HIGH-SPEED FILLING METHOD FOR COPPER

Description

TECHNICAL FIELD

The present invention relates to a method for filling holes, such as a via and a through hole, or grooves, such as a trench, formed in a substrate, by copper plating at a higher speed than the ordinary technique.

BACKGROUND ART

The substrate structure of a portable phone, which is a representative example of compact electronic equipments, is having an increased density, and a buildup technique is essential for producing the substrate. In the buildup technique, there is an increasing importance of a technique for filling holes, such as a via and a through hole, or grooves, such as a trench, formed in a substrate having multiple layers laminated, by copper plating. Furthermore, a technique of filling a through-silicon via (which is one kind of vias) by copper plating receives attention as one of three-dimensional packaging techniques in the field of semiconductor.

The filling of holes or grooves formed in a substrate, for example a via having an opening diameter of approximately 120 μm and a depth of approximately 70 μm, by acidic copper plating has required approximately one hour by using a phosphorus-containing copper anode or an insoluble anode at a current density of 2 A/dm², using an acidic copper plating solution containing approximately 56 g/L of copper ion (approximately 220 g/L in terms of copper(II) sulfate pentahydrate), approximately 135 g/L of sulfate ion (approximately 50 g/L in terms of sulfuric acid), approximately 40 mg/L of chloride ion, and additives and the like.

In general, for increasing the rate of copper plating, it is considered to increase the temperature and the copper ion concentration, and to increase the current density, but in the case where these factors are increased on filling holes or grooves by copper plating, it has been known that the leveling function and the filling capability may be lowered, the appearance of plating may be deteriorated, the properties of the plated film may be deteriorated, and the like.

In the case where copper plating is performed with a phosphorus-containing copper anode, the black film is eluted on increasing the temperature, and copper ion as monovalent copper is eluted into the bath from the black film or the surface of the anode that is not covered with the black film, and alters the additives, thereby deteriorating the capabilities including the leveling property, the uniform electrodeposition property, the filling property, and the like. For suppressing the alteration of the additives, it is necessary to retain a high dissolved oxygen concentration in the bath, but it has been considered that the saturation solubility of dissolved oxygen is decreased on increasing the temperature of the bath, which results in a vicious cycle.

Accordingly, there has been no attempt to increase the rate of copper plating for filling holes or grooves formed in a substrate, by changing the temperature, the ion concentration, other conditions, and the like, and increasing the current density.

As a technique of increasing the rate of copper plating, there has been a technique using a special additive capable of being used at an increased solution temperature (PTL 1), but the technique performs conformal plating in holes formed in a substrate, such as a via and a through hole. In the conformal plating technique, in general, it is necessary to dispose substrate to be laminated in such a manner that holes, such as vias and through holes, formed in the substrates are not aligned with each other. In the filling plating, on the other hand, holes can be aligned with each other on laminating the substrates since the holes can be filled with copper, thereby decreasing the size and the area of the substrate, but the aforementioned technique cannot be applied to the filling plating.

CITATION LIST

Patent Literature

PTL 1: JP-A-2011-84779

SUMMARY OF INVENTION

Technical Problem

Accordingly, a problem of the invention is to provide a technique of increasing a rate of filling holes or grooves formed in a substrate, by changing the temperature, the concentration, the current density on plating, and the other conditions of the ordinary acid copper plating solution, without the necessity of the use of a special additive.

Solution to Problem

As a result of earnest investigations made by the present inventors for solving the problem, it has been unexpectedly found that in the case where holes or grooves formed in a substrate is filled by copper plating, holes, such as a via and a through hole, or grooves, such as a trench, can be filled by copper plating at a high speed by performing the change of the temperature, the concentration, the current density, and the other conditions, which has not been performed due to the aforementioned reasons, and using an insoluble electrode as an anode, and thus the invention has been completed.

