JP4827446B2 - Electronic circuit board and manufacturing method thereof - Google Patents

Description

  The present invention relates to a method for manufacturing an electronic circuit board using a liquid crystal polymer sheet, and an electronic circuit board manufactured by the method.

  In recent years, the amount of information to be processed has greatly increased in the information communication field. Along with this, the frequency of information signals is increasing, and the density of electronic circuit boards is required to transmit and process more information signals and to reduce the size of devices. As a result, there are cases where the conventional electronic circuit board cannot meet the demand.

  For example, as an insulator for a conventional electronic circuit board, a sheet in which a glass cloth is impregnated with an epoxy resin or a polyimide sheet is generally used. However, these resin materials have insufficient dielectric characteristics, and there is a problem that signal loss increases when used for an electronic circuit board that handles high-frequency information signals. Further, in order to form a circuit on a sheet made of an epoxy resin, the resin is cured (cross-linked), and thus a press process for a long time is required, and the productivity is low. Even in the case of an electronic circuit board using a polyimide sheet that does not have thermoplasticity, it is necessary to go through a complicated process of imidization by heat treatment after casting a solution of the precursor polyamic acid on a copper foil. There is a problem that the polyimide sheet and the copper foil must be pasted with an adhesive having poor dielectric properties. There is also a thermoplasticized polyimide, but this thermoplastic polyimide sheet alone cannot provide sufficient dimensional stability, so it must be used as an adhesive between the copper foil and the sheet made of non-thermoplastic polyimide, and the process is also It becomes complicated.

  Furthermore, since epoxy resins and polyimide resins are highly hydrophilic, there is a problem that the characteristic impedance of the circuit changes due to the absorption of moisture and the dielectric constant increases, and the loss of information signals is further increased. Therefore, a high-frequency electronic circuit board often uses a fluororesin-based material having low water absorption and excellent dielectric characteristics. However, fluororesin is difficult to process such as plating and bonding, and it may not be possible with general substrate processing equipment.

  In addition, bismaleimide / triazine resin or polyphenylene ether resin may be used as an insulator material having relatively excellent dielectric characteristics. However, since these resins are inferior in dimensional stability, it is necessary to impregnate glass cloth and the like, and the dielectric properties cannot be effectively used. In addition, even if they can be used for rigid substrates, they are flexible substrates. It cannot be.

  Therefore, in recent years, an electronic circuit board using a liquid crystal polymer having low water absorption and excellent dielectric properties as an insulator material has been studied. Since this liquid crystal polymer can easily thermocompress the metal foil constituting the circuit due to its thermoplasticity, the circuit forming process can be simplified. In addition, in the conventional non-thermoplastic resin, it is necessary to use an adhesive to provide a cover layer for protecting the circuit surface. However, this adhesive is inferior in dimensional stability and dielectric properties and has a large water absorption. was there. On the other hand, when a thermoplastic liquid crystal polymer is used, there is an advantage that the circuit pattern sheet and the cover sheet can be thermocompression bonded without using an adhesive.

  However, there are also problems with electronic circuit boards using liquid crystal polymers. For example, as shown in FIG. 1, after a metal foil is thermocompression bonded to both surfaces of a liquid crystal polymer sheet (core sheet) 1, a signal layer 3 is formed on one side and a ground layer 2 is formed on the opposite side to form the signal layer 3 on the liquid crystal. When covering with the polymer sheet (cover sheet) 4, the signal layer 3 is embedded in the core sheet 1, and the distance between the signal layer 3 and the ground layer 2 is reduced. As a result, the distance between the signal layer and the ground layer in the transmission line greatly affects the characteristic impedance of the circuit, so that the characteristic impedance is different from the design value. In particular, when a signal layer is formed by thermocompression bonding of metal foils on both sides of the sheet as in the example of FIG. 1, moisture derived from the liquid crystal polymer is not diffused to the outside during thermocompression bonding and constitutes a core sheet. Hydrolysis reaction of the liquid crystal polymer is caused, and its molecular weight and melting point are lowered. On the other hand, since such deterioration does not occur in the liquid crystal polymer sheet (cover sheet) for the cover, the signal layer is largely embedded in the core sheet having a lowered melting point, resulting in a large change in characteristic impedance.

