JP2004221567A - Solder joint part and multilayer wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer wiring board in which a multilayer connection can be certainly carried out and has a solder joint part of high reliability. <P>SOLUTION: The multilayer wiring board is constructed so that a connecting layer, which has a wiring pattern, a conductive post formed on the wiring pattern, and a solder layer formed on a tip surface of the conductive post, and a layer to be connected, which has an interlayer connecting land with the conductive post, are connected by solder joining. There are formed a solder and an alloy composed of a metal element making up the conductive post and connecting land between the conductive post and the layer to be connected. The solder joint part, where a solder fillet is formed around the solder joint part of the conductive post, is attained. The solder joint part of high reliability is attained, and the multilayer wiring board having the solder joint part can be connected by the solder joint part having high reliability and strength, thereby, high density integration and high density mounting of electronic components using them can be made possible. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a solder joint and a multilayer wiring board. Further, the present invention relates to a solder joint between layers of a multilayer wiring board.

  2. Description of the Related Art In recent years, with the demand for higher functionality and lighter, thinner and smaller electronic devices, build-up multilayer wiring boards have been employed as circuit boards. The build-up multilayer wiring board is formed while stacking an insulating layer made of only a resin and a conductor. As a via forming method, instead of the conventional drilling, a laser method, a plasma method, a photo method, and various other methods are used, and high-density is achieved by freely arranging small-diameter via holes. Examples of the interlayer connection portion include a blind via (Blind Via) and a buried via (Buried Via: a structure in which a via is filled with a conductor). The buried via hole is classified into a method of filling the via hole with plating and a method of filling the via hole with a conductive paste or the like. On the other hand, in order to further reduce the size, weight, increase the number of pins, and achieve high-speed signal transmission, it is required to increase the density of wiring, reduce the diameter of vias, and reduce the thickness of the interlayer insulating layer. Under such circumstances, as a new interlayer connection method that replaces the sequential lamination method such as the conventional build-up method, a conductive via hole that has a wiring pattern on at least one surface of an insulating sheet and penetrates the front and back surfaces of the insulating sheet. And a method of connecting the connecting electrodes formed of a conductive adhesive, Sn-Pb solder, Au, Sn, or the like by thermocompression bonding for electrical connection (for example, see Patent Document 1) )). In addition, a solder layer is provided on a predetermined portion of the conductor circuit layer at the tip of a protrusion (metal block) made of a conductor for electrical connection between the conductor circuit layers, and the insulator resin layer is formed by heat and pressure. After the solder layer is connected to the conductor circuit layer by breaking through the protrusion, the temperature is raised to the melting temperature of the solder in this state, the solder layer is melted, the protrusion is connected to the conductor circuit layer, and then the solder is cooled. A manufacturing method for solidifying a layer (for example, see Patent Document 2) has also been proposed.

JP-A-11-204939 (pages 10-12, FIG. 1) JP-A-8-195560 (page 6-31, FIG. 1)

However, in the case of connection using a conductive adhesive or electrical connection only by physical contact, the connection reliability is low, and furthermore, the connection reliability is high if the solder layer at the tip of the protrusion is not sufficiently spread. At the present time, no joint has been formed.
The present invention has been made in view of such a current problem of interlayer connection in a multilayer wiring board on which a semiconductor chip is mounted, and has as its object to provide a highly reliable interlayer bonding part, and a multilayer wiring board having the bonding part. Aim.

That is, the present invention
(1) An adhesive is formed by bonding an solder layer formed on a tip end surface of a conductor post projecting from the insulating layer through the insulating layer and a connected layer having an interlayer connection land facing the conductor post. A solder joining portion obtained by soldering via a layer, wherein the solder layer, the conductor post, and the interlayer connection land are formed at a joint between the conductor post and the interlayer connection land. An alloy composed of components is formed, and further a solder joint, wherein a fillet made of an alloy containing solder or solder metal is formed around the solder joint,
(2) The solder joint according to (1), wherein the alloy formed between the conductor post and the connected layer has a higher melting point than solder.
(3) The solder joint according to (1) or (2), wherein the solder layer spreads more than the cross-sectional area of the conductor post and is soldered to the land for interlayer connection.
(4) The solder joint according to (3), wherein the wet spread area of the solder is 2 times or more and 7 times or less than the cross-sectional area of the conductor post.
(5) At least the solder bonding portion contacts the solder layer with the adhesive layer, heats at a temperature equal to or higher than the melting point of the solder forming the solder layer, melts the solder layer, and then press-bonds to perform solder bonding. The solder joint according to any one of (1) to (4), which is obtained by:
(6) The solder joint according to any one of (1) to (5), wherein the alloy formed between the conductor post and the connected layer is an alloy of copper and tin.
(7) The solder joint according to any one of (1) to (5), wherein the alloy formed between the conductor post and the connected layer is an alloy of gold, nickel, and tin;
(8) The solder joint according to any one of (1) to (7), wherein the alloy forming the fillet is an alloy of gold and tin;
(9) A multilayer wiring board comprising the solder joint according to any one of (1) to (8).
It is.

