JP3512554B2 - Wiring board - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a predetermined number of various passive components such as capacitors and resistors in addition to a semiconductor device housing package in which a semiconductor device is housed and mounted, and active components such as semiconductor devices. The present invention relates to a wiring board suitable for a hybrid integrated circuit device or the like that constitutes an electronic circuit.

[0002]

2. Description of the Related Art Conventionally, a wiring board used for a package for housing a semiconductor element, a hybrid integrated circuit device, etc. is usually provided from the periphery of a recess provided in the upper surface of an insulating substrate to the lower surface, or on the surface and inside thereof. , A plurality of wiring conductors made of refractory metal such as tungsten (W), molybdenum (Mo) and manganese (Mn) are arranged, and each wiring conductor is made of the same refractory metal provided in the insulating substrate. It is electrically connected by a through-hole conductor.

In the wiring board constructed as described above, for example, in a package for housing a semiconductor element, the semiconductor element is adhered and fixed to the bottom surface of the recess of the insulating substrate via an adhesive such as glass, resin, or brazing material. At the same time, each electrode of the semiconductor element is electrically connected to a wiring conductor located around the recess via a bonding wire, and a lid made of metal or ceramics is sealed in the same manner as the adhesive so as to close the recess. The semiconductor device as the final product is obtained by joining the semiconductor elements through the materials and hermetically housing the semiconductor element in the recess of the insulating base.

However, the refractory metal typified by tungsten, which constitutes the wiring conductor, has poor wettability with the brazing material used as an adhesive as described above, especially solder, and the semiconductor element is used as a wiring conductor and a bonding wire. As described above, the surface of the wiring conductor exposed on the surface of the insulating substrate is usually plated with gold (Au) because the ease of connection when connecting electrically through Layers have been deposited.

The plated coating layer made of gold is widely used at present because of its excellent weather resistance, wettability with solder and wire bonding property. However, gold is expensive and has a high melting point. A plating coating layer made of nickel (Ni) is required as an underlayer in order to firmly adhere to the metal, which causes a problem that the number of steps is increased and the cost is increased.

Therefore, in order to solve such a problem, it has been studied to use a plating coating layer made of copper instead of gold, and various electroless plating methods have hitherto been used as the plating coating method of copper. Proposed.

In the electroless plating method, since copper has a poor bondability with the refractory metal, palladium is deposited on the surface of the wiring conductor in order to activate the surface of the wiring conductor made of the refractory metal. After so-called palladium activation, a copper plating coating layer was deposited by immersing it in an electroless copper plating bath and precipitating while replacing Cu with Pd (Japanese Patent Publication No. 60-21226). Japanese Patent Laid-Open No. 63-256588).

[0008]

However, with the increasing demand for higher functionality and smaller size of the wiring board, a thick film circuit is formed on the wiring board instead of the conventional solder mounting of chip parts to increase the density. Things have come to be done.

The thick film circuit is composed of a conductor, a resistor and a protective glass, and the thick film circuit is baked at a temperature of 600 to 1000 ° C. in a nitrogen atmosphere, for example, in order to prevent oxidation of the wiring conductor.

Therefore, when a thick film circuit is formed so as to cover a part or the whole of the wiring board on which the plating coating layer made of copper is deposited, since palladium is a hydrogen storage metal, the palladium activation can be performed. Palladium deposited on the surface of the wiring conductor made of a refractory metal causes blisters between the plating coating layer and the wiring conductor, which are considered to be due to hydrogen taken in during activation or electroless copper plating, and as a result, the plating coating layer. However, there are problems such as a decrease in the adhesive strength, the inability to directly wire bond to the plating coating layer, and the inability to adopt the flip-chip connection method for directly connecting the surface electrode of the semiconductor element.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object thereof is a plating coating made of a wiring conductor exposed on the surface of an insulating substrate and copper deposited so as to cover at least a part of the wiring conductor. To provide a wiring board which does not generate blisters between the layers, firmly adheres the plating coating layer, enables direct wire bonding to the plating coating layer, and is also applicable to the flip chip connection method. It is in.