The invention relates to a method for filling holes or grooves formed in a substrate by copper plating at a high speed, containing: immersing the substrate having the holes or grooves in an acidic copper plating solution containing a copper ion, a sulfate ion, and a halide ion, at from 30 to 70° C.; and plating the substrate at a current density of 3 A/dm² or more by using an insoluble electrode as an anode.

Advantageous Effects of Invention

The method of the invention can fill holes, such as a via and a through hole, or grooves, such as a trench, formed in a substrate, by copper plating at a higher speed than the ordinary technique.

While an acidic copper plating solution used in the ordinary filling is necessarily replenished with copper source mainly by copper oxide in the case where an insoluble electrode is used as the anode, there are cases where the replenishment of copper ion is insufficient when the current density is increased due to the low solubility of copper oxide at a low temperature. However, the acidic copper plating solution used in the method of the invention achieves a high solubility of copper oxide due to the higher bath temperature than the ordinary one. Accordingly, in the method of the invention, the replenishment of the copper source to the acidic copper plating solution is sufficient, and thus the filling can be performed continuously.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is across sectional photograph of a test substrate after filling a via by copper plating according to a method 18 of Example 1.

FIG. 2 is an illustration showing a measurement position of a dent in the case where the dent is positioned around the center of the via, in a evaluation method for filling property in Example 1.

FIG. 3 is an illustration showing a measurement position of a dent in the case where the dent is positioned around the periphery of the via, in the evaluation method for filling property in Example 1.

FIG. 4 is an illustration showing a dimension of a test specimen used in a tensile test and a hardness measurement test in Example 2.

FIG. 5 is across sectional photograph of a test substrate after filling a through hole by copper plating according to a method 27 of Example 3.

FIG. 6 is an illustration showing a measurement position of a dent in the case where the dent is positioned around the center of the through hole, in a evaluation method for filling property in Example 3.

FIG. 7 is an illustration showing a measurement position of a dent in the case where the dent is positioned around the periphery of the through hole, in the evaluation method for filling property in Example 3.

DESCRIPTION OF EMBODIMENTS

The acidic copper plating solution that is used in the method for filling holes or grooves formed in a substrate at a high speed of the invention (which is hereinafter referred to as the method of the invention) contains a copper ion, a sulfate ion, and a halide ion.

The copper ion contained in the acidic copper plating solution is a divalent ion, and the source thereof used may be a copper compound used in the ordinary acidic copper plating solution without particular limitation. Specific examples of the copper compound include copper sulfate, copper oxide, copper chloride, copper carbonate, copper pyrophosphate, a copper alkanesulfonate, such as copper methanesulfonate and copper propanesulfonate, copper isethionate, a copper alkanolsulfonate, such as copper propanolsulfonate, and an organic acid copper, such as copper acetate, copper citrate, and copper tartrate, and a salt thereof. Among these copper compounds, copper (II) oxide and copper sulfate are preferred, and copper sulfate is more preferred. The copper compounds may be used solely or as a combination of two or more kinds thereof. The amount of the copper ion contained in the acidic copper plating solution is not particularly limited, and may be, for example, 25 g/L or more, preferably 40 g/L or more, and more preferably 50 g/L or more.

The source of the sulfate ion contained in the acidic copper plating solution is not particularly limited, as far as it forms a sulfate ion in the acidic copper plating solution, and examples thereof include sulfuric acid, and also include a sulfate salt, such as copper sulfate. The source of the sulfate ion may be used solely or as a combination of two or more kinds thereof. The amount of the sulfate ion contained in the acidic copper plating solution is not particularly limited, and may be, for example, 50 g/L or more, preferably from 75 to 350 g/L, and more preferably from 125 to 250 g/L.

The halide ion contained in the acidic copper plating solution is not particularly limited, examples thereof include a chloride ion, a bromide ion, and an iodide ion, and a chloride ion is preferred. The source of the halide ion is not particularly limited, and may be added as an inorganic acid, such as hydrochloric acid, hydrobromic acid, and iodic acid. Among the halide ions, a chloride ion is preferred. The halide ion may be used solely or as a combination of two or more kinds thereof. The amount of the halide ion contained in the acidic copper plating solution is not particularly limited, and may be, for example, from 5 to 300 mg/L, preferably from 20 to 200 mg/L, and more preferably from 30 to 150 mg/L.

