JP2005187920A - Electrolytic peeling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolytic stripping method in which a cyanide compound is an additive-free electrolytic stripper, and the life can be significantly extended as compared with an electrolytic stripper containing a cyanide compound.
A copper plating film exposed from a silver plating film partially covering a copper plating film formed on the entire surface of a lead frame, and a leaked silver thinner than the silver plating film formed on an exposed portion of the copper plating film As an electrolytic stripping solution, a copper compound is a copper electrolytic stripping solution with no addition of a cyanide compound and dissociated from a complex ion composed of silver and cyan. Electrolytic stripping solution to which a compound that forms complex ions with silver is added, and silver and copper are deposited on a cathode made of platinum used as a counter electrode with respect to the anode. ] None

Description

  The present invention relates to an electrolytic stripping method, and more specifically, a copper plating film exposed from a silver plating film partially covering the copper plating film formed on the entire surface of the member, and the silver plating formed on an exposed portion of the copper plating film The present invention relates to an electrolytic stripping method of stripping leaked silver thinner than a film by electrolytic stripping using the copper plating film and leaked silver as an anode.

In the lead frame used in the semiconductor device, as shown in FIG. 1, the inner leads 12, 12,... Constituting the lead frame 10 made of an iron-based alloy material such as an iron-nickel alloy (42 alloy) are arranged on the die pad 14 side. A bonding portion 12a is formed at the tip portion (hereinafter, simply referred to as the tip portion) to which the other end portion of the gold wire having one end portion connected to the semiconductor element mounted on the die pad 14 is connected.
The bonding part 12a is formed with a silver plating film and is connected to the other end of the gold wire.

As shown in FIG. 1, when forming the bonding part 12a in which the silver plating film was formed in the front-end | tip part of each inner lead 12 of the lead frame 10 which consists of an iron-type alloy, electrolytic copper is formed in the whole surface of the lead frame 10. A copper plating film is formed by plating.
As shown in FIG. 2A, the lead frame 10 on which the copper plating film is formed is exposed so that only the portion of the copper plating film 16 that forms the bonding portion 12a is exposed at the tip 20 of the inner lead 12. Electrolytic silver plating that forms a silver plating film on the exposed copper plating film 16 is applied between the rubber mask plates 18a and 18b.
Next, after the electrolytic silver plating is completed, the mask plates 18a and 18b are removed. As shown in FIG. 2B, the silver plating film is formed only on the portion where the bonding portion 12a of the tip portion 20 of the inner lead 12 is formed. 22 is formed.
Thereafter, the lead frame 10 is dipped in an electrolytic stripping solution, and the copper plating film 16 exposed without being covered with the silver plating film 22 is removed by electrolytic stripping using the lead frame 10 as an anode, whereby FIG. As shown in FIG. 5, the bonding portion 12 a made up of the copper plating film 16 and the silver plating film 22 is formed only on the portion where the bonding portion 12 a of the tip portion 20 of the inner lead 12 is formed.

By the way, when the lead frame 10 is sandwiched between the mask plates 18a and 18b and a silver plating film is formed on the exposed copper plating film 16, due to distortion of the mask plates 18a and 18b and the like, FIG. As shown, leaked silver 24 thinner than the silver plating film 22 is formed in the portions covered with the mask plates 18a and 18b by leakage of the electrolytic silver plating solution. The leaked silver 24 is also removed by electrolytic peeling of the copper plating film 16, and as shown in FIG. 2C, the silver plating film 22 is formed only on the portion forming the bonding portion 12 a of the tip portion 20 of the inner lead 12. It is formed.
Thus, when the leakage silver 24 and the copper plating film 16 are electrolytically peeled without substantially peeling the silver plating film 22, as described in Patent Document 1 below, a cyanide compound is contained. An electrolytic stripper is used.
JP 59-31900 A (pages 2 to 3)

As described in Patent Document 1, the lead frame 10 on which the silver plating film 22 is formed is immersed only in the tip portion 20 of the inner lead 12 in an electrolytic stripping solution containing a cyanide compound. By performing electrolytic peeling of copper using the frame 10 as an anode and a stainless steel plate as a cathode, the leakage silver 24 and the copper plating film 16 can be electrolytically peeled without substantially peeling the silver plating film 22.
However, if the electrolytic stripping solution containing a cyanide compound is continuously used, the copper plating film 16 and the leaking silver 24 can be removed during the electrolytic stripping of the leaking silver 24 and the copper plating film 16 in a relatively short time. The peeling speed of the is reduced. For this reason, this electrolytic stripper requires frequent replacement.
Further, if silver, which is a noble metal, is to be recovered from the electrolytic stripping solution containing a cyanide compound that is exchanged and discarded, a special recovery step is required separately.
Accordingly, an object of the present invention is to provide an electrolytic stripping method that is an electrolytic stripper solution to which a cyanide compound is not added and that can significantly extend its life compared to an electrolytic stripper solution containing a cyanide compound. There is.

