JP2003023246A - Method of filling via hole with paste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method by which a via hole made in an electronic parts mounting substrate can be filled appropriately with paste. SOLUTION: In an airtight container 6, a substrate fixing sheet 5 stuck to a sheet ring 2 is placed and a substrate 4 to which a via hole mask 4 is stuck and an O-ring 8 are put on the sheet 5. In addition, a packing sheet 1 stuck to another sheet ring 2 and coated with the paste 3 is arranged on the sheet 5 by placing the sheet 1 on a rotary jig 7 (Fig. 1 (a)). After the paste 3 is deaerated while the inside of the container 6 is maintained in an evacuated state, the packing sheet 1 is placed on the O-ring 8 by rotating the rotary jig 7 (Fig. 1 (b)). Then the via hole is filled with the paste 3 by closely adhering the paste 3 to the substrate 4 by raising the pressure in the container 6 to the atmospheric pressure (Fig. 1 (c)). Thereafter, the via hole mask 4 is stripped off from the substrate 4 after the substrate 4 is stripped off from the sheet 1 and excessive amount of the paste 3 is scratched off. Finally, the paste 3 is hardened by putting the substrate 4 in a furnace.

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 via of a substrate for mounting electronic parts with a paste such as a conductive paste or a solder paste.

[0002]

2. Description of the Related Art In recent years, in order to cope with higher density of electronic component mounting substrates (hereinafter, simply referred to as substrates), wiring pitches have been narrowed and wiring layers have been multilayered. In that case, as the substrate material used, there are a glass epoxy type rigid material, a tape-shaped flexible material in which copper foil and polyimide are laminated, and a composite material thereof.
Further, in order to electrically connect wiring layers in a laminated board having a plurality of wiring layers, vias such as through holes and blind via holes are provided in the board, and the vias are filled with a conductive material. As the filling method, a method of depositing a metal such as copper in the via by a plating method or a method of filling a paste such as a conductive paste or a solder paste by a screen printing method is widely adopted. When the paste is filled, it is kept at a high temperature after printing and the resin is cured to realize interlayer connection. When the solder paste is filled, the interlayer connection is made through the reflow process after printing.

By the way, when the method of filling the via with the paste by screen printing is adopted, the unfilled area may remain in the via. When the unfilled area is large, the layers are electrically connected. In some cases, the original purpose could not be achieved. In addition, if there is an unfilled region, even if electrical connection is made at the initial stage, it may be broken if exposed to high temperature or a sudden temperature change occurs, resulting in poor reliability. There was a problem.

Therefore, in order to solve such a problem, a method of screen-printing the paste in a vacuum, returning to atmospheric pressure, and pushing the paste into the via by utilizing a differential pressure is disclosed in Japanese Patent Laid-Open No. 11- It is proposed in Japanese Patent No. 298138. Further, as a method of filling the paste in the via in a vacuum, a resist film is formed on the substrate, a via portion is opened, and a conductive resin is directly imprinted on the via from the resist film in a vacuum. The method used is also JP-A 2000-1505.
No. 70 publication.

[0005]

However, when the screen printing method is used, the amount of paste printed on the substrate through the printing mask cannot be uniformly obtained within the printing surface, and thus the vacuum printing method as described above is used. Even if the above method is used, there is a problem that the filling amount into the via is insufficient and a via that is not interconnected is generated. There is also a method of compensating for the insufficient filling by repeated printing when such an insufficient filling occurs. However, if this is done, the vias that are already suitably filled become excessive in paste, and the paste on the substrate will not be filled. It is not a preferable solution because it may overflow, which may cause a poor appearance due to bleeding or a short circuit with an adjacent via. Moreover, in the case of the screen printing method, the problem of insufficient filling due to such nonuniformity becomes more remarkable as the substrate becomes larger and the printing area becomes larger.

Further, when the paste is screen-printed in a vacuum as described above, the entire mechanism for driving the squeegee and the print mask is housed in a chamber forming a vacuum atmosphere. Therefore, there is a problem that a large chamber must be prepared. In particular, when filling a tape-like flexible substrate continuously supplied from a reel or the like, the apparatus becomes large-scaled, which causes a further problem.

On the other hand, in the method of directly imprinting the conductive resin on the resist film on the substrate in a vacuum in a vacuum, if there is a void in the paste, the void is also imprinted in the via, so that a void is formed in the via. However, there is a problem in that the same results as in the case of insufficient filling described above. When the void in the paste is imprinted on the via, the smaller the via diameter, the more serious the defect.

