JPH08306816A - Electrode pad - Google Patents

Abstract

(57) [Summary] [Construction] In the electrode pad 15 formed on the ceramic substrate 11, Au, A
A thick film pattern 12 made of g / Pd or Cu is formed, an electroless Ni-P plated film 13 is formed on the thick film pattern 12, and an electroless Ni-B plated film 14 is further formed.
The electrode pad 15 in which is formed. [Effect] It is excellent in solder wettability and adhesion after being left at high temperature, and extremely high reliability can be obtained when the LSI is connected by the flip chip method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode pad, and more particularly to an electrode pad for connecting a silicon chip or the like on a ceramic substrate by a flip chip method.

[0002]

2. Description of the Related Art In recent years, electronic devices have become higher in performance, smaller in size, and higher in density, and semiconductor devices mounted on these electronic devices are rapidly becoming multi-pin and multi-chip. . Accordingly, as the LSI bonding method, a wire bonding method or a TAB (Tape Au) method is used.
The flip chip method has been adopted more often than the tomated bonding method.
The flip chip method is a method in which a solder bump is further formed on a pad formed on one principal surface of an LSI and is connected to an electrode pad on the substrate side. (1) The connection length can be shortened and the electrical characteristics are good. . (2) Many pads can be formed without using a narrow pitch. (3) The ratio of LSI area / package area can be increased. (4) The mounting thickness can be reduced. (5) The bonding strength can be increased. (6) It has an advantage that the mounting process can be simplified.

In the connection process by the flip chip method, the LSI on which the solder bumps are formed is aligned so that the solder bumps are on the electrode pads on the ceramics substrate, and after soldering by flux, the solder is soldered by a reflow process. It consists of a step of melting.

As a method of forming electrode pads for solder bump connection in the flip chip method on a ceramic substrate, a thick film pattern formed by applying a conductor paste to an electrode pad forming portion by a screen printing method and baking it. In addition, a method of plating Ni or the like is generally used, and there is also a method of forming it by a sputtering method. However, since the equipment cost and the production cost are extremely high, they are not actually used so much.

The plating of Ni or the like is performed for the purpose of ensuring the solder wettability of the electrode pad and forming a barrier layer for suppressing the reaction between the solder and the thick film. The electrode pad is a fine pattern having a diameter of about 100 μm,
In addition, since the number is large, an electroless plating method is often used as the plating method.

As the electroless Ni plating method, electroless Ni is used.
There are two types, the -P plating method and the electroless Ni-B plating method. In the electroless Ni-P plating method, hypophosphite is used as a reducing agent to crystallize Ni ions in a plating solution. In the electroless Ni-B plating method, sodium borohydride is used as a reducing agent. Ni in the plating solution using a borohydride such as diethylborazane or dimethylamineborazane
It crystallizes ions.

[0007]

However, Au, A
When the electroless Ni-P plated film is formed on a thick film pattern made of g / Pd, Cu, etc., the P content of the electroless Ni-P plated film is as high as 8% or more, and Since Ni ₃ P has already been deposited, the solder wettability is not so good, and there is a problem that connection failure easily occurs during flip chip connection. In addition, the Ni
There is also a problem that the deposition of ₃ P progresses, and the adhesiveness with solder is likely to decrease.

On the other hand, when the electroless Ni-B plating film is formed on the thick film pattern made of Au, Ag / Pd, Cu, etc., the B content of the electroless Ni-B plating film is as low as 5% or less. Therefore, although the solder wettability is good, there is a problem that the adhesiveness between the ceramic substrate and the thick film pattern is deteriorated when left at high temperature. This is electroless Ni-B
Since the Ni purity in the plated film is high and the thick film conductor metal of the lower layer easily reacts with the electroless Ni-B plated film,
When left at a high temperature, the thick-film conductor metal is converted into the electroless Ni-
This is because it diffuses into the B plating film.

As the thick film pattern, W, Mo,
When an electroless Ni-B plating film is formed by using W-Mo, Mo-Mn, or W-Mo-Mn, the above-mentioned adhesion deterioration due to high temperature storage does not occur, but the above-mentioned thick film pattern material is used. Has a high resistivity and a high firing temperature, and is not actually used so much.

The present invention has been made in view of the above problems, and is excellent in solder wettability and adhesiveness after being left at high temperature,
It is an object of the present invention to provide an electrode pad that can obtain extremely high reliability when an LSI is connected by a flip chip method.

