JP6616612B2 - Printed wiring board and manufacturing method thereof - Google Patents

Description

  The present invention relates to a printed wiring board in which a stub length generated in a through-hole portion is set so as not to affect electrical characteristics, and a method for manufacturing the same.

Conventionally, in order to mount electronic parts such as LSI (Large Scale Integrated Circuit) of multilayer printed wiring board, through holes that penetrate the printed wiring board are formed for connection to the inner layer circuit, and conductors in the through holes are formed. A signal circuit is formed by performing plating as a layer.
At this time, if the conductor layer (this is usually referred to as a stub) remaining in the through hole beyond the inner layer circuit is not deleted, mismatching of characteristic impedance, signal delay, etc. occur, and electrical characteristics at high frequencies Getting worse.

In order to solve this problem, for example, Patent Document 1 defines a rise or fall time required for a signal transmitted through each signal line in order to avoid signal resonance and signal waveform step caused by the presence of a stub. The wiring and external connection terminal arrangement satisfying the specifications are described.
Further, Patent Document 2 considers a harmonic component 10 times that of a transmission signal used in a semiconductor element, and sets the stub length in an open state to less than ¼ of the upper limit wavelength of the frequency band (about 1 GHz). (Less than 3.5 mm).

As described above, in order not to deteriorate the electrical characteristics at high frequencies, the stub is removed from one direction of the printed wiring board to the front of the inner layer circuit after plating in the through hole. The backdrill method is usually used to remove the stub.
At this time, since the influence of the stub length on the electrical characteristics is not known, processing was performed with a stub length of 0 mm, which has no possibility of adverse effects, as a target.

However, when the stub is removed by the back drill method, it is difficult to reduce the stub length to 0 mm even when performing accurate back drill processing while confirming the finish between the layers. This is because multilayer printed wiring boards are usually formed by alternately heat-pressing insulating material (resin layer) and inner layer circuit (conductor wiring layer), resulting in variations in the thickness and thickness of each layer. This is because the finish of the interlayer thickness varies depending on the position even in the individual production work of the substrate and the same production work.
Furthermore, since the influence of the stub length on the electrical characteristics is unknown, the basis for making the stub length 0 mm has not been clarified.

JP 2000-269379 A JP 2001-110927 A

  An object of this invention is to provide the printed wiring board which does not have a bad influence on an electrical property, even if it does not make stub length 0 mm, and its manufacturing method.

The present invention has been completed in order to solve the above problems, and has the following configuration.
(1) It has a through hole penetrating the front and back surfaces and having a conductor layer formed on the inner wall surface, a signal circuit is formed from one surface of the through hole to an inner layer circuit inside, and the inner layer circuit from the other surface The printed wiring board from which the conductor layer up to immediately before is removed, and the stub length L (mm), which is the remaining removal of the conductor layer extending from the inner layer circuit toward the other surface, satisfies the following relational expression: A printed wiring board characterized by:
L ≦ 0.1014λ−0.1305 (where λ is the signal wavelength (mm), L> 0)
(2) It has a through hole penetrating the front and back surfaces and having a conductor layer formed on the inner wall surface, a signal circuit is formed from one surface of the through hole to an inner layer circuit inside, and the inner layer circuit from the other surface The signal wavelength λ is obtained from the relative dielectric constant εr of the insulating material, the relative magnetic permeability μr of the insulating material, and the frequency f of the signal. The printed wiring board as described in 1).
(3) The printed wiring board according to (1) or (2), wherein a conductor layer from the other surface of the printed wiring board to immediately before the inner layer circuit is removed by a back drill method.
(4) It has a through hole penetrating the front and back surfaces, and a conductor layer is formed on the inner wall surface. A signal circuit is formed from one surface of the through hole to an inner layer circuit inside, and the inner layer circuit is formed from the other surface. Is a printed wiring board manufacturing method for removing the conductor layer up to immediately before the stub length L (mm), which is the remaining removal of the conductor layer extending from the inner layer circuit toward the other surface, The printed wiring board manufacturing method is characterized by removing the conductor layer from the other surface of the printed wiring board to immediately before the inner layer circuit so as to satisfy the above.
L ≦ 0.1014λ−0.1305 (where λ is the signal wavelength (mm), L> 0)
(5) The method for producing a printed wiring board according to (4), wherein a conductor layer from the other surface of the printed wiring board to immediately before the inner layer circuit is removed by a back drill method.
(6) The method for manufacturing a printed wiring board according to (4) or (5), wherein the stub length L is calculated using a CAD device, a program, or a simulation tool in which the relational expression according to claim 1 or 2 is incorporated. .

