CN110958762B - printed wiring board - Google Patents

Abstract

The printed wiring board (1) of the present disclosure comprises: a plurality of insulating layers (5) stacked in the thickness direction; a plurality of wiring conductors (3) respectively located between the plurality of insulating layers (5); a through hole (6) penetrating the plurality of insulating layers (5) and the plurality of wiring conductors (3) in the thickness direction; and a via conductor (3 a) located on the wall surface of the via (6). The 1 st surface 3s of the wiring conductor facing the through hole (6) is located on the outer side of the 2 nd surface (5 s) of the insulating layer facing the through hole (6) with reference to the central axis penetrating the through hole (6) in the thickness direction.

Description

printed wiring board

technical field

The present disclosure relates to printed wiring substrates.

Background technique

Currently, printed wiring boards on which high-performance package substrates and electronic components are mounted are being developed. The printed wiring board has a plurality of laminated insulating layers and wiring conductors. The wiring conductors are located on the upper and lower surfaces of the laminated insulating layers or between the insulating layers. Wiring conductors located in mutually different layers are electrically connected by via conductors in via holes penetrating through the insulating layer in the thickness direction. Such a printed wiring board is mounted with a package substrate, electronic components, and the like, and is mounted, for example, in electronic equipment such as a server.

In recent years, along with the high functionality of electronic equipment, the high functionality of package substrates and electronic components has progressed, and the number of signal systems and the amount of power supply tend to increase. Therefore, the printed wiring board requires an increase in the number of wiring conductors. In order to meet such demands, printed wiring boards sometimes secure a wiring conductor formation area by increasing the number of insulating layers. For example, Japanese Patent Application Laid-Open No. 2000-244129 describes a wiring board including a layered capacitor composed of a composite dielectric layer and a metal layer at a position close to an electronic component such as an IC chip.

Contents of the invention

The printed wiring board according to this embodiment includes: a plurality of insulating layers stacked in the thickness direction; a plurality of wiring conductors respectively correspondingly located between the plurality of insulating layers; and via holes in the thickness direction. penetrating through a plurality of the insulating layers and the plurality of wiring conductors; and a via conductor located on a wall surface of the via hole. The first surface of the wiring conductor facing the through hole is located closer to the second surface of the insulating layer facing the through hole on the basis of the central axis passing through the through hole in the thickness direction. outboard position.

Description of drawings

FIG. 1 is a schematic cross-sectional view illustrating an embodiment example of a printed wiring board of the present disclosure.

2 is an enlarged cross-sectional view of main parts showing an embodiment example of a printed wiring board of the present disclosure.

3 is a schematic cross-sectional view showing main parts of another embodiment example of the printed wiring board of the present disclosure.

4 is a schematic cross-sectional view showing another embodiment example of the printed wiring board of the present disclosure.

FIG. 5A is an electron micrograph of a portion shown as a schematic cross-sectional view in FIG. 3 , and FIG. 5B is an enlarged photograph of a region X shown in FIG. 5A .

FIG. 6 is an electron micrograph showing the interface between a wiring conductor and a via-hole conductor in a conventional printed wiring board.

Detailed ways

Next, the printed wiring board of the present disclosure will be described based on FIGS. 1 and 2 . Printed wiring board 1 has insulating base 2 , wiring conductor 3 , and solder resist 4 . The printed wiring board 1 mounts, for example, a wiring board such as a package board, electronic components, and the like on the upper surface. The thickness of the printed wiring board 1 is about 0.04 to 10.0 mm.

The insulating base 2 has five insulating layers 5 stacked in the thickness direction. The insulating layer 5 includes, for example, an insulating material obtained by impregnating glass cloth for reinforcement with epoxy resin, bismaleimide triazine resin, or the like. The insulating base 2 has a function of securing an arrangement area of the wiring conductor 3 in the printed wiring board 1, a function of a support body maintaining flatness, and the like. The thickness of each insulating layer 5 is set to, for example, 20 to 400 μm.