As a result of studies to achieve the above-mentioned problems, the present inventors have found that an electrolytic stripping solution to which a cyanide compound is not added, forms a copper ammonium complex as an oxidizing agent for copper, and forms a complex of silver and cyan. The tip of the inner lead 12 shown in FIG. 2 (b) is formed using an electrolytic stripping solution containing triammonium phosphate, copper hydroxide and aqueous ammonia, which forms a complex ion of silver and ammonium that is more easily dissociated than ions. Electrolytic peeling was performed with the lead frame 10 having the silver plating film 22 formed only on the portion 20 as an anode. At this time, when a cathode made of platinum was used for the counter electrode of the lead frame 10 as an anode, the leakage silver 24 and the copper plating film 16 were electrolytically peeled without substantially peeling the silver plating film 22, and the cathode was used. It was found that silver and copper were precipitated.
Furthermore, by performing electrolytic stripping while precipitating silver and copper on the cathode as described above, it has also been found that the lifetime of the electrolytic stripping solution is longer than that of an electrolytic stripping solution containing a cyanide compound. Reached.

  That is, the present invention provides a copper plating film exposed from a silver plating film partially covering the copper plating film formed on the entire surface of the member, and a leaked silver thinner than the silver plating film formed on the exposed part of the copper plating film Is removed by electrolytic stripping using the copper plating film as an anode, and as the electrolytic stripping solution, a copper compound is an electrolytic stripping solution to which no cyanide compound is added, and a complex ion composed of silver and cyan is used. It is composed of a metal that is chemically stable with respect to the electrolytic stripper used as a counter electrode with respect to the anode, using an electrolytic stripper to which a compound that forms complex ions with silver that is easily dissociated is added. In the electrolytic stripping method, silver and copper are deposited on the cathode.

In the present invention, as a compound that forms a complex ion with silver that is more easily dissociated than a complex ion composed of silver and cyan, a complex with silver having a lower complex stability constant than a complex ion composed of silver and cyan. It is preferable to use a compound that forms ions.
As this compound, 1 type, or 2 or more types of compounds chosen from the group which consists of aqueous ammonia, ammonium salt, tartrate, phosphoric acid, and citrate can be used.
Moreover, since the electrolytic stripping solution used in the present invention is a copper electrolytic stripping solution for electrolytically stripping a copper plating film, it contains a copper compound or an aromatic nitro compound as a copper oxidizing agent and has a pH of 9. It is preferably adjusted to ˜12.
Here, as the electrolytic stripping solution containing a copper compound as a copper oxidizing agent, an electrolytic stripping solution to which an ammonium source capable of forming a copper ammonium complex and a copper source are added is preferably used.
Furthermore, silver and copper particles composed of silver and copper deposited at the cathode can be collected by the cathode back by wrapping the cathode with the cathode back, and silver deposited at the cathode by taking out the cathode back from the electrolytic stripping solution. Silver and copper particles composed of copper and copper can be recovered.
As a member, a lead frame made of an iron-based alloy can be suitably used.

The reason for the short life of the electrolytic stripping solution to which a cyan compound conventionally used is added is considered as follows.
The cyan ion in the electrolytic stripping solution forms a stable complex ion with the silver ion in the electrolytic stripping solution, so the silver concentration in the electrolytic stripping solution gradually increases as the amount of electrolytic stripping of leaked silver increases. . When the silver concentration in the electrolytic stripping solution increases, the stripping rate of the leaked silver and the copper plating film is decreased.
On the other hand, in the present invention, as an electrolytic stripping solution, a copper-based electrolytic stripping solution containing no cyanide compound is formed, and complex ions with silver that are more easily dissociated than complex ions composed of silver and cyan are formed. Using the electrolytic stripping solution to which the compound is added, electrolytic stripping is performed while depositing silver and copper on the copper plating film as the anode and the cathode used as the counter electrode against the leaked silver.
As a result, according to the electrolytic stripping method of the present invention, it is possible to prevent a decrease in the stripping rate of the copper plating film and leaked silver due to the accumulation of silver in the electrolytic stripping solution, and the conventional electrolysis in which a cyanide compound is added. Compared with stripping solution, its life can be greatly extended.