  According to the present invention, by removing the stub by back drilling or the like so that the stub length L satisfies the above relational expression, the difficulty in manufacturing the substrate becomes lower than setting the stub length to 0 mm. Production efficiency can be increased.

It is sectional drawing which shows the printed wiring board which concerns on one Embodiment of this invention. It is a graph which shows the TDR waveform in the difference in stub length. It is a graph which shows the transmission waveform in the difference in stub length. It is a graph which shows the relationship between the transmission characteristic in each frequency, and stub length. It is the graph produced using the value of the stub length of Table 2, and a wavelength. It is a calculation flowchart which concerns on one Embodiment of this invention. It is a graph which shows an example of the graph result obtained by FIG. (A)-(f) is sectional drawing which shows the manufacturing method of the printed wiring board which concerns on one Embodiment of this invention.

A printed wiring board according to an embodiment of the present invention will be described with reference to FIG.
The printed wiring board 10 of the present invention is obtained by alternately laminating insulating materials 1 and inner layer circuits 2, and a solder resist 3 is formed on at least one of the front and back surfaces of the printed wiring board 10.
Further, the printed wiring board 10 is provided with a through hole 5 penetrating the front and back surfaces and having the conductor layer 4 formed on the inner wall surface. The conductor layer 4 of the through hole 5 is a circuit component and becomes a signal circuit 6 connected to the inner layer circuit 2.
Such a printed wiring board 10 should have a plate thickness of 2 to 10 mm and the number of conductor layers 4 of about 2 to 100 layers.

As the insulating material 1, for example, polyphenylene ether (PPE) resin or the like is used.
The relative dielectric constant (εr) in this case is, for example, 3.6 (at a frequency of 1 GHz). Needless to say, the insulating material 1 can be used without being particularly limited from the printed wiring board material. The relative dielectric constant (εr) corresponds to about 3.3 to 4.9.

Copper is generally used as the conductor layer 4, and the conductivity is 5.8 × 10 ⁷ [S / m] (25 ° C.).

  The relative permittivity (εr) of the solder resist 3 is, for example, 4.3 (at a frequency of 1 GHz). It goes without saying that the solder resist 3 can be used without particular limitation from the solder resist for printed wiring boards. The relative dielectric constant (εr) corresponds to about 4.3 to 4.6.

The through-hole 5 is a through-hole penetrating the front and back surfaces of the printed wiring board 10, includes the conductor layer 4 on the inner wall surface, and forms the signal circuit 6 from the surface of the printed wiring board 10 to the inner layer circuit 2 inside. is there.
The through-hole 5 is formed by forming a conductive layer 4 (plating treatment) with a conductive material on the periphery and the inner wall surface of the through-hole after providing a through-hole in the printed wiring board 10 by laser or drilling. The At this time, a signal circuit 6 in which the conductor layer 4 in the through hole 5 is connected to the inner layer circuit 2 is formed.

In the through hole 5 in which the signal circuit 6 is formed from one surface of the printed wiring board to the inner layer circuit 2, the conductor layer 4 extending from the inner layer circuit 2 toward the other surface does not contribute to the signal circuit 6. It is removed by a well-known back drill method using a drill 8.
When the conductor layer 4 of the through hole 5 is removed from the other surface to a position immediately before the inner layer circuit 6 by the back drill method, the remaining portion of the removal becomes a stub 7.

