating. SOLUTION: A tantalum oxide layer 15 is formed between a region 12a for brazing electronic components on a conductive circuit and a pad site 13a. The tantalum oxide layer 15 can withstand the melting point of Ag alloy wax. Therefore, even when an element 25 is brazed in an IC package 20 where the a printed wiring board 1 is such that the element 25 brazed later is brazed to a body 22 and a heat sink 21 for assembly, a non-wet brazing layer can be formed without fail. Also, the tantalum oxide layer 15 is not exposed to an Au plating layer 16, thus the tantalum oxide layer 15 is formed at a substrate aggregate stage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wiring board (circuit board) made of ceramic or the like to which electronic components such as a semiconductor integrated circuit element (hereinafter, also referred to as a semiconductor element or simply an element) such as an IC package are joined (mounted). ).

[0002]

2. Description of the Related Art In a ceramic wiring board of this type (hereinafter, also referred to as a ceramic substrate or simply a substrate),
When a semiconductor element is brazed to an element (electronic component) brazing region on a die attach surface, for example, if necessary, a molten solder is not placed in an appropriate position to prevent the molten solder from spreading from the joint surface. A wetting layer is formed. For example, a semiconductor element brazed to a die attach surface (an element mounting surface of a conductive circuit) with an Au alloy-based solder (Au-Si-based alloy solder, Au-Sn-based alloy solder, Au-Ge-based alloy solder, or the like). When wire bonding is performed between an electrode and a bonding pad portion (hereinafter, also referred to as a pad portion) connected to the device brazing region, when the molten solder at the time of device brazing wets and spreads on the pad portion, wire bonding (hereinafter, referred to as “pad bonding”) is performed. , Simply referred to as bonding), so that such wetting spreading (flow) is prevented,
A brazing non-wetting layer is formed between the element brazing region (bonding surface) and the pad portion.

[0003] Such a wax non-wetting layer can be formed as follows in the case where a conductive circuit (thick metal film) is formed by simultaneously firing even a ceramic wiring board. That is, it is necessary to form a non-wetting layer after printing a metallizing paste mainly containing a refractory metal such as W (tungsten) or Mo (molybdenum) on an unfired ceramic (green sheet) so as to form a conductive circuit. For example, a ceramic paste which does not wet the above-mentioned molten solder is applied to the portion, and the paste is baked to form a wax non-wetting layer made of ceramic on the conductive circuit (thick metal film). In the case where the conductive circuit is formed by co-firing as described above, the braze non-wetting layer can be formed of ceramic without any problem.

On the other hand, in the case of a wiring board which requires high precision for miniaturization and high density of electrode pitch, it is not suitable to form a conductive circuit by simultaneous firing. For this reason, in such a wiring substrate, a metal thin film (hereinafter, referred to as Ti (Ti) or Mo) is formed on a fired ceramic substrate by a physical vapor deposition method (hereinafter, also simply referred to as sputtering) such as sputtering, vapor deposition, or ion plating. , Simply referred to as a thin film) to form a conductive circuit. Conventionally, when the conductive circuit is formed of a thin film, glass or resin (solder resist, polyimide, or the like) is applied (printed) on the thin film to form a wax non-wetting layer.

[0005]

However, for example, a ceramic wiring board (part) to which a semiconductor element is brazed, such as a high-frequency IC package on which a wiring (circuit) board for communication is mounted, is externally mounted. Ag together with (simultaneously with) external terminal members such as leads and heat sinks (radiation members)
In a wiring board that can be finished by brazing with a Cu-based alloy braze or the like, assembling it as an IC package, and then performing Au plating (gold plating), there is a problem that a brazing non-wetting layer made of glass or resin cannot be formed. .

The reason is that the melting point of the Ag-Cu alloy brazing used for assembling such an IC package is about 7 mm.
This is because the temperature is usually 80 ° C. or higher, and when the brazing non-wetting layer is formed of glass or resin, it cannot withstand the brazing temperature. As described above, there is a problem that even with a circuit board on which a conductive circuit is formed by a thin film, a wax non-wetting layer cannot be formed in a high-frequency IC package assembled by brazing as described above.

On the other hand, the following technique can be proposed to solve such a problem. That is, for example, Mo is sputtered onto a conductive circuit of a thin film on a substrate as a metal which is not easily wetted by a wax, a resist is applied, and a predetermined pattern is exposed and developed to make the Mo thin film a non-wetting layer. is there. However, when forming a non-wetting layer with a thin film of Mo or the like, it must be formed after Ni plating and finish Au plating are applied to the conductive circuit. Because if it is formed before applying Au plating,
This is because the Mo thin film is plated with Au and does not become a wax non-wetting layer.

