JP2005286122A - Printed wiring board and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printed wiring board which reconciles both a thin-line and high-density conductor pattern and connection reliability, and to provide its manufacturing method. <P>SOLUTION: Thin steps 21 are formed at peripheral edges of through holes of conductor patterns 2 formed on both top and reverse surfaces 1A and 1B of an insulating substrate. On the thin steps 21, surface-directional plating parts 42 are laminated on the thin steps 21 to protrude from both ends of penetration-directional plating parts 41 deposited on the inner wall of the through hole 3 along the insulating substrate 1. Consequently, the conductor patterns 2 and the plated through holes 3 are interconnected having contact surfaces extending along the conductor patterns 2 and in a direction crossing it. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a printed wiring board in which conductor patterns formed on both front and back surfaces of an insulating substrate are interlayer-connected at appropriate positions, and a method for manufacturing the same.

Printed wiring boards are used in all types of electronic equipment, from mass production equipment such as televisions to equipment that requires high reliability such as rockets, for the purpose of improving productivity, ensuring mass production quality, and improving reliability. Yes. In recent years, electronic devices have been miniaturized, and accordingly, there has been a demand for higher precision and higher density of printed wiring boards.
This type of printed wiring board generally has a configuration in which conductor patterns formed on both front and back surfaces of an insulating substrate are electrically connected at appropriate positions via plated through holes.

Depending on the use of the printed wiring board, it may be preferable to fill the plated through hole. As the hole filling method, the copper foil on the insulating substrate is overlaid by plating the entire through hole to fill the hole, so-called filled plating method (for example, refer to Patent Document 1), or after the primary plating over the copper foil, So-called lid plating that fills through holes with conductive paste, etc., polishes both ends of this conductive paste body to make it flush with the primary plating layer, and then applies plating on these primary plating layer and conductive paste body The law (see, for example, Patent Document 2) is known.
JP 2003-046248 A JP 2003-069228 A

  However, in the case of these filled plating methods and lid plating methods, the through hole is filled and a plating layer is further formed on the through hole, so that the plated portion applied to the inner wall of the through hole and both the front and back surfaces are formed. However, since the plating layer is laminated on the copper foil, the thickness of the conductor layer (copper foil and plating layer) for forming the conductor pattern increases. There is a problem that pattern formation becomes difficult. In particular, in the lid plating method, since two plating layers are laminated on the copper foil, the tendency becomes remarkable.

On the other hand, when the through hole is not filled, since the plated portion can be formed on the inner wall of the through hole without changing the thickness of the initial copper foil, the conductor pattern for forming the conductor pattern can be easily formed. In addition, it is possible to reduce the line thickness and increase the density.
However, since the copper foil on the insulating substrate, that is, the contact between the conductor pattern and the through-hole plating is only the edge portion of the copper foil, the more the conductor pattern is thinned and densified, that is, the copper foil As the thickness is reduced, there is a problem that it becomes difficult to ensure connection reliability.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a printed wiring board having both thin and dense conductor patterns and connection reliability, and a method for manufacturing the same. is there.

In order to solve the above problems, a printed wiring board according to the present invention has a thin stepped portion formed on the periphery of a through hole of a conductor layer provided on both front and back surfaces of an insulating substrate, and the inner wall of the through hole is formed on the thin stepped portion. A second plating portion extending along the insulating substrate from both ends of the first plating portion deposited on the substrate is laminated.
Further, the printed wiring board of the present invention has a contact surface in which a conductor layer provided on both front and back surfaces of an insulating substrate and a plated through hole for interlayer connection extend in the thickness direction of the conductor layer and in a direction intersecting therewith. And are interconnected.

The method for producing a printed wiring board of the present invention includes a mask process for forming a plating resist layer on the front and back surfaces of a copper-clad laminate having a through hole, leaving an opening peripheral edge of the through hole, and
An etching step of partially etching the copper foil exposed at the opening peripheral edge of the through hole in the thickness direction; and a first plating step of depositing a plating layer on the inner wall of the through hole and the partially etched copper foil surface; It is characterized by providing.
In this case, it is also possible to include a second plating step in which the inner space of the plated through hole formed by the first plating step is filled by electroplating using the copper foil under the plating resist layer as a power feeding portion. Good.

