JPH04364092A - Multilayer board - Google Patents

Abstract

PURPOSE:To improve production efficiency by constituting a multilayer board such that it has uniform stability and reproducibility at mass production. CONSTITUTION:In the constitution of a four-layer board, microstrip lines are made, respectively, at laminates A and B both sides of which are lined with copper. On the first layer L1 and the fourth layer L4 of this four-layer board are made strip conductors 10 and 11, respectively, and on the second layer L2 and the third layer L3 are made plane conductor plates 12 and 13, respectively. Moreover, for the core material being a dielectric board, for example, epoxy resin glass fabric base materials (a) and (b) are used. The laminates A and b both sides of which are lined with copper are bonded and stacked with a prepreg 14.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer substrate used in high frequency circuits that require high-density packaging.

0002

2. Description of the Related Art In general, a multilayer board has a basic structure in which a prepreg is sandwiched between one-sided or double-sided printed circuit boards and laminated with adhesive. FIG. 5 shows a schematic cross-sectional view of a four-layer board as a specific example. Here, the prepreg is a material obtained by impregnating glass fiber or the like with a resin before being molded for the purpose of insulation and adhesion. The appearance standards for this prepreg are that the surface is smooth;
Each base material is bonded in such a way that there are no practically harmful substances such as resin unevenness, protrusions, glass cloth stains, discoloration, tears, wrinkles, and foreign matter contamination.

A printed wiring board has a structure in which a copper foil, which is a conductive layer, is provided on the surface of an insulating substrate, also called a core material. The insulating substrate is formed, for example, by impregnating a glass cloth base material with epoxy resin, which is a type of synthetic resin. The multilayer board is formed by bonding and laminating the printed boards with prepreg made of epoxy resin. For example, in the case of a four-layer board, the prepreg mentioned above is
Core material 32 on which the copper foil 30 of the first layer L1 shown in FIG. 5 is disposed
and the copper foil 36 of the third layer L3 disposed on the prepreg 33 and the core material 35 between the copper foil 34 of the second layer L2 and the fourth layer L
A prepreg 37 is sandwiched between two core materials 38 of No. 4 and bonded to each printed circuit board.

In the four-layer board shown in FIG. 5, a circuit pattern is formed by using the copper foil 30 of the first layer L1 as an extremely thin strip conductor. The copper foil 34 of the second layer L2 has a planar conductor as a ground pattern on almost the entire surface. Similarly, a circuit pattern is formed using the strip conductor 31 on the fourth layer L4, and the planar conductor 36 on the third layer L3 is used as a ground pattern.

[0005] Also, a six-layer substrate will be explained with reference to FIG. Here, the common parts shown in FIG. 5 are given the same reference numerals and the explanation will be omitted. 1st layer L1 and 6th layer L6
A wiring pattern is formed using a strip conductor on a single-sided copper-clad laminate made of core materials 32 and 38, respectively, and the second layer L2
Almost the entire surface of the fifth layer L5 is used as a plane conductor plate to form ground patterns 34 and 41, respectively. This 6-layer board is a double-sided printed board (for example, copper foils 34 and 36 on both sides of an epoxy resin glass cloth base material 35, respectively) in the case of the above-mentioned 4-layer board.
) and another copper foil 3 on the surface of the core material 40.
9 and 41 are added, and the copper foil 39 of the fourth layer L4 and the copper foil 41 of the fifth layer L5 are adhered with prepregs 37 and 42, respectively. In addition, 6 shown in FIG.
Copper foils 36, 3 of the third layer L3 and fourth layer L4 in the layer board
9 may form a circuit portion for a purpose different from the circuit portion formed in the first layer L1 or the second layer L2. These laminates are adhesively laminated with prepregs 33, 37, and 42.

The four-layer board and six-layer board shown in FIGS. 5 and 6, respectively, can basically be represented by a model shown in FIG. 7. That is, it is constructed by laminating microstrip lines having strip conductors and flat conductor plates as ground patterns. The characteristic impedance Z of the strip conductor 50 of the basic model shown in FIG. 7 is expressed by the following equation 1.