  Further, when the circuit is formed at a high density, the distance between the lines of the circuit is shortened, so that the cover sheet 4 cannot be in close contact with the core sheet 1 or the signal layer 3 in the vicinity of the signal layer 3, and is shown in FIG. Thus, the gap 5 may be generated. If moisture enters the gap, migration occurs and the insulation resistance value decreases, so that the reliability of the product decreases. On the other hand, when the pressure and temperature at the time of thermocompression bonding of the cover sheet are increased in order to prevent such a phenomenon, the entire liquid crystal polymer flows, resulting in a positional deviation of the circuit pattern and a defective thickness.

By the way, conventionally, the technique which improves the adhesiveness with copper foil etc. by processing the surface of a liquid crystal polymer molded object is known. For example, the technique of Patent Document 1 activates the surface of a liquid crystal polymer (melted liquid crystalline polyester resin in Patent Document 1) with ultraviolet rays or the like including a wavelength of 254 nm, and the surface and the metal are used as the resin flow start temperature. The heat fusion is performed as described above. Moreover, the technique of patent document 2 irradiates the surface of a liquid crystal polymer (liquid crystal polyester in patent document 2) molded body with ultraviolet rays including a wavelength of 184.9 nm in order to perform coating or the like. In the examples of these patent documents, the adhesion between the copper foil and the molded body and the adhesion between the coating film and the molded body are tested.
JP 2000-233448 A (claims, paragraph [0039], Tables 2 and 3) JP-A-1-216824 (Claims, page 8, lower right column, Appendix 1)

  As described above, in order to improve the adhesion between the liquid crystal polymer and the metal foil or the like, a technique for subjecting the surface of the liquid crystal polymer molded body to ultraviolet irradiation has been known. However, when an electronic circuit board is manufactured, if the core sheet surface made of a liquid crystal polymer is subjected to ultraviolet irradiation treatment with reference to the above-mentioned patent document, the adhesion with the metal foil is improved, but there is a problem as an electronic circuit board for high frequency. Arise. That is, since the surface of the liquid crystal polymer core sheet deteriorates due to ultraviolet irradiation, the conductor layer constituting the circuit is largely embedded in the core sheet when the cover sheet is thermocompression bonded.

  Furthermore, in the technique of Patent Document 1, the liquid crystal polymer and the metal are thermally fused at a temperature higher than the flow start temperature of the resin. This is because the technique aims only at improving the adhesion between the liquid crystal polymer sheet and the metal foil. However, the metal foil is further etched to form a circuit, and when this circuit surface and the cover sheet are thermocompression bonded, applying the technology will cause the resin to flow and the circuit accuracy will decrease, so a particularly high-density circuit In the case of, it becomes a problem.

  Therefore, the problem to be solved by the present invention is an electronic circuit board having a liquid crystal polymer sheet as an insulator, and the generation of voids in the vicinity of the conductor layer and the embedding of the conductor layer in the core sheet is suppressed, An object of the present invention is to provide a method capable of manufacturing a high-quality or high-density one that can sufficiently cope with a high-frequency information signal.

  In order to solve the above-mentioned problems, the present inventor has intensively studied on the manufacturing conditions of the electronic circuit board. As a result, when the liquid crystal polymer sheet is used as an insulator, the present invention has been completed by finding that the above problem can be solved by performing the same treatment on the cover sheet instead of subjecting the core sheet to ultraviolet irradiation treatment as in the prior art.

  That is, the method for manufacturing an electronic circuit board according to the present invention includes a step of forming a circuit on one or both sides of a liquid crystal polymer sheet, a step of irradiating one side of a liquid crystal polymer sheet for covering the circuit surface with short wavelength ultraviolet rays, A step of laminating a liquid crystal polymer sheet on which a circuit is formed and a liquid crystal polymer sheet for covering the circuit surface so that the ultraviolet irradiation treatment surface is in contact with the circuit surface, and a step of thermocompression bonding the obtained laminate. It is characterized by including.

As the integrated light quantity of the short wavelength ultraviolet rays irradiated by the above ultraviolet irradiation treatment, 100 to 10,000 mJ / cm ² is preferable. This is because, if it is less than 100 mJ / cm ² , a sufficient effect may not be obtained, but if it exceeds 10,000 mJ / cm ² , the sheet strength may decrease.

