JP3325150B2 - Electrolytic production of tin sulfate and bismuth sulfate for tin-bismuth alloy plating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for electrolytically producing tin sulfate and bismuth sulfate for tin-bismuth alloy plating.
Tin-lead alloy plating is often used as a surface treatment for electronic components. However, since harmful lead is contained in a plating bath and a resulting plating film, alloy plating in place of the harmful lead is strongly demanded. Thus, the present invention provides a tin-bismuth alloy plating which can replace such a tin-lead alloy plating and has a radioactive α particle count of less than 0.1 CPH / cm ^2. And a method for electrolytically producing a tin sulfate or a bismuth sulfate.

[0002]

2. Description of the Related Art With the recent remarkable development of the electronic industry, tin and solder plating having good solderability are applied to electronic components. Conventionally, a borofluoride bath has been used for solder plating, but fluorine, which is one of the constituent elements of borofluoric acid, is a very toxic element and at the same time it is difficult to treat waste liquid. Organic sulfonates having lower toxicity than borofluoride have been widely used, and there have been reports on plating techniques and additives around these. However, recently, since harmful lead is contained in the wastewater treatment and the obtained film when using the solder plating, there is a strong demand for a tin alloy plating instead of the harmful lead. Corresponding to conventional solder plating (Sn / Pb), tin-bismuth alloy plating having similar thermal and mechanical properties such as melting point and solderability is promising as an alternative alloy to solder plating. Further, tin-lead alloy plating (Sn / Pb = 90/10) mixed with a small amount of lead has been put into practical use to prevent tin whiskers, but tin-mixed with a small amount of bismuth instead of this lead. Bismuth alloy plating (Sn / Bi = 90/10) can also prevent whisker of tin similarly to tin-lead alloy.

[0003] On the other hand, the production process of tin sulfate and bismuth sulfate used for a tin-bismuth alloy plating solution includes:
A method has been adopted in which oxides, chlorides and hydroxides of these metals are dissolved in sulfuric acid to prepare them. However, these oxides, chlorides and hydroxides contain a large amount of uranium and thorium, which are sources of α-rays. In such a chemical dissolution method, these impurities are mixed in tin sulfate and bismuth sulfate. However, since a large amount of α-rays are generated from the tin-bismuth alloy electrodeposit after plating, there is the greatest drawback of causing a so-called soft error in a memory device. For plating of electronic parts which dislike chloride on the order of several ppm, chloride is inevitably mixed in commercially available tin sulfate or bismuth sulfate.

[0004]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention has been made as a result of repeated studies to suppress the occurrence of memory errors in semiconductors and to provide a tin-bismuth alloy plating solution which can replace solder containing no chloride. It removes uranium and thorium, which are radioactive isotopes contained as inevitable impurities in Sn and Bi, which are the main components of the film formed by plating, using sulfuric acid that has no problem in pollution control. The present inventors have found a method for producing a tin sulfate or bismuth sulfate capable of providing a tin-bismuth alloy plating capable of suppressing the count number of α particles to 0.1 CPH / cm ² or less, and reached the present invention. Accordingly, an object of the present invention is to provide a method for electrolytically producing a tin sulfate or bismuth sulfate capable of providing a tin-bismuth alloy plating film having a reduced count of radioactive α particles. Still another object of the present invention is to provide a method for electrolytically producing tin sulfate or bismuth sulfate free of chloride.

[0005]

That is, the subject of the present invention is to use an electrolytic cell in which an anode and a cathode are separated by an anion exchange membrane or an anion exchange membrane and a cation exchange membrane, use a sulfuric acid solution as an electrolyte, and use tin as an anode. Or using bismuth, and then applying a DC voltage to the anode and cathode to dissolve tin or bismuth in the sulfuric acid electrolyte, and the radioactivity α of the coating plated with the resulting tin and bismuth salts. An electrolytic production method of tin sulfate or bismuth sulfate for tin-bismuth alloy plating, characterized in that the particle count is less than 0.1 CPH / cm ² . Furthermore, the subject of the present invention is the tin sulphate and bismuth sulphate salts obtained by the above-mentioned production process, tin-bismuth alloy plating baths containing such tin sulphate and bismuth sulphate salts, and the baths obtained therefrom. Count of radioactive alpha particles in the coated film is 0.1
It is in a tin-bismuth alloy plated electrodeposit that is less than CPH / cm ² .

