JP2003209353A - Method for filling conductive paste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely fill a conductive paste in a through hole. <P>SOLUTION: The method for filling the conductive paste comprises the steps of fixing a mesh sheet 2 to the side of one surface of a board 1 in which through holes 1c are formed by a thermal sticky tape 3, filling the conductive paste 4 in the holes 1c from the side of another surface of the board 1, drying the paste 4, heating the paste 4, and then releasing the tape 3 and the sheet 2 from the board 1. Thus, at the filling time, an escape route of the gas in the hole 1c is assured to prevent a cavity from occurring. When the sheet 2 is released, the paste 4 cured in the hole 1c can be prevented from being released, and hence the paste 4 can be surely filled in the hole 1c. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for filling a conductive paste, and more particularly to a method for filling a conductive paste in through holes formed in a substrate.

[0002]

2. Description of the Related Art In recent years, a laminated wiring board in which a plurality of wiring boards are stacked has become widespread from the viewpoint of miniaturization of electronic equipment and high-density mounting of various electronic components on a wiring board.

In the laminated wiring board, in addition to wiring grooves corresponding to the wiring patterns to be formed on each wiring board, through holes for electrically connecting the wiring boards are formed. Then, these wiring grooves and through holes are filled with a conductive paste and cured by heating, and then each wiring board is pressure-bonded in a laminated state to form a laminated wiring board.

Conventionally, as a method of filling the conductive paste in the through holes, a method of squeezing the conductive paste in a state where the substrate having the through holes is sucked from the back surface side and filling the conductive paste in the back surface side of the substrate A method of arranging a shield to prevent the conductive paste from falling through the through holes, or a method of supporting the substrate at its end and filling the substrate with the conductive paste in the air is used. ing.

[0005]

However, when filling the through holes with the conductive paste, there are the following problems.

FIG. 3 is a diagram for explaining one example of a conventional conductive paste filling method. Note that FIG. 3 is a cross-sectional view of the substrate, showing only one through-hole among a plurality of through-holes formed in the substrate and showing wiring grooves corresponding to a wiring pattern formed on the substrate. Omitted.

When the conductive paste 20 is filled, a paste for preventing sagging of the conductive paste 20 which is excessively filled and penetrates the through hole 10a on the back surface side of the substrate 10 in which the through hole 10a is formed. The shield 11 is arranged. With the paste shield 11 placed,
By moving the squeegee 12 on the surface of the substrate 10 on which the conductive paste 20 is prepared, the conductive paste 2
0 is filled in the through hole 10a and a wiring groove (not shown). Then, the substrate 10 is heated with the paste shield 11 attached, and the conductive paste 20 filled in the through holes 10a is cured.

In the case of filling the conductive paste 20 by such a method, when the paste shield 11 on the back surface side of the substrate 10 is peeled off after the conductive paste 20 is hardened, In many cases, the conductive paste 20 that adheres to this and is hardened is also peeled off.
At this time, the filled and hardened conductive paste 20 may be partially cracked inside the through hole 10 a, and the portion may be separated together with the paste shield 11. As a result, the conduction resistance between the front surface and the back surface of the substrate 10 may be increased or may not be conducted.

Further, since the paste shield 11 is arranged on the back surface side of the substrate 10, the escape of the gas existing in the through hole 10a is blocked by the inflow of the conductive paste 20 during the filling, and the squeegee. After that, a void may be generated in the through hole 10a, or unfilling may be caused.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a conductive paste filling method for surely filling a conductive paste in a through hole.

[0011]

According to the present invention, in a method of filling a conductive paste into a through hole formed in a substrate, a heat-adhesive sheet is provided on one surface side of the substrate in which the through hole is formed. Use to fix the mesh sheet,
The through-hole is filled with a conductive paste from the other surface side of the substrate to which the mesh sheet is fixed, the filled conductive paste is dried, and the conductive paste is dried substrate and the There is provided a method for filling a conductive paste, which comprises heating a mesh sheet and the heat-adhesive tape, and peeling the heat-adhesive tape and the mesh sheet from the substrate after heating.