  The thermocompression bonding temperature is preferably not less than the flow start temperature of the liquid crystal polymer sheet on which the circuit is formed and not lower than −50 ° C. This is because pressure bonding may not be sufficient when the flow start temperature is lower than −50 ° C. On the other hand, at a temperature higher than the flow start temperature, the conductor layer constituting the circuit has to be thinned particularly in a high-density circuit pattern, and the conductor layer easily peels off from the core sheet. It is because there is a possibility of doing.

  Further, it is preferable that the circuit surface is subjected to ultraviolet irradiation treatment with short wavelength ultraviolet light after the circuit is formed. The adhesion between the core sheet exposed on the circuit surface and the cover sheet is increased, and the core sheet resin under the circuit is not affected, so there is no problem of embedding the conductor layer. is there. The “circuit surface” in the present invention is a concept including the conductor layer itself constituting the circuit and the exposed portion of the core sheet surface on which the circuit is not formed.

  As the method of the present invention, it is preferable to produce a single-sided electronic circuit board in which a circuit surface of a liquid crystal polymer sheet having a circuit formed on one side is covered with a liquid crystal polymer sheet. This single-sided electronic circuit board is particularly suitable as a so-called flexible board for small equipment that handles a large amount of information.

  A liquid crystal polymer film is preferably used as the liquid crystal polymer sheet. In particular, a single-sided plate or a double-sided plate using a liquid crystal polymer film as an insulator has flexibility, so that damage during insertion into a relatively small device is reduced and convenience is high.

  The electronic circuit board manufactured by the above method is characterized by excellent dielectric characteristics.

  In the electronic circuit board manufactured by the method of the present invention, the problem that the characteristic impedance of the circuit is greatly different from the design value is suppressed, and the circuit pattern sheet and the cover sheet Because of its good adhesion, migration hardly occurs. Therefore, the present invention is extremely useful industrially as an electronic circuit board that can deal with a large amount of information and can be used for transmission and processing of high-frequency information signals.

A method for manufacturing a circuit board according to the present invention includes:
A step of forming a circuit on one or both sides of the liquid crystal polymer sheet (hereinafter referred to as “circuit forming step”),
A step of irradiating one side of the liquid crystal polymer sheet for covering the circuit surface with short wavelength ultraviolet rays (hereinafter referred to as “ultraviolet irradiation treatment step”),
A step of laminating a liquid crystal polymer sheet on which a circuit is formed and a liquid crystal polymer sheet for covering the circuit surface (hereinafter referred to as a “sheet laminating step”) so that the ultraviolet irradiated surface is in contact with the circuit surface; A step of thermocompression bonding the obtained laminate (hereinafter referred to as “thermocompression step”). Hereinafter, each process will be described.

Circuit formation process Electronic circuit boards are mainly classified into single-sided boards, double-sided boards, and multilayer boards. In a single-sided plate or a double-sided plate, a circuit is formed on one or both sides of a core sheet, and a cover sheet for protecting the circuit is provided on the circuit surface. In the case of a multilayer board, a plurality of core sheets are laminated, and a circuit having three or more layers is formed between the core sheets. Therefore, in the case of a multilayer board, since the surface opposite to the circuit surface of the core sheet on which a circuit is to be formed is in contact with the circuit surface of another core sheet, the core sheet can simultaneously serve as a cover sheet. In the case of a multilayer board, a cover sheet may be provided on the outermost circuit surface.

  In the present invention, the core sheet is composed of a liquid crystal polymer sheet. This is because a high-quality and high-density electronic circuit board that can sufficiently cope with high-frequency information signals can be obtained by using a liquid crystal polymer having excellent dielectric properties as an insulator material. This liquid crystal polymer is a heat-resistant thermoplastic resin, and examples thereof include a thermotropic liquid crystal polymer that exhibits liquid crystallinity in a molten state. In the present invention, a thermotropic liquid crystal polymer is preferable, and more specifically, a thermotropic liquid crystal polyester or a thermotropic liquid crystal polyester amide is preferable.

