Printed circuit board manufacturing method

Abstract

[Problem] To fill a through-hole of a printed board with a filler properly even when the printed board is of a type such that the through-hole is difficult to fill by conventional methods. [Solution] A seal film 12 is affixed to a lower surface of a printed board 10, and a filler 16 is pushed into a through-hole 11 from the upper surface side of the printed board 10 by screen printing under an evacuated atmosphere, thus filling the through-hole 11 with the filler 16. Thereafter, the film 12 is peeled off the printed board 10 and, in a state in which the printed board 10 is placed over a jig plate 18 having a recess 17 formed in a position corresponding to the through-hole 11, an auxiliary filling step is performed whereby a slight amount of the filler 16 is re-supplied so as to cause the filler 16 to protrude from the lower surface side of the through-hole 11.

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a printed circuit board, in which through holes in the printed circuit board are filled with resin. [Background technology]

[0002] Build-up wiring boards are used as high-density mounting boards for electronic devices. They are configured by stacking multiple circuits on both sides of a core board with through holes via insulating layers. The through holes of the core board are filled with resin for filling holes, and both sides are flattened by buffing, and then multiple circuits are formed on the through holes. Since the core board is made into a multi-layer board by stacking layers in sequence as described above, if the flatness of the core board is poor, it will have a negative effect on the flatness of the layers stacked on top, and therefore on the accuracy of the circuit pattern. For this reason, a high degree of flatness is required for the core board. In addition to the core board of this type of build-up wiring board, for example, a printed circuit board of an IC package carrying a semiconductor chip also requires a high degree of flatness because poor flatness can cause a decrease in the reliability of the connection with the semiconductor chip.

[0003] As described above, methods described in Patent Documents 1 and 2 below are known as methods for manufacturing printed circuit boards that have through-holes and require a high degree of flatness. In these methods, an adhesive film is attached to the underside of the printed circuit board to make the through-holes bottomed, and then a filler is placed on the printed circuit board in a vacuum atmosphere and a squeegee is slid over the filler to push it into the through-holes. After that, the filler is cured, the adhesive film on the back surface is peeled off, and the resin remaining on both sides of the printed circuit board is removed by buffing to flatten it. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2003-188308 A [Patent Document 2] JP2005-57109A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the above method, the adhesive film is peeled off after the filler is hardened, so the adhesive layer of the adhesive film adheres to the hardened filler in the through-hole and then peels off from the adhesive film, leaving the adhesive layer in the through-hole together with the filler, thereby reducing the properties of the printed circuit board.

[0006] However, if the adhesive film is peeled off before the filler hardens, some of the unhardened filler will adhere to the adhesive film and escape from the through-hole, resulting in a shortage of filler on the back side of the printed circuit board and creating a dent of several tens of microns after the filler hardens, which impairs the flatness of the printed circuit board.

[0007] Therefore, the present inventors have invented the following method as an undisclosed technique. As shown in FIG. 1(A), a fixture plate 4 is prepared in which a recess 3 is formed in advance at a position corresponding to a through hole 2 of a printed circuit board 1, and the fixture plate 4 is placed against the back surface of the printed circuit board 1. Then, as shown in FIG. 1(B), for example, a screen printing method using a screen plate 5 and a squeegee 6 is used to fill the through hole 2 of the printed circuit board 1 with a filler 7. In this way, the filler 7 is filled in the through hole 2, and can be made to protrude from both the front and back surfaces of the printed circuit board 1 as shown in FIG. 1(C). Therefore, if the filler 7 is hardened and both surfaces of the printed circuit board 1 are polished, for example, by buffing, the hardened filler 7 remaining on both surfaces of the printed circuit board 1 can be removed, and both surfaces of the printed circuit board 1 can be smoothed.

[0008] For printed circuit boards of conventional specifications, the above-mentioned undisclosed invention makes it possible to fill each through hole 2 evenly with filler 7, and as a result, a printed circuit board 1 that is sufficiently flat can be manufactured by polishing both the front and back sides.