  According to the printed wiring board of the present invention, it is possible to increase the contact area between the conductor pattern provided on both the front and back surfaces of the insulating substrate and the plated through hole for interlayer connection. Even if the thickness of the conductor pattern is equal to or less than that of the copper foil of the copper-clad laminate, the connection reliability can be improved without impairing the connection reliability.

According to the method for manufacturing a printed wiring board of the present invention, since the thickness of the conductor layer etched during pattern formation becomes the thickness of the copper foil originally laminated on the copper-clad laminate, the formation of the conductor pattern is easy. At the same time, the thinning and high density can be easily realized.
Further, since the plated through hole is filled, the copper foil is not dragged in the polishing direction during surface polishing, and a printed wiring board with high reliability of interlayer connection can be manufactured.

The best mode for carrying out the present invention will be described below with reference to FIGS.
First, an example of a printed wiring board will be described with reference to FIGS.
In this printed wiring board P, a conductive pattern (conductor layer) 2 cut out from, for example, a copper foil (conductor layer) of a copper-clad laminate is provided on both the front and back surfaces 1A and 1B of the insulating substrate 1. Of the conductor pattern 2, the conductor pattern 2a formed on the periphery of the opening of the filled through hole 3 is formed with a thin step portion 21 that is recessed by one step from the outermost surface 2A as shown in FIG. .

The thin step portion 21 includes an upper wall surface 21A and a lower wall surface 21C along the thickness direction of the conductor pattern 2, and a floor surface 21B that extends perpendicularly to the wall surfaces 21A and 21C and extends along the insulating substrate 1. On the surface 21 </ b> B, a surface direction plating portion (second plating portion) 42 of the plated through hole 4 is laminated flush with the outermost surface 2 </ b> A of the conductor pattern 2.
That is, the conductor pattern 2 provided on the front and back surfaces 1A and 1B of the insulating substrate 1 and the plated through hole 4 for interlayer connection are arranged at the periphery of the opening of the plated through hole 4 (through hole periphery). The interconnections have a thickness direction of 2 and a contact surface extending in a direction crossing the thickness direction.

  In the present embodiment, the upper wall surface 21A of the thin-walled step portion 21 and the outer peripheral surface 42A of the surface-direction plated portion 42 in contact therewith, and the axially opposite ends of the lower wall surface 21B of the thin-walled step portion 21 and the through-direction plated portion 41 in contact therewith. Is a contact surface extending in the thickness direction, and a contact surface extending in a direction (a direction along the insulating substrate 1) in which the floor surface 21B of the thin-walled step portion 21 and the lower surface 42B of the surface-direction plating portion 42 in contact therewith intersect the thickness direction. is there.

The plated through hole 4 extends along the insulating substrate 1 from a cylindrical through direction plated portion (first plated portion) 41 formed on the inner wall of the through hole 3 and from both axial ends of the through direction plated portion 41. The inner space part surrounded by the through-direction plating part 41 is filled with a hole filling part 5 made of, for example, plated copper.
The thickness T of this surface direction plating part 42 and the overhanging dimension L in the surface direction are set, for example, to T = 5 to 6 μm and L = 0.1 to 0.2 mm. The thickness of the conductor patterns 2 and 2a is set to be equal to or slightly smaller than the thickness of the copper foil previously laminated on the copper-clad laminate, for example, 12 μm or less.

  As described above, according to the printed wiring board P of the present embodiment, the thin step portion 21 is formed in the conductor pattern 2a in the opening peripheral portion of the plated through hole 4 in the conductor pattern 2, and the conductor pattern 2 and the plated through hole 4 are contacted not only on the wall surfaces 21A and 21C of the thin stepped portion 21, the outer peripheral surface 42A of the corresponding surface-direction plated portion 42, and both axial ends of the through-direction plated portion 41. In addition, since it is secured also on the floor surface 21B of the thin stepped portion 21 extending in the surface direction of the insulating substrate 1 and the lower surface 42B of the corresponding surface-direction plated portion 42, the conductor pattern 2 can be reduced in size and density. However, the reliability of interlayer connection is high.

