JP5613918B2 - Manufacturing method of flexible printed circuit board - Google Patents

Description

  The present invention relates to a flexible printed circuit board in which a circuit is formed on a flexible insulating film and a method for manufacturing the same, and more particularly to a flexible print that improves the reliability by preventing peeling of a coverlay covering the circuit. The present invention relates to a substrate and a manufacturing method thereof.

  Conventionally, a coverlay film (see, for example, Patent Document 1 (page 2-3, FIG. 1)) has been known as a technique for improving the reliability of a flexible printed circuit (FPC). This coverlay film is composed of an electrically insulating film layer, an adhesive layer and a release material layer. The release material forming the release material layer is obtained by coating the base paper with a resin with a predetermined thickness.

  For this reason, when drilling or the like, the release material residue does not adhere to the inside of the hole or the cover lay film and the release material are not fused, and this is the case of punching with a mold. However, it is said that there is no generation of burr or deformation.

  Further, as a method for detecting the protective film left in the substrate opening as such a burr, an insulating substrate inspection method and inspection apparatus (for example, Patent Document 2 (page 4-6, FIGS. 1-4)). See). In this inspection method, light is irradiated to the inspection region in which the opening is formed, and it is detected whether the protective film is left in the opening based on the light transmitted through the insulating substrate.

  And in these, it is comprised so that a cut surface may become perpendicular | vertical to a board surface at the time of the external shape process of a coverlay film, a protective film, and an insulated substrate.

JP 2002-252450 A Japanese Patent No. 3705129

  However, in the above-described conventional coverlay film disclosed in Patent Document 1 and the inspection method disclosed in Patent Document 2, the cut surface (processed surface) is formed perpendicular to the plate surface. The area where the adhesive touches the outside air at the exposed portion of the end of the adhesive layer of the film cannot be reduced. For this reason, the coverlay film may be peeled off due to the deterioration of the adhesive, and in this case, a problem may arise in the long-term reliability of the flexible printed circuit board.

  In recent years, in consideration of the environment, non-halogenation of the adhesive of the cover lay film has progressed, and with this, the blending ratio of the flame retardant to the adhesive has increased. For this reason, there is a current situation that the coverlay film is more easily peeled off.

  The present invention provides a flexible printed circuit board and a method for manufacturing the same that can improve the reliability by preventing peeling of a coverlay covering a circuit in order to solve the above-described problems caused by the prior art. Objective.

  In order to solve the above-described problems and achieve the object, a flexible printed circuit board according to the present invention includes an insulating base film, a circuit formed on the base film and made of a conductor pattern, and a cover covering the circuit. And the cover lay is configured to cover the circuit through an adhesive layer, and the thickness of the adhesive layer at the end of the base film excludes the circuit It is characterized by being formed thinner than the thickness of the adhesive layer in other parts.

  On the surface of the adhesive layer on the cover lay side, for example, an inclined portion is formed that is inclined so that the distance from the base film becomes shorter toward the end portion. The inclined portion is formed by, for example, bending or bending a cover lay, and the inclined surface may be curved or flat.

  The adhesive which comprises the said adhesive bond layer does not contain a halogenated flame retardant, for example.

  The coverlay is configured to include a film layer on which the adhesive layer is formed, for example, and the film layer is made of any one of polyethylene terephthalate, polyethylene naphthalate, polyimide, and polyamide, for example.

  The flexible printed board may be mounted with an electronic device including an active element connected to the circuit, for example.

  The electronic device is heated and mounted in a reflow furnace through, for example, a solder paste mounted on a substrate.

  The solder paste does not contain lead, for example.

  Moreover, the manufacturing method of the flexible printed circuit board concerning this invention comprises the process of forming the said edge part by cutting | disconnection, after forming the said circuit and the said coverlay on the said base film in the said invention, and forming the said edge part The inclined portion is formed by a pressure applied during the process.

  Further, after forming the circuit and the cover lay on the base film, the end portion is formed by forming the inclined portion by applying pressure from the surface side of the cover lay, and then cutting the inclined portion. It is characterized by forming.