The electrolytic stripping solution used in the present invention is a copper electrolytic stripping solution to which no cyanide compound is added. As this electrolytic stripping solution, an electrolytic stripping solution containing a copper compound or an aromatic nitro compound as an oxidizing agent for copper can be suitably used.
The copper compound as the copper oxidizing agent is preferably a copper ammonium complex. Such a copper ammonium complex can be formed by adding ammonia water or an ammonium salt as an ammonium source and copper sulfate, copper carbonate, copper oxalate or copper hydroxide as a copper source to the electrolytic stripping solution.
Copper ammonium complexes formed in the electrolytic stripping solution to which such an ammonium source and a copper source are added are [Cu (NH ₃ ) ₂ ] ²⁺ , [Cu (NH ₃ ) ₄ ] ²⁺ and [Cu ( It consists of one or more of NH ₃ ) ₆ ] ²⁺ .
As the aromatic nitro compound, chloronitrobenzoic acid, 2-chloro-4-nitrobenzoic acid, orthonitrobenzoic acid, metanitrobenzoic acid, paranitrobenzoic acid, ethyl paranitrobenzoate, sodium paranitrobenzoate are preferably used. it can.
Although the electrolytic stripping solution containing an aromatic nitro compound as an oxidizing agent for copper and added with a cyanide compound cannot extend the life of the electrolytic stripping solution.

Furthermore, in such an electrolytic stripping solution, the pH is preferably adjusted to 9-12. Such pH adjustment may be carried out with ammonia water as an ammonium source added as a compound that forms a copper ammonium complex, or a pH regulator such as sodium hydroxide may be used.
Here, when the pH of the electrolytic stripping solution is less than 9, or when the pH of the electrolytic stripping solution exceeds 12, the stripping rate of the copper plating film tends to decrease.

A compound that forms a complex ion with silver that is more easily dissociated than a complex ion composed of silver and cyan is added to the copper electrolytic stripper used in the present invention. This compound is a compound that forms a complex ion with silver having a lower complex stability constant than a complex ion composed of silver and cyan. Specifically, one or two or more compounds selected from the group consisting of aqueous ammonia, ammonium salt, tartrate, phosphoric acid and citrate are used.
Ammonia water and ammonium salts, which are compounds that form a complex ion with silver, may be used as an ammonium source that forms a copper ammonium complex.

かかる平衡反応において、銀とシアンとの錯イオンの解離し難さを指標する安定度定数（Ｋ_CN）は下記数１で表すことができ、その値はＫ_CN＝１×１０²¹である。

一方、銀とアンモニウムとの錯イオンの解離し難さを指標する安定度定数（Ｋ_NH3）は下記数２で表すことができ、その値はＫ_NH3＝１．５×１０⁷である。

この様に、Ｋ_CN＞Ｋ_NH3であるため、銀とアンモニウムとの錯イオンは、銀とシアンとの錯イオンに比較して銀イオンとアンモニアとに解離し易い。
従って、電解剥離液中の銀イオンを除去することによって、銀とアンモニウムとの錯イオンは銀イオンとアンモニアとに更に解離し易くなる。 Here, the complex stability constant is a constant representing the degree of dissociation of complex ions, and the lower the constant, the more complex ions formed are more unstable and easier to dissociate.
For example, complex ions of silver and cyan are equilibrium reactions between silver ions and cyan ions as shown in the following chemical formula 1, and complex ions of silver and ammonium are also expressed as chemical formula 2 below. It is an equilibrium reaction between silver ions and ammonia.

In this equilibrium reaction, the stability constant (K _CN ) indicating the difficulty of dissociation of complex ions of silver and cyan can be expressed by the following formula 1, and the value is K _CN = 1 × 10 ²¹ .

On the other hand, the stability constant (K _NH3 ) indicating the difficulty of dissociation of complex ions of silver and ammonium can be expressed by the following formula 2, and the value is K _NH3 = 1.5 × 10 ⁷ .

Thus, since K _CN > K _{NH 3} , the complex ion of silver and ammonium is more easily dissociated into silver ion and ammonia than the complex ion of silver and cyan.
Therefore, by removing silver ions in the electrolytic stripping solution, the complex ions of silver and ammonium are further easily dissociated into silver ions and ammonia.

  The silver ions in the electrolytic stripping solution are easily removed by depositing silver on the cathode, which is the counter electrode of the lead frame 10 serving as the anode, when electrolytic stripping of the copper plating film 16 and the leaked silver 24 shown in FIG. it can. It is preferable to use an electrode made of a metal that is chemically stable with respect to the electrolytic stripper, such as platinum or stainless steel, as the cathode.

