JP2014170909A - Flexible circuit board and endoscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flexible circuit board having high design flexibility, and an endoscope having the flexible circuit substrate, capable of suppressing the occurrence of a restored bending and bending deformation.SOLUTION: A flexible circuit board 10 includes: an insulating base material film 12; a conductive wiring layer 14 formed on one or both surfaces of the base material film 12; an insulating protection layer 16 formed on the wiring layer 14; and a plastic deformation layer 18 provided on the outermost surface of at least one surface side of the base material film 12. The plastic deformation layer 18 includes a plurality of hole groups 20 disposed linearly to configure a bent line.

Description

  The present invention relates to a flexible circuit board that is used in a state in which a three-dimensional shape is maintained after pattern formation and component mounting in a planar state, and an endoscope having the flexible circuit board.

  In recent electronic equipment circuits, flexible circuit boards are increasingly used to meet the demand for downsizing of electrical equipment. The most general-purpose application of the flexible circuit board is typically used at the hinge portion of a folded mobile phone. When used in this way, development has been undertaken with a policy of reducing the thickness of each component in order to improve the repeated bending resistance necessary for use in the relevant part and to save space.

  In addition, since the flexible circuit board can obtain a three-dimensional structure by bending the wiring pattern creation and electronic component mounting in a planar state, compared to the case of using a conventional rigid board, Installation space can be reduced. For this reason, a flexible circuit board is used for an electronic device having a small installation space for a circuit board, for example, an imaging unit of an endoscope.

  With respect to this flexible circuit board, the tendency of the wiring width of the board to become narrower and the thickness of copper, which is a conductive layer, to become thinner is remarkable as electronic circuits become more accurate. In connection with this, the disconnection failure of copper by handling including bending is very easy to occur. Many proposals have been made to improve such problems.

  Patent Document 1 describes a flexible circuit board in which a copper foil is left on the side of the flexible circuit board on which the wiring pattern is not formed in order to prevent damage to the flexible circuit board and partially impart hardness. By this method, the risk of disconnection due to handling such as bending can be avoided.

  Patent Document 2 describes a flexible circuit board in which a conductive layer capable of wiring is provided on both sides or an inner layer of a flexible circuit board, and the copper thickness of the conductive layer in the bent portion is made thinner than that in the non-bent portion. ing. Thereby, it is possible to designate the position to be bent, triggered by the fact that the copper in the bent portion is thin.

  Patent Document 3 describes a flexible circuit board in which portions to be bent are designated by arranging holes of a predetermined size arranged in a line on the substrate. Thereby, even when the conductive layer is thin or the wiring density is not uniform, the bending line can be designated by the elasticity of the substrate itself.

JP 2000-315840 A JP 2007-250884 A JP 2005-223186 A

  By the way, after performing pattern formation or component mounting in a planar state, the flexible circuit board is bent with a small radius in a case where the flexible circuit board is bent and accommodated in a limited volume. In addition, it is required to include stability including bending position and angle variation, not to be deformed except for the bent portion, and to reduce the area other than the wiring and the bent region as much as possible.

  However, in the flexible circuit board, as the electronic circuit becomes more accurate, the wiring width of the board becomes narrower, and the thickness of copper as the conductive layer becomes thinner. Problems of lack of stability (so-called bending return) and occurrence of deformation other than the bent portion (so-called flex deformation) have become apparent.

  Such a problem is caused by the following. The deformation when a material receives an external force is roughly divided into elastic deformation and plastic deformation. While the force is small, the substance has a force to return to its original shape (this is called elastic force), and it can return to its original shape if there is no disturbing external force (this is called elastic deformation) When it exceeds a certain size, the deformation is maintained (this is called plastic deformation). When the flexible circuit board is bent, the copper wiring as the conductive layer is plastically deformed, and the substrate and the insulating protective layer are elastically deformed.

  Conventionally, both the copper thickness and the wiring width are large, and the amount of copper in the bent part is sufficient, so it is not enough to deform the copper wiring whose elastic force is deformed by the substrate or the insulating protective layer, so only the bent part is present. Even after deforming by drawing an arc, the flatness of the periphery was maintained, and it was fixed at the desired angle. However, as described above, as the electronic circuit becomes more accurate, the wiring width of the substrate becomes narrower or the thickness of the copper foil becomes thinner. The bending back phenomenon that the elastic force exceeds the size necessary for deforming copper and opens at a large angle with respect to the target opening angle becomes prominent.

