TWI862835B - Intermittent plating method - Google Patents

Abstract

The present invention provides a technology that can improve the filling property of micropores during intermittent electroplating. An intermittent electroplating method is performed on a plated object having micropores, and the intermittent electroplating method includes using a plating solution containing multivalent metal ions.

Description

Intermittent plating method

Field of the invention The present invention relates to an intermittent electroplating method, etc.

Background technology In recent years, with the high functionality and high speed of electronic equipment, high density is also required in printed wiring boards. In order to achieve high density of printed wiring boards, the build-up process is indispensable, among which via filling is an important plating technology. In this build-up process, in the past, a uniform plating was applied to non-through vias, and then an insulating resin or conductive paste was filled to form a circuit. However, this method cannot form vias on vias, which will deprive the freedom of circuit design. Therefore, the method adopted in recent years is to use plating to fill the vias in the through holes and stack the wiring layers.

On the other hand, from the perspective of increasing the efficiency of the electroplating process, especially from the perspective of efficiently electroplating long strips of the article to be plated, intermittent electroplating is sometimes used. The intermittent plating method is performed using a plurality of plating tanks in a reel-to-reel process line such as shown in FIG. 1 .

Prior art documents Patent documents Patent document 1: Japanese Patent Publication No. 2011-058093

Summary of the invention Problems to be solved by the invention During research, the inventors of this case found that when intermittent electroplating is performed on a substrate having micro-holes such as through holes, the degree of metal precipitation (filling property) in the micro-holes will be significantly reduced.

Therefore, the subject of the present invention is to provide a technology that can improve the filling property of micro-holes during intermittent electroplating.

Means for solving the problem The inventors of this case found that the reduction of filling property during intermittent electroplating is caused by a phenomenon unique to the intermittent plating method, that is, the plating liquid slightly attached to the coated material discharged from the plating tank and the coated material supplied to the plating tank (in the case of the embodiment shown in FIG. 1, it is the plating liquid slightly leaking from the side of the plating tank) resulting in the problem of low current density. In addition, the inventors of this case found that the above-mentioned problem can be solved by using a plating liquid containing polyvalent metal ions. The inventors of this case further conducted research based on these insights and completed the present invention.

That is, the present invention includes the following aspects.

Item 1. An intermittent electroplating method is performed on a substrate having micropores, the intermittent electroplating method comprising using a plating solution containing polyvalent metal ions.

Item 2. The intermittent electroplating method of Item 1, wherein the valence of the aforementioned polyvalent metal ions is 3 or more.

Item 3. An intermittent plating method as in Item 1 or 2, wherein the aforementioned polyvalent metal ions are at least one selected from the group consisting of Fe ³⁺ , V ⁵⁺ , Mn ⁷⁺ , Mo ⁶⁺ , W ⁶⁺ , Ce ⁴⁺ , Cr ³⁺ , Cr ⁶⁺ , Ti ⁴⁺ , Sn ⁴⁺ and Co ³⁺ .

Item 4. The intermittent plating method of any one of items 1 to 3, wherein the aforementioned polyvalent metal ions are at least one selected from the group consisting of Fe ³⁺ and V ⁵⁺ .

Item 5. An intermittent electroplating method as in any one of items 1 to 4, wherein a long strip of the object to be coated is continuously supplied to a coating tank on an operation line, and the object to be coated is repeatedly discharged from the coating tank and supplied to the coating tank.

Item 6. The intermittent electroplating method of Item 5, wherein the object to be plated passes through a plurality of plating tanks.

Item 7. An intermittent electroplating method as described in Item 5 or 6, wherein the aforementioned discharge and the aforementioned supply are carried out on the side of the plating tank.

Item 8. An intermittent electroplating method as described in any one of Items 5 to 7, which is carried out on a reel-to-reel operation line.

Item 9. An intermittent electroplating method as described in any one of Items 1 to 8, wherein the aforementioned micro-holes are micro-conducting holes.

Item 10. An intermittent electroplating method as described in any one of Items 1 to 9, wherein the metal deposited onto the plated object comprises at least one selected from the group consisting of Cu, Ni and Sn.

