JPH03217072A - Mounting method for electronic component on printed circuit board - Google Patents

Abstract

PURPOSE:To obtain a parts-mounting method which enables the amount of adhesive to be controlled easily without being controlled by the surface condition of a printed circuit board and uses an adhesive dispersing method for securing a certain amount given constantly by providing the adhesive onto the printed circuit board from a pressurized supply bath through a tube, a opening/closing valve, and a nozzle. CONSTITUTION:In a method for mounting electronic components onto a printed circuit board 7 where an adhesive is provided at a specified part where electronic components of the printed circuit board 7 are to be mounted, the electronic components are tentatively fitted onto a part where the adhesive is provided, and then soldering is made between an external terminal of the electronic component and a specified conductor of the printed circuit board, the above adhesive is given onto the printed circuit board 7 from a supply bath 2 through a conduit 3, an opening/closing valve 4 which is connected to the tube 3, and a nozzle 5, the above supply bath 2 is pressurized fully so that a liquid drip 6 of adhesive is injected from the nozzle 5 through opening of the opening/closing valve 4, and the amount to be injected can be adjusted by controlling the opening time of the opening/closing valve 4.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for mounting electronic components on a printed circuit board, and more specifically, to a method for mounting an electronic component on a printed circuit board by applying an adhesive to the printed circuit board in advance. Concerning a method for dispensing only a fixed amount.

[Prior art and its problems] To mount small electronic components on a printed circuit board, the electronic components are temporarily attached to a predetermined position on the printed circuit board with adhesive, and then soldered using reflow soldering to connect the electronic components and wiring. Fixing and electrically connecting conductors is widely practiced. Various methods are used to automatically carry out this process, but basically a large number of electronic components are temporarily attached onto a horizontally placed printed circuit board using an automatic mounting device.
The printed circuit board is then turned over so that the electronic component side faces downward, and the entire printed circuit board is brought into contact with the flowing solder.

Therefore, the adhesive used for temporary bonding must have sufficient adhesion or adhesion to prevent the electronic components from moving even if the printed circuit board is turned over. The requirements for this are various factors, but the main ones are the viscosity and tackiness of the adhesive, the reproducibility and adjustability of the dispensed amount from shot to shot of the adhesive dispenser, and the (no stringiness coming out of the dispenser), etc. Another requirement is the ability to easily reorient the electronic components when they are improperly oriented. This is in some ways inconsistent with the above requirements.

A commonly used method involves gently extruding a thermosetting adhesive such as epoxy through the nozzle of a pneumatic dispensing device, holding it at the tip of the nozzle, and pressing it against a predetermined position on a printed circuit board to release the adhesive. There is a method of transferring onto a substrate, temporarily attaching electronic parts, and curing (JP-A-55-110097, JP-A-61-268375).
Publication No.). There is also a method that is equipped with a coating bottle and applies adhesive from a container containing adhesive to the tip of a coating pin, moves and transfers it onto a substrate, temporarily attaches electronic components, and hardens it (Utility Model Publication No. 57-12783). issue). However, with these methods, the amount of adhesive dispensed is almost determined by the nozzle diameter, coating bottle diameter, adhesive viscosity, etc., and the amount cannot be controlled. To depend on the state,
Variations due to the unevenness and surface condition of the printed circuit board,
There is a problem in that it is difficult to secure a fixed amount. An even bigger problem is that the viscosity of thermosetting adhesives varies over time, requiring frequent adjustments to the dispenser extrusion pressure to maintain a constant dispensing amount. Another problem is that the orientation of the electronic component cannot be corrected because the adhesive has hardened. Note that if the adhesive is thermoplastic, there are problems such as not being able to obtain sufficient component holding power when the printed circuit board is turned upside down and exposed to flow soldering, so the viscosity must be increased. If the viscosity is increased, it becomes impossible to extrude it from the dispenser, so no practical solution has been proposed so far.

Dispensing methods that can avoid the drawbacks of such contact-type dispensing devices are being researched, but one proposal is a non-contact method that repurposes the inkjet method traditionally used in printers. (Unexamined Japanese Patent Publication No. 63-2286
Publication No. 99). However, in the inkjet method, the adhesive is made into fine particles by the action of an electric field and is sprayed, so only minute droplets (about 10-8 cc) can be obtained. Since it takes a long time for the adhesive to adhere to the surface, it seems impossible to put it into practical use at present.

Therefore, a dispensing method that uses a thermoplastic adhesive with sufficient adhesive strength, is not influenced by the surface properties of the printed circuit board, can easily control the dispensing amount, and can always ensure a constant dispensing amount is desired. It will be done.

[Object of the Invention] The object of the present invention is to provide a component mounting method using a dispensing method that is not influenced by the surface properties of a printed circuit board, that allows easy control of the dispensing amount, and that can always ensure a constant dispensing amount. It is about providing.