  Further, during bending, the copper wiring is deformed even by a slight force that is diffused and applied to other than the bent portion, and the problem that the bent portion is deformed into a gentle arc shape becomes prominent.

  As described above, when the wiring width of the substrate is narrowed or the copper foil is thinned, the amount of copper in the bent portion is reduced. In addition to known problems such as fear of disconnection in handling and a method for specifying the bent line. A new problem of bending back and bending at the time of bending arises. If any of these problems occur, it becomes difficult to store the circuit board in a predetermined space such as in a small electronic device.

  However, in Patent Document 1, since the copper foil is left on the non-patterned surface, it can be achieved that the deformed portion is not deformed except for the bent portion. It is difficult to accommodate the flexible circuit board in a limited space. Further, no consideration is given to the bending of the flexible circuit board with a small radius and the stability of the bending position.

  In Patent Document 2, the copper thickness of the bent portion is reduced. However, if the copper thickness in a region other than the bent portion is reduced with the increase in accuracy of the electronic circuit, a sufficient difference in thickness cannot be obtained. It becomes difficult to obtain the effect of stabilizing the bending position. In addition, it is not considered that the copper bends with a small radius when the copper thickness is thin, and that other than the bent portion is not deformed. Further, when handling or three-dimensional processing, stress is likely to concentrate at the copper thickness changing portion, and disconnection may occur.

  In Patent Document 3, holes are formed in the substrate film and the protective layer along the refraction line. For this reason, when the substrate film and the protective layer are made thin, it becomes difficult to bend with a small radius and to realize stability including variation in the bending position and angle. Since insulation is lost when holes are made in the wiring part, an area for the hole part is required, so the volume after three-dimensionalization increases and it becomes difficult to accommodate the flexible circuit board in a limited space. . Furthermore, stress tends to concentrate on the drilled part, and there is a risk of damage during handling or three-dimensional processing.

  In view of the actual situation, the present invention is capable of suppressing the occurrence of new problems such as bending back and bending deformation in addition to known problems such as the radius at the bending of the substrate, fear of disconnection at the handling, and the method of specifying the bending line. It is an object of the present invention to provide a flexible circuit board having a high degree and an endoscope having the flexible circuit board.

  The inventor of the present invention particularly studied the structure of a flexible circuit board that can be stored in a predetermined installation space. The most general-purpose application of the flexible circuit board is typically used at the hinge portion of a folded mobile phone. Development has been promoted with a policy of reducing the thickness of each component member in order to improve the repeated bending resistance necessary for use in the part and to save space. Therefore, copper, which is a conductive layer, has become thinner along with the thinning of the base film and the insulating protective layer. As a result of bending the flexible circuit board developed in this way to obtain a three-dimensional structure, the force applied to the non-bent portion during bending and the elastic force from the base film and insulating protective layer after bending On the other hand, it was found that the insufficient amount of copper caused new problems such as bending back and deflection. However, in order to realize another requirement for realizing a compact and three-dimensional flexible circuit board such as miniaturization of wiring, it is necessary to keep the copper thickness of the wiring layer thin.

  Therefore, contrary to the conventional idea of thinning, while maintaining the copper thickness of the wiring layer, by applying a plastic deformation layer having a plurality of holes for designating the bent portion to the outermost surface of the base film, The present inventors have found that the securing of the amount of plastic deformation material necessary for maintaining plastic deformation and the thinness of the conductive layer necessary for miniaturization of wiring can be achieved at the same time.

  A flexible circuit board according to an embodiment of the present invention includes an insulating base film, a conductive wiring layer provided on one or both sides of the base film, and an insulating film formed on the wiring layer. A protective layer, and a plastic deformation layer provided on the outermost surface on at least one side of the base film, and the plastic deformation layer has a plurality of hole groups arranged in a line constituting a bending line. .

  Preferably, when the base film is bent along the bending line, the radius of curvature of the outermost peripheral layer of the bent portion is 500 μm or less.

  Preferably, the plurality of hole groups have a shape of a circle, an ellipse, or a rounded rectangle.

  Preferably, the plurality of hole groups have an elliptical or rounded rectangular shape, and the long axes of the plurality of hole groups are orthogonal to the bending line.

  Preferably, the plurality of hole groups have an elliptical or rounded rectangular shape, and the length of the long axis of the plurality of hole groups is 800 μm or less.

