JPH0455552B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for forming a film on an electronic circuit board and an apparatus used to carry out the method, and more specifically to a circuit incorporating a large number of electronic circuit components. The present invention relates to a method and apparatus for forming an insulating film on a substrate by airlessly spraying a molten resin onto the substrate.

(Prior art) Conventionally, acrylic resin has been applied to electronic circuit boards to form a film for insulation, moisture proofing, etc., and film coating or air spraying has been used as the method. It is being
As a film coating method, the Nordson film coating method manufactured by Nordson Corporation in the United States is well known, and in this method, as shown in FIG. 13b, molten resin is sprayed in a film form from a nozzle 200 to coat an electronic circuit board. It is something. The air spray method, as shown in FIG. 13c, is a method of coating by atomizing and spraying molten resin using compressed air.

(Problems to be Solved by the Invention) However, in the above-mentioned conventional technology, in the case of the film coating method, molten resin is coated in the form of a film, and as a result, a relatively large amount of resin is required to form the film. The film (film coat) is relatively thick, resulting in wasted amount of resin, and there are disadvantages in that so-called liquid drips occur after coating. Furthermore, the nozzle 200 is set at a height z so that the maximum width of the film matches the height of the circuit component surface.
Therefore, if the amount of movement in the z direction is large, the spray pattern width will become non-uniform and the coating film thickness will become non-uniform. There was a problem in that the coating film became excessively thick when the spray amount was controlled in the area.

Furthermore, since the resin is discharged from the nozzle in the form of a film, breaks 201 in the film may occur near the boundaries of the uneven parts of the part, as shown in FIG. 13b, and bubbles 2 may occur.
There was a problem in that areas were likely to be insufficiently coated, such as inclusion of 02. Furthermore, since it is applied in the form of a film, it cannot be applied sufficiently to the back surface of hollow supporting parts such as IC pins or lead wires, resulting in poor insulation or moisture proofing. Therefore, in order to deal with these inconveniences, a thicker coating film is required, which requires a larger amount of resin and solvent, and as a result, more liquid drips are likely to occur. There is also the inconvenience that the substrate cannot be turned over, and on the other hand, when the maximum width of the film is made small in order to prevent the film from breaking, there are also inconveniences such as a longer working time.

On the other hand, in the case of the air spray method, it is necessary to extremely reduce the viscosity of the molten resin in order to atomize and spray the molten resin with compressed air.As a result, the amount of solvent consumed increases and the coating film thickness increases with one spray. In some cases, it was not possible to obtain a sufficient thickness, and the drying and spraying steps had to be repeated many times to obtain the desired thickness. Furthermore, when blowing off the resin attached to the nozzle tip with air, so-called stringing tends to occur.
There were also some inconveniences, such as unevenness on the coated surface, which reduced marketability. In particular, in the case of the air spray method, it is necessary to mask areas that should not be coated, such as LEDs (light emitting diodes), in advance because of the atomized spray, which poses the problem of requiring an extra work process. .

SUMMARY OF THE INVENTION It is therefore an object of the present invention to overcome the above-mentioned drawbacks of the prior art and to provide a coating of desired thickness without uneven coating or dripping and with minimal consumption of resin and solvent. It is an object of the present invention to provide a method and an apparatus for forming a film on an electronic circuit board, which can be used to form a film on an electronic circuit board, and also eliminates the need for mask work because the spray pattern does not spread.

(Means and effects for solving the problem) In order to achieve the above object, the method for forming a film on an electronic circuit board according to the first invention includes a step of positioning the electronic circuit board at a predetermined position, and an insulating resin agent. 50
It is melted to a viscosity of 23 to 44 cps under the temperature condition of 30°C, and is pressure-fed to an injection nozzle with a cat-eye hole shape while adjusting the pressure to 3 to 5 kg/cm ² , and is sprayed onto the positioned electronic circuit board into a roughly elliptical plane. a step of airlessly spraying while moving so as to draw a shaped spray pattern and with its long axis substantially parallel to the board traveling direction; and a step of drying the electronic circuit board after the airless spraying. It is structured as follows.

