JP5406252B2 - Printed wiring circuit and manufacturing method thereof - Google Patents

Description

  The present invention relates to a printed wiring circuit suitable for high-speed transmission and a manufacturing method thereof.

  Conventionally, as a printed wiring circuit, a three-layer CCL (copper-clad laminate) is often used because of its quality and characteristics being stable and inexpensive. In the three-layer CCL, an insulating layer such as polyimide and a conductor circuit layer are bonded via an adhesive layer. This adhesive layer needs a certain thickness in order to ensure adhesive strength.

  On the other hand, in recent years, with an increase in communication speed, this type of printed wiring circuit has been required to have high frequency characteristics. In particular, an insulator that exists between the microstrip line and the ground line requires a material with low dielectric loss. In this regard, the above-described three-layer CCL has a problem that the dielectric loss tangent of an adhesive layer that requires a certain thickness is much larger than that of polyimide, and is not suitable for high-speed signal transmission.

  For these reasons, a material having a relatively low dielectric loss tangent has been developed, and in general, a substrate made of a material such as a liquid crystal polymer (LCP) has been developed. For example, in the multilayer circuit board disclosed in the following Patent Document 1 in which polyimide resin is used as an insulating layer, an electric signal is propagated by lowering the dielectric loss tangent so that the signal line on the insulating layer is an air layer. The speed is increased.

JP-A-11-168279

  However, considering the recent advancement of high-functionality of printed wiring circuits and the wide range of required characteristics, or the great demand for reduction in manufacturing costs, the material is changed to LCP only for electrical characteristics. In addition, there is a problem that it is practically difficult to make structural changes such as providing an air layer as in Patent Document 1.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a printed wiring circuit and a method for manufacturing the printed wiring circuit that can eliminate the above-described problems caused by the prior art and can reduce the loss of electric signals at a low cost.

  The printed wiring circuit according to the present invention includes an insulating layer, a conductor circuit layer formed on both sides of the insulating layer, and at least one of the conductor circuit layer and the insulating layer. In a printed wiring circuit having an adhesive layer for bonding an insulating layer, the interface between the conductor circuit layer and the adhesive layer is the insulating layer of the adhesive layer where the conductor circuit layer is not present. It is characterized by being closer to the insulating layer than the surface located on the opposite side.

  According to the printed wiring circuit of the present invention, the interface between the conductor circuit layer and the adhesive layer is more insulative than the surface of the adhesive layer in the portion where the conductor circuit layer is not present, which is located on the side opposite to the insulating layer. It is close to. That is, the thickness of the adhesive layer between the conductor circuit layer and the insulating layer is thinner than the thickness of other portions. For this reason, it is possible to reduce the dielectric loss due to the adhesive layer in the portion from the lower surface of the conductor circuit layer where the electric field is most concentrated to the insulating layer. In addition, since the conductor circuit layer is embedded in the adhesive layer, and the thickness of the adhesive layer where the conductor circuit layer is not formed is sufficiently secured, the conductor circuit layer and the insulating layer It is also possible to prevent a decrease in the adhesive strength between the two.

  In one embodiment of the present invention, the dielectric tangent of the insulating layer is lower than the dielectric tangent of the adhesive layer.

  In another embodiment of the present invention, the distance in the thickness direction between the interface between the conductor circuit layer and the adhesive layer and the surface of the adhesive layer where the conductor circuit layer is not provided is 5 μm. It is as follows.

  In still another embodiment of the present invention, the at least one conductor circuit layer is a signal line for high speed transmission.

  In the printed wiring circuit manufacturing method according to the present invention, conductor circuit layers are formed on both sides of an insulating layer, and the conductor circuit layer and the adhesive layer are provided between at least one of the conductor circuit layers and the insulating layer. Processing the at least one conductor circuit layer of the wiring board having the first adhesive layer to be bonded into a predetermined pattern, on the surface of the wiring board on which the conductor circuit layer processed into the predetermined pattern is formed A cover lay is disposed via a second adhesive layer, the cover lay is thermocompression bonded to the wiring board, and the conductor circuit layer processed into the predetermined pattern is bonded to the first adhesive layer by the thermocompression bonding. It is characterized by being sunk into the side.