[0011]

In order to achieve the above object, an electrode pad according to the present invention is an electrode pad formed on a ceramic substrate, in which A is formed on the ceramic substrate.
A thick film pattern made of u, Ag / Pd, or Cu is formed, an electroless Ni-P plated film is formed on the thick film pattern, and an electroless Ni-B plated film is further formed. Is characterized by (1).

Further, the electrode pad according to the present invention is defined by claim 1.
An electroless Au plating film is formed on the surface of the electrode pad described above (2).

To form the electrode pad on the ceramic substrate, a conductor paste containing any of Au, Ag / Pd, and Cu as a conductor main component is applied on the ceramic substrate in a predetermined electrode pattern and fired. Later, electroless N
i-P plating and electroless Ni-B plating are applied.

The raw material of the conductor paste comprises conductor powder, powder of glass or the like, resin, and solvent. As the conductor powder, powders of Au, Ag / Pd and Cu can be used, but Au powder is expensive. Therefore, when a thick film is formed of Ag / Pd powder, Cu powder is more preferable because it may cause Ag electromigration in a wet atmosphere. Further, powder such as glass may be added to the conductor paste in order to enhance the adhesion between the thick film pattern and the ceramic substrate.

The resin has a function of imparting an appropriate viscosity for imparting coatability to the conductor paste, and fixing the conductor powder and the like to the ceramic substrate after the conductor paste is applied and dried. Further, the solvent has a function of dissolving and liquefying the resin.

The conductor paste is prepared by kneading the conductor paste raw material by a known method such as a three roll method.

The conductor paste is applied to the ceramic substrate by a known coating method such as a screen printing method. Further, the paste for forming the wiring may be applied at the same time as applying the paste for forming the electrode pad.

After the conductor paste is applied to the ceramic substrate, the applied conductor paste is dried and then fired under predetermined firing conditions. By the firing treatment, the conductor powder is sintered to form a conductor thick film pattern, and the glass powder is softened to bond the conductor thick film pattern to the ceramic substrate.

Next, the conductor thick film pattern formed in the above step is subjected to electroless Ni-P plating. Electroless Ni-P
The plating film is formed by a known process. For example, as a plating pretreatment step, the surface of the conductor thick film pattern is sensitized and activated, and then immersed in an electroless Ni-P plating solution. The thickness of the electroless Ni-P plated film is not particularly limited, but it is preferably 1 μm or more for forming a uniform film.

Next, electroless Ni-B plating is applied. The electroless Ni-B plating film is formed by a known process, similar to the electroless Ni-P plating. Electroless Ni
The thickness of the -B plating film is not particularly limited, but it is preferably 1 μm or more for forming a uniform film.

Further, in the electrode pad (2) according to the present invention, the electroless Au plating film is formed on the electrode pad formed through the above steps. The purpose of forming the electroless Au plating film is to form the electroless N formed on the surface layer of the electrode pad.
This is to prevent oxidation of the i-B plating film. The thickness of the electroless Au plating film may be about 0.1 μm, and the plating method is also a known process.

[0022]

According to the electrode pad (1) of the present invention, a thick film pattern made of Au, Ag / Pd, or Cu is formed on a ceramic substrate, and the electroless Ni-P is formed on the thick film pattern. A plated film is formed, and electroless Ni-
Since the B plating film is formed, the electroless Ni-B plating film having high Ni purity is present on the surface layer of the electrode pad, and the electroless Ni-B plating film has a wettability with respect to solder. Since it is good, the solder wettability of the electrode pad is also good.

The thick film pattern and the electroless Ni--
Since the electroless Ni-P plated film is interposed between the B-plated film and the B-plated film, the thick-film conductive metal does not diffuse into the electroless Ni-B plated film, and the electroless Ni- P
Since P and Ni ₃ P contained in the plating layer suppress the reaction between the thick film conductor metal and Ni, the bonding interface between the thick film pattern and the ceramic substrate does not change. For this reason, the adhesiveness between the electrode pad and the ceramic substrate does not deteriorate due to being left at a high temperature.

Further, since the electrode pad (2) according to the present invention has the electroless Au plating film formed on the surface of the electrode pad according to claim 1, the same action as the above (1) is obtained, and Oxidation prevention of the plating film is promoted and durability is improved.

[0025]

EXAMPLES AND COMPARATIVE EXAMPLES Examples of electrode pads according to examples of the present invention will be described below with reference to the drawings.

