JP2004055846A - Method for isolating wiring pattern of printed wiring board and fire detector equipped with printed wiring board whose wiring pattern is isolated thereby - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve insulating properties at cutting parts of wiring lines, and to prevent adhesion of moisture to the cutting faces or occurrence of corrosion thereon. <P>SOLUTION: Wiring lines 102 composed of a copper foil and connected with connection branched parts 104 each other are formed on the surface of an insulating substrate 101, and a solder resist 103 for protecting the wiring line 102 is laminated to form a printed wiring board 100. Through-holes 105 penetrating the printed wiring board 100 are arranged by punching parts including some of the connection branched parts 104 to cut unneeded wiring lines 102, thereby obtaining a required wiring pattern. Cutting parts and cutting faces of the wiring lines 102 exposed to the through-holes 105 are protected with a sealing material 106 by sealing the through-holes 105, with the sealing material 106 composed of an insulative synthetic resin to improve insulating properties at the cutting parts of the wiring lines 102, and to prevent adhesion of moisture to the cutting faces or occurrence of corrosion thereon. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for insulating a wiring pattern of a printed wiring board and a fire detector including a printed wiring board having a wiring pattern insulated by the method.
[0002]
[Prior art]
Today, printed wiring boards are used in various devices. However, there are many cases in which a circuit must be changed by adding a function or changing specifications after forming a wiring pattern. For this reason, conventionally, an extra wiring pattern is formed in advance in anticipation of a circuit change, and a desired wiring pattern is formed by cutting the extra wiring pattern as necessary. Heretofore, no special treatment for insulation has been applied to the cut portion of the wiring pattern.
[0003]
Here, a case in which a wiring pattern is formed on a printed wiring board made of glass epoxy as a base will be briefly described. After mechanical processing for making holes such as through holes is performed on an insulating substrate having a copper foil laminated on the entire surface, conductor patterning is performed using a resist. This patterning is generally performed by a photoengraving method using a photomask and a photosensitive resist. In a method of leaving a resist on a conductor pattern necessary for conductor wiring (a so-called positive method), an unnecessary copper foil is removed by an etchant after this patterning, and a conductor pattern of the copper foil is formed after removing the resist. Will be. In the case where such a conductor pattern is formed on both the front and back surfaces to form a double-sided mounting substrate that conducts through the through holes, it is necessary to copper-plate the inside of the through holes.
[0004]
By the way, when a bare chip is mounted on a printed wiring board by wire bonding or the like, the surface of a wiring line (conductor) needs to be in a state necessary for ensuring reliability. Specifically, when gold is used as the bonding wire, the surface of the wiring line of the printed wiring board is subjected to electrolytic gold plating with a thickness of about 0.3 μm. In order to perform electrolytic plating, it is necessary to supply a current to a wiring line that requires plating. Therefore, a wiring line for plating must be formed on a printed wiring board. However, since the wiring line for plating is essentially unnecessary, it must be separated from the originally necessary wiring line after plating. In this way, the work of separating the wiring lines for plating is most troublesome by cutting unnecessary wiring lines when finally processing the outer shape of the printed wiring board, which is particularly troublesome in design. Unless there is no wiring pattern design, a wiring pattern for plating is routed outside the outer shape of the final printed wiring board. However, it may be difficult to route the plating wiring line to the outside depending on the convenience of conductor patterning and the wiring density. In this case, the plating wiring line may be formed at the center of the printed wiring board or the like.
[0005]
[Problems to be solved by the invention]
By the way, since the end face of the copper foil is exposed from the cut surface when the wiring line for plating which becomes unnecessary after the electrolytic plating is cut as described above, the exposed end face of the copper foil is easily affected by corrosion or moisture. In addition, it becomes difficult to secure moisture resistance, dew condensation resistance, or corrosion resistance of a device using a printed wiring board. In particular, fire detectors that detect smoke, heat, or flame generated by a fire need to withstand severe conditions different from ordinary equipment, such as the corrosion test specified in the firefighting certification. Failures must be reliably prevented.
[0006]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a printed wiring board capable of improving insulation properties of a cut portion of a wiring line and preventing adhesion of moisture and corrosion to a cut surface. It is an object of the present invention to provide a wiring pattern insulating method and a fire detector provided with a printed wiring board whose wiring pattern is insulated by the method.
[0007]
[Means for Solving the Problems]
According to a first aspect of the present invention, in order to achieve the above object, a plurality of wiring lines connected to each other at a plurality of connection branches are formed on the surface of a printed wiring board, and unnecessary portions are formed at portions including any of the connection branches. In a wiring pattern insulating method for a printed wiring board, which obtains a desired wiring pattern by cutting a wiring line and insulates a cut portion of the wiring line, a through hole penetrating the printed wiring board is provided in a portion including the connection branch portion. In this way, unnecessary wiring lines are cut off, and the through holes are sealed with a sealing material made of an insulating synthetic resin.