  Preferably, the ratio of the sum of the dimensions of the plurality of hole groups in the direction parallel to the bending line to the dimension of the base film on the bending line is 30 to 70%.

  Preferably, the plastic deformation layer is made of metal.

  Preferably, the plastic deformation layer has a thickness of ½ or more of the total of the thickness of the base film and the thickness of the protective layer.

  An endoscope according to another aspect of the present invention includes an insertion portion that is inserted into an observation target, an observation optical system that is provided at a distal end portion of the insertion portion, and an imaging that is provided on a proximal side with respect to the observation optical system. And an above-described flexible circuit board in a state of being bent along a bending line.

  Preferably, a sealing resin for fixing the flexible circuit board in a bent shape is included.

  According to the present invention, in addition to solving known problems such as fear of disconnection in handling and a method of specifying a bent line, it is possible to suppress the occurrence of bending back and bending deformation, and a flexible circuit board having a high degree of design freedom, and this flexible circuit An endoscope having a substrate can be realized.

The perspective view which shows the structure of the flexible circuit board of 1st Embodiment. The perspective view which shows the structure of the flexible circuit board of 2nd Embodiment. The perspective view which shows the structure of the flexible circuit board of 3rd Embodiment. The top view which shows the structure of the flexible circuit board of this embodiment. The perspective view which shows the structure of the flexible circuit board which mounted the electronic component. The elements on larger scale of the state which bent the flexible circuit board. The top view which shows the shape of the hole formed in a plastic deformation layer. 1 is an overall configuration diagram of an endoscope. The external view of the front-end | tip part of an endoscope. AA line sectional view of FIG. Schematic which shows the evaluation method.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. The present invention will be described by the following preferred embodiments, but can be modified in many ways without departing from the scope of the present invention, and other embodiments than the present embodiment are utilized. be able to. Accordingly, all modifications within the scope of the present invention are included in the claims.

  Here, in the drawing, portions indicated by the same symbols are similar elements having similar functions. In addition, in the present specification, when a numerical range is expressed using “˜”, upper and lower numerical values indicated by “˜” are also included in the numerical range.

  FIG. 1 is a perspective view of the flexible circuit board according to the first embodiment. The flexible circuit board 10 includes a base film 12 having a first surface 12A and a second surface 12B, a conductive wiring layer 14 formed on the first surface 12A of the base film 12, and an upper surface of the wiring layer 14. And a plastic deformation layer 18 having a plurality of hole groups 20 along the bending line L, formed on the second surface 12B of the base film 12.

  The base film 12 is made of an insulating material such as polyimide resin, LCP (Liquid Crystal Polymer) or the like. The base film 12 has a thickness of 5 to 50 μm.

  The wiring layer 14 is generally formed by using an electrolytic copper foil, a rolled copper foil, or the like, and creating a wiring pattern by etching or the like. The wiring layer 14 has a thickness of 2 to 25 μm. In order to perform high-density mounting, the thickness of the wiring layer 14 below this may be used.

  The protective layer 16 is made of an insulating solder resist. As the solder resist, it is preferable to select a solder resist having a high elongation rate for flexible circuit boards. Moreover, various coverlay films can be used instead of the solder resist. When a solder resist is used for the protective layer 16, the protective layer 16 has a thickness of 10 to 30 μm.

  The plastic deformation layer 18 is made of a metal such as copper, silver, gold, tin, or aluminum. In this embodiment, since a wiring layer is provided only on one side of the flexible circuit board 10, a double-sided copper clad laminate in which copper foil is previously bonded to both sides of the base film 12 is used for simplification of the production procedure. A copper foil layer present on a surface not used as the wiring layer 14 can be used as the plastic deformation layer 18. A copper foil layer that becomes the wiring layer 14 and the plastic deformation layer 18 can be integrally formed on the base film 12.

  As the plastic deformation layer 18, various metal foils that are separate from the base film 12 may be bonded together with an adhesive or the like, and furthermore, a metal sheet material in which an adhesive / adhesive material is applied to the back surface of the various metal foils. You may stick together. The plastic deformation layer 18 has a thickness of 25 to 50 μm.

  FIG. 2 is a perspective view of the flexible circuit board according to the second embodiment. The flexible circuit board 10 includes a base film 12 having a first surface 12A and a second surface 12B, a conductive wiring layer 14 formed on the first surface 12A of the base film 12, and an upper surface of the wiring layer 14. And an insulating protective layer 16 formed on the protective layer 16, and a plastic deformation layer 18 formed on the protective layer 16 and having a plurality of hole groups 20 along the bending line L.