[0006] The electrolytic production method of the present invention uses an electrolytic cell in which the anode and the cathode are separated by an anion exchange membrane or an anion exchange membrane and a cation exchange membrane, uses a sulfuric acid solution as an electrolyte, and tin or bismuth as an anode. And applying a DC voltage to the anode and cathode to electrolyze and dissolve tin or bismuth in the sulfuric acid electrolyte. Here, an example of an electrolysis apparatus that can be used to carry out the electrolytic production method of the present invention is described in FIG. In FIG. 1, an electrolytic cell 1 for producing tin sulfate and bismuth sulfate is shown.
Are provided with two cathodes 4, for example a platinum plate, between which an anode 2, for example a tin or bismuth bar, is provided, around which the granular tin or bismuth 3 to be dissolved is arranged. Further, an electrolytic cell having an anion exchange membrane 5 disposed between the anode 2 and the cathode 4 is used. A shielding film 6 is provided between the anode 2 and the cathode 4 to define an anode chamber and a cathode chamber, respectively. An electrolyte solution 7 made of a sulfuric acid solution is introduced into the anode chamber and the cathode chamber, and is stirred and cooled by a circulation pump, for example, a chemical pump 9 and a heat exchanger 10. A DC power supply 8 is connected to the anode and the cathode. The solution of tin sulfate or bismuth sulfate obtained by electrolysis is taken out from the product outlet 11.

[0007] For the production of tin sulfate and bismuth sulfate containing usually less than a few ppm of chloride, an electrolytic cell as shown in Fig. 1 in which only an anion exchange membrane is set between an anode chamber and a cathode chamber is used. Although it is sufficient, in order to suppress the count number of radioactive α particles to 0.1 CPH / cm ² or less, a multilayer electrolytic cell having an anion exchange membrane and a cation exchange membrane between an anode and a cathode is required. is necessary.

FIG. 2 shows an example of such an electrolytic cell. In this case, since the shielding plate 6 has a hole of an arbitrary diameter, the electrolytic solution containing tin sulfate or bismuth salt dissolved in the anode chamber passes through the perforated shielding plate 6 and moves to the cathode chamber. can do. A cation exchange membrane 12 is set on the side of the perforated shielding plate 6 in the anode chamber, and tin or bismuth cations can pass through the cation exchange membrane.
On the other hand, an anion exchange membrane 5 is set on the cathode 4 side, and tin or bismuth cation cannot pass through this anion exchange membrane. Thus, the produced solution containing tin sulfate or bismuth salt is taken out from the product taking-out port 11.

The conditions for the electrolysis according to the invention are as follows: the current density for the membrane is between 0.2 and 50 A / dm ² , preferably 5
-30 A / dm ² , liquid temperature is 10-50 ° C., preferably 2
0-35 ° C, voltage is 0.5-15V. The electrolytic solution is obtained by diluting commercially available concentrated sulfuric acid with pure water, and then 5 to 50%, preferably 1
0 to 20%. Further, hydroquinone, resorcinol, pyrocatechol, p-phenolsulfonic acid and cresolsulfonic acid may be added as an antioxidant for tin, and 0.05 to 2.0%, preferably 0.1 to 0.5%. Tin and bismuth used as the anode have a quality of 3 or more nines, and may have any shape, but are preferably granular or spherical. As the cathode material, those which are inert to the electrolytic solution are preferable, and platinum, nickel,
Titanium, stainless steel, carbon, or those plated with platinum on titanium are preferred.

[0010] The cation exchange membrane and the anion exchange membrane must basically have low electric resistance and good acid resistance, durability and heat resistance. In addition, the cation exchange membrane must allow dissolved tin or bismuth cations to pass from the anode, and the anion exchange membrane must act to prevent tin or bismuth cations from migrating to the cathode. Although many cation and anion exchange membranes are known today, preferred cation exchange membranes are those made from polystyrene or styrene copolymer type resins having strongly acidic groups such as sulfonic acid groups, and are also preferred. The anion exchange membrane is manufactured from a polystyrene type or styrene copolymer type resin having a strongly basic group such as an amino group or a quaternary ammonium group. Here, particularly preferred exchange membranes to be used include, for example, CMS, C66-10F (cation exchange membrane) manufactured by Tokuyama Soda,
ACL-5P, AM-2 (anion exchange membrane) and the like.

The reason why the radioactive α particles are reduced in the present invention is that tin or bismuth cation dissolved from the anode is present in the electrolyte as it is, but uranium and thorium are dissolved in the electrolyte to form an anion complex salt. Form and therefore do not pass through the cation exchange membrane, only the tin or bismuth ions pass through it, while the anion exchange membrane prevents tin or bismuth ions from migrating to the cathode, and consequently This is probably because the solution of tin sulfate or bismuth salt from which uranium and thorium have been removed is continuously taken out between the cation exchange membrane and the anion exchange membrane.