[0008]
According to a second aspect of the present invention, in the first aspect of the present invention, the sealing material is made of an epoxy resin having relatively high viscosity and thixotropic property before curing and relatively high shape retention performance after curing. It is characterized.
[0009]
According to a third aspect of the present invention, in the first aspect of the invention, the sealing material is made of urethane resin.
[0010]
According to a fourth aspect of the present invention, in order to achieve the above object, a plurality of wiring lines connected to each other at a plurality of connection branch portions are formed on the surface of a printed wiring board, and unnecessary portions are formed at portions including any of the connection branch portions. In a wiring pattern insulating method for a printed wiring board, in which a desired wiring pattern is obtained by cutting a wiring line and a cut portion of the wiring line is insulated, an unnecessary wiring line is formed by providing a concave portion in a portion including the connection branch portion. In addition to cutting, the recess is sealed with a sealing material made of a synthetic resin having an insulating property.
[0011]
A fifth aspect of the present invention is characterized in that, in the fourth aspect of the present invention, the sealing material is made of a synthetic resin having a light transmitting property.
[0012]
According to a sixth aspect of the present invention, in the fourth aspect of the invention, the sealing material is made of urethane resin.
[0013]
According to a seventh aspect of the present invention, there is provided a detecting means for detecting smoke, heat or flame due to a fire and outputting an electric signal, and processing an electric signal output by the detecting means to output the electric signal to the outside. And a printed circuit board on which a circuit component constituting the signal processing circuit is mounted, the wiring pattern being insulated by the method according to any one of claims 1 to 6. I do.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
(Embodiment 1)
As shown in FIG. 2, wiring lines 102 made of copper foil and connected to each other at connection branch portions 104 are formed on a surface of an insulating base material 101 such as glass epoxy, and a solder resist 103 for protecting the wiring lines 102 is laminated. Thus, the printed wiring board 100 is configured. As shown in FIG. 1A, a through-hole 105 is formed in a portion including any of the connection branch portions 104 by punching (piercing) to penetrate the printed wiring board 100, and unnecessary wiring lines are formed by the through-hole 105. By cutting 102, a desired wiring pattern can be obtained.
[0015]
By the way, in the related art, the wiring line 102 cut in the through hole 105 is left as it is, and the cut portion is not subjected to a process for insulation, but the cutting of the wiring line 102 exposed in the through hole 105 is performed. The surface is not protected by the solder resist 103, and for example, there is a possibility that the moisture in the atmosphere may adhere due to dew condensation or may be corroded by being exposed to a corrosive gas.
[0016]
Therefore, in the present invention, as shown in FIG. 1, the cut portion of the wiring line 102 exposed in the through hole 105 is insulated by sealing the through hole 105 with a sealing material 106 made of a synthetic resin having an insulating property. At the same time, the cut surface is protected by the sealing material 106 to improve the insulating property of the cut portion of the wiring line 102 and to prevent moisture from attaching to the cut surface of the wiring line 102 and to prevent corrosion. Here, as the sealing material 106, an epoxy resin having a relatively high viscosity and thixotropic property (thixotropic property) before curing, and a relatively high shape retention performance after curing (for example, a thermal resin manufactured by Matsushita Electric Works, Ltd.) When the curable liquid sealing material CV5181D) is used, the chemical resistance and heat resistance of the sealing material 106 can be improved, and the sealing material 106 does not easily spread around the through hole 105. There is an advantage that it can be made large and the moisture resistance and corrosion resistance can be further improved. Further, a urethane resin may be used as the sealing material 106, and in that case, the chemical resistance can be improved.
[0017]
(Embodiment 2)
This embodiment is characterized in that a concave portion 107 is provided instead of providing a through hole 105 for cutting unnecessary wiring lines 102 as shown in FIG. The other points are the same as those of the first embodiment. Therefore, the same reference numerals are given to the same components, and the description will be omitted.
[0018]
The concave portion 107 is provided by shaving a portion including any of the connection branch portions 104 so as not to penetrate the printed wiring board 100 by, for example, a drill. When the concave portion 107 is filled with a liquid synthetic resin and sealed, the cut surface of the wiring line 102 is protected by the sealing material 106. As the sealing material 106, an epoxy resin or a urethane resin is used as in the first embodiment. Note that if a synthetic resin having a light-transmitting property (for example, a thermosetting liquid sealing material CV5130A manufactured by Matsushita Electric Works, Ltd.) is used for the sealing material 106, bubbles generated in the sealing material 106 as shown in FIG. Since the portion 106a can be confirmed from the outside, there is an advantage that the presence or absence of the bubble 106a inside the sealing material 106 can be easily determined.