  The composition and thickness of the base film 12, the wiring layer 14, the protective layer 16, and the plastic deformation layer 18 are the same as those in the first embodiment.

  FIG. 3 is a perspective view of a flexible circuit board according to the third embodiment. The flexible circuit board 10 includes a base film 12 having a first surface 12A and a second surface 12B, a conductive wiring layer 14 formed on the first surface 12A of the base film 12, and an upper surface of the wiring layer 14. An insulating protective layer 16 formed on the conductive film 14 formed on the first surface 12A of the base film 12, an insulating protective layer 16 formed on the wiring layer 14, And a plastic deformation layer 18 having a plurality of hole groups 20 along the bending line L, which is formed on the protective layer 16 on the first surface 12A side.

  The composition and thickness of the base film 12, the wiring layer 14, the protective layer 16, and the plastic deformation layer 18 are the same as those in the first embodiment.

  In the first embodiment of FIG. 1, the second embodiment of FIG. 2, and the third embodiment of FIG. 3, an example in which the plastic deformation layer 18 is formed on the outermost surface of one side of the base film 12 was shown. . However, the present invention is not limited to this, and the plastic deformation layer 18 can also be formed on the outermost surfaces of both surfaces of the base film 12. By forming the plastic deformation layer 18 on both surfaces, the flat portion can be made stronger.

  FIG. 4 is a plan view of the flexible circuit board 10 according to the present embodiment. A patterned wiring layer 14 is formed on the first surface 12 </ b> A of the base film 12. The shape of the pattern is appropriately changed depending on the arrangement of the drive circuit components to be mounted. A protective layer (not shown) and a plastic deformation layer 18 are formed on the wiring layer 14. A plurality of hole groups 20 are formed along the bending line L in the plastic deformation layer 18.

  In the present embodiment, a plastic deformation layer 18 having a higher elastic modulus than a polymer member such as the base film 12 and the protective layer 16 and capable of plastic deformation when bent is formed on the outermost surface of the base film 12. Is done. Therefore, since the elastic force resulting from the deformation of the polymer member such as the base film 12 and the protective layer 16 is not sufficient to deform the plastic deformation layer 18, it is possible to suppress the occurrence of bending back. Further, even when the load at the time of bending cannot be absorbed only by the region of the bending line L and it acts on the regions on both sides thereof, the load remains at a force that is insufficient to plastically deform the plastic deformation layer 18. Therefore, it is possible to suppress the occurrence of flexural deformation in the regions on both sides of the band-shaped region formed by the plurality of hole groups 20.

  In the present embodiment, a plastic deformation layer 18 having a higher elastic modulus than a polymer member such as the base film 12 and the protective layer 16 and capable of plastic deformation when bent is formed on the outermost surface of the base film 12. In addition, a plurality of hole groups 20 are formed along the bending line L in the plastic deformation layer 18. In the plastic deformation layer 18, a difference in elastic modulus is generated between the region of the bending line L and the regions on both sides thereof. As a result, the load applied during bending can be absorbed in the region of the bending line L. Thereby, the flexible circuit board 10 can be bent to a radius of curvature of 500 μm or less. Here, the radius of curvature refers to the arc radius of the outermost periphery seen from the cross section of the flexible circuit board 10 when bent. Further, even when an error occurs in the setting position of the flexible circuit board 10 in the bending process, and the portion most receiving the load is deviated from the center in the direction orthogonal to the bending line L in the hole group 20, the load is transferred to the plurality of holes. By dispersing in the direction orthogonal to the bending line L in the group 20, the action of bringing the apex of deformation closer to the center in the direction orthogonal to the bending line L in the hole group 20 works, Variations in shape can be kept very small.

  In the flexible circuit board 10 of the present embodiment, the base film 12, the wiring layer 14, and the protective layer 16 are not subjected to drilling or thinning. This also exhibits the effect of maintaining the strength at the time of handling and flexible processing of the flexible circuit board 10.