  According to the present invention, a highly reliable solder joint can be provided, and the multilayer wiring board having the solder joint of the present invention can perform interlayer connection by a solder joint having high reliability and strength. Therefore, it is possible to achieve high-density integration and high-density mounting of electronic components using this.

The solder joint according to the present invention is a connected part having a solder layer formed on a tip end surface of a conductor post formed so as to penetrate an insulation layer and protrude from the insulation layer, and a land for interlayer connection facing the conductor post. When the layers are connected to each other via an adhesive layer, the layers are obtained by soldering a solder layer formed on the tip surface of the conductor post and the land for interlayer connection.
In the solder joint of the present invention, an alloy layer composed of a metal component forming the solder layer, the conductor post and the land for interlayer connection is formed between the conductor post and the land for interlayer connection. ing. Further, a fillet of solder or an alloy containing solder metal is formed at the base of the solder joint so as to reinforce the joint. The formation of a fillet of solder or an alloy containing a solder metal can prevent stress concentration on the solder joint by the thermal shock test, and the reinforcing effect of the solder joint by the fillet itself can increase the bonding strength. By increasing itself, high connection reliability is ensured.

  Further, it is preferable that the alloy formed in the solder joint is designed to be higher than the melting point of the solder. For example, when the solder is made of a metal containing tin as a main component, and the conductor posts and the lands for interlayer connection are made of a metal containing copper as a main component, an alloy of copper and tin is formed at a joint obtained by soldering. Is formed. The melting point of the formed alloy is 400 ° C. or higher. Generally, the temperature of the reflow step when a semiconductor chip is mounted does not exceed 400 ° C. Therefore, in the reflow step in which the semiconductor chip is mounted on the multilayer wiring board having the solder joint of the present invention, the solder joint of the multilayer wiring board does not melt, so that the solder joint does not break. , And stable conduction can be maintained. This is the same in package mounting.

  Furthermore, in the solder joint portion of the present invention, the solder layer formed on the conductor post wets and spreads on the interlayer connection land and performs the solder joint, but the wet spread area of the solder is larger than the cross-sectional area of the conductor post. Is preferred. When the cross-sectional area is larger than that of the conductor post, a fillet of a good solder or an alloy containing a metal of the solder is formed, and the bonding strength is further increased. Further, the wet spread area of the solder is preferably at least 2 times and not more than 7 times the cross-sectional area of the conductor post. If the ratio is less than twice, good fillet of solder or alloy containing solder metal may not be formed, and sufficient bonding strength may not be obtained. On the other hand, if it exceeds 7 times, the solder will spread widely over the lands, and sufficient solder may not be secured to form a fillet of the solder or an alloy containing the metal of the solder, and sufficient bonding strength may not be obtained. There is.

  As a method of obtaining these good solder joints, in solder joining, first, at least the solder layer is brought into contact with the adhesive layer, and heated at a temperature equal to or higher than the melting point of the solder forming the solder layer to melt the solder layer. Then, a method of bonding by pressing is preferable.

Next, the step of forming a solder joint according to the present invention will be described using an example of a method for manufacturing a multilayer wiring board, but the present invention is not limited thereto.
FIG. 1 is a view for explaining an example of a method for manufacturing a multilayer wiring board having a solder joint according to the present invention, and FIG. 1H is a cross-sectional view showing the structure of the obtained multilayer wiring board.

  As an example of the method for manufacturing a multilayer wiring board of the present invention, first, a two-layer structure composed of a metal foil 101 and an insulating film 102 is prepared, and a via 103 is formed in the insulating film 102 at a position where a conductor post is to be formed. (FIG. 1A). Next, using the metal foil 101 as a lead for electrolytic plating (electrode for power supply), a conductor post 104 is formed in the via 103 by electrolytic plating, and then the insulating layer 102 is protruded from the front end surface of the conductor post 104, A solder layer 105 is formed (FIG. 1B). Next, the conductive circuit 106 is formed by selectively etching the metal foil 101 to obtain the connection layer 110 (FIG. 1C).