  Thermotropic liquid crystal polyester (hereinafter simply referred to as “liquid crystal polyester”) is, for example, an aromatic polyester synthesized mainly from aromatic dicarboxylic acid and monomers such as aromatic diol and aromatic hydroxycarboxylic acid. Sometimes it exhibits liquid crystallinity. Typical examples thereof include type I [Formula (1)] synthesized from parahydroxybenzoic acid (PHB), terephthalic acid, and 4,4′-biphenol, PHB and 2,6-hydroxynaphthoic acid. Type II [Formula (2)] synthesized from the above, Type III [Formula (3)] synthesized from PHB, terephthalic acid, and ethylene glycol.

  Examples of the liquid crystal polymer according to the present invention include units represented by the above formulas (1) to (3), as long as they exhibit liquid crystallinity (particularly thermotropic liquid crystallinity) and can achieve the object of the present invention. It may be a copolymer type polymer (for example, 50 mol% or more in all constituent units of the liquid crystal polymer) and also having other units. Examples of the other unit include a unit having an ether bond, a unit having an imide bond, and a unit having an amide bond.

  In obtaining the liquid crystal polymer sheet, various known methods may be employed depending on the resin constituting the liquid crystal polymer sheet. In addition, the sheet using the above-exemplified liquid crystal polyester particularly suitable in the method of the present invention is, for example, a film-like sheet, but a commercially available product such as “BIAC (registered trademark)” manufactured by Japan Gore-Tex Corporation should be used. Can do.

  Moreover, as liquid crystal polyester amide, the said liquid crystal polyester which has an amide bond as another unit corresponds, for example, what has a structure of the following Formula (4) is mentioned. For example, in the formula (4), the molar ratio of the unit of s, the unit of t, and the unit of u is 70/15/15.

  The liquid crystal polymer sheet of the present invention may contain a polymer other than the liquid crystal polymer as long as the object of the present invention can be achieved, such as not giving up excessive dielectric properties. The polymer may be simply mixed with a liquid crystal polymer or may be chemically bonded. Such an alloy polymer has a melting point of 220 ° C. or higher, preferably 280 to 360 ° C., such as polyether ether ketone, polyether sulfone, polyimide, polyether imide, polyamide, polyamide imide, polyarylate, etc. However, it is not necessarily limited to these. The mixing ratio of the liquid crystal polymer and the alloy polymer is not particularly limited. For example, the mass ratio is preferably 50:50 to 90:10, and more preferably 70:30 to 90:10. A polymer alloy containing a liquid crystal polymer can also have excellent properties due to the liquid crystal polymer.

  In the liquid crystal polymer sheet, the linear expansion coefficient in the direction parallel to the sheet plane is preferably adjusted to 25 ppm / ° C. or less. More preferably, it is 21 ppm / ° C. or less. The lower limit of the linear expansion coefficient of the liquid crystal polymer sheet is desirably 8 ppm / ° C. The linear expansion coefficient of the liquid crystal polymer sheet was determined by instrumental analysis (TMA method, Thermal Mechanical Analysis), with a test piece width of 4.5 mm, a distance between chucks: 15 mm, and a load of 1 g. (Temperature rate: 5 ° C./min), temperature decrease rate: a value obtained from dimensional change of the test piece measured between 160 ° C. and 25 ° C. when cooling at 5 ° C./min, for example, MD direction of the sheet Any of the linear expansion coefficients in the (traveling direction during sheet manufacturing) and the TD direction (direction orthogonal to the MD direction) only needs to satisfy the above range.

  As the core sheet of the present invention, a liquid crystal polymer film is suitable. In particular, in the case of a single-sided board or a double-sided board, a flexible electronic circuit board suitable for a small device can be obtained. The thickness of the liquid crystal polymer film is not particularly limited, but is preferably 10 μm to 1000 μm. If the thickness is less than 10 μm, the strength may be insufficient, and film formation exceeding 1000 μm may be difficult.

  In the circuit forming step, a circuit is formed on one side or both sides of a liquid crystal polymer sheet (core sheet). Examples of the conductor for forming the circuit pattern include copper, aluminum, gold, silver, and alloys based on these metals. For the circuit pattern, a conventional method such as etching after providing a thin film made of these metals on a circuit pattern sheet can be used. As a method of forming a metal thin film, in addition to a method of bonding an insulator sheet and a metal plate (including metal foil, metal film, etc.), a vacuum deposition method, a sputtering method, an ion plating method, plating on the surface of the insulator sheet A method of forming by a CVD method or a CVD method can also be employed.