[0009] However, in recent years, for example, in printed circuit boards on which semiconductor chips are mounted, the wiring patterns and through-holes in the related areas have been getting narrower and narrower in pitch as the semiconductor chips become smaller, resulting in areas in the printed circuit board where extremely small through-holes are densely packed, and the opening diameter of through-holes in the same board becoming wider, i.e., through-holes with a variety of different opening diameters are mixed.

[0010] When the filler 7 is filled into the through-hole 2 by the above-mentioned screen printing, the smaller the opening diameter of the through-hole 2, the larger the filling resistance of the filler 7 to the through-hole 2. For this reason, for example, if the above-mentioned undisclosed invention is used to fill holes in a printed circuit board in which the opening diameters of the through-holes 2 vary widely within the same board, the filler is more easily pushed into the through-holes 2 with larger opening diameters than into the through-holes 2 with smaller opening diameters. For this reason, as shown in FIG. 1(C), a phenomenon occurs in which the amount of protrusion of the filler 7 on the back side of the printed circuit board 1 is significantly larger in the through-holes 2 with larger opening diameters than in the through-holes 2 with smaller opening diameters. The protrusion of the filler 7 is buffed after the filler 7 hardens. For this reason, if an attempt is made to sufficiently polish the protrusion of the filler 7 in the through-hole 2 on the large diameter side, the polishing proceeds excessively on the side of the through-hole 2 with the smaller opening diameter, and there is a possibility that even the copper foil of the printed circuit board 1 will be scraped off. In addition, the polishing burden is large, and abrasives are consumed in large quantities, resulting in a large amount of expensive filler being wasted. However, if the printing conditions are determined so that the amount of filler 7 protruding from the larger diameter through-hole 2 is appropriate in terms of polishing ability, a problem occurs in that the filling into the smaller diameter through-hole 2 is insufficient.

[0011] In addition, not only when through holes of various sizes are mixed, but also when the printed circuit board has an area where extremely small through holes are densely packed in a lattice pattern, such as directly under a large semiconductor chip, the following problem occurs. That is, a wide recess 3 that covers the entire through hole area must be formed in the jig plate 4 that supports the printed circuit board having this type of densely packed through holes. Then, during screen printing, the printed circuit board 1 is supported by the jig plate 4 and does not bend much at the outer periphery of the dense through hole area, but in the center of the area, the printed circuit board 1 is bent in a concave manner due to the downward pressure of the squeegee 1. The thinner the printed circuit board 1 is, the more noticeable this unevenness in the amount of bending becomes, which ultimately leads to unevenness in the amount of filling material. Furthermore, in a printed circuit board having a large through hole with an opening diameter of about 0.5 mm or more, the large through hole has an extremely small filling resistance to the filler, so it is difficult to adjust the screen printing conditions to make the filling amount uniform.

[0012] The present invention was completed based on the above-mentioned circumstances, and its object is to provide a method for manufacturing printed circuit boards that can properly fill filler material into through-holes, even in printed circuit boards with through-hole specifications that are difficult to fill using conventional methods. [Means for solving the problem]

[0013] The present invention is a method for manufacturing a printed circuit board having through-holes penetrating the board and filled with a filler, which includes a filler filling step in which, with an opening end face of the through-hole on one side of the printed circuit board being sealed so that the filler does not leak out, the filler is pushed into the through-hole from the other side of the printed circuit board, and the filler is filled into the through-hole from the other side of the printed circuit board after the filler filling step and before the filler hardens, with the opening end face of the through-hole left open.

[0014] In the filler filling process, the filler is filled to the back of the through-hole with one of the opening end faces sealed, and then, before the filler hardens, an auxiliary filling process is carried out with the opening end face of the through-hole open, so that the filler can also protrude out from one of the opening end faces of the through-hole.

[0015] This auxiliary filling process can employ a filling method that uses a smaller force to push the filler in than the filler filling process. Therefore, even if the opening diameters of the through holes vary from large to small, even if there are a large number of very small through holes, or even if large through holes are included, the additional amount of filler filled for each through hole does not vary significantly, and an appropriate amount of filler can be supplied from each through hole.