[0012] Tin sulfate obtained by the electrolytic production method of the present invention
Alternatively, the bismuth salt may be tin or bismuth dissolved in the electrolyte.
Obtained as a solution of sulfuric acid and therefore also contains free sulfuric acid
Things. In general, the resulting solution is
Sn²⁺5 to 25% by weight, preferably 10
１５15% by weight tin sulfate, 5-50% by weight, preferably
An aqueous solution containing 10 to 20% by weight of free sulfuric acid
You. In the case of bismuth salt, Bi³⁺Expressed as 5
~ 25 wt%, preferably 10-15 wt% bisulfate
Trout salt, 5 to 50% by weight, preferably 10 to 20% by weight
Is an aqueous solution containing free sulfuric acid. Like this
The resulting aqueous solution can be used directly for alloy plating.
But usually tin and tin to obtain the desired alloy plating.
The bismuth concentration as well as the free sulfuric acid concentration are adjusted. This
The composition of the plating bath is easily determined by those skilled in the art.
Can be. In addition, the plating bath thus prepared includes:
Various additives used in tin-bismuth alloy plating baths,
For example, surfactants, brighteners, etc. can be added
You. Tin sulfate and bis obtained by the electrolytic production method of the present invention
The plating film obtained from the plating bath containing the mass salt is
The counted number of the radioactive α particles is 0.1 CPH / cm ^Two 
Is less than.

[0013]

EXAMPLES Next, examples of the present invention will be described. However, the present invention is not limited to these examples, and the above-mentioned tin sulfate having a radioactive α particle count of 0.1 CPH / cm ² or less and Electrolysis conditions and operating conditions can be arbitrarily changed according to the purpose of obtaining bismuth sulfate.

EXAMPLE 1 Preparation of Tin Sulfate This example relates to a method for the electrolytic production of tin sulfate. The electrolytic cell is made of an acrylic plate having a thickness of 6 mm and has an anode chamber capacity of 20 mm.
0 ml, product room 80 ml x 2 rooms, 5 x 16 = 80 cm ²
Two cation exchange membranes (C66-10F) and two anion exchange membranes (ACLE-5P) at 2.5 mm intervals {2.
A set of two shielding plates each having a hole of 5 mm was used. Then put 99.9% pure tin rod for contact in the center of the anode and 99.9% granular tin around it, and use ^two 0.8 dm ² platinum-plated titanium-plated titanium plates as the anode and cathode. Sulfuric acid was added and the anolyte flow rate was 3.0 L /
min, the solution was circulated and cooled at a catholyte flow rate of 1.8 L / min, and a DC voltage was applied to the anode and the cathode to perform electrolysis. Table 1 shows the concentrations of sulfuric acid and tin sulfate and the dissolving efficiency of Sn in each solution of the product chamber and the cathode chamber obtained after the electrolysis, together with the electrolysis conditions.

[Table 1]

Example 2 Preparation of Bismuth Sulfate The electrolytic cell and operating conditions used in this example were the same as those used in Example 2 above, with a 99.9% contact bismuth rod on the anode and the same 99 surrounding it. 9.9% of granular bismuth was charged and electrolyzed. Table 2 shows the concentration of sulfuric acid and bismuth sulfate and the dissolution efficiency of Bi in each solution of the product chamber and the cathode chamber obtained after the electrolysis, together with the electrolysis conditions.

[Table 2]

Example 3 : Implementation of tin-bismuth alloy plating These tin sulfate and bismuth sulfate salts taken out of the product chamber of the electrolytic cell used in the above example were each dissolved in an aqueous sulfuric acid solution and dissolved in a suitable surfactant (for example, polypropylene). Glycol polyethylene glycol nonyl phenyl ether)
Was added to prepare a tin-bismuth alloy plating bath, and plating was performed using an insoluble anode plated with Pt on Ti, using a Cu plate as a cathode, and connecting a DC power supply. Table 3 below shows the composition of the plating solution (in the composition of the plating solution, the concentrations of tin sulfate and bismuth sulfate are expressed as Sn ²⁺ and Bi ^3+, respectively), plating conditions, composition of the electrodeposit and radioactivity. Shows the count number of α particles.