Item 11. The intermittent electroplating method according to any one of items 1 to 10, wherein the plating solution further contains an additive for via filling.

Item 12. A plating solution for use in a discontinuous electroplating method as described in any one of Items 1 to 11, wherein the plating solution contains polyvalent metal ions.

Item 13. An intermittent electroplating method is performed on a substrate having micropores; The method includes using a copper plating solution containing polyvalent metal ions and copper ions; And includes: The long strip of substrate is continuously supplied to the plating tank on the operation line, and the substrate is repeatedly discharged from the plating tank and supplied to the plating tank; And it is performed on the reel-to-reel operation line; And it is performed under conditions that generate low current density between the plating tanks; And the micropores are filled.

Effect of the invention According to the present invention, a technology can be provided that can improve the filling property of micro-holes during intermittent plating, specifically, an intermittent plating method, a micro-hole filling method, a plating solution, etc.

Forms for implementing the invention In this specification, the expressions "contain" and "include" include the concepts of "contain", "include", "substantially constituted by", and "consisting only of".

The present invention, in one aspect, relates to a method for intermittent electroplating of an object having micropores (sometimes referred to as "the intermittent electroplating method of the present invention" in this specification), which includes using a plating solution containing polyvalent metal ions.

Furthermore, in one aspect, the present invention relates to a plating solution for use in the intermittent electroplating method of the present invention, which contains polyvalent metal ions.

Furthermore, the present invention relates to a method for filling micro-holes (via filling) by intermittent electroplating on a substrate having micro-holes, the method comprising using a plating solution containing polyvalent metal ions.

The following is an explanation of these.

The polyvalent metal ions are not particularly limited as long as they are metal ions having a valence of 2 or more.

The valence of the polyvalent metal ion is preferably 3 or more. By using the polyvalent metal ion with a valence of 3 or more, the filling property of the micropores can be greatly improved. The upper limit of the valence of the polyvalent metal ion is not particularly limited, and is, for example, 7, 6, 5, or 4.

Specific examples of polyvalent metal ions include Fe ³⁺ , V ⁵⁺ , Mn ⁷⁺ , Mo ⁶⁺ , W ⁶⁺ , Ce 4+ , Cr ³⁺ , Cr ⁶⁺ , Ti ⁴⁺ , Sn ⁴⁺ , Co ³⁺ , etc. Among them, from the perspective of micropore filling, Fe ³⁺ , V ⁵⁺ , ^{Mn 7+} , Mo ⁶⁺ , W ⁶⁺ , Ce ⁴⁺ , Cr ³⁺ , etc. are preferred. Among them, from the perspective of micropore filling, Fe ³⁺ and V ⁵⁺ are particularly preferred, and Fe ³⁺ is particularly preferred.

The polyvalent metal ions may be present alone or in combination of two or more.

A plating solution containing polyvalent metal ions can be prepared by adding a metal compound when preparing the plating solution. For example, when preparing a plating solution containing Fe ³⁺ , iron sulfate (III) hydrate can be cited as the metal compound used. anhydrous, iron nitrate (III) nonahydrate, anhydrous iron bromide (III), ammonium ferric citrate, iron (III) citrate hydrate, iron (III) oxide, ammonium iron (III) sulfate hydrate, etc.; in the case of preparing a plating solution containing V ⁵⁺ , for example, sodium metavanadate, potassium metavanadate, ammonium metavanadate, etc. can be listed; in the case of preparing a plating solution containing Mn ⁷⁺ , for example, potassium permanganate, sodium permanganate, etc. can be listed; in the case of preparing a plating solution containing Mo ⁶⁺ , for example, sodium molybdate, potassium molybdate, lithium molybdate, hexaammonium heptamolybdate tetrahydrate, etc. can be listed; in the case of preparing a plating solution containing W In the case of preparing a plating solution containing ^Ce 6+, for example, sodium tungstate (IV) dihydrate, sodium metatungstate, potassium tungstate, etc. can be listed; in the case of preparing a plating solution containing Ce ⁴⁺ , for example, ammonium tungstate (IV) nitrate, ammonium tungstate (IV) sulfate hydrate anhydrate, tetraammonium tungstate (IV) sulfate dihydrate, etc. can be listed; in the case of preparing a plating solution containing Cr ³⁺ , for example, chromium sulfate hydrate can be listed. anhydrous, chromium acetate, potassium chromium sulfate, etc.; when preparing a plating solution containing Cr ⁶⁺ , for example, sodium dichromate, potassium dichromate, etc. can be listed; when preparing a plating solution containing Ti ⁴⁺ , for example, titanium oxysulfate, etc. can be listed; when preparing a plating solution containing Sn ⁴⁺ , for example, sodium tinate trihydrate, etc. can be listed; when preparing a plating solution containing Co ³⁺ , for example, hexaamminecobalt (III) chloride, etc. can be listed.

