JP2005324143A - Method of cleaning metal part - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method capable of cleaning a metal part washing away sulfate ions, SO<SB>4</SB><SP>2-</SP>, adhered to the surface of the part to minimize sulfate ions remaining on the part after cleaning in an adsorbed form. <P>SOLUTION: In cleaning the metal part to which sulfate ions, SO<SB>4</SB><SP>2-</SP>are adhered, with cleaning water, the method uses the alkaline electrolytic water prepared by electrolysis of water containing triammonium citrate as the cleaning water. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a method for cleaning metal parts, and more particularly to a method for cleaning metal parts having sulfate ions (SO ₄ ²⁻ ) attached to the surface.

In a semiconductor device using a lead frame, as shown in FIG. 2A, a semiconductor element 20 wire-bonded to a lead 24 is placed on a heat radiating plate 22 and sealed with a sealing resin 26. In such a semiconductor device, most of the heat generated in the semiconductor element 20 is radiated to the entire sealing resin 26 via the heat radiating plate 22.
Further, in order to further improve the heat dissipation of the semiconductor device, as shown in FIG. 2B, the heat dissipation plate 22 may be provided so that one surface is exposed from the sealing resin 26.
In order for the heat sink 22 to exhibit the desired heat dissipation, it is important that the sealing resin 26 and the heat sink 22 are in close contact.
Thus, in order for the heat sink 22 and the sealing resin 26 to adhere to each other, it is necessary that the heat sink 22 and the sealing resin 26 have good wettability. As a result, the wettability with the sealing resin 26 is improved.

By the way, since the heat sink 22 which plated and took out from the plating tank has the plating solution adhering, it is normally wash | cleaned with washing water.
Generally, pure water is used as cleaning water as described in Patent Document 1 below when cleaning plated electronic components for semiconductor devices.
JP 2004-59991 A (Claims)

The heat radiating plate 22 taken out from the plating tank is further dried after washing the plating solution adhering to it by washing with pure water.
Usually, nickel plating or copper plating using a plating bath to which a sulfuric acid component is added is generally used for plating the heat sink 22. Even if the heat sink 22 plated with such a plating bath is cleaned with pure water, sulfate ions (SO ₄ ²⁻ ) remain on the surface of the heat sink 22 after cleaning.
The amount of sulfate ions remaining in the heat radiating plate 22 is related to the wettability between the heat radiating plate 22 and the sealing resin 26, and when the amount of remaining sulfate ions increases, There is a tendency that the wettability is lowered and the heat radiating plate 22 and the sealing resin 26 are easily peeled off.
In particular, in the semiconductor device shown in FIG. 2B, since one surface of the heat radiating plate 22 is exposed from the sealing resin 26, the other surface in contact with the sealing resin 26 is in close contact with the sealing resin 26. It is necessary to further improve the properties.
For this reason, even if pure water washing is repeated a plurality of times to reduce the remaining sulfate ions to the radiator plate 22 where sulfate ions remain on the surface, a certain amount of sulfate ions remains on the radiator plate 22. Remains. This means that sulfate ions remaining on the surface of the heat sink 22 are adsorbed on the heat sink 22.
Therefore, an object of the present invention is to wash sulfate ions (SO ₄ ²⁻ ) adhering to the surface of metal parts, and to reduce the sulfate ions remaining on the metal parts after washing as much as possible. Another object of the present invention is to provide a cleaning method for metal parts.

The present inventors take out the heat sink 22 immersed in an aqueous solution to which a sulfuric acid component has been added and dry it, then wash it with various washing water, and measure the amount of sulfate ions adsorbed and remaining on the heat sink 22. did.
As a result, when the heat radiating plate 22 with sulfate ions attached thereto was washed using alkaline electrolyzed water obtained by electrolyzing water added with ammonium citrate, the heat radiating plate 22 was adsorbed and remained. Knowing that the amount of sulfate ions can be reduced as much as possible, the present invention has been achieved.
That is, the present invention provides an alkaline electrolysis obtained by electrolysis of water containing citrate as the washing water when washing metal parts to which sulfate ions (SO ₄ ²⁻ ) are adhered with washing water. A method for cleaning metal parts characterized by using water.

