JP2001144420A - Hole-plugging liquid-shaped resin for printed-wiring board, and build-up wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermosetting resin system hole-plugging resin for small diameter with an improved continuous filling property to through holes and inner via holes with small diameter and high density and an improved polishing property after curing, and a build-up wiring board with an improved adhesion property and hence an improved connection reliability. SOLUTION: The thermosetting resin system hole-plugging resin for small diameter as a yield value of 100-800 Pa in the CASSON viscosity expression and a residual viscosity of 0.5-8.0 Pa.s. In the build-up wiring board, the hole- plugging resin has been filled into a through hole and an inner via hole.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid resin and a build-up wiring board for filling a hole in a printed wiring board, and more particularly, to a resin board between adjacent holes at the time of filling which is excellent in continuous filling on a mass production scale. No connection on the surface), and a thermosetting resin-based small-diameter hole-filling liquid resin having excellent polishing properties after curing, and this thermosetting resin-based small-diameter hole-filling liquid resin,
The present invention relates to a build-up wiring board in which through holes and / or via holes provided in a board are filled.

[0002]

2. Description of the Related Art In recent years, as electronic devices have become smaller in diameter and higher in density,
Wiring boards used in such electronic devices are also required to have smaller diameters and higher densities. In addition, semiconductor elements are also area-mounted, with 0.8mm to 0.5mm pitch C
SPs have become available in large quantities and are accelerating their movement. For example, a build-up multilayer wiring board has been frequently used as a wiring board for realizing such a small diameter and high density.

In such a build-up multilayer wiring board, a conductor circuit including a through hole and an inner via hole is formed in a core substrate, and a recess is formed. For this reason, when the interlayer insulating material is applied to the surface of the core substrate with the hollow portions between the conductor circuits including the through holes provided in the core substrate and the via holes formed on the surface of the substrate being left as they are, the through holes are formed in the surface of the formed interlayer insulating material layer. And a dent is generated at the position of the dent and the dent portion. This dent also appears on the surface of the multilayer wiring board, causing problems such as insufficient adhesion of the resist film for circuit formation during the formation of the outermost circuit, and when electronic components are mounted even if the circuit is formed In many cases, it caused continuous failure.

[0004] On the other hand, as means for solving the above-mentioned generation of dents, for example, as disclosed in Japanese Patent Application Laid-Open No. Hei 6-260756, a paste-like filling of through holes is performed without mixing air bubbles. A resin filler containing inorganic particles coated with a silane-based coupling agent as an additional component, or a multilayer filled with the resin filler, as disclosed in Japanese Patent Application Laid-Open No. H10-224034. Printed wiring boards have been proposed.

[0005]

However, in the method disclosed in JP-A-6-260756, a solvent such as methyl ethyl ketone or methyl cellosolve is used for adjusting the viscosity. Although removal is required, it is extremely difficult to completely remove the solvent from the charged resin. As a result, when the solvent remains in the resin filler, like a build-up multilayer wiring board,
When forming an interlayer insulating material layer by applying an interlayer insulating material to a surface of a resin filler filled in a through hole or the like provided in a core base material, a residual solvent in the resin filler is volatilized and the interlayer insulating material is volatilized. There is a problem that the layers are pushed up and delamination occurs.

Further, the multilayer printed wiring board filled with a resin filler proposed in Japanese Patent Application Laid-Open No. H10-224034 has a silane-based resin in which the resin filler suppresses cracking even under high temperature and high humidity conditions. Although inorganic particles coated with a coupling agent are included as an additive component, coating inorganic particles of a filler with a silane-based coupling agent improves wettability with a resin, but viscosity adjustment is not easy. As a result, it becomes difficult to perform continuous printing with the printer, resulting in a problem of continuous filling workability.
In addition, if the viscosity adjustment is not sufficient, bleeding during printing (connection of the resin between adjacent holes on the substrate surface at the time of filling) occurs,
As a result of the filler being cured in a shape spread on the substrate, the polishing property during polishing after curing has been a problem.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and a main object of the present invention is to provide a printed wiring board, especially a build-up multilayer wiring board, with a small-diameter high-density board provided on the board. That is, the hole diameter is 300
Filling small-diameter or less high-density through holes or inner via holes and smoothing the surface of the substrate to provide a substrate with excellent adhesion and excellent connection reliability. Excellent continuous filling of
There is no bleeding (connection of the resin between the adjacent holes at the surface of the substrate at the time of filling), and the polishing resin after curing is excellent. An object of the present invention is to provide a build-up wiring board having excellent connection reliability.