  The thickness of the metal plate is not particularly limited, but is preferably about 1 to 200 μm. If it is too thin, there is a possibility that a conduction failure may occur due to the circuit being cut, and if it is too thick, a gap is easily formed in the vicinity of the metal plate when the cover sheet is thermocompression bonded.

  As a method of bonding the metal plates, a heat fusion method is preferable. As the heat fusion method, the surface of the thermoplastic resin is softened by heating and a metal plate is laminated thereon and then cooled, or the core sheet and the metal plate are overlapped, and this is heated between a pair of heated rolls. A method of fusing and then cooling can be employed.

  Moreover, if the thing which roughened the surface of the side which contact | connects at least a core sheet of metal plates, such as metal foil, the adhesiveness of a core sheet and a metal plate can be improved further.

  In the method of the present invention, after a metal layer is provided on one or both surfaces of the core sheet, a desired circuit pattern is formed by etching. The metal layer forming the circuit pattern may be a single layer or a laminate of two or more metal layers.

Ultraviolet irradiation treatment step In the method of the present invention, short-wave ultraviolet rays are irradiated on one side of a liquid crystal polymer sheet for covering the circuit surface separately from the circuit forming step.

  As the liquid crystal polymer sheet (hereinafter referred to as “cover sheet”) for covering the circuit surface used in the step, the same core sheet used in the circuit forming step can be used. However, although not limited to this, a thickness of 5 μm to 500 μm is preferable. If the thickness is less than 5 μm, the strength may be insufficient, and the protective effect on the circuit surface may not be sufficiently exhibited. If the thickness exceeds 500 μm, the gap in the vicinity of the conductor layer may not be sufficiently filled.

  In this step, one side of the cover sheet is subjected to ultraviolet irradiation treatment. In addition, in a multilayer board, the surface opposite to the surface on which the circuit of the core sheet is formed may be disposed so as to be in contact with the circuit surface of another core sheet. In this case, since the core sheet also serves as a cover sheet, the surface opposite to the surface on which the circuit of the core sheet is formed, that is, the surface in contact with the circuit surface of another core sheet is irradiated with ultraviolet rays. To process.

  Ultraviolet rays are mainly classified into long wavelength ultraviolet rays of 321 to 400 nm, medium wavelength ultraviolet rays of 291 to 320 nm, and short wavelength ultraviolet rays of 290 nm or less. In the present invention, at least one surface of the cover sheet is irradiated with at least short wavelength ultraviolet rays. This is because sufficient effects cannot be obtained with only long / medium wavelength ultraviolet rays. However, as long as the ultraviolet rays to be irradiated have a short main wavelength, those containing medium wavelength ultraviolet rays and long wavelength ultraviolet rays can also be used. Moreover, you may use what contains other light rays other than an ultraviolet-ray.

The ultraviolet irradiation apparatus to be used is not particularly limited as long as it can irradiate short wavelength ultraviolet rays. For example, a low pressure mercury lamp having main wavelengths of 254 nm and 175 nm, a KrCl excimer lamp having main wavelengths of 222 nm, and a main wavelength of 172 nm. A Xe ₂ excimer lamp or the like can be used. A Kr ₂ excimer lamp having a dominant wavelength of 146 nm, an Ar ₂ excimer lamp of 126 nm, or the like may be used. However, since ultraviolet light having a wavelength of 170 nm or less is easily absorbed by oxygen, irradiation in the air is inefficient. Is preferably irradiated in a nitrogen environment or a vacuum environment.

As an integrated light quantity of the short wavelength ultraviolet-ray irradiated at the said process, 100-10,000mJ / cm < ² > is suitable. This is because, if it is less than 100 mJ / cm ² , sufficient effects may not be obtained, but if it exceeds 10,000 mJ / cm ² , the sheet may be deformed or the strength may be reduced. Since this integrated light quantity is the product of the ultraviolet intensity (mW / cm ² ) and the irradiation time (seconds), the integrated light quantity can be adjusted by the intensity of the ultraviolet light used and the irradiation time.

  In addition, when using the ultraviolet irradiation device which generate | occur | produces heat, such as a low pressure mercury lamp, it is preferable that the distance with a cover sheet shall be 10-200 mm. This is because if the distance is too close, the cover sheet may be deformed due to heat generation, and if it is too far, the effect of irradiation may not be sufficient.

