KR20130035677A - Solution for electroless plating and method of manufacturing a printed circuit board using the same - Google Patents

Abstract

PURPOSE: An electroless nickel plating solution and a printed circuit board manufacturing method using the same are provided to prevent a non-plating portion and a deviation in plating thickness when plating a printed circuit board with an electroless nickel plating solution. CONSTITUTION: A method for manufacturing a printed circuit board using an electroless nickel plating solution comprises a step of preparing a printed circuit board formed with a solder resist layer having an opening and a step of electroless plating nickel on the printed circuit board using an electroless nickel plating solution containing 0.05-3.0g per 1L. [Reference numerals] (AA) Preparing a printed circuit board formed with a solder resist layer; (BB) Forming a nickel plating layer on an opening of the solder resist layer; (CC) Forming a metal plating layer on the nickel plating layer; (DD) Printed circuit board;

Description

Electroless nickel plating solution and method for manufacturing a printed circuit board using the same {Solution for electroless plating and method of manufacturing a printed circuit board using the same}

The present invention relates to a nickel plating solution and a method of manufacturing a printed circuit board using the same, and more particularly, to an electroless nickel plating solution and a method of manufacturing a printed circuit board using the same for improving unplated and plating thickness variation.

Plating methods include electroplating and electroless plating, and are widely used for ultra-high integrated circuit processes by providing process simplicity, process stability, low cost, short process time, low deposition temperature, high purity thin film and low resistivity. have.

Electroless plating is a plating method using the principle that the metal is precipitated by spontaneous redox reaction of materials present in the solution without applying electricity from the outside. Electroless plating is widely used for printed circuit boards.

Since the electroless plating method is made in an aqueous solution, the process continuity with the subsequent electrolytic plating is excellent, and since the penetration of the aqueous solution into the pattern is easy, it is possible to form a metal layer having uniform and excellent properties without the problem of step coverage.

Recently, in accordance with the trend of miniaturization and high functionalization of electronic products, high integration of printed circuit boards is required, and as a result, the size of solder resist opening (SRO) of the printed circuit board is miniaturized.

As the size of the solder resist opening (SRO) is reduced to 80 μm or less, electroless nickel plating of electroless nickel immersion gold (ENIG) or electroless nickel nickel electroless palladium immersion gold (ENEPIG) occurs.

In order to solve the above problem, plasma treatment is performed before plating, but unplating problems such as nickel skip (Ni-skip) defects continue to occur according to an increase in process cost and treatment conditions.

An object of the present invention is to provide an electroless nickel plating solution capable of improving unplated and plating thickness variation in electroless nickel plating and a method of manufacturing a printed circuit board using the same.

The electroless nickel plating solution, which is an embodiment of the present invention, may contain 0.05 to 3.0 grams of surfactant in 1 liter.

The surfactant is an anionic surfactant such as sodium lauryl sulfate, ammonium dodecyl sulfate, sodium lauryl ether sulfate, lauryl sarcosinate, sodium alkyl isocionate, sodium dodecyl tetraethoxyphosphate, lauryl sarcosinate And it may be any one or more selected from the group consisting of polyoxyethylene alkyl ether, polyethylene glycol and the like.

The electroless nickel plating solution may further include 20 to 36 grams of nickel sulfate, 5 to 10 grams of sodium citrate, 40 to 50 grams of ammonium sulfate, 10 to 20 grams of sodium hypophosphite, and 0.5 to 1 grams of thiourea in 1 liter. .

According to another aspect of the present invention, there is provided a method of manufacturing a printed circuit board, comprising: preparing a printed circuit board having a solder resist layer having an opening; And electroless plating nickel on the printed circuit board using an electroless nickel plating solution containing 0.05 to 3.0 grams of a surfactant in 1 liter.

The electroless nickel plating solution may further include 20 to 36 grams of nickel sulfate, 5 to 10 grams of sodium citrate, 40 to 50 grams of ammonium sulfate, 10 to 20 grams of sodium hypophosphite, and 0.5 to 1 grams of thiourea in 1 liter. .

