JP4420519B2 - Method for manufacturing printed circuit board filled with paste - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a printed circuit board, and more particularly to a filling method capable of sufficiently removing bubbles in the paste when the paste is filled into a bottomed via or a through hole formed on the printed circuit board. is there.
[0002]
[Prior art]
When filling holes such as bottomed vias and through-holes formed on printed circuit boards, screen-printing paste-like fillers such as liquid resin, thermosetting ink, or conductive paste on the surface of printed circuit boards There is a method in which it is applied by a method or the like, filled in the holes of the printed circuit board, and then cured.
[0003]
[Problems to be solved by the invention]
By the way, when the paste is attached to the substrate by the screen printing method or the like as described above, air is entrained in the paste at the time of printing, and this may be mixed into the paste as fine bubbles. Since such bubbles in the paste remain as they are even when the paste is cured, voids may be generated in the cured paste, and voids may be ruptured at the heating stage in the subsequent process.
[0004]
For this reason, as a means for removing bubbles in the conventional paste, for example, the paste is printed on a printed circuit board in a reduced pressure environment, and then returned to atmospheric pressure, thereby increasing the filling density of the paste using the differential pressure. The method to do is adopted. However, in this method, there is a concern that volatile components in the paste are scattered and the paste is deteriorated. Moreover, when the viscosity of the paste is relatively high and the wettability to the adhesion surface of the filler is poor, there is a problem that the paste adhered to the corner easily peels from the adhesion surface due to the differential pressure.
[0005]
There is also a method in which the printed circuit board is allowed to stand for as long as possible after the paste is attached to the substrate, and waits for bubbles to rise up and disappear. When the viscosity of the liquid was relatively high, there was a problem that bubbles were not sufficiently removed.
[0006]
The present invention has been made in view of the above circumstances, and is a paste filling method capable of sufficiently removing bubbles in a paste when the paste is filled into a bottomed via or a through hole of a printed circuit board. It is intended to provide .
[0007]
[Means for Solving the Problem and Action]
The invention according to claim 1 made to solve the above-described problem is a method of manufacturing a printed circuit board in which a hardened paste is filled in a bottomed via, and the paste enters the bottomed via. The paste is attached to the printed circuit board, and then the printed circuit board is rotated with the opening direction of the bottomed via directed toward the center of rotation, and the paste that has hardened the paste and then polished the paste that protrudes from the surface of the circuit board. characterized in removal to Rutokoro.
[0008]
According to the present invention, the printed circuit board to which the paste is attached is rotated with the opening direction of the bottomed via directed toward the center of rotation, whereby centrifugal force is applied to the paste in the bottomed via. In other words, when bubbles are included in the paste in the bottomed via, the paste having a heavier mass than the bubbles is pressed against the bottom of the bottomed via located in the direction opposite to the center of rotation by centrifugal force. On the contrary, bubbles that are lighter than the paste gather on the opening side of the bottomed via located in the direction of the center of rotation and float near the surface of the paste. Then, the bubbles floating on the surface are pushed out from the paste surface and released to the outside.
[0009]
At this time, even if bubbles remain in the paste, the density increases as the surface approaches, and hardly exists near the center in the bottomed via. When the internal bubbles are completely discharged, the paste surface becomes flat. Conversely, when bubbles remain in the paste, the surface layer of the paste having a high bubble density exhibits an uneven state. It will be. Therefore, it is possible to easily determine whether or not bubbles have been removed from the paste simply by observing the surface state of the paste after rotation.
If bubbles remain near the surface of the paste, they can be completely removed by polishing the surface after the paste is cured.
[0010]
Thus, according to the present invention, by applying centrifugal force to the paste in the bottomed via, even if the paste has a high viscosity, the bubbles in the paste are surely and quickly lifted to the surface and removed. By doing so, it is possible to obtain a printed circuit board having uniform and excellent electrical characteristics.
[0011]
The invention according to claim 2 is a method of manufacturing a printed board filled with a hardened paste in a through hole, the paste being attached to the printed board so as to enter the through hole, Thereafter, the printed circuit board was rotated with the other surface side directed toward the center of rotation in a state where the closing body covering the opening of the through hole was assigned to one surface side of the printed circuit board, and the paste was cured. characterized in Rutokoro be polished remove protruding paste on the surface of the substrate after.