The electrolytic stripping using such an electrolytic stripper can be performed with the apparatus shown in FIG. In the apparatus shown in FIG. 3, the lead frame 10 made of iron-nickel alloy (42 alloy) shown in FIG. 1 is immersed in the electrolytic stripping solution 30 stored in the electrolytic stripping tank 32 provided with the stirrer 34. ing. The lead frame 10 has a copper plating film 16 formed on the entire surface thereof by electrolytic copper plating, and a bonding portion 12a connected to each tip portion of the inner leads 12, 12,. A silver plating film 22 is formed on the bonding portion 12a, and leaked silver 24 is also present.
The lead frame 10 is connected to the anode of the DC power source 36, and a cathode 38 made of platinum connected to the cathode of the DC power source 36 is immersed in the electrolytic stripping solution 30 as a counter electrode of the lead frame 10 as the anode. The cathode 38 is encased in a cathode back 40. The cathode back 40 collects silver and copper particles composed of silver and copper deposited on the cathode 38, and is a fiber having durability against the electrolytic stripping solution 30, such as PTFE (Poly Tetra Fluoro Ethylene). It is formed in a bag shape with fibers made of PP (Poly Propylene).

The electrolytic stripping solution 30 stored in the electrolytic stripping tank 32 is circulated by a circulation pump 42, and a filter 46 for separating particles floating in the electrolytic stripping solution 30 is provided in the middle of the circulation pipe 44. It has been.
By exposing a direct current from a direct current power source 36 between a lead frame 10 as an anode immersed in an electrolytic stripping solution 30 stored in an electrolytic stripping tank 32 shown in FIG. The copper plating film 16 and the leaked silver 24 are peeled off. Silver ions in the electrolytic stripping solution 30 generated by stripping the leaked silver 24 or the like do not form stable complex ions such as complex ions of silver and cyan. For this reason, the silver ions and copper ions in the electrolytic stripping solution 30 are collected in the cathode back 40 as silver and copper particles composed of silver and copper deposited on the cathode 38 and passed through the cathode back 40. Silver particles and the like are collected by a filter 46 provided in the circulation pipe 44.
Thus, the silver concentration in the electrolytic stripping solution can be reduced by separating the silver ions in the electrolytic stripping solution 30 as silver particles made of silver or the like. Therefore, unlike conventional electrolytic stripping using an electrolytic stripping solution to which a cyanide compound is added, stable complex ions composed of cyanide and silver are not formed in the electrolytic stripping solution. A decrease in the peeling rate of the copper plating film and leaked silver due to the accumulation of silver in the stripping solution can be prevented, and the life can be greatly extended compared to a conventional electrolytic stripping solution to which a cyanide compound is added.

  In FIG. 3, the metal lead frame 10 is used as an anode. However, when a resin substrate is used, a copper plating film or the like formed by electroless plating on the entire surface of the resin substrate is used as an anode. The electrolytic stripping can be performed.

表２示す電解剥離液を用いた電解剥離では、いずれも陰極３８、カソードバック４０及びフィルター４６に、粒子等となった銀が捕集されており、電解剥離液３０中の銀濃度は低いものであった。 A copper plating film was formed on the entire surface of the lead frame made of iron-nickel alloy (42 alloy) by electrolytic copper plating, and then a silver plating film was formed on the copper plating film by electrolytic silver plating.
Next, using the apparatus shown in FIG. 3, the copper plating film and the silver plating film formed on the lead frame 10 as the anode using the electrolytic stripping solution shown in Table 1 below are connected to the anode 38 made of platinum in the following table. When the electrolytic stripping was continuously performed under the conditions shown in No. 2 and the silver treatment amount reached 1000 ppm, the silver concentration in the electrolytic stripping solution 30 stored in the electrolytic stripping tank 32 was measured, and the results are shown in Table 2. Also shown.

In the electrolytic stripping using the electrolytic stripping solution shown in Table 2, all the silver particles are collected in the cathode 38, the cathode back 40, and the filter 46, and the silver concentration in the electrolytic stripping solution 30 is low. Met.

When electrolytic stripping was performed using the electrolytic stripping solution 1, the silver concentration in the particles and the like attached to the cathode 38 and collected on the cathode back 40 and the filter 46 was also measured. The results are shown in Table 3. . This silver concentration is measured by dissolving particles or the like attached to the cathode 38 and collected by the cathode back 40 and the filter 46 in 50% nitric acid.