  In the flexible circuit board 10 of the present embodiment, a plastic deformation layer 18 independent of the base film 12, the wiring layer 14, and the protective layer 16 constituting the substantial circuit board is formed, and the plastic deformation layer 18 has holes. Group 20 is formed. Thereby, since it is not necessary to process a circuit board, the flexible circuit board 10 with a high design freedom with respect to the wiring layer 14 is realizable. Since the plastic deformation layer 18 is a separate member from the wiring layer 14, the wiring layer 14 can be formed on both the first surface 12A side and the second surface 12B side of the base film 12. As a result, the drive circuit component can be efficiently mounted on the flexible circuit board 10.

  Bending of the flexible circuit board 10 in the direction parallel to the bending line L of the sum N · β (N: number of holes, β: vertical length of the holes) of the dimensions of the plurality of hole groups 20 in the direction parallel to the bending line L The ratio (N · β / W) to the dimension W at the part is preferably 30 to 70%. When the ratio is 30%, it indicates that the region of the plastic deformation layer 18 that remains without opening is larger than the region of the hole group 20, and conversely when the ratio is 70%, the region that leaves the hole of the plastic deformation layer 18 without opening. Is smaller than the region of the hole group 20.

  By setting (N · β / W) to 30 to 70%, it is possible to secure a necessary amount of plastic deformation. In addition, an error may occur in the setting position of the flexible circuit board 10 in the bending process, and the portion that receives the load most may deviate from the center in the direction orthogonal to the bending line L in the hole group 20. Under such circumstances, the load is distributed in a direction perpendicular to the bending line L in the hole group 20, so that the apex of deformation approaches the center of the direction orthogonal to the bending line L in the hole group 20. The action works. Therefore, the curvature radius and the variation in shape after bending can be extremely reduced.

  FIG. 5 is a perspective view showing a configuration of a flexible circuit board on which electronic components are mounted. As shown in FIG. 5, when an electronic component is mounted on the wiring layer 14 when the plastic deformation layer 18 is formed on the wiring layer 14, the electronic component 30 in the plastic deformation layer 18 is positioned so as to overlap. A punching hole 24 for penetrating the electronic component 30 is provided. Thereby, the plastic deformation layer 18 can be formed before or after the electronic component 30 is mounted. The position where the electronic component 30 is mounted is hard and it is substantially difficult to bend. Therefore, the plurality of hole groups 20 and the punched holes 24 along the bending line L do not overlap. That is, the flexible circuit board 10 is not bent at the position where the electronic component 30 is mounted. Therefore, even if the punching hole 24 is opened, the plurality of hole groups 20 along the bending line L can be opened. Thus, the flexible circuit board 10 that can be bent with high accuracy can be obtained regardless of whether or not the electronic component 30 is mounted.

  The thickness of the plastic deformation layer 18 is preferably 1/2 or more of the total thickness of the base film 12 and the protective layer 16. The bending return after bending the flexible circuit board 10 is caused by the elastic force between the base film 12 and the protective layer 16. In order to resist this elastic force, the thickness of the plastic deformation layer 18 is preferably set in the above-mentioned range.

  FIG. 6 is a partially enlarged view of the state in which the flexible circuit board 10 is bent along the bending line L. FIG. In this embodiment, since the plastic deformation layer 18 having the plurality of hole groups 20 is bent along the bending line L, the radius of curvature R can be set to 500 μm or less. In obtaining a three-dimensional structure that can be accommodated in a limited space, the radius of curvature R is preferably equal to or less than 400 μm, and more preferably equal to or less than 300 μm. In addition, in the planar region 22 of the flexible circuit board 10, it is possible to suppress the occurrence of bending deformation and bending back. That is, variations in the bent shape of the flexible circuit board 10 can be suppressed.

  The plurality of hole groups 20 are preferably, for example, a circle as shown in FIG. 7 (A), an ellipse as shown in FIG. 7 (B), and a rounded rectangle as shown in FIG. 7 (C). It can prevent that a crack etc. arise by having a curve part. As shown in FIG. 7A, when the hole group 20 is circular, the length of the radius R is preferably 500 μm or less, and more preferably 300 μm or less. When the hole group 20 in FIG. 7B has an elliptical shape, the length of the major axis α is preferably 800 μm or less, and more preferably 500 μm or less. The minor axis β is preferably 400 μm or less, and more preferably 200 μm or less. Moreover, when the hole group 20 is elliptical, it is preferable to arrange the plurality of hole groups 20 so that the major axis α is orthogonal to the bending line L. This is because if the bending line L becomes thin, high-precision positioning is required when applying a punch at the time of bending, resulting in a cost for jig production.