Further, in both of the above two methods, a squeegee is used to fill the paste, but if the substrate is warped, the force for pushing the paste toward the bottom of the via is within the plane of the substrate. There is also a problem that it becomes non-uniform and unevenness occurs in the filling amount of the paste.

The present invention has been made in order to solve such a problem, and an object thereof is to uniformly fill all the vias in the substrate surface and perform interlayer connection with a high yield. It is an object of the present invention to provide a method for filling vias of a paste that enables the above.

[0010]

In order to achieve the above object, a method of filling a via of a paste according to the present invention is performed by defoaming a paste applied on a filling sheet with a constant thickness under a reduced pressure atmosphere. The paste and the electronic component mounting board are brought into close contact with each other under a reduced pressure atmosphere, and in that state, the pressure of the atmosphere is increased to fill the via with the paste. And in that case, it is preferable that the filling sheet is in the form of a film. Further, when the electronic component mounting substrate is a tape-shaped substrate, it is preferable that the reduced pressure atmosphere is formed on both front and back surfaces of the tape-shaped substrate, and in that case, the tape It is preferable that the substrate is intermittently supplied from a reel or the like to the filling processing position.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The method of the present invention removes voids in a paste by applying a paste on a filling sheet with a constant thickness and applying a reduced pressure atmosphere such as a vacuum atmosphere to the paste. After that, the paste is brought into close contact with the substrate having the via in a reduced pressure atmosphere, and the atmosphere is pressurized to fill the paste with the via.

In this case, when the substrate is a tape-shaped flexible substrate, if the depressurized atmosphere is formed only on the surface having the via, the tape-shaped substrate becomes a partition forming a space of the depressurized atmosphere and is deformed by a differential pressure. Therefore, when there is such a concern, it is necessary to depressurize the front and back surfaces of the tape-shaped substrate almost at the same time so that the depressurization degree (vacuum degree) is approximately the same. And in order to form such a state, a through hole may be provided in the tape-shaped substrate,
The tape-shaped substrate may be separately evacuated from the front and back sides to reduce the pressure.

The paste is applied to the position corresponding to the via when the filling sheet is brought into close contact with the substrate. Solder paste, conductive paste such as silver paste and copper paste,
When the atmosphere is depressurized, bubbles are observed to be blown out, and when the defoaming is completed, the surface becomes uneven. The thickness of the paste applied on the filling sheet must be determined so that the minimum value (recess) after degassing is sufficient for filling. The thickness cannot be unconditionally specified because it depends on the physical properties such as the viscosity of the paste used and the size and depth of the filled via. It will be decided experimentally depending on the paste and substrate used.

After the defoaming of the paste on the filling sheet is completed, the paste is brought into close contact with the substrate in a reduced pressure atmosphere. In this way, a large gas pool (void) is eliminated between the substrate and the filling sheet. When the atmosphere is pressurized in this state, the space between the filling sheet and the substrate is maintained in a reduced pressure state, and the filling sheet is in a pressurized state. Since the space in the via which is not yet filled with the paste is in a reduced pressure state, the paste on the via is pushed to the bottom of the via due to the pressure difference between the via and the filled sheet. Through the above process, the via is differentially filled with the void-free paste.

The filling sheet to which the paste is applied is preferably in the form of a film. When a film-shaped filling sheet is used, even if the substrate warps, the deformation of the filling sheet makes it possible to maintain a reduced pressure between the substrate and the substrate and the filling sheet when the atmosphere is pressurized. A pressure difference is generated between the paste layers in between, and the force for filling the vias with the paste can be applied. Further, at this time, the tension generated in the filling sheet itself serves as a force for pushing the paste toward the substrate, and for example, it is possible to fill the paste with a force of 10 ⁵ Pa or more only by returning the atmosphere to normal pressure.

When the paste is filled only in the vias and the paste is not applied to the other parts, a mask (hereinafter, referred to as a via mask) having only the vias to be filled is provided on the substrate, and After the via filling of the paste by the method is completed, the via mask may be peeled off. The via mask may be attached with a via hole previously formed, or after the attachment, the via mask may be opened by a method such as a laser beam machine.

[0017]

Next, five embodiments of the present invention will be described with reference to the drawings. 1 to 5 show the respective embodiments, substantially the same parts are denoted by the same reference numerals between the embodiments.

