JP2005159074A - Electrode for connection of via-hole having projected part at internal layer side - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an increase in resistance in a via hole due to the contraction of conductive paste filling the via hole formed to electrically connect layers. <P>SOLUTION: A projected part toward a conductive paste side is formed to an electrode for connecting both ends of a via hole and thereby the contraction of the conductive paste is dispersed. The depth (height) of the projected part is set to 6 μm or more. The conductive paste of the electrode is roughed. For the manufacturing of the electrode having the projected part, a transfer foil process, plating, etching or the like are employed. A circuit is also manufactured together with a land and a pad to which electrodes are formed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an interlayer connection electrode of a multilayer wiring board, and more particularly to a via hole connection electrode having a convex portion toward an inner layer side (substrate side, conductive pace side).

In recent years, with the rapid progress of miniaturization, light weight, and high functionality of 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 foil is 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 laminated substrate.
(4) The copper foil is subjected to predetermined etching using photolithography or the like to form a wiring pattern on the substrate surface.
(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 already 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 following patent documents 2-patent documents 5 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. However, since these are so-called well-known technologies at the present time and are not directly related to the present invention, description thereof will be omitted. JP 2001-203459 A JP 2003-188533 A Japanese Patent Laid-Open No. 2003-258013 JP 2003-298240 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 metal fine pores (such as filler). For this reason, the volume may be reduced due to overheating in the post-process after the state (4) in the background art column described above or due to deterioration due to the passage of time after manufacture, and as a result, the via resistance may increase. This reduction is shown in FIG.
(1) of this figure shows the cross section of the via hole immediately after manufacture, and (2) shows the cross section of the via hole in which the conductive paste is reduced after several hundred hours under heating after manufacture for the acceleration test. In addition, 10 of this figure is a resin-made insulating board (base material of a circuit board). 27 is a conductive paste immediately after being filled in a columnar shape in the via hole, and 28 is a conductive paste reduced due to heating in a later process. Reference numeral 90 denotes a space generated by contraction of the conductive paste. Reference numeral 48 denotes an electrode (connection electrode). For this reason, the via resistance was initially 2.7Ω to 4.5Ω, but it may become 80Ω to 170Ω after 800 to 950 hours.

  The above is the result under high temperature and high temperature for the accelerated test. In reality, the shrinkage amount and thus the increase in via resistance are much smaller, but it may occur. For this reason, there has been a demand for the development of a via hole connection structure that does not increase such via resistance and, if any, increases much less than the conventional one.

  The present invention has been made for the purpose of solving the above-described problems. A convex portion is formed on the inner layer side (base material side) of the electrode on the end face of the via hole, and the conductive paste in the via hole shrinks with time. The amount of shrinkage and the non-contact part accompanying shrinkage are made small by dispersing the minute. Further, the depth of the convex portion is devised. Further, the electrode surface is roughened to prevent non-contact due to expansion and contraction of the electrical contact surface. In addition, the method of forming the convex portion is devised with respect to processes and steps such as using transfer, and further using plating and etching. Specifically, the configuration is as follows.

  In the basic mode, part of the electrodes on both end faces at the position where the via hole is blocked, as a rule, a part protruding in the inner layer side is formed at the center, and the contraction amount of the conductive paste inside is dispersed. In order to prevent the electrode and the conductive paste from separating and the via resistance from increasing due to the space generated by the shrinkage. Further, since the conductive paste is compressed by the amount of the protruding portion, the shrinkage after the manufacturing is reduced from this aspect.

  In another aspect, the convex portion is set to 6 μm or more, preferably 10 μm or more, and reduction by dispersion of an appropriate shrinkage rate in the case of a via hole having a normal size is achieved.

  In another aspect, minute irregularities are formed on the surface of at least the conductive paste side of the electrode to promote good mechanical contact with the conductive paste, and also from this surface, shrinkage is reduced.

  In another aspect, the electrode is manufactured in the same process as that of a land or pad that is electrically connected to the part or other circuit configuration, and is naturally made of the same material. To save contact and process.