Therefore, the IC package as described above, that is, the wiring board (parts) is used as a heat sink for the Ag-C
In the case where the IC package is finished by brazing together with the main body and external leads with a u-based alloy braze and then plating with Au, the non-wetting layer is formed after the assembly and finishing in this way. Will do. However, in such an IC package, the die attach surface (electronic component mounting surface) formed by the wiring board is usually configured to be lower than the surface of the IC package body. Since there is a gap between the two, it is often difficult to realize the proposed technique.

[0009] Even if it can be realized, for each IC package (wiring board) after finishing Au plating,
Since Mo or the like is sputtered, the production efficiency is extremely low. In the case of a flat substrate such as a flip-chip connection type wiring substrate in which the die attach surface does not become low, there is no problem in exposure and development as described above, but sputtering of Mo or the like is still performed after finishing Au plating. Becomes Therefore, even in such a wiring substrate, the substrate assembly (large format) is cut and divided into individual substrates, external leads are brazed if necessary, and after Au plating, Mo or the like is sputtered. Therefore, production efficiency is poor.

As described above, in a wiring board in which a conductive circuit forming a die attach surface is formed by a metal thin film, an appropriate non-wetting layer capable of withstanding the brazing temperature of a high melting point brazing such as an Ag-Cu alloy brazing. There was no wax non-wetting layer that could be formed efficiently even though it could withstand the same melting point. The present invention has been made in view of these problems, and an object of the present invention is to withstand the brazing temperature of a high melting point brazing such as an Ag-Cu alloy brazing, and to assemble a substrate assembly before Au plating. An object of the present invention is to provide a wiring board having a wax non-wetting layer that can be efficiently formed in a body (large format) state.

[0011]

In order to achieve the above object, a wiring board according to the present invention is provided with a tantalum oxide layer (Ta2
O5 layer).

In the present invention, the tantalum oxide layer is provided as a means for preventing the wetting and spreading of the wax (the non-wetting layer for the wax).
This prevents the wetting and spreading of the brazing joining electronic components and the like. In addition, the tantalum oxide layer can withstand the brazing temperature (for example, 800 ° C.) of the Ag alloy brazing without any problem. The tantalum oxide layer may be appropriately formed between the starting point of the wetting and spreading of the wax and the target portion for preventing the wetting and spreading so as to prevent the wetting and spreading of the wax to the target portion.

Further, such a tantalum oxide layer can be efficiently formed in the state of a substrate aggregate as follows. That is, after sputtering, for example, Ti or Mo on a ceramic substrate, a resist coating, an exposure / development process, and the like are performed.
A conductive circuit (without Au plating) is formed by applying Ni plating thereon. Tantalum nitride (Ta)
2N) is sputtered. Next, a resist is applied, a mask is set, exposure and development are performed, etching is performed to form the tantalum nitride film into a pattern of a wax non-wetting layer, and after the resist is removed, oxidation treatment is performed. Then, the surface of the tantalum nitride layer becomes a tantalum oxide layer, and the surface of the Ni plating layer becomes a nickel oxide layer. Then, thereafter, a reduction treatment is performed to remove the oxide film on the surface of the Ni plating layer. By doing so, the tantalum oxide layer is not reduced, so that the tantalum oxide layer is formed as a wax non-wetting layer at a desired portion (location). After that, even if Au plating is applied, no precipitation occurs on the tantalum oxide layer, so that the wetting and spreading of the wax can be stopped.

As described above, according to the present invention, in a state of a substrate assembly (a so-called large format before dividing into substrate units) before final Au plating (gold plating), that is, in a same process for many substrates, Since the means for preventing the wetting and spreading of the wax (wax non-wetting layer) can be formed, a desired wax non-wetting layer and a wiring board having the same can be manufactured very efficiently. That is, a wiring board used for an IC package that can be assembled by being brazed together with a heat sink and external leads, etc.
Even when the wiring board forms the C package body, a wax non-wetting layer can be formed when the wiring board assembly is manufactured.

