JPS60131996A - Plated stainless steel and its production - Google Patents

Abstract

PURPOSE:To provide a plated stainless steel suitable particularly for an application as an electronic part material or the like for which high performance and high reliability are required by providing an extremely thin intermediate Ni layer between an electroplating layer and a base stainless steel layer. CONSTITUTION:A clean base stainless steel subjected to an ordinary pretreatment such as degreasing or the like is subjected to a cathode reduction treatment in a soln. contg. >=50g/l free hydrochloric acid at >=0.5A/dm<2> cathode current density with said stainless steel as a cathode and Ni (alloy) as an anode. The use of an Ni-Fe alloy, etc. which are more inexpensive than costly Ni as the anode is practical. The stainless steel is rinsed in succession to the above- mentioned cathode reduction treatment to deposit Ni and is then subjected to desired plating by which the intended plated stainless steel is obtd. The metal plating is accomplished by Ag plating using a cyanide bath, Cu plating using a cyanide bath or sulfuric acid bath, Pd plating using an amine complex bath, etc. Such plated stainless steel has extremely smaller contact resistance than the conventional product even after humidification and heating and maintains an excellent electrical contact characteristic in a severe environment for a long period of time.

Description

[Detailed Description of the Invention] The present invention provides stainless steel with P d r A g + (3
The present invention relates to a plated stainless steel plated with a metal such as URSN, and a method for manufacturing the same, and particularly to a plated stainless steel suitable for use in precision electrical machinery and electronic parts.

Stainless steels include austenitic, ferritic, martensitic, and precipitation-hardened stainless steels, all of which have excellent physical properties such as mechanical strength and have a strong passivation film on their surfaces. It is also widely used industrially because of its excellent corrosion resistance.

However, since this passive film is extremely harmful to soldering of electrical connections in electronic component applications, it is customary to plate at least the electrical connections in advance with a dissimilar metal, particularly Ag, Pd1Cu+Sn, etc.

Plating is usually performed by electroplating, but physical plating such as ion plating sputtering is also in practical use.

During these platings, the presence of the passive film makes it impossible to form a metallic bond between the stainless steel and the plated metal, so this film must be removed beforehand.

To remove the passive film, a dissolution treatment with a concentrated mixed acid or cathodic reduction in a sulfuric acid or hydrochloric acid solution is usually carried out.

However, even with these methods, in many cases, plating with sufficient adhesion cannot be obtained, and in addition to these methods, N1 strike plating is performed.

NiC1t 24 is the method of N1 strike plating.
0 t/l, HCl 80-120 f/2-2 in solution
It is common practice to perform cathode treatment at a current density of '0A/d- for 2 to 1I minutes to perform N1 strike plating to a thickness of quoooX or more, usually about 1μ. (According to "Stainless Steel Handbook" published by Nikkan Kogyo Shimbun, 1976.) However, such N1 strike plating requires a lot of man-hours and is not only complicated but also has some practical problems.

This will be explained using an example of austenitic stainless steel plated with Ag, which is used as a spring contact for a small switch, which is one of the typical electronic components.

This material can withstand bending due to press molding and drawing of contacts, and can also withstand the high-temperature environment of terminal soldering, which reaches temperatures of approximately 300 to 400 degrees Celsius, and has good performance under weak current conditions for a long period of time. It is necessary to exhibit electrical contact properties, and from an economic point of view, it is required to apply as thin Ag plating as possible in order to save expensive Ag.

However, stainless steel plated by the above-mentioned conventional method is often unable to meet these demands.

The inventor of the present invention has confirmed that the reason for this is cracking of the Ag plating layer due to deformation of strength during the pressing process, and also a peeling embrittlement phenomenon of the Ag plating layer due to high temperature heating.

That is, cracks in the Ag plating layer cause electrolytic corrosion, resulting in a significant increase in contact resistance due to corrosion products.

The peeling of the Ag plating layer is achieved by the high-temperature heating process.
This is because 2 passes through and reaches the surface of the N1 strike plating layer, oxidizes the surface, and breaks the metal bond between Ag and N1.

This phenomenon is unavoidable at temperatures above 180 to 190°C, at which Ag and O are thermally decomposed.

0 for metals other than Ag! Solid-state diffusion is not a practical problem, but 0t can pass through unavoidable pinholes in thin metal plating.
This often causes the Ni surface to be oxidized, leading to similar results.