[0012]

Means for Solving the Problems The inventors of the present invention have made earnest studies on the above-mentioned problems, and as a result, when palladium deposited on the surface of a wiring conductor made of a palladium-active and refractory metal and copper of a plating coating layer are alloyed, 60 when baking thick film circuits
The plating layer starts to sinter from around 0 to 700 ° C.
It has become clear that it becomes difficult for the palladium to discharge hydrogen taken in during activation or electroless copper plating, and as a result, blisters are generated in the portion where the plating coating layer and the wiring conductor have poor adhesion.

That is, the palladium only diffuses when it is in solid solution with the copper of the plating layer, and the hydrogen taken up by the palladium is discharged to the outside of the system during the baking of the thick film circuit without any problem, and The present invention has been completed by finding out that the above does not occur.

In the wiring board of the present invention, a wiring conductor made of a refractory metal is integrally formed on an insulating base, and copper (Cu) is used to cover at least a part of the wiring conductor exposed on the surface of the insulating base. A wiring board having a plated coating layer formed thereon, wherein the plated coating layer made of copper (Cu) is solid-dissolved and diffused in copper without alloying with copper.
/ Cm ² of palladium (Pd), and is characterized by being heat-treated after plating. Further, the wiring board of the present invention is characterized in that, in the above structure, the heat treatment is a baking treatment for forming a thick film circuit on the outer surface of the insulating substrate so as to come into contact with the plating coating layer. It is a thing. Further, the wiring board of the present invention is characterized in that, in the above structure, the plating coating layer has an adhesive strength of 3.6 kg / mm ² or more. Further, the wiring board of the present invention is formed by integrally forming a wiring conductor made of a refractory metal on an insulating base and making copper (Cu) so as to cover at least a part of the wiring conductor exposed on the surface of the insulating base. A wiring board coated with a plating coating layer, the copper (C
u) a plating layer formed of 0.1 to 7 μg / cm ² of palladium (P
d) is included and heat treatment is performed after plating, and the adhesive strength of the plating layer is 3.6 kg / mm ²
The above is a feature.

In the present invention, when the amount of palladium contained in the plating layer made of copper is less than 0.1 μg / cm ² , the activation is insufficient and the initial reaction at the time of copper deposition in electroless copper plating is unsatisfactory. Sufficiently, pinholes are not formed in the plated film, and the plated film is not evenly deposited on the surface.

Further, the palladium content is 10 μg /
If it exceeds cm ² , blisters will occur between the wiring conductor and the plated coating layer.

Therefore, the palladium content of the plating layer made of copper is preferably 0.1 to 10 μg / cm ^2, but it is 0 from the viewpoint of suppressing grain growth of the plating particles which affects the adhesive strength of the plating layer. 0.1 to 7 μg / cm ² .

[0018]

According to the wiring board of the present invention, the amount of palladium contained in the plating coating layer made of copper is 0.1 to 7 μg / c.
Since it is specified as m ² , palladium does not form an alloy with copper of the plating coating layer and diffuses as a solid solution in the copper, and hydrogen occluded in the palladium is relatively easy at a temperature of 600 to 700 ° C. It is possible to suppress the particle growth of the plating particles which is discharged to the outside of the system and causes the blisters as described above and which affects the adhesive strength of the plating coating layer.

Therefore, the plated conductor layer made of copper can be firmly adhered to the wiring conductor, the wire can be directly bonded to the plated conductor layer, and even a small pad such as a flip chip land can be mounted without any problem. Up,
It also has excellent corrosion resistance and solder erosion resistance.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The wiring board of the present invention will be described in detail below.

First, the insulating substrate is made of, for example, alumina (Al
₂ O ₃ ), silica (SiO ₂ ), calcia (CaO),
Various binders are added to raw material powder such as magnesia (MgO) to prepare slurry, and the slurry is formed into a sheet by a known forming method such as a doctor blade method or a calender roll method, and the obtained ceramic green sheet is obtained. A punching process is performed to form through holes, and a conductive paste described later is applied to the ceramic green sheet by a screen printing method to apply a predetermined wiring pattern by printing, and after filling the through holes as well, a plurality of them are formed. It is formed by stacking and firing at a temperature of 1500 to 1600 ° C. in a reducing atmosphere.

