JPH11284000A - Wiring board and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the generation of an intermetallic compound and prevent the decline in bonding strength of the intermetallic compound, even if a chip is exposed to high temperatures when Sn is used by specifing the rate of content of cobalt to electrolytic nickel plating layer containing cobalt. SOLUTION: Interconnection layers, including a die-attached position 3 at the center of an upper face 2 of an alumina ceramic multilayer interconnection board 1, are formed by being baked simultaneously with high melting point metal such as W, Mo and the like. In the high-melting point metal layer (metallized layer) 4 which constitutes the die-attached section 3, an electrolytic nickel plating layer 5 containing 3 wt.% or less of cobalt is formed. On the surface of the high melting point metal layer 4, an electrolytic gold plating layer 6 for preventing corrosion is formed. Chip samples having a metallized layer of Ag/Pd are soldered to the wiring board 1 with Pb-Sn eutectic solder as an alloy, containing Sn to manufacture bonded samples, for example 100 samples on each wiring board 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wiring board mainly composed of ceramics, such as a ceramic IC package, and more particularly to a surface of a refractory metal layer forming a bonding surface (die attach surface) of electronic parts such as ICs. And a wiring board on which an electrolytic nickel (Ni) plating layer is formed.

[0002]

2. Description of the Related Art Conventionally, this type of wiring board has a die attach surface made of a high melting point metal such as W (tungsten) or Mo (molybdenum), and is formed by simultaneous firing. The refractory metal layer (metallized layer) that forms the die attach portion (surface) has a solder wettability and prevents oxidation, etc.
Nickel plating (Ni) and gold (Au) plating are applied, and each plating layer is formed. This plating layer is generally formed by electrolytic plating (hereinafter, also simply referred to as plating) which is as easy as possible in process control. For joining an electronic component (hereinafter, also referred to as a chip) including a semiconductor element to the die attach portion, a high melting point solder having a melting point of, for example, about 390 ° C. (for example, Au 98%, Si 2 %) Is used.

On the other hand, the Ni plating layer under the Au plating layer formed in such a die attach portion is Au
Conventionally, a Ni—Co alloy plating layer in which 2% by weight or more of cobalt (Co) is eutectoid is usually formed because the diffusion of Ni into the plating layer can be prevented.
That is, with respect to such a Ni plating layer, heat (about 390 ° C. or more) at the time of soldering (joining) the semiconductor element.
Thus, a Ni plating layer containing 2% by weight or more of Co is intentionally formed so that Ni in the base Ni plating layer does not diffuse to the surface of the Au plating layer to lower the bonding property and the sealing property.

[0004] Incidentally, since such a semiconductor element may reach a high temperature of 100 ° C. or more during use, the bonding strength in a thermal environment is extremely important. Conventionally, heat treatment such as a temperature (heat) cycle test or high-temperature aging has been performed to guarantee such bonding strength.

[0005]

However, there are cases where such high melting point Au-Si alloy solder cannot be used for joining electronic parts such as semiconductor elements having a low heat resistance temperature. As described above, in a special case where the Au-Si alloy solder cannot be used for bonding, a low melting point Pb-S
An alloy containing Sn such as n (lead-tin alloy) eutectic solder, Au-Sn (gold-tin alloy) solder, Sn-Ag (tin-silver) solder, or Sn is used. However, the die attach part is Ni
A semiconductor element was joined to an alloy containing Sn such as Pb-Sn solder or Sn on a Co alloy plating layer (hereinafter, also simply referred to as a Ni plating layer) or a layer finished with the Ni plating layer and an Au plating layer. However, there is a problem that the bonding strength is low.

The cause is that Sn in the solder and Ni in the Ni plating layer react with each other to form a hard and brittle intermetallic compound of Ni—Sn between the Ni plating layer and the solder, and after the joining, It is considered that this is further generated and grown by the heat treatment as described above, and cracks are generated in the joint due to the stress generated at that time. From this, it is considered effective to increase the bonding strength by making it difficult to generate an intermetallic compound. It should be noted that such a decrease in bonding strength and the presence of an intermetallic compound that causes such a decrease are caused by, for example, applying a tensile load perpendicularly to the surface (bonding surface) so as to separate the chip from the die-attached portion, thereby forcing the chip. When a test for peeling (peeling) is performed, it is confirmed that the test is easily separated (cut) at the interface between the Ni plating layer and the solder.

