JPH09256163A - Nickel plating treatment on ceramic substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a plating film more crystalline and stable by applying electrolyses No-Co-O plating treatment and sintering treatment to a substrate in which an external contact pin is foxed onto a metallic layer. SOLUTION: A metallic layer is formed in part on the surface of a ceramic substrate, and an external contact pin is fixed onto this metallic layer. After the composition of the conventional film is changed to a composition containing Ni, Co, and P, sintering treatment is carried out at 400-700 deg.C in a reducing atmosphere. By this procedure, the plating film can be made more crystalline and stable. Accordingly, even in the case where an Au plating film is formed as upper layer and then the ceramic substrate is heated to about 200-400 deg.C, the diffusion of Ni constituting an Ni plating layer in the surface of the Au plating film as upper layer can be prevented and sufficiently high bonding strength can be secured when wire bonding and joining of lid are carried out, and the sealing of semiconductor device can be completely performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to an i-plating method, and more particularly, to a Ni-plating method for a ceramic substrate adopted when manufacturing a ceramic package on which a semiconductor element such as an LSI chip is mounted.

[0002]

2. Description of the Related Art A semiconductor element such as an integrated circuit which constitutes a semiconductor device is usually housed in a cavity portion provided on a substrate, and the cavity portion is hermetically sealed by a lid and is put to practical use. Ceramics such as alumina are heat resistant,
Since it is excellent in durability and reliability, it is suitable as a material for the substrate and the lid, and a ceramic IC package made of alumina or the like (hereinafter referred to as a ceramic package) is actively used.

FIG. 1 is a sectional view schematically showing a state in which semiconductor elements and the like are mounted on a ceramic substrate used for a PGA (Pin Grid Array) type ceramic package.

A cavity portion 12 is formed in the central portion of the ceramic substrate 11, and a base metal layer 16 used for sealing with a lid (not shown) is formed outside the cavity portion 12, and further, a base metal layer. External connection pins 17 for connecting to a motherboard (not shown) are fixed to pads 18 for external connection pins outside the periphery of 16. Cavity 1
In general, 2 has a peripheral portion formed in a staircase shape, a pad portion 15 for wire bonding is formed in the staircase portion, a semiconductor element mounting portion 13 is formed in the bottom surface portion, and a semiconductor element such as an LSI is formed. 14 is mounted. The pad (not shown) formed on the semiconductor element 14 and the pad portion 15 on the ceramic substrate 11 are connected to the wire 21.
Are connected by wire bonding using. On the other hand, in the figure, a heat dissipation board 19 for dissipating heat generated from the semiconductor element 14 is disposed on the lower surface, that is, the surface opposite to the surface on which the semiconductor element 14 is mounted.

The pad portion 15 and the underlying metal layer 16 formed on the surface of the ceramic substrate 11 are both metal layers 15a and 16 of W, Mo or the like partially formed on the surface of the sintered body.
a, and a Ni plating film (not shown) and an Au plating film (not shown) sequentially formed on the metal layers 15a and 16a. Further, the external connection pin 17 and the heat dissipation board 19 are fixed to the external connection pin pad 18 and the heat dissipation board pad 20 by brazing, respectively, through a Ni plating film.
An i-plated film and an Au-plated film (both not shown) are sequentially formed.

The ceramic substrate 11 provided with the external connection pins 17 and the like is manufactured through the following steps. First, a slurry made of ceramic raw material powder and a binder is molded by a doctor blade method or the like to prepare a green sheet, and then a conductive paste containing W or the like is printed at a predetermined position on the green sheet. Next, a plurality of green sheets including a green sheet on which the conductive paste is printed are laminated to produce a green sheet laminate. Next, the ceramic substrate 11 is manufactured by degreasing and firing the green sheet laminate.

On the surface of the ceramic substrate 11 manufactured by the above process, the pad portion 15, the underlying metal layer 16, the external connection pin pad 18, and the W for the heat dissipation substrate pad 20 shown in FIG. Metal layers 15a, 16
a, 18a, 20a, etc. are formed. However, when a solder layer is directly formed or brazed on these metal layers 15a, 16a, 18a, 20a, sufficient adhesion strength is obtained between the solder or brazing material and the metal layers 15a, 16a, 18a, 20a. I can't get it. Therefore, the ceramic substrate 11 is subjected to various plating treatments to secure the adhesion strength with solder or the like, and at the same time, provide the corrosion resistance and the like.

