KR910000841B1 - Silver coated material and making method - Google Patents

Abstract

No content.

Description

Silver-coated electric material and manufacturing method thereof

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to silver coated electrical materials that are excellent in electrical connectivity, metallurgical bonding (solderability, bonding) and corrosion resistance.

Silver or silver alloys, such as Ag-Au, Ag-, on some or all of the surface of conductive substrates such as copper or copper alloys, nickel or nickel alloys, iron alloys, aluminum or aluminum alloys or non-conductive substrates such as ceramics and plastics Coating electrical materials coated with Sb, Ag-In, Ag-Cu, Ag-Se, Ag-Pt and the like are widely used as electric and electronic materials.

Since silver is excellent in electrical conductivity and corrosion resistance, it is the best as an electrical material, but it is expensive as a precious metal. Therefore, it should be used only for the part that needs excellent electrical connection. Do.

For example, an electric material coated with silver on the surface of the substrate is used as an electric or electronic material. For example, in a lead frame of a semiconductor, silver coating is applied only to a mounting portion for soldering silicon chips or a wire bonding portion for Au wire.

Silver-covered electrical materials are also used as wiring materials for electrical contacts such as switches, relays, connectors and the like, and lead wires and terminals that touch printed board mounting portions of various electronic components, and also electrical equipment and aircraft. Silver coating by partial plating only on a part of the surface of the substrate is also widely used for processing applications.

In other words, the electrical material coated on the substrate, which is the object of the present invention, is required to be excellent in the use of electrical properties such as solderability and bonding properties and excellent electrical connection by utilizing the physical and chemical properties peculiar to silver. It is widely used for uses, such as an electrical contact.

The silver-coated electrical materials used for these applications will of course not degrade their properties over the long term of their practical use, nor will they lose their properties by the thermal and chemical treatments received in the manufacturing process of the parts in which they are used. Is required.

According to this request, in order for the silver-coated electric material to exhibit its original performance, the thickness of the silver-coated is required to be at least 1 μ, usually 3 to 6 μ.

However, as already explained, since silver is expensive, there is a strong demand for thinner silver coatings for cost reduction.

Thus, if the thickness of the silver coating is thinned for cost reduction, the following problems occur.

(1) Silver coating Depending on the manufacturing method and manufacturing conditions of the electrical material, the silver coating has a porosity, so that a so-called pin hole is formed in the silver coating, and thus the substrate is easily exposed.

(2) In the case of a conductive base material, the non-noble metal component in the base material undergoes a solid phase diffusion reaction in the silver coating, reaches the outermost surface of the silver coating, is oxidized there, and corrosion products easily accumulate on the surface of this electrical material.

This is particularly noticeable when the electrical material is exposed to high temperatures since the solid-state diffusion reaction proceeds at an exponential rate of temperature.

The above two problems are more remarkable in gold-coated electrical materials using gold, which is more expensive than silver, but in the case of gold-coated electrical materials, they are solved by forming an intermediate layer as Ni or between the gas and the gold-coated electrical materials.

Also in the silver-coated electric material, forming the Ni intermediate layer has been put to practical use when used in semiconductor lead frames, electrical contacts, or the like. Conventionally, by forming a Ni intermediate layer with a thickness of 0.5 to 3 mu, the formation of pinholes and solid phase diffusion in the silver coating of the base metal are prevented.

However, even when such a Ni intermediate layer is formed, when the silver coating of the silver-coated electric material is made thinner, it is not a problem solution when it is exposed to high temperature in the process of assembling this electric material as a component.

For example, electronic parts in which silver-coated electric materials are used in the industrial mass as the constituent members of components are assembled by soldering these electric materials, and the electronic parts themselves are generally mounted by soldering on printed circuit boards. This electrical material is exposed to high temperatures. Moreover, it exposes to high temperature also in processes, such as resin casting, hardening, and aging, drying, vapor deposition, and sputtering for adjusting performance. These processes are normally performed at the temperature of 150-400 degreeC, and they are performed in air | atmosphere in many cases.

One of the advantages of using silver-coated electric materials is that various treatment steps can be performed in such a high temperature atmosphere, and in some resin curing, the presence of high temperature oxygen is indispensable.