[Examples 1 to 6] FIG. 1 is a schematic sectional view showing the electrode pads according to Examples 1 to 6. In the figure, 11 indicates a square alumina ceramics substrate having a thickness of 2 mm and a side length of 50 mm. On the alumina ceramics substrate 11, Cu powder 85 wt%, glass (P
_{bO-B 2 O 3 -SiO 2} ) powder 3 wt%, ethyl cellulose resin 1 wt%, printing a Cu conductor paste containing terpineol solvent 11 wt%, by firing, a thickness of about 10 [mu] m, 2 mm × 2 mm □ Cu thick film of Pattern 1
2 is formed. An electroless Ni-P plating film 13 having a film thickness of 1.5 μm is formed on the Cu thick film pattern 12.
Further, an electroless Ni-B plated film 14 having a film thickness of about 1.5 μm is formed thereon to form an electrode pad 15.

In order to form the electrode pad 15 having the above structure, first, a Cu conductor paste is applied onto the alumina ceramic substrate 11 by a screen printing method, dried at about 100 ° C. for about 10 minutes, and then under a nitrogen atmosphere. Cu by baking at a peak temperature of about 900 ° C and a peak holding time of about 10 minutes
The thick film pattern 12 is formed.

Next, as a plating pretreatment step, a sensitizing solution (component SnCl ₂ : 10 g / liter, HCl: 40) was used.
ml / liter, bath temperature 50 ° C.), then activation solution (component PdCl ₂ : 0.3 g / liter, HCl 10 ml /
The bath is successively immersed in a liter and a bath temperature of 50 ° C.) to adsorb the Pd catalyst species, which is a plating nuclei for plating, on the surface of the Cu thick film pattern 12.

Next, as an electroless Ni-P plating treatment step, the electroless Ni-P plating solution 13 is immersed in the following electroless Ni-P plating solution a to form the electroless Ni-P plating film 13, and then the electroless Ni-P plating film 13 is formed.
As the -B plating treatment step, the electroless Ni-B plating film 14 is formed by immersing in the electroless Ni-B plating solution c, d or e.

The samples taken out from each solution were thoroughly washed with water and immersed in the next solution.

The components of the electroless Ni-P plating solution a or b, the electroless Ni-B plating solution c, d or e and other conditions are as follows.

[0032] Of these compositions, the electroless Ni-P plating solution a and the electroless Ni-B plating solution c are preferable in terms of performance, cost, and safety when practically applied industrially.

The results of testing the adhesive strength and solder wettability of the electrode pads according to the examples when the compositions of the electroless Ni-P plating solution and the electroless Ni-B plating solution were changed as described above are shown below. It shows in Table 1. Also, as a comparative example,
An electrode pad formed by forming a copper thick film pattern on an alumina ceramics substrate and then performing activation treatment to form only an electroless Ni-P plated film or an electroless Ni-B plated film to a film thickness of 3 μm Tested as well,
The results are shown.

Regarding the adhesive strength of the electrode pattern, the alumina ceramic substrate 11 was solder-dipped (Pb-Sn eutectic solder, temperature 230 ± 5 ° C.) into the solder bath (after 5 ± 0.5 seconds) to obtain a 2 mm □ pad. The solder is wetted on top, a tin-plated copper wire with a diameter of 1 mmφ is soldered in an L shape on the solder, and the copper wire is pulled vertically upward by a tensile tester at a speed of 10 mm / min 90. It was measured by a peel test. The adhesive strength after standing at high temperature was measured in an oven heated to 150 ° C with the solder wet on the 2 mm □ pad.
After holding for 000 hours, 90. It was measured by a peel test.

The solder wettability was determined by measuring the deposition rate of solder after the solder dipping.

As an evaluation standard, the adhesive strength after being left at high temperature is 4.0 kgf / 2 mm □ or more, and the solder wettability is 1
The evaluation was made such that those having a value of 00% were regarded as good and those other than the above were regarded as defective.

[0037]

[Table 1]

As is clear from Table 1, in the electrode pads in which the electroless Ni-P plating film is formed on the thick film patterns according to Examples 1 to 6 and the electroless Ni-B plating film is further formed. The adhesive strength immediately after plating was 4.5 kgf / 2 mm □ in both cases where the compositions of the electroless Ni-P plated film and the electroless Ni-B plated film were changed, showing sufficient adhesive strength. The adhesive strength after being left at a high temperature was 4.3 to 4.5 kgf / 2 mm □, which was a sufficient adhesive strength. In addition, solder wettability is 100%
The evaluations were all good.