[Embodiment 1] As a substrate of this embodiment, a copper epoxy tape is attached to a glass epoxy substrate having a copper wiring on the surface with a thermoplastic polyimide, and a thickness is formed on a copper layer of the copper polyimide tape. A composite substrate having a 40 μm solder resist film formed thereon was used. From copper layer of copper polyimide tape to copper layer of glass epoxy substrate, diameter 15
A via hole having a diameter of 0 μm and a depth of 50 μm was opened, and an opening having an inner diameter of 250 μm was provided in the solder resist film. The size of the substrate is 50 × 70 mm, the pitch of vias is 500 μm, and the number of vias is 1344. A slightly adhesive film having a thickness of 19 μm was attached as a via mask on the solder resist film, and an opening having the same inner diameter of 250 μm as the solder resist film was provided. A silver / epoxy conductive adhesive was used as the paste, and a PET film was used as the filling sheet. Further, the same substrate fixing sheet as the filling sheet was used.

The process of this embodiment will be described with reference to FIG. Attach the filling sheet 1 to the seat ring 2,
The paste 3 was applied to the filling sheet 1 with a thickness of 1 mm.
A substrate 4 having a via mask attached on the upper surface is placed on a substrate fixing sheet 5 attached to a sheet ring 2 different from the above, and is placed in an airtight container 6 together with the filling sheet 1 coated with the paste 3 as shown in FIG. ). At that time, in order to prevent the filling sheet 1 coated with the paste 3 from sticking to the substrate fixing sheet 5, the sheet ring 2 on which the filling sheet 1 is stuck is placed on the rotating jig 7 and placed on the substrate fixing sheet 5. An O-ring 8 was placed on. Then, the lid of the airtight container 6 is closed, and the airtight container 6 is evacuated to a vacuum degree of about 10 ³ Pa.
This state was maintained for 2 minutes, and the paste 3 was defoamed. After the defoaming of the paste 3 was completed, the filling sheet 1 coated with the paste 3 was placed on the O-ring 8 by rotating the rotating jig 7 while maintaining the vacuum atmosphere. The state at that time is shown in FIG.

Next, gas was introduced into the airtight container 6 and pressurized to atmospheric pressure. At this time, the space formed by the three members of the filling sheet 1, the substrate fixing sheet 5 and the O-ring 8 was held in vacuum, the filling sheet 1 was deformed, and the paste 3 was brought into close contact with the substrate 4. The state is shown in FIG. After that, the filling sheet 1 and the substrate fixing sheet 5 are taken out from the airtight container 6 in a state where the filling sheet 1 and the substrate fixing sheet 5 are in close contact, and
I peeled it off. And the surplus paste 3 on the via mask
When the via mask was peeled off from the substrate 4 after scraped off with rubber, all the vias were filled with the paste 3. Then, the substrate 4 filled with the paste 3 is
The paste 3 was placed in a furnace at 30 ° C. for 30 minutes to cure. As a result of observing the cross section of the via portion of the substrate 4, no unfilled region or void was found.

[Second Embodiment] A second embodiment will be described with reference to FIG. The same filling sheet 1, paste 3, substrate 4 and substrate fixing sheet 5 as in Example 1 are used. First, the filling sheet 1 was attached to the seat ring 2, and the paste 3 was applied on the filling sheet 1 to a thickness of 1 mm. A substrate fixing sheet 5 in which a substrate 4 having a via mask attached on the upper surface is attached to a seat ring 2 different from the above.
2 and placed in a vinyl bag 9 together with the filling sheet 1 coated with the paste 3 and set in the vacuum packaging machine 10 as shown in FIG. And the vacuum packaging machine 10
The inside was evacuated and the paste 3 was degassed by maintaining the vacuum degree at about 10 ³ Pa for 2 minutes.

After the defoaming of the paste 3 was completed, the vinyl bag 9 was sealed as shown in FIG. 2 (b), and gas was introduced into the vacuum packaging machine 10 to pressurize it to atmospheric pressure. The plastic bag 9 is crushed, the filling sheet 1 is deformed, and the paste 3 is applied to the substrate 4
Close contact with. The state is shown in FIG. Then, the vinyl bag 9 was taken out from the vacuum packaging machine 10 and opened, and the filling sheet 1 was peeled from the substrate 4. Next, when the excess paste 3 on the via mask was scraped off with rubber and the via mask was peeled off from the substrate 4, all the vias were filled with the paste 3. After that, the substrate 3 filled with the paste 3 was put in a furnace at 150 ° C. for 30 minutes to cure the paste 3, and the cross section of the via portion was observed. As a result, no unfilled region or void was found.

[Third Embodiment] A third embodiment will be described with reference to FIG. In the present embodiment, the above-mentioned two embodiments are the methods of placing the entire substrate 4 in the vacuum atmosphere and filling the paste, whereas the space of the vacuum atmosphere is formed only above the substrate 4. , Which is filled with paste.
This method is suitable for filling the vias arranged in a part of a large-sized substrate or the vias of a tape-shaped substrate with the paste.