  In another embodiment, the conductive paste in the via hole is made of a metal body such as Au, Ag, Cr, Pb, Zn, Ni, and Sn, and a resin, particularly a thermosetting resin. It is designed to facilitate conduction and work. And the effect of this invention is fully exhibited. The shape of the metal body may be any of particles, powders, and fibers (fibers), and is not particularly limited.

  In another aspect, an electrode having a small convex portion directed toward the inner layer at the center or the like is formed by performing at least two steps of plating or etching in order to ensure workability and accuracy. In addition to the above, as a matter of course, a predetermined resist film is formed and cleaned by photolithography, dry or wet etching, and other processes such as degreasing are performed.

  Further, in the above aspect, the electrode is formed of, for example, stainless steel for the convenience of cost, process and work, and is thus formed on the surface of the transfer substrate made of a material different from the electrode such as copper. This not only facilitates transfer, but also facilitates roughening of the conductive paste side of the electrode.

  By adopting the above measures, especially by forming a convex part on the inner layer side of the electrode, even if there is no shrinkage due to heating in the subsequent process of the conductive paste or the passage of time after completion of the circuit board, As a result, the connection resistance of the via hole is greatly reduced compared to the conventional product. For reference, the electrical resistance after the acceleration test is about 4 to 70Ω when the convex portion is formed, and about 3 to 30Ω when further roughening is used. As a result, not only the prepreg and the multilayer wiring board but also the reliability of the electronic device is improved.

  Further, if the circuit configuration is formed on the transfer substrate together with the electrodes, the process and cost can be further eliminated, and the substrate is flattened and thinned, which is excellent in this respect.

Hereinafter, the present invention will be described based on preferred embodiments (examples).
(First embodiment)
In the present embodiment, convex portions in the direction of the conductive paste are formed at the centers of the electrodes formed at both ends (upper and lower in the figure) of the via hole. By this convex portion, the contraction of the conductive paste is dispersed and constrained, and even if it contracts, the contact with the electrode as much as possible can be ensured.
FIG. 2 shows this state. (1) of this figure shows the cross section of the connection part of the via hole in the initial stage or immediately after manufacture, and the conductive paste 20 is not contracted. (2) shows a cross section of the via hole in a state where the conductive paste is contracted while being constrained by the convex portion.

  In this figure, reference numeral 40 denotes an electrode in which a convex portion is formed in the central portion on the inner layer (base material) side. 42 is the convex part. 26 is a contracted conductive paste. Reference numeral 91 denotes a space generated between the inside of the electrode 40 due to contraction of the conductive paste, that is, an electrical non-contact portion. However, this space is not only the dispersion action of the shrinkage due to the convex part, but also the effect that the conductive paste is excessively compressed from the beginning, so that the space 90 of the prior art shown in FIG. It is much smaller or almost absent.

Hereinafter, a method of manufacturing the via hole connection structure itself will be described with reference to FIG.
(1) in this figure shows that a transfer electrode 40 and a circuit pattern 49 having a convex portion 42 in the center are formed on the surface of a resin insulating substrate 10 in which a conductive paste 25 is filled in a via hole. The transfer metal foil 50 is aligned so that the electrode 40 fits into the via hole formed in the insulating substrate 10 and is shown to be attached from both sides.
(2) of this figure shows the state which this metal foil for transfer 50 is pressed in the state arrange | positioned correctly at the resin-made insulating substrates 10, and is further heated.
(3) of this figure is a state in which electrical connection is made through a via hole formed through the front and back of the substrate on the surface of the substrate 10 of the circuit substrate. The transfer metal foil has already been removed. After that, depending on the case, 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 on the copper foil, etc., and this is repeated to form a multilayer circuit pattern. It will be formed.

  In addition, the lowermost part of (1) in this drawing is a view of the electrode 40 on which the central convex portion 41 is formed as viewed from above, and is shown only in (1) for reference.

  Next, although the order may have been reversed, a method of manufacturing a transfer substrate in which a copper foil having a convex portion on the resin insulating substrate side at a position corresponding to the via hole is formed will be described.

