JPH10265973A - Production of copper alloy material for electronic parts having good silver plating property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a copper alloy material capable of being directly and excellently plated with silver without applying a substrate plating by pickling the copper alloy material contg. Fe with an aq. acidic soln. contg. sulfuric acid, an oxidizing agent and ethylene glycol in specified concn. at least after final annealing. SOLUTION: The oxide of Fe is completely dissolved in an aq. acidic soln. contg. sulfuric acid, an oxidizing agent and 1 to 100 g/l ethylene glycol, and its redeposition is effectively prevented by the soln. Hydrogen peroxide and a persulfate are preferably used as the oxidizing agent. When sulfuric acid is combined with hydrogen peroxide, the sulfuric acid concn. is controlled to 100 to 500 g/l and the hydrogen peroxide concn. to 5 to 100 g/l from the standpoint of etching power and economy. While both concns. are controlled in such a range, the molar ratio (sulfuric acid/hydrogen peroxide) is adjusted to >=0.35. Meanwhile, pickling is preferably carried out in the aq. acidic soln. at 20 to 70 deg.C for 1 to 300 sec to sufficiently improve the silver plating property.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a copper alloy material for electronic parts having good silver plating properties, and more particularly, to a Fe-containing copper alloy used for electronic parts such as lead frames, terminals and connectors. The present invention relates to a surface treatment method for obtaining good silver plating properties for a material.

[0002]

2. Description of the Related Art In the process of assembling ICs and LSIs, die bonding for mounting a semiconductor on a silver-plated lead frame is performed. In this die bonding, the semiconductor chip is joined by melting the solder placed on the heated silver plating island portion. In order to completely join the semiconductor chip to the lead frame, the molten solder must spread sufficiently. That is, silver plating having good solder wettability is required. For that purpose, it is preferable that the silver crystal grains of silver plating are large and coarse. This is because the molten solder tends to spread due to the capillary phenomenon when the crystal grains are coarse. In order to obtain such coarse silver plating with large crystal grains, plating manufacturers strictly control plating conditions.

On the other hand, materials for semiconductor lead frames include:
Copper alloys to which elements such as Fe, P, Ni, Si, and Sn are added are used. Among them, copper alloys on which Fe or Fe ₂ P is precipitated have excellent conductivity and strength, and are widely used for electronic parts. This Fe-containing copper alloy material is manufactured by repeating cold rolling and intermediate annealing after passing through steps such as melting casting and hot rolling.

[0004]

By the way, the above-mentioned silver plating is usually performed by applying a copper base plating before the silver plating, but recently, for the purpose of cost reduction, the copper base plating before the silver plating is omitted. That is being considered. However, silver plating is susceptible to the influence of the underlayer, and in particular, the precipitation form of silver plating may change due to the influence of trace elements, precipitates, crystallization, oxides, and the like present on the copper alloy surface.

[0005] Even in the case of the above-mentioned Fe-containing copper alloy material, if silver plating is directly applied to the material without occupying the underlying copper plating, there is a problem that the silver particles to be deposited become finer and the subsequent solder wettability decreases. There is. In this case, luster appears on the surface after silver plating, which should be dull. The cause of the decrease in solder wettability of the silver-containing Fe-containing copper alloy material was investigated.
When the oxide of Fe remained, it was found that the silver particles precipitated became finer, the surface after silver plating appeared glossy, and the solder was hardly spread.

As described above, the copper alloy material for electronic parts is subjected to pickling after annealing in the manufacturing process. Conventionally, sulfuric acid has been used for pickling after annealing. However, the Fe-containing copper alloy material pickled with sulfuric acid had poor silver plating properties. That is, the silver plating crystal grains are refined under the influence of the Fe oxide on the material surface. This is because, with sulfuric acid, even if a copper oxide layer on the surface generated by annealing can be removed, an internal oxide layer (a layer containing a large amount of Fe oxide) existing thereunder cannot be removed.

[0007] Annealing in an inert gas atmosphere containing no oxygen or a reducing gas atmosphere such as hydrogen so as not to form an internal oxide layer can be considered, but the former is difficult in actual operation, and the latter is hydrogen gas. Using this leads to increased costs. For this reason, it is difficult to prevent the internal oxide layer from being formed by annealing. Therefore, it is necessary to remove this internal oxide layer.