  That is, the conductor pattern 2 provided on the front and back surfaces 1A and 1B of the insulating substrate 1 and the plated through hole 4 for interlayer connection are arranged in the thickness direction of the conductive pattern 2 at the periphery of the opening of the plated through hole 4. Since not only the contact surface along the contact surface but also the contact surface along the surface direction of the insulating substrate 1 are interconnected, the contact area is increased as compared with the conventional case. Even if the thickness of the conductor pattern 2 is equal to or less than that of the copper foil of the copper-clad laminate in order to cope with higher density, the connection reliability can be drastically improved on the contrary rather than impairing the connection reliability.

Furthermore, in this printed wiring board P, since the plated through hole 4 is filled with the hole filling portion 5 made of plated copper, the plated through hole 4 has good heat conductivity as well as electrical conductivity.
Therefore, a multilayer printed wiring board with good heat dissipation can be configured even when the printed wiring board P is required to have multiple layers.

Next, an example of a method for manufacturing the printed wiring board P will be described with reference to FIGS.
First, a copper-clad laminate Q having copper foils 12 for forming the conductor pattern 2 on both the front and back surfaces of the insulating substrate 1 is prepared (FIG. 1) and insulated from one surface to the other surface. Through-holes 3 are formed for interlayer connection of conductor patterns 2 formed on both the front and back surfaces of the substrate 1 at appropriate positions (FIG. 2).
Next, surface preparation and desmearing are performed, and a catalyst for improving the adhesion of electroless copper plating, for example, palladium (Pd), is adsorbed on the surface of the copper foil 12 and the inner wall of the through hole 3.

Next, the plating resist layer 13 is formed so that the copper foil 12 is exposed at the opening peripheral portion of the through hole 3 while leaving (removing) the opening peripheral portion of the through hole 3 (FIG. 3, mask process). ), The copper foil 12a exposed at the peripheral edge of the opening is partially etched in the thickness direction to form the thin stepped portion 21 (FIG. 4, etching step).
The thickness of the copper foil 12a removed by this partial etching, that is, the height of the upper wall surface 21A of the thin stepped portion 21 is set to 5 to 6 μm, for example, with respect to the initial thickness 12 μm of the copper foil 12. In the case of partial etching, an alkaline type etchant is used, so that the Pd catalyst adsorbed in the previous step remains on the surface of the copper foil 12 and the inner wall of the through hole 3, while the copper foil 12a. Only selectively etch.

Next, as a result of partial etching, electroless copper plating is applied to the thin stepped portion 21 that is recessed one step lower than the copper foil 12 immediately below the plating resist layer 13 and the inner wall of the through hole 3 to deposit copper plating.
Then, a cylindrical penetration direction plating portion 41 extending in the penetration direction is deposited on the inner wall of the through hole 3 and protrudes in the surface direction of the insulating substrate 1 to the thin stepped portion 21 of the copper foil 12, in other words, the through hole. The ring-shaped surface direction plating part 42 which protrudes along the radial direction outer side of 3 precipitates (FIG. 5, 1st plating process).

Since the through-direction plated portion 41 and the surface-direction plated portion 42 are deposited together, the through-hole 3 is electrically connected between the conductor patterns 2 and 2 formed on both surfaces of the insulating substrate 1 in a later step. The plated through hole 4 is formed.
Next, electrolytic copper plating is performed using the copper foil 12 immediately below the plating resist layer 13 as a power feeding portion, and the inner space portion 14 surrounded by the cylindrical through-direction plating portion 41 is filled with plated copper ( FIG. 6, second plating step). The hole filling portion 15 is formed until it bulges from the outer surface 12A of the copper foil 12.

Next, the plating resist layer 13 is removed, and the front and back surfaces of the copper-clad laminate Q are polished. At the time of polishing, not only the bulging portion of the hole filling portion 15 is polished, but a polishing margin is set such that the copper foil 12 is polished by 0.1 to 0.2 μm from its outer surface. The outer surface is polished so that the portion of 12 that is not partially etched, the surface-direction plated portion 42 of the plated through hole 4, and the hole filling portion 15 are flush with each other (FIG. 7).
At this time, an external force acts on the plated through hole 4 in the polishing direction, that is, in the direction along the insulating substrate 1. However, since the plated through hole 4 is filled, the surface direction plated portion 42 is dragged in the polishing direction. However, even if it may be dragged, the contact state between the lower surface 42A of the planar plating portion 42 and the floor surface 21B of the thin stepped portion 21 is maintained as it is, so that interlayer connection is ensured.