[0008]

Means for Solving the Problems The present inventors have conducted various studies to achieve the above object. As a result, CAS
The present inventors have found that an extremely good result can be obtained by using a thermosetting resin-based filling liquid resin in which the yield value and the residual viscosity of the SON viscosity formula are within specific ranges, and have completed the invention.

That is, the present invention relates to a thermosetting resin-based filling liquid resin for a small-diameter high-density hole having a hole diameter of 300 μm or less formed in a printed wiring board, wherein the yield value in a CASSON viscosity formula is 100 to 800 Pa; Residual viscosity is 0.
The above object has been achieved by a liquid resin for filling holes in a printed wiring board, which has a pressure of 5 to 8.0 Pa · s.

The present invention also provides a first insulating layer having a first via hole and / or a through hole plated with copper for use in a build-up wiring board, particularly, an electric circuit, and a first insulating layer formed on the first insulating layer. A second insulating layer having a second copper plated via hole for electrical circuit connection formed in contact therewith, and the second copper plated via hole for the second electrical circuit connection is provided with the first insulating layer. A build-up board formed immediately above or in the vicinity of via holes and / or through-holes subjected to copper plating for electric circuit connection, wherein the filling resin is filled in via holes or / and through-holes provided in the board. The above object has been achieved by a build-up substrate characterized by being filled.

In the present invention, in order to be excellent in continuous filling property, free from bleeding (connection of resin between adjacent holes on the substrate surface at the time of filling), excellent in polishing property after curing, and suitable for use, it is necessary to use CASSON. The yield value in the viscosity equation is 100 to 80
0 Pa and a residual viscosity of 0.5 to 8.0 Pa · s.

Here, the CASSON viscosity equation is τ ^1/2
= Τ _c ^1/2 + (μ _c · γ) ^1/2 where τ, τ _c , μ _c , and γ are the shear stress, yield value, residual viscosity, and shear rate, respectively. is there. The thermosetting resin-based small-diameter hole filling liquid resin of the present invention exhibits non-Newtonian flow characteristics, is pseudoplastic flow, and has thixotropic (thixotropic). Therefore, in the liquid filling resin of the present invention, the viscosity characteristic changes depending on the filling conditions (shear rate).

Generally, the shear rate γ applied to the filling resin during filling by screen printing or the like is 10 ³ to 10 ⁴
[1 / sec], and it is important to grasp the flow characteristics of the filling resin at this time. In other words, the lower the viscosity when the shear rate γ is 10 ³ to 10 ⁴ [1 / sec], the easier it is to fill the holes.

However, if the shear rate γ is 10 ³ to
The viscosity in the range of 10 ⁴ [1 / sec] cannot be measured using a current viscometer, and the viscosity at the time of filling cannot be measured from the result of the shear rate range that can be actually measured. (Viscosity at a shear rate γ of 10 ³ to 10 ⁴ [1 / sec])
Need to predict.

The yield value and the residual viscosity can be determined by performing fitting from the actually measured shear stress, shear rate, and viscosity using the CASSON viscosity equation. Here, the residual viscosity is the viscosity at the time when the shear rate is infinite, and the viscosity at the time of filling that cannot be measured due to the residual viscosity (shear rate γ is 10 ³ to 10 ⁴ [1 / sec]. ), That is, the viscosity at the actual shear rate at the time of filling can be predicted.

If the residual viscosity is too large, it is difficult to fill the hole. The smaller the residual viscosity is, the easier it is to fill the holes. However, if it is too low, the print-out property during screen printing or the like will deteriorate, so that the residual viscosity must be in the range of 0.5 to 8.0 Pa · s as described above.

