KR20090062618A - Method of preflux coating on pwb - Google Patents

Abstract

A method for coating the free flux composition for a printed circuit board is provided to improve heat resistance and solderability by maintaining the stability of free flux. A method for coating the free flux composition for a printed circuit board comprises the step of coating a free flux composition comprising a benzimidazole derivative represented by the formula 1, a low molecular weight fatty acid, and a high molecular weight fatty acid on a printed circuit board, wherein the concentration of the components is measured and the components are supplemented so as to maintain the concentration of the components to be constant.

Description

Coating method of preflux composition for printed circuit board {Method of preflux coating on PWB}

The present invention relates to a coating method of an aqueous surface treatment agent that can be applied to the surface of copper or copper alloy, and more particularly, pre-flux coating for preventing precipitation by maintaining a constant content of the components in the pre-flux coating by dipping. It is about a method.

Preflux is a surface treatment agent used to prevent corrosion and to maintain solderability so as to prevent oxidation of a circuit portion of a printed circuit board (PWB). Recently, the surface mounting method has been used as a method of bonding electronic components to PWB, and PWB has been exposed to high temperatures due to temporary fixing of needle parts, double-sided mounting of parts devices, or mixing needle parts and discrete parts. Therefore, the preflux for protecting the copper circuit on the printed circuit board must satisfy excellent heat resistance.

The preflux includes a resin-based preflux which covers the entire printed circuit board with a coating, and an alkylimidazole preflux which selectively chemically reacts with copper or a copper alloy. Resin-based preflux dissolves natural rosin, rosin ester, rosin-modified maleic acid resin, etc. in an organic solvent, and then applies it to the entire printed circuit board and dries to form a coating. Since such resin-based preflux uses an organic solvent, the solvent is in the atmosphere. It has a drawback that volatilizes in the inside and significantly impairs environmental and safety aspects.

Therefore, the water-soluble alkylimidazole-based preflux has been widely used because of its excellent working environment and stability. However, when the coating layer reacted with copper or a copper alloy of a printed circuit board due to poor heat resistance, oxygen and air in the air are exposed. Reactions deteriorate and oxidize the surfaces of copper and copper alloys, which impairs the action of postflux, resulting in poor solderability.

Accordingly, many surface treatment agents have been developed that use benzimidazole compounds as an active ingredient in place of alkylimidazole prefluxes having poor heat resistance. Korean Patent Publication No. 10-2005-0115652 describes a preflux for printed wiring boards having excellent heat resistance and solderability, and Korean Patent Publication No. 10-0668129 has a good heat resistance and a selective coating on copper and copper alloy. Possible benzimidazole-based preflux compositions are described.

However, the benzimidazole-based preflux as described above has a problem in that benzimidazole compounds are easily precipitated as crystals as the pH of the solution prepared in actual use increases or the treatment solution evaporates. Once crystallized solid benzimidazole-based compound, crystallized solid benzimidazole-based compound is difficult to re-dissolve the active ingredient once precipitated even if the organic acid is added or the evaporated water is added to maintain the proper pH of the treatment solution. There is this.

The present invention has been made to solve the above problems, and the precipitation of solid materials and metal compounds of the conventional benzimidazole-based printed circuit board preflux does not occur, while the stability of the preflux is continuously maintained, copper and copper alloy An object of the present invention is to provide a method of coating a preflux for a printed circuit board, in which the coating layer formed on the substrate has excellent heat resistance and solderability.

The preflux coating method for a printed circuit board according to the present invention, when coating a preflux composition comprising a benzimidazole derivative of the general formula (1) By replenishing, the concentration of the component is kept constant to prevent precipitation of the benzimidazole compound and is characterized by having excellent heat resistance and solderability.

[Formula 1]

(Wherein R 1 is an alkyl group having 1 to 10 carbon atoms, R 2 and R 3 are H or one or more carbon alkyl groups)

It is preferable that the initial content of the said preflux contains 0.05-1.5 g / L of benzimidazole derivatives, 0.01-10 g / L of lower fatty acids, and 0.03-0.1 g / L of higher fatty acids.

It is characterized in that the concentration of the ingredient is maintained in the range of 95 ~ 105% benzimidazole derivatives, 85 ~ 105% lower fatty acids, 80 ~ 100% higher than the initial manufacturing concentration. The pH is characterized by maintaining in the range of 2.2 ~ 3.2.

The coating of the preflux for the printed circuit board according to the present invention prevents the precipitation of the benzimidazole derivative, which is an active ingredient of the preflux during coating, and improves the stability of the solution so that the coating layer formed on copper and copper alloy has excellent heat resistance and soldering. It can hold a last name.

Referring to the configuration of the present invention in detail as follows.

Preflux used in the present invention contains a benzimidazole compound represented by the following formula (1) as an active ingredient.