The wiring conductors formed inside and on the surface of the insulating base are made of tungsten (W) or molybdenum (M).
o), a conductive paste prepared by adding and mixing a known organic solvent and a solvent to a high melting point metal powder such as manganese (Mn) is deposited on a predetermined wiring pattern.

Further, prior to depositing the plating coating layer made of copper so as to cover at least a part of the wiring conductor exposed on the surface of the insulating substrate formed as described above, for example, in an acidic solution of palladium chloride. The substrate is dipped in a predetermined time for activation treatment.

Thereafter, for example, copper sulfate is 7 g / l, Rochelle salt is 75 g / l, and triethanolamine is 10 g / l.
1, formalin 25g / l, sodium hydroxide 20
Liquid temperature 50 g / l and sodium carbonate 10 g / l
A wiring board is manufactured by immersing the insulating substrate having the activated wiring conductor in an electroless copper plating bath at ˜55 ° C. and depositing copper on the exposed surface of the wiring conductor.

The wiring board thus obtained is further coated with a thick film circuit made of copper. The thick film circuit has various passive components such as capacitors and resistors in addition to active components such as semiconductor elements. Connected.

In the thick film circuit, copper powder is mixed with glass frit and an appropriate organic solvent, solvent, etc. to prepare a copper paste, and a part of the copper paste is applied to a wiring conductor by plating. Printed onto the outer surface of the insulating substrate in contact with the layer, and then applying this to about 900 in a neutral atmosphere.
It is applied to the outer surface of the insulating substrate by firing at a temperature of ° C.

In this case, a large amount of glass frit is added to the thick film circuit in order to firmly adhere the thick film circuit by chemical bonding or glass bonding, and the thick film circuit is provided with copper and a plating coating layer. Although the adhesion area of is narrow, both are firmly adhered because they are made of the same kind of copper, and as a result, they do not separate from the plating layer even when external force is applied to the thick film circuit, and The electrical connection between the plating layer and the thick film circuit is also reliable and good.

In this way, the wiring board has components such as semiconductor elements and capacitors mounted on the surface thereof, and the semiconductor elements and the like are joined to a thick film circuit via an adhesive such as solder to form a hybrid integrated circuit device. .

[0029]

EXAMPLES When evaluating the wiring board of the present invention, first, as an insulating base made of an alumina sintered body, an average particle size of 3 was obtained.
90% by weight of Al ₂ O _{3 of} μm, SiO ₂ , MgO, C
Prepare a slurry by adding and mixing an appropriate organic binder, plasticizer, and solvent to the raw material powder containing aO added in a total amount of 10% by weight.
The slurry was formed into a ceramic green sheet having a thickness of about 300 μm by a tape forming technique such as a well-known doctor blade method or calendar roll method, and then punched at a predetermined position of the ceramic green sheet to form a through hole. .

Next, using a conductive paste prepared by mixing tungsten powder and glass powder in a predetermined ratio and adding a known organic binder, the ceramic green sheet is screen-printed with wiring for evaluation. The pattern is printed and applied, and the through holes are also filled.
After stacking multiple layers, hydrogen (H ₂ ) and nitrogen (N ₂ )
Insulating of 25.4 mm in length, 25.4 mm in width, and 0.76 mm in thickness by firing and integrating at a temperature of about 1600 ° C. in a reducing atmosphere composed of mixed gas of, or in a neutral atmosphere such as argon (Ar) gas. A substrate was prepared.

The insulating substrate is made of palladium chloride or NaO.
The Pd is deposited on the wiring conductor exposed on the surface of the insulating substrate by immersing in an active liquid containing H and KOH as main components for different times to perform so-called palladium activation.

After that, it is dipped in an electroless copper plating solution containing copper sulfate, formalin and NaOH as the main components, and then about 2.5-
A copper plated coating with a thickness of 3.0 μm was obtained. The thickness of the copper-plated coating layer can be freely changed by changing the dipping time according to the intended plating thickness.