  Next, an adhesive layer 108 is formed on the surface of the insulating film 102 (FIG. 1D). Next, the solder layer 105 of the connection layer 110 and the land 107 for interlayer connection of the connected layer 120 are aligned so as to face each other (FIG. 1E). Next, the connection layer 110 and the connection-target layer 120 are bonded via the adhesive layer 108 such that the solder layer 105 and the interlayer connection land 107 of the connection layer 110 and the interlayer connection land 107 are in contact with the adhesive layer 108 (FIG. 1). (F)).

Next, the connection layer 110 and the connected layer 120 are heated to a temperature equal to or higher than the melting point of the solder forming the solder layer 105 to melt the solder, and then pressurized and pressed (FIGS. 1 (g) to (h)). ).
In the heating and pressing steps, for example, the solder layer 105 is heated to a temperature equal to or higher than the melting point of the solder by using a vacuum press. At this time, the adhesive layer 108 has a metal surface surface cleaning function. Is preferred. That is, the function is to remove at least the oxide film formed on the solder surface. By using the adhesive, the oxide film on the surface of the solder layer 105 is reduced and melted, and a convex shape is formed by the surface tension of the molten solder (FIG. 1 (g)). At this time, it is more preferable that the convex shape is the most stable dome shape or drop shape. Thereafter, the apexes of the solder layer 105 having a convex shape formed by pressing are brought into contact with the interlayer connection lands 107, and the solder is wet and spread concentrically from the contact points, and the conductor posts are pressed until they hit the metal lands. . At this time, a fillet is formed around the joint portion of the conductor post by the spread solder, so that the joint portion has a shape reinforced by the fillet of the solder or the alloy containing the metal of the solder.

Furthermore, since the solder melted in the pressing step is extruded to the periphery of the joint, the solder itself does not exist directly below the conductor post. At the joint portion, an alloy of solder and a metal constituting the conductor post and the interlayer connection land is formed.
For example, when the conductor posts and the lands for interlayer connection are made of copper, and the solder is made of a metal containing tin as a main component, an alloy layer is formed at the solder joint. In such a case, the solder joint is made of Cu. A typical copper-tin alloy such as ₃ Sn, Cu ₆ Sn ₅ is formed. The melting points of these alloys are all 400 ° C. or higher.

In addition, it is preferable that an alloy of gold, nickel, and tin is mainly formed at a solder joint between the solder layer, the conductor post, and the land for interlayer connection in order to obtain a high-melting-point alloy joint. In this case, for example, For the purpose of suppressing Kirkendall voids generated due to the difference in diffusion rate in the metal layer forming each layer, a nickel layer serving as a diffusion preventing metal layer is formed between the conductor layer and the copper post and the solder layer, An alloy can be obtained by forming and joining a gold layer on the surface of the diffusion preventing metal layer to further improve solder wettability, but more specifically, a copper layer, a nickel layer, and a gold layer are formed. The nickel layer is also formed between the conductor circuit of the interlayer connection land or the connection layer and the copper layer and the solder layer containing tin as a main component, and by joining, a nickel layer is formed between the conductor post and the connection layer. It is possible to obtain the serial alloy. The fillet formed around the joint is mainly made of an alloy of gold and tin containing AuSn and AuSn ₂ as main components. The melting points of these alloys are about 420 ° C. and 350 ° C., respectively, according to the alloy phase diagram.
Therefore, in the semiconductor chip mounting step, the semiconductor package mounting step, and the like, there is no fear that the metal of the solder joint of the present invention is remelted and disconnected.
In the above example of the multilayer wiring board, the example of the solder bonding of two layers is shown, but even if there are three or more layers, each layer is prepared and obtained by the same method.

  Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited thereto.

<Preparation of connection layer 110>
UV-YAG laser was applied to the polyimide resin insulation film of a flexible printed wiring board (Sumitomo Bakelite, A1 flexible) composed of copper foil (metal foil 101, thickness 18 μm) and polyimide resin insulation film (insulation film 102, thickness 25 μm). Using this, 300 vias (vias 103) having a top diameter of 45 μm and a bottom diameter of 25 μm were formed. After cleaning the inside of the via and the periphery of the via with a permanganate resin etching solution, electrolytic copper plating is performed using the copper foil on the back as a lead (electrode for power supply) for electrolytic plating, and the via is filled with copper. Then, a copper post (conductor post 104) was formed. Here, the time of electrolytic copper plating was adjusted so that the diameter of the copper post was 45 μm. Next, a Sn-Pb eutectic solder layer (solder layer 105) was formed on the surface of the copper post with a thickness of 4 µm by electrolytic plating. The height of the tip surface of the solder layer protruding from the insulating film surface was 10 μm. Next, the copper foil was selectively etched to form a wiring pattern (conductor circuit 106). Through the above steps, a connection layer (connection layer 110) was obtained.

