JP2798768B2 - How to join electronic components to printed circuit boards - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a method for joining electronic components to a printed circuit board. Metal particles are attached to the leads of the electronic component to which the adhesive has been applied, the component leads are placed on the footprint of a printed circuit board, and an adhesive sheet is further placed on the component leads of the electronic component and heated and pressed. The metal particles are not attached by lightly pressing the adhesive-applied component leads over the metal particles arranged in a plane, and the alignment is inspected in a plane on a transparent plate. Irradiate the light from one of the upper and lower surfaces of the aligned metal particles, receive the transmitted light on the opposite surface, perform photoelectric conversion, determine based on the obtained electric signal, and mixed the metal particles After applying the adhesive on either side of the lead of the electronic component or the footprint of the printed circuit board, the lead is placed on the footprint, and further, an adhesive sheet is placed on the component lead of the electronic component. And heated and pressurized.

[Industrial applications]

The present invention relates to a printed circuit board, and more particularly to a method for joining electronic components to a printed circuit board.

(Prior art)

With the demand for miniaturization of electronic devices, the miniaturization of electronic components and the density of printed circuit boards on which the electronic components are mounted are increasing. Conventionally, the lead of the electronic component and the footprint of the printed circuit board were joined by soldering to the electronic component and the printed circuit board.
Attempting to join the leads and footprints of the current package components by soldering as described below may cause a short circuit between the footprints (between the leads).

Therefore, attempts have been made to mix metal powder into a synthetic resin and use an electrically conductive sheet that exhibits conductivity only in the direction in which pressure is applied.

That is, as shown in FIG.
The anisotropic conductive sheet 16 is arranged between the footprint 11 and the component lead 21 and the heating tool 40 presses and heats the component lead 21 from above the component lead 21 as shown in FIG. The conductivity between the component lead 21 and the footprint 11 is ensured, and the component lead is formed by the adhesive force of the material of the anisotropic conductive sheet 16 (for example, epoxy or polystyrene).
21, to be joined to the footprint 11.

[Problems to be solved by the invention]

By the way, in recent years, TAB (Tape Automated Bondin
g) or lead spacing like flip chip parts
Package parts of about 0.1 mm to 0.3 mm have appeared, and at such a lead interval, the diameter (for example, about 15 μm) of the metal particles 10 mixed in the anisotropic conductive sheet 16 cannot be ignored, and the There is a problem that sufficient insulation between the prints 11 (between the leads 21) cannot be ensured.

Further, as the amount of the metal particles is increased in order to secure the current amount, it becomes more difficult to secure the insulating property.

Furthermore, the above-mentioned conventional method has an anisotropic conductive sheet having a thin junction.
Since only 16 is used, warpage in the printed circuit board weakens the bonding strength and impairs long-term reliability.

Japanese Patent Application Laid-Open No. 57-167665 discloses a technique in which powdery solder is attached to the outside of a rotating roller from a nozzle, and the rotating roller is moved while contacting a lead to which flux has been previously attached. This describes a configuration in which solder is adhered to the back surface of the lead, and the problem of ensuring the insulating property is considerably improved by preventing excessive solder adhesion. However, in this configuration,
Since the solder may not be uniformly attached, there remains a problem that it is difficult to always ensure sufficient insulation and bonding strength.

The present invention has been proposed in view of the above-mentioned conventional circumstances, and has as its object to provide a method of joining a footprint of a component lead which can ensure sufficient insulation and has a large joint strength. .

[Means for solving the problem]

The present invention employs the following means to achieve the above object. That is, as shown in FIG.
The metal particles 10 are adhered to the leads 21 of the electronic component 20 to which the component is applied, and the component leads are attached to the footprint 11 of the printed circuit board 1.
The adhesive sheet 15 is placed on the component lead 21 of the electronic component 20 and heated and pressed.

The metal particles 10 are arranged in a plane as shown in FIG. Further, as shown in FIG. 4, light was irradiated from one of the upper and lower surfaces of the metal particles 10 arranged on the transparent plate 30, and the transmitted light was received and photoelectrically converted on the opposite surface. The alignment state of the metal particles 10 before or after the attachment of the metal particles 10 to the component lead 21 can be inspected based on the electric signal.