In this way, the insulating base 2 is formed, for example, as follows. First, prepare two double-sided copper-clad laminates. The double-sided copper-clad laminate is, for example, a laminate in which copper foil is attached to the upper and lower surfaces of an insulating board made of glass cloth impregnated with insulating resin. Next, wiring conductor 3 having a predetermined pattern is formed by etching the copper foil of each double-sided copper-clad laminate. Next, prepare three pieces of prepreg and two pieces of copper foil. The prepreg is, for example, an insulating material in a semi-cured state obtained by impregnating glass cloth with an insulating resin. Next, with a prepreg as the center, double-sided copper-clad laminates, prepregs, and copper foils are sequentially laminated on the upper and lower surfaces. Next, the above-mentioned insulating base 2 is formed by performing press working under heating.

As described above, the wiring conductor 3 formed from the copper foil of the double-sided copper-clad laminate may have, for example, elongated crystal grains with respect to the thickness direction. In other words, most of the crystal interfaces between the crystal grains are oriented in the thickness direction, and few are oriented in the horizontal direction perpendicular to the thickness direction. Therefore, it is advantageous in that the fracture resistance of the wiring conductor 3 can be improved when the printed wiring board 1 thermally expands and a stress in the thickness direction is applied.

The insulating base 2 has a plurality of through holes 6 penetrating in its thickness direction. The via hole 6 has a via hole in which the second surfaces 5 s of the plurality of insulating layers and the first surfaces 3 s of the plurality of wiring conductors are exposed. The wiring conductors 3 on the upper and lower surfaces of the insulating base 2 , or the wiring conductors 3 between the upper and lower surfaces of the insulating base 2 and the insulating layer 5 are electrically connected through the via holes 6 . The diameter of the through hole 6 is set to, for example, 50 to 2000 μm.

As shown in FIG. 2 , in the via hole 6 , the first surface 3s of each wiring conductor is located outside the second surface 5s of the insulating layer based on the central axis penetrating the via hole 6 in the thickness direction. The difference in height between the first surface 3s of the wiring conductor and the second surface 5s of the insulating layer is set, for example, within a range of 1 to 10 μm.

If the level difference between both is less than 1 μm, the distance that a part of via-hole conductor 3 a described later enters outside is smaller than the second surface 5 s of the insulating layer. Therefore, the effect of locking the via-hole conductor 3a to the insulating layer 5 becomes small. If it is larger than 10 μm, the plating treatment liquid cannot flow back well to the first surface 3 s of the wiring conductor when forming the through-hole conductor 3 a described later, and copper plating metal may not be deposited well. Therefore, there is a possibility that the connection between the via-hole conductor 3a and the first surface 3s of the wiring conductor becomes incomplete. In consideration of these viewpoints, it is advantageous in terms of quality and production if the level difference between the first surface 3 s of the wiring conductor and the second surface 5 s of the insulating layer is set to 3 to 7 μm.

Such through holes 6 are formed, for example, as follows. First, a through hole penetrating through the insulating base 2 in the thickness direction is formed by drilling. Next, resin chips remaining in the through holes are removed by desmearing. Finally, the wiring conductor 3 exposed in the through hole 6 is etched and dissolved until it becomes the above-mentioned level difference. As a result, the through-hole 6 as described above is formed.

This etching treatment also has the effect of removing metal shavings not completely removed by the desmear treatment and resin shavings adhering to the first surface 3 s of the wiring conductor exposed in the through hole.

The wiring conductor 3 is located between the insulating layers 5 , the upper and lower surfaces of the insulating base 2 , and the through hole 6 . The wiring conductor 3 constitutes a conductive path of the printed wiring board 1 and has functions such as propagation of signals and supply of electric power. The wiring conductor 3 contains, for example, a highly conductive metal such as copper.

Among such wiring conductors 3 , the wiring conductors located in the via holes 6 function as via-hole conductors 3 a. Each of the via-hole conductors 3 a has a function of a signal for propagation of a signal, a power supply for supply of electric power, or a function for grounding. The via-hole conductors 3 a electrically connect the wiring conductors 3 on the upper and lower surfaces of the insulating base 2 , or the wiring conductors 3 on the upper and lower surfaces of the insulating base 2 and the wiring conductors 3 between the insulating layers 5 .