[Formula 1]

[0007] Here, ε is a dielectric constant, which depends on the physical properties of the core material, such as the above-mentioned epoxy resin glass cloth base material. In the strip conductor 50, w
is the width of the strip conductor 50. t is the thickness of the strip conductor 50. Further, the strip conductor 50
The distance between the plane conductor plate 51 and the plane conductor plate 51 is expressed by a parameter called distance h. Using each of these parameters, the characteristic impedance Z of the multilayer board is determined.

[0008]

[Problem to be Solved by the Invention] By the way, when forming a microstrip line using the laminated structure of each of the above-mentioned laminated boards, prepreg is always inserted between each core material and the copper foil of the strip conductor to bond them together. . However, with the above prepreg, it is difficult to maintain accuracy in the thickness direction of the distance h between the strip conductor and the planar conductor due to the density of the inner layer pattern and the temperature and pressure during bonding, and it is also difficult to maintain uniformity and reproducibility. Unless the thickness h between the strip conductor and the plane conductor surface, which is a parameter in Equation 1, is kept constant, it is very difficult to set the characteristic impedance Z of the multilayer board to a desired value. For this reason, even if a multilayer board is manufactured according to the above-mentioned parameters set to theoretically obtain the desired characteristic impedance at the time of design, the actual characteristic impedance of the microstrip line will be different from the desired characteristic impedance calculated theoretically. A large error will occur.

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, the present invention aims to provide a multilayer substrate with easy thickness accuracy, good quality, and high reproducibility.

0010

[Means for Solving the Problems] A multilayer board according to the present invention is a multilayer board in which a plurality of microstrip lines each composed of a dielectric substrate, a strip conductor, and a flat conductor plate are laminated. The above problem is solved by using conductor layers on both sides of a double-sided copper-clad laminate for the pair of strip conductors and the above-mentioned flat conductor plate, and by adhesively laminating the double-sided copper-clad laminate with prepreg.

[0011]

[Function] The multilayer substrate according to the present invention has easy accuracy in the thickness direction, and has good characteristic impedance and high reproducibility.

0012

[Embodiment] An embodiment of a multilayer substrate according to the present invention will be described with reference to a schematic cross-sectional view shown in FIG. Figure 1
The multilayer board shown in Figure 1 is a four-layer board in which strip conductors and a ground pattern, which is a flat conductor plate, are stacked and stacked facing each other. This four-layer board uses two double-sided copper-clad laminates A and B. Using these double-sided copper-clad laminates A and B, the double-sided copper-clad laminates A and B are made of dielectric substrates such as so-called core materials a and b made of an epoxy resin glass cloth base material, strip conductors 10 and 11, and a flat surface. The conductor plates 12 and 13 each constitute two microstrip lines. In this embodiment, the above-mentioned epoxy resin glass cloth base material is used as an example of an insulating substrate.

In a multilayer board in which a plurality of microstrip lines are laminated as described above, the multilayer board according to the present invention includes a pair of strip conductors 10 and 11 and a planar conductor plate 1, respectively, which form a microstrip line.
Using copper foils on both sides of the double-sided copper-clad laminates 2 and 13, these double-sided copper-clad laminates are adhesively laminated with a prepreg 14 to construct a multilayer board.

To explain the structure of each layer in more detail, in this multilayer board, the double-sided copper-clad laminates A and B have a structure in which prepreg 14 is bonded between each layer, for example, the second layer L2 and the third layer L3. ing. Strip conductors 10 and 11 used as signal lines are disposed on the first layer L1 and the fourth layer L4 corresponding to the respective front surfaces of the double-sided copper-clad laminates A and B. The positions facing the first layer L1 and the fourth layer L4, that is, the second layer L2 and the third layer L3 on the opposing inner layer sides of the so-called core materials a and b are double-sided copper-clad as shown in FIG. The copper foil of the laminate is used as planar conductor plates 12 and 13. Planar conductor plate 12 for the strip conductors 10 and 11
, 13 are treated as grounding patterns.