In the past, in order to form these Ni plating film and Au plating film, the ceramic substrate was subjected to electrolytic plating treatment. However, with the recent increase in the driving speed of electronic devices, the lead lines (not shown) for electrolytic plating formed on the ceramic substrate 11 have a bad influence on the electrical characteristics, and therefore the electroless plating method is used. The metal layer 15a on the ceramic substrate 11 is ...
The method of forming a plating film on the substrate has been adopted (Japanese Patent Publication No. 6-84546).

When the above electroless plating method is adopted, first, the ceramic substrate 11 is subjected to electroless Ni-B plating, and N is deposited on the metal layers 15a, 16a, 18a and 20a.
An i-B plating film is formed. Next, the metal layer 18 among the metal layers 15 a, ...
The external connection pin 17 is brazed to the portion a and the heat dissipation substrate 19 is brazed to the portion of the metal layer 20a.

Next, the external connection pin 17 and the heat dissipation board 19
The ceramic substrate 11 to which is adhered is subjected to electroless Ni-P plating treatment, and the external connection pins 17 and the heat dissipation substrate 19 and the metal layers 15a, 1 on which the Ni-B plating film is formed are formed.
A Ni-P plating film is formed on 6a or the like. afterwards,
Sintering is performed in a reducing atmosphere at a temperature of about 700 ° C. to eliminate defects (pinholes and the like) and distortion existing in the Ni—P plating film, and remove the gas trapped inside. Also, the Ni-P plating film is changed to a crystalline one by the above-mentioned sintering treatment.

Next, the sintered type ceramic substrate 11 is subjected to substitutional Au in an acidic plating bath having a pH of 3 to 5.
After performing a plating process to form an Au plating film having good adhesion with the Ni-P plating film, a reduction type Au plating process is performed to provide a ceramic substrate 11 having an Au plating film on the uppermost layer of the metal layer. To manufacture.

[0012]

However, in the above-mentioned conventional electroless plating method, the above-mentioned electroless Ni-P is used.
The Ni-P plating film formed by the plating process has a problem that its characteristics are not always sufficient.

That is, usually, before and after the step of mounting the semiconductor element on the ceramic substrate 11, the ceramic substrate 11 is heated to 200 to 400 ° C. By this heating, Ni in the Ni-P plating film is an upper layer of Au. It may diffuse in the plating film and reach its surface. A
When wire bonding is performed on the pad portion 15 in which Ni is diffused on the surface of the u-plated coating, or when a lid is joined to the base metal layer 16, the bonding strength between the wire 21 and the pad portion 15 and the lid and the base metal layer 16 are formed. There is a case where the bonding strength of No. 1 is not sufficiently obtained, and the semiconductor element is not completely sealed by the lid.

The present invention has been made in view of the above problems. Even when the ceramic substrate is heated to about 200 to 300 ° C. after the Au plating film is formed on the upper layer,
Ni constituting the Ni plating layer does not diffuse to the surface of the upper Au plating film, has sufficient bonding strength even if wire bonding or bonding with a lid is performed, and is highly reliable in sealing a semiconductor element with the lid. It is an object of the present invention to provide a Ni plating treatment method for a ceramic substrate that can form a package having excellent properties.

[0015]

Means for Solving the Problems and Effects Thereof In order to achieve the above object, a method (1) for Ni plating a ceramic substrate according to the present invention is such that a metal layer is partially formed on the surface of the metal layer. After performing the electroless Ni-Co-P plating treatment on the ceramic substrate to which the external connection pin is fixed,
The sintering process is performed at 400 to 700 ° C. in a reducing atmosphere.

The Ni of the ceramic substrate according to the present invention is also used.
The plating treatment method (2) is the same as the Ni plating treatment method (1) of the ceramic substrate, and is 5 to 50% by weight of Co and 2% of P by performing the electroless Ni-Co-P plating treatment.
It is characterized in that a Ni plating film containing about 12% by weight is formed.