The via-hole conductor 3 a exists in close contact with the entire surface of the first surface 3 s of the wiring conductor facing the via hole 6 and the entire surface of the second surface 5 s of the insulating layer, and is a cylinder having a cavity in the center of the radial direction of the via hole 6 . shape. As described above, the first surface 3 s of the wiring conductor is located outside the second surface 5 s of the insulating layer on the basis of the central axis penetrating the through hole 6 in the thickness direction. Therefore, a part of via-hole conductor 3 a exists in the state which penetrated between insulating layers 5 .

In other words, in the via hole 6 , the portion where the first surface 3 s of the wiring conductor is exposed is in a recessed state with respect to the second surface 5 s of the insulating layer. The via-hole conductor 3a is in close contact with the first surface 3s of the wiring conductor located in the recess, and is also in close contact with the second surface 5s of the insulating layer.

The increase in the contact area between the via-hole conductor 3 a and the second surface 5 s of the insulating layer contributes to the improvement of the adhesion strength of the via-hole conductor 3 a. Especially in the thickness direction, the via-hole conductor 3 a in the recess acts as a lock with respect to the insulating layer 5 , so that the shear stress between the via-hole conductor 3 a and the insulating layer 5 can be suppressed. Furthermore, the shearing stress between the via-hole conductor 3a and the 1st surface 3s of wiring conductors can also be suppressed.

The first surface 3 s of the wiring conductor facing the via hole 6 has a linear shape in the cross-sectional view shown in FIG. 2 , but may also have a curved shape. In such a case, the contact area with the via-hole conductor 3a increases. Therefore, it is advantageous in that the adhesion strength between the first surface 3 s of the wiring conductor and the via-hole conductor 3 a can be improved.

The hole-filling resin 7 filled in the cavity of the via-hole conductor 3 a is located in the via-hole 6 . The hole-filling resin 7 is not essential in the present disclosure, but is used when the printed wiring board 1 has a structure in which the upper and lower openings of the through-holes 6 are closed with, for example, conductive layers or insulating layers.

In the through-hole 6 , by filling the inside of the through-hole conductor 3 a with the hole-filling resin 7 , gas and liquid are less likely to remain in the through-hole 6 . Accordingly, it is possible to avoid damage or corrosion of the wiring conductor 3 or the like due to expansion of gas, corrosion of liquid, or the like.

Hole filling resin 7 includes, for example, thermosetting resin such as epoxy resin and insulating particles such as silica.

The upper and lower surfaces of the insulating base 2 and the wiring conductors 3 located in the through holes 6 are formed, for example, as follows.

First, the insulating base 2 in which the through-holes 6 are formed through the above steps is prepared. Next, electroless copper plating and electrolytic copper plating are sequentially performed on the upper and lower surfaces of the insulating base 2 , the first surface 3 s of the wiring conductor facing the through hole 6 , and the second surface 5 s of the insulating layer. The copper-plated metal deposited on the first surface 3s of the wiring conductor and the second surface 5s of the insulating layer becomes the via-hole conductor 3a. Next, a hole-filling resin 7 is filled and cured in the through-hole 6 inside the copper-plated metal. Next, the hole filling resin 7 protruding from the through hole 6 is polished so that the copper plating metal deposited on the upper and lower surfaces of the insulating base 2 is at the same height as the exposed surface of the hole filling resin 7 . Finally, the deposited copper plating metal on the upper and lower surfaces of the insulating base 2 and the exposed surfaces of the hole-filling resin 7 are plated, and a predetermined pattern is formed by etching, whereby the wiring conductors 3 are formed on the upper and lower surfaces of the insulating base 2 .

The direction of the crystal interface of via-hole conductor 3a may have random crystal grains. In other words, the crystal interface of via-hole conductor 3a has no directionality. In such a case, it is advantageous in that the thermal stress applied to the via-hole conductor 3 a can be dispersed in random directions.

The solder resist 4 is located on the upper surface of the uppermost insulating layer 5 and the lower surface of the lowermost insulating layer 5 . The solder resist 4 has an opening 4 a exposing a part of the wiring conductor 3 located on the upper surface of the insulating base 2 and an opening 4 b exposing a part of the wiring conductor 3 located on the lower surface.

A part of the wiring conductor 3 exposed in the opening 4 a functions as an electrode connected to an electrode of a package substrate or an electronic component, for example.