[0016] In the filler filling step, a film having an adhesive layer formed on the surface of a film base material may be attached to one side of the printed circuit board to close the open end of the through hole in a state in which the filler does not come out, and then the printed circuit board may be placed on a flat jig to push the filler into the through hole from the other side of the printed circuit board. In this way, even if the flatness of the printed circuit board is poor, the open end of the through hole can be reliably closed. The film needs to be peeled off prior to the auxiliary filling step, but even if part of the filler filled in the through hole at that time adheres to the film and is removed, the filler is replenished by the auxiliary filling step, so that an appropriate amount of filler can be supplied to each through hole. In addition, even if an excess amount of the filler is supplied more than the amount removed to protrude the filler to the back side, the protruding amount can be made almost equal for each through hole.

[0017] When the auxiliary filling process has created a state in which the appropriate amount of filler protrudes approximately evenly from each through hole, a filler hardening process is then carried out to harden the filler, and if necessary, a polishing process is carried out to polish the protruding portions, thereby producing a printed circuit board with flat surfaces on both sides.

[0018] When the filler filling process and the auxiliary filling process are carried out by screen printing, not only can the filler be selectively filled into a portion of the through-hole groups in the printed circuit board, eliminating waste, but the through-hole groups can be divided into multiple groups and the holes can be filled by multiple screen printing processes, allowing the screen printing conditions to be optimally adapted to each through-hole group.

[0019] If a film used in the film attachment process has a structure in which areas where an adhesive layer is formed coexist with areas where no adhesive layer is formed throughout its entire area, air can escape from the through-holes more easily, making it easier to fill the filler deep inside. This is effective for printed circuit boards with through-holes with a particularly small opening diameter and high aspect ratio (depth / opening diameter).

[0020] When a film substrate having multiple air-permeable pores formed therethrough or multiple ventilation grooves formed on the surface is used as the film to be used in the film attachment process, air can escape from the through-holes more easily, which is effective for printed circuit boards having through-holes with a high aspect ratio.

[0021] (Effects of the Invention) According to the present invention, even in the case of a printed circuit board having through-holes that are difficult to fill using conventional methods, the through-holes can be appropriately filled with a filler. [Brief description of the drawings]

[0022] [Figure 1] Enlarged schematic cross-sectional view showing the hole filling method of the undisclosed invention [Diagram 2] Cross-section of an IC package [Diagram 3] Cross-section of a printed circuit board [Figure 4] Cross-sectional view of the printed circuit board after the film attachment process [Diagram 5] Enlarged plan view of the seal film [Figure 6]Cross-sectional view of the printed circuit board set on the jig plate [Figure 7] Cross-sectional view showing the filler filling process [Figure 8] A plan view showing the air flow during the filler filling process. [Figure 9] Cross-sectional view showing the air flow during the filler filling process [Figure 10] Cross-sectional view showing the film peeling process [Figure 11] Cross-sectional view showing the printed circuit board after the film peeling process [Figure 12] Cross-sectional view of the printed circuit board set on the counterbore jig plate [Figure 13] Cross-sectional view showing the auxiliary filling process [Figure 14] Cross-sectional view of the printed circuit board after the auxiliary filling process [Figure 15] Cross-sectional view showing a printed circuit board after a planarization process DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] <Embodiment 1> A first embodiment of the present invention will be described with reference to FIGS.

[0024] In this embodiment, an example is shown in which the present invention is applied to a printed circuit board of an integrated circuit package having a ball grid array. A printed circuit board 10 manufactured in this embodiment has a large number of through holes 11, and as shown in Fig. 2, a semiconductor chip 20 is mounted on the upper surface of the printed circuit board 10 and electrically connected to lands (not shown) formed on the upper surface of the printed circuit board 10 by a large number of solder balls 21. The semiconductor chip 20 is further fixed onto the printed circuit board 10 by an adhesive 22, and a heat sink 23 is bonded to the upper surface of the semiconductor chip 20 by an adhesive 24.