On the other hand, electroless Ni-P according to Comparative Examples 1 and 2
In the electrode pad formed so that only the plating film has a thickness of 3 μm, the adhesive strength immediately after plating is 4.5 kg.
It was f / 2 mm □ and had sufficient adhesive strength,
Adhesive strength after standing at high temperature is 1.5-2.1kgf / 2mm
□, strength is insufficient, and solder wettability is 50
% Was insufficient. Therefore, the evaluation was poor. Further, in the electrode pads formed only in the electroless Ni-B plated films according to Comparative Examples 3 to 5 to have a film thickness of 3 μm, the adhesive strength immediately after plating was 4.1 to 4.4 kgf.
It was / 2 mm □, and had sufficient adhesive strength, although not as high as that of the example. The solder wettability was 100%, which was sufficient. However, the adhesive strength after being left at high temperature is 1.2-
It was 1.4 kgf / 2 mm □, and the strength was insufficient, so that the evaluation was poor.

Next, using an electroless Au plating solution containing KAu (CN) ₂ on the electrode pads of the above-mentioned Examples and Comparative Examples (Okuno Pharmaceutical Co., Ltd. pH 5.8 bath temperature 90 ° C.),
When an electroless Au plating film having a thickness of 0.1 μm was formed,
No change was observed in the adhesive strength immediately after plating and after being left at high temperature. The electroless Au plating film enhances the oxidation resistance of the electrode pad.

[Examples 7 to 12] As electrode pads according to Examples 7 to 12, first, the alumina ceramic substrate 1 was used.
1 on top of Ag-Pd mixed powder (Ag: 80 wt%, Pd:
20wt%) 85wt%, glass (PbO-B ₂ O ₃ -
SiO ₂ ) powder 3 wt%, ethyl cellulose resin 1 wt
%, Ag-P containing 11% by weight of terpineol solvent
Apply d conductor paste by screen printing and
After drying at 10 ° C. for 10 minutes, it is baked in the air at a peak temperature of about 900 ° C. for a peak holding time of 10 minutes to form an Ag-Pd thick film. The thickness of the Ag-Pd thick film after firing was 10 μm, and the shape was 2 mm × 2 mm □.

After that, as in Examples 1 to 6 described above, Table 1
An electroless Ni-P plating film and an electroless Ni-B plating film were formed using the various plating solutions shown in 1 above, and various characteristics were evaluated in the same manner.

As is clear from Table 1, Examples 7 to 12
In the electrode pad in which the electroless Ni-P plating film is formed on the thick film pattern according to the present invention, and the electroless Ni-B plating film is further formed, the electroless Ni-P plating film and the electroless Ni-B plating film are formed. In all cases where the composition of the film was changed, the adhesive strength immediately after plating was 4.1 to 4.4 kgf / 2.
The adhesive strength was sufficient, and the adhesive strength after standing at high temperature was 4.1 to 4.2 kgf / 2 mm □, which was sufficient adhesive strength. Further, the solder wettability was 100% in all cases, and the evaluations were all good.

On the other hand, electroless Ni-P according to Comparative Examples 6 to 7
In the electrode pad formed so that only the plated film has a film thickness of 3 μm, the adhesive strength immediately after plating is 4.3 to
It had a sufficient adhesive strength of 4.4 kgf / 2 mm □, but the adhesive strength after being left at high temperature is 1.4 to 2.0 kg.
f / 2 mm □, the strength was insufficient, and the solder wettability was 50%, which was insufficient. Therefore, the evaluation was poor. Further, electroless Ni-B according to Comparative Examples 8 to 10
In the electrode pad formed so that only the plating film has a film thickness of 3 μm, the adhesive strength immediately after plating is 4.0 to
It was 4.3 kgf / 2 mm □ and had sufficient adhesive strength, although not as high as that of the example. The solder wettability is 100
% Was sufficient. However, the adhesive strength after being left at a high temperature was 1.0 to 1.3 kgf / 2 mm □, and the strength was insufficient, so that the evaluation was poor.

Then, an electroless Au plating solution containing KAu (CN) ₂ (pH 5.8 bath temperature 90 ° C., manufactured by Okuno Chemical Industries Co., Ltd.) was used on the electrode pads of the above Examples and Comparative Examples.
When an electroless Au plating film having a thickness of 0.1 μm was formed,
No change was observed in the adhesive strength immediately after plating and after being left at high temperature. The electroless Au plating film enhances the oxidation resistance of the electrode pad.

