JP2003324280A - Manufacturing method of printed circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a printed circuit board which assures excellent interlayer connection reliability and includes a higher density multilayer structure manufactured at a lower cost. <P>SOLUTION: A conductor pattern 5 is formed on one surface of a resin sheet 1 composed of a thermosetting resin, and a via hole 5 reaching the conductor pattern is formed on the other surface. A plurality of processing resin sheets 6 are laminated by precipitating and filling a low melting point metal 4 as an interlayer connection material in the via hole 3 by plating. Each processing resin sheet 6 is bonded simultaneously by pressurization and heat treatment under the this condition. By the heat treatment and pressurization, the low melting point metal 4 is connected to the adjacent conductor pattern 5 by a metal coupling process. Accordingly, the printed circuit board 8 having an excellent interlayer connection property which enables high density wiring can be manufactured at a lower cost. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a printed circuit board having a multi-layer structure, and more particularly to a technique for connecting layers.

[0002]

2. Description of the Related Art As a conventional technique, for example, Japanese Patent Laid-Open No. 58-1
Like the technique disclosed in Japanese Patent Application Laid-Open No. 21698 or Japanese Patent Application Laid-Open No. 7-176846, the via hole of the printed circuit board is filled with metal plating or conductive paste to electrically connect the conductor patterns between the layers of the printed circuit board. It is known to connect.

[0003]

However, in any of the above-described methods, since the build-up method is one in which the conductor pattern and the insulating layer are sequentially laminated one by one, the number of steps increases as the number of laminated layers increases. However, there is a problem that the manufacturing cost becomes very high. When metal plating is used, a connection terminal made of solder is formed on the conductor pattern side between the metal plating in the via hole and the conductor pattern, and the connection is made by this connection terminal. Therefore, in order to ensure the reliability of the interlayer connection, it is necessary to increase the size of the connection terminal, and it is difficult to improve the wiring density. When a conductive paste is used, the interface between the conductive paste and the conductor pattern is resin-bonded,
Further, in the conductive paste, metal particles are in contact with each other to form a conductive path, so that the reliability of interlayer connection is low and it is difficult to increase the current.

In view of the above problems, it is an object of the present invention to provide a method of manufacturing a printed circuit board having a multi-layer structure which is excellent in interlayer connection reliability, enables high-density wiring, and reduces manufacturing cost.

[0005]

According to a first aspect of the present invention, there is provided a printed circuit board manufacturing method, wherein a resin sheet made of a thermoplastic resin is applied to a resin sheet so as to reach a metal foil formed on one surface of the resin sheet. A via hole is formed from the other surface of the sheet. Then, a low melting point metal is deposited and filled in the inside of the via hole by plating, the metal foil is etched to form a conductor pattern, and then a multilayer substrate forming sheet including the resin sheet processed as described above is laminated. Next, the laminated sheets for forming a multilayer substrate are pressed and heated to collectively adhere the sheets to form a printed board having a multilayer structure.

In the present invention, since the low melting point metal is filled in the via hole by the plating process as described above, it is not necessary to provide the connection terminal on the conductor pattern side unlike the prior art. Therefore, the wiring density can be improved as compared with the conventional technique.

Further, the low melting point metal filled in the via hole at the time of pressurizing and heating forms a metal bond with the adjacent conductor pattern. Therefore, the connection reliability in the interlayer connection can be sufficiently ensured.

Further, according to the above-mentioned manufacturing method, the resin sheets which are the conductor pattern layers and the insulating layers are alternately laminated, and then the laminated body is heated and pressed to collectively form the resin sheets. Since they can be adhered to each other, the manufacturing process can be significantly shortened and the manufacturing cost can be suppressed.

The low melting point metal filled in the via hole may be composed of a single metal or a composite metal. For example, as a single metal, Sn,
Bi or the like can be adopted, and as the composite metal, Sn-Pb, Sn
-Ag, Sn-Pb-Bi, etc. can be adopted. In short, either a single metal or a composite metal may be used as long as it forms a metal bond between the adjacent conductor patterns depending on the pressing / heating conditions of the hot press.