The yield value is the value of the shear stress when the shear rate is close to 0, and is the minimum value of the shear stress required for the filling resin to move by shearing. If the yield value is too high, a large load is applied to the printing machine and the screen at the initial stage of filling such as screen printing, and the productivity becomes a problem. But if the yield value is too low,
It easily flows at the time of printing omission, is connected to the resin of the adjacent hole, and printing bleeding is likely to occur. When bleeding occurs, the filler is cured in a shape spread on the substrate,
Abrasion at the time of polishing after curing becomes a problem. Therefore, the yield value needs to be in the range of 100 to 800 Pa as described above.

In the present invention, the measurement of the shear stress, the shear rate and the viscosity was carried out using a cone plate type E-type viscometer. In addition, the liquid filling resin of the present invention exhibits non-Newtonian flow characteristics and thixotropy (thixotropic) as described above, and exhibits a so-called hysteresis loop during viscosity measurement. From a shear stress value measured when the shear rate was increased to a high shear rate and a shear rate, and determined by performing a CASSON viscosity equation fitting.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION In the CASSON viscosity formula, the yield value is 100 to 800 Pa, and the residual viscosity is 0.5 to 8.0 Pa.
In order to obtain a liquid resin for filling in s, it is preferable to add and mix an insoluble filler. As the insoluble filler, only an inorganic filler may be used, an organic filler and an inorganic filler may be used in combination, or only an organic filler may be used. The use of a thixotropic agent facilitates further adjustment.

Examples of such an inorganic filler include C
The yield value in the ASSON viscosity formula is 100 to 800 Pa,
There is no particular limitation as long as the residual viscosity can be adjusted to 0.5 to 8.0 Pa · s. For example, silica, alumina, mullite, zirconia and the like are preferred. Further, a hydroxide such as magnesium hydroxide may be used for imparting flame retardancy. It is preferable to use such an inorganic filler having a maximum particle size of 20 μm or less. If it is too large, the smoothness of the surface will be lost, and the surface treatment will be difficult, the voids will be easily bitten, and the connection reliability will be reduced. The amount of the inorganic filler is preferably in the range of 2 to 50 parts by weight based on 100 parts by weight of the thermosetting resin component. If it is less than 2 parts by weight, the effect of adding filler is thin,
If the amount is more than 50 parts by weight, the residual viscosity will be higher than 8.0 Pa · s, and it will be difficult to fill the holes. If the amount is 2 to 50 parts by weight with respect to 100 parts by weight of the thermosetting resin component, the yield value in the CASSON viscosity formula is 100 to 800 Pa, and the residual viscosity is 0.5 to 8.0 Pa · s.
Can be easily adjusted.

As the organic filler, the CAS
There is no particular limitation as long as the yield value in the SON viscosity formula can be adjusted to 100 to 800 Pa, and the residual viscosity can be adjusted to 0.5 to 8.0 Pa · s. For example, acrylic polymers, epoxy polymers, styrene polymers, and the like are preferred. . In addition, addition of flame-retardant organic fillers, such as halogen-based organic flame retardants and non-halogen-based organic flame retardants,
Since the filling resin has flame retardancy, it also contributes to the flame retardancy of the substrate, and is more preferable. It is preferable to use such an organic filler having a maximum particle size of 20 μm or less. If it is too large, the smoothness of the surface will be lost, and the surface treatment will be difficult, the voids will be easily bitten, and the connection reliability will be reduced. The amount of the organic filler is preferably in the range of 2 to 50 parts by weight based on 100 parts by weight of the thermosetting resin component. If the amount is less than 2 parts by weight, the effect of adding the filler is thin, and if it is more than 50 parts by weight, the residual viscosity becomes larger than 8.0 Pa · s, and it becomes difficult to fill the hole. If the blending amount is 2 to 50 parts by weight with respect to 100 parts by weight of the thermosetting resin component, the yield value in the CASSON viscosity formula is 100 to 800 Pa and the residual viscosity is 0.5 to 8.0 Pa · s. Easy to adjust.

In the present invention, it is more effective to use a thixotropic agent to adjust the yield value and residual viscosity in the CASSON viscosity formula. Thixotropic agents are also referred to as thixotropic agents,
It is used when imparting thixotropic properties (thixotropic) of paints and the like. Examples of such thixotropic agents include finely divided silica, bentonite, smectite, carbon black, and the like. In particular, it is preferable to use finely divided silica because it is easy to adjust and preferably has a yield value of 100 in the CASSON viscosity formula.
It is not particularly limited as long as it is a thixotropic agent capable of adjusting the viscosity to 800 Pa and the residual viscosity to 0.5 to 8.0 Pa · s.