  Next, an endoscope incorporating the flexible circuit board according to the present embodiment will be described.

  FIG. 8 is an overall configuration diagram of the endoscope according to the embodiment of the present invention. The endoscope 100 includes a main body operation unit 111 and an insertion unit 113 that is connected to the main body operation unit 111 and is inserted into a body cavity of a patient or the like. In the present embodiment, a so-called flexible mirror having a flexible portion at the distal end of the insertion portion is illustrated. However, the present invention is not limited to this, and the flexible circuit board according to the present embodiment can be applied to all endoscopes that have an insertion portion to be inserted into the observation target and observe the inside of a body cavity or an object.

  A universal cable 115 is connected to the main body operation unit 111. A connector (not shown) is provided at the tip of the universal cable 115. This connector is detachably connected to a light source device (not shown). Thereby, illumination light is sent from the light source device to the illumination optical system built in the distal end portion 117 of the insertion portion 113. A video connector is also connected to this connector. The video connector is detachably connected to a processor (not shown) that performs image signal processing and the like.

  The insertion portion 113 includes a flexible portion 119, a bending portion 121, and a distal end portion 117 in order from the main body operation portion 111 side, that is, the proximal end side. The bending portion 121 is remotely bent by turning the angle knobs 123 and 125 of the main body operation unit 111. Thereby, the front-end | tip part 117 is orient | assigned to the desired direction.

  In addition to the angle knobs 123 and 125 described above, the main body operation unit 111 is provided with various buttons 127 such as an air / water supply button, a suction button, and a shutter button. Further, a forceps insertion portion 131 is provided on the continuous portion 129 extended from the main body operation portion 111 to the insertion portion 113 side. A treatment tool (not shown) such as a forceps inserted from the forceps insertion portion 131 is led out from a forceps port 133 (see FIG. 9) formed at the distal end portion 117 of the insertion portion 113.

  FIG. 9 is a schematic external view of the above-described distal end portion 117, and FIG. 10 is a cross-sectional view taken along line AA of FIG. As shown in FIG. 9, a distal end portion (hereinafter also referred to as an endoscope distal end portion) 117 that is a distal end portion of the insertion portion 113 (see FIG. 8) is provided on the distal end surface 135 of the observation window 137 of the imaging optical system. And illumination apertures 139A and 139B of the illumination optical system disposed on both sides of the observation window 137, and a forceps port 133 disposed in the vicinity thereof. Further, a nozzle 141 that supplies air and water to the observation window 137 is disposed with the jet outlet facing the observation window 137.

  As shown in FIG. 10, the endoscope distal end portion 117 is fixed by inserting a lens barrel 145 into a distal end hard portion 143 made of a metal material such as a stainless steel material and a hole 143a formed in the distal end hard portion 143. In addition to the image pickup unit 147 and the metal forceps pipe 149 disposed in the other perforation hole 143b, the air supply / water supply tube 151 connected to the nozzle 141 and the illumination optical system are connected. Various members such as a light guide for light guide (not shown) are accommodated.

  The imaging unit 147 changes the optical path OP of incident light (observation light) from an object captured through the objective lens group 153 and an object lens group 153 including a plurality of objective lenses housed in the lens barrel 145 to a right angle. And an imaging element 159 that receives incident light whose optical path OP is changed at a right angle.

  The image sensor 159 is mounted on the flexible circuit board 10. An image signal based on the image information of the subject captured by the image sensor 159 is output through the flexible circuit board 10.

  An imaging optical system including the objective lens group 153, the triangular prism 155, and the imaging element 159 is built in the endoscope distal end portion 117 and functions as an imaging device. The objective lens group 153 constitutes an observation optical system. The image sensor 159 is provided on the base end side from the observation optical system. Further, an optical member such as a lens disposed at the irradiation ports 139A and 139B (see FIG. 9) and a light guide connected to the optical member constitute an illumination optical system. These are also built in the endoscope distal end portion 117. Image information output from the image sensor 159 is transmitted to the processor (not shown) through the signal cable 161 and processed into a display image.

  A metal sleeve (not shown) is connected to the outer periphery of the distal end hard portion 143, and a node ring (not shown) disposed on the bending portion 121 (see FIG. 8) is connected to the metal sleeve so as to be bent. The outer periphery of the metal sleeve is covered with an outer tube 150. The distal end side of the distal end hard portion 143 is covered with a distal end cover 163. The outer tube 150 and the front end cover 163 are closely bonded to each other so that there is no water immersion inside.