Among these metal compounds, from the viewpoint of micropore filling property, iron sulfate (III) hydrate, anhydrous, iron nitrate (III) nonahydrate, anhydrous iron bromide (III), ammonium ferric citrate, iron citrate (III) hydrate, iron oxide (III), ammonium iron sulfate (III) hydrate, sodium metavanadate, potassium metavanadate, ammonium metavanadate, etc. are particularly suitable. Furthermore, iron sulfate (III) hydrate is particularly suitable. Anhydrous iron (III) nitrate, iron (III) nitrate nonahydrate, anhydrous iron (III) bromide, ammonium ferric citrate, iron (III) citrate hydrate, iron (III) oxide, ammonium iron (III) sulfate hydrate, etc., and particularly preferred is iron (III) sulfate hydrate. Anhydrous.

The polyvalent metal ions contained in the plating solution may have their valence changed in the plating solution after the addition of a metal compound (the above metal compound or a metal compound other than the above metal compound).

The metal compound may be a single type or a combination of two or more types.

The concentration of polyvalent metal ions in the plating solution is not particularly limited, and is, for example, 0.01 to 20 g/L. From the perspective of micropore filling, the concentration is preferably 0.05 to 10 g/L, more preferably 0.1 to 5 g/L, more preferably 0.2 to 3 g/L, and even more preferably 0.5 to 3 g/L. From the perspective of significantly improving micropore filling, the concentration is particularly preferably 0.7 to 2.5 g/L (more preferably 0.9 to 2.2 g/L).

In the intermittent plating method of the present invention, the metal precipitated on the plated object is not particularly limited. Examples of the metal include Cu, Ni, Sn, etc. Among them, Cu is particularly preferred. The metal precipitated on the plated object may be a single metal or a combination of two or more metals.

In combination with the deposited metal, the plating solution contains other components such as ions of the deposited metal and components that are optionally mixed. Other components can be appropriately set in accordance with or in accordance with the composition of known electroplating solutions (e.g., Cu plating solutions (e.g., copper sulfate bath, copper fluoroborate bath, copper cyanide bath, copper pyrophosphate bath, etc.), Ni plating solutions (e.g., complex salt bath, conventional plating bath, roller plating bath, high sulfate bath, Watt bath, full chloride bath, sulfate-chloride bath, full sulfate bath, high-quality bath, strike nickel bath, amine sulfonic acid nickel bath, nickel fluoroborate bath, etc.), Sn plating solutions (e.g., alkaline bath, sulfuric acid bath, sulfonic acid bath, pyrophosphate bath, fluoroboric acid bath, etc.), etc.).

The Cu plating solution is described below as a representative. The Cu plating solution may be an acidic copper plating solution containing copper ions and at least one acid component selected from organic acids and inorganic acids as essential components.

The copper ion source in the acidic copper plating solution can be used without special restrictions as long as it is a copper compound that is soluble in the plating solution. Specific examples of such copper compounds include: copper sulfate, copper oxide, copper chloride, copper carbonate, copper pyrophosphate, copper alkane sulfonate, copper alkanol sulfonate, organic acid copper, etc. The copper compound can be used alone or in combination of two or more. The concentration of the copper compound in the acidic copper plating solution is not particularly limited, for example, it can be set in the range of 20~280g/L. The concentration is preferably 100~250g/L, and more preferably 150~230g/L.