[0019]
(Embodiment 3)
In the present embodiment, a fire detector using a printed wiring board whose wiring pattern is insulated by the method of Embodiment 1 or 2 will be exemplified. As described in the prior art, the fire detector is described in the Ministry of Ordinance (Ordinance No. 17 of the Ministry of Home Affairs of Japan on June 20, 1981) which specifies the technical standards for the detector and the transmitter of fire alarm equipment. Since it is necessary to withstand the corrosion test specified in Article 22, it is particularly effective to use the printed wiring board in which the wiring pattern is insulated by the method of Embodiment 1 or 2 to improve the corrosion resistance.
[0020]
Hereinafter, the fire detector of the present embodiment will be described in detail with reference to the drawings. The fire detector according to the present embodiment is a composite type having both a smoke detecting function for detecting smoke and a heat detecting function for detecting heat, and as shown in FIGS. A body 1 attached to the surface, a light emitting diode LED as a light emitting element, a photodiode PD as a light receiving element, a circuit board 2 on which circuit components of a smoke detection circuit described later are mounted, and intrusion of smoke from the outside. A smoke sensing chamber S having a substantially circular horizontal section surrounded by a labyrinth wall 9 for allowing and preventing the incidence of external light is provided, and optical components are mounted in the smoke sensing chamber S. Insects and the like enter the optical base 3 on which the circuit board 2 is mounted in a state where the light emitting diode LED and the photodiode PD face the components of the optical system, and the inside of the smoke sensing room S provided on the optical base 3. Insect repellent to prevent And -4, and a protective cover 5.
[0021]
The body 1 is formed by continuously and integrally forming a substantially disk-shaped main portion 1a and a side wall 1b projecting upward from the outer peripheral edge of the main portion 1a. The optical base 3 on which the circuit board 2 is fixed and the protective cover 5 holding the insect repellent cover 4 are inserted into the round hole 1c and fixed.
[0022]
Light emitting diodes LED are mounted on the lower surface of the circuit board 2. On the lower surface of the circuit board 2, a photodiode PD formed as a chip is mounted. Further, a thermistor 6 is mounted on the lower surface of the circuit board 2 with the heat sensing portion protruding downward. As described above, the fire detector according to the present embodiment includes the thermistor 6 as a thermal element, and has a heat sensing function in addition to a smoke sensing function.
[0023]
As shown in FIGS. 7 to 10, the optical base 3 is made of a black synthetic resin and has a substantially disk-shaped bottom plate 7, a rectangular frame-shaped side wall 8 protruding from the upper surface of the bottom plate 7, and a bottom surface 7 of the bottom plate 7. The labyrinth wall 9 composed of a plurality of partition walls 9a having a substantially rectangular cross section arranged along the outer peripheral portion is integrally formed.
[0024]
The partition 9a constituting the labyrinth wall 9 is formed in black so as not to cause reflection, and the direction in which the bent portion of the intermediate portion projects is the same as the direction of the adjacent partition 9a, and the bent portion of the intermediate portion is adjacent to the partition 9a. 9a are arranged at predetermined intervals so as to enter between both end portions. One end of the smoke introduction path formed between the adjacent partition walls 9a communicates with the outside to serve as a smoke introduction port, and the other end communicates with the smoke detection chamber S. By bending the middle part of the smoke introduction path, External light is less likely to enter the smoke sensing chamber S.
[0025]
In the recess 10 surrounded by the bottom plate 7 and the side wall 8 of the optical base 3, the circuit board 2 is mounted with the surface on which the light emitting diode LED, the photodiode PD, and the thermistor 6 are mounted on the bottom plate 7 side. . On the bottom plate 7 of the optical base 3, projecting portions 19, 20 projecting downward at portions corresponding to the light emitting diode LED and the photodiode PD, respectively, are protruded, and these projecting portions 19, 20 have a bottom plate. 7, through holes 11a and 11b are formed. Grooves 19a and 20a are formed in each of the protruding portions 19 and 20 so as to be continuous with the through holes 11a and 11b and extend toward the center of the optical base 3, and light is emitted in the grooves 19a and 20a. The prism lenses 12 and 13 as optical members on the side and the light receiving side are attached. Here, the prism lenses 12 and 13 are attached to the optical base 3 with one surface facing the through holes 11a and 11b and the other surface facing the center of the smoke sensing chamber S. The upper side and both left and right sides of 13 are covered by the protruding portions 19 and 20. That is, the prism lenses 12 and 13 are arranged so that the respective optical axes L1 and L2 face the center direction of the smoke sensing chamber S and intersect at a predetermined angle as shown in FIG.