Another object of the present invention is to use a thermoplastic adhesive with sufficient adhesive strength, so that the dispensed amount can be easily controlled without being influenced by the surface properties of the printed circuit board, and a constant dispensed amount can always be ensured. The purpose of this invention is to provide a component mounting method using a dispensing method.

[Summary of Structure and Effects of the Invention] The present invention provides a method for applying an adhesive adhesive to a predetermined location where an electronic component is to be removed on a printed circuit board, temporarily attaching the electronic component to the location where the adhesive is applied, The present invention relates to an adhesive dispensing method used in a method for mounting an electronic component on a printed circuit board, which comprises then applying solder between the external terminal of the electronic component and a predetermined conductor of the printed circuit board. As a feature of the present invention,
Adhesive adhesive is supplied from a supply tank pressurized to a constant pressure through a conduit,
an adjustable valve in the conduit and then an elongated nozzle for dispensing onto the printed circuit board, the supply reservoir being such that droplets of adhesive are ejected from the nozzle upon opening of the control valve; It is pressurized to a sufficient pressure and the dispensed amount is regulated by controlling the opening time of the control valve. According to this method, a controllable predetermined dose can be easily and stably obtained.

Preferably, the valve comprises a valve chamber communicating with the outlet of the conduit and communicating with the inlet of the nozzle, a movable valve body within said valve chamber which abuts and closes the inlet end of said nozzle, and responsive to an activation signal. and means for separating the movable valve body from the nozzle inlet end for a predetermined period of time. According to this valve structure, when the valve is opened and closed using an electromagnetic solenoid, an amount of adhesive proportional to the opening time can be released from the nozzle due to the pressure in the supply tank, and the supply tank is set to a sufficiently large capacity. By doing so, you can always ensure a constant dosage.

More preferably, the adhesive is selected from silicone adhesives or acrylic silicone emulsion adhesives. According to this, not only can a sufficient holding force be obtained for the electronic component bonded to the inverted printed circuit board, but also the direction of the electronic component can be changed when necessary. Note that Acrylic silicone emulsion adhesive is preferable because it causes less stringiness.

[Specific description of the invention] The present invention will be explained in detail below with reference to the drawings.

First, with reference to FIGS. 1 to 4, a method of dispensing adhesive onto a printed circuit board using a jet dispenser according to the present invention, and then mounting electronic components on the printed circuit board will be explained. do.

First, as shown in FIG. 1, a predetermined amount of adhesive 5 is dispensed drop by drop at a predetermined position on the surface of a printed circuit board 6 using a dispensing device (dispenser) 1 which will be described in detail later. The dispensing device 1 comprises an adhesive supply tank 2 pressurized to a constant pressure, a conduit 3 extending therefrom, a solenoid valve 4 connected to the conduit, and a nozzle 5 for discharging the adhesive. The solenoid valve 4 is an on-off valve (described in detail later) whose opening/closing time can be adjusted, and a droplet 6 of the supplied pressurized adhesive is applied to the nozzle in an amount proportional to the set opening time of the on-off valve. 4 and fly to a predetermined position on the printed circuit board 7.

The amount of droplets depends on the viscosity of the adhesive, the pressure, and the flow resistance of the nozzle 5 (
The resistance depends on the nozzle cross-sectional area (proportional to the nozzle cross-sectional area and inversely proportional to the length). The amount of adhesive droplet 6 is about 10-cc, which is much larger than that of the conventional one-type jet printer method, and each droplet is sufficient to support the electronic component. I can do it.

Next, as shown in FIG. 2, the adhesive droplet 6 is blown with dry air from a hot air blower 8 to evaporate the solvent and dry the adhesive until it has the adhesive strength necessary to hold the electronic component.

Moving to the process shown in FIG. 3, a predetermined electronic component 9 is allocated and mounted at a predetermined position and is pressed against the adhesive droplet 6, thereby completing the mounting or temporary attachment of the electronic component.

In the process shown in FIG. 4, the printed circuit board 7 is turned upside down,
When the side on which the electronic component 9 is mounted is brought into contact with the flowing solder 10, the necessary connection and fixation between the external terminal of the electronic component 9 and the printed wiring on the printed circuit board 7 is performed.

The important points in the above method are that the amount of adhesive dispensed (the amount of droplets) does not change over time and can be stably supplied, and that the amount of dispensed satisfies the specified amount required to hold the electronic components. The present invention satisfies at least one of these points. A preferable requirement is that if the orientation of the electronic component changes for some reason after it is mounted, the orientation of the component can be corrected.