  According to the printed wiring circuit manufacturing method of the present invention, when the coverlay is laminated on the wiring board by thermocompression bonding, the first adhesive layer is softened by heat and the conductor circuit layer becomes the first adhesive layer. You will sink into the side. For this reason, as described above, the thickness of the adhesive layer immediately below the conductor circuit layer is reduced at low cost by using existing facilities and structures without reducing the adhesive strength, thereby reducing the loss of electrical signals. be able to.

  According to the present invention, loss of an electric signal can be reduced at low cost.

It is sectional drawing which shows the structure of the printed wiring circuit which concerns on the 1st Embodiment of this invention. It is a flowchart which shows the manufacturing process of the printed wiring circuit. It is sectional drawing which shows the printed wiring circuit in order of a manufacturing process. It is sectional drawing which shows the structure of the printed wiring circuit of a comparative example. It is a figure which shows the relationship between the characteristic impedance and signal line | wire width of a printed wiring circuit in the Example of this invention. It is a figure which shows the relationship between the characteristic impedance and signal line | wire width of the printed wiring circuit of a comparative example. It is a figure which shows the relationship between S parameter of the printed wiring circuit in the Example, and the printed wiring circuit of a comparative example, and a frequency.

  Hereinafter, a printed wiring circuit and a manufacturing method thereof according to embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[First Embodiment]
FIG. 1 is a sectional view showing the structure of a printed wiring circuit according to the first embodiment of the present invention. The printed wiring circuit 100 according to the present embodiment is used in various signal transmission circuits, and has, for example, a microstrip line structure for high-speed signal transmission.

  As shown in FIG. 1, the printed wiring circuit 100 includes a double-sided wiring board 10 formed on the basis of a three-layer CCL (copper-clad laminate) and a cover material 20 that covers the upper surface of the double-sided wiring board 10. Is formed.

  The double-sided wiring board 10 includes an insulating layer 1 made of, for example, a polyimide resin (PI) having a thickness of 50 μm, and adhesive layers 2 and 3 made of, for example, an epoxy-based adhesive having a thickness of 10 μm formed on both surfaces of the insulating layer 1. And a signal line 4 and a ground electrode 5 as a conductor circuit layer made of, for example, a copper foil having a thickness of 20 μm, which are attached via the adhesive layers 2 and 3. The signal line 4 is a microstrip line having a width of about 150 μm, for example. The ground electrode 5 is formed on the entire lower surface of the insulating layer 1.

  On the other hand, the cover material 20 is disposed on the surface of the double-sided wiring board 10 on the signal line 4 side, and is made of an insulating material such as polyimide resin. And an adhesive layer 6 made of an epoxy adhesive.

  The signal line 4 has a structure that is recessed into the adhesive layer 2 side by thermocompression bonding of the cover material 20. That is, in this example, the interface 2b between the signal line 4 and the adhesive layer 2 is more than the surface 2a located on the opposite side of the insulating layer 1 where the signal line 4 of the adhesive layer 2 having a thickness of 10 μm is not present. Is recessed close to the insulating layer 1. The amount of penetration of the signal line 4 is desirably set to a maximum of about 5 μm in the thickness direction with respect to the surface 2a with reference to the interface 2b. The reason is as follows. That is, normally, the adhesive layers 2 and 3 are formed with a thickness of 8 to 10 μm, and in order not to significantly reduce the adhesive strength, it is desirable to secure the thickness of the adhesive layers 2 and 3 at least 5 μm. Because. For this reason, if the amount of penetration is adjusted so that it may become 3-5 micrometers, sufficient adhesive strength can be ensured. Further, since the signal line 4 is embedded in the adhesive layer 2, both are securely bonded, and the adhesive strength between the two is higher than when the signal line 4 is not embedded.

  Here, the polyimide constituting the insulating layer 1 and the adhesive of the adhesive layer 2 generally have physical property values as shown in Table 1 below.