The acidic copper plating solution is used at a temperature of from 30 to 70° C., preferably from 35 to 65° C., and particularly preferably from 35 to 55° C., as described later, and therefore the copper ion concentration can be increased as compared to the ordinary acidic copper plating solution. Accordingly, the copper ion contained in the acidic copper plating solution can be 25 g/L or more and the saturation copper ion concentration at a temperature within the aforementioned temperature range of the solution temperature of the acidic copper plating solution or less, and preferably the saturation copper ion concentration at 20° C. of the solution temperature of the acidic copper plating solution or more and the saturation copper ion concentration at a temperature within the aforementioned temperature range of the solution temperature of the acidic copper plating solution or less. In the case where the copper ion concentration is the saturation copper ion concentration at 20° C. or more, there may be cases where copper is not dissolved as a copper salt but remains undissolved at a temperature lower than the aforementioned temperature range, both the filling capability and the plating appearance cannot be achieved simultaneously, and the plating cannot be performed continuously, and therefore the solution temperature and the copper ion concentration are preferably retained during the plating.

It can be confirmed in the following manner whether the copper concentration of the acidic copper plating solution at a certain temperature is the saturation concentration or more or the saturation concentration or less. For example, for a copper plating solution containing sulfuric acid as the sulfate ion source, hydrochloric acid as the halide ion source (i.e., the chloride ion source), and copper (II) sulfate pentahydrate as the copper ion source and the sulfate ion source, having a solution temperature of 20° C., copper (II) sulfate pentahydrate, sulfuric acid, and hydrochloric acid are added to pure water to make arbitrary concentrations, and dissolved by heating to a temperature of 20° C. or more to prevent copper (II) sulfate pentahydrate from remaining undissolved, so as to provide an acidic copper plating solution. Subsequently, the acidic copper plating solution is sealed to prevent the plating solution from being evaporated, and allowed to stand in an incubator at 20° C. for two weeks, and then it can be confirmed that the concentration is the saturation concentration or more when copper (II) sulfate pentahydrate is recrystallized, whereas the concentration is the saturation concentration or less when copper (II) sulfate pentahydrate is not recrystallized. The amount of the copper salt that makes the saturation concentration of copper ion at a solution temperature of 20° C. can be obtained in this manner.

The saturation copper ion concentration in the case where the solution temperature of the acidic copper plating solution is 20° C. can be obtained according to the following expression from the amount of the copper salt obtained above.

copper ion concentration(g/L)=concentration of copper(II)sulfate pentahydrate(g/L)×63.54(atomic weight of Cu)/249.51(molecular weight of CuSO₄.5H₂O)  Expression 1

In the method for confirming the saturation copper ion concentration described above, the saturation copper ion concentrations of the acidic copper plating solutions at various temperatures can be obtained by changing appropriately the sulfate ion source, the halide ion source, the copper ion source, the temperature, and the expression.

The acidic copper plating solution may further contain an additive that has been generally added to the ordinary acidic copper plating solution used for filling a hole, such as a via, such as a brightener, a leveler, and a polymer. The acidic copper plating solution preferably contains, among the brightener, the leveler, and the polymer, two of the brightener and the leveler, and more preferably contains three of the brightener, the leveler, and the polymer.

The brightener is not particularly limited. Preferred examples thereof include a sulfur-containing organic compound, such as 3-mercapto-1-propanesulfonic acid and a sodium salt thereof, bis-3-(sulfopropyl) disulfide and a disodium salt thereof, and 3-sulfopropyl N,N-dimethyldithiocarbamate and a sodium salt thereof, and more preferred examples thereof include bis-3-(sulfopropyl) disulfide and a disodium salt thereof. The brightener may be used solely or as a combination of two or more kinds thereof. The amount of the brightener contained in the acidic copper plating solution is not particularly limited, and may be, for example, from 0.01 to 50 mg/L, and preferably from 0.1 to 10 mg/L.