As the liquid resin for filling holes for small diameter of the present invention,
Those having a volatile content of 1.5% by weight or less, particularly 0.5% or less at the time of curing are desirable. If the volatile content is more than 1.5% by weight, voids are liable to be generated, the resin shrinks after curing is increased, and problems such as adhesion, delamination, and reduction in reliability are likely to occur.

In the present invention, the resin component of the thermosetting resin-based liquid filling resin for small-diameter holes is, for example, an epoxy resin, a phenol resin, a melamine resin, a urea resin, a polyester resin, an alkyd resin, a guanamine resin, a silicon resin, or the like. One or more thermosetting resins selected from the group can be used. Due to the problem of heat resistance of the substrate, epoxy resin is preferably used. The curing agent is not particularly limited. In other words, the yield value in the CASSON viscosity equation is 100 to 800 Pa, and the residual viscosity is 0.5 to
Any resin component / curing agent that satisfies 8.0 Pa · s, the maximum particle size of the insoluble filler compounded is 20 μm or less, and the volatile matter during curing is 1.5% by weight or less.

The build-up wiring board according to the present invention, that is, the build-up multilayer wiring board in which the via hole or the through-hole is filled with the liquid resin for filling the hole-filling of the present invention is, for example, (1) a via-hole or a through-hole provided in the wiring board. Filling the holes with the filling resin of the present invention, (2) thermally curing the filling resin filled in (1),
(3) a step of polishing the surface of the liquid resin filling the hole that has been thermoset in the step (2).

[0026]

Embodiment 1 FIG. 1 is a view showing an example of a manufacturing process of a build-up wiring board using a filling resin according to the present invention. The following FIG.
The present invention will be further described based on the following.

(1) Substrate 1 made of glass epoxy resin
The circuit 20 was formed by performing a pretreatment, photolaminating, exposing, developing, and etching steps on both sides of a copper-clad laminate in which a copper foil having a thickness of 18 μm was laminated on both sides of No. 0. (See FIG. 1A).

(2) A prepreg 30 and a copper foil 40 were laminated and pressed on both sides of the substrate 10 of (1) (FIG. 1).
(B)).

(3) 300 μm on the substrate 10 of the above (2)
500 holes are formed at a distance of 600 μm between the adjacent holes, and then desmear plating is performed.
Conduction treatment in the hole was performed by m-thick copper plating 60, and rust preventive treatment was performed (see FIG. 1 (c)).

(4) 100 parts by weight of bisphenol F type epoxy resin "Epicoat 807" (manufactured by Yuka Shell) as an epoxy resin and 10 parts by weight of amine adduct type "Amicure PN-23" (manufactured by Ajinomoto Fine Techno) as a curing agent Were mixed, and 30 parts by weight of SiO ₂ particles having a maximum particle diameter of 10 μm and 7 parts by weight of finely divided silica as a thixotropic agent were mixed and dispersed by a roll mill to obtain a liquid filling resin. Table 1 shows the relationship among the viscosity, shear rate γ, and shear stress of the obtained filling resin. Measurements were made using a cone plate type E
Type viscometer (Visco Tester VT5 manufactured by HAAKE)
50) at 23 ° C. Using this value, C
A CASSON plot was performed to determine the yield value and residual viscosity in the ASSON viscosity equation. The results are shown in FIG. From FIG. 3, the yield value of the obtained filling resin is 47.
It was 0 Pa, and the residual viscosity was 3.7 Pa · s.

[0031]

[Table 1]

(5) The hole 80 of the substrate 10 shown in FIG.
Cleaning with dilute sulfuric acid was carried out for cleaning the inside and removing the rust inhibitor. After the washing, the filling resin 50 obtained in the above (4) was filled into the holes 80 of the substrate 10 by a screen printing method. Printing is mesh size # 120, opening diameter 0.
A 6 mm stainless mesh plate was used. Next, 140
A heat treatment was performed at 90 ° C. for 90 minutes to harden the filling liquid resin (see FIG. 1D).

