JP4470465B2 - Electrode for connecting via holes with through holes - Google Patents

Description

  The present invention relates to an interlayer connection electrode of a wiring board, and more particularly to an electrode for via hole connection in which an electrode in the board has a through hole.

In recent years, with the rapid development of small, light, and highly functional electronic devices, the wiring board is also a multilayer board based on resin with an all-layer inner via (also referred to as “via”) hole structure. Has been put to practical use. Hereafter, the manufacturing method of this board | substrate is demonstrated roughly.
(1) A release force bar film having a release agent layer formed only on the insulating layer side is laminated on both sides of a resin insulating substrate made of a prepreg such as an aramid base epoxy resin, and a laser is applied to a predetermined position. Open a through hole.
(2) A conductive paste in which a metal filler is mixed in a resin is filled in the through hole by a squeegee method or the like. Thereafter, the releasable cover films on both sides are peeled off from the prepreg surface.
(3) Copper foils are arranged on both sides of the prepreg, and the conductive paste protruding from the surface of the prepreg by the thickness of the releasable cover film is pressed into the through-hole of the prepreg and further heated. Then, the prepreg and the conductive paste are cured, and the copper foil is fixed to the prepreg surface to obtain a copper foil-clad laminate.
(4) The copper foil is subjected to predetermined etching using photolithography or the like to form a wiring pattern on the surface of the laminate.
(5) Further, the prepreg and copper foil after the processing of (2) above are arranged in this order on both sides or one side of the substrate after the processing of (4), the processing of (3) is performed again, and then the above (4) ).
(6) The above processing is repeated as necessary.
However, these are techniques disclosed in Patent Document 1 below. For this reason, further explanation is omitted.

JP, 2002-118338, A The above other multilayer boards are shown in the following patent documents 2-patent documents 8 for the purpose of improving the electrical connection nature of each part, especially a via hole part besides cost reduction etc. Various inventions have been made. Japanese National Patent Publication No. 10-507315 JP 2000-315867 A JP 2001-203459 A JP 2003-188533 A Japanese Patent Laid-Open No. 2003-258013 JP 2003-298240 A JP 2003-318546 A

By the way, the multilayer substrate is heated under pressure many times during its manufacture. On the other hand, in many cases, the conductive paste is a resin mixed with a metal body (fine particles, fibers, etc.). For this reason, shrinkage is caused by repeated heating in the post-process after the state of (4) in the background art section described above, or heat generation and cooling after use, and as a result, via resistance may increase. is there. The state of this contraction is shown in FIG.
(1) in FIG. 1 shows a cross section of the via hole immediately after manufacture, and (2) shows a cross section of the via hole in which the conductive paste is contracted after several hundred hours under heating after manufacture for an acceleration test. In addition, 10 of a figure is a resin-made insulating board | substrate (base material of a circuit board). 27 is a conductive paste immediately after filling a via hole in a columnar shape, and 28 is a conductive paste shrunk due to heating or the like in a later process. Reference numeral 90 denotes a space generated by contraction of the conductive paste. Reference numeral 48 denotes an electrode (a circuit land or pad which is a connection electrode). For this reason, one via resistance is initially 38 mΩ, but may be 1140 mΩ after 950 hours at 125 ° C.

  From the above, it has been desired to develop a via hole connection structure that does not increase the via resistance under heating and high temperatures.

The present invention has been made for the purpose of solving the above-mentioned problems. A through hole is provided in an electrode in a substrate at both ends of a via hole, and a conductive paste is intruded into the through hole. Prevention of contraction, even if contracted, the outer surface of the through-hole is only recessed, and the contact area with the electrode is not reduced, so that the via resistance is not increased. Furthermore, the contraction is further constrained more mechanically and physically by setting the middle of the inner diameter of the through hole as a maximum or minimum so as to be caught.

In addition, the surface of the electrode facing the conductive paste and the inside of the through hole are roughened to increase the contact area with the conductive paste and improve the adhesion, and to prevent the generation of space due to the shrinkage of the conductive paste. In the production, a transfer foil process is used. For this reason, land and pad portions as well as other circuit patterns are simultaneously formed on the transfer substrate, and the same circuit pattern including lands, pads, etc. that become electrodes as well as via-hole connection structures is transferred simultaneously to the resin substrate. It can be manufactured in the process. Further, it is considered that the surface on the conductive paste side can be easily roughened because the electrode is formed on the transfer substrate.

  By adopting the above means, in particular, the conductive paste can be put into the through-holes of the electrodes in the substrate, the direction of shrinkage can be dispersed by forming the holes, and the shrinkage can be restrained. Heating in the subsequent process and shrinkage due to the passage of time are eliminated or very little, if any. As a result, the connection resistance between the electrode and the via hole is due to repeated heating, heating during use, and cooling. The increase is very small compared to conventional products. This also improves the reliability of the electronic device.