A decrease in the bonding strength of the plated interface due to oxidation of the N1 surface leads to cracking of the plated layer during processing deformation and further peeling of the plated layer.

It has become clear that the engineering defects of cracking and peeling of the plating layer described above are all caused by the presence of the Ni strike plating layer.

In other words, the occurrence of cracks from the hard Ni strike plating layer and penetrating the thin upper plating layer is due to N1.
This becomes clear from the comparative observation of bending tests with Ag-plated stainless steel without strike plating.

The present invention has been made in view of the above circumstances, and has developed a plated stainless steel and a method for manufacturing the same, which are particularly suitable for applications requiring high performance and high reliability, such as electronic component materials. The stainless steel to be plated is a stainless steel to be plated which is metal-plated and has a nickel intermediate layer with a thickness of 300 to 12 ooX between the metal plating layer and the base stainless steel, The manufacturing method is to conduct electrolysis using a stainless steel base as a cathode, nickel or nickel alloy as an anode, and a solution containing free hydrochloric acid of 50 f/ or more as an electrolyte at a cathode current density of 0.5 A/d- or higher. This method of producing stainless steel to be plated is characterized in that a nickel intermediate layer having a thickness of 300 to 1200 times is deposited on the steel surface, and then metal plating is applied to this base stainless steel.

First, the stainless steel to be plated according to the present invention will be explained.

The plated stainless steel of the present invention is characterized by a significantly thinner N1 layer, which is the intermediate layer, compared to conventional plated stainless steel that is metal-plated after N1 strike plating. The reason why it has the effect of significantly improving corrosion resistance is as follows.

That is, the thin N1 intermediate layer is not only resistant to cracking even under severe processing conditions such as bending and drawing, but even if it breaks, the crack will not propagate to the upper metal plating layer due to the minute softening.

Methods such as electroplating and ion plating sputtering can be applied to generate the above-mentioned thin N1 layer, but any method relies on the generation and growth of two-dimensional nuclei, so fine pinholes will not occur. It is inevitable. Despite this, corrosion resistance is improved over conventional cedar-plated stainless steel at high temperatures.
1 The surface oxidation of the intermediate layer is thicker than that of the N1 intermediate layer, which is thinner.
This is thought to be because it is less likely to occur in the middle layer. The reason for this is thought to be that the thinner intermediate layer is more likely to diffuse into the stainless steel base and transform into an antioxidizing layer, but the reason for this is not clear.

The reason why the thickness of the intermediate layer is limited to 300 to 120 oX is because if it is less than 3001, the presence of the Ni intermediate layer has little effect on improving solderability or improving the metallic bonding strength between the plating layer and the stainless steel base. This is because if it exceeds 12OOx, the effect of reducing cracking and peeling of the metal plating layer will be reduced compared to conventional ones.

Next, the electroplating method, which is the most economical and reliable method for manufacturing the plated stainless steel of the present invention, will be described.

Free hydrochloric acid (hereinafter abbreviated as HOI) 50 using a clean base stainless steel that has undergone normal pretreatment such as degreasing as a cathode.
The stainless steel is cathodically reduced in a solution containing r/A or more using N1 or an N1-containing alloy as an anode at a cathode current density of 0.5 A/d- or more. According to this method, the reductive peeling of the passivation film on the stainless steel and the precipitation of the N1 intermediate layer are performed in the same process, so it is not only extremely efficient, but also reoxidizes the once activated stainless steel surface. Since there is no danger of this, it is extremely superior in terms of quality and performance. Cathode current density is less than O, 5A/dyf, Hl
ll is 50? If it is less than /L, cathodic reduction and N1 intermediate layer precipitation cannot be achieved satisfactorily, which is disadvantageous.

As an anode, a Ni--Fe alloy or stainless steel containing N1, which is cheaper than expensive N1, is used, but it is practical.

Although the treatment time depends on the bath composition, in most cases 10 seconds to 5 minutes, usually within 1 minute is often sufficient.

be given

The plated stainless steel of the present invention is manufactured by washing with water following this cathodic reduction-N1 precipitation treatment and then plating with a desired metal.

Metal plating includes Ag plating using a blue bath, Cu plating using a blue bath or sulfuric acid bath, and Pd plating using an ammine complex salt bath.

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Ag2μ plating 5U as a spring contact for a small key switch
S501 article (0,085 thickness x 705 bleaching width) was manufactured by continuous plating.