According to the above method (1) or (2) of Ni plating treatment for a ceramic substrate, the composition of the conventional plating film containing Ni and P is changed to the composition of the plating film containing Ni, P and Co. By performing the sintering treatment, the plated coating can be made more crystalline and stable.
Therefore, even when the ceramic substrate is heated to about 200 to 400 ° C. after the Au plating film is formed on the upper layer, Ni constituting the Ni plating layer can be prevented from diffusing to the surface of the Au plating film on the upper layer. Even if wire bonding or lid bonding is performed, a sufficiently large bonding strength can be secured, and the semiconductor element can be completely sealed.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a Ni plating method for a ceramic substrate according to the present invention will be described below with reference to the drawings.

In the Ni plating method of the ceramic substrate according to the embodiment, the type of the target ceramic substrate is not particularly limited, but as an example, the ceramic substrate 11 (FIG. 1) constituting the PGA type ceramic package is used. Can be mentioned. In the following, the PG
The A type ceramic substrate 11 will be described as an example.

First, a metal layer 15 of W or the like is partially formed on the surface.
The ceramic substrate 11 on which a, 16a, 18a and 20a are formed is manufactured. The manufacturing method of the ceramic substrate 11 is
Since the method is the same as the conventional method, detailed description thereof is omitted here. Next, the obtained ceramic substrate 11 is immersed in a plating bath containing a salt of Ni, a boron-containing compound and the like at 50 to 80 ° C. for 3 to 60 minutes to perform electroless Ni—B plating. The metal layer 15a formed on the surface of the ceramic substrate by the Ni-B plating process, ...
An Ni-B plating film containing B having a thickness of 8 μm is formed.

Next, of the metal layers 15a, ... Formed on the ceramic substrate 11, the metal layers 18a, 20 constituting the pads 18 for external connection pins and the pads 20 for heat dissipation substrate.
External connection pin 1 using silver solder in a reducing atmosphere
7 and the heat dissipation board 19 are brazed. The heat dissipation board 19 may not be provided depending on the type of ceramic package.

Next, the ceramic substrate 11 on which the external connection pins 17 and the like are brazed is set to a Ni salt such as nickel sulfate.
Hypophosphite, Co salt such as cobalt sulfate, lactic acid, propionic acid, etc. are contained, pH is 6.0 to 6.5, and temperature is 70.
Immerse in a plating bath at ~ 90 ° C for 5 to 60 minutes to remove Ni-Co
-P plating processing is performed. The concentration of nickel sulfate in the plating bath is 20 to 25 g / liter, the concentration of cobalt sulfate is 5 to 25 g / liter, the concentration of sodium hypophosphite is 20 to 25 g / liter, and the concentration of lactic acid is 20 to 25 g.
/ L, and the concentration of propionic acid is preferably 1 to 3 g / L. By the above Ni-Co-P plating treatment, N
A Ni-Co-P plating film containing P and Co having a thickness of 0.5 to 10 μm is formed on the metal layers 15a and 16a having the i-B plating film, the external connection pin 17, and the like.

Silver brazing remains around the external connection pins 17 by brazing, and the silver brazing is vulnerable to corrosion.
Therefore, the Ni-Co-P plating treatment is applied to form a Ni-Co-P plating film to provide corrosion resistance.

The content of Co in the Ni-Co-P plating film is preferably 5 to 50% by weight, and the content of P is 2 to 2.
12% by weight is preferred. When the content of Co in the Ni plating film is less than 5% by weight, it is easy to diffuse into the Au plating film by heat treatment similarly to the Ni-P film containing no Co, while the content of Co is 50% by weight or less. If it exceeds, the film adhesion deteriorates.

As long as a phosphorus-containing reagent is used as a reducing agent for electroless plating, it is difficult to keep the P content in the Ni coating less than 2% by weight, while the P content in the Ni coating is 12% by weight. When it exceeds%, there arises a problem of increase in film resistance.