[0012]
According to the present invention, the through hole can be brought into a state similar to that of the bottomed via as in the first aspect of the invention by allocating a closing body that closes the opening of the through hole to one side of the substrate. it can. That is, the through-hole is filled in the same manner as in the first aspect of the invention by rotating the printed circuit board with the surface opposite to the one surface addressed to the closed body of the printed circuit board directed toward the center of rotation. Centrifugal force is applied to the paste, and the paste is pressed toward the closed body, and bubbles in the paste are collected on the paste surface and released. In addition, what is necessary is just to remove an obstruction | occlusion body after hardening of a paste.
[0013]
As described above, the present invention has an excellent effect of preventing air bubbles from remaining in the paste filled in the through hole, as in the first aspect of the present invention.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
<First Embodiment>
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic perspective view of a paste filling apparatus 10 for a printed circuit board, and FIG. 2 is a side sectional view of the same. The filling apparatus 10 includes a rotating body 12 that can rotate around a rotating shaft 11, a substrate holding unit 13 provided inside the rotating body 12, a drive mechanism that rotates the rotating body 12 at a high speed, and the rotating body 12. And a fixed drum 14 provided so as to be covered.
[0018]
The rotating body 12 has a cylindrical container shape with an open upper end surface. As shown in FIG. 2, a hub 16 is provided at the center of the bottom wall, and a hub is provided at the upper end surface via a spoke portion 17 at the center. 15 is provided, and the rotary shaft 11 is fixed so as to protrude vertically through the hubs 15 and 16.
[0019]
Four substrate holders 13 are provided inside the rotating body 12. These substrate holding portions 13 are formed by attaching and fixing a pair of rectangular bars having a concave cross section to the bottom wall of the rotating body 12 so as to be parallel to the rotating shaft 11 so that the recessed portions 13a face each other. ing. As will be described later, the printed circuit board is fixed in the rotator 12 by inserting the end of the substrate into the recess 13 a of the substrate holder 13 from above, but the substrate is not attached to the rotator 12 when inserted into the substrate holder 13. The board | substrate holding | maintenance part 13 is located between each spoke part 17 of the rotary body 12 so that insertion may not be prevented by striking against the spoke part 17 (refer FIG. 3). Further, the four substrate holding portions 13 are provided so as to surround the periphery of the rotation shaft 11 so that one surface side of each substrate inserted and fixed in the vertical direction faces the rotation shaft 11 side.
[0020]
A cylindrical container-shaped fixed drum 14 having an opening on the lower side is provided so as to cover the entire rotating body 12. A flange portion 14a is formed at the opening end of the fixed drum 14, and the flange portion 14a is fixed to the upper surface of the housing 22 with a bolt (not shown). Further, a bearing 20 is provided at the center of the ceiling surface of the fixed drum 14, and the upper end portion of the rotary shaft 11 is rotatably inserted and supported by the bearing 20. On the other hand, a through hole 22a is formed at a position corresponding to the center of the fixed drum 14 on the upper surface of the housing 22, and a bearing 21 is fixed to the lower surface side. 11 is rotatably supported.
In addition, on the ceiling surface of the fixed drum 14, a single substrate loading / unloading portion 14 b that opens in a rectangular shape is formed at a position corresponding to the substrate holding portion 13 of the rotating body 12.
[0021]
The fixed drum 14 is fixed to an upper surface of a housing 22 provided below the fixed drum 14 with a bolt 23 a via a bracket 23. The bracket 23 has a generally Z shape in which both ends of the vertically long plate are bent at right angles in opposite directions, and both ends thereof are fixed to the ceiling surface of the fixed drum 14 and the upper surface of the housing 22, respectively. ing.
[0022]
A motor 24 that is a drive unit for the rotating body 12 is provided inside the housing 22, and a pulley 25 provided on a rotating shaft 24 a of the motor 24 and a pulley 26 fixed to the lower end of the rotating shaft 11. A belt 27 is provided between them, and the rotating body 12 can be rotated at high speed by the motor 24.
[0023]
Hereinafter, a case where the paste filling method for a printed circuit board according to the present invention is applied to a substrate built-in resistor using the above-described paste filling apparatus 10 will be described with reference to FIG.