(6) FIG. 1 (d) cured in the above (5)
The liquid resin 50 filling the cured hole protruding from both sides of the hole was buffed. Further, in order to remove the scratches generated by the buff polishing, the substrate 10 was buff-polished using a finer buff of abrasive grains to prepare a substrate 10 having both surfaces smooth and washed with dilute sulfuric acid (FIG. 1 (e)). reference).

(7) FIG. 1 (e) polished in the above (6)
The substrate 10 was subjected to a desmear treatment, and then electroless plating and electrolytic plating were performed to deposit a 15 μm plating 61 on the surface of the substrate 10 (see FIG. 1F).

(8) FIG. 1 plated in (7)
A circuit 21 was formed by performing a pretreatment, photolaminating, exposing, developing, and etching steps on both surfaces of the substrate 10 (f) (see FIG. 1 (g)).

(9) An interlayer insulating material 70 and a copper foil 41 are laminated on both surfaces of the substrate 10 on which the circuit 21 is formed in (8),
A build-up layer was produced (see FIG. 1 (h)).

(10) A through hole 81 was formed in the substrate 10 on which the build-up layer was formed in (9) (FIG. 1).
(See (i)).

(11) On both surfaces of the substrate 10 on which the through holes 81 were drilled in the above (10), window etching was performed directly on the circuit fabricated in the above (8) (see FIG. 1 (j)). .

(12) The etched portion of the substrate 10 window-etched on both sides in (11) above the hole where the inner layer is plated by laser processing.
After drilling holes, desmearing is performed and a 20 μm plating 62
Was applied to the entire surface of the substrate 1 (see FIG. 1 (k)).

(13) An outer layer circuit 22 is formed on both sides of the substrate 10 which has been subjected to the plating process in (12), and a solder resist 90 is applied, dried, exposed, developed, and post-cured to form a six-layer build. An up-wiring board was manufactured (see FIG. 1 (l)).

Embodiment 2 FIG. 2 is a diagram showing another example of a manufacturing process of a build-up wiring board according to the present invention. Hereinafter, the present invention will be further described with reference to FIG.

(7-2) The same steps as (1) to (6) in FIG. 1 are carried out to form a substrate 10 having smooth surfaces on both sides, and the substrate 10 obtained by washing with dilute sulfuric acid is filled. Dry film resist 9 on the upper and lower surfaces containing material (liquid filling resin)
5 (see FIG. 2 (e-2)).

(8-2) A circuit 23 was formed by performing exposure, development, and etching steps on both surfaces of the substrate 10 of (7-2) (see FIG. 2 (g-2)).

(9-2) An interlayer insulating material 71 and a copper foil 42 were laminated on both surfaces of the substrate 10 on which the circuit 23 was formed in the above (8-2) to form a build-up layer (FIG. 2 (h- 2)).

(10-2) Window etching is performed immediately above the circuit fabricated in (8-2), and then the window-etched portion of the substrate 10 is etched.
Holes were drilled up to the holes where the inner layer was plated by laser processing (see FIG. 1 (k-2)).

(11-2) Desmearing of the hole prepared in the above (10-2) is performed, and a plating 62 of 20 μm is applied to the substrate 1.
0, an outer layer circuit 24 is formed on both sides thereof, a solder resist 91 is applied, dried, exposed, developed, and post-cured to form a six-layer build-up substrate (see FIG. 2 (l-2)). ).

Test Example 1 In accordance with Example 1, liquid-filled liquid resins of Samples 1 to 5 having a yield value and a residual viscosity shown in Table 2 were prepared. Except for using each of the filling resin, 100 build-up wiring boards were manufactured for each sample in the same manner as in Example 1. The continuous filling property and polishing property of the filling resin in the manufacturing process of each wiring board were evaluated according to the evaluation criteria shown in Table 3. Table 2 shows the results.

[0048]

[Table 2]

[0049]

[Table 3]

Test Example 2 Except for using the filling resin of Samples 6 to 10 having a yield value and a residual viscosity shown in Table 4 prepared in accordance with Example 1, the continuous filling property was improved in the same manner as in Test Example 1. The polishing property was evaluated. Table 4 shows the results.