In the present invention, a metal part plated with a plating solution containing sulfate ions (SO ₄ ²⁻ ) can be used as the metal part. For plating, a plating bath to which a sulfuric acid component is added is used. The nickel plating or copper plating used can be suitably employed.
Moreover, as alkaline electrolyzed water, alkaline electrolyzed water obtained by electrolysis of water containing ammonium citrate can be suitably used.
Thus, it is preferable that the metal parts washed with alkaline electrolyzed water are further washed with pure water in order to wash ions contained in the alkaline electrolyzed water.
As the metal parts, semiconductor device parts such as lead frames and heat sinks can be used.

According to the present invention, by washing a metal part having sulfate ions attached to the surface with alkaline electrolyzed water obtained by electrolysis of water containing citrate, the sulfuric acid adsorbed and remained on the metal part Ions can be reduced as much as possible.
As a result, the adhesion between the metal part and the sealing resin can be improved, and the reliability of the final product can be improved.
In this way, by washing with alkaline electrolyzed water obtained by electrolysis of water containing citrate to wash the metal parts to which sulfate ions are attached, the sulfate ions adsorbed and remaining on the metal parts are removed. The reason why it can be reduced as much as possible can be inferred as follows.
That is, citric acid tends to form a stable complex with a metal in a neutral to alkaline atmosphere. For this reason, when a metal part adsorbing sulfate ions is immersed in alkaline electrolyzed water containing citric acid, the metal of the metal layer forming the surface of the metal part and citric acid form a stable complex. Etching can be performed on the metal layer on the surface of the component, and the sulfate ions adsorbed and remaining on the metal component can be reduced as much as possible.
As a metal that can easily form a stable complex with citric acid, nickel can be cited. A metal part having a surface formed of a nickel layer is obtained by alkaline electrolyzed water obtained by electrolysis of water containing citrate. By washing, sulfate ions adsorbed and remaining on the metal parts can be further reduced.

Metal parts used in the present invention have sulfate ions (SO ₄ ²⁻ ) attached to their surfaces, and are metal parts plated using a plating solution containing sulfate ions (SO ₄ ²⁻ ). In particular, metal parts subjected to nickel plating or copper plating using a plating bath to which a sulfuric acid component is added can be suitably used.
As such a metal component, a semiconductor device component such as a heat sink can be used. Furthermore, examples of the nickel plating bath include a watt bath, and examples of the copper plating bath include a copper sulfate bath.

As described above, alkaline electrolyzed water obtained by electrolysis of water containing citrate is used as washing water for washing metal parts to which sulfate ions are attached.
As this citrate, sodium citrate, potassium citrate, and ammonium citrate can be preferably used. However, when an electronic component is used as the metal component, ammonium citrate, particularly triammonium citrate is preferable. Can be used. The amount of citrate added is preferably 0.1 to 0.001 mol / liter.
The alkaline electrolyzed water used as the washing water in the present invention can be obtained by the electrolysis apparatus shown in FIG. The electrolytic apparatus shown in FIG. 1 includes an anode chamber 14 into which an electrolytic cell 10 is formed by a diaphragm 12 and the other end of an anode 14a formed of platinum or the like having one end connected to a DC power source 18, and one end. Is partitioned into a cathode chamber 16 into which the other end of a cathode 16a formed of platinum or the like connected to a DC power source 18 is inserted.
As the diaphragm 12, a diaphragm that can transmit ions generated in the anode chamber 14 and the cathode chamber 16 during electrolysis but cannot transmit water, such as an ion exchange membrane, can be used.

A predetermined amount of citrate is added to the electrolytic cell 10 of the electrolysis apparatus shown in FIG. 1 in water from which tap water has been passed through an ion exchange membrane or the like to remove chlorine ions or metal ions contained in the tap water. The added water is poured, and direct current is supplied from the DC power source 18 to the anode 14a and the cathode 16a to electrolyze the water in the electrolytic cell 10.
During the electrolysis, the water in the anode chamber 14 becomes acidic water that exhibits acidity. On the other hand, the water in the cathode chamber 16 becomes alkaline electrolyzed water.
Of the electrolyzed water obtained by such electrolysis, alkaline electrolyzed water collected from the cathode chamber 16 is used for cleaning metal parts.
This metal part to be washed with alkaline electrolyzed water may be washed with alkaline electrolyzed water without washing with normal water such as groundwater or pure water in advance, or after washing with normal water or pure water. You may wash | clean with electrolyzed water.

