JP2590869B2 - Manufacturing method of plating solution for solder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field) The present invention is not limited to ordinary ICs, but also includes a 256K RAM type memory or larger memory as a large-capacity memory element and various super LSIs.
The present invention relates to a low α-activity solder plating solution containing an aromatic sulfonic acid and a lead salt and a tin salt thereof suitable for plating a solder alloy on a component of a semiconductor device such as a substrate, a substrate, or the like.

(Conventional technology and its problems) Conventionally, a solder plating solution prepared using a compound containing a large amount of U and Th, which is a source of α-rays in lead and tin, generates many α-rays from the solder electrodeposit after plating. This causes a so-called soft error in the memory device.

An example of the related art will be described. That is, a solder film prepared using a solder plating solution prepared by a conventional method contains radioactive isotopes such as U and Th in an amount of 100 ppb or more. it is equivalent to the number CPH / cm ² ~ number 100CPH / cm ² as a number.
As described above, when a solder plating solution mainly containing a lead and tin compound having a high content of radioisotope which is not subjected to pre-purification is used for assembling a semiconductor device, radioactive α particles emitted from the formed solder film are stored in a memory. It caused errors and was unreliable.

The inventors of the present invention have conducted various studies to solve the above-mentioned problems of the prior art and to provide a solder plating solution for suppressing the occurrence of memory errors in a semiconductor device. As a result, a solder film formed by the plating has been developed. The amount of radioactive isotopes U and Th contained as inevitable impurities in Pb and Sn, which are the main components of
If it is less than b, the count of radioactive α particles is 0.1 CPH / cm
^They have found that they can be suppressed to ² or less, and have reached the present invention.

(Constitution of the Invention) According to the present invention, the following general formula Wherein R ₁ and R ₂ may be the same or different and each is selected from the group consisting of a hydrogen atom, a hydroxyl group, a lower alkyl group and a sulfonic acid group, and the aromatic sulfonic acid represented by the formula A method for producing a solder plating solution containing a lead salt and a tin salt of an aromatic sulfonic acid, wherein each of the lead salt and the tin salt of the high-purity aromatic sulfonic acid produced by the following steps (a) to (e) is subjected to the aromatic treatment. A method for producing a solder plating solution characterized by being dissolved in an aromatic sulfonic acid, wherein the content of a radioisotope is less than 20 ppb and the count number of radioactive α particles is less than 0.1 CPH / cm ² .

Dissolve lead and / or tin with a purity of 99.99% or more in a high-purity nitric acid aqueous solution, adjust the free nitric acid concentration of the obtained solution to 5 to 10 mol, and purify the concentration-adjusted solution with an anion exchange resin. Reducing the content of U and Th in the solution, and reacting the purified solution with aromatic sulfonic acid,
Neutralization produces a high purity lead and / or tin salt of aromatic sulfonic acid with a radioisotope content of less than 20 ppb and a radioactive α particle count of less than 0.1 CPH / cm ² .

Next, the method for producing the plating solution for solder of the present invention will be described in detail.

First, lead having a grade of 99.99% (4 nines) or more is dissolved in high-purity concentrated nitric acid, and the radioisotopes of U and Th contained in the lead are converted into complex anions, followed by pure water. The free nitric acid concentration was adjusted to 5 to 10 molar concentration to improve the adsorption efficiency of U and Th in the next step of the anion exchange resin purification treatment, and then the U, Th obtained by performing the anion exchange resin purification treatment was used. The aromatic sulfonate represented by the above general formula is added to the solution having a reduced Th content, neutralized with an alkali, and then concentrated, filtered and separated to obtain a lead aromatic sulfonate having a small amount of α-rays. Can be Similarly, tin having a grade of 99.99% (4 nines) or more is dissolved in high-purity cold dilute nitric acid, and then the concentration of free nitric acid is adjusted to 5 to 10 molar concentration, followed by the next step of anion exchange resin solution treatment. U, Th adsorption efficiency was improved, and then the anion exchange resin purification treatment was performed.
The aromatic sulfonic acid represented by the above general formula is added to the solution having a reduced U and Th content, neutralized with an alkali, and then concentrated and concentrated.
By separating and separating, an aromatic tin sulfonate having a small amount of α-rays can be obtained.