Using the thus obtained wiring board for evaluation, the content of Pd in the copper plating coating layer was 0.5 mm square in the wire bonding pad portion with HCl or H ₂ SO ₄
The copper-plated coating layer was dissolved by the method described above, and measured by ICP emission spectroscopy, fluorescent X-ray analysis, atomic absorption spectrometry, etc. to calculate the amount of Pd in the copper-plated coating.

The blisters on the copper-plated coating layer were visually inspected with a 200 × metallographic microscope to determine the presence or absence of blisters.

On the other hand, the evaluation of the adhesive strength and wire bonding property of the copper-plated coating layer was carried out by soldering Sn-plated annealed copper wire on a 2 mm square pattern prepared in the same manner as the above-mentioned wiring board for evaluation, and then Sn-plating it. The annealed copper wire was pulled in a direction substantially perpendicular to the copper-plated surface, and evaluated by the adhesive strength calculated from the breaking load.

[0036]

[Table 1]

As is apparent from the table, in Sample No. 1 whose Pd content is outside the scope of the present invention, no blistering of the copper plating coating layer is observed and wire bonding is good, but the copper plating coating layer Adhesive strength 2.5 kg / mm ²
Similarly, in Sample No. 8, although the adhesive strength of the copper plating coating layer is high, blistering is observed and the wire bonding property is poor.

On the other hand, in the present invention, no blister is observed and the wire bonding property is good,
The adhesive strength of the copper-plated coating layer is 3.6 kg / mm ² or more, which is sufficient.

The present invention is not limited to the above embodiments, but various modifications can be made without departing from the scope of the present invention.

[0040]

According to the wiring board of the present invention, a wiring conductor made of a refractory metal is integrally formed in and on the surface of the insulating substrate, and at least a part of the wiring conductor exposed on the surface of the insulating substrate is covered. As described above, since the plating coating layer made of copper which contains 0.1 to 7 μg / cm ² of palladium and is heat treated after plating is applied, the baking temperature of 600 to 1000 ° C. when forming a thick film circuit is applied. However, no blistering occurs between the wiring conductor exposed on the surface of the insulating substrate and the plating coating layer made of copper that is deposited so as to cover at least a part of the wiring conductor, which affects the adhesive strength of the plating coating layer. Since the grain growth of plated particles can be suppressed,
Wiring in which the plating coating layer can be firmly adhered, wire bonding can be directly performed on the plating coating layer, the flip chip connection method can be applied, and the reliability of plating strength after component mounting is improved. A substrate is obtained.

Continuation of front page (56) Reference JP-A-2-292896 (JP, A) JP-A-7-212009 (JP, A) JP-A-7-297514 (JP, A) JP-A-6-69632 (JP , A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H05K 1/09 H05K 3/24

Claims (4)

(57) [Claims] 1. A wiring conductor made of refractory metal is integrally formed on an insulating substrate, and a plating coating layer made of copper (Cu) is formed so as to cover at least a part of the wiring conductor exposed on the surface of the insulating substrate. A wiring board deposited, wherein the plated coating layer made of copper (Cu) does not alloy with copper
A wiring board containing 0.1 to 7 μg / cm ² of palladium (Pd) which is solid-dissolved and diffused therein and is heat-treated after plating. 2. The wiring board according to claim 1, wherein the heat treatment is a baking treatment for forming a thick film circuit on the outer surface of the insulating substrate so as to come into contact with the plating layer. 3. The adhesive strength of the plating layer is 3.6 k.
The wiring board according to claim 1 or ^{2, wherein} g / mm ² or more . 4. A wiring conductor made of a refractory metal as an insulating substrate.
Is formed integrally and is exposed on the surface of the insulating substrate.
Copper (Cu) to cover at least a part of the wiring conductor
A wiring board coated with a plating coating layer comprising:
Copper (Cu) plating layer does not alloy with copper
0.1 to 7 μg / cm ² of palladium dissolved and dissolved in
(Pd) contained and heat treated after plating
The adhesive strength of the plating layer is 3.6 kg /
A wiring board having a size of at least mm ² .