[0026]
As described above, the prism lenses 12 and 13 face the light emitting surface of the light emitting diode LED and the light receiving surface of the photodiode PD, respectively, and the light emitted from the light emitting diode LED is condensed by the prism lens 12 and irradiates the smoke sensing chamber S. Is done. When smoke enters the smoke sensing chamber S, the light emitted from the prism lens 12 is scattered by the smoke particles and enters the prism lens 13. The light that has entered the prism lens 13 is condensed on the light receiving surface of the photodiode PD by the prism lens 13, so that the intrusion of smoke can be detected from an increase in the output of the photodiode PD. Since the prism lenses 12 and 13 are arranged such that their optical axes L1 and L2 intersect at a predetermined angle, the light of the light emitting diode LED emitted from the prism lens 12 directly enters the prism lens 13. Never.
[0027]
Here, as shown in FIG. 8A, a portion of the labyrinth wall 9 (an optical trap portion 25 described later) located in front of the prism lens 13 on the light receiving side in the optical axis direction, and the prism lens on the light emitting side. A light-shielding wall 24 that shields light from the prism lens 12 is provided between the light-shielding wall 12 and the light-shielding wall 12. The light-shielding wall 24 is erected integrally from the bottom plate 7, and is arranged such that the surface facing the prism lens 12 on the light-emitting side is located outside the light-receiving area where the prism lens 13 on the light-receiving side receives light. I have. The light shielding wall 24 is disposed between the light trap section 25 and the prism lens 12 on the light emitting side, and light emitted from the prism lens 12 on the light emitting side is reflected by the light trap section 25 to form the prism lens 13 on the light receiving side. , The influence of stray light reflected by the labyrinth wall 9 can be reduced. In addition, the surface of the light shielding wall 24 facing the light emitting side prism lens 12 is located outside the light receiving area of the light receiving side prism lens 13, so that the light from the light emitting side prism lens 12 hits the light shielding wall 24. The light can be prevented from being incident on the prism lens 13, and the effect of stray light generated when the light from the light-emitting side prism lens 12 hits the light shielding wall 24 can be reduced.
[0028]
Further, between the prism lens 12 on the light-emitting side and the prism lens 13 on the light-receiving side, a columnar light-shielding wall 28 for shielding light from the prism lens 12 is provided. Light from the lens 12 is prevented from directly entering the prism lens 13 on the light receiving side. The light-shielding wall 28 is erected integrally with the bottom plate 7, and an insertion hole 11 c for inserting the thermistor 6 mounted on the circuit board 2 is formed through the light-shielding wall 28.
[0029]
By the way, the labyrinth wall 9 makes it difficult for outside light to enter the smoke detection chamber S by bending the middle part of the smoke introduction path, but as shown in FIG. The intruded external light D is reflected by the partition 9a, and the reflected light may be reflected again by the adjacent partition 9a and enter the smoke sensing chamber S. The reflected light may be received by the light receiving area of the prism lens 13 on the light receiving side. When the light enters B, a part of the disturbance light enters the prism lens 13, and the disturbance light may become stray light and malfunction.
[0030]
Therefore, in this fire detector, the two partition walls 9a which are located in front of the prism lens 13 on the light receiving side in the optical axis direction and are in the light receiving region B of the prism lens 13 are opposed to each other at the bent portions in the middle. So that the bent portion of the middle part between the two partition walls 9a is connected, and the external light that has entered between these two partition walls 9a does not enter the prism lens 13, thereby preventing malfunction due to the external light. ing. Further, by connecting the bent portions of the two partition walls 9a, the side pieces of the both partition walls 9a on the smoke sensing chamber S side have a substantially rectangular cross section and the opening is formed on the prism lens 13 on the light receiving side. An optical trap unit 25 is formed so as to face. As shown in FIG. 8A, the light trap portion 25 is formed in a substantially symmetrical shape with respect to the light receiving optical axis L2 of the prism lens 13 on the light receiving side, so that the light E reflected by the labyrinth wall 9 is formed. Is trapped by the optical trap unit 25. Therefore, the light E reflected by the labyrinth wall 9 is reflected by the labyrinth wall 9 located in front of the prism lens 13 on the light receiving side in the optical axis direction (that is, the portion of the optical trap portion 25), and enters the prism lens 13. Therefore, it is possible to prevent the light reflected by the labyrinth wall 9 from becoming stray light and malfunctioning. A protruding piece 26 protrudes in a direction substantially perpendicular to the side piece 25a on one side piece 25a of the optical trap portion 25, and a plurality of vertical grooves 27 protrudes on the other side piece 25b. Since the light incident on the light trap portion 25 is reflected by the protruding piece 26 or the vertical groove 27 and proceeds toward the opposite side piece 25b or 25a, the effect of trapping light is improved, and Malfunction can be further prevented.