In this embodiment, the copper clad laminated board 30 which bonds a copper foil on the single side | surface of the glass epoxy board of thickness 100-3000 micrometers is used as a base material, for example, The copper foil is etched by a required pattern. An electric circuit pattern 31 is formed on the surface of the substrate. An insulating layer 32 is provided on the circuit pattern 31, and a via hole 33 formed by, for example, a photoetching method is opened at a predetermined position of the insulating layer 32. As shown in FIG. 4A, a part of the electrode part 34 of the circuit pattern 31 is exposed at the opening of the via hole 33.
[0024]
The opening of the via hole 33 is filled with a carbon paste 35, which is a resistor material, in the following procedure.
First, for example, in an atmospheric pressure environment, the carbon paste 35 is filled and printed in the opening of the via hole 33 by a screen printing method or the like. At this time, the printed paste 35 may contain minute bubbles 36 (see FIG. 4B).
[0025]
Next, the printed circuit board 30 on which the paste 35 is printed is fixed to the substrate holding unit 13 in the rotating body 12 of the paste filling apparatus 10 described above. For this purpose, first, the printed circuit board 30 is placed in a vertical state so that the surface to which the paste 35 is attached faces the rotating shaft 11, and the lower end of the substrate 30 is inserted between the substrate insertion / removal portion 14 b and the pair of recesses 13 a. To do. If the lower end portion of the printed circuit board 30 fits into the recess 13a, the substrate 30 is gently lowered as it is until it comes into contact with the bottom wall of the rotating body 12, and the printed circuit board 30 is held inside the rotating body 12. At this time, as described above, the printed circuit board 30 is in the vertical direction, but the printed paste 35 has a relatively high viscosity, so that it does not flow down immediately. In this state, the motor 24 is driven to rotate the rotating body 12 at a high speed. The rotation speed is, for example, about 3000 rpm, and the rotation is continued for, for example, 3 minutes after the start of rotation.
[0026]
Thus, when the printed circuit board 30 is rotated by the paste filling device 10, centrifugal force acts on the paste 35 in the via hole 33. Then, the paste 35 is pressed against the bottom surface side of the via hole 33 by this centrifugal force, and the bubbles 36 having a lighter mass than the paste 35 are gathered so as to be pushed up to the paste surface on the rotating shaft 11 side. And most of the bubbles 36 gathered on the paste surface are finally discharged to the outside of the paste 35 (see FIG. 4C).
[0027]
After completion of the rotation, the printed circuit board 30 is taken out from the substrate loading / unloading portion 14b of the paste filling apparatus 10 and the paste 35 is thermally cured. Thereafter, the paste 35 protruding from the surface of the substrate 30 is removed by polishing and planarized. At this time, even if bubbles 36 remain in the vicinity of the surface of the paste 35, they are removed together with the paste 35 hardened by polishing, so that the bubbles 36 do not remain in the paste 35 filled in the via hole 33 (FIG. 4). (See (d)).
[0028]
As described above, according to the printed circuit board manufacturing method and apparatus of the present embodiment, a uniform and excellent electrical characteristics printed circuit board is obtained without leaving bubbles in the paste filled in the bottomed via. It has an excellent effect of being able to.
[0029]
<Second Embodiment>
Next, a second embodiment in which the present invention is applied to a printed circuit board having a through hole will be described with reference to FIG.
In this embodiment, the copper clad laminated board 40 formed by affixing copper foil on both surfaces of a glass epoxy board | substrate is used. A through hole 41 is drilled in a required portion of the copper-clad laminate 40 using, for example, a well-known drill or the like, and chemical plating and electrolytic plating are performed to cover the entire area including the inner peripheral surface of the through hole 41 with copper. A plating layer is formed. Then, from one side surface of the printed circuit board 40, an insulating paste 42 for hole filling is applied by a screen printing method so that the inside of the through hole 41 is filled with the insulating paste 42. At this time, the insulating paste 42 may contain minute bubbles 43 (see FIG. 5A).
[0030]
Next, a heat-resistant release film 44 is superimposed on the surface of the printed circuit board 40 opposite to the printed surface of the insulating paste 43 as a closing body so that the printed circuit board 40 is in perfect contact (FIG. 5B). )reference). And the printed circuit board 40 addressed to the heat-resistant release film 44 in this way is inserted and held in the board holding part 13 of the paste filling apparatus 10 so that the board 40 is in the vertical direction. At this time, the surface of the printed circuit board 40 to which the heat-resistant release film 44 is addressed is positioned on the side opposite to the rotating shaft 11. And like the said 1st Embodiment, it is made to rotate continuously for 3 minutes after the start of rotation at the speed of 3000 rpm, for example.