Next, a reducing atmosphere, for example, nitrogen of 25 to
Sintering is performed on the ceramic substrate 11 that has undergone the above steps at 400 to 700 ° C. in a gas of 100% by volume and 0 to 75% by volume of hydrogen. By this sintering treatment, Ni-Co-P
Ni-Co-P at the same time when the plating film is adhered to the base
The defects (pinholes, etc.) and strains existing in the plating film are eliminated, and the gas trapped inside the Ni-Co-P plating film is removed. At the time of plating, the Ni-Co-P plating film in an amorphous state is crystalline. By the above-mentioned sintering treatment, the upper layer A
After forming the u plating film, the ceramic substrate
Even when heated to about 400 ° C., Ni constituting the Ni plating layer can be prevented from diffusing to the surface of the upper Au plating film, and a sufficiently large bonding strength can be obtained even if wire bonding or lid bonding is performed. As a result, the semiconductor element can be completely sealed.

Hydrogen content during sintering treatment is 75% by volume
If it exceeds, hydrogen permeates into the plating film, which causes gas generation during heating. Further, if the sintering temperature is lower than 400 ° C., effects such as crystallization will not be exhibited, while if the sintering temperature exceeds 700 ° C., the crystals will be disordered or the plating film will be uneven, resulting in a poor appearance. Spoil.

The ceramic substrate 11 which has undergone the sintering process is treated with potassium dicyanogold (I) (K [Au
(CN) ₂ ]), ethylenediaminetetraacetic acid (EDT
A), pH including citric acid and the like is 3 to 5, temperature is 70 to
Immerse in a plating bath at 100 ° C for 1 to 30 minutes, and then replace Au
Apply plating treatment. By the substitutional Au plating treatment,
The thickness is 0.01 to 0.3 on the Ni-Co-P plating film.
At a thickness of μm, an Au plating film having excellent adhesion to the Ni-Co-P plating film is formed.

Next, the substitutional Au-plated ceramic substrate 11 has a pH of 12.5-1 which contains potassium dicyanogold (I), sodium borohydride and the like.
It is immersed in a plating bath having a temperature of 50 to 80 ° C. for 3.5 hours and a reducing Au plating treatment. The reduced Au
By performing the plating treatment, 1 to 2 is applied on the thin Au plating film formed by the substitutional Au plating treatment.
A plating film having a thickness of μm is formed.

[0030]

EXAMPLES AND COMPARATIVE EXAMPLES Examples of the Ni plating method for a ceramic substrate according to the present invention will be described below. As a comparative example, a case of performing Ni plating treatment on a ceramic substrate by a conventional method will also be described.

<Conditions Common to Examples and Comparative Examples> Dimensions of Ceramic Substrate Used (Same Shape as Shown in FIG. 1) Side Dimension: Approximately 55 mm x Approximately 55 mm Thickness of Cavity 12: 2 mm Thickness of outer peripheral portion: 3 mm Thickness of metal layers 15a, 16a, 18a, 20a: 30μ
m Electroless Ni-B plating treatment step Composition of plating bath Nickel sulfate (hexahydrate): 27 g / liter Dimethylamine borane: 3.5 g / liter pH: 6.4 Plating treatment conditions Plating bath temperature: 64 ° C Immersion Time: 30 minutes Plating film thickness: 3 μm External connection pin and heat dissipation board brazing process External connection pin 17 dimensions: 0.46 mm φ x 3.18 mm Material: Kovar Heat dissipation board 19 dimensions: 38 mm x 38 mm thickness Thickness: 1 mm Material: Porous W material impregnated with molten Cu Atmosphere during brazing: Reducing atmosphere Temperature: 900 ° C. <Conditions of Examples and Comparative Examples, and characteristics of plating film>
The conditions of each Example and Comparative Example and the characteristics of the plating film are shown in Tables 1 and 2 below.

[0032]

[Table 1]

[0033]

[Table 2]