[Examples 13 to 18] As electrode pads according to Examples 13 to 18, first, 85 wt% of Au mixed powder and glass (PbO-) were formed on the alumina ceramic substrate 11.
B ₂ O ₃ -SiO ₂ ) powder 3 wt%, ethyl cellulose resin 1 wt%, terpineol solvent 11 wt% Ag-Pd conductor paste is applied by screen printing method, dried at 100 ° C. for 10 minutes, and then peak temperature in the atmosphere. About 9
The Au thick film is formed by baking at 00 ° C. for a peak holding time of 10 minutes. The thickness of the Au thick film after firing is set to 10 μm,
The shape was 2 mm × 2 mm □.

After that, as in Examples 1 to 6 described above, Table 1
An electroless Ni-P plating film and an electroless Ni-B plating film were formed using the various plating solutions shown in 1 above, and various characteristics were evaluated in the same manner.

As is clear from Table 1, Examples 13 to 1
In the electrode pad in which the electroless Ni-P plating film is formed on the thick film pattern according to No. 8, and the electroless Ni-B plating film is further formed, the electroless Ni-P plating film and the electroless Ni-B plating film are formed. In all cases where the composition of the plating film was changed, the adhesive strength immediately after plating was 4.1 to 4.4 kgf /
It has a sufficient adhesive strength of 2 mm □, and has an adhesive strength of 4.1 to 4.3 kgf / 2 mm □ after being left at a high temperature.
It had sufficient adhesive strength. Further, the solder wettability was 100% in all cases, and the evaluations were all good.

On the other hand, electroless Ni according to Comparative Examples 11 to 12
In the electrode pad formed so that only the P plating film has a thickness of 3 μm, the adhesive strength immediately after plating is 4.1.
It had a sufficient adhesive strength of up to 4.2 kgf / 2 mm □, but the adhesive strength after being left at a high temperature is 1.2 to 1.8 k.
gf / 2 mm □, the strength was insufficient, and the solder wettability was 50%, which was insufficient. Therefore, the evaluation was poor. Further, electroless Ni according to Comparative Examples 13 to 15
In the electrode pad formed so that only the -B plating film has a film thickness of 3 μm, the adhesive strength immediately after plating is 4.0.
.About.4.1 kgf / 2 mm.quadrature., Which had a sufficient adhesive strength, although not as high as that of the example. The solder wettability is 10
It was sufficient as 0%. However, the adhesive strength after being left at a high temperature was 0.9 to 1.2 kgf / 2 mm □, and the strength was insufficient, so that the evaluation was poor.

Next, an electroless Au plating solution containing KAu (CN) ₂ (pH 5.8 bath temperature 90 ° C., manufactured by Okuno Chemical Industries Co., Ltd.) was used on the electrode pads of the above-mentioned Examples and Comparative Examples.
When an electroless Au plating film having a thickness of 0.1 μm was formed,
No change was observed in the adhesive strength immediately after plating and after being left at high temperature. The electroless Au plating film enhances the oxidation resistance of the electrode pad.

In the above embodiment, an alumina ceramic substrate having no wiring formed in the substrate was used as the ceramic substrate, but the present invention is not limited to this. In another embodiment, the wiring is not formed in the substrate. It may be formed, or may be a mullite ceramics substrate, a glass ceramics substrate, an aluminum nitride ceramics substrate, or the like.

[0052]

As described above in detail, according to the electrode pad (1) of the present invention, Au, Ag are formed on the ceramic substrate.
/ Pd or Cu, a thick film pattern is formed, an electroless Ni-P plating film is formed on the thick film pattern, and an electroless Ni-B plating film is further formed. Excellent in adhesiveness and adhesiveness after being left at high temperature, L
It is possible to obtain extremely high reliability when the SI is connected by the flip chip method.

Further, in the electrode pad (2) according to the present invention, since the electroless Au plating film is formed on the surface of the electrode pad according to claim 1, the same effect as the above (1) can be obtained. Further, the oxidation prevention of the plating film is promoted and the durability can be improved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an electrode pad according to an example of the present invention.

[Explanation of symbols]

 11 (Alumina) Ceramics Substrate 12 (Cu) Thick Film Pattern 13 Electroless Ni-P Plating Film 14 Electroless Ni-B Plating Film 15 Electrode Pad

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location 9169-4M H01L 21/92 604R

Claims (2)

[Claims] 1. An electrode pad formed on a ceramic substrate, wherein Au, Ag / P are formed on the ceramic substrate.
a thick film pattern made of either d or Cu is formed,
An electrode pad, wherein an electroless Ni-P plated film is formed on the thick film pattern, and an electroless Ni-B plated film is further formed. 2. An electrode pad characterized in that an electroless Au plating film is formed on the surface of the electrode pad according to claim 1.