[0025] As a starting material for the printed circuit board 10, a printed circuit board with copper clad on both sides and having a thickness of, for example, about 0.1 mm to 8.0 mm is recommended. In the printed circuit board 10, a through hole with an inner diameter of, for example, about 0.1 mm to 5.0 mm is formed in advance, and the inner wall surface of the through hole is plated with an inner surface that is conductive to the copper foil on both sides to form a through hole 11 that electrically connects the copper foil on both sides. As shown in FIG. 3, the through hole 11 has an opening end surface that opens on both the upper and lower sides of the printed circuit board 10. In this embodiment, the through holes 11 may have various opening diameters, large and small, mixed in the printed circuit board 10, and their aspect ratios (board thickness of the printed circuit board 10 / opening diameter of the through hole 11) are variously different. For example, the aspect ratio of the through hole 11A with a small opening diameter shown in FIG. 3 (the vertical and horizontal scales of the drawings are not the same) is, for example, 10 or more, and the aspect ratio of the through hole 11B with a large opening diameter is, for example, about 5.

[0026] (Film pasting process) First, a seal film 12 is attached to one surface (lower surface in FIG. 3, hereinafter referred to as "rear surface") of the printed circuit board 10 (see FIG. 4). The seal film 12 is formed by printing an adhesive layer 12B on a base film 12A made of a synthetic resin having a thickness of, for example, 35 μm to 100 μm and having a smooth surface. The adhesive layer 12B is formed in a scattered dot arrangement, for example, circular dots arranged in a staggered pattern as shown in FIG. 5, that is, the adhesive layer 12B is formed in a region of the film base material 12A in a form in which the formed region and the non-formed region of the adhesive layer 12B coexist in the entire region of the base film 12A. Note that since both the base film 12A and the adhesive layer 12B are transparent, the circular region representing the adhesive layer 12B is drawn with halftone dots to make it easier to see. The diameter of the adhesive layer 12B may be smaller or larger than the diameter of the through-hole 11 shown by the two-dot chain line in the figure, and is preferably in the range of 100 μm to 500 μm, and these are preferably arranged at intervals of 10 μm to 400 μm.

[0027] 5, the base film 12A has minute breathable pores 12C having a diameter of about 10 μm to 100 μm, which are scattered and disposed almost uniformly over the entire surface of the base film 12A in a lattice or houndstooth pattern with a pitch of, for example, 2 mm to 4 mm. These pores 12C are formed by pressing a needle with a sharp tip against the surface opposite to the surface on which the adhesive layer 12B is formed after the adhesive layer 12B is formed on the base film 12A, and minute burrs generated when the needle penetrates the base film 12A may be projected onto the surface on the adhesive layer 12B side.

[0028] Immediately after (for example, several seconds after) the hole making process for forming the pores 12C as described above, the seal film 12 is pressed with low pressure against the back surface of the printed circuit board 10 so that the adhesive layer 12B side faces the back surface of the printed circuit board 10, and the film attaching process is performed to attach the seal film 12 to the printed circuit board 10. As a result, the open end surface on the lower surface side of the through hole 11 is closed in a state in which the filler does not come out. In other words, the open end surface on the lower surface side of the through hole 11 is almost sealed in terms of viscous liquid. However, since the seal film 12 is pressed with low pressure in the film attaching process and minute burrs generated by the hole making process slightly protrude toward the printed circuit board 10, the entire area of ​​each adhesive layer 12B does not adhere tightly to the printed circuit board 10, but only minute areas of irregular shapes adhere to the printed circuit board 10, so that minute gaps exist at the interface between the printed circuit board 10 and the seal film 12, and the gaps are connected to the breathable pores 12C. Therefore, the open end face on the lower side of the through hole 11 is sealed in terms of viscous liquid as described above, but is in a state of gas communication with the outside.

[0029] (Filling material filling process) Next, as shown in Fig. 6 and Fig. 7, the printed circuit board 10 with the seal film 12 attached thereto is placed on a flat jig 13, and the seal film 12 is filled with the filler by a vacuum printer. The vacuum printer is equipped with a screen plate 14 and a squeegee 15 that slides on the screen plate 14 in a vacuum chamber maintained at an atmospheric pressure (for example, 50 Pa to 100 Pa) sufficiently lower than atmospheric pressure, and in a state where a filler 16, for example, a synthetic resin for filling holes, is supplied onto the screen plate 14, the squeegee 15 is lowered onto the screen plate 14 and slid on the screen plate 14, thereby pushing the filler 16 downward through the screen plate 14. As shown in Fig. 7, the printed circuit board 10 with the seal film 12 attached thereto is placed so that the seal film 12 side is in contact with the flat jig 13, and the other surface on the opposite side (hereinafter referred to as "front surface") is located under the screen plate 14.