Further, the film forming apparatus for electronic circuit boards according to the second invention includes a transport rail that receives the electronic circuit board, moves along the transport rail, and transports the electronic circuit board to a spraying position and a subsequent drying position. It is equipped with a transport claw that fixes the electronic circuit board at the injection position, an abutting clamp that fixes the electronic circuit board at the injection position, and a movable nozzle hole shape that is roughly cat's eye.
Melted to 23~44cps and pressure 3~ through regulating means
The insulating resin agent held at 5 kg/cm ² is sprayed airlessly onto the substrate while moving it so as to draw a roughly elliptical spray pattern in plan, with its long axis being roughly parallel to the direction in which the substrate travels. an injector, and
and a heater that heats and dries the electronic circuit board that has been transported to the drying position via the transport claw that is sprayed airlessly.

(Embodiments) Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. For convenience of understanding, the second invention, the device, will be explained first.

Figure 1 shows the overall configuration of this device. As shown in the figure, this apparatus consists of a conveyance section A, a model discrimination section B, a first injection section C, a reversing section D, a second injection section E, an initial drying section F, and a second drying section G. Furthermore, this device is equipped with a control unit 10 consisting of a computer,
Each part of this apparatus operates in response to control commands according to a program stored in the control unit 10. This will be explained below.

The transport section A is composed of rails 12 and transport claws 14, and carries an electronic circuit board 16 (hereinafter abbreviated as "board") attached to the housing of an electronic control unit of an automobile, etc., by placing it on the rails 12 and transporting it. It is configured to be pushed by a claw 14. As will be described later, the conveying claw 14 rises from the rest position below the rail 12 in response to a command from the control unit 10 and picks up the substrate 16 on the rail 12.
It is configured so that it moves forward a predetermined distance and is pushed forward, then descends and then moves back to return to the rest position.
Incidentally, illustration of a driving means such as a motor for driving this conveying claw 14 is omitted.

The model determination section B includes a light transmission sensor section 18.
As shown in the figure, the sensor section 18 is installed on the side of the rail 12, and is composed of three light receiving elements 18a, 18b, and 18c such as phototransistors that receive light from a light source (not shown). . The three light-receiving elements are arranged in parallel in the direction of board movement.
The output is varied depending on the state of blocking of transmitted light due to the shape of the housing in which the board is attached, and the signal line (not shown)
is sent to the control unit 10 via. Therefore,
The control unit 10 can determine the type of board from the output.

The first injection part C includes an abutting clamp 20 and a restraining clamp 22, as shown in FIG. 3b,
Both clamps 20 and 22 are configured to press the substrate 16 transferred via the transfer claw 14 from both sides and fix it in a predetermined position. FIG. 5 shows details of the abutting clamp 20 (holding clamp 22), including outer cases 20a, 22a and inner cases 20b, 22b accommodated therein.
The rods 20c and 22c are attached to the tip of the inner case, and when compressed air or hydraulic pressure is sent from a power supply source (not shown) in response to a command from the control unit 10, the inner case 20
b, 22b forward and rods 20c, 22c
is configured so as to come into contact with the casing to which the board 16 is attached. Note that FIG. 1 is shown in a simplified manner for convenience of illustration. The first injection section C further includes an injection mechanism 26. The injection mechanism 26 includes an X-axis arm 28 that is movable in the substrate advancing direction, a Y-axis arm 30 that is attached perpendicularly to the arm 28 and that is movable in the transverse direction, and an injector that is attached to the Y-axis arm 30. Consists of 32. As shown in FIG. 1, the injector 32 is connected to a resin tank 36 via a pressure-feeding pipe 34, and the resin tank 36 contains a mixture of an acrylic resin for insulation and a solvent consisting of toluene/xylene. There is. A pump 40 that operates by receiving driving force from compressed air or the like from a drive source 38 is inserted into the pressure-feeding pipe 34 that connects the resin tank 36 and the injector 32, and pressurizes the resin in the resin tank 36 to a predetermined pressure. and pressure-feeds it to the injector 32. A surge tank 4 is installed in the pressure feed path.
1 is provided to remove the pulsation of hydraulic pressure generated by the pump 40 and supply resin at a constant hydraulic pressure. Furthermore, a heater 42 is inserted in the pressure feeding path to control the temperature, more specifically, the viscosity, of the pumped resin to a set value, and a regulator 44 is inserted to control the liquid pressure at a constant level. Further, a return side pipe 46 is connected to the injector 32 in parallel with the pressure-feeding side pipe 34, and the molten resin flows through both pipelines 34, 46.
The injector 32 is configured to circulate through the injector 32 via the injector 32. Incidentally, reference numeral 48 indicates a filter, and reference numeral 5 indicates a filter.
0 indicates a distributor. Further, an exhaust duct 52 is provided below the rail 12 to recover toluene and the like contained in the molten resin. Although not shown, in this device, the upper part of the rail 12 is covered with a housing and is isolated from the outside air.