Hereinafter, the present invention will be described based on preferred embodiments thereof.
(First embodiment)
In the present embodiment, as shown in FIG. 2B, the inner diameter of the central portion of the through hole of the electrode 41 is the largest. For this reason, even if the conductive paste 26 is contracted, the contraction force is dispersed and, in addition, the shape of the inner peripheral surface of the electrode hole is mechanically or physically constrained. However, as shown in FIG. 2 (B), only the recess 91 is formed on the inner peripheral surface in the hole. For this reason, the contact area between the conductive paste and the electrode hardly changes, and even if there is an increase in via resistance, it can be suppressed slightly. It should be noted that, as a precaution, the drawing shows a state where the conductive paste is contracted, and of course there is no recess in the hole at the time of manufacture.

Next, a method for manufacturing the circuit board itself will be described.
FIG. 3 (1) shows a prepreg 10 that is a resin insulating substrate in which a conductive paste 25 is filled in a via hole, and a transfer electrode 40 and a circuit pattern 49 having a through hole 42 in the center. A state in which the metal foil for transfer 51 formed in (1) is positioned so that the electrode 40 fits into the via hole formed in the prepreg 10 and is going to be attached from both sides.
(2) of FIG. 3 shows a state in which the metal foil for transfer 51 is pressed and further heated in a state where it is correctly disposed on the prepreg 10.
FIG. 3 (3) shows a state in which the transferred circuit is electrically connected in the thickness direction of the substrate through a via hole formed in the resin-made insulating substrate 10. The transfer metal foil has already been removed. Thereafter, in some cases, another insulating substrate or copper foil is attached to the top and bottom by heating under pressure, etc., and a circuit pattern is formed by etching or the like on the copper foil, and this is repeated to form a multilayer circuit pattern. It will be formed.

Further, (1-a) in FIG. 3 is a view of the electrode 40 in which the central through hole 42 is formed as seen from the side of the substrate for transfer, and a circuit is connected to the land or pad of the electrode 40. . It is shown for reference.
Then, although the order is not be is reversed, the shape shown in FIG. 2 (B), i.e. a method for manufacturing the transfer substrate on which electrodes are formed on the surface of the through hole in the center, see Figure 4 However, it demonstrates in order.
(1) First, a photosensitive dry film film 60 (manufactured by DuPont, product number “FX-140”) is formed on a stainless steel transfer substrate 50, and a photomask 70 is attached thereon.
(2) Next, the photomask 70 is exposed to light from above to be developed. At this time, as shown in (2-a), the exposure condition such as the focus is slightly blurred and the thickness of the dry film is adjusted, or other diffraction of light is used to cut the center of the remaining dry film in the vertical direction. The exposure is performed so that the surface is trapezoidal, that is, spreads downward in the figure.
(3) Next, the photomask 70 is removed, and then the non-exposed portion is removed.
(4) The transfer substrate 50 is subjected to copper plating, and a copper layer is formed on the removed non-exposed portion. In this example, electroplating was performed for about 45 seconds to deposit a copper film to a thickness of 35 μm.
(5) Finally, the exposed dry film is removed by etching or the like.
In this case, it is preferable to form a circuit pattern on the transfer substrate at the same time from the viewpoints of reduction of process and cost.
When an electrode having a through hole formed in this way (narrow hole diameter is 100 μm, wide diameter is 110 μm), one via resistance having a via diameter of 300 μm and a substrate thickness of 800 μm is initially 14 mΩ, It was 54 mΩ after 950 hours at 125 ° C.

(Second Embodiment)
The manufacturing method of electrodes having other shapes will be described with reference to FIG.
FIG. 5A uses wet etching. For this reason, 85 is an etching resist and 80 is an etching resin layer. In the wet etching, the etching solution enters the inside through the opening 86 of the etching resist 85 and erodes the etching resin layer 80, so that the etching spreads downward.

  In addition, after a cured resin column having a developed shape having the shape shown in this figure is once formed, the transfer substrate is plated with copper and the resin is removed in the same manner as in FIG.

(B) of FIG. 5 forms a through-hole with a thick inner diameter at the center in the electrode. In this case,
(1) An epoxy resin layer 90 and a copper foil 95 are formed on a stainless steel transfer substrate 50, and a medium-sized hole 91 is formed using a YAG laser.
(2) The copper foil is removed, and the holes of the etching resin layer are filled with copper 96 by electroplating.
(3) The epoxy resin layer is removed by etching, and the transfer electrode 40 is manufactured.
In any production method, cleaning with 7% hydrochloric acid or pure water, degreasing, etc. are performed as necessary. However, since these are well-known techniques, description thereof is omitted.

  When an electrode having a through hole formed in this way (wide hole diameter of 100 μm, narrow diameter of 92 μm) is used, the resistance of one via having a via diameter of 300 μm and a substrate thickness of 800 μm is initially 14 mΩ. The temperature became 51 mΩ after 950 hours at 125 ° C.