The leveler is not particularly limited, examples thereof include an organic dye, such as a polyalkyleneimine, an alkylimidazoline compound, auramine and a derivative thereof, a phthalocyanine compound, and Janus green, a reaction product of a compound having three or more glycidyl ether groups and a heterocyclic compound described in WO 2011/135716, a reaction product of diglycidyl ether and a nitrogen-containing compound described in JP-A-2011-207878, and a water soluble resin obtained through reaction of a polyamine, a dibasic carboxylic acid compound, and a crosslinking agent, such as an epihalohydrin, described in JP-A-2007-107074, and preferred examples thereof include a reaction product of a compound having three or more glycidyl ether groups and a heterocyclic compound described in WO 2011/135716, a reaction product of diglycidyl ether and a nitrogen-containing compound described in JP-A-2011-207878, and a water soluble resin obtained through reaction of a polyamine, a dibasic carboxylic acid compound, and a crosslinking agent, such as an epihalohydrin, described in JP-A-2007-107074. The leveler may be used solely or as a combination of two or more kinds thereof. The amount of the leveler contained in the acidic copper plating solution may be from 0.1 to 10,000 mg/L, and preferably from 10 to 1,000 mg/L.

The polymer is not particularly limited, and examples thereof include a polyether compound, such as polyethylene glycol, polypropylene glycol, a Pluronic type surfactant, a Tetronic type surfactant, polyethylene glycol glyceryl ether, and polyethylene glycol dialkyl ether. The polymer may be used solely or as a combination of two or more kinds thereof. The amount of the polymer contained in the acidic copper plating solution may be from 0.1 to 10,000 mg/L, and preferably from 10 to 1,000 mg/L.

The acidic copper plating solution may further contain an ion of an acid other than sulfuric acid, an ion of a metal other than copper, and a component including formaldehyde or the like, in addition to the brightener, the polymer, and the leveler. The contents of the components are not particularly limited, and may be amounts that are applied to the ordinary acidic copper plating solution.

Examples of the acid other than sulfuric acid include an alkanesulfonic acid, such as methanesulfonic acid, an alkanolsulfonic acid, such as isethionic acid, and an organic acid, such as citric acid and formic acid. The acid may be used solely or as a combination of two or more kinds thereof.

Examples of the metal ion other than copper include an ion of a metal, such as germanium, iron, indium, manganese, molybdenum, nickel, cobalt, lead, palladium, platinum, rhenium, sulfur, titanium, tungsten, cadmium, chromium, zinc, tin, silver, gold, bismuth, rhodium, ruthenium, and iridium. The metal ion may be used solely or as a combination of two or more kinds thereof.

Preferred embodiments of the acidic copper plating solution include an acidic copper plating solution that contains from 150 to 350 g/L of copper sulfate pentahydrate, from 5 to 150 g/L of sulfuric acid, and from 5 to 300 mg/L of hydrochloric acid, and appropriately contains the brightener, the polymer, and the leveler.

The method of the invention can be performed by immersing a substrate having holes, such as a via or a through hole or grooves of a trench in the acidic copper plating solution that is heated and retained at from 30 to 70° C., and performing copper plating at a current density of 3 A/dm² or more by using an insoluble electrode as an anode. The method of making the acidic copper plating solution to have the aforementioned temperature is not particularly limited, and the aforementioned temperature may be achieved by using a heating device, such as an immersion heater, or a thermostatic chamber.

In the method of the invention, the substrate having holes, such as a via and a through hole, or grooves, such as a trench, formed therein includes a printed circuit board and a semiconductor substrate, such as a silicon wafer. The size of the via, the through hole, or the trench to be filled by the method of the invention is not particularly limited, and may be an opening diameter of from 50 to 150 μm and a depth of from 20 to 100 μm for the via, an opening diameter of from 50 to 100 μm and a thickness of from 50 to 250 μm for the through hole, or a width of from 1 to 50 μm and a depth of from 1 to 50 μm for the trench.