In the filling step, in the filling step, a metal having a specific resistance smaller than that of the low melting point metal is filled as the first connecting metal in the bottom of the via hole by plating, and the second connecting layer is formed on the upper layer. It is preferable to fill a low melting point metal as the metal. By using a metal having a specific resistance smaller than that of the low melting point metal as the first connecting metal, the resistance value can be suppressed as compared with the case where only the low melting point metal is contained in the via hole. In addition, such a metal having a low specific resistance generally has a high melting point. Therefore, when the low-melting-point metal is alloyed by forming a metal bond with the metal having a low specific resistance during heating and pressurization, the melting point of the low-melting-point metal rises, so that even if a process involving heating is performed later, The melting point metal does not remelt, and high connection reliability can be obtained. The same metal as the conductor pattern may be used as the first connecting metal as described in claim 4, or Cu may be used as the first connecting metal as described in claim 5. By using the same metal as the conductor pattern as the first connecting metal, the conductor pattern and the first connecting metal in the via hole have the same linear expansion coefficient,
The electrical and mechanical connection is stable. In addition, the first is Cu, which is inexpensive and has a low specific resistance and excellent high-frequency characteristics
It is preferable to use it as a connecting metal, in which case the conductor pattern is also preferably made of copper.

Also, in the process of laminating printed circuit boards,
The printed circuit board may be formed only by laminating a plurality of processed resin sheets as a multilayer substrate forming sheet as described in claim 6, or the processed resin sheet as described in claim 7. It may be formed by stacking sheets for forming a multilayer substrate including a core substrate. In either case, when pressed and heated by a hot press, the resin sheets are bonded to each other or the resin sheet and the core substrate are bonded to each other to form a multilayer substrate.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a cross-sectional view of each step showing a manufacturing process of a printed circuit board in the present embodiment.

First, as shown in FIG. 1A, a resin sheet 1 which is an insulating base material having a metal foil 2 attached to one surface thereof is prepared. In this example, the resin sheet 1 is made of polyetheretherketone (PEEK) resin 65 to 35% and polyetherimide (PEI) resin 35 to 65% and has a thickness of 50 to 50%.
A 100 μm thermoplastic resin sheet is used. As the metal foil 2, for example, a low resistance metal foil containing at least one of Au, Ag, Cu and Al is preferable, and a Cu foil which is inexpensive and does not cause migration is preferable. In this example, the metal foil 2 having a thickness of 1 to 50 μm was used.

Next, as shown in FIG. 1B, a carbon dioxide laser is irradiated from the resin sheet 1 side to form a via hole 3 which is a bottomed hole having the metal foil 2 as a bottom surface. In addition to the carbon dioxide gas laser, a UV-YAG laser, an excimer laser, or the like can be used to form the via hole 3. In addition, a via hole can be formed by drilling or the like, but it is preferable to select a laser processing method because it is necessary to perform processing so as to have a small diameter and not damage the metal foil 2.

When the formation of the via hole 3 is completed as shown in FIG. 1 (b), next, as shown in FIG. 1 (c), a low melting point metal 4 which is an interlayer connecting material is plated in the via hole 3. To deposit and fill. In this example, Sn having a melting point of 232 ° C. is used as the low melting point metal 4, and the metal foil 2
An Sn layer is deposited in the via hole 3 by electrolytic plating using the electrode as an electrode. As described above, in the plating method, the metal foil 2 is exposed on the bottom surface of the via hole 3, so that the metal foil 2
It is preferable to use electrolytic plating as the electrode. This eliminates the need for electroless plating for forming a base layer for electrolytic plating, and can reduce the number of steps. Further, the depth of the low melting point metal 4 to be deposited is within ± 10%, preferably within ± 5% with respect to the thickness of the resin sheet 1. It should be noted that the low melting point metal 4 may be any as long as it melts under pressure and heating conditions by a heating press to form a metal bond with the metal foil 2, and other materials such as Bi, Sn-Pb,
There are Sn-Ag, Sn-Pb-Bi and the like, but the present invention is not limited thereto. Further, when a process involving heating is performed later (for example, a reflow soldering process), it is desirable that the melting point of the low melting point metal 4 is equal to or higher than the temperature.