Sheet Laminating Step The circuit pattern sheet obtained in the circuit forming step and the cover sheet obtained in the ultraviolet irradiation treatment step are laminated so that the circuit surface of the circuit pattern sheet and the ultraviolet irradiation treatment surface of the cover sheet are in contact with each other. .

  Before the lamination, it is preferable to irradiate the circuit surface of the circuit pattern sheet with short wavelength ultraviolet rays. This is because the adhesion between the circuit pattern sheet and the cover sheet is increased in the next thermocompression bonding step. In the portion of the circuit surface where the core sheet is exposed, the adhesion to the cover sheet is enhanced by the ultraviolet treatment, but the resin immediately below the metal layer constituting the circuit is not affected by the ultraviolet rays. Therefore, even if this ultraviolet treatment is performed, embedding of the metal layer into the core sheet during thermocompression bonding is suppressed.

The short wavelength ultraviolet irradiation device used for the ultraviolet irradiation treatment of the circuit pattern sheet may be the same as described above. However, since the said ultraviolet irradiation process aims at the improvement of the adhesiveness of liquid crystal polymer sheets, an integrated light quantity may be comparatively small. For example, it can be set to about 100 to 5,000 mJ / cm ² .

Thermocompression bonding process Next, the laminate obtained in the sheet lamination process is thermocompression bonded by a thermocompression bonding apparatus. The conditions at the time of thermocompression bonding may be in accordance with ordinary methods, but particularly in the case of a high-density electronic circuit board, if the heating temperature or pressure is too high, the circuit pattern may be disturbed. Therefore, for example, the pressure is 0.5 to 10 MPa, and the time is about 1 to 30 minutes. The thermocompression bonding temperature is preferably a temperature at which the core sheet and the cover sheet can be sufficiently crimped. May be reduced. From such a viewpoint, it is preferable that the elastic modulus of the core sheet resin measured in the tensile mode of the DMA method (Dynamic Mechanical Analysis) is in the range of 1/10 to 1/1000 of the room temperature range. Although specific temperature changes with kinds of liquid crystal polymer to be used, for example, the flow start temperature of the core sheet resin is preferably −50 ° C. or higher and lower than the flow start temperature, and the flow start temperature −30 ° C. or higher and the flow start temperature −5 ° C. The following is more preferable, and a flow start temperature of −25 ° C. or higher and a flow start temperature of −10 ° C. or lower are more preferable. Note that the “flow start temperature” here is different from the melting point of the resin and refers to the temperature at which the resin starts to flow when the temperature is raised under a predetermined pressure. For example, when extruding at a pressure of 100 kgf / cm ² (about 9.8 MPa) while heating the resin at a heating rate of 4 ° C./min, the temperature is set to a temperature at which the melt viscosity exhibits 48000 poise.

  The type of the thermocompression bonding apparatus is not particularly limited. For example, a flat plate press, a continuous belt press, a roll laminator, or the like can be used. In these, since a water | moisture content can be removed efficiently, a vacuum type flat plate press can be used suitably.

  When the liquid crystal polymer sheets are subjected to thermocompression bonding, a release material having high heat resistance is required in order to prevent fusion between the liquid crystal polymer that is a thermoplastic resin and the thermocompression bonding apparatus. As such a release material, a fluorine-based porous film is suitable. Since the fluorine-based porous film contains almost no water because of its production conditions and high hydrophobicity, it can release water derived from the liquid crystal polymer to the outside, so that it is possible to suppress hydrolysis reaction during thermocompression bonding. Moreover, since it has high cushioning properties, it can exhibit an action as a buffer material as well as an action as a mold release material.

  Examples of the resin constituting the fluorine-based porous film include polytetrafluoroethylene (PTFE), PTFE-perfluoroalkyl vinyl ether copolymer, PTFE-hexafluoropropylene copolymer, PTFE-ethylene copolymer, and the like. be able to. Among these, PTFE is preferable, and stretched porous PTFE is particularly preferably used. Conventional methods can be used as a film forming method and a porous method for these resins.