The acid component in the acidic copper plating solution can be at least one selected from the group consisting of organic acids and inorganic acids. Specific examples of organic acids include alkane sulfonic acids such as methanesulfonic acid, alkanol sulfonic acids, etc., and specific examples of inorganic acids include sulfuric acid, etc. These acid components can be used alone or in combination of two or more. The concentration of the acid component in the acidic copper plating solution is not particularly limited, for example, it can be set to 10~400g/L. The concentration is preferably 40~200g/L, and more preferably 70~150g/L.

The acid copper plating solution preferably contains chloride ions. The concentration is usually 10~200 mg/L. The concentration is preferably 25~100 mg/L, and more preferably 40~70 mg/L. In order to set it within this concentration range, hydrochloric acid, sodium chloride, etc. can be used as needed to adjust the chloride ion concentration in the plating solution.

Acid copper plating solution may also contain various additives, among which additives for via filling are preferred.

The object to be plated is not particularly limited as long as it has micropores and can be electroplated. An example of the object to be plated is a substrate having through holes.

The micro hole is preferably a micro via. The size of the micro hole is, for example, 300-5 μm in diameter (preferably 150-30 μm) and 150-5 μm in depth (preferably 100-20 μm). According to the intermittent plating method of the present invention, good filling performance can be achieved even for micro vias.

In the intermittent electroplating method of the present invention, the substrate to be plated is preferably pre-treated. The pre-treatment method is not particularly limited and can be carried out in accordance with conventional methods. For example, for a substrate to be plated that has been subjected to a conductive treatment (e.g., electroless plating, carbon treatment, sputtering, Sn-Pd colloidal catalyst treatment, conductive polymer treatment, etc.), for example, a substrate to be plated that has been subjected to a degreasing treatment, a treatment to remove attached dirt in the previous step, a treatment to remove an oxide film by pickling, etc., can be used as the substrate to be plated.

Furthermore, the object to be plated may be one on which a coating film has already been formed by electroplating.

The intermittent electroplating method of the present invention is not particularly limited as long as it is a method of repeatedly applying current in an intermittent manner, and the method has the problem of low current density caused by the plating liquid slightly attached to the coated material discharged from the plating tank and the coated material supplied to the plating tank (if it is the case of the embodiment shown in Figure 1, it is the plating liquid slightly leaking from the side of the plating tank).

When the current density in the coating tank is set to a high current density and the current density generated between the coating tanks is set to a low current density, the high current density: low current density (both units are A/dm ² ) is preferably 1:0.005-0.1. In addition, from the perspective that the filling property is more significantly reduced and the intermittent coating method of the present invention is more suitable, the time for generating the low current density (for example, the time for the coated object to pass through the coating tanks) is preferably 2 seconds or more, and preferably 3 seconds or more. The upper limit of the time is not particularly limited, for example, 60 seconds, 30 seconds, 20 seconds, 10 seconds or 5 seconds.

The intermittent electroplating method of the present invention is preferably the following method: a long strip of the object to be coated is continuously supplied to the coating tank on the working line, and the object to be coated is repeatedly discharged from the coating tank and supplied to the coating tank.

The so-called "long strips of coated objects are continuously supplied to the coating tank on the production line" does not mean that a plurality of separated coated objects are sequentially supplied to the coating tank, but means that a long strip of coated object is transported by a roller or the like while being supplied to the coating tank from one end of the object.

There is no particular limitation on the mode of discharging the coated object from the coating tank and supplying the coated object to the coating tank. The discharging and supplying are preferably performed from the side of the coating tank. In this case, when the coated object is discharged from the side wall of the coating tank and when the coated object is supplied through the side wall of the coating tank, the coating liquid inside the coating tank may leak out of the coating tank through the coated object, and the problem in the present invention (generation of low current density) may occur.

The coating material is repeatedly supplied to and discharged from the coating tank for, for example, 2 to 30 times, preferably 5 to 25 times, and more preferably 10 to 20 times.