In the present invention, the tantalum oxide layer may be provided at an appropriate position on the conductive circuit, that is, at an appropriate position where it is desired to prevent the wet spreading of the wax. If it is desired to prevent the spread of the wet to the bonding pad portion, a tantalum oxide layer may be provided at an appropriate position on the conductive circuit so that the molten solder does not spread to the pad portion on the conductive circuit. In this way, even when an electronic component such as a semiconductor integrated circuit element is brazed on a conductive circuit, the brazing does not spread to a pad portion for bonding to an electrode of the electronic component. There is no hindrance to wire bonding after attachment. In this case, it may be formed so as to surround the electronic component brazing region. However, without surrounding in this way, oxidation between the bonding pad site and the electronic component brazing region on the conductive circuit is performed. A tantalum layer may be provided.

In addition, a tantalum oxide layer may be provided on the conductive circuit so that the molten solder does not spread from the soldering region of the electronic component on the conductive circuit. In this case, since the thickness of the brazing material layer for bonding does not become insufficient, the reliability of bonding can be improved. The greater the wetting spread of the brazing, the more the thickness of the brazing material layer becomes insufficient.However, by forming a tantalum oxide layer so as to surround the periphery of the electronic component brazing area, the wetting spreading is reduced. As a result, the thickness of the brazing material layer does not become insufficient.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a wiring board according to the present invention will be described in detail with reference to FIGS. In the figure, reference numeral 1 denotes a component constituting an IC package, which is a wiring substrate mainly composed of a ceramic substrate 2 of aluminum nitride having a constant thickness, and one main surface (upper surface) thereof
Has a Ti thin film 3 formed by sputtering, and a Mo thin film 4 formed thereon by sputtering. Then, Ni plating is applied thereon to form a Ni plating film (layer) 5, and a conductive circuit 11 before Au plating, which is electrically connected to a via (not shown), is formed on the main surface. In this example, the tantalum oxide layer 15 is formed so as to divide the conductive circuit 11 on the main surface into two right and left sides in the figure.

That is, in this example, the electronic component brazing region (the portion shown by the two-dot chain line) 1 to which the semiconductor element is to be brazed.
The tantalum oxide layer 15 has a predetermined width (0.1 to 0.2) so as to partition right and left a part 12 including 2a and a part 13 including a bonding pad part (a part shown by a two-dot chain line) 13a.
mm) so as to cross the conductive circuit 11 of the wiring board 1. However, the surface of the tantalum nitride layer (Ta2N) formed so that the upper surface thereof is higher than the upper surface of the conductive circuit (Ni plating film 5) 11 by 0.1 to 0.5 [mu] m before Au plating. Is thermally oxidized.

The wiring board 1 as shown in FIG.
As shown in the figure, a predetermined Ag brazing foil (not shown) is provided on the upper surface of a separately manufactured heat sink (with Ni plating) 21 made of a Cu-W alloy, together with an IC package body (ceramic frame with Ni plating) 22. Placed through,
Further, an external lead (made of Kovar) 23 with Ni plating is arranged via a predetermined Ag brazing foil. Then, under these conditions, the assembly is performed by brazing by heating to 800 ° C., for example. In this brazing step, the tantalum oxide layer 15 can withstand the brazing temperature without any problem. Then, as shown in FIG. 4, an Au plating layer (A) is formed on the surface of the conductive circuit 11 or the like as finish plating.
The IC package 20 is completed by forming the u-plated film 16 to a predetermined thickness (for example, 1 to 2 μm), but in this case, the tantalum oxide layer 15 is not plated with Au. Note that the upper surface of the tantalum oxide layer 15 is
6 is lower than the upper surface of No. 6 based on the difference in thickness between the two.

Therefore, thereafter, as shown in FIG. 5, the semiconductor element 25 is brazed to the electronic component brazing region (on the Au plating layer 16 surface) 12a of the wiring board 1 by, for example, an Au-Si-based brazing. However, at this time, even if the molten solder spreads wet, the wet spread stops at the tantalum oxide layer 15 and the bonding pad portion 13a
Does not spread to the region containing. Thereby, the electrode of the semiconductor element 25 and the pad portion 13a of the wiring board 1 can be wire-bonded by the wire 27 without any problem.

The wiring board 1 is manufactured as follows after firing and manufacturing the wiring board assembly of aluminum nitride (see FIGS. 6 and 7). That is, the conductive circuit 11 is formed on a predetermined portion of the upper surface of the wiring board assembly (see FIGS. 6, 7-A) 31 by sputtering (see FIGS. 6, 7-B).
reference). For example, a 2,000 angstrom thick Ti film is formed thereon, and a 5,000 angstrom thin Mo film is formed thereon, followed by resist coating, exposure and development steps, and then Ni plating, for example, by 1 to 2 μm. Next, a tantalum nitride (Ta2N) film 14 is formed on the entire surface of the conductive circuit 11 by sputtering to a thickness of 1000 to 5000 angstroms (see FIGS. 6 and 7-C).