The substrate may be subjected to a treatment that has been ordinarily performed, such as degreasing and acid activation, before copper plating.

The insoluble electrode used in the method of the invention is not particularly limited, as far as it is an insoluble electrode having been used for plating, and examples thereof include an electrode formed of titanium coated with iridium oxide, platinum, or the like.

The external side of the insoluble electrode may be covered with a neutral diaphragm. The neutral diaphragm used may be a commercially available product. Examples of the commercially available product of the neutral diaphragm include Yumicron Filter Y9205TA (produced by Yuasa Membrane Systems Co., Ltd.).

In the method of the invention, it suffices that the current density is 3 A/dm² or more, preferably from 3 to 20 A/dm², and more preferably from 3 to 10 A/dm². When the current density is less than 3 A/dm², a good filling capability and a glossy appearance of plating may not be obtained depending on the temperature condition.

In the practice of the method of the invention, the acidic copper plating solution is preferably agitated. The method of agitation is not particularly limited, and examples thereof include air agitation, jet agitation, and squeeze agitation.

In the method of the invention, furthermore, after filling holes, such as a via and a through hole, or grooves, such as a trench, by copper plating, a drying treatment, a heat treatment, a discoloration preventing treatment, a rust preventing treatment, and the like may be performed according to the ordinary methods.

According to the method of the invention, holes, such as a via and a through hole, or grooves, such as a trench, formed in a substrate can be filled at a higher speed than the ordinary technique, for example, a via having an opening diameter of approximately 120 μm and a depth of approximately 70 μm can be filled within a period of approximately from 10 to 30 minutes (which may be approximately 1 hour with an ordinary acidic copper plating solution). The method of the invention also provides a good appearance and a high filling capability, and the properties of the plated film (e.g., the tensile strength, the elongation, and the hardness) may be equivalent to properties of a film obtained by the ordinary technique.

According to the method of the invention, holes, such as a via and a through hole, or grooves, such as a trench, formed in substrates can be filled repeatedly. In the case where the copper ion in the acidic copper plating solution becomes insufficient, it suffices that the acidic copper plating solution is replenished with copper oxide is added as a copper ion source. The method of replenishing copper oxide is not particularly limited, and an ordinary method may be used.

EXAMPLE

The invention will be described in detail with reference to examples below, but the invention is not limited to the examples.

Example 1

Filling of Via

A printed circuit board having a substrate copper foil having formed therein plural vias each having an opening diameter of 120 μm and a depth of 70 μm was subjected to electroless copper plating according to an ordinary method, so as to provide a test substrate. Separately, an acidic copper plating solution containing the components shown in Table 1 was prepared by mixing and dissolving the components in pure water. The vias of the test substrate were filled by copper plating by using the acidic copper plating solution under the condition shown in Table 2. The copper plating was performed under air agitation of the acidic copper plating solution. The copper plating was terminated at the time when the thickness of the surface layer copper plating reached 20 μm.

The copper plating was performed by the following process steps in this order.

• • Acidic degreasing (PB-242D, produced by JCU Corporation): 45° C., 3 minutes
  • Water rinsing: 1 minute
  • Acid activation (50 g/L sulfuric acid solution): room temperature, 1 minute
  • Copper plating

The test substrates after subjecting to the copper plating were evaluated for the appearance and the filling property according to the methods described later. The overall evaluation was performed from the evaluation results. The evaluation results are shown in Table 2. The cross sectional photograph of the test substrate after filling the via by copper plating according to the method 18 is shown in FIG. 1.