The thus obtained lead aromatic sulfonate and tin aromatic sulfonate have a U, Th radioisotope content of less than 20 ppb, and a radioactive α particle count of 0.1 CPH / cm ² Is less than.

An aqueous solution containing the above-mentioned low α-ray generation amount of aromatic lead sulfonate, tin aromatic sulfonate and aromatic sulfonate as a composition component is used as an electrolytic solution, and plating is performed using a low α-ray radioactive solder plate as an anode. By connecting the substrates to the respective cathodes, it is possible to form a solder alloy on the substrate that generates a small amount of α-rays and significantly suppresses the occurrence of memory errors.

The attached drawings are schematic sectional views of one embodiment of the present invention. In the figure, 1 is a solder plate, 2 is a plating liquid, and 3 is a wiring board.

Next, the present invention will be described more specifically with reference to examples, but the following examples do not limit the scope of the present invention.

Example 1 Dissolved in lead-concentrated nitric acid having a grade of 4 nines or more, adjusted the concentration of free nitric acid to 5 to 10 mol with pure water, and then converted the solution to an anion exchange resin such as Diaion (trade name). ) Is passed through a column packed with U) and Th is adsorbed and removed from the solution, P-phenolsulfonic acid is added as aromatic sulfonic acid, and the solution is neutralized with caustic soda or ammonia water. Was concentrated, and the precipitated precipitate was separated, separated and dried to obtain lead aromatic sulfonate. Similarly, tin having a grade of 4 nines or more is dissolved in cold diluted nitric acid, and the concentration of free nitric acid is adjusted to 5 mol or less.
The solution is adjusted to 10 molar concentration, and then the solution is passed through a column filled with, for example, Diaion (trade name) through an anion exchange resin to remove U and Th in the solution by adsorption. After addition of P-phenolsulfonic acid and neutralization with caustic soda or ammonia water,
The solution was concentrated, and the deposited precipitate was separated, separated and dried to obtain an aromatic tin sulfonate. Analysis of the content of radioisotopes in these metal salts showed that all were less than 20 ppb, and the number of α particles was 0.1 CPH /
It was confirmed to be less than cm ² . These lead and tin aromatic sulfonates are dissolved in an aqueous solution of aromatic sulfonic acid (P-phenolsulfonic acid), respectively.
A plating solution for solder containing aromatic sulfonic acid, its tin salt and lead salt at the concentrations shown in Table 1 was prepared. The content of the radioactive isotope and the count of radioactive α particles in the obtained plating solution were as shown in Table 1, respectively.
Using this solder plating solution, radioisotope content
Is α less than the particle count 0.1CPH / cm ² at less than 20 ppb PB9
A solder plate with a composition of 0% and Sn 10% is used as an anode, and a substrate is used as a cathode.
Each was connected and plated at a current density of 60 A / cm ² to form a solder film having a composition of 89% Pb-11% Sn on the substrate. It was confirmed that the content of radioisotopes such as U and Th in the solder film was less than 20 ppb, and the count of radioactive α particles was less than 0.1 CPH / cm ² . It was confirmed that the memory prepared using this plating solution had significantly reduced occurrence of soft errors.

Example 2 A radioisotope content of less than 20 ppb and a radioactive α particle count of 0.1 CP were obtained in the same manner as in Example 1.
An aromatic sulfonic acid, a lead salt thereof, and a lead salt thereof are dissolved in an aqueous solution of aromatic sulfonic acid (P-phenolsulfonic acid) by dissolving lead aromatic sulfonate and tin aromatic sulfonate having an H / cm ^{2 of} less than H / cm ² . A plating solution for solder containing the concentrations shown in Table 1 was prepared. Using this plating solution,
Electrolysis is performed using a 90% Pb-10% Sn solder plate of low α ray as an anode and a substrate as a cathode in the same manner as in Example 1, and 89% Pb on the substrate.
A solder film of -11% Sn was produced. U in this solder film,
It was confirmed that the content of radioisotopes such as Th was less than 20 ppb, and the count number of radioactive α particles was less than 0.1 CPH / cm ² .

