JP2013089710A - Flexible printed circuit board and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure excellent high frequency characteristics and high insulation reliability.SOLUTION: A flexible printed circuit board 100 comprises: a base material 10; wiring 11; and a coverlay 12. When the coverlay 12 is thermocompression bonded to the base material 10, a subsidiary material 15 having a melting point lower than that of the coverlay 12 is mounted on the coverlay 12, and thermocompression bonding is carried out while raising the temperature from the melting point of the subsidiary material 15 toward the melting point of the coverlay 12. Consequently, the flexible printed circuit board is formed so that the thickness t1+d1 from the surface of the base material 10 in a region where the wiring 11 exists to the surface of the coverlay 12 is thicker than the thickness t2 from the surface of the base material 10 in a recess 13 that is a region where the wiring 11 does not exist to the surface of the coverlay 12. Since the edge of the wiring 11 is not exposed from the coverlay 12, excellent high frequency characteristics and high reliability can be ensured.

Description

  The present invention relates to a flexible printed circuit board excellent in high frequency characteristics and a manufacturing method thereof.

  In recent years, there has been a need to transmit high-speed signals with a flexible printed circuit board in personal computers and portable terminals. In such a flexible printed circuit board, a liquid crystal polymer having a lower dielectric constant and dielectric loss tangent than polyimide resin is used for the base substrate and the coverlay, so that the coverlay can be softened without using an adhesive. Bonded by thermocompression bonding. As a result, attempts have been made to reduce transmission loss at high frequencies (see, for example, Patent Document 1 below).

JP 2010-103269 A

  However, in the substrate disclosed in Patent Document 1, the coverlay is softened and thermocompression bonded while flowing from above the wiring into the space between the wirings. Therefore, as a result, the coverlay on the wiring is thinned, and there is a problem that the insulating reliability of the substrate is lowered due to problems such as exposure of the edge of the wiring.

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems caused by the prior art, and to provide a flexible printed board having excellent high frequency characteristics and high insulation reliability, and a method for manufacturing the same.

  A flexible printed circuit board according to the present invention is a flexible printed circuit board comprising a base substrate, wiring formed on the base substrate, and a coverlay made of a liquid crystal polymer formed thereon, The melting point of the base substrate is higher than the melting point of the cover lay, and the thickness from the surface of the base substrate to the surface of the cover lay in the region where the wiring exists is in the region where the wiring does not exist. It is characterized by being thicker than the thickness from the surface of the base substrate to the surface of the coverlay.

  According to the flexible printed board of the present invention, the melting point of the base substrate is higher than the melting point of the cover lay made of a liquid crystal polymer, and the thickness from the surface of the base substrate to the surface of the cover lay in the region where the wiring exists is In addition, it is formed so as to be thicker than the thickness from the surface of the base substrate to the surface of the coverlay in the region where no wiring exists. For this reason, the edge portion of the wiring is not exposed from the coverlay. Therefore, the insulation reliability can be increased while being excellent in high frequency characteristics.

  In one embodiment of the present invention, the thickness of the cover lay in the region where the wiring exists is substantially the same as the thickness of the cover lay in the region where the wiring does not exist.

  In another embodiment of the present invention, the base substrate is made of a liquid crystal polymer.

  Further, the flexible printed circuit board according to the present invention has a cover lay film made of a liquid crystal polymer on a base substrate on which wiring is formed, and an auxiliary material film made of a material having a melting point lower than that of the cover lay film, It was obtained by performing thermocompression bonding while increasing the temperature from the melting point of the auxiliary material film toward the melting point of the coverlay film.

  The method for producing a flexible printed board according to the present invention includes a step of forming a wiring on a base substrate, a coverlay film made of a liquid crystal polymer on the base substrate on which the wiring is formed, and the coverlay film. The method further comprises a step of thermocompression-bonding a secondary material film made of a material having a low melting point, and a step of peeling the secondary material film from the coverlay film.

  According to the method for manufacturing a printed board according to the present invention, a coverlay film made of a liquid crystal polymer and a secondary material film made of a material having a melting point lower than that of the coverlay film are placed on the base substrate and thermocompression bonded. For this reason, at the time of thermocompression bonding, the auxiliary material film melts and flows into the space between the wirings before the coverlay film, and then the coverlay film is softened and bonded. For this reason, the thickness from the surface of the base substrate to the surface of the cover lay in the region where the wiring is present is thicker than the thickness from the surface of the base substrate to the surface of the cover lay in the region where the wiring is not present. Thus, the edge portion of the wiring is not exposed from the cover lay, and a flexible printed board having excellent high frequency characteristics and high insulation reliability can be manufactured.