Here, the above-described injection mechanism 26 will be further explained with reference to FIGS. 6 to 10. As shown in FIG. 7, the X-axis arm 28 includes a slider 28b connected to a threaded rod 28a by a ball screw. The slider 28b is moved by the threaded rod being rotated by the rotation of a servo motor 28d connected via a coupling 28c. As shown in phantom lines in the figure, the Y-axis arm 30 is attached to the slider 28b of the X-axis arm 28, and the above-mentioned injector 32 is attached to the slider 30b of the Y-axis arm 30 via the attachment member 54. Ru. FIG. 8 is a sectional view showing the details of this injector 32, in which a piston rod 32a is accommodated, and a valve 32b is disposed at the tip of the piston rod 32a.
is provided. The spring 32c biases the valve 32b in the closing direction via the piston rod 32a, and when the solenoid valve 32d opens and compressed air is supplied from the air supply source 32e, the valve 32b is pushed upward and the circulating resin flows through the passage. 32f, and is injected from the cat eye 32h of the nozzle 32g. FIG. 9 is a front view of the nozzle 32g viewed from the substrate 16 side in FIG. 8. The cat eye 32h is formed in the shape of a long hole as shown in the figure, and has a slightly larger diameter in the width direction near the center. Moreover, FIG. 10 shows the injection pattern.

Returning to the description of the entire apparatus, the reversing section D includes a reversing mechanism 60 as shown in FIG. 12 (omitted in FIG. 1 for convenience of illustration). The reversing mechanism 60 includes plate bodies 62, 6 arranged oppositely on both sides.
2 and rotary disks 64, 64 which are rotatable from the plate body and similarly arranged opposite to each other. As shown, circular and I-shaped openings are bored in the plate body 62 and the rotating disk 64, and rails 12a are spanned over appropriate positions of the I-shaped openings on the rotating disk side. Note that this rail 12a is cut and separated from the rails 12 before and after the reversing portion D. Further, a pulley 66 is provided on the side of the rotating disk 64, and a belt 68 is stretched around the motor 7.
When the pulley 66 rotates in accordance with the rotation of the rail 12a, the substrate 16 on the rail 12a is rotated accordingly. In addition, the reference numeral 72 indicates a limit switch, and the reference numerals 74 and 74 indicate protrusions, and when the protrusion 7 is in a predetermined position during rotation, that is, at a position rotated by 180 degrees,
4 comes into contact with a limit switch 72 to stop rotation. In addition, when rotating, rail 1
The substrate 16 on 2a is fixed from both sides via restraint means (not shown).

The second injection section E has substantially the same configuration as the first injection section C described above. That is, it similarly includes an abutting clamp 78 and a holding clamp 80, as well as an X-axis arm 82, a Y-axis arm 84, and an injector 86, and the injector 86 is connected to the pressure-feeding pipe 8.
8 and a return pipe 90. Note that the reference numeral 92 indicates a filter, and the reference numeral 94 indicates an exhaust duct. Here, to further explain the resin return path, the return side pipes 46 and 90 of both injection parts are connected to a three-way valve 87 via a distributor 50 and a filter 92. By means of this three-way valve 87, the returned resin returns to the pump 40 through a branch path 89 and is sent out again during normal times, and returns to the resin tank 36 through a branch path 91 when liquid is drained such as when work is stopped.
Note that the valve 87 is closed when the apparatus is stopped. A back pressure regulator 93 is provided in the branch path 89, and controls the pressure of the return resin to ensure the injection pressure from the nozzle. Further, reference numeral 95 indicates a regulator which has the same configuration as the regulator 44 for the first injection part C and has a set pressure of 3 to 5 kg/cm ² .