[Formula 1]

(Wherein R 1 is an alkyl group having 1 to 10 carbon atoms, R 2 and R 3 are H or one or more carbon alkyl groups)

The benzimidazole compound is substituted with a pyridyl group which is one of the hetero rings at the 2-position of the benzimidazole ring. Representative examples of the benzimidazole-based compound are benzimidazole derivatives are 2-methylbenzimidazole, 2-propylbenzimidazole, 2-butylbenzimidazole, 2-pentylbenzimidazole, 2-hexylbenzimidazole, 2-heptylbenzimidazole, 2-octylbenzimidazole, 2-nonylbenzimidazole, 2- (4-benzyl) benzimidazole, 2- (3-phenylpropyl) benzimidazole, 2- (4-phenyl Butyl) benzimidazole, 2- (5-phenylpentyl) benzimidazole, 2- (6-phenylhexyl) benzimidazole, 2- (8-phenylheptyl) benzimidazole, 2- (8-phenyloctyl) Benzimidazole, 2- (9-phenylnonyl) benzimidazole, 2- (10-phenyldecyl) benzimidazole, 2-benzyl-4-methylbenzimidazole, 4-methyl-2-phenylethylbenzimidazole , 4-methyl-2- (3-phenylpropyl) benzimidazole, 4-methyl-2- (5-phenylpentyl) benzimidazole, 4-methyl-2- (6-phenylpentyl) benzimidazole, 4 -Methyl-2- (8-phenyloctyl) benzimidazole and the like and salts thereof.

It is preferable that content of the said benzimidazole type compound is 0.05-1.5 g / L. If the content of the benzimidazole derivative is less than 0.05 g / L, the active ingredient content is lowered, so that no coating is formed on the copper and copper alloy of the printed circuit board. When the content of the benzimidazole derivative is higher than 1.5 g / L, the coating content is high. Formed and acts as a deterrent to solderability.

Benzimidazole-based compounds, because seongyigi sparingly soluble in water in order to dissolve in water to form a solution made solubilize pre salt with an organic acid me preferred to dissolve in water, in particular an aliphatic carboxylic acid of the C ₄ or less, among the organic acid Soluble well in aqueous solution containing 0.01-10 g / L. If the content of organic acid is less than 0.01 g / L, precipitation of benzimidazole derivatives, an active ingredient of the preflux composition, occurs and the active ingredient is significantly reduced. It is formed thin so that it does not have the necessary heat resistance. In addition, higher fatty acids may be used among organic acids in order to coat the active ingredients of preflux on the surface of copper and copper alloy well.

Preferred examples of C ₄ include but are not limited to formic acid, acetic acid, propionic acid, butyric acid, glycolic acid, benzoic acid, picric acid, salicylic acid, hydroxyl, adipic acid, and the like.

The higher fatty acids are added together with the lower fatty acids to improve the solubility of the benzimidazole compound in the water. The content of higher fatty acids is preferably in the range of 0.03 to 0.1 g / L. If the content of the higher fatty acid is less than 0.03g / L coating is made non-uniform, in the case of more than 0.1g / L the coating film is thickened may cause roll marks or stains.

In addition, it may further include a metal compound and other additives to improve the heat resistance of the coating layer of copper and copper alloy.

In the practice of the present invention, after the copper or copper alloy surface is polished, degreased, soft etched, pickled, dried, etc. so as to form an excellent coating on the surface, the metal surface is immersed in the treatment liquid or coated with the treatment liquid. Or you can spray it.

It is also important to prepare preflux with excellent heat resistance, but when applied to the actual process, the components contained in the composition are not all consumed in the same ratio, so that each component plays a sufficient role in the preflux solution, and the balance thereof is balanced. Should be maintained. If the balance of the components of the preflux solution is not adjusted, defects such as difficulty in controlling the coating thickness or uncoated parts occur.

Benzimidazole derivatives, which constitute the main component of the coating film of copper and copper alloy, are solid components, and can be adjusted by finding out their contents through concentration analysis from time to time. The organic acid of C4 or less in the organic acid serves to dissolve the solid component and to adjust the pH of the composition. Therefore, it is necessary to manage the appropriate concentration in accordance with the change while grasping the thickness of the film. If the fatty acid is out of the control range, the thickness of the coating is not uniform, and the coating surface is stained, so the balance of concentration should be set and managed. In particular, the concentration of higher fatty acids should not simply be maintained within a certain numerical range, but should be maintained in balance with the content of active ingredients and the content of organic acids below C4.

It is preferable to maintain and control the concentration of the preflux-containing component in the range of 95 to 105% of benzimidazole derivatives, 85 to 105% of lower fatty acids, and 80 to 100% of higher fatty acids relative to the initial concentration. When the concentration of the benzimidazole derivative is less than 95% of the initial concentration, the content of the active ingredient is low, so that almost no coating is formed on the copper and copper alloy of the printed circuit board, and there is a problem of deteriorating solderability, In this case, the coating film is formed high, which acts as a deterrent to solderability. If the lower fatty acid concentration is less than 85% of the initial concentration, the benzimidazole derivative, an active ingredient of the preflux solution, is precipitated and the content of the active ingredient in the solution is significantly reduced. Formed thin, there is a problem that does not have heat resistance. If the concentration of higher fatty acid is less than 80% of the initial concentration, the surface of copper and copper alloy coating film of the printed circuit board is uneven and solderability is lowered. If the concentration of higher organic acid is more than 100% of the initial concentration of the printed circuit board Staining and foreign substances are generated in the copper and copper alloy coating film, and the problem of deterioration of solderability occurs as foreign substances continue to accumulate on the roll.