Further, in order to bond the second layer L2 and the third layer L3, the prepreg 14 is sandwiched between the core materials a and b. In this laminated structure, in addition to the core material 32, a prepreg 33 is placed between the strip conductor 30 and the copper foil 34 shown in FIG. Unlike the multilayer board shown in FIG. 5, double-sided copper-clad laminates A and B are used to remove the prepreg 33, which is an uncertain element shown in FIG. 5, from the area of distance h between the strip conductor and the plane conductor plate. The core materials a and b shown in FIG. 1 are manufactured under strictly constant conditions and control in the manufacturing process and quality control. Therefore,
Through this control, the thickness h, which is a parameter in manufacturing the multilayer board, is controlled within a certain error range without variation.

In this way, the characteristic impedance Z basically depends on the characteristics of the double-sided copper-clad laminate A shown in FIG. It is regarded as a stripline, and a double-sided copper-clad laminate is used, excluding the prepreg 33 shown in FIG. Strip conductor 11 of fourth layer L4 and third layer L3
The flat conductor plate 13 can also be regarded as a pair of microstrip lines similar to the microstrip line formed by the first layer L1 and the second layer L2.

Here, even if the prepreg 14 between the second layer L2 and the third layer L3 is bonded, when calculating the characteristic impedance using the model shown in FIG. Since it is not included in the parameter distance h, the characteristic impedance Z of each microstrip line is not affected in any way and can be ignored. Therefore, for the first layer L1 and the second layer L2, or the fourth layer L4 and the third layer L3, the accuracy of the parameter in the thickness h direction can be easily obtained, and the uniformity and reproducibility can be improved.

Next, a six-layer multilayer substrate will be explained with reference to the sectional view shown in FIG. 2. Here, the same reference numerals as in FIG. 1 are given to common parts, and the description thereof will be omitted. In this way, a six-layer multilayer board is formed by the three double-sided copper-clad laminates A, B, and C. The copper foil 12 of the second layer L2 and the copper foil 1 of the third layer L3, which are the inner layers of this six-layer board.
Prepregs 14 and 17 are respectively inserted between the copper foils 15 of 3 and 4th layer L4 and the copper foil 16 of the 5th layer L5 provided on the core material c of the newly added double-sided copper-clad laminate C and bonded. This forms one multilayer substrate. At this time, the characteristic impedance Z of the microstrip line is determined by the model for determining the characteristic impedance Z of the microstrip line in which the relationship between the first layer L1 and the second layer L2 and the sixth layer L6 and the fifth layer L5 is shown in FIG. is in the same state. Therefore, as in the case of the above-mentioned four-layer substrate embodiment, the desired characteristic impedance Z can be realized with good reproducibility in accordance with the theoretical calculation even in the six-layer multilayer substrate. The above-mentioned double-sided copper-clad laminate b may have a ground pattern on both sides, or may be provided with another circuit.

In this way, by using a double-sided copper-clad laminate to avoid sandwiching the prepreg, which constitutes an uncertain element, between the target boards, it is possible to create a multilayer board with high reproducibility and a desired characteristic impedance. The board can be supplied to the user.

Next, another embodiment of the multilayer substrate according to the present invention will be described with reference to FIG. Here, common parts are given the same reference numerals and explanations are omitted. This example shows that a characteristic impedance Z that matches the theoretical calculation can be obtained with good reproducibility even when the multilayer substrate of the present invention includes a conventional adhesive structure as well. The part related to the multilayer board of the present invention is the second layer L2 and the third layer L2 of the inner layer.
A double-sided copper-clad laminate A is placed in the section 3. This double-sided copper-clad laminate A has a strip conductor 10 disposed on the second layer L2 above the so-called core material a, and a third layer L3 below the core material a, as in the case of the above-mentioned embodiment. A flat conductor plate 12 is used. At this time, the first layer L1 on the surface of the multilayer board avoids the strip conductor 10 of the second layer L2, and the copper foils 20a and 2
It is necessary to allocate 0b. This is because if the first layer L1 were entirely copper-clad, the model would have a configuration different from that shown in FIG. 7. The theoretical formula for calculating the characteristic impedance Z of the microstrip line is also different from Formula 1.