The initial drying section F includes heaters 96, 96, which are installed at appropriate positions on the substrate 16 to blow warm air onto the substrate 16 to initially cure the coated surface. Also, heaters 96, 96
Fans 97, 97 are provided at the back of the rail 12 to supply fresh air, and hot air is sucked through a blower (not shown) provided on the side of the rail 12.

The second drying section G is equipped with a belt conveyor 104 composed of rollers 100, 100 and an endless belt 102 stretched between them, and a suitable number of box-shaped cups 106 are mounted on the endless belt 102. be done. The cup 106 is configured to partially house the substrate 16 therein and hold the substrate 16 in an inverted position on top of the conveyor belt. The reason why the substrate 16 is turned upside down is to reduce the space it occupies in the transport direction. or,
At the top of the belt conveyor 104, fans 108a, 108b, 108c,
108d are arranged in parallel, and fan 1
A heater 110 is provided below 08a.
Note that the reference numeral 112 indicates a controller that controls the temperature of the heater 110, and the reference numeral 114 indicates an exhaust duct.

Next, the first invention, the film forming method, will be explained while explaining the operation of the present apparatus. Figure 2 shows the flowchart of the control unit 10 that controls the operation of this device.
FIG. 3 is a process diagram showing an embodiment of the first invention.

The operation of this apparatus will be explained according to the flow chart in FIG. 2. In step 130, the board 16 is transported by the transport claws 14 on the rail with its component mounting side facing up. As shown in a, the model is first determined by the light transmission sensor section 18. In this case, three pairs of light receiving elements 18a, 18
The outputs of b and 18c are as shown in FIG. 4, for example, and three types of substrates can be distinguished from these output results. In the figure, "0" indicates no output from the light receiving element, and "1" indicates output. In particular, the output of the light receiving element 18a is also used to determine the presence or absence of the substrate 16.

After the model discrimination is completed, the substrate 16 is then pushed to the first injection section C by the transport claw 14 in step 132. The substrate 1 at the first injection part C
6 is pressed and positioned by the abutting clamp 20 and the holding clamp 22 from a direction perpendicular to the conveyance path (step 134). In this case, since the conveying claw is in contact with the rear of the substrate 16, it is fixed in a predetermined position by being pressed from the side by the rods 20c, 22c of both clamps.
Note that the protruding pressure of the protruding clamp 20 is relatively large,
The holding clamp 22 is set relatively small. In this case, the fixed position is determined in step 13.
Control unit 1 according to the board model determined by 0
Determined by the storage program of 0.

Next, in step 136, molten resin is injected onto the component side of the substrate 16 via the injection mechanism 26. In this case, the acrylic resin and the solvent (toluene or xylene) are mixed in the resin tank 36 at a ratio of 1:1, and by setting the temperature of the heater 42 to 50°C, the viscosity of the resin is increased from 23°C to 23°C.
The injection pressure from the injector 32 is set to 44 cps, preferably around 36 cps, and the injection pressure from the injector 32 is 3 to 5.
Kg/cm ² , preferably around 4 Kg/cm ² , so the injector 32's cat eye 32h
The molten resin discharged is sprayed in the form of atomization, as shown in FIG. 13a. In the case of the formal method according to the present invention, compared to the conventional air spray method, spraying is performed without the aid of compressed air, so the spray pattern is relatively narrow as shown in FIG. 10, and mask work is performed. Moreover, compared to conventional film coating methods, the coating film thickness can be made relatively thin, and the spray can be applied sufficiently to the back side of the hollow support portion by spreading the spray around. What is characteristic here is that at a temperature of 50℃
Regulator 44 melts the resin at 23~44cps,
Since the resin is discharged from the cat eye 32h of the injector 32 while regulating the pressure to 3 to 5 Kg/cm ² through the injector 95, the pressure is increased at the constricted portions at both ends of the cat eye 32h, and tension is generated between the resin particles. As shown in the figure, a film is formed around the resin being sprayed. This film is thickest near the exit of the cat eye 32h and becomes thinner as it descends, and when it descends about 40 mm, the tension between the particles is lost and the particles are dispersed into an atomized state. FIG. 13a is an explanatory cross-sectional view of the jetting state before the jetting pattern shown in FIG. 10 is formed, viewed from the direction perpendicular to the long axis, that is, from the lateral direction. Although the thickness is thinner than that, it is also formed around the long axis direction,
The atomized resin is enclosed inside to prevent it from scattering. The thickness of the film is approximately several hundred microns. In this case, the injection mechanism 26 moves according to the stored program in the control unit 10, and the injector 32
As shown in FIG. 11, the cat eye 32h (or nozzle 32g) moves reciprocatingly in the direction perpendicular to the rail 12 while keeping the long axis of the cat eye 32h parallel to the direction in which the board 16 advances (or in the backward direction).
, and injects the molten resin onto the substrate 16 from the same appropriately set height, for example, 40 mm or more.
Although the height of the nozzle is not controlled in this embodiment, it is of course possible to adjust the height direction. During this airless spraying, the moving speed and pitch "p" (Fig. 11) of the nozzle are controlled according to the amount of coating per unit area, in other words, the effective area of the coating. Part 12
At 0, injection is stopped. The purpose of stopping the injection in this manner is to avoid overcoating on the moving path and prevent waste of resin or occurrence of liquid dripping. In addition, the moving speed and moving pitch p of the nozzle may vary depending on the size (height) of the parts and the high integration density, or insulated parts such as CPUs, connectors, etc.
The speed should be slowed down or the pitch p should be narrowed at locations where there are parts that are highly important for preventing moisture leaks.