(First manufacturing method)
This manufacturing method uses two-step plating.
This procedure will be described with reference to FIG. As shown in (1) of this figure, a 35 μm-thick plating resist film 60 is first formed by photolithography or the like at a place other than the position where the electrode is formed on the stainless steel foil 50 after washing and degreasing. Note that photolithography itself is a so-called well-known technique, and various types of photoresists that are commercially available (for example, DuPont product number FX-140) can be used as appropriate.
As shown in (2) of this figure, the stainless steel foil in this state is subjected to an acid treatment with a 7% hydrochloric acid aqueous solution for 45 seconds, and then plated using copper sulfate (electrolytic copper plating), and then a resist film for plating Copper is adhered to a portion where no is formed, and the convex portion 41 is formed. This convex portion becomes the electrode body. Thereafter, the resist film for plating is removed.
As shown in (3) of this figure, a new plating resist film 61 is formed again at a location excluding the position where the convex portion of the electrode on the convex portion is formed. In this formation, the lower resist film is first formed at the same height as the convex part by spin coating or the like, and then the upper resist film is formed by photolithography and etching on the part other than the position corresponding to the convex part. Formed.

  As shown in (4) of this figure, the copper foil in this state is acid-washed under the above-mentioned conditions and then plated again under the same conditions, and further protruded by 35 μm above the wide convex part 41 located at the lower part of the figure The narrow convex portion 42 is formed.

  Finally, as shown in FIG. 5 (5), the plating resist film is removed by cleaning, etching, or the like.

In the present embodiment, the electrode is transferred to the resin insulating substrate by the procedure shown in FIG. 3, and the transfer substrate itself is removed by dissolution or peeling.
At this time, as shown in FIG. 3, it is possible to form not only the via hole connection electrode 40 but also the circuit pattern 49 on the transfer metal foil 50. If it does in this way, it will become possible to manufacture the resin insulation board | substrate which is flat and thin so that there is no protrusion of the thickness for a circuit pattern on an outer surface.

(Second manufacturing method)
This manufacturing method employs two-stage etching. This procedure will be described with reference to FIG. As shown in (1) of this figure, a plate is prepared by depositing a copper film 45 conforming to the thickness of the convex portion of the electrode on the stainless steel foil 50 as a transfer substrate by plating or the like. An etching resist 65 is attached only to a position where the etching is performed by photolithography or the like. In addition, 46 is a part for forming an electrode and its convex part.

  As shown in (2) of this figure, the copper foil in the place where the resist 65 is not formed is removed by wet etching or dry etching. For this reason, a thick portion 46 corresponding to the convex portion of the electrode portion is formed on the transfer stainless steel foil 50.

  As shown in (3) of this figure, etching resists 66 and 67 are attached except for the position above the thick portion 46 and not corresponding to the convex portion of the electrode. For this reason, depending on the case, the etching resist 67 is also attached to the upper surface of the transfer stainless steel substrate 50.

  As shown in (4) of this figure, the portion where the resist for etching is not formed by etching again is removed by etching so that the thickness is the same as the electrode protrudes, in this embodiment 35 μm. .

  Finally, as shown in (5) of this figure, the resist is removed, and an electrode 41 having a convex portion 42 formed at the center is formed on the surface of the stainless steel substrate 50 for transfer.

(Second Embodiment)
In the present embodiment, the inner layer side of the electrode in contact with the conductive paste is roughened in the previous embodiment. As a means for roughening, electroless copper plating, micro-etching, etc. were adopted instead of the inner layer blackening treatment in order to make the electric resistance as good as possible. However, since these are so-called well-known techniques, description thereof is omitted.

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. For example, the following may be performed.
(1) Other materials are used for the base material and the conductive paste.
(2) The circuit pattern is formed by etching the transfer substrate for forming this electrode from the state shown in (2) of FIG. For this reason, the circuit pattern indicated by 49 in this figure is formed in a separate process from the electrodes.
(3) Depending on the width of the electrode and the thickness of the substrate, the convex portion may be formed not only in the center but also in the periphery thereof, and a plurality of the convex portions may be formed, or may be an annular shape or a disconnected annular shape.