According to the above structure, the mesh sheet is fixed to the one surface side of the substrate on which the through holes are formed with the heat-adhesive tape, and in this state, the other surface side of the substrate is changed to the through holes. Fill with conductive paste. As a result, when filling the conductive paste, a path for allowing the gas in the through holes to escape to the mesh sheet side is secured. Further, by using the mesh sheet, the conductive paste excessively filled in the through holes is prevented from dripping, and the adhesion area with the conductive paste is reduced.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a diagram for explaining a substrate arrangement state in the conductive paste filling method.

In this embodiment, the substrate 1 filled with the conductive paste is formed of a thermoplastic resin and has a thickness of approximately 0.
A 1 mm sheet is used. The substrate 1 has a pattern region 1a in which a wiring pattern to be formed on the substrate 1 is formed in the center thereof, and an outer region 1 surrounding the pattern region 1a.
The area b is an area where nothing is formed in the work process.

In the pattern region 1a of the substrate 1, wiring grooves (not shown) corresponding to the wiring pattern to be formed and a plurality of through holes (not shown) penetrating between the front surface and the back surface of the substrate 1 are formed. . When the through-hole is filled with the conductive paste, the front surface and the back surface of the substrate 1 are electrically connected to each other so that the substrates are electrically connected in a laminated state.

On such a substrate 1, the pattern area 1a is formed.
The heat-adhesive tape 3 to which the mesh sheet 2 formed with an area large enough to cover the entire back side of the surface where the wiring groove is formed is adhered from the rear surface of the substrate 1 to the outer region 1b. Is stuck. That is, the mesh sheet 2 is fixed on the back side of the pattern area 1 a while being sandwiched between the substrate 1 and the thermoadhesive tape 3. Therefore, the heat-adhesive tape 3 is not adhered to the back side of the pattern area 1a and does not block one end side of the through hole.

Here, the mesh sheet 2 fixed to the back side of the pattern area 1a has a mesh opening of, for example, about 1 mm to 5 mm. As such a mesh sheet 2, one made of a polymer material such as polypropylene, polyethylene terephthalate or polytetrafluoroethylene, or one made of a metal material such as stainless steel can be used. In particular, if the mesh sheet 2 made of a metal material is used, it can be washed after use and repeatedly used.

The heat-adhesive tape 3 for fixing the mesh sheet 2 on the back surface of the substrate 1 has a property of losing its adhesive force by being heated at a temperature of about 90.degree.

FIG. 1 is a diagram for explaining a method of filling a conductive paste. However, FIG. 1 is a cross-sectional view in which the mesh sheet and the heat-adhesive tape are fixed to the substrate, and only one of the plurality of through holes formed in the substrate is shown. The wiring groove formed in the above is not shown.

As described above, the through hole 1c is formed in the pattern region 1a of the substrate 1 so as to penetrate the substrate 1 with the wiring groove and hole (not shown) having a diameter of about 0.2 mm. The mesh sheet 2 adhered to the thermoadhesive tape 3 is fixedly arranged so as to face the through hole 1c.

The mesh sheet 2 has a mesh structure in which each of the wires forming the mesh sheet 2 is woven. Of these lines, one line 2a is shown in FIG.
And only two lines 2b and 2c orthogonal to this are shown. For these lines 2a, 2b, 2c, those having a diameter substantially the same as the diameter of the through hole 1c, for example, about 0.2 mm to 0.3 mm are preferably used. As a result, the conductive paste 4 is applied to the through hole 1c.
Is excessively filled, the area where the conductive paste 4 adheres to the mesh sheet 2 can be reduced.