Thereafter, when the copper foil 12 is etched in a predetermined pattern by the subtractive method, conductor patterns (circuit patterns) 2 are formed on the front and back surfaces 1A and 1B of the insulating substrate 1, and the conductor patterns 2 are plated through holes. A printed wiring board P electrically connected to each other through 4 is formed (FIG. 8).
At this time, since the thickness of the conductor layer to be etched is the thickness obtained by subtracting the polishing margin from the copper foil 12 originally laminated on the copper-clad laminate Q, the formation of the conductor pattern 2 is facilitated. Thinning and high density can be easily realized.

In addition, this invention is not limited to the said Example, A various design change is possible in the range which does not deviate from the summary.
For example, the conductor pattern 2 may be formed by leaving the inner space 14 shown in FIG.

It is sectional drawing which shows the copper clad laminated board used for manufacture of the printed wiring board by one Example of this invention. It is sectional drawing which shows the state which formed the through hole in the copper clad laminated board shown in FIG. FIG. 3 is a cross-sectional view illustrating a state in which a plating resist layer is formed on the copper foil, leaving the opening peripheral edge of the through hole, following FIG. 2. FIG. 4 is a cross-sectional view showing a state in which the copper foil exposed at the peripheral edge of the opening is partially etched following FIG. 3. FIG. 5 is a cross-sectional view showing a state in which electroless plating is applied to the inner wall of the through hole and the partially etched copper foil portion following FIG. 4. FIG. 6 is a cross-sectional view illustrating a state in which the inside of the through hole is filled with electroplating using the copper foil under the plating resist layer as a power feeding portion following FIG. 5. FIG. 7 is a cross-sectional view showing a state in which, after removing the plating resist layer, the substrate surface is polished and the hole filling portion and the copper foil are flush with each other after FIG. 6. FIG. 8 is a cross-sectional view illustrating a state in which the copper foil is etched into a predetermined conductor pattern to obtain a printed wiring board, following FIG. 7. It is a principal part expanded sectional view of the printed wiring board shown in FIG.

Explanation of symbols

1 Insulating substrate 1A, 1B Front and back both sides 2 Conductor pattern (conductor layer)
3 Through hole 12 Copper foil (conductor layer)
13 Plating resist layer 14 Inner space 21 Thin stepped portion 21A Upper wall surface (contact surface)
21B Floor (contact surface)
21C Lower wall surface (contact surface)
41 Penetration direction plating part (first plating part)
42 Plane direction plating part (second plating part)
42A Outer peripheral surface (contact surface)
42B bottom surface (contact surface)
P Printed wiring board Q Copper-clad laminate

Claims (4)

  A thin step portion is formed at the periphery of the through hole of the conductor layer provided on both the front and back surfaces of the insulating substrate, and the thin step portion is formed on the insulating substrate from both ends of the first plating portion deposited on the inner wall of the through hole. A printed wiring board, wherein a second plating portion extending along the side is laminated.   Conductor layers provided on both front and back surfaces of the insulating substrate and plated through holes for interlayer connection are interconnected with contact surfaces extending in the thickness direction of the conductor layer and in a direction crossing the conductor layer. Characteristic printed wiring board. A mask process for forming a plating resist layer on both the front and back surfaces of the copper-clad laminate having a through hole, leaving an opening peripheral edge of the through hole; and
Etching process of partially etching the copper foil exposed at the opening peripheral edge of the through hole in the thickness direction;
A printed wiring board manufacturing method comprising: a first plating step for depositing a plating layer on the inner wall of the through hole and the partially etched copper foil surface. 2. The method according to claim 1, further comprising a second plating step of filling an inner space of the plated through hole formed by the first plating step by electroplating using the copper foil under the plating resist layer as a power feeding portion. 3. A method for producing a printed wiring board according to 3.

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