  In the electronic circuit board obtained by the above method, the problem that the characteristic impedance of the circuit is greatly different from the design value is suppressed, and even if the circuit is designed at a high density, the circuit pattern sheet and the cover sheet Due to the good adhesion, migration hardly occurs. Therefore, the electronic circuit board according to the present invention is extremely suitable for transmission and processing of high-frequency information signals that can handle a large amount of information.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. It is also possible to implement, and they are all included in the technical scope of the present invention.

Production Example 1 Production of Electronic Circuit Board by Method of the Present Invention Copper foil of liquid crystal polymer film single-sided copper-clad plate (Japan Gore-Tex, BIAC BC050-S12-B6, substrate thickness: 50 μm, copper foil thickness: 12 μm) Was etched to form a comb circuit pattern with a line / space of 50/50 μm. Separately, on one side of a liquid crystal polymer film (Japan Gore-Tex, BIAC BC050, thickness: 50 μm) using a low-pressure mercury lamp (Nihon Battery Co., Ltd., main wavelengths: 175 nm and 254 nm), 2,000 mJ / cm ² or Ultraviolet treatment was performed with an integrated light amount of 10,000 mJ / cm ² , and this was used as a cover sheet. In addition, about the liquid crystal polymer resin used as the core sheet, when the flow start temperature was separately measured using a Koka type flow tester (manufactured by Shimadzu Corporation, CFT-500 type), it was 292 ° C. Specifically, when a resin heated at a heating rate of 4 ° C./min is extruded from a nozzle having an inner diameter of 1 mm and a length of 10 mm with a load of 100 kgf / cm ² (about 9.8 MPa), the melt viscosity is 48,000 poise. Was measured, and this was taken as the flow start temperature. Next, the circuit pattern sheet and the cover sheet are laminated so that the ultraviolet irradiation treatment surface is in contact with the circuit surface, and a stretched porous PTFE film (manufactured by Japan Gore-Tex, HRCF-090) is disposed on both sides as a release material. Using a thermocompression bonding apparatus (manufactured by Kitagawa Seiki Co., Ltd., vacuum hot / cold press VH3-1377), thermocompression bonding was performed at a temperature of 275 ° C. and a pressure of 3 MPa for 5 minutes.

Comparative production example 1
In the production example 1, a metal halide lamp (manufactured by Nippon UV Co., main wavelength: 340 to 460 nm) is used instead of the low-pressure mercury lamp (manufactured by Nippon Battery Co., Ltd., main wavelengths: 175 nm and 254 nm), and 1,300 mJ / cm ² to An electronic circuit board was produced in the same manner except that the ultraviolet treatment was performed with an integrated light amount of 13,000 mJ / cm ² . Also, an electronic circuit board was prepared in the same manner except that no ultraviolet irradiation was performed.

Production Example 2
An electronic circuit board was produced in the same manner as in Production Example 1 except that the thermocompression bonding temperature was 295 ° C., which is higher than the flow start temperature of the liquid crystal polymer constituting the core sheet.

Test example 1
The electronic circuit boards obtained in Production Example 1 and Comparative Production Example 1 were cut along the plane including the circuit surface, and the cross-section was polished with a rotary polishing apparatus (Stroers, Rotopol-11), and then stereo microscope (Nikon Corporation) Manufactured by SMZ1500), and measured the thickness of the cover sheet in the portion where the circuit exists and the core sheet thickness of the circuit pattern sheet for each electronic circuit board, (cover sheet thickness) / (core sheet thickness) Was calculated and the average was obtained. The results of Production Example 1 are shown in FIG. 3, and the results of Comparative Production Example 1 are shown in FIG.

  As shown in FIG. 4, when the cover sheet is treated with ultraviolet light having a dominant wavelength of 340 to 460 nm, the embedding of the conductor layer in the core sheet is not improved even if the integrated light quantity is increased. On the other hand, as shown in FIG. 3, when the cover sheet is processed with ultraviolet rays having dominant wavelengths of 175 nm and 254 nm, the conductor layer is embedded on the cover sheet side as the integrated light quantity increases, and the core sheet side is embedded. Is suppressed. Therefore, according to the present invention, it was demonstrated that the change in characteristic impedance of the electronic circuit board can be reduced.