After the nickel plating step may further comprise a gold plating step.

The diameter of the opening may be 80 μm or less.

When nickel is plated on a printed circuit board using the electroless nickel plating solution according to the present invention, unplating and plating thickness variation can be improved.

1A is a schematic diagram of a printed circuit board used in one embodiment of the present invention.
1B is a schematic diagram of a printed circuit board on which a nickel plating layer is formed.
1C is a schematic diagram of a printed circuit board on which a gold plating layer is formed.
2 is a flowchart schematically showing a procedure of a method of manufacturing a printed circuit board according to one embodiment of the present invention.
3 is an optical micrograph of a printed circuit board according to a comparative example.
4 (a) to 4 (b) are optical micrographs of the printed circuit boards according to Examples 1 to 4;
5A is a cross-sectional photograph of a printed circuit board according to a comparative example.
5B is a cross-sectional photograph of a printed circuit board according to the first embodiment.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

The embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below.

Furthermore, embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art.

The shape and the size of the elements in the drawings may be exaggerated for clarity and the same elements are denoted by the same reference numerals in the drawings.

One embodiment of the present invention may be an electroless nickel plating solution added with a surfactant.

In general, the electroless plating solution may have a metal salt containing a metal ion to be plated and a reducing agent that reduces metal ions and precipitates them.

Complexing agent for stably dissolving metal ions, pH adjusting agent for providing hydrogen ions necessary for oxidation reaction of reducing agent, catalyst for redox reaction well, accelerator for increasing redox reaction, abnormality of metal Stabilizers to prevent precipitation can be added.

The electroless nickel plating solution according to the present embodiment further contains 20 to 36 grams of nickel sulfate, 5 to 10 grams of sodium citrate, 40 to 50 grams of ammonium sulfate, 10 to 20 grams of sodium hypophosphite, and 0.5 to 1 grams of thiourea in 1 liter of the plating solution. It may include.

Nickel sulfate is a metal salt containing nickel, and may serve as a nickel ion source for supplying nickel ions to the plating liquid.

Sodium hypophosphite may serve as a reducing agent to reduce nickel ions to nickel metal to form a nickel plating layer on the surface of the substrate.

Sodium citrate and ammonium sulfate may serve to adjust the pH of the plating solution. This is because the redox reaction of the electroless plating is greatly influenced by the pH of the plating liquid.

Thiourea may play a role of increasing the speed of the redox reaction to reduce the size of the precipitated nickel particles and increase the gloss of the nickel plating layer.

In the present embodiment, 1 liter of the electroless nickel plating solution may contain 0.05 to 3.0 grams of surfactant.

If the content of the surfactant is less than 0.05 grams, the effect of improving the wettability at the interface of the plated body of the plating liquid is insignificant. If the content of the surfactant is more than 3.0 grams, the plating workability may deteriorate due to the deposition of carbon in the plating film or the generation of bubbles. have.

A surfactant is dissolved in a liquid and adsorbed to an interface, thereby significantly reducing the energy of the interface, thereby acting as wetting, emulsification, dispersing, foaming, solubilization, and washing. The substance that says.

Surfactants are ionic surfactants that dissociate in water to act as surfactants and nonionic surfactants that are ionically neutral without dissociation in water. Ionic surfactants are again anionic, cationic, amphoteric surfactants.

Anionic surfactants include carboxylate (-COOH), sulfonate (-SO ₃ H), sulfate ester salt (-OSO ₃ H), phosphate ester salt, phosphonate, alkylbenzenesulfonate, a-olefin sulfonate , Alkyl sulfate ester salts, alkyl ether sulfate ester salts, alkanesulfonic acid salts, and the like may be used. As the cationic surfactant, amine salts, quaternary ammonium salts, sulfonium salts, phosphonium salts, and the like may be used. As the amphoteric surfactant, an amino acid type cation or betaine type can be used.