Next, in step 138 shown in FIG. 2, it is confirmed that the coating on the component side of the board 16 is completed, and then in step 140, the rods 2 of both clamps are
0c and 22c are separated from the substrate 16 and the positioning state is released. Subsequently, the substrate 16 is transported in the advancing direction by the transport claw 14, and the substrate 16 is transferred to the reversing mechanism 6 of the reversing section D.
0 and rotated half a turn, with the solder side facing upward (steps 144 and 146). FIG. 3c shows this situation. That is, since the coating is applied to only the minimum necessary thickness by airless spraying, it can be reversed immediately after application.

When the reversing operation is completed, the transport claw 14 is raised as the reversing mechanism 60 stops, and the substrate 16 is transferred to the reversing mechanism 6.
0 and transferred to the second injection section E (step 148). At this position, the same operation as in the first injection section described above is performed, and positioning and injection are performed (steps 150 and 15).
2). Figure 3d shows this situation. Next, when it is confirmed that the solder side coating is completed (step 15)
4), both clamps 78 and 80 are retracted, and the board 16
The positioning of the substrate 16 is released (step 156), and the substrate 16 is transferred to the initial drying section F (step 15).
8). Note that the application order may be such that the solder side is applied first and the component side is applied last.

In this initial drying section F, as shown in Figure 3e,
Heating and drying is performed by drawing in outside air using the fan 97 and heater 96, and the coated surface is initially cured. (Step 160).

When this initial drying is finished, the substrate 16 is transferred to the transport claw 1
4 to the second drying section G, and the tip thereof is inserted into the cup 106 as shown in FIG. 162). In this state, first the heater 110 and the fan 108a
The heated air is blown and the substrate is heated and dried. Then three fans 108b, 108
c and 108d to dry at room temperature (step 164). Note that the drying time in this second drying section G is, for example, 13 minutes. As mentioned above, since the coating is applied to the necessary minimum thickness by airless spraying, dripping does not occur even if the coating is left upside down for a long period of time with only a short period of initial drying. Figures 3g and 3h show this state. Finally, as shown in FIG. 3i, the substrate 16 is taken out from the belt conveyor to complete the process (step 166). In addition, cup 10
If you create an opening on the side of 6 to increase ventilation,
It is convenient because it can accelerate drying.

In the above embodiment, the type determination of the electronic circuit board 16 was performed only before the first injection part, but the invention is not limited to this, and it may be performed at a position after positioning is completed. It can be executed again after the positioning is completed before the section E, thereby making it possible to reconfirm the model when restarting the work after the work has been temporarily interrupted, and it is possible to avoid erroneous application.