Test Example 2 HAST (Highly Accelerated Temperature & Humidity Stress Test) Test Regarding the electronic circuit board of Production Example 1 and Comparative Production Example 1 and the electronic circuit board that was not subjected to the ultraviolet irradiation treatment in Production Example 1, HAST tester Using an Espec Corp. HAST chamber EHS-210), an AC voltage of 30 V was applied under conditions of a temperature of 130 ° C. and a relative humidity of 85%, and the resistance value was measured every hour. As a result, as shown in FIG. 5, the resistance value decreases with time under severe conditions, and it is considered that the insulation is deteriorated due to migration. However, as shown in FIG. 6, when the resistance after 10 hours of each electronic circuit board was measured in the result, the resistance value was increased as the integrated light quantity of short wavelength ultraviolet rays irradiated to the substrate which was not irradiated with ultraviolet rays increased. You can see that it is getting higher. This is because the adhesion of the cover sheet to the core sheet is increased by the ultraviolet irradiation treatment, and the gap in the vicinity of the conductor layer constituting the circuit is narrowed, which makes it difficult for the insulation to deteriorate due to migration due to water absorption even under high humidity. It is considered that

  As described above, according to the method of the present invention, it has been demonstrated that a highly reliable electronic circuit board can be manufactured because the gap between conductor layers constituting the circuit is reduced.

It is a figure which shows the one aspect | mode of the electronic circuit board manufactured by the conventional method. The signal layer is buried on the core sheet side, and the distance between the signal layer and the ground layer is shortened. It is a figure which shows the one aspect | mode of the electronic circuit board manufactured by the conventional method. Between the circuit surfaces, the core sheet and the cover sheet of the circuit pattern sheet cannot be adhered to each other, and a gap is generated in the vicinity of the circuit. It is a figure which shows the ratio of the core sheet thickness and cover sheet thickness in the position where a circuit exists in the electronic circuit board manufactured by this invention method. It can be seen that the greater the integrated amount of ultraviolet light applied to the cover sheet, the lower the embedding of the circuit on the core sheet side. It is a figure which shows the ratio of the core sheet thickness and cover sheet thickness in the position where the circuit of the electronic circuit board produced using the ultraviolet rays outside the regulation range of this invention exists. It can be seen that the ratio hardly changes even if the integrated light quantity is increased. It is a figure which shows the time-dependent change of the resistance value in a HAST test. It can be seen that the resistance value decreases with time. It is a figure which shows the HAST test result of the electronic circuit board manufactured by the method of this invention. It can be seen that the resistance value increases as the cumulative amount of UV irradiation increases.

Explanation of symbols

  1: Core sheet, 2: Ground layer, 3: Signal layer, 4: Cover sheet, 5: Air gap generated in the vicinity of signal layer

Claims (7)

An electronic circuit board manufacturing method comprising:
Forming a circuit on one or both sides of a thermotropic liquid crystal polymer sheet;
Irradiating one side of the thermotropic liquid crystal polymer sheet to cover the circuit surface with short wavelength ultraviolet rays,
The step of laminating the thermotropic liquid crystal polymer sheet on which the circuit is formed and the thermotropic liquid crystal polymer sheet for covering the circuit surface so that the ultraviolet irradiated surface is in contact with the circuit surface, and the obtained laminate is heated. Crimping process,
The manufacturing method of the electronic circuit board characterized by including. The manufacturing method of the electronic circuit board of Claim 1 which makes the integrated light quantity of the short wavelength ultraviolet rays to irradiate 100-10,000mJ / cm < ² >. The manufacturing method of the electronic circuit board of Claim 1 or 2 thermocompression-bonded at the flow start temperature of -50 degreeC or more and less than the flow start temperature of the thermotropic liquid crystal polymer sheet in which the circuit was formed.   The method for manufacturing an electronic circuit board according to claim 1, further comprising a step of irradiating the circuit surface with short-wavelength ultraviolet light after forming the circuit. The manufacture of an electronic circuit board according to any one of claims 1 to 4, wherein the circuit board of a thermotropic liquid crystal polymer sheet having a circuit formed on one side is covered with a thermotropic liquid crystal polymer sheet. Method. The thickness of the thermotropic liquid crystal polymer sheet forming the circuit is 10 μm to 1000 μm, and the thickness of the thermotropic liquid crystal polymer sheet for covering the circuit surface is 5 μm to 500 μm. A method of manufacturing a circuit board.   An electronic circuit board manufactured by the method according to claim 1 and having excellent dielectric characteristics.

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