In addition, the coating state upon coating of copper and copper alloy is affected by the pH of the preflux solution. If the pH of the preplus solution increases during the same deposition time, the coating becomes thicker. The pH of the preplus solution according to the present invention is preferably in the range of 2.2 to 3.2 and requires constant control of acidity during the coating operation. If the pH of the preflux solution is less than 2.2, the coating of copper and copper alloy will not be formed, and if the pH is above 3.2, the film thickness will be high, causing problems in solderability, and benzimi in the preflux solution. The dazole compound is precipitated.

Hereinafter, the present invention will be described in more detail.

EXAMPLE

1 g / L of 2-pyridylbenzimidazole, 10 g / L acetic acid, 0.05 g / L of higher fatty acids and 0.02 g / L of copper chloride, the remainder is added water and the pH is adjusted to 2.7 using ammonia water to preflux Was prepared. After immersing the copper specimen in the liquid tank for 40 seconds while maintaining the temperature of the prepared preflux at 35 ° C, the specimen was washed with water and dried to prepare a sample.

The concentration of the preflux solution of the liquid bath was measured by using an HPLC (High performance liquid chromatography) device, and the content of the coating film was observed according to the amount of change of the component.

Table 1 shows the state of the coating according to the change of the lower fatty acid content in the liquid tank. Insufficient low organic acid components were added together when replenishing the liquid and circulated for 20 minutes to mix well. When the ratio of the low organic acid component is 11.5g / L, 11g / L, the content is 115% and 110% (HPLC analysis result). The state is uncoated and partially coated, and the ratio of the shortage factor is 10.5g / L, At 10g / L and 9g / L, the content is 105%, 100%, 90% (HPLC analysis result). The condition is good. At 8g / L, the content is 80% (HPLC analysis result). Occurred

Table 1

Based on content ratio 1L content(%) pH Film condition 11.5g / L 115 2.7 Uncoated 11g / L 110 2.7 Partial coating 10.5g / L 105 2.7 usually 10 g / L 100 2.7 Good 9g / L 90 2.7 usually 8g / L 80 2.7 Foreign substance occurrence

Table 2 shows the state of the coating according to the change in the content of higher fatty acids in the bath.The concentrations are 110% and 105% (HPLC analysis results) when the contents of premium fatty acids are 0.055g / L and 0.0525g / L. The occurrence was so severe that the coating was not normal. When the content of higher fatty acids was 0.05g / L, 0.04g / L concentration was 100%, 80% (HPLC analysis results), the condition was good, no staining.

[Table 2]

Based on content ratio 1L content(%) pH Film condition 0.055g / L 110 2.7 Severe staining 0.0525 g / L 105 2.7 Spot 0.05g / L 100 2.7 Good 0.04 g / L 80 2.7 Good

Table 3 shows the state of the coating according to the change in the content of 2-pyridylbenzimidazole component in the bath. Insufficient 2-pyridylbenzimidazole component was added and circulated for 20 minutes to mix well. When the concentration of 2-pyridylbenzimidazole component is 1.1 g / L and 1.05 g / L, the content is 110% and 105% (HPLC analysis). , The content is 100% and 95% (HPLC analysis result) at 0.95g / L, and the condition is good, and the coating film thickness is thin when the content is 90% (HPLC analysis) at 0.9g / L. there was.

Table 3

Based on content ratio 1L content(%) pH Film condition 1.1 g / L 110 2.7 usually 1.05 g / L 105 2.7 usually 1.0 g / L 100 2.7 Good 0.95 g / L 95 2.7 Good 0.9 g / L 90 2.7 Thinner

Claims (4)

When coating a preflux composition comprising a benzimidazole derivative of Formula 1, a lower fatty acid and a higher fatty acid on a printed circuit board, the concentration of the component is measured and the concentration of the component is kept constant by replenishing the component A preflux coating method for a printed circuit board, characterized by preventing precipitation of an imidazole compound and having excellent heat resistance and solderability. [Formula 1]

(Wherein R 1 is an alkyl group having 1 to 10 carbon atoms, R 2 and R 3 are H or one or more carbon alkyl groups) The method of claim 1, A preflux coating method for a printed circuit board, wherein the initial content of the preflux is 0.05 to 1.5 g / L of benzimidazole derivative, 0.01 to 10 g / L of low fatty acid, and 0.03 to 0.1 g / L of higher fatty acid. The method of claim 1, Method of coating a printed circuit board, characterized in that the concentration of the component is maintained in the range of 95 ~ 105% benzimidazole derivatives, 85 ~ 105% lower fatty acids, 80 ~ 100% higher than the initial manufacturing concentration The method of claim 1 Coating method of the printed circuit board, characterized in that to maintain the pH of the preflux in the range of 2.2 ~ 3.2.