[0031]
By the way, since the output current from the photodiode PD is very small and weak against external noise such as electrostatic noise, it is necessary to shield the photodiode PD from such external noise. Therefore, in the present embodiment, a box-shaped shield cover 14 having an open surface is insert-molded at the portion of the optical base 3 facing the photodiode PD, and when the circuit board 2 is placed in the recess 10, A shield cover 14 covers around the photodiode PD and the smoke detection circuit mounted on the circuit board 2, and electrostatically shields the photodiode PD and the smoke detection circuit. The shield cover 14 is provided with an earth pin 14 a protruding toward the circuit board 2. The earth pin 14 a is inserted into a through hole provided in the circuit board 2 and soldered to a ground line of the circuit board 2. Further, a communication hole 14b communicating with the through hole 11b is formed in the shield cover 14, and the light collected by the prism lens 13 through the communication hole 14b is applied to the light receiving surface of the photodiode PD. .
[0032]
Further, four terminal pins 15 are insert-molded on the optical base 3, and each terminal pin 15 is inserted into a through hole provided in the circuit board 2 and soldered, so that each terminal pin 15 is formed. The distal ends of the terminal pins 15 that are electrically connected to the wiring lines of the circuit board 2 and protrude from the circuit board 2 on the opposite side serve as external connection terminals. Further, the circuit board 2 is held on the optical base 3 by soldering the terminal pins 15 formed by insert molding on the optical base 3 to the circuit board 2.
[0033]
Here, a manufacturing process of the optical base 3 will be briefly described with reference to FIGS. First, as shown in FIG. 11, a hoop material 40 formed of a metal material in the shape of a strip is punched out, and the hatched portion in FIG. 11 is bent toward the inner side of the paper surface, and shown in FIGS. 12 (a) and 12 (b). As described above, the shield cover 14 is formed in a box shape, and the terminal pins 15 are projected in a direction substantially orthogonal to the plane direction of the hoop member 40. Thereafter, as shown in FIGS. 13A and 13B, the base portion including the bottom plate 7 and the side wall 8 is insert-molded (primarily molded) into the hoop material 40, and the labyrinth is formed as shown in FIGS. 14A and 14B. After secondary molding of the wall 9, the frame portion is cut to form a shape as shown in FIGS. Needless to say, the base portion composed of the bottom plate 7 and the side wall 8 and the labyrinth wall 9 may be insert-molded into the hoop member 40 at one time.
[0034]
As described above, since the shield cover 14, the terminal pins 15, and the optical base 3 are integrated by simultaneous molding (insert molding), the number of components can be reduced, and the workability of the assembling operation can be improved. . Further, the optical base 3 and the labyrinth wall 9 are integrated, so that the number of parts is reduced to improve the assembling workability, and the positioning accuracy between the labyrinth wall 9 and the optical base 3 is increased, thereby reducing stray light. Generation can be suppressed. Further, since the shield cover 14 and the terminal pins 15 are formed by punching and bending one sheet metal, the process of processing the shield cover 14 and the terminal pins 15 can be easily automated. The manufacturing cost can be reduced.
[0035]
Further, the insect repellent cover 4 is formed in a bottomed cylindrical shape from a synthetic resin having an insulating property. The bottom plate 4a of the insect repellent cover 4 is formed with a through hole 4d which communicates with the through hole 11c provided in the optical base 3 and through which the thermistor 6 mounted on the circuit board 2 is inserted. Are formed in a mesh portion 4c that opens in a lattice shape. The insect repellent cover 4 is attached to the optical base 3 with the lower end of the optical base 3 inserted into the cylinder, and the labyrinth wall 9 is covered by the peripheral wall 4b on which the mesh part 4c is formed. In addition, foreign substances such as insects can be prevented from entering the smoke sensing chamber S surrounded by the labyrinth wall 9. As shown in FIG. 7, the bottom plate 4 a of the insect-proof cover 4 faces upward (toward the optical base 3) at a position facing the protruding portions 19 and 20 provided on the bottom plate 7 of the optical base 3. Lids 21 and 22 that protrude and fit into grooves 19a and 20a provided in protruding portions 19 and 20 are integrally formed.
[0036]
Thus, when the insect cover 4 is put on the optical base 3, the lids 21 and 22 provided on the insect cover 4 are fitted into the grooves 19 a and 20 a provided on the optical base 3, respectively, and the emission of the prism lens 12 is performed. By surrounding the surface and the entrance surface of the prism lens 13 with the protruding portions 19 and 20 and the lid portions 21 and 22, it is possible to optically seal, so that extra light such as external light is incident. Malfunction can be prevented. A groove 23 running in a direction substantially orthogonal to the optical axis direction is formed in a portion of the bottom plate 4a of the insect repellent cover 4 located in front of the lid portion 22 in the optical axis direction, so that stray light is generated. Preventing. As described above, in the present embodiment, since the lids 21 and 22 as the light shielding members are integrated with the insect repellent cover 4, the number of parts can be reduced and the assembly workability can be improved, and the lids 21 and 22 can be improved. The positioning accuracy is improved as compared with the case where is formed separately from the insect repellent cover 4.