[Table 3] Comparative bath 1 shown in Table 3 above is a plating bath prepared using tin sulfate and bismuth sulfate manufactured by a commercially available conventional method. It can be seen that the count number of radioactive α particles in the plating film obtained from this plating solution is very high. On the other hand, in each of the plating baths 1 to 3 according to the present invention, the counted number of radioactive α particles in the plating film is 0.1.
It can be seen that a low value of less than CPH / cm ² was obtained.

EXAMPLE 4 Implementation of Tin-Bismuth Alloy Plating Similar to the electrolytic cell used in Example 1 above, except that electrolysis was performed using only an anion exchange membrane between the anode and cathode compartments, and tin sulfate, respectively. And bismuth sulfate. Using the tin sulfate and bismuth sulfate thus obtained, a tin-bismuth plating bath was prepared and plated. Composition of plating solution (in the composition of plating solution, the concentrations of tin sulfate and bismuth sulfate are represented as Sn ²⁺ and Bi ^3+, respectively), plating conditions, composition of electrodeposits, and chloride ion in plating solution Is shown in Table 4.

[Table 4] Comparative bath 2 shown in Table 4 above is a plating bath prepared using tin sulfate and bismuth sulfate manufactured by a commercially available conventional method. The chloride ions in the plating solution were very high, whereas the plating bath 4 according to the present invention obtained a low chloride ion value.

[0018]

According to the present invention, an electrolytic cell in which an anode and a cathode are separated by an anion exchange membrane or an anion exchange membrane and a cation exchange membrane is used to electrolyze and dissolve tin and bismuth metal having a grade of 3 or more. This provides a method for producing tin sulfate and bismuth sulfate suitable for use in a tin-bismuth alloy plating bath. In the plating bath using tin sulfate and bismuth sulfate thus produced, chloride ions are not present, and the number of radioactive α particles in the plating film formed therefrom is 0.1 CPH.
/ Cm ² . Accordingly, it is possible to form a tin-bismuth alloy plating film that significantly suppresses the occurrence of memory errors without the adverse effect of chloride ions, so that a memory device having a memory capacity of 256K or more and a super LS
It is possible to plate components of semiconductor devices such as I, and it is also free from lead pollution.

[Brief description of the drawings]

FIG. 1 shows one embodiment of an electrolysis device that can be used to carry out the method of the present invention.

FIG. 2 is another embodiment of an electrolysis device that can be used to practice the method of the present invention.

[Description of Signs] 1 electrolytic cell 2 tin or bismuth for anode contact 3 granular tin or bismuth 5 anion exchange membrane 7 electrolyte 12 cation exchange membrane

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI C25D 3/56 C25B 1/00 (72) Inventor Yoshiaki Okuhama 21-8 Minami-Futami, Futami-cho, Akashi-shi, Hyogo Pref. (56) References JP-A-52-90493 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C25D 21/14 C01G 1/10 C01G 19/00 C01G 29/00 C25B 1 / 00 C25D 3/56

Claims (5)

(57) [Claims] 1. An electrolytic cell in which an anode and a cathode are separated by an anion exchange membrane or an anion exchange membrane and a cation exchange membrane, a sulfuric acid solution is used as an electrolytic solution, and tin or bismuth is used as an anode. A direct current voltage is applied to the anode and the cathode to dissolve tin or bismuth in the sulfuric acid electrolyte, and the number of radioactive α particles of the coating plated with the obtained tin and bismuth salt is 0.1 CPH.
/ Cm ² , wherein the tin sulfate or bismuth sulfate is electrolytically produced for tin-bismuth alloy plating. 2. The method according to claim 1, wherein an antioxidant is added to the electrolytic solution. 3. A plating film which contains tin sulfate and bismuth sulfate obtained by the production method according to claim 1 and free sulfuric acid and has a counted number of radioactive α particles of 0.1 in a plating film obtained.
A tin-bismuth alloy plating bath, wherein the plating bath is less than CPH / cm ² . 4. The plating film obtained from the plating bath according to claim 3, wherein the counted number of radioactive α particles is 0.1 CPH / cm.
Tin-bismuth alloy plated electrodeposits less than ² . 5. A cation exchange membrane and a shielding plate comprising one anode chamber and two cathode chambers, each having a hole of an arbitrary diameter on both sides of the anode chamber, and an anion exchange membrane on the cathode side of the cathode chamber. And a system for circulating an electrolytic solution comprising a sulfuric acid solution introduced into the anode chamber and the cathode chamber, a DC power supply connected to the anode and the cathode, and a cation exchange membrane and an anion exchange membrane. 2. An electrolytic apparatus for carrying out the electrolytic production method according to claim 1, further comprising a product takeout port set in the apparatus.