That is, if the diameter of the wires 2a, 2b, 2c is too small as compared with the diameter of the through hole 1c, the conductive paste 4 will be hardened in a state of dripping toward the heat adhesive tape 3 side. In this case, the conductive paste 4 hardened inside the through hole 1c may be partially broken or may be peeled together with the mesh sheet 2 due to the force of peeling the heat-adhesive tape 3 and the mesh sheet 2. It can happen. As a result, problems such as an increase in conduction resistance or no conduction may occur inside the through hole 1c.

If the diameter of the wires 2a, 2b, 2c is too large as compared with the diameter of the through hole 1c, the area where the overfilled conductive paste 4 adheres becomes large, so that the mesh sheet 2 is peeled off. At this time, the conductive paste 4 inside the through hole 1c may be partially cracked or the portion may be peeled off together with the mesh sheet 2, which may cause a problem such as an increase in conduction resistance.

The mesh sheet 2 itself has no adhesive force, and the mesh sheet 2 is fixed to the substrate 1 by being adhered to the thermoadhesive tape 3 at the portion facing the through hole 1c.

With the substrate 1, the mesh sheet 2 and the thermoadhesive tape 3 arranged in this way, the conductive paste 4 is formed.
In order to fill the through hole 1c with a squeegee printer, a squeegee printer which is generally used in the past can be used.

As the conductive paste 4 to be filled in the through holes 1c, epoxy resin mixed with silver flake powder is used. The substrate 1 to which the mesh sheet 2 and the thermal adhesive tape 3 are fixed is vacuum-adsorbed and fixed to the printing base of the squeegee printer. The conductive paste 4 is applied by moving the squeegee 5 prepared on the substrate 1 at room temperature, and filling the through holes 1c formed in the substrate 1 and wiring grooves (not shown) at that time. It

At this time, since the mesh sheet 2 is arranged on the back surface of the substrate 1, the gas in the through holes 1c comes to escape as the conductive paste 4 flows in at the time of filling. As a result, it becomes possible to reliably fill the conductive paste 4 without generating a cavity in the through hole 1c. Further, the filled conductive paste 4 is prevented by the mesh sheet 2 from dripping toward the heat-adhesive tape 3.

After the conductive paste 4 is filled in the through holes 1c, the substrate 1, the mesh sheet 2 and the heat-adhesive tape 3 are kept in the arranged state at a temperature of 70.degree.
Dry for minutes. As a result, the conductive paste 4 filled in the through holes 1c is dried. At this temperature of 70 ° C., the thermoadhesive tape 3 still has an adhesive force,
It does not peel off from the substrate 1.

Next, the substrate 1, the mesh sheet 2 and the heat-adhesive tape 3 are heated at a temperature of 9 while keeping the arrangement state.
Heat at 0 ° C. As a result, the conductive paste 4 is completely cured, and the adhesive force of the heat-adhesive tape 3 is lost, so that the heat-adhesive tape 3 can be easily separated from the substrate 1 and the mesh sheet 2.

At this time, the conductive paste 4 is attached to the mesh sheet 2 that has prevented the conductive paste 4 from dripping. Therefore, when the mesh sheet 2 is peeled from the substrate 1 after the heat-adhesive tape 3 is peeled off, the conductive paste 4 attached to the mesh sheet 2 is also peeled off. However, the lines 2a, 2b of the mesh sheet 2,
Since 2c has a circular cross-sectional shape, the area where the conductive paste 4 adheres is minimized. As a result, the portion where the conductive paste 4 is peeled off is very small, and the peeling of the conductive paste 4 which is filled inside the through hole 1c and hardened is prevented. As a result, the through hole 1c is reliably filled with the conductive paste 4, and the problem that the conduction resistance is increased or the conduction is not performed is avoided.