[0037]
On the other hand, the protective cover 5 is formed in a cylindrical shape with a bottom by a synthetic resin having elasticity, and an engaging claw 16 projecting outward is protruded from an upper end portion of the peripheral wall 5a. A plurality of strip-shaped openings 17 extending in the circumferential direction are opened, project upward from the bottom plate 5b, and a plurality of ribs 18 are provided at the tip portions of which are in contact with the bottom plate 4a of the insect cover 4. In a state where the fire detector is assembled, the thermistor 6 projects downward from the through hole 4d of the insect repellent cover 4, and the tip of the thermistor 6 is disposed between the bottom plate 4a of the insect repellent cover 4 and the bottom plate 5b of the protective cover 5. You. The plurality of ribs 18 are arranged radially around the thermistor 6 and rectify the flow of the air so that the air flowing into the inside from the opening 5c hits the heat-sensitive portion of the thermistor 6.
[0038]
Next, a circuit configuration of the fire detector will be described with reference to FIG. FIG. 16 is a block diagram of the smoke sensing circuit. The light emitting diode LED irradiates the smoke sensing chamber S with infrared light through the prism lens 12, and the scattering of infrared light emitted from the light emitting diode LED due to smoke. It comprises a photodiode PD that receives light via the prism lens 13, a light emitting and receiving circuit 50, a microcomputer (hereinafter, referred to as a microcomputer) 60, and a transmission circuit 61.
[0039]
The light emitting / receiving circuit 50 includes a light emitting current control circuit 51 for controlling a current flowing to the light emitting diode LED, and an I / V conversion circuit 52 for converting an output current of the photodiode PD into a voltage signal. Is amplified with a predetermined gain by the gain switching circuit 53, the voltage level is adjusted by the gain adjustment circuit 54, and the offset voltage is adjusted by the offset adjustment circuit 55, and then output to the microcomputer 60. The microcomputer 60 performs A / D conversion of the output of the light emitting and receiving circuit 50 and compares it with a preset threshold level. When the output of the light emitting and receiving circuit 50 exceeds the threshold level, the smoke density is reduced. An alarm signal indicating that the predetermined density has been reached is output to the transmission circuit 61, and the transmission circuit 61 transmits the alarm signal to a fire receiver (not shown) by a multiplex transmission signal. The light emitting and receiving circuit 50 includes a sensitivity adjusting circuit 56 that changes the output of the light emitting current control circuit 51 and selectively switches the gain of the gain switching circuit 53 according to a test signal input from the microcomputer 60. I have. Although not shown in FIG. 16, the output of the thermistor 6 is input to the microcomputer 60, and the ambient temperature is monitored from the output of the thermistor 6.
[0040]
Thus, as shown in FIGS. 17 and 18, the light emitting diode LED, the photodiode PD, the light emitting and receiving light are provided on the circuit board 2 formed of the printed wiring board in which the wiring pattern is insulated by the method described in the first or second embodiment. Components such as a circuit 50, a microcomputer 60, and a transmission circuit 61 are mounted. In the present embodiment, in order to increase the mounting density and reduce the size of the circuit board 2, an IC 70 constituting the photodiode PD, the light emitting / receiving circuit 50, the microcomputer 60, the transmission circuit 61, and the like is provided on the surface (the upper surface in FIG. 17). Are mounted on a bare chip, and other discrete components 71 are mounted on the back surface (the bottom surface in FIG. 17). Here, in the process of mounting the discrete component 71 on the back surface of the circuit board 2, it is necessary to heat the circuit board 2 when connecting the discrete component 71 to the wiring line 102 with solder or a conductive adhesive similar thereto. Since residues such as flux used for soldering and additives for conductive adhesives may spread on the mounting surface, IC 70 and photo, which require high cleanliness in order to ensure reliability, are required. It is necessary to mount the diode PD on a bare chip first.