  In one embodiment of the present invention, in the step of thermocompression bonding, thermocompression bonding is performed while increasing the temperature from the melting point of the auxiliary material film toward the melting point of the coverlay film.

  According to the present invention, it is excellent in high frequency characteristics and insulation reliability can be increased.

It is sectional drawing which shows the structure of the flexible printed circuit board concerning the 1st Embodiment of this invention. It is a flowchart which shows the manufacturing process of the flexible printed circuit board. It is sectional drawing which shows the flexible printed circuit board in order of a manufacturing process. It is sectional drawing which shows the structure of the flexible printed circuit board concerning the 2nd Embodiment of this invention.

  Hereinafter, a flexible printed circuit board 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 cross-sectional view showing the structure of a flexible printed circuit board according to the first embodiment of the present invention. The printed circuit board 100 according to the first embodiment includes a base substrate 10 and wirings 11 formed on the base substrate 10. A coverlay 12 is formed on the surface of the base substrate 10 on which the wiring 11 is formed.

  The base substrate 10 may be made of, for example, a polyimide resin, but here is made of a thermoplastic liquid crystal polymer (LCP). Similarly, the coverlay 12 is made of a thermoplastic liquid crystal polymer. The liquid crystal polymer mainly includes (1) aromatic or aliphatic dihydroxy compounds, (2) aromatic or aliphatic dicarboxylic acids, (3) aromatic hydroxycarboxylic acids, (4) aromatic diamines, and aromatic hydroxyamines. Or aromatic aminocarboxylic acid.

  And well-known thermotropic liquid crystal polyester, polyesteramide, etc. which are synthesize | combined from these compounds and its derivative (s) can be used. In addition, in order to form a polymer liquid crystal, a known appropriate range is applied to each combination of raw material compounds. The base substrate 10 and the coverlay 12 are preferably formed of liquid crystal polymers having different melting points as will be described later.

  On the other hand, the wiring 11 is preferably made of a conductive material such as gold, silver, copper, nickel, aluminum, or an alloy thereof. Here, the wiring 11 is formed by patterning a conductive material such as a copper foil, and the thickness d1 is from 8 μm to 8 μm. It is formed on the base substrate 10 so as to be in the range of 25 μm. As copper foil, what was manufactured by the rolling method, the electrolysis method, etc. can be used. The surface of the wiring 11 is subjected to a physical surface treatment such as a roughening treatment by plasma, or a chemical surface treatment such as a roughening treatment by acid cleaning, so that the adhesive force with the coverlay 12 is improved. ing.

  The base substrate 10 is formed with a thickness D in the range of 25 μm to 100 μm, for example, and the cover lay 12 is formed with a thickness t1 (and t2) in the range of 25 μm to 50 μm, for example. That is, the cover lay 12 is formed such that the thickness t1 of the region where the wiring 11 is present is substantially the same as the thickness t2 in the region where the wiring 11 is not present (recess 13).

  Therefore, the thickness of the wiring 11 on the surface of the base substrate 10 and the thickness of the cover lay 12 on the wiring 11 is t1 + d1> t2 in relation to the thickness of the cover lay 12 on the surface of the base substrate 10 in the recess 13. Become. Further, the distance d2 from the surface of the cover lay 12 in the recess 13 to the same height as the cover lay 12 on the wiring 11 is the difference between t1 + d1 and t2. Note that the thickness x of the coverlay 12 on the edge of the wiring 11 is also formed with a sufficient thickness due to the presence of the recess 13 formed at the time of thermocompression bonding by an auxiliary material described later.

  The liquid crystal polymer of the base substrate 10 and the coverlay 12 is configured such that the melting point of the base substrate 10 is higher and the difference between the melting points is 15 ° C. or more. If the difference between the melting points is less than 15 ° C., the base substrate 10 is also softened when the coverlay 12 is thermocompression bonded onto the base substrate 10, so that the wiring 11 is easy to move and positioning control is difficult. This is because there is a risk of becoming.

  The melting point temperature of the base substrate 10 is set to about 310 ° C. to 335 ° C., for example, and the melting point temperature of the cover lay 12 is set to about 280 ° C. to 295 ° C., for example. The auxiliary material 15 (see FIG. 3 (e)) used for thermocompression bonding these is made of an ultra-high molecular weight polyethylene innovate film having a melting point lower than the melting point temperature of the cover lay 12, and is easily connected to the cover lay 12. Has releasability.