The composition and pH of the plating bath in each plating treatment step are as follows. Electroless Ni-Co-P plating treatment step Composition of plating bath Nickel sulfate: 20 g / liter Cobalt sulfate: 10 g / liter Sodium hypophosphite: 20 g / liter Lactic acid: 20 g / liter Propionic acid: 2 g / liter pH: 6. 5 Electroless Ni-P plating treatment step Composition of plating bath Nickel sulfate: 20 g / liter Sodium hypophosphite: 20 g / liter pH: 4.6 Electrolytic Ni-Co plating treatment step Composition of plating bath Nickel sulfate: 300 g / liter Cobalt sulfate: 15 g / liter Boric acid: 30 g / liter pH: 5.0 Substitution type Au plating process (electroless method) Composition of plating bath Potassium dicyanogold (I) ate: 5.9 g / liter EDTA: 6 g / liter Sodium citrate: 3 g / liter pH: 4.0 Reduced Au Treatment process (electroless method) Plating bath composition Potassium dicyanogold (I): 3.5 g / liter Sodium borohydride: 15 g / liter pH: 13.0 Electrolytic Au plating treatment process Plating bath composition Dicyanogold Potassium (I): 8 g / liter Sodium citrate: 50 g / liter Potassium dihydrogen phosphate: 140 g / liter Potassium cyanide: 1.5 g / liter pH: 6.0 <Evaluation> Ceramic substrates according to the above Examples and Comparative Examples 1
1 to 100-500 using the heater block in the atmosphere
Heat treatment is performed at 5 ° C for 5 minutes, and Ni on the surface of the Au plating film is analyzed using SAM (scanning Auger analyzer).
Was measured. FIG. 2 is a graph showing the results, in which the vertical axis represents the Ni concentration on the surface of the Au plating film and the horizontal axis represents the heating temperature.

As is apparent from the graph of FIG. 2, when the electroless Ni-Co-P plating treatment and the sintering treatment were performed (Examples 1 to 3), the sintering treatment was not performed after the Ni-P plating treatment. (Comparative Example 1), Ni-P plating treatment, and sintering treatment (Comparative Example 2), and N
The amount of Ni diffused on the surface of the Au plating film is smaller than that in the case where the sintering treatment is not performed after the i-Co-P plating treatment (Comparative Example 3).

Further, in the cases of Examples 1 to 3, the case where the electrolytic plating method was adopted for the Ni plating treatment (Comparative Example 4), and N
Even when the electrolytic plating method is adopted for the i plating treatment and the Au plating treatment (Comparative Example 5), there is almost no difference in the Ni concentration, and in the cases of Examples 1 to 3, the case where the electrolytic plating method is used A plating film having equivalent characteristics is formed.

Next, an Au wire is used for the pad portion 15 of the ceramic substrate 11 according to the example and the comparative example, and the temperature is set to 300.degree.
After heat treatment, wire bonding was performed by thermocompression bonding, and a tensile test was performed to measure the wire bonding strength. As a method of the tensile test, a method of sandwiching an Au wire in a jig and pulling it in a vertical direction at a speed of 10 mm / min was adopted, and the strength at the time of breakage was defined as the wire bonding strength. The tensile test was performed 30 times for each of the examples and comparative examples. As a result, in the case of the example, all were in the wire break mode, and the average value of the wire bonding strength was 9.5 g, the maximum value was 12.2 g, and the minimum value was 8.5 g, which were at no problem level. It was On the other hand, in Comparative Examples 1 to 3, the wire break mode was also used, but the average value of the wire bonding strength was 7.5 g, the maximum value was 9.5 g, and the minimum value was 4.8 g, which were low. .

As is clear from the results of the above test, in Examples 1 to 3 and Comparative Examples 4 and 5, since the amount of Ni diffused to the Au surface by heating was small, wire bonding was performed. Even if there is no problem with the adhesiveness with the pad portion 15, however, it was found that in the cases of Comparative Examples 1 to 3, the adhesiveness was not so good, and problems with the adhesiveness were likely to occur. .

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing a state in which a semiconductor element is mounted on a PGA type ceramic substrate.

FIG. 2 is a graph showing the relationship between the heating temperature and the Ni concentration on the surface of the Au plating film when the ceramic substrate is heat-treated.

[Explanation of symbols]

 11 Ceramic Substrate 15a, 16a, 18a, 20a Metal Layer 15 Pad Part 16 Base Metal Layer 18 Pad for External Connection Pin 19 Heat Dissipation Board

Claims (2)

[Claims] 1. A metal layer is partially formed on a surface of the metal layer,
A ceramic substrate having external connection pins fixed to the metal layer, subjected to electroless Ni-Co-P plating, and then subjected to sintering at 400 to 700 ° C in a reducing atmosphere. Ni plating method. 2. A Ni plating film containing 5 to 50% by weight of Co and 2 to 12% by weight of P is formed by performing an electroless Ni-Co-P plating treatment. A method for Ni-plating a ceramic substrate as described above.