In the case of the treatment in the presence of such high temperature oxygen, the provision of a nickel intermediate layer in the silver-coated electric material is no problem solution, and the solderability of the electric material is drastically reduced, and in some cases even peeling of the silver-coated material occurs. This is a problem inherent in silver-coated electrical materials that do not appear in coated electrical materials with nickel interlayers. The inventors have found that this is due to the following reasons. In other words,

(1) At temperatures between 150 and 400 ° C, oxygen in the atmosphere quickly penetrates through the silver-coated layer and reaches the surface of the nickel intermediate layer underneath the silver-coated to cause oxidation with Ni. The permeated oxygen is assumed to be atomic, and since it is particularly active, the surface of the nickel interlayer is encased in nickel oxide (NiO), and the metal bond between silver and nickel is interrupted, resulting in the loss of adhesion between the silver coating and the nickel interlayer, causing the silver coating to peel off. do.

(2) Silver is the metal which dissolves most rapidly in the soldering bath. In the soldering conditions normally used, it dissolves in thickness of 2 to 3 μm for 1 second. Therefore, when the silver coating is thin, the nickel oxide produced by the above-described method When exposed to the surface, the solderability of this electrical material is significantly reduced.

The present invention has been developed in view of the above situation, the silver-coated electric material and its manufacturing method are as follows.

As a covering electrical material, what has the following characteristics is obtained.

(1) It should have corrosion resistance which can support gas corrosion effectively even in thin silver coating.

(2) Corrosion resistance should be better in sulfided environment than in conventional silver-coated electric materials.

(3) Good adhesion of silver coating and no peeling of silver coating even when exposed to high temperature.

(4) The gas should not diffuse in the silver coating even at high temperatures, and the performance of the silver coating, such as conductivity and corrosion resistance, should not be reduced.

(5) Metallurgical bonding such as solderability should be maintained highly in a non-oxidizing atmosphere as well as in an oxidizing high temperature atmosphere.

(6) Even if it is stored for a long time, it should be able to maintain high electrical connectivity such as contact resistance.

(7) The susceptibility of silver migration, one of the major defects of silver, should be low.

측의 온도체로부터 Ag 이온이 Migration하여

측에 석출하여 성장하여서 단락을 일으키는 현상이다.Note: Silver migration means that between the authorized electrical circuits of direct current

Ag ions migrate from the temperature body on the side

It is a phenomenon that precipitates on the side and grows to cause a short circuit.

(8) Silver coating has high mechanical strength and good wear resistance.

As a manufacturing method, the manufacturing method which manufactures the silver coating electrical material which satisfy | fills the above various characteristics efficiently and on an industrial scale is discovered.

In order to achieve the above object, the present invention constitutes the following configuration. That is, the first invention is a silver-coated electric material which is silver-coated on a part or all of the surface of a conductive or non-conductive gas, and the metal group selected from Ni, Co, Cr, Pd or alloys thereof between the gas and the silver-coated A first intermediate layer of at least one of the following, and a second intermediate layer of at least one of a group of metals selected from Sn, Cd, Td, Ru, or an alloy thereof, from the base to the first intermediate layer, and the second intermediate layer. A silver-coated electric material characterized in that the second invention is the first invention, in particular, when the base is conductive, the first intermediate layer, the second intermediate layer, three layers of the silver coating by the electroplating, respectively It is a manufacturing method of a silver-coated electric material characterized by forming sequentially.

Such a construction in the first invention improves the metallurgical bonding (solderability, bonding), electrical connectivity, corrosion resistance, and wear resistance of the silver-coated electrical material, thereby lowering the susceptibility to silver migration.

In the first invention, when the substrate is Ni, Co, Cr, Pd or an alloy thereof, or when Ni, Co, Cr, Pd or an alloy layer thereof is already formed on the surface of the substrate, the first intermediate layer is formed by the substrate. It is obvious in the configuration of the present invention that can be substituted as.