Under these circumstances, the inventors of the present application considered that the easiness of formation of the intermetallic compound is related to Co contained in the electrolytic Ni plating layer. That is, when Pb-Sn solder is used for bonding semiconductor elements, for example, Co in the Ni plating layer accelerates or accelerates the formation of the Ni-Sn intermetallic compound, and as a result, lowers the bonding strength. I thought. Therefore, in the electrolytic Ni plating layer,
Contrary to the conventional method, a substrate sample made by intentionally or positively removing Co is made, a joined body sample in which a chip is joined is made, a heat treatment is performed, and then the peeling test as described above is repeatedly performed. did.

As a result, there is a tendency that the smaller the amount of Co, the higher the joining strength. In particular, the ratio of Co in the Ni plating layer (coating), that is, the ratio of Co to the Ni plating layer containing Co (total). To 3% by weight or less, it was found that good bonding strength was maintained. That is, when an alloy containing Sn or Sn such as Pb-Sn solder is used for joining the semiconductor element,
It has been found that it is not preferable to intentionally or positively co-deposit Co as in the case of using Au-Si solder.

[0009] Even in a commonly used electrolytic Ni plating solution of a watt bath to which Co is not intentionally added, Co is contained as an impurity in Ni sulfate or Ni chloride used in a building bath. 0.1 to 0.1 wt.
0.8% by weight. When plating is performed with this Ni plating solution, the ratio of Co in the Ni plating layer is 0.5 to 3.6.
%, And the desired stable high bonding strength cannot be obtained even when bonding to such a Ni plating layer is performed using a Sn alloy or Sn. This is probably because the ratio of Co in the Ni plating layer varies in the range of 0.5 to 3.6% by weight, and substantially exceeds 3% by weight. In addition, like electroless Ni-B plating, electroless N
Although it is conceivable to use i-plating, electroless plating is more difficult in process management and the like than electrolytic plating, and is not appropriate in terms of cost.

The present invention has been made based on such knowledge, and an object thereof is to form an electrolytic Ni plating layer or an electrolytic Ni plating layer on the surface of a refractory metal layer (metallized layer) such as tungsten or molybdenum. Plating layer and A
A u-plated layer is formed to form a die-attach portion, and a chip such as Pb-Sn solder is used for bonding the chip to the die-attach portion.
In the case where an alloy containing n or Sn is used, even if the chip is exposed to a high temperature, generation of an intermetallic compound can be suppressed, and the bonding strength is not reduced.

[0011]

In order to achieve the above-mentioned object, the present invention provides an electrolytic nickel plating layer or an electrolytic nickel plating layer and a gold plating layer formed on a surface of a high melting point metal layer, on which the surface (surface) is formed. In a wiring board to which an electronic component is soldered with tin or an alloy containing tin, the ratio of cobalt to the electrolytic nickel plating layer (total) containing cobalt is set to 3% by weight or less.

In the present invention, as described above, the content of cobalt (Co) in the electrolytic nickel plating layer is set to 3% by weight or less. Thus, even when an electronic component including a semiconductor element is soldered on the electrolytic nickel plating layer using an alloy containing Sn such as Pb-Sn solder or Sn, a wiring board having high bonding strength even in a high temperature environment can be obtained. Can be In the present invention, “on the electrolytic nickel plating layer” means the surface thereof, and, when a gold plating layer is formed thereon, on the gold plating layer (surface). That is, even when such a wiring board is placed in a high-temperature environment, a conventional electrolytic nickel plating layer to which conventional Co is positively added or a normal electrolytic nickel plating layer (Co is 0.5 to
As in the case of the electrolytic nickel plating layer which varies in the range of 3.6% by weight, the bonding strength does not decrease and the same strength as before heating is maintained.