It is a figure which shows notionally a mode that the electrically conductive paste with which the inside was shrink | contracted in the via hole of a prior art, and a space arises in the interface with an electrode. It is a figure which shows notionally a mode that shrinkage | contraction of an internal electrically conductive paste decreases in the connection structure of the via hole of the 1st Embodiment of this invention. It is a figure which shows the manufacturing procedure of the via hole itself of the connection structure of the said embodiment. It is a figure which shows the procedure which manufactures the electrode which has a convex part in the center part of the said embodiment on a transcription | transfer board | substrate by the two-step plating method. It is a figure which shows the procedure which manufactures the electrode which has a convex part in the center part of the said embodiment on a transfer substrate with a two-step etching method.

Explanation of symbols

10 Insulating resin substrate (base material for circuit boards)
20 Conductive paste (initial state)
25 Conductive paste (when filling)
26 Conductive paste (Example after shrinkage)
27 Conductive paste (initially, conventional technology)
28 Conductive paste (conventional technology after shrinkage)
40 Electrode for connection (Example)
41 Electrode for connection (convex part for formation)
42 Convex part of electrode for connection 45 Copper film for forming connection electrode 46 Copper film with only electrode part left 48 Connection electrode (conventional technology)
49 Circuit pattern 50 Metal foil for manufacturing transfer metal foil 60 Resist film for plating (first stage)
61 Plating resist film (second stage)
65 Etching resist (first stage)
66 Etching resist (second stage, electrode protrusion)
67 Etching resist (second stage, on transfer substrate)
90 Space in conductive paste (conventional)
91 Space in conductive paste (Example)

Claims (8)

  The electrode of the interlayer connection portion formed by filling the via hole formed in the base material with the conductive paste is made of the same material as the land or pad member to be electrically connected, and further has a convex portion toward the conductive paste side. A via hole connection structure characterized by that.   2. The via hole connection structure according to claim 1, wherein the protrusions have a depth of unevenness of 6 μm or more formed by the protrusions.   The via hole connection structure according to claim 1, wherein the electrode has a roughened surface toward the conductive paste.   The via hole connection structure according to any one of claims 1 to 3, wherein the conductive paste filled in the via hole is a conductive material in which a metal body is dispersed in a resin or a filler. . A method for producing a transfer electrode used for connecting a via hole in which a via hole formed in a base material is filled with a conductive paste, and electrodes having protrusions on the conductive paste side are mounted on upper and lower end faces thereof Because
A first-stage resin film forming step of forming a resin film serving as a plating resist on the surface of the transfer substrate excluding the electrode forming portion in order to form a portion excluding the convex portion of the electrode on the transfer substrate; ,
A first-stage plating step of plating the transfer substrate after the first-stage resin film formation step to form an electrode excluding the protrusions;
In order to form the convex portion of the electrode portion formed in the first plating step, a resin film serving as a plating resist is formed on the surface of the transfer substrate except the portion where the convex portion is formed. A second-stage resin film forming step to be formed;
And a second-stage plating step of forming a convex portion by plating the transfer substrate after the second-stage resin film formation step. Electrode manufacturing method.   When the transfer electrode is formed by the resin film formation and plating, other circuit configurations are also formed for transfer together with the land portion and pad portion on which the electrode is formed. For this reason, the first plating step is simultaneously performed. 6. The method for producing a transfer electrode used for connecting via holes according to claim 5, wherein a resin film is not formed on the surface of the transfer substrate at a portion to be formed. A method for producing a transfer electrode used for connecting a via hole in which a via hole formed in a base material is filled with a conductive paste, and electrodes having protrusions on the conductive paste side are mounted on upper and lower end faces thereof Because
A first-stage etching step of removing a material layer in a location other than a portion serving as an electrode from a transfer substrate having a layer serving as an electrode formed on the surface;
A second-stage etching step of removing a predetermined thickness of the material layer at a location other than the portion that becomes the convex portion of the electrode from the material layer left at the first etching step. A method for producing a transfer electrode used for connecting via holes.   When forming the transfer electrode by the two-stage etching, other circuit configurations are also formed for transfer together with the land portion and the pad portion where the electrodes are formed. 8. The method for manufacturing a transfer electrode used for connecting via holes according to claim 7, wherein the transfer electrode is left behind in an etching step.

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