[0041]
Here, a process of mounting the IC 70 and the photodiode PD on a bare chip by wire bonding will be briefly described. First, the IC 70 and the photodiode PD configured as a bare chip are fixed (die-bonded) at predetermined positions on the surface of the circuit board 2 by using an adhesive, and the IC 70 and the photo diode are thinned with gold or aluminum (diameter: 10 μm to 300 μm). An electrode formed on the surface of the diode PD and a pad (electrode) formed on the wiring line 102 are connected. Thereafter, the IC 70 and the photodiode PD are sealed with a sealing material 72 made of a synthetic resin in order to protect the IC 70 and the photodiode PD from the external environment. This sealing varies in form depending on the characteristics required for the IC 70, but is performed so as to cover the entire IC 70 unless a particularly high airtightness is required. The photodiode PD is sealed with a sealing material 73 made of a synthetic resin having a light-transmitting property. After the sealing of the IC 70 and the photodiode PD is completed in this manner, the discrete component 71 is mounted on the back surface of the circuit board 2 and connected to the pads formed on the wiring lines 102 using solder or the like. The through-hole 105 for cutting the unnecessary wiring line 102 is formed before the bare chip is mounted, and a sealing material 106 for sealing the through-hole 105 is used as a sealing material (synthetic resin) for sealing the IC 70. When the same material (for example, a thermosetting liquid epoxy resin) is used, the step of sealing the through-hole 105 and the step of sealing the IC 70 can be performed at the same time, thereby reducing the cost by simplifying the manufacturing process. In addition, there is an advantage that productivity can be improved. Further, as described in the first embodiment, if an epoxy resin having relatively high viscosity and thixotropic before curing and relatively high shape retention performance after curing is used for the sealing material 106, the necessary minimum Since the sealing can be performed by the area, the escape of the wiring pattern for preventing the sealing material 106 from being applied to the necessary wiring lines 102 or electrodes can be reduced, and the circuit board 2 can be downsized.
[0042]
By the way, since the strength of the circuit board 2 may be reduced by providing the through-hole 105, a through-hole may be provided at a place where such a reduction in strength needs to be avoided, for example, near a position where the IC 70 is wire-bonded. Unnecessary wiring lines 102 are cut by providing recesses 107 instead of 105 (see FIG. 18). When the unnecessary wiring line 102 is cut by providing the concave portion 107, unlike the through hole 105, there is no need to worry that the sealing material 106 goes around the back surface of the circuit board 2. The viscosity of the synthetic resin before curing and the permissible range of thixotropic properties are widened, and the choice of materials can be increased. Moreover, since the wiring lines 102 can be formed on the back surface of the circuit board 2 also on the back side of the concave portion 107, the degree of freedom of wiring patterning is increased, and the circuit board 2 is downsized, and the fire detector is downsized. be able to.
[0043]
【The invention's effect】
According to the first aspect of the present invention, a plurality of wiring lines connected to each other at a plurality of connection branches are formed on the surface of the printed wiring board, and unnecessary wiring lines are cut at a portion including any of the connection branches. In the method for insulating a wiring pattern of a printed wiring board, which obtains the wiring pattern and insulates a cut portion of the wiring line, an unnecessary wiring line is cut by providing a through hole penetrating the printed wiring board in a portion including the connection branch portion. In addition, the through hole is sealed with a sealing material made of a synthetic resin having an insulating property, and unnecessary wiring lines can be cut by a simple processing method such as punching and exposed to the through hole. Since the cut surface of the wiring line is sealed with a sealing material made of synthetic resin having an insulating property, the insulation of the cut portion of the wiring line is improved and the cut surface is cut. It is possible to prevent moisture deposition and corrosion may occur.
[0044]
According to a second aspect of the present invention, in the first aspect of the present invention, the sealing material is made of an epoxy resin having relatively high viscosity and thixotropic property before curing and relatively high shape retention performance after curing. By using epoxy resin as a sealing material, chemical resistance and heat resistance can be improved. In addition, the epoxy resin having a relatively high viscosity and thixotropic property before curing and having a relatively high shape retention performance after curing is used as the sealing material, so that the sealing material is formed around the through hole. The thickness of the sealing material can be increased, and the moisture resistance and corrosion resistance can be further improved.
[0045]
According to a third aspect of the present invention, in the first aspect, the sealing material is made of a urethane resin, and the chemical resistance can be improved by using the urethane resin as the sealing material.
[0046]
According to a fourth aspect of the present invention, a plurality of wiring lines connected to each other at a plurality of connection branches are formed on the surface of the printed wiring board, and unnecessary wiring lines are cut at a portion including any of the connection branches. In the method of insulating a wiring pattern of a printed wiring board for obtaining a wiring pattern and insulating a cut portion of a wiring line, an unnecessary wiring line is cut by providing a concave portion in a portion including the connection branch portion, and the insulating property is provided. The concave portion is sealed with a sealing material made of a synthetic resin, and a cut portion and a cut surface of the wiring line exposed in the concave portion are sealed with a sealing material made of a synthetic resin having an insulating property. It is possible to improve the insulation properties of the cut portion of the wiring line and to prevent the adhesion or corrosion of moisture on the cut surface. Also, since the concave portion for cutting unnecessary wiring lines does not penetrate the printed wiring board, when the printed wiring board is used as a mounting surface on both front and back sides, the sealing material protrudes and the wiring lines are contaminated. Does not occur.