  ADVANTAGE OF THE INVENTION According to this invention, the flexible printed circuit board which can prevent peeling of the coverlay which coat | covers on a circuit, and can aim at reliability can be provided, and its manufacturing method.

It is explanatory drawing for demonstrating the flexible printed circuit board concerning one Embodiment of this invention. It is explanatory drawing for demonstrating the example of the manufacturing process by the manufacturing method of the flexible printed circuit board. It is explanatory drawing for demonstrating the other example of the manufacturing process by the manufacturing method of the flexible printed circuit board.

  Preferred embodiments of a flexible printed circuit board and a manufacturing method thereof according to the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is an explanatory diagram for explaining a flexible printed circuit board according to an embodiment of the present invention. As shown in FIG. 1, the flexible printed board 10 includes, for example, a copper clad laminate 11 and a coverlay 15 disposed on one side of the copper clad laminate 11.

  The copper-clad laminate 11 has a heat resistance on one surface of a base film 12 having an insulating property made of a resin such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), and polyamide (PA). And a circuit 13 in which a Cu metal conductor is patterned through an adhesive 14 made of a thermoplastic polyimide resin or the like.

  The coverlay 15 includes a film material 16 made of an insulating resin such as polyimide, and an adhesive layer 17 such as the above-described heat-resistant thermoplastic polyimide resin, and the copper-clad via the adhesive layer 17. The laminated plate 11 is bonded so as to cover the circuit 13.

  The copper-clad laminate 11 may have a structure having circuits 13 provided on both surfaces of the base film 12 via an adhesive 14. In this case, the cover lay 15 covers the circuits 13 on both sides. It is good to provide so that it may coat | cover. The copper-clad laminate 11 having the circuits 13 on one side or both sides may have a multilayer structure in which a plurality of layers are laminated. In this case, the coverlay 15 covers at least the outermost circuit 13 in the lamination direction. It is good to be provided.

  In the flexible printed circuit board 10 configured as described above, the layer thickness C of the adhesive layer 17 of the cover lay 15 at the end 19 of the base film 12, for example, is the circuit 13 except for the end 19. By being formed so as to be thinner than the layer thickness B of the adhesive layer 17 in a portion other than the above (other portions), for example, the distance between the coverlay 15 and the base film 12 is shortened toward the end portion 19. An inclined portion 19a is formed so as to be inclined. That is, if the layer thickness of the adhesive layer 17 on the circuit 13 is A, the layer thickness C> the layer thickness A may be satisfied, but the layer thickness C <the layer thickness B is always formed. Has been.

  Accordingly, the exposed portion of the adhesive layer 17 at the end portion 19 is formed narrower, and the area where the adhesive touches the outside air (exposed area) at the end portion 19 of the adhesive layer 17 of the cover lay 15 than the conventional one. ) Can be reduced. For this reason, according to the flexible printed circuit board 10 concerning this embodiment, it becomes possible to aim at the improvement of reliability by preventing the peeling by the deterioration of the adhesive agent of the coverlay 15 which covers the circuit 13 top.

  In addition, since the adhesive which comprises the adhesive bond layer 17 in the coverlay 15 of the flexible printed circuit board 10 mentioned above is mix | blended so as not to contain what is called a halogenated flame retardant, it has a structure which is hard to deteriorate. Moreover, when the coverlay 15 is arrange | positioned at the both surfaces side of the copper clad laminated board 11, the said curved part 19a should just be formed about each coverlay 15, respectively. And although illustration is abbreviate | omitted, this flexible printed circuit board 10 may be mounted with an electronic device including an active element connected to the circuit 13 of the flexible printed circuit board 10.

  In this case, when the electronic device is mounted by heating in a reflow furnace so as to be connected to the circuit 13 via a solder paste (not shown) that does not contain lead mounted (printed) on the flexible printed circuit board 10. Good. When mounting by heating in a reflow furnace, the deterioration of the adhesive layer 17 is usually likely to proceed due to the thermal history during manufacture. Therefore, if the exposed portion of the adhesive layer 17 is narrowly formed at the end 19, the deterioration is effective. Can be prevented. In addition, if a solder paste not containing lead is used, the heating temperature in the reflow furnace becomes high, so that the effect can be made more remarkable.