[0031]
Then, as in the first embodiment, centrifugal force acts on the insulating paste 42 in the through hole 41, and the insulating paste 42 is applied to the opening on one end side of the through hole 41 by this centrifugal force. While being pressed against the release film 44, the bubbles 43 having a lighter weight than the paste 42 gradually gather on the surface of the paste on the rotating shaft 11 side, and are finally discharged to the outside of the paste 42 (see FIG. 5C).
[0032]
Thereafter, the printed circuit board 40 is taken out from the paste filling apparatus 10 and the paste 42 is thermally cured, and after the heat-resistant release film 44 is peeled off, the paste portion protruding from the surface of the substrate 40 is subjected to smooth polishing. At this time, even if the bubbles 43 remain on the surface of the paste 42, they are removed together with the paste 42 by polishing, so that the bubbles 43 do not remain in the paste 42 filled in the through holes 41 (FIG. 5). (See (d)).
[0033]
As described above, the paste filling method for the printed circuit board according to the present embodiment does not leave bubbles in the paste filled in the through-holes as in the first embodiment, and a highly reliable substrate can be obtained. There is an excellent effect that it can be obtained.
[0034]
<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention, and further, within the scope not departing from the gist of the invention other than the following. Various modifications can be made.
[0035]
(1) In the first embodiment, the case where the paste filling method for a printed circuit board according to the present invention is applied to a board built-in resistor has been described. However, when a paste is filled in a via hole for interlayer connection of a multilayer printed circuit board. Can also be applied.
[0036]
(2) In the above embodiment, a carbon paste or an insulating paste is used as a paste. However, other than this, a normal printed circuit board such as a conductive or non-conductive metal paste, a sealing material such as a potting resin or a transfer mold, etc. Other pastes used as a hole filling material may be used.
[0037]
(3) In the above embodiment, the paste filling device is rotated at 3000 rpm for 3 minutes after the start of rotation, but the rotation speed and rotation time are the substrate weight and solid weight difference, paste mass, It can be appropriately changed depending on the hole shape or the like.
[0038]
(4) In the above embodiment, the hole filling of the substrate is performed by one printing / rotation. However, when the via or the through hole is deep and the paste is insufficient in quantity, the above process is repeated several times. The paste may be filled by this.
[Brief description of the drawings]
1 is a schematic perspective view of a paste filling apparatus according to the present invention. FIG. 2 is a side sectional view of the paste filling apparatus. FIG. 3 is a top view of a rotating body. FIG. 4 is a paste according to a first embodiment of the present invention. FIG. 5 is a partially enlarged cross-sectional view of a printed circuit board showing the steps of the filling method. FIG. 5 is a partially enlarged cross-sectional view of the printed circuit board showing the steps of the paste filling method according to the second embodiment of the present invention.
DESCRIPTION OF SYMBOLS 10 ... Paste filling apparatus 11 ... Rotating shaft 12 ... Rotating body 13 ... Substrate holding part 14 ... Fixed drum (fixed housing)
24 ... Motor (drive mechanism)
25, 26 ... pulley (drive mechanism)
27 ... Belt (drive mechanism)
30, 40 ... Printed circuit board 33 ... Via hole (bottom via)
35, 42 ... paste 36, 43 ... bubble 41 ... through hole 44 ... heat-resistant release film (occlusion body)

Claims (2)

  A method of manufacturing a printed circuit board in which a hardened paste is filled in a bottomed via, the paste being attached to the printed circuit board so as to enter the bottomed via, and then opening the bottomed via A method of manufacturing a printed circuit board filled with paste, wherein the printed circuit board is rotated with its direction directed toward the center of rotation, and the paste that has hardened is polished and removed from the surface of the substrate.  A method of manufacturing a printed circuit board in which a hardened paste is filled in a through hole, the paste being attached to the printed circuit board so as to enter the through hole, and then, on the one surface side of the printed circuit board In a state where the obstruction covering the opening of the through hole is addressed, the printed circuit board is rotated with the other surface side directed toward the center of rotation, and after the paste is cured, the paste that protrudes from the surface of the substrate is removed. A method for producing a printed circuit board filled with a paste, characterized by polishing and removing.

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