(Effects of the Invention) As described above, the present invention performs airless spraying while allowing a film to be formed around the atomized resin so as to surround the atomized resin and prevent it from scattering while spraying the resin agent onto an electronic circuit board. Because of this structure, there are no inconveniences such as dripping, coating leakage, or inclusion of air bubbles, and the required thickness can be coated with the minimum amount of resin and solvent consumed, and the work time can be reduced. It has the advantage that it can be shortened. In addition, even if there are irregularities on the component mounting surface for atomizing and applying resin, it has the advantage of being able to reliably apply the coating to the side surfaces or the back surfaces of hollow support parts such as IC pins. Since the pattern does not spread unnecessarily, there is no need for mask work, which has the advantage of simplifying the coating process. In addition, since the spray pattern is designed to draw a spray pattern that is approximately elliptical in plane, and to spray airlessly while moving so that its long axis is approximately parallel to the direction in which the substrate travels, for example, Compared to the case of moving spray while drawing a circular spray pattern consisting of
Even when coating from row to row in the movement trajectory shown in the figure, there is little overlap between coated films, so
Coating unevenness can be reduced.

[Brief explanation of drawings]

FIG. 1 is an explanatory perspective view showing the overall configuration of a film forming apparatus for an electronic circuit board according to the second invention, and FIG. 2 is a flowchart showing the control operation of a control unit in the apparatus.
Chart, Figures 3a to 3i are explanatory process diagrams showing an embodiment of the method of forming a film on an electronic circuit board according to the first invention, Figure 4 is an output diagram of a light transmission sensor showing model discrimination operation, and Figure 5 is a diagram showing an example of a method for forming a film on an electronic circuit board according to the first invention. Fig. 6 is an explanatory cross-sectional view showing the structure of the support clamp (holding clamp), Fig. 6 is an explanatory perspective view showing the outer shape of the injection mechanism, and Fig. 7 is an explanatory cross-sectional view showing the structure of the presser clamp.
Fig. 8 is an explanatory cross-sectional view of the injector, Fig. 9 is a front view of the nozzle of the injector, Fig. 10 is an explanatory view of the injection pattern, and Fig. 11 shows the movement locus of the nozzle. Explanatory diagram, 12th
The figure is an explanatory perspective view showing details of the reversing mechanism and the 13th figure.
Figures a to c are explanatory diagrams showing airless injection in the present invention in comparison with the prior art. 10...Control unit, 12...Rail, 14
...Conveyance claw, 16...Electronic circuit board, 18...Light transmission sensor section, 26...Injection mechanism, 32...Injector, 32g...Nozzle, 36...Resin tank, 86...Injector, 96... Heater, 1
04... Belt conveyor, 106... Cup, 1
08a, 108b, 108c, 108d...fan, 110...heater, A...conveying section, B...model discrimination section, C...first injection section, D...reversing section, E
...Second injection section, F...Initial drying section, G...Second
drying section.

Claims (1)

[Claims] 1 a. A step of positioning the electronic circuit board at a predetermined position; b. A step of adjusting the insulating resin material to a viscosity of 23 to 23 at a temperature of 50°C.
It is melted at 44 cps, and while adjusting the pressure to 3 to 5 kg/cm ² , it is force-fed to an injection nozzle equipped with a cat-eye hole shape, so as to draw an approximately elliptical spray pattern in plan on the positioned electronic circuit board. and (c) drying the electronic circuit board after the airless spraying. Method of forming a film on a circuit board. 2 a: a transport rail that receives the electronic circuit board; b: a transport claw that moves along the transport rail and transports the electronic circuit board to the spraying position and a subsequent drying position; c: fixes the electronic circuit board at the spraying position. d A movable abutment clamp with a roughly cat's-eye nozzle hole shape, and a viscosity of 23 to 23 at a temperature of 50°C.
Pressure 3-5 through regulating means melted to 44cps
The insulating resin agent held at Kg/cm ² is sprayed onto the substrate in such a way as to draw a roughly elliptical spray pattern in plan.
and an injector that sprays airlessly while moving so that its long axis is approximately parallel to the direction of board movement; An apparatus for forming a film on an electronic circuit board, comprising: a heater for drying; 3. The film forming apparatus for an electronic circuit board according to claim 2, further comprising a discriminating means for discriminating the type of the electronic circuit board before the injection position.