[0030] The screen plate 14 has through holes (not shown) formed at positions corresponding to the through holes 11 of the printed circuit board 10. By accurately positioning the printed circuit board 10 with respect to the screen plate 14, the through holes formed in the screen plate 14 communicate with the through holes 11 of the printed circuit board 10, and the filler 16 is forced into the through holes 11.

[0031] The flattening jig 13 has a flat surface not only in the area corresponding to the through-hole 11 but also in the entire area, and supports the seal film 12 from below, keeping the open end face on the back side of the through-hole 11 blocked by the seal film 12. This makes it possible to prevent the filler 16 pressed into the through-hole 11 from leaking out from the gap between the seal film 12 and the printed circuit board 10.

[0032] As is well known, the squeegee 15 is a plate made of synthetic resin, and by adjusting the pressing angle and pressing pressure against the screen plate 14, the force with which the filler 16 is pressed under the screen plate 14, and therefore the amount of filler 16 pressed in, can be adjusted.

[0033] Since the adhesive layer 12B is formed in a scattered pattern on the seal film 12 and a large number of pores 12C are formed in the seal film 12, when screen printing is performed on the printed circuit board 10 in a vacuum printing machine, when the filler 16 is forced into the through-hole 11, a small amount of gas remaining in the through-hole 11 is discharged into the vacuum chamber through the gaps between the scattered adhesive layers 12B, the pores 12C, and the tiny gap between the seal film 12 and the flat jig 13, as shown by the dashed lines in Figures 8 and 9. Therefore, the filler 16 smoothly fills the through-hole 11 until it reaches the seal film 12.

[0034] On the other hand, on the surface of the screen plate 14 opposite the seal film 12, after the squeegee 15 has passed, a protrusion 16A is formed in which the filler 16 slightly rises from the opening end face of the through-hole 11, as shown in Fig. 7. This protrusion 16A is formed by the filler 16 leaking out of the through holes of the screen plate 14 when the screen plate 14 separates from the surface of the printed circuit board 10, so the protrusion dimension from the opening end face of each of the through-holes 11 is roughly uniform for each of the through-holes 11, regardless of the diameter of the through-holes 11.

[0035] (Film peeling process) Next, the printed circuit board 10 is removed from the vacuum printing machine, and the seal film 12 is peeled off from the printed circuit board 10 as shown in Fig. 10. In this embodiment, the filler 16 used has the property of being completely cured by heating or ultraviolet irradiation, but after the above-mentioned filler filling step, before the curing of the filler 16 starts, the seal film 12 is peeled off from the printed circuit board 10, so that a part of the filler 16 in the through-hole 11 may come out from the through-hole 11 while remaining attached to the adhesive layer 12B. As a result, a recess 16B of about 10 µm may be formed in the small-diameter through-hole 11A, and a recess 16C of about 30 µm may be formed in the large-diameter through-hole 11B (see Fig. 11).

[0036] (auxiliary filling process) Next, the printed circuit board 10 from which the seal film 12 has been peeled off is set in the vacuum printer again. In this case, instead of the flat flat jig 13, a support jig 18 having recesses 17 formed at positions corresponding to the through holes 11 of the printed circuit board 10 is set in advance in the vacuum printer, and the printed circuit board 10 is placed on the support jig 18 by positioning the printed circuit board 10 so that each recess 17 corresponds to each through hole 11. The recesses 17 may be independent recesses 17A having an inner diameter slightly larger than the opening diameter of the through hole 11A and corresponding one-to-one to each through hole 11A as shown in FIG. 12, or may be integrated recesses 17B in which one recess corresponds to the formation area of ​​a plurality of through holes 11B. The area of ​​the upper surface of the support jig 18 other than the recesses 17A and 17B is flat and is in close contact with the back surface of the printed circuit board 10 to support the printed circuit board 10.