As another method, as shown in FIGS. 6 and 7,
The adhesive mixed with the metal particles 10 is applied to the leads 21 of the electronic component 20,
Or after applying to either side of the footprint 11 of the printed circuit board 1, the lead is placed on the footprint,
Further, the adhesive sheet 15 is placed on the component leads 21 of the electronic component 20.
And heat and press.

[Action]

When the component lead 21 to which the adhesive Ra is applied is brought into contact with the metal particles 10, the metal particles 10 are in a state of being bonded to the leads 21. In this state, the component 20 is placed on the footprint 11, and the adhesive sheet 15 is further placed thereon and heated and pressed, so that the conductivity of the component lead 21 and the footprint 11 can be secured, and By curing the agent sheet 15, high adhesive strength can be secured.

In the above case, the metal particles 10 need to be arranged as densely and homogeneously as possible. When light is emitted from the light source 33 to the aligned metal particles 10, the transmitted light is
Reflects 10 alignments. Therefore, the alignment state can be grasped based on the electric signal obtained by photoelectrically converting the transmitted light. The state of the metal particles 10 coming off after the metal particles 10 are bonded to the component leads 21 indicates the bonding state of the metal particles 10 to the component leads 21. Therefore, after bonding to the metal particle 10 to the component lead 21, the light is emitted from the light source 33 as described above, and the bonding state to the metal particle 10 can be detected based on the transmitted light.

Further, an adhesive Ra mixed with metal particles 10 is applied to the footprint 11 of the printed circuit board 1 in advance, components are placed thereon, and the adhesive sheet 15 is placed thereon similarly to the above. Also exhibits the same effect. Further, in the above example, an adhesive mixed with the metal particles 10 may be applied to the component lead 21 side.

〔Example〕

FIG. 1 shows an embodiment of the present invention. While the adhesive Ra is applied to the lower surface of the component lead 21 in advance, the component lead 21 to which the adhesive Ra has been applied as described above is lightly contacted from above the metal particles 10 arranged on a plane. As a result, the aligned metal particles 10 adhere to the lower surface of the component lead 21 (FIG. 1 (a),
(B)).

The component 20 with the metal particles 10 adhered to the component lead 21 is placed so that the component lead 21 is placed on the footprint 11 of the printed circuit board 1, and the adhesive sheet 15 is further placed thereon. The adhesive sheet 15 is arranged and hardened by heating and pressing with a heat tool 40 from above (FIGS. 1 (c) and 1 (d)).

Thereby, the conductivity of the component lead 21 and the footprint 11 can be secured by the metal particles 10, and the adhesive strength can be secured by curing the adhesive sheet 15.

FIG. 2 shows an example of the above-mentioned adhesive application device. That is, the lower half of the endless belt 26 stretched over the two rollers 25a and 25b is soaked in the adhesive Ra put in the adhesive tank 27, and the endless belt 26 is rotated to rotate the endless belt 26. The adhesive is thinly adhered to the upper surface of the belt 26, and the component leads 21 of the component 20 are lightly pressed against the upper surface of the endless belt 26.

For example, as shown in FIG. 3, the metal particles 10 (for example, having a diameter of 15 mm) mixed with a solvent such as alcohol are arranged as shown in FIG.
μm) is filled with a little more than it can fit into the concave portion 31 of the alignment plate 30, and is lightly pressed with a plate 32 from above. As a result, the metal particles 10 are aligned in the recess 31.

The metal particles 10 are required to be aligned in a state as dense as possible in order to secure sufficient conductivity. Then, with the metal particles 10 aligned in the recesses 31 as described above, light is transmitted downward from the light source 33 above the alignment plate 30 as shown in FIG. The transmitted light is received by a two-dimensional optical sensor 34 disposed on the monitor. Further, based on an image signal obtained by the optical sensor 34,
The arrangement state of the metal particles 10 can be displayed to visually confirm whether or not the arrangement of the metal particles 10 is missing. Alternatively, a defective portion can be automatically detected based on the image signal.

Further, when it is determined that there is no defect in the defect detection process, the metal particles 10 adhere to the component lead 21 as described above. Here, too, metal particles in contact with component leads 21
It is necessary to check whether or not 10 has completely adhered to the component lead 21.