Nonionic surfactants include monoglycerine, polyglycol ester, sorbitan ester, fat sugar ester, alkanolamide, polyethylene glycol and sorbitol, such as -OH group, -COO- group, -CO.NH- group, and -O- group. Polyhydric alcohol derivatives such as saccharin and polyhydroxy compounds can be used.

In the present invention, the surfactant is added to the electroless nickel plating solution, thereby lowering the surface tension of the plating solution to improve the filling performance of the plating solution.

In other words, the contact with the plating liquid may not be smooth in narrow portions such as bends, through holes, and via holes. By adding a surfactant to the plating liquid, the plating liquid can be smoothly wetted at such a portion, thereby increasing the plating reaction force and the hydrogen bubbles. Defoaming can suppress the occurrence of unplated sites.

In this embodiment, the surfactant is sodium lauryl sulfate, ammonium dodecyl sulfate, sodium lauryl ether sulfate, lauryl sarcosinate, sodium alkyl isionate, sodium dodecyl tetraethoxyphosphate, lauryl sarcosinate At least one selected from the group consisting of anionic surfactants and nonionic surfactants such as polyoxyethylene alkyl ether and polyethylene glycol.

Hereinafter, the manufacturing method of the printed circuit board which is another embodiment of this invention is demonstrated.

1 and 2, a method of manufacturing a printed circuit board according to the present embodiment includes preparing a printed circuit board on which a solder resist layer 30 having an opening 31 (SRO, Solder Resist Opening) is formed; And electroless plating nickel on the printed circuit board using an electroless nickel plating solution containing 0.05 to 3.0 grams of a surfactant in 1 liter.

The insulating layer 10 serves to structurally support the printed circuit board and also to insulate the conductors formed in the substrate.

The internal circuit 22, the via conductor 21, and the conductor pad 20 may be formed in the printed circuit board.

The internal circuit 22 may be located inside the insulating layer of the circuit pattern, and may be formed of a plurality of layers. When the internal circuit 22 is formed of a plurality of layers, the internal circuit 22 formed in another layer may be connected by the via conductor 21.

The conductor pad 20 may be positioned outside the insulating layer 10 and used to form an electrode on the substrate.

In order to expose the conductive pads 20 formed on the surface of the printed circuit board to the outside, a portion of the solder resist sheet layer may be removed by etching to form an opening 31 penetrating the solder resist layer 30. . This is referred to as solder resist layer opening 31 or SRO (Solder Resist Opening) 31.

First, the printed circuit board may be washed to remove organic contaminants such as oil.

Next, by performing soft etching to form fine roughness on the surface, the adhesion with the nickel plating layer formed later can be increased.

Next, the surface may be activated by performing a pre-dip process.

Next, a substituted palladium catalyst of Cl type or S04 type can be formed. Through such catalysis, plating can be progressed by spontaneous redox reaction on the non-conductive substrate and nuclei can be initiated to initiate a reduction reaction in the plating liquid.

Next, electroless nickel plating can be performed.

One liter of the electroless nickel plating solution may contain 0.05 to 3.0 grams of surfactant.

In addition, the electroless nickel plating solution may further include 20 to 36 grams of nickel sulfate, 5 to 10 grams of sodium citrate, 40 to 50 grams of ammonium sulfate, 10 to 20 grams of sodium hypophosphite, and 0.5 to 1 grams of thiourea in 1 liter. have.

Next, palladium (Pd) plating and electroless substitution type gold (Au) plating may be performed to form a thin gold plating layer.

Next, electroless thickness gold (Au) plating may be performed to form a thick gold (Au) plating layer.

By the above process, a printed circuit board having nickel and gold plating layers formed thereon may be manufactured.

The printed circuit board may have an SRO diameter A of about 80 μm or less.

In the case of a printed circuit board having an average SRO diameter (A) of about 85 to 120 um, pretreatment is performed by plasma prior to electroless nickel plating. However, unplated portions continue to occur.

In addition, there is a problem that the manufacturing cost is increased due to the addition of the plasma process.