Some of these requirements can also be achieved by using known thermosetting or thermoplastic adhesives that have been used for conventional mounting of electronic components, and the present invention also includes this case. However, most or all of these effects can be achieved by carrying out the above mounting method using a silicone adhesive or an acrylic silicone emulsion adhesive, which is more preferably a thermoplastic adhesive. Note that Acrylic silicone emulsion adhesive is preferable because it has fewer strings. These adhesives have sufficient fluidity upon dispensing and can be easily reduced to droplets under pressure. When the solvent in the droplets is evaporated, it exhibits sufficient adhesion or holding power even under the action of heat during soldering, but is still soft enough to change the orientation of electronic components.

11 Next, the adhesive dispensing device 1 used in the adhesive dispensing process shown in FIG. 1 will be explained with reference to FIGS. 5 and 6.

Referring to FIG. 5, the supply tank 2 of the adhesive 11 is connected to the solenoid valve 4.
is maintained at a predetermined constant pressure so that a droplet of adhesive is ejected from the nozzle 5 by opening of Retained. The capacity of supply tank 2 is nozzle 5.
It is set to be sufficiently thicker than the volume of the tank so that even if the liquid level of the adhesive in the tank fluctuates, the dispensed amount will not be affected.

The adhesive 11 is then led from the conduit 3 to the solenoid valve 4 . A fixed amount of adhesive metered in the solenoid valve 4 is discharged from the nozzle 5. Preferably, the nozzle 5 has a cap 13 to prevent volatilization of the solvent in the adhesive when the device is not in use. Furthermore, in order to prevent the tip of the nozzle 5 from drying out when the nozzle 5 is not in use, it is preferable that the tip of the nozzle 5 is constantly moistened with water vapor 16 by a micro-humidifier 14 supplied with water from an l 2 water container 15. or,
The tip of the nozzle is preferably coated with a liquid-repellent coating such as fluororesin to protect it from liquid leakage.

FIG. 6 shows details of the solenoid valve 5. Although this device is known per se, it has been used in the medical field for dispensing things such as normal saline water, but has never been used for dispensing adhesives.

The adhesive enters the valve chamber 19 from the conduit 3 via the internal passage 17 of the housing 25. The upper end of the nozzle 5 forms an outlet valve seat 26, and since the valve body 20 is always biased downward by the compression spring 21, the outlet valve seat 26 is normally closed. When the valve body 20 is pulled up by the electromagnetic coil 24,
The valve body 20 allows the adhesive to flow into the nozzle 5, causing the adhesive under pressure to form droplets and be ejected from the nozzle 5.

The valve body 20 is made of a soft magnetic material, and a magnetic core 22 is similarly screwed into the upper part of the valve body 20 and fixed with a nut 23 . The electromagnetic coil 24 is powered by a lead 27. The power supply time is set to an arbitrary predetermined value by a regulator (not shown).

The present inventor conducted various experiments using the apparatus having the above configuration. According to the report, by changing the opening time of the solenoid valve, the amount of adhesive required for mounting electronic components can be adjusted over a fairly wide range, and by setting the supply tank to a sufficiently large capacity, the amount of adhesive always remains constant. It was confirmed that it was possible to obtain the various effects mentioned above, such as being able to secure the amount. It was found that within a certain opening time range, the adhesive did not form a continuous string, but instead formed a near-spherical droplet onto the printed circuit board due to surface tension while flying toward the printed circuit board.

Examples of the present invention will be described below.

[Explanation of Examples] First, various experiments were conducted to determine the types of adhesives that can be used in the present invention, and it was found that silicone adhesives or acrylic silicone emulsion adhesives, which are thermoplastic adhesives, were used in the present invention. I found it suitable. Note that it is clear that the present invention is not limited to these adhesives, and that other similar adhesives can be used. In particular, emulsion-type adhesives have many advantages, such as being water-based, low viscosity, non-sticky, non-stringy, and easy to dispense.

The silicone adhesive used in the experiment was a mixture of silicone resin and silicone rubber. Moreover, xylene was used as a solvent, and the nonvolatile content was about 54%. The viscosity is about 5
It was X10' cp. 50% relative humidity at 25℃
So, the nozzle tip will dry for about 5 minutes, at 80% it will take about 36 minutes, 9
It did not dry at 0%.

The average molecular structure of the acrylic silicone emulsion adhesive used in the experiment was mainly composed of a copolymer of methyl acrylate, butyl acrylate, and styrene, and water was used as the suspension. The non-volatile content was about 45%. The viscosity was approximately 20 cp. At 25°C and 50% relative humidity, the nozzle tip dried in about 6 minutes, at 80% it took about 43 minutes, and at 90% it did not dry.

The adhesive strength of the adhesive spread to a size of 10 mm in diameter (approximately 1
When measuring the change over time of ooog), the rate of increase after 24 hours at 2515 °C and 90% relative humidity was approximately 5%.
stayed within.