  According to Table 1, since polyimide has low dielectric constant and dielectric loss tangent (tan δ) as compared with the adhesive, it can be understood that transmission loss can be suppressed and high frequency characteristics are excellent. The glass transition temperature (Tg) is higher for polyimide. Specifically, regarding the physical property values, the dielectric constant of the adhesive is 3.9, whereas the dielectric constant of polyimide is 3.3, so that the high frequency characteristics are excellent. In addition, since the dielectric loss tangent of the adhesive is 0.02, whereas the dielectric loss tangent of polyimide is 0.004, the dielectric loss is small.

  In the printed wiring circuit 100 configured as described above, when an electric signal passes through the signal line 4, an electric force line 9 between the signal line 4 and the ground electrode 5 is as shown in FIG. 1. As is clear from FIG. 1, the electric lines of force concentrate on a portion from the lower surface of the signal line 4 toward the ground electrode 5. Thus, in the electric signal transmission characteristics in the microstrip line structure, the influence of the material physical properties of the portion where the electric lines of force 9 are concentrated (that is, the lower portion of the signal line 4) is increased.

  For this reason, in this embodiment, the transmission characteristics are improved by preferentially improving the characteristics of this portion. The printed wiring circuit 100 is configured such that the thickness of the adhesive layer 2 with respect to the total thickness between the signal line 4 and the ground electrode 5 is reduced in proportion. As is clear from Table 1 above, the dielectric loss tangent, which has a large influence on the dielectric loss in high-speed signal transmission, is larger in the adhesive than in the polyimide, and therefore the thickness of the adhesive layer 2 with respect to the total thickness. By reducing the ratio, the dielectric loss tangent becomes equivalently small, and as a result, the loss (dielectric loss) of the electric signal can be reduced.

Next, a method for manufacturing a printed wiring circuit according to the present embodiment will be described.
FIG. 2 is a flowchart showing the manufacturing process of the printed wiring circuit. FIG. 3 is a cross-sectional view showing printed wiring circuits in the order of manufacturing steps.
First, as shown in FIG. 3A, a copper clad laminate (CCL) in which a conductor circuit layer 4A and a ground electrode 5 which is a conductor circuit layer are bonded to both surfaces of an insulating layer 1 via adhesive layers 2 and 3. ), And the conductor circuit layer 4A on one surface side is processed into a predetermined pattern by etching or the like to form the signal line 4 (step S100). ).

Next, as shown in FIG. 3C, the cover material 20 is arranged on the double-sided wiring board 10 on which the signal lines 4 are formed with the adhesive layer 6 on the bottom surface (step S101), and the arrow in the figure. As shown in FIG. 8, the coverlay 6 is thermocompression bonded to the signal line 4 side of the double-sided wiring board 10 (step S102). The heating temperature at the time of thermocompression bonding is set to about 160 ° C., which is higher than the glass transition temperature (40 to 60 ° C.) of the adhesive layer 2. As a result, the printed wiring circuit 100 having a structure in which the signal line 4 is recessed into the adhesive layer 2 is manufactured as shown in FIG. In addition, the applied pressure at the time of thermocompression bonding is 30-60 kgf / cm < ² > with respect to the area of a board | substrate, for example. Thus, the printed wiring circuit 100 can be manufactured at low cost because it can be manufactured by an existing manufacturing process using existing equipment. Since the signal line 4 is patterned to a predetermined width (for example, about 150 μm), the signal electrode 4 is embedded in the adhesive layer 2 by thermocompression bonding. However, since the ground electrode 5 has a large area, such an indentation does not occur. Almost no. For this reason, the adhesive strength on the ground electrode 5 side does not change. This point also contributes to reducing the adhesive layer 2 only in the portion where the electric field is concentrated.

Next, specific electrical characteristics of the printed wiring circuit 100 according to the present embodiment will be described with reference to a comparative example.
FIG. 4 is a cross-sectional view showing the structure of a printed wiring circuit of a comparative example. As shown in FIG. 4, the printed wiring circuit 100A of the comparative example has the same structure as that of the printed wiring circuit 100 of the present embodiment, except that the signal line 4 is not recessed into the adhesive layer 2 side. Yes.