As a method of removing the internal oxide layer, a method of mechanically polishing and a method of chemically etching are considered. Mechanical polishing is a method of polishing a material with a brush. However, in order to remove a thick internal oxide layer, a large amount of polishing must be taken. In this case, the outermost surface of the copper alloy receives a large stress due to the polishing process and is deformed, thereby forming a damaged layer. This affected layer is more chemically active than the base material. For this reason, when silver plating is performed on the work-damaged layer and heat treatment is performed in an assembly process or the like, the work-damaged layer is oxidized by oxygen diffused in the silver plated layer, and the adhesion of the silver plating is reduced. When oxidation is remarkable, silver plating may be blistered. Further, the polishing allowance tends to change due to deterioration of the polishing brush and the like, and it is very difficult to control the polishing allowance. Moreover,
In actual operations, it is impossible to measure the polishing allowance.
For this reason, it is inappropriate to remove the internal oxide layer with a polishing brush.

On the other hand, in the case of etching, the amount of etching can be controlled by the composition, temperature, and etching time of the etching solution, and the amount of etching can be known by measuring the concentration of Cu ions in the etching solution. For this reason, removal of the internal oxide layer must be performed by a chemical method.

[0010] As a copper alloy etching solution, there has been conventionally known a rinsing solution obtained by adding nitric acid (HNO ₃ ) as an oxidizing agent to sulfuric acid. Sulfuric acid has the ability to dissolve copper oxides,
HNO ₃ has the ability to oxidize metallic copper. That is, the rinsing solution can be dissolved (etched) while oxidizing the copper surface. However, the rinsing liquid generates harmful gases such as nitrous acid gas. Therefore, it cannot be used as a pickling solution for a copper alloy material for electronic components.

On the other hand, in recent years, in order to solve the above-mentioned problems, a peroxide such as hydrogen peroxide (H ₂ O ₂ ) or a persulfate or chromium trioxide (CrO ₃ ) is used as an oxidizing agent in an acid. Added etchants have been developed. However, even if the internal oxide layer was removed with these etchants, the silver plating property of the Fe-containing copper alloy material could not be completely improved for the reasons described below.

In view of the above-mentioned problems, the present invention provides a method for producing a copper alloy material for electronic parts, which can be directly plated with a good silver without plating an Fe-containing copper alloy having excellent conductivity and strength. It is intended to do so.

[0013]

In order to achieve the above object, a method for producing a copper alloy material for electronic components having good silver plating properties according to the present invention comprises the steps of: , At least after final annealing, sulfuric acid, oxidizing agent and 1-10
Pickling is performed with an acidic aqueous solution containing 0 g / l of ethylene glycol.

In the above-mentioned method for producing a copper alloy material for electronic parts having good silver plating properties, it is desirable to set the liquid temperature of the acidic aqueous solution to 20 to 70 ° C. and perform acid pickling for 1 to 300 seconds. It is desirable to use hydrogen peroxide as the oxidizing agent. Further, it is desirable to adjust the molar ratio of sulfuric acid to hydrogen peroxide (sulfuric acid / hydrogen peroxide) to 0.35 or more.

Hereinafter, the configuration and operation of the present invention will be described in detail. The present inventors have repeated research on a method for producing a Fe-containing copper alloy material having good silver plating properties. As a result, in the pickling after annealing, the oxidant and 1 to 10
If it is an acidic aqueous solution containing 0 g / l of ethylene glycol, the internal oxide layer can be chemically removed, and it has been found that an Fe-containing copper alloy material having good silver plating properties can be obtained.
The present invention has been completed.