[0051]

[Table 4]

Test Example 3 Build-up wiring was carried out in the same manner as in Example 1 except that the filling resin of Samples 11 to 13 having the volatility, yield value and residual viscosity shown in Table 5 and prepared according to Example 1 was used. 100 substrates were manufactured for each sample. The delamination property of each of the obtained wiring boards was evaluated according to the evaluation criteria shown in Table 6. Table 5 shows the results.

[0053]

[Table 5]

[0054]

[Table 6]

Test Example 4 Samples 14 to 16 having a yield value of 200 Pa and a residual viscosity of 6.5 Pa · s in the same manner as in Example 1 except that the filler (SiO ₂ particles) having the maximum particle size shown in Table 7 was blended. And a continuous filling property and an abrasive property were evaluated in the same manner as in Test Example 1. Table 7 shows the results.

[0056]

[Table 7]

[0057]

The liquid filling resin of the present invention is excellent in continuous filling into small-diameter, high-density through holes and inner via holes having a small diameter of 300 μm or less, especially in a mass production scale, and is excellent in bleeding. There is no connection between adjacent holes on the substrate surface of the resin), and since it has excellent polishing properties after curing, it is possible to efficiently manufacture a build-up wiring board having excellent adhesion and therefore excellent connection reliability. .

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional explanatory view showing an example of a manufacturing process of a build-up wiring board of the present invention.

FIG. 2 is a schematic sectional explanatory view showing another example of the manufacturing process of the build-up wiring board of the present invention.

FIG. 3 is a CASSON plot for obtaining a yield value and a residual viscosity in a CASSON viscosity equation.

[Explanation of symbols]

 10: Substrate 20, 21, 22, 23, 24: Circuit 30: Prepreg 40, 41, 42: Copper foil 50: Filling liquid resin 60, 61, 62: Plating 70, 71: Interlayer insulating material 80, 81: Through hole 90, 91: Solder resist 95: Dry film resist

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Yoshino 6-5-1, Nishi-Shinjuku, Shinjuku-ku, Tokyo Japan CMK Co., Ltd. (72) Inventor Takashi Kawahara 19-17 Ikedanakamachi, Neyagawa-shi, Osaka Japan Paint (72) Inventor Takahiro Nakano 19-17 Ikedanakamachi, Neyagawa-shi, Osaka F-term (reference) 4J002 AA021 BC032 BG002 CC031 CC161 CC181 CC191 CD001 CD002 CF001 CF011 CP031 DE076 DE096 DE146 DJ016 FD012 FD016 GQ00 5E314 AA25 AA32 AA33 BB06 CC07 EE02 FF08 GG11 5E346 AA43 CC09 CC13 EE09 EE33 FF15 GG15 GG18 GG19 GG28

Claims (9)

[Claims] 1. A printed circuit board having a hole diameter of 3
A thermosetting resin-based filling liquid resin for small-diameter, high-density holes of not more than 00 μm, having a yield value of 100 to 800 Pa and a residual viscosity of 0.5 to 8.0 Pa · s in the CASSON viscosity formula.
A liquid filling resin for printed wiring boards, characterized in that: 2. The filling resin according to claim 1, wherein a volatile component at the time of curing has a volatility of 1.5% by weight or less. 3. The filling resin according to claim 1, further comprising an insoluble filler, wherein the maximum particle diameter of the insoluble filler is 20 μm or less. 4. The filling resin according to claim 3, wherein the insoluble filler is an inorganic filler. 5. The filling resin according to claim 3, wherein the insoluble filler comprises an organic filler and an inorganic filler. 6. The filling resin according to claim 3, wherein the insoluble filler is an organic filler. 7. The filling resin according to claim 1, further comprising a thixotropic agent as an insoluble filler component. 8. A build-up wiring board, characterized in that via-holes and / or through-holes provided in the board are filled with the filling resin liquid according to any one of claims 1 to 7. 9. A build-up wiring board is formed in contact with a first insulating layer having a first via hole and / or a through-hole plated with copper for electric circuit connection and on the first insulating layer. A second insulating layer having a copper-plated via hole for connection to a second electric circuit.
The via hole plated with copper plating for electrical circuit connection is formed immediately above or near the via hole and / or through hole plated with copper for the first electrical circuit connection. 9. The build-up wiring board according to 8.