When the deposition / filling of the low melting point metal 4 into the via hole 3 shown in FIG. 1C is completed, the process shown in FIG.
As shown in (d), the metal foil 2 is formed into a desired conductor pattern 5 by etching.

Through the above steps, the resin sheet 1 (hereinafter referred to as the processed resin sheet 6) having the conductor pattern 5 on the surface and the low melting point metal 4 filled in the via hole 3 is formed as a multilayer substrate forming sheet. Then, FIG. 1A to FIG.
A plurality of processed resin sheets 6 are prepared by performing the step (d) in parallel or repeatedly. The plurality of processed resin sheets 6 are laminated as shown in FIG. At this time, the orientation of the processed resin sheet 6 is reversed with the folding line 7 as a boundary so that the conductor patterns 5 appear on both outermost surfaces so that the elements and the like can be mounted on both front and back surfaces of the formed multilayer substrate. Stacked. Here, FIG. 1 (e)
The fold line 7 shown by the chain line in FIG. 3 coincides with the center line on which the processed resin sheet 6 is laminated, but it does not necessarily have to be so. Further, in this example, the direction of the processed resin sheet 6 is reversed with reference to the folding line, but the processed resin sheets 6 may be laminated in the same direction.

Finally, as shown in FIG. 1 (f), the processed resin sheets 6 are adhered to each other by pressing and heating the laminated body of the processed resin sheets 6 from both sides with a heating press machine (not shown). Then, the printed circuit board 8 having a multilayer structure is formed. The pressurization / heating conditions include, for example, a pressure of 1 to 2 MPa, a heating temperature of 300 to 330 ° C. and 1 to 2 hours.
The printed board 8 can be obtained by pressurizing and heating.

As described above, the low melting point metal 4 deposited in the via hole 3 is melted in the pressing / heating process,
A metal bond is formed between the adjacent conductor patterns 5.
When the folded structure is provided as shown in this example, the low melting point metals 4 facing each other with the folded line 7 in between also form a metal bond. Furthermore, since the low melting point metal 4 can be deposited inside the via hole 3 by the electrolytic plating method using the metal foil 2 as an electrode on the printed circuit board 8, the wiring (interlayer connection) density can be improved. Therefore, according to the method for manufacturing the printed circuit board 8 of the present embodiment, the multilayer printed circuit board 8 having high interlayer connection strength and high electrical connection reliability and capable of high-density wiring can be manufactured at low cost. Can be manufactured.

(Second Embodiment) Next, the second embodiment of the present invention will be described.
The embodiment will be described with reference to FIG.

Since the printed circuit board manufacturing method according to the second embodiment has a lot in common with that according to the first embodiment, a detailed description of the common parts will be omitted below, and different parts will be focused on. explain.

The second embodiment is different from the first embodiment in that the metal filled in the via hole 3 is not only the low melting point metal 4 but also the first metal at the bottom of the via hole 3.
A metal having a specific resistance smaller than that of the low melting point metal (hereinafter referred to as a low resistance metal) is filled as the connecting metal 4a, and an upper layer thereof is provided between the first connecting metal 4a and the conductor pattern 5 as a second connecting metal 4b during hot pressing. That is, the low melting point metal 4 capable of forming a metal bond is filled.

In FIGS. 2A and 2B, the same steps as those in the first embodiment described above are performed, and the bottomed via holes 3 are formed in the resin sheet 1. In the step shown in FIG. 2C, a low resistance metal is first filled by a plating process as the first layer connecting metal 4a that contacts the bottom surface side of the via hole 3, that is, the metal foil 2. Here, as the metal used as the first connecting metal 4a, a metal having a resistance value lower than that of the low melting point metal 4,
For example, a low resistance metal containing at least one of Au, Ag, Cu and Al is preferable, and Cu is preferable because it is inexpensive and does not cause migration. As a result, the conductor pattern 5
The resistance value of the interlayer connection portion between them can be suppressed. Further, if the first connecting metal 4a and the metal used for the conductor pattern 5 are the same, the conductor pattern 5 and the first connecting metal 4a in the via hole 3 also have the same linear expansion coefficient even during pressurization / heating, and thus are stable. The connected state is obtained.