The filling sheet 1 and the paste 3 of this embodiment are
Same as the first embodiment. The substrate 4 was the same as in Example 1 except that the width was 250 mm. The thicknesses of the copper layer and the polyimide layer are 18 μm and 50 μm, respectively. A 40 μm thick solder resist film was formed on the copper layer.
The via had a diameter of 50 μm and a depth of 50 μm, and an opening having an inner diameter of 150 μm was provided in the solder resist film of this via portion. The via pitch is 500 μm and the number of vias is 1.
It is 344. Further, a slightly adhesive film having a thickness of 19 μm was attached on the solder resist film as a via mask, and an opening having the same inner diameter of 150 μm as the solder resist film was provided.

First, the tape-shaped substrate 4 is sent out from a reel (not shown) and placed on the tape holding plate 13, and further two O's having different sizes are placed on the substrate 4.
Place the ring 8. On the other hand, paste 3 is 1mm thick
The filling sheet 1 applied to 1 is attached to the sheet push rod 11. Next, the sheet push rod 11 is attached to the vacuum box 12.
With the vacuum box 12 pulled up inside, the vacuum box 12 is placed on the larger O-ring 8 mounted on the substrate 4. Then, in this state, the inside of the vacuum box 12 was evacuated, and the paste 3 was degassed by holding the vacuum at about 10 ³ Pa for 2 minutes. The state is shown in FIG. In this way, after the defoaming of the paste 3 is completed, as shown in FIG. 3B, the sheet pushing rod 11 is pushed and placed on the smaller O-ring 8, and the filling sheet 1 coated with the paste 3 is applied.
Is pressed onto the substrate 4 to which a via mask is previously attached,
The paste 3 was brought into close contact with the substrate 4.

Next, as shown in FIG. 3 (c), gas was introduced into the vacuum box 12 and pressurized to atmospheric pressure. As a result, the filling sheet 1 is deformed and the paste 3 becomes the substrate 4
Close contact with. Then, the filling sheet 1 was peeled off from the substrate 4, the surplus paste 3 on the via mask was scraped off with rubber, and then the via mask was peeled off from the substrate 4. As a result, all the vias were filled with the paste 3. Then, the substrate 4 filled with the paste 3 was put in a furnace at 150 ° C. for 30 minutes to cure the paste 3 and the cross section of the via portion was observed. As a result, no unfilled region or void was found.

[Fourth Embodiment] A fourth embodiment will be described with reference to FIG. In the present embodiment, the space of the vacuum atmosphere is formed only on the upper side of the tape-shaped substrate 4 and the paste is filled in the third embodiment, whereas the upper and lower (front and back) surfaces of the substrate 4 are The pressure is reduced by, and the possibility that the tape-shaped substrate 4 may be deformed due to the pressure difference between the both surfaces is wiped off. The filling sheet 1 and the paste 3 of this embodiment are the same as those of the first embodiment, and the tape-shaped substrate 4 is the same as that of the third embodiment.

First, the tape-shaped substrate 4 is pulled out from a reel (not shown) onto the tape holding plate 13 attached to the vacuum box 14 so that the plurality of through holes 4a formed in the substrate 4 hold the tape. It is stopped when it overlaps the plurality of through holes 13a formed in the plate 13. As a result, the substrate 4 is placed on both the tape holding plate 13 and the O-ring 8 provided on the edge of the vacuum box 14. Then, two O-rings 8 having different sizes are placed on the substrate 4 stopped in this way, similarly to the third embodiment. As a result, the substrate 4 is sandwiched from above and below by the two large O-rings 8 having the same size.

On the other hand, the filling sheet 1 coated with the paste 3 in a thickness of 1 mm is attached to the sheet pushing rod 11 of the vacuum upper box 15 having the same structure as the vacuum box 12 of the third embodiment. Then, the sheet push rod 11 is attached to the vacuum upper box 1.
The vacuum box 1
5 is placed on the larger O-ring 8 resting on the substrate 4. The state is shown in FIG.
As described above, the vacuum box of this embodiment is composed of the upper vacuum box 15 and the lower vacuum box 14. In this state, the inside of the vacuum box is evacuated to a vacuum degree of about 10
^The paste 3 was degassed by holding at ³ Pa for 5 minutes.