When the SRO diameter is 80 μm or less, since the hole is narrow enough that the plating liquid cannot easily penetrate, the contact between the plating liquid and the plated body cannot be made smoothly, and thus a plating layer may not be formed.

In order to solve this problem, the plating solution of the present invention is to include 0.05 ~ 3.0 grams of surfactant in 1 liter.

By adding the surfactant, the interfacial tension of the plating liquid can be reduced, and the wettability of the plating liquid can be improved on the surface of the plated body, thereby allowing the plating liquid to penetrate more easily even in a narrow space.

Therefore, since the contact between the surface of the plated body and the plating liquid can be made better, it is possible to prevent an unplated portion from which the plating layer is not formed.

Due to the increase in wettability of the plating liquid, contact between the plating body and the plating liquid may be smoothed.

Therefore, contact between the plated body or the already formed plating layer and the plating liquid may occur more frequently than otherwise, whereby the plating layer may be formed thicker. In addition, the plating layer may be formed more uniformly.

Other matters concerning the composition of the plating liquid are the same as described above.

<Examples>

Hereinafter, the present invention will be described in detail with reference to specific examples.

First, the printed circuit board was prepared to have a solder resist layer opening (SRO) having a size of 80 um, washed and soft etched to remove foreign substances present on the surface.

Next, a pre dip process was performed to activate the surface of the printed circuit board.

Next, the nickel plating layer was formed on the surface of the printed circuit board by the electroless plating method.

The electroless nickel plating solution was prepared as follows. That is, one liter of the plating solution contains 25 grams of nickel sulfate, 8 grams of sodium citrate, 45 grams of ammonium sulfate, 15 grams of sodium hypophosphite, and 1 gram of thiourea. An electroless nickel plating solution was prepared while changing the active agent.

Example 1 added 0.05 grams of sodium lauryl sulfate as a surfactant.

Example 2 added 0.05 grams of sodium lauryl ether sulfate as a surfactant.

Example 3 added 0.05 grams of ammonium dodecyl sulfate as a surfactant.

Example 4 added 0.96 grams of polyoxyalkylene alkyl ether as surfactant.

Electroless plating was performed while maintaining the temperature of the electroless nickel plating solution at 80 ° C. to form a nickel plating layer on the SRO of the printed circuit board.

Next, a palladium (Pd) plating layer was formed on the nickel plating layer by electroless plating, and a gold (Au) plating layer was formed on the palladium plating layer by electroless plating again.

The comparative example was prepared by the same method as the example, except that no surfactant was added to the electroless nickel plating solution.

About the comparative example and the Example, the plating rate, the palladium liquid contamination, the unplated, the wire bonding test, and the ball pull test were implemented, and the result is shown in Table 1.

The plating rate was 30 minutes x 30 mm sized copper clad laminate (CCL, Copper Clad Laminate) to the electroless plating for 25 minutes, the value obtained by dividing the thickness of the formed plating layer by the required time as the plating rate.

Unplating was confirmed by observation with an optical microscope, and the results are shown in FIG.

When any unplated part generate | occur | produced, the case where defect (NG) and an unplated part do not generate | occur | produce at all was judged as good (OK).

A wire bonding test and a ball pull test were conducted.

The wire bonding test is a test of wire bonding to a plated portion of a printed circuit board, and a test of the ability to withstand the pulled wire while pulling it. This test checks for destruction.

When working in the ENEPIG process, electroless plating can occur with the surfactant contaminated with palladium liquid. In preparation for such a case, an evaluation was made on the use of a surfactant contaminated with palladium liquid.

In other words, the surfactant was contaminated with a palladium solution, nickel and gold plating were performed, and then a wire bonding test and a ball pull test were conducted to evaluate reliability.

In addition, in order to compare the thickness and uniformity of the nickel plating layer, electroless nickel plating was performed on the copper-clad laminate to observe the thickness and shape of the plating layer, and a cross-sectional photograph thereof is shown in FIG. 5.