Next, as shown in FIG. 2D, the low melting point metal 4 shown in the first embodiment is formed as the second connecting metal 4b.

Here, as a method of forming the first and second connection metals 4a and 4b, it is preferable that both are electrolytic plating. In order to meet the recent demand for miniaturization and high functionality of electronic devices, it is preferable that the diameter of the via hole 3 in the multilayer substrate forming sheet 6 be smaller. For that purpose, the first and second
Rather than forming the connection metals 4a and 4b into a paste and processing the via holes 3, the first and
By depositing the second connection metals 4a and 4b, a more uniform and dense metal film can be formed in the via hole 3.
As a result, high adhesive strength and electrical connection reliability can be obtained.
In the electroplating, since the metal foil 2 can be used as an electrode, it is not necessary to previously perform electroless plating in the via hole 3.

The depths of the first and second connecting metals 4a and 4b can be variously combined within the range of the thickness of the resin sheet 1, but the depth of the first connecting metal 4a and the second connecting metal 4a can be changed.
The total depth of the connecting metal 4b is ± 1 of the thickness of the resin sheet 1.
It is preferably within 0%, more preferably within ± 5% of the thickness of the resin sheet 1. Also, the first connection metal 4a
Is preferably 90 to 99% of the total, and the depth of the second connecting metal 4b is preferably about 1 to 10%. This is the first connection metal 4
This is because the resistance in the via hole 3 can be suppressed to a low level by using a lot of low-resistance metal having a small specific resistance as a. Further, since the amount of the second connecting metal 4b is as small as 1 to 10%, it diffuses into the metal forming the adjacent conductor pattern 5 or the first connecting metal 4a, and the melting point is increased by alloying almost all the amount, so that This is because even if there is a step involving heating, high connection reliability can be exhibited regardless of the heating.

Also in this embodiment, as in the first embodiment, a plurality of processed resin sheets 6 formed as sheets for forming a multilayer substrate are laminated, and the laminated body is pressed and heated, The processed resin sheets 6 are collectively adhered to each other, and the printed board 8 having a multilayer structure can be obtained (FIGS. 2F and 2G). Although the folded structure in which the laminated surfaces are opposed to each other with the folded line 7 sandwiched therebetween is shown in FIG. 2, the present embodiment is not limited to this, as in the first embodiment.

From the above, the printed circuit board 8 in the present invention
Is capable of reducing the resistance value in the interlayer connection by forming a low resistance metal having a small specific resistance as the first layer connection metal 4a in the via hole 3, and the second connection metal 4b used as the second layer is formed. Since a metal bond is formed between the first connection metal 4a and the conductor pattern 5 of the processed resin sheet 6 which are adjacent to each other at the time of stacking, high density and high interlayer connection reliability can be obtained.

(Third Embodiment) Next, the third embodiment of the present invention will be described.
The embodiment will be described with reference to FIG.

Since the method of manufacturing the printed circuit board according to the third embodiment has a lot in common with the method according to the first embodiment, the detailed description of the common parts will be omitted and the different parts will be mainly described. explain.

The third embodiment differs from the first embodiment in that the core substrate 6a is used in addition to the processed resin sheet 6 as the multilayer substrate forming sheet used for forming the printed circuit board 8. . The core substrate 6 used
For example, a is formed by alternately laminating a resin sheet in which epoxy resin, which is a thermosetting resin, is mixed with glass cloth, and conductor patterns. This resin sheet can be adhered to the processed resin sheet 6 by a pressing / heating process using a hot press machine.

The manufacturing method is shown in FIGS. 3A to 3D are the same as the steps according to the first embodiment. After forming the processed resin sheet 6 by the steps shown in FIGS. 3A to 3D, as shown in FIG. 3E, the core substrate 6a is arranged at the center position of the stack, for example.
A desired number of processed resin sheets 6 are arranged on the upper and lower surfaces thereof. The stacking position of the core substrate 6a is not particularly limited to the center position. Thereafter, the laminated body of the processed resin sheet 6 and the core substrate 6a is pressed and heated to bond the processed resin sheets 6 to each other and the processed resin sheet 6 and the core substrate 6a to each other, including the core substrate 6a. The printed circuit board 8 can be formed.