TABLE 1
		By way of		By way		By way of
		copper(II)		of		36%

Copper

Copper

sulfate

Sulfate

sulfuric

Chloride

hydrochloric

Leveler

plating	ion	pentahydrate	ion	acid	ion	acid	Brightener		Amount	Polymer
solution	(g/L)	(g/L)	(g/L)	(g/L)	(mg/L)	(mL/L)	(mg/L)	Kind	(mg/L)	(mg/L)

1	50.9	200	106.3	30	60	0.15	1	B	80	100
2	50.9	200	125.9	50	40	0.10	2	C	40	100
3	50.9	200	153.3	80	40	0.10	1	A	100	500
4	50.9	200	153.3	80	60	0.15	1	A	100	500
5	50.9	200	153.3	80	80	0.20	1	A	100	500
6	63.6	250	145.2	50	60	0.15	1	A	100	500
7	76.3	300	193.8	80	60	0.15	1	A	100	500
8	76.3	300	144.8	30	60	0.15	1	B	80	500
9	76.3	300	193.8	80	60	0.15	2	C	300	500
10	76.3	300	193.8	80	80	0.20	1	A	100	500
11	76.3	300	193.8	80	100	0.25	1	A	100	500
Leveler A: a reaction product of a compound having three or more glycidyl ether groups and a heterocyclic compound (the compound represented by [Chem 10] of WO 2011/135716, according to the method described in the literature)
Leveler B: a reaction product of diglycidyl ether and a nitrogen-containing compound (the reaction product of CAS 2224-15-9 and CAS 110-95-2, according to the method described in JP-A-2011-207878)
Leveler C: a water soluble resin obtained through reaction of a polyamine, a dibasic carboxylic acid compound, and a crosslinking agent, such as an epihalohydrin (according to Synthesis Example 1 of JP-A-2007-107074)
Polymer: polyethylene glycol (average molecular weight: 6,000)
Brightener: disodium bis-3-(sulfopropyl) disulfide

TABLE 2
	Copper plating	Temperature		Current density	Time	Evaluation

	solution	(° C.)	Anode	(A/dm2)	(min)	Appearance	Filling property	Overall

Method 1	1	23	insoluble electrode	2	50	A	A	A+
Method 2	2	23	insoluble electrode	2	50	A	A	A+
Method 3	3	23	insoluble electrode	2	50	A	A	A+
Method 4	3	23	insoluble electrode	3.5	28.6	B	B	B
Method 5	3	23	insoluble electrode	5	20	C	C	C
Method 6	3	23	insoluble electrode	7.5	13.3	C	C	C
Method 7	3	23	insoluble electrode	10	10	C	C	C
Method 8	4	23	insoluble electrode	10	10	B	C	C
Method 9	5	23	insoluble electrode	10	10	C−	C	C
Method 10	1	23	insoluble electrode	7.5	13.3	C	C	C
Method 11	2	23	insoluble electrode	7.5	13.3	C	C	C
Method 12	6	35	insoluble electrode	3.5	28.6	A	A	A+
Method 13	7	50	insoluble electrode	5	20	A	A	A+
Method 14	8	50	insoluble electrode	7.5	13.3	A	A	A+
Method 15	9	50	insoluble electrode	7.5	13.3	A	A	A+
Method 16	10	40	insoluble electrode	5	20	A	A	A+
Method 17	10	50	insoluble electrode	7.5	13.3	A	A	A+
Method 18	11	50	insoluble electrode	10	10	A	A	A+
Method 19	11	50	phosphorus-containing	10	10	B	C	C
			copper electrode
Insoluble electrode: an iridium oxide-coated titanium electrode covered with a neutral diaphragm (Yumicron Filter Y9205TA, produced by Yuasa Membrane Systems Co., Ltd.)

Evaluation Method for Appearance

The appearance after the copper plating was visually evaluated by the following evaluation standard.

Evaluation: content

A: glossy appearance found over entire surface

B: glossy appearance found with less than 10% of rough surface

C: glossy appearance found with 10% or more of rough surface

C−: non-glossy appearance found over entire surface

Evaluation Method of Filling Property

The via after the copper plating was measured for the dent thickness by observing the cross section. The measurement position of the dent thickness is shown in FIGS. 2 and 3.