<Formulation of adhesive varnish>
106 g of cresol novolak resin (PR-HF-3, manufactured by Sumitomo Durez Co., Ltd.), 105 g of phenolphthaline (manufactured by Tokyo Chemical Industry), and diallyl bisphenol A type epoxy resin (RE-810NM, manufactured by Nippon Kayaku Co., Ltd.) 450 g were dissolved in 165 g of methyl ethyl ketone to prepare a metal bonding adhesive varnish.

  Next, the metal bonding adhesive varnish obtained above was applied to the surface of the insulating film, that is, a eutectic solder layer of Sn-Ag (2.5%) by bar coating on the connection layer obtained above. After coating on the formed surface, it was dried at 80 ° C. for 20 minutes to form an adhesive layer (adhesive layer 108) having a thickness of 30 μm.

Further, using a glass epoxy double-sided copper-clad laminate equivalent to FR-5 (manufactured by Sumitomo Bakelite, ELC) having 12 μm-thick copper foil formed on both sides as a layer to be connected, the connecting layer obtained in the above step was heated at 100 ° C. Preliminary pressure bonding was performed at a temperature to bring the surface of the connection layer into contact with the surface of the opposing connected layer. When the cross-section of the temporarily pressed sample was observed, the solder layer was not in contact with the land for interlayer connection, and there was a gap (adhesive layer) of about 30 μm.
Finally, the preliminarily pressure-bonded sample was heated to a temperature equal to or higher than the melting point of the solder (219 ° C.), pressurized, and finally pressure-bonded to obtain a multilayer wiring board.

<Observation of solder joint>
The SEM observation of the cross section of the solder joint obtained in the above example was performed. FIG. 2 shows the results. In addition, the solder joints between the copper posts and the connection lands and the fillet portions were subjected to elemental analysis by energy dispersive X-ray spectroscopy (EDX).

From the cross-sectional SEM photograph, the conductor circuit layer 201 of the connection layer and the interlayer connection land 204 of the connected layer are formed by the interlayer connection copper post 205 penetrating the insulating layer 202 and the solder joint 206 formed at the tip thereof. It was confirmed that a fillet 207 was formed around the connected and soldered portions. According to the EDX analysis result of the joint, an alloy of Cu ₃ Sn and Cu ₆ Sn ₅ was formed between the copper post and the connection land. Further, almost only Sn was detected from the fillet portion, and a Sn ₃ Ag alloy unevenly distributed was formed partially.

FIG. 4 is a cross-sectional view illustrating an example of a method for manufacturing a multilayer wiring board according to an embodiment of the present invention. 4 is a SEM photograph of a cross section around a solder joint in an example of the present invention.

Explanation of reference numerals

101 Metal foil 102 Insulating film 103 Via 104 Conductor post 105 Solder layer 106 Conductor circuit 107 Interlayer connection land 108 Adhesive layer 110 Connection layer 120 Connected layer 130 Multilayer wiring board 201 Conductor circuit layer 202 Insulating film 203 Adhesive layer 204 Interlayer Connection land 205 Interlayer connection copper post 206 Interlayer joint (solder joint)
207 fillet

Claims (9)

  A solder layer formed on the tip surface of a conductor post projecting from the insulating layer, penetrating the insulating layer, and a connected layer having an interlayer connection land opposed to the conductor post are connected via an adhesive layer. And a metal component forming the solder layer, the conductor post, and the interlayer connection land at a junction between the conductor post and the interlayer connection land. A solder joint, wherein a fillet made of solder or an alloy containing solder metal is formed around the solder joint.   2. The solder joint according to claim 1, wherein the alloy formed between the conductor post and the connected layer has a higher melting point than solder.   3. The solder joint according to claim 1, wherein the solder layer spreads more than the cross-sectional area of the conductor post and is solder-bonded to the interlayer connection land. 4.   4. The solder joint according to claim 3, wherein the spread area of the solder is 2 to 7 times the cross-sectional area of the conductor post.   A solder joint is obtained by contacting at least the solder layer with the adhesive layer, heating at a temperature equal to or higher than the melting point of the solder forming the solder layer, melting the solder layer, and then pressing and joining the solder. The solder joint according to any one of claims 1 to 4, wherein:   The solder joint according to claim 1, wherein the alloy formed between the conductor post and the connected layer is an alloy of copper and tin.   The solder joint according to any one of claims 1 to 5, wherein the alloy formed between the conductor post and the connected layer is an alloy of gold, nickel, and tin.   The solder joint according to claim 1, wherein the alloy forming the fillet is an alloy of gold and tin.   A multilayer wiring board comprising the solder joint according to claim 1.

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