Therefore, also in the present embodiment, it is possible to obtain the printed board 8 having low cost, high density and high connection reliability, and by using the core board 6a, the rigidity of the printed board 8 itself is increased. be able to.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, but can be implemented with various modifications.

In the above-mentioned embodiment, the resin sheet is a thermoplastic resin sheet composed of PEEK resin 65 to 35% and PEI resin 35 to 65%, but PEEK and PEI can be used alone. . Further, polyether sulfone (PES), polyphenylene ether (PPE), polyethylene naphthalate (PEN), liquid crystal polymer, styrene resin having a syndiotactic structure, etc. may be used alone, or PEEK, PEI.
You may mix and use any of these including each. In short, it is possible to perform adhesion by collective pressing, and it is possible to suitably use any resin sheet having heat resistance necessary for reflow soldering or the like which is a post process.

Further, in the present invention, the printed circuit board has a structure in which a plurality of processed resin sheets are stacked, or a structure in which a single-layer printed circuit board is arranged above and below a core substrate, but both surfaces are replaced by a core substrate. A processed resin sheet made of a thermoplastic resin on which a conductor pattern is formed may be used.

Further, in the above-mentioned embodiment, an example of electrolytic plating is shown in the plating method of filling the second connection metal in the via hole, but other than that, electroless plating, vapor deposition method, metal coating, printing. You may use the method etc.

[Brief description of drawings]

FIG. 1 is a sectional view for each step showing a manufacturing process of a multilayer substrate according to a first embodiment of the present invention.

FIG. 2 is a sectional view for each step showing a manufacturing process of a multilayer substrate according to a second embodiment of the present invention.

FIG. 3 is a sectional view for each step showing the manufacturing process of the multilayer substrate according to the third embodiment of the present invention.

[Explanation of symbols]

1 ... Resin sheet, 2 ... Metal foil, 3 ... Via hole, 4 ...
Connection metal, 4a ... First connection metal, 4b ... Second connection metal,
5 ... Conductor pattern, 6 ... Processed resin sheet, 6a ... Core substrate, 8 ... Printed circuit board

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 5E346 AA02 AA43 CC08 CC32 CC34                       CC38 CC39 EE14 FF06 FF08                       FF14 GG15

Claims (7)

[Claims] 1. A via hole forming step of forming a via hole reaching the metal foil on the other surface of a resin sheet made of a thermoplastic resin and having a metal foil on one surface, and depositing the inside of the via hole by plating. Filling step of filling with the low melting point metal, a conductor pattern forming step of forming a conductor pattern by etching the metal foil, and a plurality of multilayer substrates including the resin sheet filled in the via hole with the low melting point metal A step of laminating the forming sheets and a step of heating and pressing the laminated sheets for forming the multilayer substrate to collectively adhere the sheets for forming the multilayer substrate to each other to form a printed circuit board having a multilayer structure. A pressure / heating step, wherein in the pressure / heating step, a metal bond is formed between the low melting point metal and the adjacent conductor pattern. A method of manufacturing a printed circuit board, comprising: 2. The method of manufacturing a printed circuit board according to claim 1, wherein, in the filling step, the low melting point metal filled in the via hole is made of a single metal or a composite metal. 3. A step of forming a metal having a specific resistance smaller than that of the low melting point metal as a first connecting metal at the bottom of the via hole by electrolytic plating using the metal foil as an electrode in the filling step, The method for manufacturing a printed circuit board according to claim 1 or 2, further comprising: after filling the connection metal, filling the upper layer with the low-melting-point metal as a second connection metal. 4. The same metal as the conductor pattern is filled as the first connecting metal.
A method for manufacturing a printed circuit board according to. 5. The method of manufacturing a printed circuit board according to claim 3, wherein Cu is filled as the first connecting metal. 6. The method for manufacturing a printed circuit board according to claim 1, wherein in the laminating step, the multilayer substrate forming sheet is composed of only a plurality of the resin sheets. 7. The method for manufacturing a printed circuit board according to claim 1, wherein, in the stacking step, the multilayer substrate forming sheet includes a core substrate in addition to the resin sheet.