Washing of the metal parts with alkaline electrolyzed water can be performed by immersing the metal parts in the stored alkaline electrolyzed water for several seconds to several tens of seconds. The alkaline electrolyzed water may be stirred during this washing.
Since the metal component that has been washed with alkaline electrolyzed water is adhered with ions contained in the alkaline electrolyzed water, it is preferable to further wash the metal component with pure water.
Metal parts that have undergone a series of cleaning have lower sulfate ions adsorbed and remaining on the surface than when cleaned with pure water. Compared to other parts such as lead frames and semiconductor chips, In a final product obtained by combining, for example, a resin-encapsulated semiconductor device, the adhesiveness with the encapsulating resin is good, and the reliability of the final product can be improved.
Of the electrolyzed water obtained by electrolysis, the acidic electrolyzed water in the anode chamber 14 is not effective in cleaning the metal parts, and is mixed with the alkaline electrolyzed water that has been cleaned, neutralized and discharged. .

By the way, in Japanese Patent Laid-Open No. 7-263430, when rinsing an etched semiconductor wafer, water added with ammonium citrate is electrolyzed to reduce the amount of chemicals used in the semiconductor manufacturing process. The use of alkaline electrolyzed water obtained in this way is described.
However, in this publication, water containing ammonium citrate is electrolyzed as a cleaning solution for cleaning metal parts to which sulfate ions have adhered in order to reduce as much as possible sulfate ions adsorbed on metal parts. In addition to using the alkaline electrolyzed water obtained in this way, there is no description suggesting this at all.

表１から明らかな様に、アルカリ性電解水で洗浄した放熱板に残留する硫酸イオンを含む各種イオン量は、アンモニウムイオンを除いて純水のみで洗浄した放熱板に比較して減少している。
尚、放熱板に残留するアンモニウムイオンは、純水の洗浄を更に繰り返すことによって除去できる。 (1) Sample preparation
(i) A plate-like heat sink having a nickel plating on the surface of a copper material using a plating bath containing nickel sulfate, and a solution obtained by dissolving 1 mmol / liter each of sodium chloride, sodium sulfate, and sodium nitrate in pure water. After dipping for 3 minutes, the sample was pulled up and dried to prepare a cleaning sample.
(ii) Each of the anode chamber 14 and the cathode chamber 16 forming the electrolytic cell 10 of the electrolyzer shown in FIG. 1 is 700 ml, and each of the anode 14a and the cathode 16a is formed with a platinum film on titanium. A 74 mm × 113 mm electrode was used.
Into this electrolytic cell 10, water in which 0.01 mol / liter triammonium citrate is added is poured into water from which tap water has been passed through an ion exchange membrane to remove chlorine ions, metal ions and the like, Electrolysis was performed on the water in the electrolytic cell 10 by flowing a direct current of 100 V at 0.6 A from the DC power source 18 to the anode 14 a and the cathode 16 a for 5 to 15 minutes.
The alkaline electrolyzed water collected from the cathode chamber 16 had a pH of 7.2 or higher and an oxidation-reduction potential (ORP) of −400 mV or lower.
(2) Cleaning The heat sink prepared as a cleaning sample is immersed for 3 seconds in stored water in which 0.7 liters of alkaline electrolyzed water at room temperature obtained by electrolysis is stored for the first time. After that, the second cleaning was performed by immersing in stored water in which 0.7 liters of pure water at room temperature was stored for 3 seconds. After the radiator plate subjected to the second cleaning was naturally dried, various ions remaining on the surface of the radiator plate were analyzed by an ion chromatograph analyzer. The results are shown in Table 1 below.
As a comparative example, the first and second cleanings were performed by immersing a heat sink prepared as a cleaning sample in stored water in which 0.7 liters of pure water at room temperature was stored for 3 seconds. Table 1 also shows the amounts of various ions adsorbed and remaining on the heat sink.
Further, Table 1 also shows the amounts of various ions present on the surface of the heat sink prepared as a cleaning sample.
(3) Results

As is apparent from Table 1, the amount of various ions including sulfate ions remaining on the heat sink washed with alkaline electrolyzed water is reduced as compared with the heat sink washed only with pure water except for ammonium ions.
The ammonium ions remaining on the heat sink can be removed by further repeating the cleaning with pure water.