[0047]
According to a fifth aspect of the present invention, in the fourth aspect, the sealing material is made of a light-transmitting synthetic resin, and the presence or absence of air bubbles inside the sealing material can be easily determined.
[0048]
According to a sixth aspect of the present invention, in the invention of the fourth aspect, the sealing material is made of urethane resin, and the chemical resistance can be improved by using the urethane resin as the sealing material.
[0049]
According to a seventh aspect of the present invention, there is provided a detecting means for detecting smoke, heat or flame due to a fire and outputting an electric signal, a signal processing circuit for processing an electric signal output by the detecting means and outputting the processed signal to the outside, And a printed circuit board on which at least circuit components constituting the signal processing circuit are mounted, wherein the wiring pattern is insulated by the method according to any one of 1 to 6, It is possible to provide a fire detector with improved corrosion resistance by using a printed wiring board in which the adhesion and corrosion of the printed wiring board are prevented.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a main part of a first embodiment after a through hole provided in a printed wiring board is sealed with a sealing material.
2 (a) is a plan view before a through hole is sealed with a sealing material, and FIG. 2 (b) is a cross-sectional view before the through hole is sealed with a sealing material. .
FIG. 3 is a cross-sectional view illustrating a main part of the second embodiment after a recess provided in a printed wiring board is sealed with a sealing material.
FIG. 4 is a cross-sectional view showing a main part of the above and showing a state in which bubbles are generated in a sealing material for sealing the concave portion.
FIG. 5 is an exploded sectional view showing a fire detector according to a third embodiment.
FIG. 6 is an exploded perspective view of the same.
FIG. 7 is a sectional view of the same.
8A and 8B show the optical base of the above, wherein FIG. 8A is a plan view and FIG. 8B is a cross-sectional view along AA ′.
FIG. 9 is a rear view of the optical base;
FIG. 10 is an enlarged view of a portion C of FIG. 8 showing the optical base same as the above.
FIG. 11 is an explanatory view illustrating a manufacturing process of the optical base.
FIGS. 12A and 12B are explanatory views illustrating another manufacturing process of the optical base according to the first embodiment.
FIGS. 13A and 13B are explanatory views illustrating another manufacturing process of the optical base according to the first embodiment.
FIGS. 14A and 14B are explanatory views illustrating still another manufacturing process of the optical base according to the embodiment.
FIGS. 15A and 15B are explanatory views illustrating still another manufacturing process of the optical base according to the embodiment.
FIG. 16 is a circuit block diagram of the above.
FIG. 17 is a side view of the circuit board in the above.
FIGS. 18A and 18B show the circuit board of the above, wherein FIG. 18A is a plan view after mounting and sealing components such as ICs, and FIG. 18B is a plan view before mounting components such as ICs.
[Explanation of symbols]
100 printed wiring board
102 Wiring line
104 connection branch
105 through hole
106 sealing material

Claims (7)

A plurality of wiring lines connected to each other at a plurality of connection branches are formed on the surface of the printed wiring board, and unnecessary wiring lines are cut at portions including any of the connection branches to obtain a desired wiring pattern and to perform wiring. In a method of insulating a wiring pattern of a printed wiring board for insulating a cut portion of a line, an unnecessary wiring line is cut by providing a through hole penetrating the printed wiring board in a portion including the connection branch portion, and the insulating property is provided. A method of insulating a wiring pattern of a printed wiring board, wherein the through hole is sealed with a sealing material made of a synthetic resin. 2. The wiring of the printed wiring board according to claim 1, wherein the sealing material is made of an epoxy resin having relatively high viscosity and thixotropic properties before curing and having relatively high shape retention properties after curing. Pattern insulation method. The method according to claim 1, wherein the sealing material is made of urethane resin. A plurality of wiring lines connected to each other at a plurality of connection branches are formed on the surface of the printed wiring board, and unnecessary wiring lines are cut at portions including any of the connection branches to obtain a desired wiring pattern and to perform wiring. In a method of insulating a wiring pattern of a printed wiring board for insulating a cut portion of a line, a sealing material made of a synthetic resin having an insulating property while cutting unnecessary wiring lines by providing a concave portion in a portion including the connection branch portion A method for insulating a wiring pattern of a printed wiring board, comprising sealing the recess. The method according to claim 4, wherein the sealing material is made of a synthetic resin having a light transmitting property. The method according to claim 4, wherein the sealing material is made of urethane resin. 7. A detecting means for detecting smoke, heat or flame due to a fire and outputting an electric signal, a signal processing circuit for performing signal processing on the electric signal output by the detecting means and outputting the processed signal to the outside, and any one of claims 1 to 6. A fire detector comprising: a printed circuit board on which a wiring pattern is insulated by the method described above and at least circuit components constituting the signal processing circuit are mounted.

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