As described as a comparative example of the embodiment described later, the silver plating property can be improved even if the internal oxide layer of the Fe-containing copper alloy material is removed with an acidic aqueous solution (etching solution) containing only sulfuric acid and an oxidizing agent. Did not. On the other hand, when the internal oxide layer of the Fe-containing copper alloy material is removed with an acidic aqueous solution containing the sulfuric acid and the oxidizing agent according to the present invention and 1 to 100 g / l of ethylene glycol, the Fe-containing copper having good silver plating property is obtained. An alloy material is obtained. This is because, unless an acidic aqueous solution containing a certain amount of ethylene glycol, the oxide of Fe cannot be completely dissolved even if the internal oxide layer is etched, or the Fe oxide once dissolved re-adheres to the outermost surface. Think to do. That is, it is presumed that the acidic aqueous solution containing ethylene glycol has an effect of completely dissolving the Fe oxide and preventing its re-adhesion.

In order to obtain the above effects, the amount of ethylene glycol must be added in the range of 1 to 100 g / l. When the amount of ethylene glycol is less than 1 g / l, the effect of preventing the redeposition of the Fe oxide is insufficient, and when the amount of ethylene glycol exceeds 100 g / l, the effect of preventing the redeposition is provided. However, the effect is not improved and it is economically useless.

The oxidizing agent is preferably hydrogen peroxide (H ₂ O ₂ ) or persulfate. The same effect can be obtained with any acid such as phosphoric acid, hydrochloric acid, hydrofluoric acid and nitric acid, but sulfuric acid is preferred in view of wastewater regulations and generation of harmful gases. If the combination of sulfuric acid and H ₂ O _2, the sulfuric acid concentration in terms of etching power and economy is _{100 ~500g / l, H 2 O} 2 concentration of 5 to 100 g / l is desired. If the H ₂ O ₂ concentration exceeds 100 g / l, an oxide will remain on the copper alloy surface after pickling, and if it is less than 5 g / l, the etching power will decrease. On the other hand, if the sulfuric acid concentration is less than 100 g / l, the etching power is reduced, and if it exceeds 500 g / l, the effect of improving the silver plating property is saturated, which is economically useless. It is desirable that the sulfuric acid and hydrogen peroxide (H ₂ O ₂ ) be within the above range and the molar ratio (sulfuric acid / H ₂ O ₂ ) be 0.35 or more. If the molar ratio is less than 0.35, the amount of H ₂ O ₂ is increased, so that oxidation is a concern, and there is a concern that the effect of removing Fe oxide (etching power) cannot be sufficiently expected.

Although the thickness of the internal oxide layer varies depending on the oxygen concentration on the surface, the Fe content in the alloy, and the heat treatment conditions (temperature and time), the internal oxide layer must be completely removed for silver plating. That is, the oxidizing agent according to the present invention and 1 to 10
After chemical removal with an acidic aqueous solution containing 0 g / l of ethylene glycol, analysis of the surface of the copper alloy by X-ray photoelectron spectroscopy (ESCA) should not result in the detection of Fe oxides.

In order to sufficiently improve the silver plating property, it is desirable that the pickling (etching) be performed with the acidic aqueous solution according to the present invention at a solution temperature of 20 to 70 ° C. for 1 to 300 seconds. Liquid temperature is 20 ℃
If it is less than 1, the etching time becomes very long. 70 ℃
When H exceeds _2, the decomposition of H ₂ O ₂ is severe, the etching reaction is also intense, and it is difficult to control the etching amount. The pickling (etching) processing time has optimum conditions depending on the liquid temperature and the thickness of the internal oxide layer, but the processing time is preferably 1 to 300 seconds. If the processing time is less than 1 second, the liquid temperature must be increased, and it is difficult to control the etching amount. When the treatment time exceeds 300 seconds, the silver plating property is improved, but the productivity is deteriorated.

The acid with the above-mentioned acidic aqueous solution according to the present invention
Washing (etching) is Fe or Fe _TwoAfter precipitation annealing of P
It may be performed before silver plating. For example, precipitation annealing
Immediately after or after the final cold rolling,
It may be performed as a pretreatment (pickling). Also machinery
Brush polishing is chemically performed by the acidic aqueous solution according to the present invention.
Before or after etching to assist in proper etching
You can go to

The Fe-containing copper alloy for electronic parts which is the object of the present invention is C19200 (Cu-0.1Fe-0.03P), C19700
(Cu-0.6Fe-0.2P-0.1Zn), C194 (Cu-2.3Fe-0.03P-0.15Z)
n), C195 (Cu-1.5Fe-0.8Co-0.4Zn-0.4Sn)
And the like. Copper alloys containing 0.01% or more of these include Fe oxides formed by internal oxidation during annealing.