Ni, Co, Cr, and Pd are selected as the first intermediate layer because they are high melting point metals, which do not react with silver or under practical conditions, and are the most common and large amounts of gases for silver-coated electric materials. This is because it is difficult to react with the copper or copper alloy used. Cr is particularly effective as a barrier to copper base materials, but in general, it is hard and soft and should be used for applications requiring excessive thickness or processability.

As a preferable 1st intermediate | middle layer, it is good to contain 10% or more of 1 type, or 2 or more types of Ni, Co, Cr, Pd single body, or Ni, Co, Cr, Pd in total. This is because the diffusion preventing effect of the gas on the silver coating is less than 10%. Examples of alloys include Ni-Co, Ni-Pd, Ni-Co-Pd, Co-Pd, Ni-Cr, Ni-Zn, Ni-Fe, Co-Zn, Ni-Cu, Co-Sn, Ni-P, Co -B and so on. The thickness of the first intermediate layer is suitably 0.1 to 5 mu in many practical conditions. This is because if the thickness is less than 0.1 µ, the diffusion prevention of the gas, which is a function of the intermediate layer, in the silver coating and the function of the second intermediate layer described below are not sufficiently exhibited.

The second intermediate layer may be Sn, Cd, Pd, Ru, or an alloy thereof. The second intermediate layer prevents high temperature oxidation of the first intermediate layer, but the metal constituting the second intermediate layer is Sn, Cd, and Pd, Ru. It is assumed that the mechanism for preventing high temperature oxidation is different from the case.

That is, in the case of Sn and Cd, these are low melting point metals, which are soluble in silver and have a high affinity with oxygen, so they diffuse quickly in the silver coating and combine with oxygen that enters the silver coating from an external gas, or increase the oxygen penetration rate. It is supposed to suppress or prevent oxygen from reaching the surface of the first intermediate layer.

On the other hand, in the case of Pd and Ru, Pd and Ru are high melting point metals and have a very low affinity with oxygen, so that they become barriers to oxygen passing through the silver coating from an external gas and oxygen reaches the surface of the first intermediate layer. It is estimated to stop.

As thickness of a 2nd intermediate | middle layer, 0.01-2 micrometers is suitable in normal practical conditions. This is because the effect of inhibiting oxygen attainment on the surface of the first intermediate layer is not so remarkable at less than 0.01 mu, and it is economically disadvantageous even if it exceeds 2 mu.

Pd and Ru are precious metals belonging to the platinum group, which are relatively inexpensive precious metals. They are about 10 times the price of silver, so if the thickness of the silver coating can be greatly reduced by using such a thin film, especially 0.01 ~ 0.1μ, Economical silver savings are also effective.

As described above, not only Sn, Cd, Pd, and Ru, but also alloys thereof are effective as the second intermediate layer, and in some cases, the alloy is also effective.

Sn and Cd are active metals, which may be eluted in some plating liquids or replaced by silver when the silver is coated thereon by electroplating, which may cause a decrease in adhesion to silver coating. In such a case, Alloys such as Sn-Pd, Sn-Bi, Sn-Cu, Sn-Ni, Sn-Zn, Sn-Co, Cd-Cu and the like are effective as the second intermediate layer.

Since Pd and Ru are expensive as noble metals, the cost can be reduced by using Pd-Ni, Pd-Co or Pd-Ni-Co alloy containing 40% or more of Pd as the second intermediate layer.

Among the metals used as the second intermediate layer, Sn is less toxic than Cd and excellent in reactivity with silver, which is particularly effective in practical use, but the excessive thickness of Sn causes a decrease in the performance of the silver coating, so Sn is used as the second intermediate layer. In the case of use, the thickness of Sn is particularly preferably about 1/500 to 1/10 of the thickness of the sound coating.

In the present invention, since Ni, Co, Cr, Pd, or alloys thereof, which are difficult to react with Sn and Cd, which are part of the second intermediate metal, Sn, Cd, which is the second intermediate layer due to the presence of the first intermediate layer, It can diffuse stably in silver coating without reacting with gas, and can exhibit the oxygen retention effect in such silver coating. If there is no such first intermediate layer, especially if the gas is copper or copper alloy, it will react with copper and the effect as the second intermediate layer will not be obtained.

The effect of the first intermediate layer for exerting the function of the second intermediate layer is particularly effective when the first intermediate layer is a Ni—Zn alloy.