Then, a resist 17 is applied (FIGS. 6 and 7).
-D), and the resist 17 is left only in a portion that forms a wax non-wetting layer by exposure and development (see FIGS. 6 and 7-E).
Then, the tantalum nitride film 14 is removed by etching except for the portion forming the wax non-wetting layer, and the tantalum nitride film 14 is left at the portion forming the wax non-wetting layer.
Is removed (see FIGS. 6, 7-F). Then, the nickel plating film 5 is exposed on the surface of the wiring board assembly (ceramic large format) 31, and the tantalum nitride layer 14 is exposed on the portion forming the brazing non-wetting layer.

Next, this wiring board assembly 31 is
The substrate is oxidized by passing it through an oxidizing atmosphere such as in dry air at 00 ° C. to oxidize the surfaces of the Ni plating film and the tantalum nitride layer to obtain a Ni oxide film 5a and a tantalum oxide layer 15, respectively (FIGS. 6, 7-G). reference). And under hydrogen atmosphere 70
A reduction heat treatment is performed at 0 ° C. Then, the oxide film of the Ni plating film is removed, but the tantalum oxide layer 15 is not reduced. In this way, the tantalum oxide layer 15 that does not undergo Au plating and is not wetted by the wax is formed on the Ni plating film 5 (see FIGS. 6 and 7H). Thereafter, by cutting into wiring board units, the desired wax non-wetting layer, that is, the tantalum oxide layer 1 is cut.
A wiring substrate (single unit) provided with the conductive circuit (with Ni plating) formed with No. 5 is obtained. Therefore, thereafter, as described above, this wiring board is set together with a heat sink, an IC package body, and external leads, brazed, and plated with Au to complete a desired IC package.

Next, another embodiment of the present invention will be described with reference to FIGS. 8 and 9. The wiring board in this embodiment is a component of an IC package. The only difference is that it forms the IC package body of the bonding connection type.
Since there is no essential difference, the description will be focused on the difference, the same portions will be denoted by the same reference numerals, and the description thereof will be appropriately omitted.

That is, although not shown in detail, the wiring board 41 of this embodiment is a flat plate formed by laminating alumina ceramics. Are formed. The electronic component brazing region 1 formed by the conductive circuit 11
A tantalum oxide layer 15 similar to the previous example is formed between 2a and the bonding pad portion 13a on the right side thereof. Note that a sealing lid 42 is provided on the periphery of the upper surface of the substrate 41.
Are formed in a frame shape in the same manner as the conductive circuit 11. Then, an external lead 23 is brazed to the back surface, and the surface of the conductive circuit 11 and the metal thin film 43 for sealing is removed except for the tantalum oxide layer 15.
The u plating layer 16 is applied.

The wiring board 41 of this embodiment can be formed collectively in the board assembly up to the formation of the tantalum oxide layer 15 as in the above embodiment. Then, after manufacturing the substrate assembly, the substrate assembly is divided into substrate units, and if necessary, external leads 23 are formed.
Then, the surfaces of the conductive circuit 11 and the metal thin film 43 for sealing are plated with Au to complete the wiring board 41 with the external leads 23. In this manufacturing process, the tantalum oxide layer 15 has no problem with the brazing temperature of the external leads 23 and does not require Au plating.
Therefore, after that, the semiconductor element 25 is brazed and
Even if the wax spreads, the wet spreading is stopped by the tantalum oxide layer 15 and does not reach the bonding pad portion 13a. Thus, the spread of the molten wax can be prevented without any problem.

In the case of the flat wiring substrate 41 as in this example, a wax non-wetting layer can be formed with a Mo thin film after the finish Au plating. However, as described above, in such a case, in advance, the substrate is cut in units of a substrate, the external leads 23 are brazed for each substrate, Au plating is performed, and then Mo is sputtered for each substrate. Therefore, the production efficiency is extremely low. On the other hand, according to the present invention, the tantalum oxide layer can be formed collectively in the state of the substrate assembly before the Au plating step, and the production can be performed very efficiently, just like the above embodiment.