The intermittent electroplating method of the present invention is preferably a method in which the substrate passes through a plurality of plating tanks, for example, 2 to 30, preferably 5 to 25, and more preferably 10 to 20.

The intermittent electroplating method of the present invention is preferably a method performed on a reel-to-reel operation line.

There is no particular limitation on the method for stirring the coating liquid, and air stirring, jet stirring, mechanical stirring, etc., or a combination of multiple stirring methods may be used.

When the plating treatment is performed, the anode can be either a soluble anode or an insoluble anode. For example, the soluble anode can be phosphorus-containing copper with a phosphorus content of 0.02 to 0.06%. In addition, the insoluble anode can be titanium coated with iridium oxide, titanium plated with platinum, etc. There is no particular limitation on the shape of the anode, and various shapes such as rods, balls, plates, and meshes can be used.

During the plating process, the cathode may use the material to be plated.

The temperature of the plating solution is usually set to 10~50℃. The temperature is preferably 20~35℃.

In the intermittent electroplating method of the present invention, the current density (current density in the plating tank) is, for example, 2-15 A/dm ² , preferably 2-10 A/dm ² .

The time for each additional current in the intermittent plating method of the present invention (the time for a certain point in the object to be plated to be immersed in the plating solution in the plating tank) is, for example, 5 to 120 seconds, preferably 10 to 60 seconds, and more preferably 20 to 40 seconds.

The number of current additional cycles in the intermittent plating method of the present invention is, for example, 2 to 30 times, preferably 5 to 25 times, and more preferably 10 to 20 times.

Embodiments The present invention is described in detail below based on embodiments, but the present invention is not limited to these embodiments.

Test Example 1. Intermittent Plating Test 1 <Test Example 1-1. Preparation of Plating Solution> Prepare a plating solution having the composition shown in Table 1 below.

[Table 1]

<Test Example 1-2. Pretreatment> A copper foil resin substrate with a thickness of 64μm (layer structure: copper foil 7μm/resin (polyimide) layer 50μm/copper foil 7μm) has many through holes with a diameter of 100μm and a depth of 57μm, and the inner wall of the through-hole resin is made conductive by a carbon direct plating system. The substrate (Figure 2) thus constructed is used as the plated object and is immersed in a degreasing solution (trade name: DP-320 CLEAN, manufactured by Okuno Pharmaceutical Industries, 100ml/L aqueous solution) at 45°C for 5 minutes, then rinsed with water for 1 minute, and immersed in 100g/L dilute sulfuric acid for 1 minute for pretreatment.

<Test Example 1-3. Electroplating> The pre-treated substrate was immersed in the electroplating solution prepared above and electroplated in the cycle shown in Table 2. The plating conditions are shown in Table 3. The specific values of the low current density and the power-on time in Table 2 are shown in Table 4. In addition, a graph showing an example of the cycle (low current density = 0.2A/ ^dm2 , power-on time 5 seconds) is shown in FIG3.

[Table 2]

[Table 3]

<Test Example 1-4. Evaluation of filling property> After the electroplating, the cross-section of the via portion of the plated object was observed, and the amount of depression in the via portion was measured as shown in Figure 4. Based on the measured value, the filling property was evaluated using the following evaluation criteria (○: depression amount 48μm or less, △: depression amount: 48~53μm, ×: depression amount 53μm or more).

<Test Example 1-5. Results> The results are shown in Table 4. In Table 4, low current density refers to the low current density in the cycle of Table 2, and power-on time refers to the power-on time (X) of low current density in the cycle of Table 2.

[Table 4]

As shown in Table 4, when electroplating is performed in a cycle that does not generate low current density (Comparative Example 1), the filling property is relatively good. However, in intermittent electroplating, especially in intermittent electroplating where a long strip of coated material is continuously supplied to a coating tank on a production line and the coated material is discharged from the coating tank and supplied to the coating tank several times, it is inevitable that the coating liquid slightly adheres to the coated material discharged from the coating tank and the coated material supplied to the coating tank, resulting in low current density. After simulating the above situation (Comparative Examples 2 to 5), it can be seen that the filling property will be greatly deteriorated.