In this embodiment, the mesh sheet 2 is
As described above, the one having the opening of about 1 mm to 5 mm is used, but when the opening is smaller than 1 mm,
Conductive paste 4 excessively filled in the through hole 1c
Becomes larger on the mesh sheet 2, and when the mesh sheet 2 is peeled off, the conductive paste 4 inside the through-hole 1c is partially cracked or peeled off to increase the conduction resistance. The problem may occur. Further, when the opening is larger than 5 mm, the conductive paste 4 excessively filled in the through hole 1c passes through the mesh sheet 2 and reaches the heat-adhesive tape 3, so that the mesh sheet 2 is peeled off. At this time, the conductive paste 4 inside the through hole 1c may be partially cracked or peeled off, which may cause a problem such as an increase in conduction resistance.

Finally, the front surface and the back surface of the substrate 1 are polished to remove the conductive paste 4 which is sticking out from the through hole 1c and hardened, and then flattened.
A desired wiring pattern is formed on the.

As described above, when the conductive paste 4 is filled in the through holes 1c, the mesh sheet 2 is arranged on the one surface side of the substrate 1 so that the gas in the through holes 1c is filled at the time of filling. An escape route is ensured, and after the conductive paste 4 is hardened, peeling of the hardened conductive paste 4 inside the through-hole 1c can be prevented and the through-hole 1c can be reliably filled with the conductive paste 4. it can.

Further, as compared with the conventional method, the conductive paste 4
It is possible to reduce the amount of wiring used and to reduce the cost of the wiring pattern forming process.

[0035]

As described above, according to the present invention, the mesh sheet is fixed to the one surface side of the substrate on which the through holes are formed with the heat-adhesive tape, and in this state, the other surface of the substrate is fixed. The through hole is filled with a conductive paste from the side, and after drying and heating the paste, the heat-adhesive tape and the mesh sheet are peeled from the substrate. With this, when filling, it is possible to secure an escape path for gas in the through hole, and it is possible to prevent the cured conductive paste inside the through hole from peeling when the mesh sheet is peeled off. Can be reliably filled in the through hole.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a method of filling a conductive paste.

FIG. 2 is a diagram illustrating a substrate arrangement state in a conductive paste filling method.

FIG. 3 is a diagram illustrating an example of a conventional conductive paste filling method.

[Explanation of symbols]

1 ... Substrate, 1a ... Pattern area, 1b ... Outside area, 1c ... Through hole, 2 ... Mesh sheet, 2
a, 2b, 2c ... Line, 3 ... Thermal adhesive tape, 4, 20
…… Conductive paste, 5,12 …… Squeegee, 10 ……
Substrate, 10a ... through hole, 11 ... paste shield.

Claims (6)

[Claims] 1. A method of filling a conductive paste into a through hole formed in a substrate, wherein a mesh sheet is fixed to one surface side of the substrate in which the through hole is formed using a heat-adhesive sheet, The conductive paste is filled into the through hole from the other surface side of the substrate to which the mesh sheet is fixed, the filled conductive paste is dried, and the substrate and the mesh where the conductive paste is dried are dried. A method for filling a conductive paste, comprising heating a sheet and the heat-adhesive tape, and peeling the heat-adhesive tape and the mesh sheet from the substrate after heating. 2. The mesh sheet has an opening of 1 mm.
The filling method of the conductive paste according to claim 1, wherein the filling amount is 5 mm to 5 mm. 3. The method for filling a conductive paste according to claim 1, wherein the mesh sheet has a diameter of a wire forming the mesh substantially equal to a diameter of the through hole. 4. The diameter of the wire is from 0.2 mm to 0.
It is 3 mm, The filling method of the electrically conductive paste of Claim 3 characterized by the above-mentioned. 5. The heat-adhesive tape has a property of losing its adhesive force when heated at a predetermined temperature, and when the substrate, the mesh sheet and the heat-adhesive tape are heated, the temperature is kept at the temperature. The method of filling a conductive paste according to claim 1, wherein heating is performed. 6. The conductive paste filling method according to claim 1, wherein the substrate is formed of a thermoplastic resin in a sheet shape.