表２から明らな様に、アルカリ性電解水で洗浄した放熱板に残留している硫酸イオンを含む各種イオン量は、純水のみで洗浄した放熱板に比較して６０％程度に減少している。
また、アルカリ性電解水で洗浄した放熱板に残留するアンモニウムイオンは、純水での洗浄を繰り返すことによって除去されている。 The copper heat sink with electrolytic nickel plating on the surface using a Watt bath was washed with ground water and then washed with the alkaline electrolyzed water used in Example 1. Furthermore, after washing twice with pure water, the heat sink was naturally dried, and then various ions remaining on the surface of the heat sink were analyzed by an ion chromatograph analyzer. The results are shown in Table 2 below.
Further, as a comparative example, a heat sink that had been subjected to electrolytic nickel plating using a watt bath was washed with ground water and then washed with pure water three times. Then, after naturally drying a heat sink, the various ions which remain | survived on the surface of a heat sink are analyzed with an ion chromatography analyzer, and the result is combined with following Table 2, and is shown.

As is clear from Table 2, the amount of various ions including sulfate ions remaining on the heat sink washed with alkaline electrolyzed water is reduced to about 60% compared to the heat sink washed only with pure water. Yes.
Further, ammonium ions remaining on the heat sink washed with alkaline electrolyzed water are removed by repeating washing with pure water.

表３から明らな様に、アルカリ性電解水で洗浄した放熱板に残留する硫酸イオンを含む各種イオン量は、純水のみで洗浄した放熱板に比較して半分以下に減少している。 The copper heat sink whose surface was subjected to electrolytic copper plating using a copper sulfate bath was washed in the same manner as in Example 2, and various ions remaining on the surface of the heat sink were analyzed by an ion chromatography analyzer. The results are shown in Table 3 below.
In addition, as a comparative example, a copper heat sink whose surface was subjected to electrolytic copper plating using a copper sulfate bath was washed with ground water and then washed with pure water three times. Then, after naturally drying the heat sink, various ions remaining on the surface of the heat sink are analyzed by an ion chromatograph, and the results are shown in Table 3 below.

As is apparent from Table 3, the amount of various ions including sulfate ions remaining on the heat sink washed with alkaline electrolyzed water is reduced to less than half that of the heat sink washed only with pure water.

It is the schematic for demonstrating an example of the electrolyzer for obtaining alkaline electrolyzed water. It is sectional drawing explaining an example of the semiconductor device using a heat sink.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electrolysis cell 12 Diaphragm 14a Anode 14 Anode chamber 16a Cathode 16 Cathode chamber 18 DC power supply

Claims (6)

When washing metal parts to which sulfate ions (SO ₄ ^2- ) are adhered with washing water, alkaline electrolyzed water obtained by electrolysis of water containing citrate is used as the washing water. Cleaning method for metal parts. The method for cleaning a metal part according to claim 1, wherein the metal part is a metal part plated with a plating solution containing sulfate ions (SO ₄ ²⁻ ).   The metal part cleaning method according to claim 1 or 2, wherein a metal part subjected to nickel plating or copper plating using a plating bath to which a sulfuric acid component is added is used as the metal part.   The manufacturing method of the metal component as described in any one of Claims 1-3 using the alkaline electrolyzed water obtained by electrolysis of the water containing ammonium citrate as alkaline electrolyzed water.   The method of manufacturing a metal part according to any one of claims 1 to 4, wherein the metal part is washed with alkaline electrolyzed water and then washed with pure water.   The method for manufacturing a metal part according to claim 1, wherein a semiconductor device part is used as the metal part.

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