Test Example 2. Intermittent Plating Test 2 The plating solution was prepared in the same manner as in Test Example 1-1, except that iron sulfate n-hydrate was added to the plating solution to adjust the Fe ³⁺ concentration to the concentration shown in Table 5. The pretreatment, plating, and filling evaluation were performed in the same manner as in Test Example 1.

The results are shown in Table 5. In Table 5, low current density refers to the low current density in the cycle of Table 2, and power-on time refers to the power-on time (X) of the low current density in the cycle of Table 2. In addition, FIG. 5 shows a cross-sectional observation of the via portion of the plated object after the electroplating of Example 2 and Comparative Example 3.

[Table 5]

As shown in Table 5, it can be seen that the deterioration of filling properties caused by the generation of low current density (comparison between Comparative Example 1 and Comparative Examples 2 to 5) can be greatly improved by using a plating solution containing Fe ³⁺ .

Test Example 3. Intermittent Plating Test 3 The plating solution was prepared in the same manner as in Test Example 1-1, except that various metal compounds were added to the plating solution to adjust the polyvalent metal ion concentration to the concentration shown in Table 6. The pretreatment, plating, and filling evaluation were performed in the same manner as in Test Example 1. In this test, the low current density was 0.2 A/dm ² and the current-on time was 5 seconds.

The results are shown in Table 6.

[Table 6]

As shown in Table 6, it can be seen that the deterioration of filling properties caused by the generation of low current density (comparison between Comparative Example 1 and Comparative Examples 2 to 5) can be greatly improved by using a plating solution containing polyvalent metal ions.

FIG1 is a schematic diagram showing an implementation form of the intermittent plating method and showing a current diagram in the plating method. FIG2 is a schematic diagram of a cross section of a substrate used in Test Example 1-2. FIG3 is a graph showing an example of a plating cycle of Test Example 1-3. FIG4 is a cross-sectional observation diagram showing the object (depression amount) measured in the filling evaluation and the via portion of the plated object after the completion of the plating. FIG5 is a cross-sectional observation diagram of the via portion of the plated object after the completion of the plating in Example 2 and Comparative Example 3.

(without)

Claims (10)

An intermittent electroplating method is performed on a coating material having micropores. The intermittent electroplating method includes using a coating liquid containing polyvalent metal ions, and the intermittent electroplating method is that the long strip of coating material is continuously supplied to the coating tank on the working line, and the coating material is repeatedly discharged from the coating tank and supplied to the coating tank, and the intermittent electroplating method is performed on the working line from reel to reel. As in the intermittent electroplating method of claim 1, wherein the valence of the aforementioned polyvalent metal ions is 3 or more. The intermittent plating method of claim 1 or 2, wherein the aforementioned polyvalent metal ions are at least one selected from the group consisting of Fe ³⁺ , V ⁵⁺ , Mn ⁷⁺ , Mo ⁶⁺ , W ⁶⁺ , Ce ⁴⁺ , Cr ³⁺ , Cr ⁶⁺ , Ti ⁴⁺ , Sn ⁴⁺ and Co ³⁺ . The intermittent plating method of claim 1 or 2, wherein the aforementioned polyvalent metal ions are at least one selected from the group consisting of Fe ³⁺ and V ⁵⁺ . An intermittent electroplating method as claimed in claim 1 or 2, wherein the aforementioned coated material passes through a plurality of coating tanks. The intermittent electroplating method as claimed in claim 1 or 2, wherein the aforementioned discharge and the aforementioned supply are performed on the side of the plating tank. The intermittent electroplating method of claim 1 or 2, wherein the aforementioned micro-holes are micro-conducting holes. The intermittent electroplating method of claim 1 or 2, wherein the metal precipitated onto the plated object includes at least one selected from the group consisting of Cu, Ni and Sn. The intermittent electroplating method of claim 1 or 2, wherein the aforementioned plating solution further contains an additive for via filling. A plating solution for use in a discontinuous electroplating method as claimed in any one of claims 1 to 9, wherein the plating solution contains polyvalent metal ions.