Fu Jingdan used the dispensing device shown in Figures 5 and 6, used acrylic silicone emulsion adhesive as the adhesive, and measured the relationship between the opening time of the solenoid valve and the diameter of the released adhesive droplet. . The nozzle used has an inner diameter of 0.21 mm and a length of 5.5 m.
m cylindrical tube, with an inner diameter of 0.2 mm and an outer diameter of 0.8 mm at the tip.
A piece of fluororesin with a length of 0.8 mm and a length of 0.8 mm was attached. The pressure in the adhesive supply tank was 0.5 Kg/cm2.

As a result, the results shown in FIG. 7 were obtained. The figure shows the droplet diameter and height. As is clear from the figure, the opening time and the size of the droplet are directly proportional over a wide range, and the diameter is on the order of mm, making it ideal for the purpose of mounting electronic components. It was found that there was no risk of contaminating the printed circuit board.

Next, the relationship between adhesive strength and temperature for the above two types of adhesives was investigated. However, the adhesive strength is shown when the adhesive is spread to a diameter of 10 mm. The value 16 for a diameter of 1 mm is a converted value. The results are shown in FIG. according to this,
It can be seen that both adhesives have sufficient heat resistance even at temperatures above 250°C.

Then using acrylic silicone emulsion adhesive,
An experiment was conducted under the same conditions as the experiment that produced the results shown in Figure 7.
The relationship between the dispensed amount and the opening time of the solenoid valve was measured. The results are shown in Figure 9. However, the pressure of the adhesive supply tank should be set to 3 to 103
g/cm". When calculated using the inner diameter of the nozzle, this pressure range is 24 to 1259 mm.
This corresponds to an injection speed of /secC.

An important result is that when the pressure is below the dotted line in the figure, droplets are ejected from the nozzle tip.
In other words, it was found that no jet was generated. Therefore,
A pressure of about 300 mm/sec (about 102 g/cm2) or more is required. This pressure will depend on the viscosity of the adhesive, but will be less dependent on the type of adhesive.

[Operation and Effect] Considering the results of the examples, the present invention can be applied over a wide range by selecting an appropriate thermoplastic adhesive as the adhesive, adjusting the pressure applied to the adhesive, and adjusting the opening time of the solenoid valve. It can be seen that a desired and appropriate amount of droplets can be generated, thus allowing non-contact adhesive dispensing. Therefore, it is possible to mount electronic components without being influenced by the surface properties of the printed circuit board.

In particular, water-based emulsion type adhesives do not cause stringiness and can fully provide the advantages of the jet method.

[Brief Description of the Drawings] Fig. 1 is a diagram showing the adhesive dispensing step in the electronic component mounting method of the present invention, Fig. 2 is a diagram showing the drying process, and Fig. 3 is a diagram showing the mounting of electronic components. Figure 4 is a diagram showing the flow soldering process, Figure 5 is an overall view of the adhesive dispensing device used in the present invention, Figure 6 is a vertical sectional view showing details of the solenoid valve, and Figure 7 is the opening of the solenoid valve. A graph showing the relationship between time and the amount of droplets, Figure 8 is 2
9 is a graph showing the relationship between the adhesive force and temperature of the seed adhesive, and FIG. 9 is a graph showing the relationship between the solenoid valve opening time and the amount of droplets using the pressure of the adhesive supply tank as a parameter. Figure 7 Bibi Luca P JP-A-3 217072 (7) Procedural amendment February 5, 1990

Claims (3)

[Claims] (1) Apply adhesive to the predetermined locations on the printed circuit board where the electronic components are to be attached, temporarily attach the electronic components to the locations where the adhesive has been applied, and then connect the external terminals of the electronic components to the predetermined conductors on the printed circuit board. In a method of mounting electronic components on a printed circuit board, the adhesive is distributed from a supply tank onto the printed circuit board through a conduit, an on-off valve connected to the conduit, and a nozzle. the supply tank is pressurized to a pressure sufficient to cause a droplet of adhesive to be ejected from the nozzle upon opening of the on-off valve, and the dispensed amount is increased upon opening of the control valve. A method for mounting electronic components on a printed circuit board, characterized in that adjustment is made by controlling time. (2) The valve includes a valve chamber that communicates with the outlet of the conduit and the inlet of the nozzle, a movable valve body that is located within the valve chamber and that abuts against and closes the inlet end of the nozzle, and that responds to an activation signal. 2. The mounting method according to claim 1, further comprising means for separating the movable valve body from the nozzle inlet end for a predetermined period of time in response. (3) The mounting method according to item 1 or 2, wherein the adhesive is selected from a silicone adhesive and an acrylic silicone emulsion adhesive.