In this way, after the defoaming of the paste 3 is completed, as shown in FIG. 4B, the sheet push rod 11 is pushed and placed on the smaller O-ring 8, and the paste 3 is applied and filled. The sheet 1 was pressed onto the substrate 4 to which a via mask was previously attached, and the paste 3 was brought into close contact with the substrate 4.
Next, as shown in FIG. 4C, after introducing gas into the vacuum box and pressurizing it to atmospheric pressure, the upper vacuum box 15
And the filling sheet 1 was peeled off from the substrate 4. Then, when the excess paste 3 on the via mask was scraped off with rubber and then the via mask was peeled off from the substrate 4, all the vias were filled with the paste 3. Then, the substrate 4 filled with the paste 3 was put in a furnace at 150 ° C. for 30 minutes to cure the paste 3 and the cross section of the via portion was observed. As a result, no unfilled region or void was found.

[Fifth Embodiment] A fifth embodiment will be described with reference to FIG. This embodiment has the same purpose as that of the above-described fourth embodiment, but in the case of the fourth embodiment, the tape-shaped substrate 4 and the vacuum lower box 14 are respectively provided with a plurality of through holes 4.
Whereas a and 13a are provided, in the case of this embodiment, the through holes 4a and 13a need not be formed. Instead, the upper vacuum box 15 and the lower vacuum box 14 are configured as separate chambers, and the exhaust ports of both are connected so that one pump can simultaneously perform vacuum exhaust. The filling sheet 1, the paste 3, and the tape-shaped substrate 4 of this embodiment are the same as those of the fourth embodiment.

Also in the case of this embodiment, the filling sheet 1 is attached to the sheet push rod 11, and the paste 3 is applied on the filling sheet 1.
Was applied in a thickness of 1 mm. The tape-shaped substrate 4 was sent out from the reel, placed on the O-ring 8 and the tape holding plate 13 attached to the vacuum box 14, and the two O-rings 8 having different sizes were placed thereon. Further, the vacuum upper box 15 is placed on the two O-rings 8 with the sheet push rod 11 pulled up, which is the set state shown in FIG. In this state, the inside of the vacuum upper box 15 and the inside of the vacuum lower box 14 were evacuated by one pump, and the paste 3 was degassed by maintaining the vacuum degree at about 10 ³ Pa for 5 minutes. Since the subsequent steps are the same as in Example 4, the description thereof will be omitted, but the filling state of the obtained paste was as good as in Example 4.

[0033]

According to the present invention, it becomes possible to realize paste filling without an unfilled area with a simple device and at a high yield.

[Brief description of drawings]

1A to 1C are process explanatory diagrams of a first embodiment.

FIG. 2A to FIG. 2C are process explanatory diagrams of a second embodiment.

3A to 3C are process explanatory diagrams of a third embodiment.

FIG. 4A to FIG. 4C are process explanatory diagrams of the fourth embodiment.

FIG. 5 is an explanatory diagram showing a set state in the fifth embodiment.

[Explanation of symbols]

1 Filling sheet 2 seat ring 3 paste 4 substrates 5 PCB fixing sheet 6 Airtight container 7 Rotating jig 8 O-ring 9 plastic bags 10 vacuum packaging machine 11 sheet push rod 12 vacuum box 13 Tape holding plate 14 Under vacuum box 15 Vacuum top box

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) B41M 3/00 B41M 3/00 Z H05K 1/11 H05K 1/11 N 3/46 3/46 N (72) Inventor Keiichi Osawa 1-6-1, Suehiro-cho, Ome-shi, Tokyo Sumitomo Metal Mining Co., Ltd. Electronic Business Division F-term (reference) 2H113 AA01 AA06 BA00 BA21 BB07 BB22 BC12 CA17 FA03 FA28 5E317 AA24 BB01 BB11 CC17 CC25 CD27 GG11 GG14 5E346 AA43 BB01 CC01 FF18 FF19 GG19 HH07 HH32

Claims (4)

[Claims] 1. After defoaming a paste applied to a filling sheet with a certain thickness under a reduced pressure atmosphere, the paste and the electronic component mounting substrate are brought into close contact with each other under a reduced pressure atmosphere, and the atmosphere A method of filling a via of a paste, characterized in that a pressure is increased to fill the paste with a paste. 2. The paste via filling method according to claim 1, wherein the filling sheet is in the form of a film. 3. The electronic component mounting substrate is a tape-shaped substrate, and the reduced pressure atmosphere is formed on both front and back surfaces of the tape-shaped substrate. Via filling method of the described paste. 4. The paste via filling method according to claim 3, wherein the tape-shaped substrate is intermittently supplied from a reel or the like to a filling processing position.