[0023]

Embodiments of the present invention will be described below. Melt casting, hot rolling and cold rolling and intermediate annealing are repeated in the usual manner, and after the final precipitation annealing, pickling is performed using an acidic aqueous solution containing sulfuric acid, an oxidizing agent and 1 to 100 g / l ethylene glycol. This was processed to produce a copper alloy material for electronic components containing Fe. In this production process, the pickling after the intermediate annealing may be performed using any of a commonly used pickling solution or an acidic aqueous solution after the final precipitation annealing.

[0024]

【Example】

Example 1 A Fe-containing copper alloy having a chemical composition shown in Table 1 was subjected to hot rolling, cold rolling and intermediate annealing to a thickness of 0.15.
A copper alloy plate having each component composition of mm was obtained. Each of these copper alloy sheets was subjected to precipitation annealing in a nitrogen gas (50 ppm oxygen) atmosphere at a temperature of 500 ° C. for 2 hours. Thereafter, using the obtained copper alloy plates of the respective component compositions as test materials, the oxide layer generated by annealing was subjected to an etching treatment with a pickling solution shown in Table 2. During this pickling, the liquid temperature was set to 50 ° C, and the etching amount was changed by changing the processing time.
It was 0.5 μm.

[0025]

[Table 1]

[0026]

[Table 2]

The test material of each component composition after pickling obtained above was applied to a silver plating bath containing 50 g / l of AgCN and 115 g / l of KCN at a current density of 1.0 A / dm ² for 500 times. In order to evaluate the silver plating crystal state, the gloss was measured for the purpose of evaluating the crystal state of the silver plating (the larger the coarse crystals were, the lower the gloss was. Means that there was nothing). The glossiness was measured using a densitometer GAM MODEL RD-144 manufactured by Graphic Art. Table 3 shows the measurement results of the glossiness.

The test material after the silver plating was heated to 370 ° C. by a hot plate in an N 2 atmosphere, and a solder ball was placed on the silver plating. Spread area of molten solder (mm ²
)), The solder wettability of silver plating was evaluated. The solder balls used had a composition of Pb-3Sn-1.5Ag and a diameter of 1.4 mmφ. Table 3 shows the measurement results of the solder wettability (spread area) and the overall evaluation in consideration of the glossiness.
○, Δ, and × in the overall evaluation are based on the following criteria. ○: Solder spread area of 80 mm ² or more, Δ: Solder spread area of 50 to 80 mm ² , ×: Solder spread area of less than 50 mm ² .

[0029]

[Table 3]

As is clear from Table 3, in the present invention,
Glossiness of silver plating a combination of any of the copper alloy and pickling solution is as low as 0.1 or less, pickling by being Fe oxides test piece surface removal, also large and is 100 mm ² before and after solder spreading area Solder Excellent wettability. On the contrary,
In the comparative example using the pickling solution having a low ethylene glycol content of less than 1 g / l, the gloss of each of the alloys A, B, C, D and E was increased, or the spread area was relatively small. Solder wettability also decreased. In addition, only sulfuric acid or sulfuric acid
In the conventional example of the pickling solution to which only H ₂ O ₂ is added, each alloy A,
In all of B, C, D and E, an increase in gloss was observed, or the spread area was small and solder wettability was poor.

Example 2 Using the test material after precipitation annealing obtained in Example 1 above, the oxide layer formed by annealing was subjected to etching treatment with a pickling solution shown in Table 4. During this pickling, the solution temperature was set to 30 ° C, and the etching time was changed by changing the processing time.
It was 0.5 μm. In the same manner as in Example 1, the test material of each component composition after pickling was subjected to a current density of 1.0 A / dm ² using a silver plating bath containing 50 g / l of AgCN and 115 g / l of KCN. The silver plating was performed under the conditions of seconds, the glossiness was measured for the purpose of evaluating the silver plating crystal state, and the solder wettability of the silver plating was evaluated based on the spread area (mm ² ) of the molten solder.
These gloss measurement results and solder wettability (spread area)
Table 5 also shows the measurement results and the overall evaluation in consideration of the glossiness.