A part of the wiring conductor 3 exposed in the opening 4b functions as an electrode connected to an electronic component, for example.

Solder resist 4 is formed, for example, by attaching a film of photosensitive thermosetting resin such as acrylic modified epoxy resin to the surface of insulating layer 5, forming opening 4a or opening 4b by exposure and development, and then thermosetting.

As described above, the printed wiring board 1 of the present disclosure has a plurality of insulating layers 5 stacked in the thickness direction, a plurality of wiring conductors 3 respectively correspondingly existing between the plurality of insulating layers 5 , and a plurality of wiring conductors 3 penetrating in the thickness direction, The via holes 6 through which the second surfaces 5s of the plurality of insulating layers and the first surfaces 3s of the plurality of wiring conductors are exposed. The via-hole conductor 3 a that is in close contact with the entire surface of the second surface 5 s of the insulating layer and the first surface 3 s of the wiring conductor is located in the via hole 6 . In the via hole 6 , the first surfaces 3 s of the plurality of wiring conductors are located outside the second surfaces 5 s of the plurality of insulating layers based on the central axis penetrating the via hole 6 in the thickness direction. In other words, in the via hole 6, the portion where the first surface 3s of the wiring conductor is exposed is in a recessed state with respect to the second surface 5s of the insulating layer.

Therefore, the via-hole conductor 3 a is in close contact with the first surface 3 s of the wiring conductor and the second surface 5 s of the insulating layer in a state where a part of the via-hole conductor 3 a has entered the recess. This increases the contact area between the via-hole conductor 3 a and the first surface 3 s of the wiring conductor and the second surface 5 s of the insulating layer, which contributes to improving the adhesion strength of the via-hole conductor 3 a. Especially in the thickness direction, the via-hole conductor 3 a in the recess acts as a lock with respect to the insulating layer 5 , and the shear stress between the via-hole conductor 3 a and the insulating layer 5 can be suppressed. As a result, breakage between the via-hole conductor 3a and the first surface 3s of the wiring conductor can be reduced.

In this manner, according to the present disclosure, it is possible to reduce breakage between the via-hole conductor 3 a having a function for signal, power supply, or ground, and the first surface 3 s of the wiring conductor. Therefore, it is possible to provide a printed wiring board excellent in signal propagation or power supply characteristics.

The present disclosure is not limited to an example of the above-mentioned embodiment, and various changes can be made without departing from the scope of the present disclosure.

For example, in an example of the above-mentioned embodiment, as shown in FIG. 2 , the state where the interface between the via-hole conductor 3 a and the hole-filling resin 7 has no recess is shown.

Unlike this case, as shown in FIG. 3 , via-hole conductor 3 a may have annular recess 8 on the inner peripheral surface facing first surface 3 s of a plurality of wiring conductors facing via-hole 6 . In other words, the inner peripheral surface of the cylindrical via-hole conductor 3a has the ring-shaped recessed part 8 at the position which opposes the above-mentioned pit.

In such a case, for example, when the printed circuit board 1 thermally expands, the via-hole conductor 3 a is pressed toward the first surface 3 s of the wiring conductor by the hole-filling resin 7 entered into the recess 8 . Thereby, the adhesion strength between the via-hole conductor 3a and the 1st surface 3s of wiring conductors improves.

The depth of the concave portion 8 is set to, for example, 2 to 5 μm. When it is less than 2 μm, the effect of the above-mentioned pressing becomes small, and there is a possibility that the improvement of the adhesion strength between the via-hole conductor 3 a and the first surface 3 s of the wiring conductor cannot be contributed. If it is larger than 5 μm, it may be difficult to fill the hole-filling resin 7 into the concave portion 8 .

Such a concave portion 8 is formed by adjusting the electrolytic plating treatment time so that the exposed portion of the first surface 3s of the wiring conductor has a thickness such that it remains recessed from the second surface 5s of the insulating layer. In addition, when the concave portion 8 is unnecessary, the electrolytic plating treatment time may be further extended, or the electrolytic plating treatment may be performed twice.