Evaluation: content

A: dent thickness of less than 15 μm

B: dent thickness of from 15 to 30 μm

C: dent thickness of 30 μm or more

Overall Evaluation Standard

Evaluation: content

A+: Both the appearance and the filling property were A.

A: The appearance and the filling property were B or higher, but both of them were not A.

B: Both the appearance and the filling property were B.

C: One of the appearance and the filling property was C or C−.

It was found from the results that approximately 50 minutes was required (i.e., the period of time required for forming a film of approximately 20 μm at 2 A/dm²) for filling a via by the methods 1 to 3, i.e., the ordinary methods, whereas the methods 12 to 18, i.e., the methods of the invention, shortened the plating time, and the period of time required for filling a via was half or less of the ordinary technique. It was also found that when the solution temperature was higher, both the filling property and the plating appearance were achieved even under the condition with a higher current density. Furthermore, it was found that in the case where the solution temperature of the acidic copper plating solution and the current density were to be increased, it was necessary to use an insoluble electrode as the anode.

It has been known that: when the copper ion concentration is higher, good filling property is obtained, but the appearance is deteriorated; when the sulfuric acid concentration is higher, the appearance and the uniform electrodeposition property are improved, but the filling property is deteriorated; and a halogen (chlorine) contributes to the enhancement of the appearance (e.g., rough surface), and when the concentration thereof is higher, the effect is increased, but the filling property is deteriorated, with a too higher concentration thereof resulting in a non-glossy appearance. In the method of the invention, however, it is expected that the copper concentration can be set higher than an ordinary plating bath due to the higher solution temperature, and the sulfuric acid concentration can also be retained, which largely contribute to the achievement of both the filling property and the appearance even under the condition with a higher current density.

Example 2

Evaluation of Property of Film

A smooth stainless steel plate was degreased with a degreasing agent (SK-144, produced by JCU Corporation), lightly rubbed with polyurethane sponge (Scotch Brite, produced by 3M Company), then rinsed with water, acid-activated with a 10% sulfuric acid solution, and subjected to copper plating under the condition shown in Table 3, so as to provide a copper plated film having a thickness of approximately 50 μm. The resulting copper plated film was peeled off from the base, and subjected to a heat treatment at 120° C. for 1 hour.

The copper plated films thus obtained above each were punched out into a test specimen having a dumbbell shape with the size shown in FIG. 4, measured for the thickness of the plated film with a digital micrometer, and then subjected to a tensile test and a hardness measurement test under the following conditions, whereby the elongation and the tensile strength (tensile test) and the hardness of the plated film (hardness measurement test) were measured. The measurement results are shown in Table 3.

TABLE 3
						Evaluation of properties

	Copper			Current		Tensile		Vickers
	plating	Temperature		density	Time	strength	Elongation	hardness
	solution	(° C.)	Anode	(A/dm2)	(min)	(kgf/mm2)	(%)	(Hv)

Method 20	3	23	insoluble electrode	2	135	32.2	31.0	112
Method 21	6	35	insoluble electrode	3.5	77	33.0	32.2	110
Method 22	10	40	insoluble electrode	5	54	31.5	32.4	107
Method 23	10	50	insoluble electrode	7.5	36	32.6	31.7	108
Method 24	11	50	insoluble electrode	10	27	31.1	33.6	108
Insoluble electrode: an iridium oxide-coated titanium electrode covered with a neutral diaphragm (Yumicron Filter Y9205TA, produced by Yuasa Membrane Systems Co., Ltd.)

Tensile Test Condition

Measurement method: JIS Z2241 (1980)

Measurement instrument: Shimadzu Autograph AGS-H 500N (produced by Shimadzu Corporation)

Measurement Condition:

Tensile speed: 10 mm/min

Tensile load: 50 kgf for full scale

Hardness Measurement Condition

Measurement instrument: Vickers Hardness Measuring Device (produced by Akashi Seisakusho Co., Ltd.)