Examples in which P-phenolsulfonate, benzenesulfonate, and P-toluenesulfonate were used as the aromatic sulfonate, and P-phenolsulfonate, benzenesulfonate, and P-toluenesulfonate were also used. Comparative examples using fluoric acid are shown in Table 1 as Examples 1 to 5 and Comparative Examples 1 to 4, respectively. Example 1
In No. 5, lead and tin of high purity of 4 nines or more were dissolved in nitric acid, preliminarily purified according to the method of the present invention, and then reacted with aromatic sulfonic acid.
In No. 4, lead and tin having a high purity of 4 nines or more were dissolved in nitric acid and reacted with aromatic sulfonic acid without any preliminary purification.

Comparative Example 5 Except that the concentration of free nitric acid was adjusted to 1 to 4 mol with pure water,
As in Example 1, lead and tin P-phenolsulfonates were prepared using lead and tin having a grade of 4 nines or more. The content of radioactive isotopes of these lead and tin P-phenol sulfonates is 100 to 150 ppb, and the count number of α particles is 1.3 to 150 ppb.
It was confirmed to be 4.9 CPH / cm ² .

A plating solution was prepared in the same manner as in Example 1, and plating was performed in the same manner. The occurrence of a soft error was recognized in the memory prepared using this plated plate.

Comparative Example 6 Except that the concentration of free nitric acid was adjusted to 11 to 12 mol with pure water,
As in Example 1, lead and tin P-phenolsulfonates were prepared using lead and tin having a grade of 4 nines or more. The content of the radioactive isotope of these lead and tin P-phenol sulfonates is 150 to 210 ppb, and the count number of α particles is 1.7 to 210 ppb.
It was confirmed to be 5.0 CPH / cm ² .

A plating solution was prepared in the same manner as in Example 1, and plating was performed in the same manner. The occurrence of a soft error was recognized in the memory prepared using this plated plate.

(Effects of the Invention) As is clear from the above, the present invention dissolves in high purity nitric acid using lead and tin having a grade of 4 nines or more as follows.

(B) Adjust the concentration of free nitric acid to 5 to 10 molar with pure water.

(C) Perform anion exchange resin cleaning treatment.

(D) An aqueous solution containing lead aromatic sulfonate, tin tin aromatic sulfonate, and aromatic sulfonic acid with low generated α dose is used as the electrolytic solution.

20 ppb radioisotope content
The present invention provides a method for producing a high-purity plating solution for solder, wherein the count is less than 0.1 CPH / cm ² . By using a solder plating solution manufactured by the method of the present invention, a solder film can be formed which significantly suppresses the occurrence of memory errors.
It is possible to apply a solder alloy to parts of a semiconductor device such as a memory of a formula or more or various super LSIs, a substrate, and the like.

[Brief description of the drawings]

The drawing is a sectional view of an electrolytic cell containing the plating solution of the present invention. In the figure, 1 is a solder plate, 2 is a plating liquid, and 3 is a wiring board.

Continuation of the front page (56) References JP-A-59-227722 (JP, A) JP-A-62-6793 (JP, A) JP-B-49-16176 (JP, B1)

Claims (1)

(57) [Claims] 1. The following general formula: Wherein R ₁ and R ₂ may be the same or different and each is selected from the group consisting of a hydrogen atom, a hydroxyl group, a lower alkyl group and a sulfonic acid group, and the aromatic sulfonic acid represented by the formula A method for producing a solder plating solution containing a lead salt and a tin salt of an aromatic sulfonic acid, characterized by comprising the following steps, wherein the content of the radioisotope is less than 20 ppb, A method for producing a plating solution for solder having a count of less than 0.1 CPH / cm ² . Dissolve lead and / or tin with a purity of 99.99% or more in a high-purity nitric acid aqueous solution, adjust the free nitric acid concentration of the obtained solution to 5 to 10 mol, and purify the concentration-adjusted solution with an anion exchange resin. Reducing the content of U and Th in the solution, and reacting the purified solution with aromatic sulfonic acid,
It is neutralized and concentrated, and the deposited precipitate is separated and dried to obtain lead aromatic sulfonate and tin aromatic sulfonate. The thus obtained lead aromatic sulfonate and tin aromatic sulfonate are separated from the aromatic sulfonate. Dissolve in an aqueous solution containing sulfonic acid.