  The length (stub length) L of the stub 7 that remains after removal of the conductor layer 4 by the back drill method is ideally 0 mm so as not to adversely affect the electrical characteristics. It is difficult to make it 0 mm because of accuracy. Therefore, if the stub length L (mm) is set so as to satisfy the relational expression; L ≦ 0.1014λ−0.1305 (where λ is the signal wavelength (mm), L> 0), the electrical characteristics are adversely affected. And making the stub length L 0 mm lowers the difficulty of manufacturing the substrate and increases the production efficiency.

<Stub length and transmission characteristics>
Next, in the printed wiring board 10, the stub length L of the back drill via used for the signal transmitted from the first conductor layer 40 to the fifth conductor layer 44 as shown in FIG. The transmission characteristics when changed in the range of 1 mm were evaluated.

FIG. 2 shows a TDR (Time Domain Reflectometry) waveform simulation result for different stub lengths.
As shown in FIG. 2, the impedance mismatch increases as the stub length increases. There is a difference of about 10Ω between 0 μm stub and 1 mm stub.

  FIG. 3 shows a simulation result of the transmission waveform in the stub length difference. FIG. 3 shows that there is almost no influence due to the difference in the stub length L at 10 GHz or less. Furthermore, if the stub length is 500 μm or less, resonance does not occur at a frequency lower than 50 GHz. Moreover, the shorter the stub length, the better the transmission loss of the transmission waveform.

  FIG. 4 is a graph of a simulation result showing the relationship between transmission characteristics and stub length in frequency. In FIG. 4, the stub length is taken on the X axis, the transmission loss (dB) is taken on the Y axis, and the target frequency is represented by a line.

Table 1 is a table showing numerical values narrowed down by FIG. Table 2 is a table in which the stub length is calculated according to the specific frequency from the result of Table 1. S21 is defined by the S parameter and is transmission loss (dB).

  From Table 2, with the stub length (0 μm) as a reference, it can be said that if the attenuation rate (BA) is −0.5 dB, it is hardly attenuated. That is, the stub length at this time does not affect the electrical characteristics of the printed wiring board.

FIG. 5 is a graph created using the simulation results of the values of stub length L and wavelength λ in Table 2.
In order to calculate the stub length, Table 2 is used to derive a calculation formula using approximate lines (L1, L2). Table 3 shows the calculation results based on the calculation formula. Note that L1 is a value obtained by linear approximation of the stub length [SIM value] by the least square method, and L2 is obtained by subtracting 0.02 from L1. The SIM value is the stub length L in Table 2.

From Table 3, the calculated value 1 is slightly larger than the SIM value in the equation L1 derived from the approximate line L1 in FIG. 5. However, if the equation L2 is used, the calculated value 2 should be smaller than the SIM value at all wavelengths λ. Can do.
As described above, the stub length L may be set to 0.1014λ−0.1305 or less in accordance with the specific frequency (from 10 GHz to 50 GHz).

  The relational expression of the stub length L can be incorporated into a program and used in a method for manufacturing a printed wiring board. In this program, when the relative permittivity, relative permeability, and frequency of the insulating material forming the printed wiring board are input, the stub length L is displayed as a graph or a number.

FIG. 6 shows a calculation flowchart in the program. This program may be used by being incorporated in a tool such as a computer calculation software.
In order to calculate the stub length, first, an insulating material for forming a printed wiring board is input (step 101).
Next, as shown in step 102, a material for which a relative permittivity and a relative permeability have been input in advance is called by a button (step 103A), or a relative permittivity and a relative permeability are manually input (step 103B). Select.
In this case, examples of the material include high performance FR-4 for multilayer printed wiring boards manufactured by Mitsubishi Gas Chemical Co., Ltd.
Next, it is selected whether the stub length to be calculated is displayed as a graph result (relationship between the wavelength λ and the stub length L) or a numerical result (step 104).
If the graph result is selected in step 104, then the interval frequency is input (step 105A) and the calculation is started. Then, the equation of stub length L and wavelength λ (L = 0.014λ−0.1305) is read. Then (step 106A), the graph result is displayed (step 107). The graph result is displayed as a graph as shown in FIG. 7, for example.