In order to reduce the proportion of Co in the Ni plating layer to 3% by weight or less, the purity of nickel sulfate or nickel chloride used in the bath composition of the Watt bath is increased to reduce the amount of cobalt in the solution. Electrolysis N using the removed plating solution
i-plating may be performed. That is, nickel sulfate and nickel chloride, which are commonly available nickel plating chemicals, contain a considerable amount of cobalt as an impurity, and the amount is 0.1 to 0.8% by weight based on the total weight. When plated with a Ni plating solution using this as it is, Ni
Co is included in the plating layer in a range of about 0.5 to 3.6% by weight. Among such Ni plating layers,
If the proportion of Co exceeds 3% by weight, the joining strength is reduced. Therefore, plating is performed using the plating solution thus decobalted so that the proportion of Co in the Ni plating layer does not exceed 3% by weight. However, the weight of cobalt in the nickel plating solution is reduced. It is preferable that the electrolytic nickel plating layer is formed so that the weight of the nickel is 1/148 or less. Details will be described later.

In the present invention, the proportion of cobalt in the electrolytic nickel plating layer containing cobalt may be 3% by weight or less, but the electrolytic nickel plating layer may not contain cobalt. . That is, Co in the Ni plating layer is 0% by weight. Here, “cobalt-free (0% by weight)” means EDS (ENERGY DISPERSIVE SPECTROMETE).
R) It means that the detected amount of cobalt in the analysis is 0% by weight. Note that a nickel sulfamate plating solution may be used for such Ni plating.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described in detail with reference to FIGS. In the figure, reference numeral 1 denotes a multilayer wiring layer substrate made of alumina ceramic, which is formed by simultaneously firing a wiring layer (not shown) including a die attach portion 3 at the center of the upper surface 2 with a high melting point metal such as W or Mo. Have been. Then, an electrolytic Ni plating layer (hereinafter, referred to as a Ni plating layer) 5 containing 3% by weight or less of Co is formed on a refractory metal layer (metallized layer) 4 forming the die attach portion 3, and the surface thereof is for preventing corrosion. An electrolytic Au plating layer (hereinafter, referred to as an Au plating layer) 6 is formed. In this example, C in such Ni plating layer 5
100 wiring boards (samples) 1 each having 0% by weight, 1% by weight, 2% by weight, and 3% by weight were prepared, and a joined body sample was prepared as described below, and a chip peeling (tensile) test was performed. did. However, the Co content (rate) is a value obtained by EDS analysis.

The Ni plating layer may be formed by a single plating, but in this example, the Ni plating layer is formed so as to have a thickness of 1 μm at the first time and sintered at about 800 ° C. Adhesion of the Ni plating layer was ensured by mutual diffusion between the layers (W and Mo) 4 and Ni, and a second Ni plating layer having a thickness of 2 μm was formed for the second time. Note that the thickness of the Ni plating layer 5 is
The thickness is not limited to this, and may be an appropriate thickness. The Au plating layer 6 was formed so as to have a thickness of 1.5 μm.
In the case where there is no problem in solder wettability or the case where oxidation of the Ni plating layer is not a problem, it is not necessary to form it.

Then, such a wiring board (sample) 1
Next, as shown in FIG. 2, a chip sample 11 having a metallized layer 10 made of Ag / Pd is used as a Sn-containing alloy in this example as a Pb-Sn eutectic solder (Sn63: Pd37).
100 pieces of the joined body sample 21 soldered in 7 were produced. In this example, a Pb-Sn eutectic solder paste is screen-printed on a die-attached portion (for example, a □ 20 mm area) 3 of each wiring board 1, and □ 1 having a metallized layer 10 on one main surface.
A 5 mm chip sample 11 is positioned and placed (set) with its main surface in contact with the die attach portion (solder paste printed surface) 3 at 180 ° C. to 200 ° C. in the air or in a nitrogen atmosphere. Hold for 1 minute. Thus, the chip sample 11 was soldered by reflowing the solder 7, and then the flux was washed to obtain a bonded sample 21.