As apparent from the above description, the intermediate layer must be formed from the gas in the order of the first intermediate layer and the second intermediate layer.

Although the present invention is industrially possible to form each layer by mechanical creep, vapor deposition, and sputtering as the method for producing a coated electrical material, it is most practical by the electroplating method.

This is because the first intermediate layer, the second intermediate layer, and the silver coating can all be efficiently formed by a conventional electroplating method, and these three layers can be formed sequentially in succession. In addition, it is important to control each layer to a predetermined thickness, and in particular, to control a thin layer such as a second intermediate layer to a predetermined thickness can be easily realized by inputting an electric quantity according to Faraday's law during electroplating. Is the point.

Next, an Example demonstrates this invention.

Example 1

As the lead wire for the diode, there is an Ag plated Cu wire (0.6 mmØ). The Si chip is bonded to the tip of the header machined line by high Pb soldering and cured with an encapsulating resin to complete the diode. The soldering is performed at 350 ° C. × 15 minutes (in H ₂ ), and the curing is at 215 ° C. Solderability must be maintained even after these treatments as a heating step performed at 10 hrs (in air). As an example, a Cu wire of 0.6 mm Ø was electrolytically degreased by a general method, washed with acid, and then electroplated using the following bath to obtain Ag-plated Cu wire having various intermediate layers shown in Table 1.

The Ag-plated Cu wire was heat-treated at 350 ° C. × 15 minutes (in H ₂ ) and 215 ° C. × 10 hours (in air) under the same conditions as those of the above diode manufacturing, and then 5 seconds in Eutectic Solder bath 235 ° C. in accordance with MIL-Standard After immersion, the ratio of the solder wetted area was measured, and the results are shown in Table 1.

TABLE 1

As apparent from Table 1, the present inventions Nos. 1 to 13 have a wetness ratio of 90%, which is the minimum target of solderability, in a silver coating thickness of 1.0μ. However, in the conventional products (Nos. 14 and 15) without an intermediate layer, It is barely reached 90% at the silver coating thickness of 3.5μ, and it can be seen that in the conventional products having only Ni intermediate layer (No. 16, 17), the wet rate is only 40% even at the thickness of 3.5μ of the silver coating.

Although Pd or Ru used as the second intermediate layer is about 10 times more expensive than silver, the thickness of 0.08 μm as the second intermediate layer can reduce the thickness of the silver coating to 2.6 μm, which is economically sufficient.

Example 2

Fe-14Cr alloy bath (0.32t) was used as a semiconductor lead frame. It is press-molded by a general method to make a 16-pin frame, followed by plating 7μ Ag on the front surface. The present invention was applied to reduce the Ag of the product to 3.5μ. An integrated circuit element of Si is soldered to the center tab portion, and ultrasonic welding is performed between the electrode on the element and the inner lead portion of the frame with an Au wire of 30 탆 diameter. The former must withstand heating conditions (in air) at 400 ° C for 5 minutes and the latter at 200 ° C for 15 minutes.

By the plating method shown in Example 1 and the following plating method, various silver-coated lead frames shown in Table 2 were made, and the following tests were performed for each.

[Test I: Solderability Test]

After 400 ° C × 5 minutes atmospheric heating, the sample was immersed in a 350 ° C bath of 95% Pb-5% Sn for 3 seconds, and the wet area was measured.

[Test II: Bonding Test]

After heating at 400 ° C. for 5 minutes, cooling, and again heating at 200 ° C. for 15 minutes, the Au wire was ultrasonically welded with a bonding pressure of 45 gr. The average tensile strength of 20 minutes was obtained.

[Test III: Silver Migration Test]

The two lead portions were cut out and fixed on a qualitative filter at 2 mm intervals after the heat treatment, and a DC voltage of 25 V was applied at 60 ° C. × 95% RH, and the interpole resistance after standing for 24 hours was measured.

Table 3 shows the test results of the above three types.

TABLE 2

As is apparent from Table 2, the lead frames Nos. 1 to 8 of the present invention are excellent in metallurgical bonding (tests I and II) even with 3.5μ silver coating, and have a large gap resistance due to test III and a low risk of silver migration. It can be seen that.