  Similarly, if a numerical result is selected in step 104, then a specific frequency is input (step 105B) and calculation is started. When the calculation is started, an expression of stub length L and wavelength λ (L = 0.014λ−0.1305). ) Is read (step 106B), and the numerical result is displayed (step 108).

  From the above graph results or numerical results, a printed wiring board that does not adversely affect the electrical characteristics can be manufactured by removing the stub by back drilling or the like so that the stub length L satisfies the above relational expression. . Therefore, the difficulty in manufacturing the printed wiring board is lower than when the stub length L is processed to 0 mm, and the production efficiency can be further increased.

  The relational expression of the stub length L described above; L ≦ 0.1014λ−0.1305 (where λ is the signal wavelength (mm), L> 0) may be used by being incorporated into a CAD device or a simulation tool, for example. it can.

Next, a method for manufacturing a printed wiring board according to the present invention will be described. The method for producing a printed wiring board according to the present invention includes the following steps (i) to (vii).
(I) A step of alternately laminating insulating materials and inner layer circuits to obtain a laminate.
(Ii) A step of providing a through hole pilot hole for forming a through hole penetrating the laminated body by laser processing or drilling the laminated body.
(Iii) A step of forming a conductor layer on the surface of the laminate and the inner wall surface of the through-hole pilot hole.
(Iv) After applying a dry film on the surface of the laminate, exposure and development are performed to peel off the dry film except where the conductor layer is to be formed. After etching, the remaining dry film is peeled off, and the inside of the through hole is removed. Forming signal circuits on both surfaces of the wall surface and the laminate;
(V) The signal wavelength is obtained from the relative dielectric constant of the insulating material, the relative magnetic permeability of the insulating material, and the frequency of the signal, and the stub length that is the remaining removal of the conductor layer extending from the inner layer circuit toward the other surface is calculated. The process to seek.
(Vi) A step of removing the stub from the other surface of the laminate by a back drill method until the length of the stub is reached.
(Vii) A step of forming a solder resist on the surface of the laminate.

  A method for manufacturing a printed wiring board according to the present invention will be described with reference to FIG. In addition, the description about the member mentioned above is abbreviate | omitted.

First, as shown in FIG. 8A, a laminate 12 is formed by alternately laminating a plurality of insulating materials 1 and inner layer circuits 2. More specifically, the laminated body 12 is formed by alternately stacking a plurality of other insulating materials 1 ′ on the surface of the insulating material 1 by heating and pressing with a hot press so as to embed the inner layer circuit 2.
Insulating material 1 'may be formed with the same material as insulating material 1, and may be formed with a different material. Furthermore, the insulating material 1 ′ may have the same thickness as the insulating material 1, or may have a different thickness.

Next, as shown in FIG. 8B, a through-hole prepared hole 5a for forming the through-hole 5 that penetrates the laminate 12 is formed by laser processing or drilling. Examples of laser light used in this laser processing include a CO ₂ laser and a UV-YAG laser.
In addition, the through-hole lower hole 5a may have a residue (not shown) of the insulating materials 1 and 1 ′ left open on the hole wall or the like regardless of the drill or laser method. In that case, the residue is removed by desmear treatment.

  Next, as shown in FIG. 8C, the inner wall surface of the through-hole prepared hole 5a and both surfaces of the laminate 12 are plated to form the conductor layer 4 made of copper plating.

Next, after plating the through-hole lower hole 5a, the dry film 9 is stuck on the surface of the laminate 12, and the dry film 9 other than the place where the circuit pattern is to be formed is peeled off by exposure and development by a known method. The conductor layer 4 on the surface of the multilayer body 12 is etched to form a circuit pattern on the conductor layer 4 to form the signal circuit 6.
When the remaining dry film 9 is peeled after the etching, as shown in FIG. 8D, a signal circuit 6 is formed in the laminate 12 by the conductor layer 4 and the through hole 5 having the conductor layer 4 on the inner wall surface. .

Next, the signal wavelength is obtained from the relative dielectric constant of the insulating material 1, the relative magnetic permeability of the insulating material 1, and the frequency of the signal circuit 6. Further, the length (stub length L) of the stub 7 which is the remaining removal of the conductor layer 4 extending from the inner layer circuit 2 toward the other surface of the multilayer body 12 is obtained.
The stub length L can be obtained using a calculation flowchart in the program as shown in FIG.