[0037] In this manner, the printed circuit board 10 is positioned and placed on the support jig 18 in the vacuum printing machine, and if necessary, the vacuum atmosphere is returned to and the filler 16 is screen-printed from the front side of the printed circuit board 10. In this case, the through-holes 11 are already filled with the filler 16 almost entirely, i.e., in the areas other than the recesses 16B and 16C, and the open end faces on the back side of each through-hole 11 are in communication with the recesses 17A and 17B of the support jig 18, so that the filling resistance of the filler 16 is extremely small. Therefore, even if the filling force of the filler 16 is extremely small, for example by reducing the pressing dimension when the squeegee 15 is brought into contact with the screen plate 14, the filler 16 is supplied supplementarily into the through-holes 11, and the filler 16 protrudes from the open end faces on the back side of the through-holes 11 as shown in FIG. 13, forming the protrusions 16D.

[0038] This screen printing is performed under conditions in which the filling force of the filler 16 is extremely small, so regardless of the opening diameter of the through-hole 11, whether it is a small-diameter through-hole 11A or a large-diameter through-hole 11B, the protruding volume from the opening end face of each protrusion 16D can be kept to a smaller variation than in the past.

[0039] (filler curing process) Next, the printed circuit board 10 having completed the auxiliary filling process is removed from the vacuum printing machine, and the filler 16 is completely cured by heating or irradiating with ultraviolet light.

[0040] (flattening process) After the filler 16 has completely hardened, both sides of the printed circuit board 10 are polished, for example by buffing, to remove the protrusions 16A, 16D protruding from both opening end faces of the through holes 11 on both sides of the printed circuit board 10, and the entire surfaces of the printed circuit board 10 are flattened as shown in FIG. 15.

[0041] Here, the buff polishing machine is not shown, but is equipped with a plurality of buffs having a rotation axis extending along the surface of the printed circuit board 10 and in a direction perpendicular to the conveying direction while the printed circuit board 10 is placed on rollers and conveyed in a predetermined direction. The buffs are arranged on both the upper and lower sides of the printed circuit board 10, and a plurality of buffs, for example, two buffs are arranged on each side at intervals in the conveying direction of the printed circuit board 10. In this embodiment, the printed circuit board 10 is first polished by the first buff on the back side, then polished by the first buff on the front side, then polished by the second buff on the front side, and finally polished by the second buff on the back side. When polishing with each buff, an abrasive is supplied, and the printed circuit board 10 is supported by a backup roll provided on the opposite side to the buffs.

[0042] In the initial buffing, the volume of the protruding portion 16D of the filler 16 on the back side of the printed circuit board 10 varies little regardless of the diameter of the through hole 11, so that the polishing of the protruding portion 16D can proceed evenly over the entire back side of the printed circuit board 10.

[0043] Furthermore, when moving on to polishing the front surface side of the printed circuit board 10, the volume of the protruding portion 16A of the filler 16 also varies little regardless of the diameter dimension of the through hole 11, so that the polishing of the protruding portion 16A can also proceed evenly over the entire front surface side of the printed circuit board 10. Therefore, polishing proceeds similarly on both the back side and the front side, no localized polishing residue occurs due to volumetric variations in the protrusions 16, and when moving to polishing the opposite side, the printed circuit board 10 is not pressed strongly against the buff by the polishing residue partially remaining on the back side, and both sides are polished evenly. This makes it possible to prevent excessive copper foil removal locally on both the front and back sides of the printed circuit board 10 and excessive remaining filler material 16.

[0044] Thus, according to this embodiment, when filling the through holes 11 of the printed circuit board 10 with the filler 16, even if the opening diameters of the through holes 11 vary from large to small, the protruding volume of the protruding portions of the filler 16 on both the top and bottom surfaces of the printed circuit board 10 can be kept to a small variation regardless of the opening diameter of the through holes 11, so that in the subsequent flattening process, the protruding portions 16A, 16D of the filler 16 can be polished evenly over the entire area.