Next, the bonded sample 21 was divided into 10 pieces, each of which was subjected to a heat treatment (high-temperature aging) at 150 ° C. for 150 hours, 300 hours, 600 hours, or 1000 hours. Then, as shown in FIG. 3, an aluminum stud S is adhered to the surface of the chip 11 with an epoxy-based adhesive together with the unheated ones (ten pieces), while the upper surface of the wiring board 1 is clamped by a clamp C. The chip 11 is forcibly peeled off by applying a tensile load P vertically to the joining surface so as to separate the chip 11 from the wiring board 1 so as to separate the chip from the wiring board 1 and the chip 11.
The number of pieces cut at the interface between the surface of the plating layer 5 and the solder 7) was measured.

In the case of such a peeling failure mode, a hard and brittle Sn—Ni-based intermetallic compound is largely formed and grown on the interface between the surface of the Ni plating layer and the solder 7. Peels off easily with low load. On the other hand, the one that is peeled off in such a manner as to be cut between the layers of the bonding solder 7 has high bonding strength. In the above-described embodiment, the Au plating layer 6 is formed on the die attach portion 3, but Au in the Au plating layer is Au-Si melted at the time of soldering.
Since it diffuses into the solder, an intermetallic compound is generated at the interface between the surface of the Ni plating layer 5 and the solder 7. As comparative examples, 3.5% by weight, 4% by weight, 5% by weight, 6% by weight of Co were used.
Those containing 10 to 10% by weight and 15 to 30% by weight were also tested. The results are as shown in Table 1.

[0020]

[Table 1]

As is clear from Table 1, the content of Co is 6% by weight.
If the heat treatment time is longer than 150 hours, all of them are peeled off and are in a failure mode (ones that have been cut off at the interface between the Ni plating layer and the solder).
However, the rate of occurrence increased as the heat treatment time increased. In the case of 5% by weight, 600 hours or more, 3.5% by weight and 4.5% by weight of 100%.
At 0 hours or more, a failure mode occurred. On the other hand, when the content of Co was 3% by weight or less, none of the samples after any heat treatment time was cut at the bonding interface between the Ni plating layer and the solder, as in the case without heating.
It was cut between the layers of bonding solder 7. These facts demonstrate that when the content of Co in the Ni plating layer is set to 3% by weight or less, generation of a Sn—Ni-based intermetallic compound by heat treatment and the like are suppressed. It shows that the reliability of the joint does not decrease even when used in a thermal environment.

In the above embodiment, the sample in which Co in the Ni plating layer was 0% by weight was plated using a nickel sulfamate plating solution. The sample containing 1-3% by weight of Co in the Ni plating layer was prepared by increasing the purity of nickel sulfate and nickel chloride used in the bath composition of the Watt bath so as to obtain such a plating composition. The plating was carried out using a plating solution in which the amount was reduced and adjusted. When the content of Co is 3.5% by weight or more, the nickel watt bath is prepared by adding an appropriate amount of cobalt sulfate as Co to the Ni plating layer so that the Ni plating layer contains each weight% of Co. It is.

In the above, in order to reduce the proportion of Co in the Ni plating layer to 3% by weight or less, the proportion of Co in the Ni plating solution (= Co weight / (Ni weight + Co weight)) is set to 0.67.
% By weight or less. This is based on the experiment (plating solution: watt bath, current condition: 1 A / dm ² , plating temperature: 45).
C.), it was found from the relationship between the ratio of Co in the Ni plating solution and the Ni plating layer (= Co weight / (Ni weight + Co weight)) (see Table 2 and FIG. 4 which is a graph of this).