  Next, as shown in FIG. 8 (e), the through hole 5 is removed from the other surface of the laminate 12 by a back drill method using the back drill 8 until the length of the stub length L is reached. The diameter of the back drill 8 is larger than the diameter of the through hole 5.

  Finally, when the solder resist 3 is formed as an insulating resin layer on the surface of the laminate 12, a printed wiring board 10 'shown in FIG. 8 (f) is completed.

  As described above, in the method for manufacturing a printed wiring board according to the present invention, when the printed wiring board 10 is manufactured, the manufacturing difficulty is lower than when the stub length L is processed to 0 mm, and the production efficiency is increased. be able to.

DESCRIPTION OF SYMBOLS 1, 1 'Insulation material 2 Inner layer circuit 3 Solder resist 4 Conductor layer 40 First layer conductor layer 44 Fifth layer conductor layer 5 Through hole 5a Through hole pilot hole 6 Signal circuit 7 Stub 8 Back drill 9 Dry film 10, 10 'printed wiring board 12 laminate 101-108 steps

Claims (5)

The through-hole has a through hole penetrating the front and back surfaces of the insulating material, and a conductor layer is formed on the inner wall surface. A signal circuit is formed from one surface of the through hole to the inner layer circuit inside, and the inner layer circuit from the other surface. A printed wiring board from which the conductor layer up to immediately before is removed,
The stub length L (mm 2 ) , which is the remaining removal of the conductor layer extending in the direction of the other surface from the inner layer circuit, satisfies the following relational expression (1), and the signal wavelength λ in the relational expression (1) is A printed wiring board satisfying the relational expression (2) from the relative dielectric constant ε r of the insulating material, the relative magnetic permeability μr of the insulating material, and the frequency f of the signal flowing through the through hole. However, the insulating material is limited to a material having a relative dielectric constant εr of 3.3 to 4.9.
(1) L = 0.014λ−0.1305 (where λ is the signal wavelength (mm), L> 0, and the signal wavelength λ is the highest frequency signal used for the through hole of the printed wiring board. (Signal wavelength in insulating layer material)
(2) λ = c / (f × √ (εr × μr)) (c is the speed of light in vacuum) It has a through hole that penetrates the front and back surfaces of the insulating material and has a conductor layer formed on the inner wall surface. A signal circuit is formed from one surface of the through hole to the inner layer circuit inside, and the inner layer circuit from the other surface. A method for producing a printed wiring board that removes the conductor layer until immediately before,
The stub length L (mm 2 ) , which is the remaining removal of the conductor layer extending in the direction of the other surface from the inner layer circuit, satisfies the following relational expression (1), and the signal wavelength λ in the relational expression (1) is The inner layer circuit from the other surface of the printed circuit board so that the relational expression (2) is satisfied from the relative permittivity ε r of the insulating material, the relative permeability μr of the insulating material, and the frequency f of the signal flowing through the through hole. A method for producing a printed wiring board, wherein the conductor layer up to immediately before is removed. However, the insulating material is limited to a material having a relative dielectric constant εr of 3.3 to 4.9.
(1) L = 0.014λ−0.1305 (where λ is the signal wavelength (mm), L> 0, and the signal wavelength λ is the highest frequency signal used for the through hole of the printed wiring board. (Signal wavelength in insulating layer material)
(2) λ = c / (f × √ (εr × μr)) (c is the speed of light in vacuum)   The manufacturing method of the printed wiring board of Claim 2 which removes the conductor layer from the other surface of a printed wiring board to just before the said inner layer circuit by a back drill method. The method for producing a printed wiring board according to claim 2 or 3, wherein the stub length L is calculated using a CAD apparatus incorporating the relational expressions (1) and (2). The printed wiring board manufacturing method according to claim 2 or 3, wherein the stub length L is calculated using a program or a simulation tool in which the relational expressions (1) and (2) are incorporated.

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