  Drawing 2 is an explanatory view for explaining an example of a manufacturing process by a manufacturing method of a flexible printed circuit board concerning one embodiment of the present invention. As shown in FIG. 2, the flexible printed circuit board 10 in which the coverlay 15 is attached to one side of the copper clad laminate 11 is set between an upper mold 51 and a lower mold 52 which are outer shape processing molds. In FIG. 2, the flexible printed circuit board 10 shown in FIG. 1 is set upside down.

  Then, the upper mold 51 is moved in the direction of the lower mold 52, for example, as indicated by the white arrow in the figure, and the flexible printed circuit board 10 is cut so as to be divided into the product part P and the cutting part D. At this time, the film material 16 of the cover lay 15 in the product portion P is cut while being deformed in the direction of the copper-clad laminate 11 under the pressure from the edge portion of the lower mold 52 on the cut surface ct.

  As a result, it is possible to manufacture the flexible printed board 10 in which the inclined portion 19a is formed in the cover lay 15 at the end portion 19 described above, and the exposed portion of the adhesive layer 17 is narrowly formed. Further, as shown in FIG. 3, prior to performing the outer shape processing of the flexible printed board 10, for example, when the cover lay 15 is bonded to the copper clad laminate 11, the following may be performed.

  That is, when the cover lay 15 is bonded to the copper clad laminate 11 by heating and pressing, the pressure in the vicinity of the cut surface ct, which is the end 19, is increased, and the adhesive of the cover lay 15 in this portion The coverlay 15 is bonded to the copper-clad laminate 11 so that the layer thickness of the layer 17 is previously made thinner than the layer thickness of the adhesive layer 17 other than the end portion 19 except on the circuit 13. Thereby, the inclined portion 19a is formed in advance.

  Then, the upper mold 51 is moved in the direction of the lower mold 52 indicated by the white arrow in the figure, and the flexible printed circuit board 10 is cut so as to be divided into the product part P and the cutting part D. Even in this case, it is possible to manufacture the flexible printed circuit board 10 provided with the inclined portion 19a and in which the exposed portion of the adhesive layer 17 at the end portion 19 is narrowly formed, and the above-described functions and effects can be obtained. . Although illustration is omitted, the lower mold 52 may be moved in the direction of the upper mold 51 and cut.

  Here, in order to verify the effect of the flexible printed circuit board 10 according to the present invention, a plurality of samples having different layer thicknesses C of the adhesive layer 17 implemented by the present applicant are stored in a high-temperature and high-humidity atmosphere. The measurement test (peel test) of the peel strength (peeling strength) after having been performed will be described. In this test, the thickness of the base film 12 of the copper-clad laminate 11 of the flexible printed board 10 was 25 μm, the thickness of the adhesive 14 was 10 μm, and the thickness of the circuit 13 was 35 μm.

  Further, seven types of samples of the flexible printed circuit board 10 were manufactured by setting the thickness of the film material 16 of the cover lay 15 of the flexible printed circuit board 10 to 25 μm and the thickness of the adhesive layer 17 to 35 μm. These seven types of samples are formed such that the layer thickness B is constant at 35 μm, but the layer thickness C is different.

  Then, the peel strength of the coverlay 15 of each sample was measured in a state after cutting out these seven types of samples and in a state after being stored for 1000 hours in an atmosphere at a temperature of 85 ° C. and a humidity of 85%. . In addition, the measuring method of peel strength was implemented in accordance with the following. First, after measuring the width of the sample in a predetermined direction, a predetermined reinforcing plate is bonded to the sample cover lay 15 using a double-sided adhesive tape.