表４から明らかなように、実施例１と同様に、電解剥離液３０中の銀濃度は低く、陰極３８及びフィルター４６に銀が捕集されていることが解る。 The copper plating film formed on the lead frame 10 under the same current density and bath temperature as in the electrolytic stripping solution 1 of Example 1, except that the electrolytic stripping solution 1 was used and the cathode back 40 was removed. And when the silver plating film is electrolytically stripped continuously and the amount of silver processed becomes 1000 ppm, the silver concentration in the electrolytic stripping solution 30 stored in the electrolytic stripping tank 32 is adhered to the cathode 38 and collected on the filter 46. The silver concentration of each of the particles, etc., was also measured, and the results are shown in Table 4. The silver concentration was measured in the same manner as in Example 1.

As is apparent from Table 4, as in Example 1, the silver concentration in the electrolytic stripping solution 30 is low, and it can be seen that silver is collected in the cathode 38 and the filter 46.

Comparative Example 1

表５から明らかなように、シアン系電解剥離液では、陰極３８に多少の銀が析出するものの、フィルター４６に捕集される粒子等を形成する程にまで銀は析出しない。このため、電解剥離液３０中の銀濃度は高い。 The current density and bath temperature are the same as those of the electrolytic stripping solution 1 of Example 1, except that a cyan electrolytic stripping solution (potassium cyanide 80 g / L, p-nitrobenzoic acid 10 g / L, pH 11) was used as the electrolytic stripping solution. The copper plating film and the silver plating film formed on the lead frame 10 are continuously electrolytically stripped, and when the amount of silver processed becomes 1000 ppm, the electrolytic stripping solution 30 stored in the electrolytic stripping tank 32 The silver concentration and the silver concentration of each particle etc. adhering to the cathode 38 and collected on the filter 46 were also measured, and the results are shown in Table 5. The silver concentration was measured in the same manner as in Example 1.

As apparent from Table 5, in the cyan electrolytic stripping solution, some silver is deposited on the cathode 38, but silver is not deposited to such an extent that particles collected by the filter 46 are formed. For this reason, the silver concentration in the electrolytic stripping solution 30 is high.

It is a fragmentary top view explaining the lead frame as a member which performs electrolytic peeling. It is a fragmentary sectional view explaining the partial silver plating and leakage silver which are given to the lead frame shown in FIG. It is a basic diagram explaining an example of an electrolytic peeling apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Lead frame 12 Inner lead 12a Bonding part 14 Die pad 16 Copper plating film 22 Silver plating film 24 Leakage silver 30 Electrolytic peeling liquid 36 DC power supply 38 Cathode 40 Cathode back 42 Circulation pump 44 Circulation piping 46 Filter

Claims (7)

A copper plating film exposed from a silver plating film partially covering the copper plating film formed on the entire surface of the member, and a leaked silver thinner than the silver plating film formed on the exposed portion of the copper plating film,
When peeling by electrolytic peeling with the copper plating film as the anode,
Electrolytic exfoliation solution in which a cyanide compound is not added as an electrolytic exfoliation solution, and a compound that forms a complex ion with silver that is more easily dissociated than a complex ion composed of silver and cyan is added. Using liquid,
An electrolytic stripping method comprising depositing silver and copper on a cathode made of a metal that is chemically stable with respect to the electrolytic stripper used as a counter electrode with respect to the anode.   A compound that forms a complex ion with silver having a lower complex stability constant than a complex ion composed of silver and cyan as a compound that forms a complex ion with silver that is more easily dissociated than a complex ion composed of silver and cyan The electrolytic stripping method according to claim 1, wherein   The compound that forms a complex ion with silver that is more easily dissociated than a complex ion composed of silver and cyan is selected from the group consisting of aqueous ammonia, ammonium salt, tartrate, phosphoric acid, and citrate. Or the electrolytic stripping method of Claim 1 or Claim 2 which uses 2 or more types of compounds.   The electrolytic stripping solution according to any one of claims 1 to 3, wherein an electrolytic stripping solution containing a copper compound or an aromatic nitro compound as a copper oxidizing agent and having a pH adjusted to 9 to 12 is used. The electrolytic stripping method described.   The electrolytic stripping method according to any one of claims 1 to 4, wherein an electrolytic stripping solution to which an ammonium source capable of forming a copper ammonium complex and a copper source are added is used as the electrolytic stripping solution.   The electrolytic stripping method according to any one of claims 1 to 5, wherein the cathode is wrapped by a cathode bag for collecting silver particles and the like made of precipitated silver.   The electrolytic stripping method according to claim 1, wherein a lead frame made of an iron-based alloy is used as the member.

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