Unplated site occurrence Plating rate
(Μm / min) Wirebonding test Ball pool test Reliability test after palladium liquid contamination Comparative example NG 0.18 OK OK - Example 1 OK 0.18 OK OK OK Example 2 OK 0.18 OK OK OK Example 3 OK 0.18 OK OK OK Example 4 OK 0.18 OK OK OK

Referring to FIGS. 3 and 4, in the case of the comparative example, an unplated portion B was generated, but in Examples 1 to 4, all of the unplated portions did not occur.

The effective action of the surfactant was to lower the surface energy of the plating liquid, so that the electroless nickel plating liquid could effectively penetrate into the narrow space of the plated body, thereby smoothly contacting the surface of the plated body with the electroless nickel plating liquid. Inferred to be due to progress.

Referring to Table 1, the plating rate was equivalent to 0.18 um / min in both Comparative Examples and Examples.

It can be inferred that Comparative Examples and Examples do not have much difference in plating speed, so there will be little difference in productivity.

Both the comparative examples and the examples showed good results in both the wire bonding test and the ball pull test.

Even when the electroless nickel plating solution of the present invention is used, it can be confirmed that there is no problem in reliability.

In the case of using a surfactant contaminated with palladium liquid, all of the reliability test results proved good.

In light of this, it is expected that the surfactant of the present invention can be applied to the ENEPIG process.

Referring to FIG. 5, in the comparative example shown in FIG. 5A, the thickness of the plating layer is 2.81 μm, and the nickel plating layer may not be uniformly formed.

On the other hand, in the case of Example 1 shown in Figure 5 (b) it can be seen that the thickness of the plating layer is 4.21um, and the nickel plating layer is formed uniformly.

That is, it can be inferred that the nickel plated layer is thicker and more uniformly formed in the Example than the Comparative Example by the surfactant added to the plating liquid to improve the wettability between the plating target and the plating liquid.

The terms used in the present invention are intended to illustrate specific embodiments and are not intended to limit the invention. The singular presentation should be understood to include plural meanings, unless the context clearly indicates otherwise.

The terms 'comprise' or 'have', etc., mean that there is a feature, number, step, operation, component, or combination thereof described on the specification, but not intended to exclude it.

The present invention is not limited by the above-described embodiments and the accompanying drawings, but is intended to be limited only by the appended claims.

It will be apparent to those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. something to do.

10: Insulation layer
20: conductor pad
21: via conductor
22: internal circuit
30: solder resist layer
40: nickel plating layer
50: gold plated layer
A: solder resist opening
B: unplated site

Claims (7)

An electroless nickel plating solution containing 0.05 to 3.0 grams of surfactant in 1 liter.
The method of claim 1,
The surfactant is an anionic surfactant such as sodium lauryl sulfate, ammonium dodecyl sulfate, sodium lauryl ether sulfate, lauryl sarcosinate, sodium alkyl isocionate, sodium dodecyl tetraethoxyphosphate, lauryl sarcosinate And a nonionic surfactant such as polyoxyethylene alkyl ether and polyethylene glycol.
The method of claim 1,
An electroless nickel plating solution further comprising 20-36 grams of nickel sulfate, 5-10 grams of sodium citrate, 40-50 grams of ammonium sulfate, 10-20 grams of sodium hypophosphite, and 0.5-1 grams of thiourea in 1 liter.
Preparing a printed circuit board having a solder resist layer having an opening; And
Electroless plating nickel on the printed circuit board using an electroless nickel plating solution containing 0.05 to 3.0 grams of surfactant in 1 liter;
Method of manufacturing a printed circuit board comprising a.
5. The method of claim 4,
The electroless nickel plating solution further includes 20 to 36 grams of nickel sulfate, 5 to 10 grams of sodium citrate, 40 to 50 grams of ammonium sulfate, 10 to 20 grams of sodium hypophosphite and 0.5 to 1 grams of thiourea in 1 liter. Method of manufacturing a substrate.
5. The method of claim 4,
The method of manufacturing a printed circuit board further comprising a gold plating step after the nickel plating step.
5. The method of claim 4,
The diameter of the opening is 80um or less manufacturing method of a printed circuit board.

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