[0045] In particular, in this embodiment, since the filling of the filler 16 is performed by screen printing in the filler filling step, the filler 16 can be selectively filled only in the target through holes 11. Therefore, for example, a multiple division type filler filling step can be adopted in which all the through holes to be filled are divided into two types according to their aspect ratios, and only the through holes with a high aspect ratio are filled in the first screen printing, and only the through holes with a low aspect ratio are filled in the second screen printing. This allows the printing conditions suitable for the target through holes in each screen printing to be adopted, and is particularly suitable for filling printed circuit boards containing through holes with a high aspect ratio.

[0046] Furthermore, in this embodiment, the adhesive layer 12B of the sealing film 12 is formed by a collection of multiple dots scattered within the area of ​​the base film 12A, so that residual air in the through-hole 11 can easily escape through the gaps between the dots (areas where the adhesive layer is not formed), facilitating the filling of the filler.

[0047] <Other embodiments> The present invention is not limited to the embodiments described above and illustrated in the drawings, and the following embodiments, for example, are also included within the technical scope of the present invention.

[0048] (1) In the above embodiment, an example was shown in which the printed circuit board was applied to a printed circuit board for an IC package on which an IC chip is mounted, but the present invention is not limited to this. The present invention is suitable as a method for filling holes in printed circuit boards having through holes with a high aspect ratio, and can of course also be applied to, for example, the core substrate of a build-up board.

[0049] (2) In the above embodiment, an example was shown in which the filler filling step and the auxiliary filling step were performed by screen printing, but instead of using a screen plate, the filler may be supplied to the entire surface of the printed circuit board and the filler may be pushed into the through-holes using, for example, a squeegee, or a pressure difference may be generated on both sides of the printed circuit board and the filler may be pushed in using the pressure difference. In addition, when the filler filling step and the auxiliary filling step are performed by screen printing, both steps are not limited to being performed by the same vacuum printer as in the above embodiment, but may be performed by separate vacuum printers. In that case, the flattening jig and the support jig can be set in each vacuum printer in advance, and there is no need to replace each jig with one vacuum printer, thereby improving productivity.

[0050] (3) In the above embodiment, in the filler filling step, a seal film is attached to one side of the printed circuit board to close the open end surface of one side of the through hole, but the film is not necessarily required, and when the flatness of the printed circuit board is good, the printed circuit board may be placed on a flat fixture plate and the filler may be filled. In addition, in this embodiment, when closing the open end surface of the through hole with a film, the adhesive layer is adhered to the printed circuit board, but the adhesive layer is divided into a plurality of small regions within the region of the film base material and is formed together with the non-forming region where the adhesive layer is not formed, so that air circulation through the non-forming region where the adhesive layer is not formed and thus air discharge from the through hole are permitted, and the filling of the filler is smoothly performed.

[0051] (4) In the above embodiment, a plurality of air-permeable pores are formed in the film substrate of the seal film, so that degassing from the through-holes is promoted when printing the filler in a vacuum atmosphere, and the filling of the filler is smoothly performed. However, it is not essential to form pores in the film substrate, and for example, a porous film (e.g., made of ultra-high molecular weight polyethylene) having air permeability due to continuous pores can be used as the film substrate. In addition, even if an air passage is not necessarily formed through the film substrate, for example, by using a film substrate having a number of grooves of minute depth in a lattice shape or irregular shape on the surface to be attached to the printed circuit board by an adhesive, an air passage communicating with the outside is formed at the interface between the seal film and the printed circuit board when the seal film is attached to the printed circuit board, so that degassing from the through-holes is promoted when printing the filler in a vacuum atmosphere, and the filling of the filler can be smoothly performed.

[0052] (5) In the above embodiment, the auxiliary filling process is performed before the hardening of the filler material begins, but this is not limited to the above and may be performed after the hardening has inevitably or intentionally begun. In short, the auxiliary filling process may be performed in a situation where additional filler material is supplied into the through hole so that a portion of the filler material already filled protrudes from the opening end face of the through hole.