Measurement Condition:

Load: 10 gf/cm²

Retention time: 15 seconds

It was found from the results that the copper plated film obtained by the method of the invention had properties that were equivalent to a copper plated film obtained by an ordinary method.

Example 3

Filling of Through Hole

A printed circuit board having a substrate copper foil having formed therein plural through holes each having an opening diameter of 100 μm and a thickness (including the copper foil) of 120 μm was subjected to electroless copper plating according to an ordinary method, so as to provide a test substrate. Separately, an acidic copper plating solution containing the components shown in Table 4 was prepared by mixing and dissolving the components in pure water. The through holes of the test substrate were filled by copper plating by using the acidic copper plating solution under the condition shown in Table 5. The copper plating was performed under jet agitation of the acidic copper plating solution. The copper plating was terminated at the time when the thickness of the surface layer copper plating reached 20 μm.

The copper plating was performed by the following process steps in this order.

• • Acidic degreasing (PB-242D, produced by JCU Corporation): 45° C., 3 minutes
  • Water rinsing: 1 minute
  • Acid activation (50 g/L sulfuric acid solution): room temperature, 1 minute
  • Copper plating

The test substrates after subjecting to the copper plating were evaluated for the filling performance according to the methods described later. The evaluation results are shown in Table 4. The cross sectional photograph of the test substrate after filling the through hole by copper plating according to the method 27 is shown in FIG. 5.

TABLE 4
		By way of		By way		By way
		copper(II)		of		of 36%

Copper

Copper

sulfate

Sulfate

sulfuric

Chloride

hydrochloric

Leveler

plating	ion	pentahydrate	ion	acid	ion	acid	Brightener		Amount	Polymer
solution	(g/L)	(g/L)	(g/L)	(g/L)	(mg/L)	(mL/L)	(mg/L)	Kind	(mg/L)	(mg/L)
12	56.0	220	133.6	50	60	0.15	1	A	100	500
13	76.3	250	145.2	50	60	0.15	1	A	100	500
14	76.3	300	184.0	70	80	0.20	1	A	100	500
Leveler A: a reaction product of a compound having three or more glycidyl ether groups and a heterocyclic compound (the compound represented by [Chem 10] of WO 2011/135716, according to the method described in the literature)

TABLE 5
	Copper			Current
	plating	Temperature		density	Time	Filling
	solution	(° C.)	Anode	(A/dm2)	(min)	property

Method 25	12	23	insoluble	2	50	A
			electrode
Method 26	12	23	insoluble	3.5	23.6	B
			electrode
Method 27	13	35	insoluble	3.5	23.6	A
			electrode
Method 28	14	50	insoluble	7.0	14.3	A
			electrode
Insoluble electrode: an iridium oxide-coated titanium electrode covered with a neutral diaphragm (Yumicron Filter Y9205TA, produced by Yuasa Membrane Systems Co., Ltd.)

Evaluation Method of Filling Performance

The through hole after the copper plating was measured for the dent thickness by observing the cross section. The measurement position of the dent thickness is shown in FIGS. 6 and 7. The dent thickness was measured on the surface having a larger dent.

Evaluation: content

A: dent thickness of less than 15 μm

B: dent thickness of from 15 to 30 μm

C: dent thickness of 30 μm or more

It was found from the results that the same tendency as the filling of a via was observed in the filling of a through hole, and the period of time required for filling a through hole was half or less of the ordinary technique, as similar to the filling of a via.

INDUSTRIAL APPLICABILITY

The method of the invention can be applied to the production of a substrate for a portable phone, a smartphone, a tablet, a personal computer, and the like.

REFERENCE SIGN LIST

• 1 via test substrate
• 2 copper layer
• 3 resin layer
• 4 copper plated layer
• 10 through hole test substrate
• a thickness of surface layer copper plating
• b dent thickness