  The objective lens group 153 is connected to the incident side end face 155 a of the triangular prism 155. A cover glass 165 that is a translucent protective substrate is bonded to the emission-side end surface 155b of the triangular prism 155. On the opposite side of the cover glass 165 from the triangular prism 155, an image sensor 159 is disposed via an air gap 167. The air gap 167 is set to a predetermined volume by the frame body 160 disposed around the image sensor 159.

  The flexible circuit board 10 on which the image sensor 159 is mounted is bent at the first bent line L1 in FIG. 10 and further bent at the second bent line L2. The flexible circuit board 10 is bent in a curved state upward from the horizontal plane in the drawing along the total reflection slope of the outer surface of the prism that becomes the total reflection surface of the triangular prism 155 along the third bending line L3. As a result, the flexible circuit board 10 presses the total reflection slope of the triangular prism 155.

  Here, the triangular prism 155 is illustrated as an optical member that guides light to the image sensor 159, but the present invention is not limited thereto, and other shapes and other types of optical path changing members may be used. Moreover, the cover glass 165 should just have translucency with respect to observation light, and may be other materials, such as not only a glass material but transparent resin.

  A driving circuit component 179 for driving and controlling the image sensor 159 is mounted on the flexible circuit board 10. Further, a regulator 177 is mounted on the flexible circuit board 10.

  In the endoscope 100 of the present embodiment, a flexible circuit board 188 for heat dissipation is provided in order to improve the heat dissipation characteristics of heat generated in the image sensor module. The flexible circuit board 188 has one end-side surface bonded to the entire back surface of the image sensor 159 with an adhesive or the like. Further, the flexible circuit board 188 is brought into thermal contact with the planar region 22 of the flexible circuit board 10 and is bonded to the outer cover of the signal cable 161 in a wider area than a predetermined area.

  The cable connection portion 173 includes a land 181. Each lead wire 161a of the signal cable 161 is connected by soldering or the like.

  A space surrounded by the flexible circuit board 10 is formed by bending and three-dimensionalizing the flexible circuit board 10. The space may be filled and solidified with a sealing resin (not shown). The shape of the flexible circuit board 10 can be maintained and the drive circuit component 179 can be protected by the sealing resin. At that time, since the flexible circuit board 10 has the plastic deformation layer 18 having a high elastic force, deformation and distortion due to external force can be suppressed from the time of filling the resin to the completion of the heat curing.

  In the endoscope 100 of the present embodiment, the flexible circuit board 10 includes the plastic deformation layer 18 (not shown) having a plurality of hole groups 20, and thus the flexible circuit board 10 is three-dimensionally formed with a small curvature radius R and high dimensional accuracy. Can be processed. That is, the flexible circuit board 10 can be accommodated in a predetermined installation space.

  Hereinafter, the present invention will be described more specifically with reference to examples of the present invention. In addition, the material, usage-amount, ratio, processing content, processing procedure, etc. which are shown in the following Examples can be changed suitably unless it deviates from the meaning of this invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

(Sample 1)
A copper-clad laminate (Panasonic Electric Works, RF758) having a length of 20 mm and a width of 50 mm was prepared. The copper-clad laminate is composed of a polyimide base film having a thickness of 12 μm and a wiring layer having a thickness of 12 μm formed of electrolytic copper formed on the base film. By etching, L (line width) / S (space width) = 100 μm / 100 μm, and wiring layers of three sets of six wiring patterns extending in parallel in the horizontal direction shown in FIG. 3 were formed on the base film. . A protective layer having a thickness of about 10 μm was formed on the wiring layer with a solder resist.

  A plurality of elliptical punched holes having a horizontal axis length of 500 μm and a vertical axis length of 200 μm are formed in a copper foil having the same dimensions as the copper-clad laminate and having a thickness of 18 μm in the horizontal direction at intervals of 200 μm. It was formed so as to be aligned in the vertical axis direction in the vicinity of the center. This copper foil was bonded to the protective layer of the copper clad laminate with an adhesive. The layer configuration of the flexible circuit board is the same as in FIG.