In the above, in order to prevent the solder for electronic component brazing from spreading to the bonding pad site.
Although the case where the tantalum oxide layer is formed has been described, the tantalum oxide layer in the present invention is not limited to such a purpose. It can be provided at an appropriate position on the conductive circuit so as to prevent the molten solder from spreading and spreading, for example, to prevent the solder from spreading when the external leads are brazed.

The planar form (pattern) of the tantalum oxide layer is related to the flow direction of the wetting and spreading wax, and the like.
An appropriate form may be used so that the molten wax does not spread to the target site. Therefore, the tantalum oxide layer does not necessarily need to be provided linearly so as to cross the metal thin film surface as described above, and does not necessarily encircle the target portion such as the pad portion for preventing the spread of wetness, or does not surround the target portion. Between the starting point of the wetting and spreading of the wax and the target site for preventing the wetting and spreading, such as a straight line, an arc (curved shape), or a "C" shape, the wetting and spreading of the wax to the target site can be prevented. What is necessary is just to provide. Further, the width of the tantalum oxide layer may be appropriately set within a range in which the wetting and spreading can be prevented, depending on the wetting and spreading properties of the wax used, the set thickness (amount) of the wax, and the like.

In the above, aluminum nitride (Al
Although the case where the present invention is embodied with a wiring substrate containing N) or alumina as a main component is exemplified, the present invention can be similarly embodied with a wiring substrate made of mullite, silicon carbide (SiC), or the like. Further, the thin film (underlying Ni plating) forming the conductive circuit is made of Ti
And Mo, W may be used instead of Mo, and a tantalum oxide layer can be formed in the same manner using Ti and Pa (palladium) or Ti and At (platinum). In addition,
The wiring board according to the present invention can be widely applied to components as components of an IC package, and further to those forming an IC package body of a wire bonding connection system.

[0031]

As is apparent from the above description, according to the wiring board of the present invention, the means for preventing the molten wax from spreading and spreading (the non-wetting layer) is a tantalum oxide layer (Ta2 O5 layer).
, It can withstand the brazing temperature of a high melting point brazing such as an Ag-Cu alloy brazing without any problem. Therefore,
Even a high-frequency IC package or the like in which a conductive circuit is formed of a thin film and is assembled by being brazed to a heat sink together with a main body or the like can be used as a braze non-wetting layer without any problem thereafter. Therefore, according to the present invention, by providing a tantalum oxide layer at an appropriate position between a target portion, such as a bonding pad portion, where the wetting and spreading of the molten wax is to be prevented, and a portion serving as a starting point of the wetting and spreading of the molten wax. It is possible to prevent the spread and spread of the brazing without being affected by the brazing temperature and without any problem even after brazing.

Also, since the tantalum oxide layer is not plated with Au and can be formed in the state of a substrate assembly (large format) before Au plating, the wiring board having a conductive circuit made of a metal thin film can be used. Those having a wetting layer can be manufactured efficiently.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view illustrating an embodiment of a wiring board (wiring board) according to the present invention.

FIG. 2 is a plan view of the wiring board of FIG. 1;

FIG. 3 is a schematic cross-sectional view showing a state where the wiring board of FIG. 1 is brazed and assembled as an IC package.

FIG. 4 is an explanatory cross-sectional view showing a state where the Au package is applied to the IC package of FIG. 3;

FIG. 5 is a diagram in which a semiconductor element is brazed on a wiring board of the IC package of FIG.

FIG. 6 is a sectional view for explaining a manufacturing process of the wiring board of FIG. 1;

FIG. 7 is a manufacturing process diagram of the wiring board of FIG. 1;

FIG. 8 is a schematic cross-sectional view illustrating another embodiment of the wiring board according to the present invention.

FIG. 9 is a plan view of the wiring board of FIG. 8;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Wiring board 11 Conductive circuit 12a Electronic component brazing area 13a Bonding pad part 15 Tantalum oxide layer

Claims (4)

[Claims] 1. A wiring board, wherein a tantalum oxide layer is provided at an appropriate position on a conductive circuit as a means for preventing the molten wax from spreading. 2. A wiring board, wherein a tantalum oxide layer is provided at an appropriate position on a conductive circuit so that molten solder does not spread to a bonding pad portion on the conductive circuit. 3. A wiring board, wherein a tantalum oxide layer is provided between a bonding pad site on a conductive circuit and an electronic component brazing region. 4. A wiring board, wherein a tantalum oxide layer is provided on a conductive circuit of a conductive circuit so that molten solder does not spread from an electronic component brazing region on the conductive circuit.