  In the flexible printed circuit board 100 according to the first embodiment, the thickness t1 + d1 from the surface of the base substrate 10 to the surface of the cover lay 12 in the region where the wiring 11 is present is the recess 13 which is the region where the wiring 11 is not present. Since it is formed to be thicker than the thickness t2 from the surface of the base substrate 10 to the surface of the cover lay 12, the edge portion of the wiring 11 is not exposed from the cover lay 12 and is excellent in high frequency characteristics. Insulation reliability can be increased.

  The flexible printed circuit board 100 configured as described above is manufactured, for example, as follows. FIG. 2 is a flowchart showing a manufacturing process of the flexible printed circuit board. FIG. 3 is a cross-sectional view showing the flexible printed circuit board in the order of the manufacturing process. First, as shown to Fig.3 (a), the base base material 10 in which the conductor layer 19 was formed is prepared (step S100).

  Next, as shown in FIG. 3B, a dry film resist is attached on the conductor layer 19 and exposure / development is performed to form a predetermined mask pattern 18 at a wiring formation location. Then, as shown in FIG. 3C, etching or the like is performed to form the wiring 11 on the base substrate 10 (step S102), and the mask pattern 18 is removed.

  After that, as shown in FIG. 3D, the cover lay 12 and the film of the auxiliary material 15 are placed on the base substrate 10 on which the wiring 11 is formed (step S104), and the cover from the melting point of the auxiliary material 15 is covered. Thermocompression bonding is performed while increasing the temperature toward the melting point of the ray 12 (step S106).

  Then, as shown in FIG. 3 (e), since the auxiliary material 15 that was first melted flows into the space between the wirings 11, the coverlay 12 that is melted later, as shown by the arrows and x marks in the figure, It is thermocompression bonded to the wiring 11 and the base substrate 10 without being able to flow into the space. The flexible printed circuit board thus subjected to thermocompression bonding is cooled and cured (step S108), the auxiliary material 15 is peeled off from the cover lay 12 (step S110), and the flexible print having the recess 13 as shown in FIG. 1 is formed. The substrate 100 is manufactured.

[Second Embodiment]
FIG. 4 is a sectional view showing the structure of a flexible printed circuit board according to the second embodiment of the present invention. The printed circuit board 100A according to the second embodiment differs from the flexible printed circuit board 100 according to the first embodiment in that the printed circuit board 100A has a multilayer structure in which a plurality of base substrates 10, wirings 11, and coverlays 12 are stacked. Yes.

  In the case of such a multilayer structure, the thickness of the region where the wiring 11 exists is thinner than the thickness of the region where the wiring 11 does not exist, except for the cover layer 12 of the outermost layer, but is in a state between the layers. As described above, there is an effect that the insulation reliability can be enhanced while being excellent in the high frequency characteristics as described above.

DESCRIPTION OF SYMBOLS 10 Base base material 11 Wiring 12 Coverlay 13 Recessed part 15 Secondary material 100 Flexible printed circuit

Claims (6)

A flexible printed circuit board comprising a base substrate, wiring formed on the base substrate, and a cover lay made of a liquid crystal polymer formed thereon,
The melting point of the base substrate is higher than the melting point of the coverlay,
The thickness from the surface of the base substrate to the surface of the coverlay in the region where the wiring is present is thicker than the thickness from the surface of the base substrate to the surface of the coverlay in the region where the wiring is not present A flexible printed circuit board characterized by that.   The flexible printed circuit board according to claim 1, wherein a thickness of the cover lay in a region where the wiring is present is substantially the same as a thickness of the cover lay in a region where the wiring is not present.   The flexible printed circuit board according to claim 1, wherein the base substrate is made of a liquid crystal polymer. On the base substrate on which the wiring is formed, a cover lay film made of a liquid crystal polymer and a secondary material film made of a material having a melting point lower than that of the cover lay film are placed,
A flexible printed circuit board obtained by performing thermocompression bonding while increasing the temperature from the melting point of the auxiliary material film toward the melting point of the coverlay film. Forming a wiring on the base substrate;
On the base substrate on which the wiring is formed, a step of thermocompression bonding a coverlay film made of a liquid crystal polymer and a secondary material film made of a material having a lower melting point than the coverlay film;
And a step of peeling the sub-material film from the coverlay film. A method for producing a flexible printed board, comprising:   6. The method of manufacturing a flexible printed circuit board according to claim 5, wherein in the step of thermocompression bonding, thermocompression bonding is performed while increasing the temperature from the melting point of the auxiliary material film toward the melting point of the coverlay film.

Images