[0053] (6) In the above embodiment, an example was shown in which a conductive copper plating layer was formed on the inner wall surface of the through hole, but this is not limited to this. It is also possible to form a resin layer containing a functional material having the required characteristics selected in terms of conductivity, magnetism, or dielectric property, and the filler may also be a functional material having the required characteristics selected in terms of conductivity, magnetism, or dielectric property.

[0054] (7) In the above embodiment, an example was shown in which the method was applied to a case in which through holes of different diameters were formed in a printed circuit board, but the present invention is not limited to this, and may be applied to filling holes in a printed circuit board having an area where extremely small through holes are densely packed in a lattice or houndstooth pattern (for example, a rectangular area with a narrow through hole pitch of 0.5 mm or less and one side of 20 mm or more), such as directly under a large semiconductor chip. This is because in the filler filling process in which the filler is filled with the filler while the bottom surface of the through hole is sealed with a seal film, the filler is filled into the entire through hole, and the filler is gradually replenished in the subsequent auxiliary filling process, thereby making it possible to suppress bending of the printed circuit board as much as possible and to protrude the filler downward almost evenly.

[0055] Furthermore, even in the case of a relatively large through-hole, for example with an opening diameter of 0.5 mm or more, the filler is first filled into the entire through-hole in the filler filling process, and then the filler is gradually replenished in the subsequent auxiliary filling process, making it easy to control the amount of filler protruding downward, thereby achieving an even protrusion state.

[0056] (8) In the above embodiment, the filler is filled by screen printing, but the present invention is not limited to this, and other filling methods that do not use a screen plate, such as a filling method that uses only a squeegee or a filling method that presses the filler from one side of the printed circuit board without using a squeegee, may be adopted. In short, the filler can be supplied into the through-hole in two stages by carrying out the filler filling step and auxiliary filling step of the present invention using various filler filling methods or a filling method that combines them.

[0057] (9) In the above embodiment, an example was shown in which the adhesive layer 12B is dotted with circular dots, but the shape of the dots is not limited to circular and may of course be non-circular, such as rectangular, polygonal, elliptical, etc. Furthermore, the adhesive layer may be formed in a number of strip-shaped regions. In short, it is desirable that the adhesive layer is not formed over the entire area to be attached to the printed circuit board, but rather that areas in which the adhesive layer is formed and areas in which it is not formed coexist within the area to be attached to the printed circuit board. [Explanation of symbols]

[0058] 10: Printed circuit board 11: Through hole 12: Seal film (film) 12A: Film substrate 12B: Adhesive layer 12C: Pore 13: Flat jig 18: Support jig 14: Screen version 15: Squeegee 16: Filling material 16A,16D: Protrusion

Claims

1. 1. A method for manufacturing a printed circuit board having a through hole penetrating the board, the through hole being filled with a filler, comprising the steps of: a film attachment step of attaching the film with the pores formed therein to one side of the printed circuit board with the adhesive layer to seal the opening end faces of the through-holes so that the filler does not leak out; a filler filling step of pushing the filler from the other side of the printed circuit board to fill the through-holes with the filler; a film peeling step of peeling the film from the printed circuit board after the filler filling step; and an auxiliary filling step of re-supplying the filler from the other side of the printed circuit board after the film peeling step and before the filler hardens, with the opening end faces of the through-holes left open.

2. A method for manufacturing a printed circuit board as described in claim 1, wherein, in the auxiliary filling process, the printed circuit board is positioned and stacked on a support jig having a recess formed at a position corresponding to the through hole, with the one side of the printed circuit board in contact with the support jig and the through hole corresponding to the recess, and the filler is then supplied from the other side of the printed circuit board.

3. A method for manufacturing a printed circuit board as described in claim 1 or claim 2, wherein, in the auxiliary filling process, the filler is supplied from the other side of the printed circuit board so as to protrude from the opening end face on the one side of the through hole.

4. A method for manufacturing a printed circuit board as described in any one of claims 1 to 3, wherein the filler filling step is performed by screen printing in which a screen plate is placed on the other side of the printed circuit board, and the filler is supplied onto the screen plate while a squeegee is slid along the screen plate, thereby filling the filler from pores formed in the screen plate into the through holes, and the filler filling step is performed in multiple screen printing steps with different printing conditions.

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