On the other hand, the conventional leadframe No. 9 is not sufficient in bonding and has a high risk of silver migration. In addition, it can be seen that the conventional leadframe No. 10 having a silver coating thickness of 7 mu is good in bonding but has a risk of silver migration.

Example 3

As a contact spring for keyboard switches, 0.5μAg plating and ph-osphorous bronze (0.08t Sn = 8.0%) are used. In order to apply the present invention to the product, various silver-covered contact springs shown in Table 3 were prepared using the plating methods shown in Examples 1 and 2 and below. In order to confirm the long-term performance as these contacts, the contact resistance was measured after the aging treatment under the following two conditions. This measurement was carried out by pressing a semi-circular tip (R = 4.0 mm) Ag rod to a contact spring with a 75gr load and passing a current of 100 mA. The results are shown in Table 3.

Aging I

1000hr in a humidification tank with 60 ℃ and 95% relative humidity

Aging II

10hr in air at 200 ℃

TABLE 3

As apparent from Table 3, the silver-coated contact spring to which the present invention is applied has a smaller contact resistance after aging and a deterioration in contact resistance due to aging compared to the conventional products.

Next, as a result of analyzing the corrosion products on the surface of the contact spring surface subjected to the aging treatment I in the third embodiment by Cathodic Reduction, oxides of Cu and sulfides of Ag were detected. Table 4 shows the amount by the amount of electricity required for reduction.

TABLE 4

In other words, the surface of the silver-coated contact spring to which the present invention is applied has less corrosion products than the conventional products, and is particularly remarkable in Nos. 1, 2, and 3 using Sn as the second intermediate layer. This is presumably because a small amount of Sn diffused in the silver coating and alloyed to increase the corrosion resistance of the silver coating.

As described above, the silver-coated electric material of the present invention is a method of easily and efficiently obtaining each intermediate layer and silver-coated which is excellent in metallurgical bonding, electrical connection and corrosion resistance, and its manufacturing method is electric and electronic industry. It shows a significant effect.

Claims (11)

In silver-coated electrical materials with silver or silver-coated (hereinafter referred to as silver-coated) on part or all of the conductive or non-conductive substrate, Ni, Co, Cr, Pd or these The first intermediate layer comprising at least one or more of the metal groups selected from the alloys of the alloys and the second intermediate layer of at least one or more of the metal groups selected from Sn, Cd, Pd, Ru, or alloys thereof from the base, Silver-coated electrical material, characterized in that formed in the order of the second intermediate layer. The gas itself is replaced by the first intermediate layer when the base is Ni, Co, Cr, Pd or an alloy thereof, and when Ni, Co, Cr, Pd or its alloy layer is already formed on the surface of the base. Silver-coated electrical material characterized in that. The silver-coated electric material according to claim 1, wherein when the first intermediate layer is an alloy, it is an alloy containing 10% or more in total of one kind or two or more kinds of Ni, Co, Cr, and Pd. The silver-coated electric material according to claim 1, wherein the thickness of the first intermediate layer is 0.1 to 5 mu. The silver-coated electric material according to claim 1, wherein the thickness of the second intermediate layer is 0.01 to 2 mu. The silver-coated electric material according to claim 1, wherein the second intermediate layer is Sn or Sn alloy. The silver-coated electric material according to claim 6, wherein the thickness of Sn is 1/500 to 1/10 of the thickness of the silver coating when the second intermediate layer is Sn. The silver-coated electric material according to claim 1, wherein the second intermediate layer is a Pd-Ni, Pd-Co or Pd-Ni-Co alloy containing at least 40% of Pd. The silver-coated electric material according to claim 1, wherein the first intermediate layer is a Ni—Zn alloy. The silver-coated electric material according to claim 1, wherein the base is Cu or a Cu alloy. When the substrate is conductive, the first intermediate layer of Ni, Co, Cr, Pd or an alloy thereof, the second intermediate layer of Sn, Cd, Pd, Ru or an alloy thereof, and three layers of silver coating are respectively provided on the substrate. Silver-coated electrical material, characterized in that formed sequentially by electroplating.