As shown in FIG. 4 , build-up insulating layers 9 and wiring conductors 3 may be further laminated on the upper and lower surfaces of the insulating base 2 . In this example, two layers of build-up insulating layer 9 and wiring conductor 3 are located on the upper surface and the lower surface, respectively.

The build-up insulating layer 9 has a function of securing a region for arranging the wiring conductor 3 on the upper and lower surfaces of the insulating base 2 . Therefore, the structure having the build-up insulating layer 9 corresponds to the increase in the signal system and power supply accompanying the high-functioning electronic equipment. Therefore, it is advantageous in that the wiring conductors 3 of the printed wiring board 1 can be increased.

The build-up insulating layer 9 covers the wiring conductors 3 and has a function of ensuring the insulation between the wiring conductors 3 adjacent to each other.

The build-up insulating layer 9 includes, for example, glass fiber such as E glass or S glass, insulating resin such as polyimide resin, epoxy resin, or bismaleimide triazine resin, and silicon dioxide (SiO ₂ ) or alumina. (Al ₂ O ₃ ) and other insulating particles. It is also not necessary for glass fibers to be included.

The build-up insulating layer 9 is formed, for example, by covering the film for the insulating layer, performing thermocompression bonding, and curing so that the wiring conductor 3 is covered on the upper and lower surfaces of the insulating base 2 under vacuum, or the already formed build-up layer The surface of the insulating layer 9.

The build-up insulating layer 9 has a plurality of via holes 10 having the wiring conductor 3 as a bottom surface. The wiring conductors 3 positioned above and below via the build-up insulating layer 9 are electrically connected to each other via the wiring conductors 3 in the via hole 10 . The diameter of the via hole 10 is set to, for example, 30 to 100 μm.

Via hole 10 is formed, for example, by performing laser processing on build-up insulating layer 9 . After laser processing, the inside of the via hole 10 is cleaned to remove foreign substances such as carbides, thereby improving the adhesion between the wiring conductor 3 and the build-up insulating layer 9 exposed in the via hole 10 and the wiring conductor 3 strength.

Wiring conductor 3 is located on the upper surface or lower surface of build-up insulating layer 9 and inside via hole 10 . The wiring conductor 3 is formed by, for example, a plating treatment technique such as a semi-additive method or a subtractive method, and contains a highly conductive metal such as copper.

The solder resist 4 is located on the upper surface of the uppermost insulating build-up layer 9 and the lower surface of the lowermost insulating build-up layer 9 . The solder resist 4 has the opening 4a which exposes part of the wiring conductor 3 located in the upper surface of the buildup insulating layer 9, and the opening 4b which exposes a part of the wiring conductor 3 located in the lower surface.

A part of the wiring conductor 3 exposed in the opening 4 a functions as an electrode connected to an electrode of a package substrate or an electronic component, for example. A part of the wiring conductor 3 exposed in the opening 4b functions as an electrode connected to an electronic component, for example.

FIG. 5A shows an electron micrograph of the portion shown as a schematic cross-sectional view in FIG. 3 . An enlarged photograph of the region X shown in FIG. 5A is shown in FIG. 5B. The symbols shown in FIGS. 5A and 5B are the same as those shown in FIG. 3 , and description thereof will be omitted.

For example, in FIGS. 2 and 3 , the position of the first surface 3 s of the wiring conductor is clearly shown. This is only for the convenience of showing the position of the first surface 3s of the wiring conductor when shown in the cross-sectional view. As shown in FIG. The boundary surfaces of the via-hole conductors 3 a may be non-linearly staggered and integrated. In other words, when the wiring conductor 3 is etched, the first surface 3s of the wiring conductor is non-linearly staggered, in other words, it is processed into a concave-convex shape, and the copper-plated metal that becomes the via-hole conductor 3a is precipitated, thereby wiring. The interface between the first surface 3 s of the conductor and the via-hole conductor 3 a is in the state described above.