(Sample 2)
Similar to Sample 1, the wiring pattern shown in FIG. 3 was created on the wiring layer of the copper clad laminate, and a protective layer was created thereon. A copper foil provided with a punched hole similar to that of Sample 1 was bonded onto the surface of the base film opposite to the wiring layer forming surface to produce a flexible circuit board. The layer configuration of the flexible circuit board is the same as in FIG.

(Sample 3)
Similar to Sample 1, a wiring pattern shown in FIG. 3 was formed on the wiring layer of the copper-clad laminate. Avoid a portion with wiring so that a plurality of elliptical punched holes having a length of 500 μm on the horizontal axis and a length of 200 μm on the vertical axis are arranged in the vertical direction near the center in the horizontal direction at intervals of 200 μm. Formed. A protective layer was created thereon.

(Sample 4)
Similar to Sample 1, a wiring pattern shown in FIG. 3 was created on the wiring layer of the copper clad laminate, and a solder resist was formed on the wiring layer as a protective layer. A plurality of elliptical holes having a length of 500 μm on the horizontal axis and a length of 200 μm on the vertical axis are arranged in this protective layer at 200 μm intervals so that the wires are arranged in the vertical direction near the center in the horizontal direction. It was formed by an etching process, avoiding certain parts.

<Processing and evaluation method>
A sample is placed on a die having a parallel gap so that the gap and the row of holes are aligned, a punch is applied to the bending line, and the opening angle of the sample is 90 ° when viewed from the cross-sectional direction. The load was applied until it became (FIG. 9A), and then the load was removed (FIG. 9B). The number of samples n = 10 was performed for each sample. The processed sample is observed from the side with an optical microscope, and the radius (curvature radius) obtained by approximating the deformation curve of the outer peripheral layer at the time of bending to an arc, the opening angle formed on the outer side of the bending line, and the bending line The presence or absence of deflection on the outside (planar region) was visually confirmed. For Samples 1 and 2, the plastic deformation layer was folded into a mountain and a valley. Sample 3 was folded in a base film, and sample 4 was folded in a protective layer.

<Evaluation>
Table 1 summarizes the evaluation results. Samples 1 and 2 gave almost the same results. It shows that the surface on which the plastic deformation layer is formed and the folding direction (mountain fold / valley fold) are not affected. In Samples 3 and 4, although disconnection did not occur, both the radius of curvature and the opening angle were large. In addition, the range of variation increased and deflection occurred in the planar area.

  DESCRIPTION OF SYMBOLS 10, 188 ... Flexible circuit board, 12 ... Base film, 1 ... Wiring layer, 16 ... Protective layer, 18 ... Plastic deformation layer, 20 ... Hole group, 22 ... Planar area, 24 ... Hole

Claims (10)

An insulating base film;
A conductive wiring layer provided on one or both sides of the base film;
An insulating protective layer formed on the wiring layer;
A plastic deformation layer provided on the outermost surface on at least one side of the base film,
The plastic deformation layer is a flexible circuit board having a plurality of hole groups arranged in a line constituting a bent line.   The flexible circuit board according to claim 1, wherein when the base film is bent along the bending line, a radius of curvature of the outermost peripheral layer of the bent portion is 500 μm or less.   The flexible circuit board according to claim 1, wherein the plurality of hole groups have a shape of a circle, an ellipse, or a rounded rectangle.   The flexible circuit board according to claim 1, wherein the plurality of hole groups have an elliptical or rounded rectangular shape, and a long axis of the plurality of hole groups is orthogonal to the bending line.   The flexible circuit board according to claim 4, wherein the plurality of hole groups have an elliptical or rounded rectangular shape, and a length of a major axis of the plurality of hole groups is 800 μm or less.   The ratio of the sum of the dimensions of the plurality of hole groups in a direction parallel to the bending line to the dimension of the base film on the bending line is 30 to 70%. Flexible circuit board.   The flexible circuit board according to claim 1, wherein the plastic deformation layer is made of metal.   The flexible circuit board according to any one of claims 1 to 7, wherein the plastically deformable layer has a thickness of ½ or more of a total thickness of the base film and the protective layer. An insertion part to be inserted inside the observation object;
An observation optical system provided at the distal end of the insertion portion;
An image sensor provided on the base end side of the observation optical system;
The flexible circuit board according to any one of claims 1 to 8, wherein the imaging element and a drive circuit component of the imaging element are mounted and bent along a bending line;
An endoscope comprising:   The endoscope according to claim 9, comprising a sealing resin that fixes the flexible circuit board in a bent shape.

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