  In the printed wiring circuits 100 and 100A of these examples and comparative examples, the width of the signal line 4 is set to 150 μm in order to make the characteristic impedance 50 Ω in general. FIG. 5 shows the relationship between the characteristic impedance and the signal line width of the printed wiring circuit 100 of the example in this case, and FIG. 6 shows the relationship between the characteristic impedance and the signal line width of the printed wiring circuit 100A of the comparative example. FIG. 7 shows the relationship between the input / output characteristics (S parameters) and the frequencies of the printed wiring circuit 100 in the example and the printed wiring circuit 100A in the comparative example.

  As shown in FIGS. 5 and 6, the printed wiring circuit 100 (FIG. 5) of the example is 150 μm because the signal line 4 is closer to the ground electrode 5 than the printed wiring circuit 100 </ b> A (FIG. 6) of the comparative example. It can be seen that the characteristic impedance is somewhat lower than that of the comparative example. However, this reduction can be dealt with by the design of the width of the signal line 4 and therefore does not cause a problem. That is, as shown in FIG. 5, in order to set the characteristic impedance to 50Ω, the width of the signal line 4 may be set to about 140 μm.

  As shown in FIG. 7, in both the example and the comparative example, the loss increases as the electric signal flowing through the signal line 4 becomes higher in frequency, so that it is greatly affected by the loss during high-speed signal transmission. It was found that the loss is smaller in the high frequency band than the comparative example. Therefore, according to the printed wiring circuit 100 of the present embodiment having the structure in which the signal line 4 is embedded in the adhesive layer 2 and the interface 2b is closer to the insulating layer 1 than the surface 2a, the adhesion enhancement and the electric signal are performed at low cost. It is possible to achieve both reductions in loss.

  In the above embodiment, the printed wiring circuit 100 is described as having a microstrip line structure for high-speed signal transmission. However, the printed wiring circuit 100 is not limited to this, and various electric signal transmission circuits can be used. Etc. can be applied.

DESCRIPTION OF SYMBOLS 1 Insulation layer 2,3 Adhesive layer 2a Surface 2b Interface 3 Conductor 4 Signal line 5 Ground electrode 6 Adhesive layer 7 Coverlay 9 Electric force line 100 Printed wiring circuit

Claims (5)

A double-sided wiring board having a conductor circuit layers formed on both sides of the insulating layer and the insulating layer made of a polyimide resin through a first adhesive layer,
In a printed wiring circuit having a cover lay attached via a second adhesive layer on one of the conductor circuit layer side surfaces of the double-sided wiring board ,
An interface between the first adhesive layer and said one conductive circuit layer, than the field surface between the second adhesive layer and the first adhesive layer of the absence of one of the conductor circuit layer portion printed wiring circuit, characterized in that is closer before Symbol insulating layer. The printed wiring circuit according to claim 1 , wherein a dielectric loss tangent of the insulating layer is lower than a dielectric loss tangent of the first adhesive layer. Wherein one of the conductive circuit layer and the interface between the first adhesive layer, with the field surface with the first adhesive layer and the second adhesive layer of the absence of one of the conductor circuit layer portion The printed wiring circuit according to claim 1, wherein the distance in the thickness direction is 5 μm or less. Prior Symbol hand conductor circuit layer of a printed wiring circuit according to any one of claims 1 to 3, characterized in that a signal line for high-speed transmission. The conductor circuit layer of hand of the first double-sided wiring board in which the conductor circuit layer is formed via an adhesive layer on both sides of the insulating layer made of polyimide resin is processed into a predetermined pattern,
A coverlay is disposed on the surface of the double-sided wiring board on the surface on which the conductor circuit layer processed into the predetermined pattern is formed via a second adhesive layer,
The printed wiring circuit, wherein the coverlay is thermocompression bonded to the double-sided wiring board and the conductor circuit layer processed into the predetermined pattern is embedded in the first adhesive layer side by the thermocompression bonding. Manufacturing method.

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