First, the base SUS 501 strip was cathodically degreased in a NaOH aqueous solution, and then this strip was used as a cathode in an HCI 110 f//L aqueous solution, and the other 5US 301 strip was used as an anode, and the cathode current density was 7.5 A/d. After various cathode reduction treatments with AgCN 5ri/1XKCN 501
Ag strike plating (5A/dyn'X2
sec)j, followed by AgCN 45 F//4 KC
2μAg plating in N 90f/L bath (IA/cln?
x1 minute) Shida. The above cathode reduction treatment liquid was prepared in advance at a temperature of about 2
A time-conditioned electrolyzed one was used.

For Honjima, tape peeling tests were conducted before and after heating in the air at 380° C. for 1 hour to test the adhesion and especially the heat resistance during high temperature processing steps such as soldering of terminal parts. JIS D
According to O202, a cut was made in the shape of the substrate with a cutter knife, and then a peel test was performed using a polyester adhesive tape. In addition, the actual switch contacts are press-molded and meet JIS standards.
Z-2571 was subjected to a salt spray test for a period of time, then washed and dried, and the contact portion was brought into contact with an Au plate under a load of 50 gr to measure the contact resistance. In addition, the contact part is O, 7rranφ,
It was machined into a semicircular shape with a height of 04.

Table 1 shows the results of tests for various cathode treatments.

After sword reduction processing, N1GIt 21t 0? /
t % HGll 00 f/ in a bath at 10 A/
drF? An example (Nα8) in which the above-mentioned Ag plating was applied after N1 strike plating treatment for x2 is also included.

In addition, in order to demonstrate the conditions of the present invention, an example (
Na7) is also listed.

Table 1 As is clear from Table 1, the stainless steels to be plated according to the present invention (N [L1 to 11) do not peel off the tape either before or after heating, are superior to conventional products, and have contact resistance that is lower than that of conventional products. It is much smaller and better than the product.

On the other hand, when the thickness of the Ni intermediate layer is outside the limits of the present invention (N (L5, 6.7)), tape peeling occurs.
Contact resistance is also large.

Example 2 Sushi plating S [JS3C11J strip (O15 thickness x 25 area 14]) was manufactured as a connector contact for an rC socket for heat resistance testing.

- First, the base material 5US301i is 10 times N1. After degreasing the cathode in an OH aqueous solution, Hc175 t/ was used as a cathode in an aqueous solution, another 5rs50 wire was used as an anode, and the cathode was treated with a cathode current density of 3.5 A/at♂ for 50 seconds, and then washed with water. PNP80 bath (PH8
, 9) was used to apply Pd-15Ni alloy plating to a thickness of 0.8μ on an α5A7d door. r by the usual method using the main island
a) Pressed into a misokerat connector.

As a conventional method for comparison, Pa-
A 15Ni alloy plated stainless steel was obtained, and a connector for a 1C socket was manufactured from the bar.

Both connectors were heated at 60°C x 95% R, H at 100°C.
After humidifying for 0 hours, insert Au Metsukibi/,
Contact resistance was measured in the same manner as in Example. 200 again
The contact resistance was measured in the same manner after processing for 1000 hours at ℃ atmospheric conditions. The results are shown in Table 2.

Table 2 As is clear from Table 2, the product of the present invention has significantly lower contact resistance than the conventional product, both after humidification and heating, and maintains excellent electrical contact over a long period of time in the harsh environment required as an electronic component material. I know what I can do.

As described above, the present invention provides a stainless steel to be plated that is most suitable for precision processing parts such as electronic parts that require high performance and high reliability, and an economical manufacturing method thereof, which has a remarkable effect on the electronic industry. It is something that plays.

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Claims (1)

[Claims] (1) In metal-plated stainless steel, there is a thickness of 5 mm between the metal plating layer and the base stainless steel.
Plated stainless steel characterized by having a nickel intermediate layer 1 of 00 to 1200X (2) The base stainless steel is used as a cathode, nickel or a nickel alloy is used as an anode, and a solution containing free hydrochloric acid of 501/ or more is used as an electrolyte. As 05A/dtf? A method for producing stainless steel to be plated, which comprises depositing a nickel intermediate layer with a thickness of 500 to 120 OX on the surface of the base stainless steel by performing electrolysis at the above cathode current density, and then applying metal plating to the base stainless steel.