  Next, one end of the circuit 13 of the sample copper-clad laminate 11 is peeled off to an appropriate length and bent by 180 °, and then attached to the support bracket, and the remaining tip of the copper-clad laminate 11 is grasped by a known tensile tester. Grab with tools. And it pulls so that the pulling direction of the flexible printed circuit board 10 may become parallel to the plate | board surface of the copper clad laminated board 11, and it peels 50 mm or more continuously, The peeling strength (peel strength) in the meantime is the following formula ( It calculated for every sample using 1).

  At this time, the sample width is 5 mm as a reference, but when it cannot be peeled off, peeling is performed at 3 mm or 1 mm. In addition, the calculation method of the average peeling load in each sample shall be performed by the method as described in JIS C 5016 8.1.6. That is, the peel strength was calculated for each sample from the average peel load according to the above equation (1), and the average value of the 5 sheets was taken as the peel strength.

  Each sample was cut out with a width of 5 mm from the inside of the end portion 19 as shown in FIG. 1 according to the method described above, and a portion where the circuit 13 was not formed was used. For each sample, (A) the sample after cutting, (B) the peel strength of each sample after storing in the above atmosphere is measured, and the peel strength of (B)-(A) is measured. did. The measurement results are shown in Table 1.

  Sample No. No. 1 is a comparative example, and the layer thicknesses B and C are both 35 μm as described above. Sample No. The layers 2 to 7 have all the layer thickness B of 35 μm, but the layer thickness C is 30 μm, 25 μm, 20 μm, 15 μm, 10 μm, and 0 μm, respectively. According to this test, when the peel strength ratio is 1.0, sample No. 1 shows that the peel strength is reduced by about 20%.

  However, sample no. 2, when the layer thickness C is 5 μm thinner than the comparative example, the decrease in peel strength is suppressed to about 10%. As shown in FIG. 3, it was found that when the layer thickness C was 10 μm thinner than that of the comparative example, the peel strength was hardly reduced.

  Thus, according to the present invention, the exposed portion is narrowed by forming the inclined portion 19a and making the layer thickness C of the adhesive layer 17 of the cover lay 15 at the end portion 19 smaller than the layer thickness B. Thus, deterioration of the adhesive layer 17 can be suppressed, and peeling of the cover lay 15 that covers the circuit 13 of the flexible printed circuit board 10 can be effectively prevented. Thereby, the reliability of the flexible printed circuit board 10 can be improved.

DESCRIPTION OF SYMBOLS 10 Flexible printed circuit board 11 Copper clad laminated board 12 Base film 13 Circuit 14 Adhesive 15 Coverlay 16 Film material 17 Adhesive layer 19 End 19a Inclined part 51 Upper mold | type 52 Lower mold | type

Claims (5)

An insulating base film, a circuit formed on the base film and made of a conductor pattern, and a coverlay covering the circuit, the coverlay being made of an adhesive not containing a halogen flame retardant It is comprised so that the said circuit may be covered through an adhesive bond layer, Between the said base film and cover lay formed by the external shape process in the said cover lay covering the said circuit via the said adhesive bond layer The thickness of the adhesive layer at the end of the adhesive layer is formed to be thinner than the thickness of the adhesive layer in other parts except on the circuit, and the end of the adhesive layer is formed on the surface of the cover layer. A manufacturing method of a flexible printed circuit board in which an inclined portion is formed so that the distance from the base film is reduced toward the
After forming the circuit and the cover lay on the base film, comprising the step of forming the end by cutting,
The method of manufacturing a flexible printed board , wherein the inclined portion is formed by a pressure applied when forming the end portion . The coverlay includes a film layer on which the adhesive layer is formed,
The method for producing a flexible printed board according to claim 1, wherein the film layer is made of any one of polyethylene terephthalate, polyethylene naphthalate, polyimide, and polyamide. The method of manufacturing a flexible printed circuit board according to claim 1, wherein an electronic device including an active element connected to the circuit is mounted. The method of manufacturing a flexible printed circuit board according to claim 3, wherein the electronic device is mounted by heating in a reflow furnace through a solder paste mounted on the substrate. The method for manufacturing a flexible printed circuit board according to claim 4, wherein the solder paste does not contain lead.

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