As indicated by the arrows in FIG. 5B , for the conductor forming the wiring conductor 3 , crystals extend in the depth direction of the through hole 6 , that is, along the central axis direction of the through hole 6 . In other words, the crystal has an elongated shape extending in the stacking direction of the upper insulating layer 5 and the lower insulating layer 5 in a cross-sectional view. In this way, if the crystals of the conductors forming the wiring conductor 3 extend in the depth direction of the via hole 6 , the wiring conductor 3 can be brought into closer contact with the insulating layer 5 . For example, when a load is applied to the printed wiring board, the via-hole conductor 3 a tends to apply the load in a direction perpendicular to the depth direction of the via hole 6 , that is, in a direction horizontal to the main surface of the wiring conductor 3 and the insulating layer 5 . Even if such a load is applied to the wiring conductor 3 , the wiring conductor 3 is tightly adhered to by the insulating layer 5 , so that the displacement of the via-hole conductor 3 a due to the load can be reduced, making it less likely to break. Here, “the crystal extends in the direction along the central axis of the through hole 6 ” means that the crystal extends substantially in the direction along the central axis of the through hole 6 . In other words, the direction in which the crystals extend is substantially along the central axis of the through hole 6 . Therefore, the angle of the crystal with respect to the direction in which the central axis of the through hole 6 extends may be 0 to 30 degrees, more specifically 0 to 10 degrees.

When etching the wiring conductor 3 exposed in the through hole 6 , it is performed by flowing an etchant into the through hole 6 . As shown in the region Y of FIG. 5B , the corner between the wall surface of the via hole 6 on the upstream side of the flow of the etching solution and the via-hole conductor 3 a has a tapered shape, and the corner portion is removed. By removing the corners in this way and having a tapered shape, the plating solution at the time of forming the via-hole conductor 3 a easily flows in the direction of the wiring conductor 3 .

As shown in FIG. 6 , in the conventional printed wiring board, the boundary surface between the wiring conductor 13 and the via-hole conductor 13 a appears relatively clearly in the vicinity of the wall surface of the via hole as indicated by a region Z. If the boundary surface between the wiring conductor 13 and the via-hole conductor 13a exists near the wall surface of the through hole, for example, when a load is applied to the printed circuit board, it is easy to separate the crystal of the conductor forming the wiring conductor 13 and the via-hole conductor 13a. The cracks between the crystals of the conductors are prone to poor conduction. In contrast, the printed wiring board of the present disclosure is excellent in signal propagation or power supply characteristics.

In the above-mentioned embodiment, the case where the via-hole conductor 3a is cylindrical was shown. Unlike this case, when the hole-filling resin 7 or the recess 8 is unnecessary, the via-hole conductor 3 a may fill the inside of the via-hole 6 . In this case, the resistance of the via-hole conductor 3a decreases. Therefore, it is advantageous from the viewpoint of improving signal propagation or power supply characteristics.

Claims (8)

1. A printed wiring substrate, characterized in that it has: a plurality of insulating layers are laminated in the thickness direction; A plurality of wiring conductors are correspondingly located between the plurality of insulating layers; a via hole penetrating the plurality of insulating layers and the plurality of wiring conductors in the thickness direction; and via-hole conductors located on the wall of the via-hole, in, Each of the plurality of wiring conductors has a first surface facing the through hole, each of the plurality of insulating layers has a second surface facing the through hole, The first surface is further away from the central axis penetrating the through hole than the second surface in the thickness direction, The first surface has a concavo-convex portion located on the outside of the second surface on the basis of the central axis, The via-hole conductor is in contact with the concave-convex portion. 2. The printed wiring board according to claim 1, wherein, The through-hole conductor is cylindrical. 3. The printed wiring board according to claim 2, wherein, The inside of the cylinder is filled with resin. 4. The printed wiring board according to claim 2, wherein, The via-hole conductor has a portion corresponding to the first surface, and the portion has a recess. 5. The printed wiring board according to claim 4, wherein, The recess is annular in shape. 6. The printed wiring board according to claim 1, wherein, The wiring conductor has a crystal extending in a direction along the central axis of the through hole. 7. The printed wiring board according to claim 1, wherein, The wiring conductor has elongated crystal grains with respect to the thickness direction, and among crystal interfaces between the crystal grains, more crystal interfaces face the thickness direction than crystal faces face a horizontal direction perpendicular to the thickness direction. 8. The printed wiring board according to claim 1, wherein, The via-hole conductor includes a first portion facing the first surface, a second portion facing the second surface, and a third portion located between the first portion and the second surface, The third portion has a conical shape.

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