[0024]

[Table 2]

That is, according to the experiment, the ratio of Co in the Ni plating layer is substantially proportional to the ratio of Co in the Ni plating solution. / (Ni weight + Co weight)) is 0.67
This is because the ratio of Co in the Ni plating layer becomes 3% by weight or more when the content is more than 3% by weight. Therefore, the proportion of Co in the Ni plating solution (= Co weight / (Ni weight + Co weight))
Is set to 0.67% by weight or less to form the Ni plating layer. That is, the weight of cobalt in the Ni plating solution is changed to N
If the electrolytic Ni plating layer is formed on the surface of the refractory metal layer at a ratio of 1/148 or less of the weight of
The ratio of Co to the i-plated layer can be reduced to 3% by weight or less.

The ratio of Co in the Ni plating solution is set to 0.1.
The method of reducing the content to 67% by weight or less may be an appropriate method, and the following method is exemplified. (1) Wat bath improvement. That is, a first-class reagent (Co impurity amount of 0.1% by weight or less) is used for Ni sulfate and Ni chloride used in the building bath. (2) Reduce the ratio of Co by performing dummy plating in a watt bath. While the Watt bath contains up to 0.8% by weight of Co, the Co / Ni ratio in the deposited plating layer is larger than the Co / Ni ratio in the plating solution. Therefore, Ni consumed in the dummy plating is dissolved in the plating solution from the anode and is supplemented, but the proportion of Co in the Ni rod of the anode is as low as 0.1% by weight or less. By performing dummy plating in this manner, the proportion of Co in the plating solution can be reduced. (3) Use of Ni sulfamate plating solution. The Ni sulfamate plating solution can be used as it is because the proportion of Co in the solution is 0.1% by weight or less.

In the above description, the case where the semiconductor element is joined has been described. However, in the present invention, not only other electronic parts but also the case where external leads are joined can be similarly improved in joining strength. . In the above description, the present invention is embodied by a wiring board for an IC package, but the present invention can be widely applied to other wiring boards.

[0028]

As is apparent from the above description, according to the wiring board of the present invention, the ratio of cobalt to the electrolytic nickel plating layer containing cobalt is set to 3% by weight or less. A wiring board or a semiconductor device in which a semiconductor element is bonded using an Sn-containing alloy such as Pb-Sn solder or Sn on the above, and this is used in a high-temperature environment. Thus, no intermetallic compound is generated and grown. Therefore, the bonding strength does not decrease, and the same strength as before the high temperature environment is maintained. As described above, according to the present invention, the electronic component is placed on the die attach portion or the like formed by the electrolytic nickel plating layer.
-Even if it is soldered with an alloy containing Sn such as Sn solder or Sn, a highly reliable joint can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view and an enlarged view of a main part of a wiring board according to the present invention.

FIG. 2 is a conceptual diagram of a bonded sample obtained by bonding a chip sample to the wiring board of FIG. 1;

FIG. 3 is an explanatory view showing a state in which a stud is bonded to a chip sample and a peeling test is performed on the bonded sample of FIG.

FIG. 4 is a graph showing the relationship between the proportions of Co in a nickel plating solution and in a Ni plating layer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Wiring board 3 Die attach part 4 High melting point metal layer 5 Electrolytic nickel plating layer

Claims (4)

[Claims] 1. A wiring board in which an electrolytic nickel plating layer or an electrolytic nickel plating layer and a gold plating layer are formed on a surface of a high melting point metal layer, and an electronic component is soldered with tin or an alloy containing tin thereon. The ratio of cobalt to the electrolytic nickel plating layer containing cobalt is 3% by weight.
A wiring board characterized by the following. 2. A wiring board on which an electrolytic nickel plating layer or an electrolytic nickel plating layer and a gold plating layer are formed on a surface of a high melting point metal layer, and on which electronic components are soldered with tin or an alloy containing tin, A wiring board, wherein the electrolytic nickel plating layer does not contain cobalt. 3. The electronic component according to claim 1, wherein said electronic component is tin or an alloy containing tin and soldered on said electrolytic nickel plating layer.
Or the wiring board according to 2. 4. The method according to claim 1, wherein the weight of cobalt in the nickel plating solution is less than 1/148 of the weight of nickel to form the electrolytic nickel plating layer.