Then, as shown in FIG. 4 (b), after contacting the component leads 21 with the metal particles 10 aligned on the alignment plate 30, the light from the upper light source 33 is transmitted to the alignment plate 30 in the same manner as in checking the alignment state. The two-dimensional optical sensor 34 disposed below the alignment plate 30 detects the state of the detachment of the aligned metal particles 10, and displays an image signal output from the optical sensor 34 on a monitor. The state can be visually checked or automatically checked electrically. For example, as shown in FIG. 4 (b), when the metal particles 10 in the portion in contact with the component leads 21 are completely removed, the transfer of the metal particles 10 is successful.

For example, as shown in FIG. 5, the adhesive sheet 15 attached to the heat-resistant sheet 41 having a predetermined width is sent out and wound around a roller 42, and
The adhesive sheet 15 pulled out along the upper surface of the component lead 21 mounted thereon is wound up by a winding roller 43. Then, when the heating tool 40 is heated and pressed from above the heat-resistant sheet 41, the adhesive sheet 15 is completely cured, and then the heat tool 40 is lifted, and the delivery roller 42 and the winding roller 43 are lifted. The cured portion and the uncured portion of the adhesive sheet 15 are cut off, and the heat-resistant sheet 41 is removed.
Peels off from the cured part. Thereafter, a method of sending out the adhesive sheet 15 and preparing for the next operation is conceivable.

 FIG. 6 is a conceptual diagram showing another embodiment of the present invention.

First, the metal particles 10 are mixed in the adhesive Ra, and the adhesive Ra is applied to the back surface of the component lead 21 using the dispenser 50. Thereafter, the adhesive Ra is temporarily cured by heating,
As shown in FIGS. (C) and (d), the component 20 is
The adhesive sheet 15 is placed on the component lead 21 and heated and pressed by the heat tool 40.

FIG. 7 is a flowchart showing another embodiment of the present invention. That is, as shown in FIGS. 7A and 7B, similarly to the embodiment shown in FIG. 6, the adhesive Ra mixed with the metal particles 10 has a width corresponding to the squeegee 3 and the footprint 11 (FIG. It is applied on the footprint 11 of the printed circuit board 1 using a printing plate 5 having an opening window 51 of, for example, 0.1 mm to 0.3 mm). In this way, after the applied adhesive Ra is heated and temporarily cured, the component 20 is placed so that the lead 21 and the footprint 11 coincide with each other as shown in FIG.
Further, the adhesive sheet 15 is disposed on the lead 21, and as shown in FIG. 1 (d), the adhesive sheet 15 is heated and pressed by the heat tool 40 from above.

The metal particles 10 used in the present invention are those obtained by electrolessly plating a conductive metal on the surface of plastic particles of about 10 to 20 μm, but may be a simple conductive metal powder or a needle-like body.

〔The invention's effect〕

As described above, according to the present invention, since the metal particles are concentrated on the component lead portion or the footprint portion by the adhesive, the insulation between the footprints (between the leads) can be ensured and the conductive property can be secured. Since the density of the conductive metal particles can be increased, a large current can flow, and since the adhesive sheet is pressed from above, a high adhesive force can be secured.

[Brief description of the drawings]

FIG. 1 is a flow chart showing one embodiment of the present invention, FIG. 2 is a conceptual diagram of an apparatus for applying an adhesive to component leads, FIG. 3 is a conceptual diagram of an alignment plate, and FIG. Conceptual diagram, 5th
FIG. 6 is a conceptual diagram of a heating and pressurizing device, FIG. 6 is a conceptual diagram showing another embodiment of the present invention, FIG. 7 is a flowchart showing another embodiment of the present invention, and FIG. FIG. 4 is a flow chart of joining to a printed circuit board. In the figure, 1 ... printed circuit board, 10 ... metal particles, 11 ... footprint, 15 ... adhesive sheet, 20 ... electronic parts, 21 ... part leads, Ra ... adhesive.

Claims (2)

(57) [Claims] A metal lead is pressed onto a component lead coated with an adhesive from above a metal particle arranged in a plane to attach the metal lead to the component lead, and the component lead is placed on a footprint of a printed circuit board. Placing the adhesive sheet on a component lead of the electronic component and heating and pressurizing the adhesive sheet, and bonding the electronic component to a printed circuit board. 2. A method of irradiating light from one of upper and lower surfaces of metal particles arranged in a plane on a transparent plate, receiving transmitted light on the opposite side and performing photoelectric conversion on the basis of the obtained electric signal. The method for bonding an electronic component to a printed circuit board according to claim 1, wherein an alignment state of the metal particle before or after the metal particle is attached to the component lead is inspected.