[0032]

[Table 4]

[0033]

[Table 5]

As is clear from Table 5, in the present invention,
Glossiness of silver plating a combination of any of the copper alloy and pickling solution is as low as 0.1 or less, pickling by being Fe oxides test piece surface removal, also large and is 100 mm ² before and after solder spreading area Solder Excellent wettability. On the contrary,
In the comparative example using the pickling solution having a low ethylene glycol content of less than 1 g / l, the gloss of each of the alloys A, B, C, D and E was increased, or the spread area was relatively small. Solder wettability also decreased. Furthermore, in the conventional examples of the pickling solution containing only sulfuric acid or only a persulfate added to sulfuric acid, each of the alloys A, B, C, D, and E shows an increase in glossiness or a small spread area. Solder wettability was also poor.

Example 3 Using the test materials of the copper alloy A shown in Table 1 after the precipitation annealing obtained in Example 1 above, the oxide layer formed by annealing was pickled as shown in Table 2. No.4
And etching was performed under the etching conditions (temperature × time) shown in Table 6. The test material after the pickling was subjected to silver plating at a current density of 1.0 A / dm ² for 500 seconds in a silver plating bath containing AgCN: 50 g / l and KCN: 115 g / l in the same manner as in Example 1. The plating was applied, the glossiness was measured for the purpose of evaluating the crystal state of the silver plating, and the solder wettability of the silver plating was evaluated based on the spread area (mm ² ) of the molten solder. Table 6 shows the measurement results of the glossiness, the measurement results of the solder wettability (spread area), and the overall evaluation in consideration of the glossiness.

[0036]

[Table 6]

As is clear from Table 6, in the present invention,
The glossiness of silver plating is low under any of the etching conditions,
Good solder wettability was exhibited. On the other hand, in the case of the liquid temperature of 10 ° C. shown as a comparative example, good solder wettability cannot be obtained unless the etching time is long because the liquid temperature is low,
Very low productivity. In the case of a liquid temperature of 80 ° C., the liquid temperature is high and good solder wettability can be obtained, but H ₂ O ₂ is strongly decomposed and is not practical in terms of maintaining the performance of the pickling liquid. On the other hand,
Even at 50 ° C and 70 ° C, if the pickling time is as short as 0.5 seconds, the glossiness is increased, or the spread area is relatively small, the solder wettability is low, and there is no effect of improving silver plating. Was. This is because the internal oxide layer could not be completely removed.

[0038]

As described above, according to the method for producing a copper alloy material for electronic parts having good silver plating property according to the present invention, a Fe-containing copper alloy material having excellent conductivity and strength can be plated by undercoating. It can be used as a copper alloy material for electronic components by performing silver plating directly without performing the above.

Claims (5)

[Claims] 1. Good silver, characterized in that a copper alloy material for electronic parts containing Fe is pickled with an acidic aqueous solution containing sulfuric acid, an oxidizing agent and 1 to 100 g / l of ethylene glycol at least after final annealing. A method for producing a copper alloy material for electronic components having plating properties. 2. The method for producing a copper alloy material for electronic parts having good silver plating properties according to claim 1, wherein the acidic aqueous solution is pickled at a liquid temperature of 20 to 70 ° C. for 1 to 300 seconds. A method for producing a copper alloy material having plating properties. 3. The method for producing a copper alloy material having good silver plating properties according to claim 1, wherein the Fe-containing copper alloy material for electronic components is a lead frame. 4. The method according to claim 1, wherein the oxidizing agent is hydrogen peroxide.
4. The method for producing a copper alloy material having good silver plating properties according to item 3. 5. Sulfuric acid 100-500 g / l, hydrogen peroxide 5-100 g
The method for producing a copper alloy material having good silver plating properties according to claim 4, wherein the molar ratio of sulfuric acid to hydrogen peroxide (sulfuric acid / hydrogen peroxide) is 0.35 or more at / l.