(Third embodiment)
In the present embodiment, the surface of the contact surface side with the conductive paste including the inner surface of the through hole of the electrode in the substrate is subjected to a roughening treatment. Therefore, the following processing is performed in a state in which the electrodes are formed on the transfer substrate, that is, the state shown in FIG. 4 (5) (three holes are opened, the narrow hole diameter is 75 μm, and the wide hole diameter is 80 μm). . In this embodiment, in order to ensure good electrical resistance with the conductive paste, in this embodiment, not black oxidation treatment in which copper oxide is formed on the surface, but plating such as gold, etching and blast treatment, etc. Perform mechanical processing. However, since these processes themselves are well-known techniques, description thereof is omitted.

  In the present embodiment using gold plating, one via resistance having a via diameter of 300 μm and a substrate thickness of 800 μm was initially 14 mΩ, and became 41 mΩ after 950 hours at 125 ° C.

As mentioned above, although this invention has been demonstrated based on the some embodiment, it cannot be overemphasized that this invention is not limited to them. That is, for example, the following may be performed.
(1) Use aluminum or the like as the electrode in the substrate, or use other plated materials such as gold plating, etc. Other than the substrate, transfer substrate, conductive paste, and chemicals used in manufacturing, etc. Materials are used.
(2) The thickness of the electrode in the substrate is also set to other dimensions. Further, depending on the size of the electrode and the diameter of the via hole, the cross-sectional shape of the through hole is not only a circle but also an ellipse or a polygon.

It is a figure which shows notionally that a conventional via hole shrinks and a space is generated, resulting in poor contact with an electrode. FIG. 6 is a reference diagram illustrating a via hole having a through hole in an electrode, and the inner diameter of the through hole is smaller toward the center of the thickness of the substrate. In the via hole according to the present invention, the inner diameter of the through hole is caught with the middle of the thickness of the substrate being minimized or maximized, so that the contact with the electrode in the substrate is maintained well even when the conductive paste contracts. It is a figure which shows notably a mode that it is performed. It is a figure which shows the manufacture procedure of the circuit board itself which has a through-hole in an electrode . It is a reference drawing which shows the manufacturing procedure of the electrode for via holes which has a through-hole . It is a figure which shows the principal part of the manufacture procedure of some other embodiment of the electrode for via holes which concerns on this invention.

Explanation of symbols

10 Prepreg (resin insulating substrate)
20 Conductive paste in via hole 25 Conductive paste in via hole (before manufacture)
26 Shrinked conductive paste (after accelerated test of example)
40 Electrode in substrate with through hole at both ends of via hole 42 Through hole of electrode 48 Electrode at both ends of via hole (prior art)
50 Transfer Substrate 51 Transfer Substrate with Electrodes 60 Photosensitive Resin Film (Dry Film)
70 Photolithographic Mask 80 Etching Resin Layer 85 Etching Resist 86 Mask Opening 90 Epoxy Resin Layer 95 Copper Foil

Claims (4)

Electrode in the substrate interlayer connection portion formed by filling a conductive material obtained by dispersing metal body into the resin in the via holes formed in the substrate has a through hole in the center, the conductive material into the interior of the through hole there invaded, and a via-hole of the connecting structure in which part the contact of the conductive material the inner surface of the flash circuit to buried the electrodes on the substrate, the inner diameter of the through hole, the thickness of the substrate A via hole having a connection structure characterized in that there is a trapping with a minimum or maximum halfway , and the electrode has a roughened surface on the conductive material side and an inner surface of the through hole. The via hole of the connection structure according to claim 1, wherein the electrode is a land or a pad member that is electrically part of a circuit. A circuit board electrode having a via hole connection structure in which a conductive material is filled in a via hole of a substrate, and an electrode in which a through hole into which the conductive material has penetrated is formed on the upper and lower end surfaces thereof. A method of manufacturing a plating substrate, wherein the photoresist film formed on the surface of the transfer substrate is removed from the photoresist film using photolithography to remove the portion of the photoresist that becomes the electrodes and circuits, and the manufacturing step A plating step of plating the plated substrate and plating the metal at a place where the photoresist has been removed, and a transfer electrode substrate completion step of removing all the photoresist on the surface of the transfer substrate after the completion of the plating step; The manufacturing method of the electrode for transfer used for the via-hole connection of the circuit board of Claim 1 characterized by the above-mentioned. A circuit board electrode having a via hole connection structure in which a conductive material is filled in a via hole of a substrate, and an electrode in which a through hole into which the conductive material has penetrated is formed on the upper and lower end surfaces thereof. And a plating substrate manufacturing step of removing a portion of the resist that is to be the electrode and circuit from the resist film formed on the surface of the transfer substrate by etching, and the plating manufactured in the step. A plating step of plating the substrate for plating and plating the metal at a place where the resist is removed, and a transfer electrode substrate completion step of removing all the resist on the surface of the transfer substrate after the plating step is completed. The method for producing a transfer electrode used for via-hole connection of a circuit board according to claim 1.

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