Therefore, the density of the pattern formed on the first layer L1 is reduced because the relief area 20c is formed in accordance with the strip conductor 10 formed on the second layer L2. Even if the laminated plates D and E are used, a multilayer substrate with good reproducibility of the characteristic impedance Z can be obtained. At this time, the first layer L1, the second layer L2, and the third layer L
The prepregs 18 and 19 inserted between the third layer L4 and the fourth layer L4 do not affect the characteristic impedance Z of the microstrip line formed on the double-sided copper-clad laminate A. Similar to the conventional structure in which the prepreg 18 is sandwiched between the layers L2, it can be used for bonding substrates. The single-sided copper-clad laminates D and E have copper foils 20a, 20b and 2 on one side of the core materials d and e, respectively.
1 is arranged and formed.

Similarly to the embodiment shown in FIG. 3, in the six-layer substrate, not only the second layer L2 and the third layer L3 but also the fourth layer L
4 and the fifth layer L5 by adding double-sided copper clad laminate B.
forming a multilayer substrate of layers. Here, common parts are given the same reference numerals and explanations are omitted. As an example of a structure that satisfies the above conditions, as shown in FIG.
The first layer, which is the upper layer of these four layers, and the sixth layer, which is the lower layer, are each made of single-sided copper-clad laminates D and E. In addition, in order to obtain the same state as the model shown in FIG. 7, the first layer L1, which is the surface of each core material d and e of the single-sided copper-clad laminate, is coated with copper foils 20a and 20b and the sixth layer L6. copper foil 2
1a and 21b, and outer layer reliefs 20c and 21c are provided in each layer, respectively.

In this way, when a single-sided copper-clad laminate and a double-sided copper-clad laminate are mixed and used, the desired characteristic impedance can be achieved by ensuring that the area where the strip conductor pattern formed on the inner layer is formed is avoided. Reproducibility can be improved.

Although the above-mentioned embodiment shows a multilayer board having a laminated structure with the strip conductors facing outward and the flat conductor plates facing inward, the structure is not limited to this, and the structure shown in FIG. A similar effect can be achieved by considering the relationship between the models and forming a microstrip line using double-sided copper-clad laminates. Further, the so-called core material is not limited to the epoxy resin glass cloth base material, and the same effects as described above can be obtained even if a core material formed by impregnating polyimide resin or the like, for example, is used.

With the above structure, the multilayer substrate can maintain high uniformity and reproducibility. In particular, according to this method, a multilayer board manufactured according to the parameter settings at the time of designing the multilayer board can obtain the desired characteristic impedance Z of the microstrip line with good reproducibility. In this manner, a multilayer board with good reproducibility can reduce the incidence of lot-outs due to defects in the multilayer board during mass production.

[0026]

Effects of the Invention As is clear from the above description, according to the multilayer board of the present invention, the copper foils on both sides of the double-sided copper-clad laminate are applied to the pair of strip conductors and the flat conductor plate forming the microstrip line. By adhesively laminating this double-sided copper-clad laminate with prepreg, high uniformity and reproducibility of the multilayer board can be maintained during mass production. especially,
The characteristic impedance of the multilayer board can be set to the desired value,
Productivity efficiency can be increased.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a four-layer board as an example of a multi-layer board according to the present invention.

FIG. 2 is a schematic cross-sectional view of a six-layer board in the multilayer board according to the present invention.

FIG. 3: 4 in another embodiment of the multilayer substrate according to the present invention.
FIG. 3 is a schematic cross-sectional view of a layered substrate.

FIG. 4 is a schematic cross-sectional view when a double-sided copper-clad laminate is added to the inner layer of the embodiment shown in FIG. 3 to make a six-layer board.

FIG. 5 is a schematic cross-sectional view of a conventional four-layer board.

FIG. 6 is a schematic cross-sectional view of a conventional six-layer board.

FIG. 7 is a schematic diagram when determining the characteristic impedance of a microstrip line.

[Explanation of symbols]

A, B・・・・・・・・・Double-sided copper clad laminate a, b・
・・・・・・・・・Core material

Claims (1)

[Claims] Claim 1. A multilayer board in which a plurality of microstrip lines each composed of a dielectric substrate, a strip conductor, and a flat conductor plate are laminated, wherein a pair of strip conductors forming the microstrip line and the flat conductor plate have double-sided conductors. A multilayer board characterized by using conductor layers on both sides of a copper-clad laminate, and adhesively laminating these double-sided copper-clad laminates with prepreg.