JPS6242035B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a stripping solution for tin or tin alloys on metallic copper, and more particularly to a stripping solution for tin or tin alloys on printed wiring boards made of metallic copper.

In the production of printed wiring boards, there has recently been an increasing demand for so-called copper through-hole wiring boards. There are three methods for manufacturing this copper through-hole wiring board: hole filling method, tenting method, and metal resist peeling method. The hole filling method is a method in which ink is filled into the holes of a copper through-hole board before circuit formation, and circuits on the surface are formed through an etching ink printing process and an etching ink removal process. In this method, a dry film is applied to both sides of a copper through-hole board, the circuit is developed using a photographic method, and the circuit is formed by etching and removing the dry film. With these two methods, the defective rate of the product increases as the number of holes increases and the circuit becomes finer, so the metal resist stripping method has been attracting attention for manufacturing copper through-hole wiring boards with fine circuits. This third method is a method in which, for example, a solder through-hole wiring board is made by a conventional solder plating method, and then only the solder on the surface is removed to make a copper through-hole wiring board. As a metal resist for etching copper, any resist may be used as long as it can withstand the etching agent, but tin or a tin alloy (solder) is generally preferred industrially.

The present invention relates to a stripping solution for tin or tin alloy on metallic copper in such a metal resist stripping method.

The main properties required of a tin or tin alloy stripping agent for copper through-hole production are as follows: 1. To dissolve as much tin or tin alloy as possible per unit volume of stripping solution; 2. Generally, when tin is dissolved, if an oxidizing acid or oxidizing agent is present, the divalent tin ions are oxidized and a white precipitate of metastannic acid as shown in the following formula is formed, but this white precipitate is formed on top of the copper. Sn ²⁺ + 1/2O ₂ + 2H 2 must have a liquid composition that makes it difficult to form metastannic acid precipitates, as it may redeposit or adhere to containers, causing various problems on an industrial _scale. O →H ₂ SnO ₃ ↓＋2H ⁺ 3. There is little dissolution of the underlying copper. 4. The resulting copper surface is completely clean and shiny.

The present invention provides a tin or tin alloy stripping solution that meets these objectives.

Patents that prevent metastannic acid from precipitating or redepositing onto copper include the following: 1. Stabilization of tin ions by fluorine ions or fluorine-containing complex ions (Japanese Patent Application Laid-Open No. 1989-1999) -8716), 2. Stabilization of tin ions by titanium ions, chromium ions, antimony ions, vanadium ions, etc. (Japanese Patent Application Laid-Open No. 1983-28425), 3. Stabilization of tin ions by iron ions (Japanese Patent Application Laid-Open No. 1983-28425).
-135840), 4 Prevention of dissolution of copper and prevention of redeposition of tin by the addition of a copper inhibitor containing a nitrogen atom in the form of =NH or ≡N by the present inventors (Japanese Patent Application Laid-Open No. 1983-197-
164984).

However, in method 1), many of the fluorine compounds used are highly toxic and have an adverse effect on the human body, and the fluorine ions contained in wastewater are difficult to treat, resulting in various difficulties in wastewater treatment. This is an industrial problem.
Method 2) has the disadvantage that many metal compounds containing titanium ions are toxic substances, and method 3) has the disadvantage that the iron ions present also accelerate the decomposition of the oxidizing agent. However, in the presence of inorganic acids, metal copper is severely etched, which is a disadvantage. In any of the methods 1) to 4), if the tin concentration in the liquid exceeds 30 g/l, a white precipitate will occur, making it difficult to control the quality of the liquid, and industrially it is difficult to further dissolve tin ions. The reality is that it is difficult to raise it.

However, according to the present invention, tartaric acid, citric acid,
By using an organic compound having the ability to form a complex with tin ions selected from the group consisting of gluconic acid and salts thereof as a component of the stripping solution,
It is possible to stabilize the complex ions and improve the tin dissolving ability of the stripping solution.

According to the invention, no precipitation occurs up to a tin content of 40-50 g/l. Even if the tin content exceeds this value, it will take 2 days (48 hours) to 15 days for precipitation to occur after dissolution, and there is no problem in industrially handling it as if no precipitation occurs.

In the present invention, organic compounds that have the ability to form a complex and stabilize tin ions include tartaric acid, tartrates such as sodium salt, potassium salt, Rothsiel's salt, citric acid, citric acid salts such as diammonium citrate, and gluconic acid. , gluconate salts such as sodium salt and potassium salt. It is thought that these complexing agents and tin ions form, for example, a complex as shown in the following formula in the treatment solution, which stabilizes the tin ions and promotes the dissolution of tin.

As the inorganic acid used in the stripping solution of the present invention, nitric acid and hydrochloric acid are industrially practical, and the amount thereof is 1 to 5.
Mol/l is preferred. By adding a suitable organic acid in addition to these inorganic acids, the copper surface can be kept shiny and clean. Suitable low-molecular organic acids having 2 or 3 carbon atoms include acetic acid, propionic acid, glycolic acid, lactic acid, etc., and the amount of each added is 1 type or 2 or more types in total. ~3 mol/l is desirable. Further, as the peroxide, any ordinary oxidizing agent in the technical field can be used, but it is easiest to use commercially available 35% hydrogen peroxide, and the amount is 5 to 5%.
50g/l is desirable.

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 An aqueous solution consisting of 300 g/l of 35% hydrochloric acid, 200 g/l of acetic acid, 50 g/l of 70% glycolic acid, and 30 g/l of 35% hydrogen peroxide with 70 g/l of tartaric acid added and one without tartaric acid. 40 g/l of tin was dissolved in the solution. Both of these solutions were placed in a constant temperature bath at 40°C and the formation of precipitates was observed.The samples without tartaric acid started to form precipitates after 10 minutes, but the samples with tartaric acid did not contain any precipitation even after 48 hours. No precipitate was formed.

Example 2 67.5% nitric acid 300g/l, glycolic acid 200g/l,
Propionic acid 100g/l, 35% hydrogen peroxide 20g/l
A tin-lead alloy (60 g of tin) was added to an aqueous solution of
(containing) 100g/l was dissolved. 40% of both liquids
When we observed the precipitation of precipitate by placing it in a constant temperature bath at ℃, we found that the sample without citric acid precipitated almost instantaneously, but the sample with citric acid did not precipitate slightly until 5 days (120 hours) later. was generated.

As can be seen from the above examples, a stripping solution containing an organic compound that has the ability to form a complex with tin ions does not form a precipitate at all, or takes a considerable amount of time to form a precipitate, compared to a stripping solution containing no additive. Therefore, it is clear that the organic compound contributes to the stabilization of the stripping solution.

Furthermore, if a copper inhibitor such as benzotriazole is added to the stripping solution, etching of the underlying copper can be suppressed, resulting in a composition most suitable as a stripping agent for tin or tin alloys for producing copper through-holes. .

Claims (1)

[Claims] 1 A system consisting of an inorganic acid, a low-molecular-weight organic acid with 2 or 3 carbon atoms, and a peroxide is given the ability to form a complex with tin ions selected from the group consisting of tartaric acid, citric acid, gluconic acid, and their salts. A stripping solution for tin or tin alloys on metallic copper, characterized in that it contains an organic compound containing: