JP2000299550A - Wiring board and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve connection reliability by preventing occurrence of crack between a solder and electrode. SOLUTION: A wiring board 4 comprises a wiring comprising a copper plating layer formed on an insulating substrate and, at a place where soldering is performed to the wiring, a nickel plating layer formed on the wiring as well as a gold plating layer formed on the nickel plating layer. The nickel plating layer is formed by electric nickel plating. Thus, when soldering is performed to the wiring which is covered with the gold plating layer and nickel plating layer, the tight fitting between the solder and nickel plating layer is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board and a method for manufacturing the same. The printed wiring board according to the present invention is particularly suitable for use in mounting an electronic element mounted on a portable device.

[0002]

2. Description of the Related Art FIG. 6 shows a conventional mounting structure of an electronic element on a substrate. FIG. 6 shows a structure in which a ball grid array (hereinafter, BGA) package 101 is mounted on a multilayer printed wiring board 109 as a package component.

[0003] The BGA package 101 has a circuit wiring 10
2 is formed on the interposer 103 on which the adhesive 104 is formed.
a, and the semiconductor chip 104 is mounted via
02 and the semiconductor chip 104 are electrically connected by an Au wire 105 or the like.
4 and the Au wire 105 are sealed. Holes 1 in an array on the back of interposer 103
03a is formed. The solder ball 10 soldered to the interposer 103 through the hole 103a
7, electrical connection between the semiconductor chip 104 and the wiring formed on the multilayer printed wiring board 109 is enabled.

[0004] The BGA package 1 thus configured
01 is mounted on the multilayer printed wiring board 109 so that the solder balls 107 are in contact with the plurality of electrodes 108 provided in the wiring pattern, and the solder balls 107 are melted. Thereby, the solder balls 107 and the electrodes 108 are joined, and the mounting of the BGA package 101 on the multilayer printed wiring board 109 is performed.

Here, the wiring on the multilayer printed wiring board 109 is generally formed by copper (Cu) plating, and the electrode 108 of the wiring is made of gold (Au) for reasons such as improving solder wettability. A plating process may be applied.

[0006] However, it is generally said that the gold plating layer and the copper plating layer have weak adhesion. Usually, a nickel (Ni) plating layer is formed on the copper plating layer, and the nickel plating layer is formed on the nickel plating layer. A gold plating layer is formed. On this occasion,
The copper plating layer and the nickel plating layer are formed on the printed wiring board 109 by electroless plating.

[0007]

As described above, when the BGA package 101 is mounted on a multilayer printed wiring board 109 and mounted in a portable device, for example, when the portable device receives an impact due to a drop or the like, the printed wiring is The substrate 109 is subjected to stress such as warpage. This stress may cause cracks at the interface between the solder ball 107 and the electrode 108, resulting in poor contact between the solder ball 107 and the electrode 108.

The present inventors have conducted intensive studies in order to elucidate the cause of this problem, and as a result, the following facts have been clarified for the first time.

As described above, the nickel plating layer formed on the copper plating layer is formed by electroless plating. This electroless nickel plating is performed by impregnating the printed wiring board 109 with a nickel plating solution in a state where only the portions to be plated with nickel are exposed. This nickel plating solution contains hypophosphorous acid as a catalyst. Therefore, the nickel plating layer formed on the printed wiring board 109 by electroless nickel plating mainly contains nickel and phosphorus (P).

[0010] The solder balls 107 are melted to form electrodes 108.
When joining, the gold plating layer formed on the nickel plating layer melts into the solder. Therefore, the melted solder reaches the nickel plating layer. When the melted solder reaches the nickel plating layer, nickel in the nickel plating layer melts into the melted solder similarly to gold. As a result, only the phosphorus remains on the surface portion of the nickel plating layer to form a concentrated layer of phosphorus.

The concentrated layer of phosphorus is formed by solder balls 107
Has a larger coefficient of thermal expansion. Therefore, when the phosphorus-enriched layer expands and contracts due to fluctuations in the environmental temperature used, the adhesion between the phosphorus-enriched layer and the solder ball 107 is weakened, and cracks are easily generated at the interface. It will be lost.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has been made in view of the above circumstances. It is an object of the present invention to provide a manufacturing method thereof.

[0013]

According to a first aspect of the present invention, there is provided a wiring board comprising: an insulating substrate; a wiring made of a conductive metal formed on the insulating substrate; At the place where the attachment is performed, the device includes a nickel plating layer formed on the wiring and a gold plating layer formed on the nickel plating layer, and the nickel plating layer is formed by electric nickel plating.

Further, the wiring board according to the second aspect is
An insulating substrate, a wiring made of a conductive metal formed on the insulating substrate, a nickel plating layer formed on the wiring, and a gold plating layer formed on the nickel plating layer, at least at locations where soldering is performed on the wiring When soldering is performed on a predetermined portion of the wiring, the gold plating layer dissolves in the solder, and the solder and the nickel plating layer are directly joined without interposing an impurity layer such as a phosphorus-enriched layer. It is characterized by.

As described above, when a nickel plating layer is formed on a wiring made of a conductive metal by electric nickel plating, the content of impurities such as phosphorus in the nickel plating layer becomes very small. For this reason, even when soldering is performed on the wiring covered with the gold plating layer and the nickel plating layer, the solder and the nickel plating layer are directly joined without interposing a layer made of an impurity such as phosphorus. . Therefore, it is possible to effectively prevent the occurrence of cracks based on the difference in the coefficient of thermal expansion between the solder and the surface layer of the nickel plating layer.

The above-mentioned wiring board can be manufactured by the manufacturing method described in claim 6. That is, the method of manufacturing a wiring board includes a wiring forming step of forming a wiring of a predetermined pattern made of a conductive metal on an insulating substrate, and nickel plating on the wiring by electro-nickel plating at least at locations where the wiring is soldered. The method includes a nickel plating layer forming step of forming a layer, and a gold plating layer forming step of forming a gold plating layer on at least a part of the nickel plating layer.

In the wiring forming step, the conductive material is formed on the surface of the insulating substrate, and the conductive material formed by the conductive material is used as an electrode. Preferably, the method comprises an electroplating step of electroplating the conductive metal.

That is, a conductive substance is first formed on the surface of an insulating substrate to be used as an electrode for performing electroplating. After that, a conductive metal functioning as a wiring is formed by electroplating. This makes it possible to form the wiring by using a high-quality conductive metal formed by electroplating.

The wiring forming step may include a step of forming a conductive material on the entire surface of the insulating substrate and a step of forming a wiring of a predetermined pattern. A resist forming step of forming a plating resist having a pattern on the electroless plating layer, and conducting electroplating of a conductive metal using the conductive substance formed in the conductivity providing step as an electrode, and forming the conductive metal in a predetermined pattern by the plating resist. An electroplating step of forming an electroplating layer, a stripping step of stripping a plating resist, and an etching step of etching a conductive material immediately below the plating resist may be included.

In the above case, the wiring can be formed by a high-quality conductive metal, and the conductivity imparting step is performed before the plating resist is formed, so that the handling of the substrate is facilitated.

When the wiring is formed by the method according to claim 7 or 8, the thickness of the conductive metal formed by the electroplating step is reduced by the conductivity providing step. Preferably, the thickness is larger than the thickness of the conductive material to be formed. That is, it is sufficient that the conductive substance formed in the conductivity imparting step functions as an electrode when performing electroplating, and the formation of an unnecessarily thick conductive substance leads to an increase in cost and should be avoided.

It is to be noted that the step of imparting conductivity includes the steps of claim 1
As described in No. 0, an electroless plating step of forming a conductive metal on the surface of the insulating substrate by electroless plating can be performed.

In the case where the wiring is formed by the method described in claim 8, the nickel plating layer forming step may be performed between the electroplating step and the peeling step. preferable. In other words, while using a conductor metal having a predetermined pattern formed by the electroplating process as an electrode, a plating resist is shared between electroplating for forming a conductor metal and electroplating for forming a nickel plating layer. can do.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a BGA package 1 and a four-way flat package (hereinafter referred to as a QFP) as package components.
2 is mounted on a printed wiring board 4 provided with electrodes (copper lands) 3. As shown in FIG. 1, the BGA package 1 is provided on its bottom surface with solder balls 9 functioning as connection terminals. Also, QF
Regarding P2, the connection pins 10 extend from each side.
The solder balls 9 of the BGA package 1 and the connection pins 10 of the QFP 2 are connected to the electrodes 3 formed on the printed wiring board 4.
, Each package component is mounted on the printed wiring board 4.

On the printed wiring board 4, the above-mentioned electrodes 3
In addition, a copper wiring is formed in a predetermined pattern to enable electrical connection between a package component mounted on the printed wiring board 4 and the outside.

FIG. 2 shows a detailed view of the mounting structure of the BGA package 1 on the printed wiring board 4. As shown in FIG. 2, the printed wiring board 4 of the present embodiment is formed in multiple layers in order to mount a plurality of electronic elements at high density.

FIG. 3 shows the electrodes 3 provided on the printed wiring board 4 corresponding to the solder balls 9 of the BGA package 1.
The following shows the sequence pattern of. FIG. 3 shows a simplified arrangement pattern of the electrodes 3 and shows that the circular electrodes 3 indicated by oblique lines are arranged on the array.

Here, a method of manufacturing the BGA package 1 will be described.

First, an interposer 15 for mounting the semiconductor chip 14 is prepared. This interposer 1
After a copper thin film is adhered to one surface (front surface) of No. 5 using an adhesive or the like, the copper thin film is pattern-etched to form circuit wiring 16. Thereafter, holes 15a forming an array are formed on the back surface of the interposer 15 where the circuit wiring 16 is not formed by laser processing.
5 is formed. Through this hole 15a
Electrical connection with the circuit wiring 16 can be made from the back side of the interposer 15.

Then, electric nickel plating is performed using the circuit wiring 16 formed on the surface of the interposer 15 as an electrode, and an electric nickel plating layer is formed on the circuit wiring 16. At this time, the electric nickel plating layer is also formed on the back surface side of the circuit wiring 16 via the hole 15a formed from the back surface side of the interposer 15. Thereafter, gold electroless plating or electroplating is performed to form a gold plating layer on the electronickel plating layer. This gold plating can reduce the contact resistance when making electrical connection with the semiconductor chip 14 by wire bonding or the like.

Next, the semiconductor chip 14 is mounted on the interposer 15 via an adhesive or the like, and the circuit wiring 16 and the semiconductor chip 14 are electrically connected by wire bonding using an Au wire 17 or the like. Thereafter, the semiconductor chip 14 and the Au wires 17 are resin-sealed with a sealing resin 18 such as an epoxy resin.

Next, at least tin (Sn) is provided in each of the holes 15a formed in an array on the interposer 15.
Is placed. By melting these solder balls 9 and joining them to the circuit board 16, a BG having the solder balls 9 arranged in an array on the back surface is formed.
The A package 1 is completed.

The multilayer printed wiring board 4 is formed by laminating a large number of wiring layers 20. In the wiring layer on the outermost layer side of these wiring layers 20, the electrodes 3 arranged in a pattern as shown in FIG. 3 are formed. The arrangement pattern of the electrodes 3 corresponds to the arrangement of the solder balls 9. Therefore, at the time of mounting, the solder balls 9 of the corresponding BGA package 1 and the electrodes 3 of the multilayer printed wiring board 4 are joined by solder.

Hereinafter, a method for manufacturing a multilayer printed wiring board will be described. In this embodiment, the four wiring layers 2
A method of manufacturing the multilayer printed wiring board 4 made of zeros will be described, but the number of the wiring layers 20 can be arbitrarily increased or decreased.

First, a core material 30 as shown in FIG.
Is prepared, and then, as shown in FIG.
A through hole (blind via hole) 31 is formed by drilling a hole at a predetermined position. And FIG.
As shown in (c), the entire surface including the front and back surfaces of the core material 30 and the inner surface of the through hole 31 is subjected to electroless copper plating to form an electroless copper plating layer 32. Specifically, the core material 30 in which the through holes 31 are formed is impregnated with a copper plating solution containing formalin as a catalyst, and an electroless copper plating layer 32 is formed on the entire surface of the core material 30. The electroless copper plating layer 32 functions as an electrode in the subsequent electrolytic copper plating. Therefore, since it is only necessary to have conductivity, it is formed as a very thin film of, for example, 1 μm or less.

Thereafter, as shown in FIG.
A plating resist 33 is formed on the electroless copper plating layer in order to form a wiring having a predetermined pattern. FIG.
As shown in (e), the plating resist 33 is used as a mask, and the electroless copper plating layer 32 is used as an electrode. The copper electroplated layer 34 is also formed on the inner surface of the through hole 31. The thickness of the electroplated copper layer 34 formed at this time is about 20 μm. The copper electroplated layer 34 has higher copper purity than electroless copper plating, and can form high-quality electrodes 3 and wiring patterns.

Thereafter, as shown in FIG. 4F, using the same plating resist 33 as a mask,
By applying electric nickel plating with 4 as an electrode,
An electric nickel plating layer 35 is formed on the electric copper plating layer 34. The electric nickel plating layer 3 formed at this time
The thickness of 5 is about 2 μm.

Next, as shown in FIG. 4G, the plating resist 33 is peeled off, and as shown in FIG. 4H, the electroless copper plating layer 32 formed immediately below the plating resist 33 is etched. Soft etching is performed to remove it. Thereby, mutual insulation between the electrode 3 and the wiring is ensured.

Next, through the above-described steps, two substrates on which electrodes, wiring patterns, etc. are formed are prepared. Then, a heat press process is performed with the prepreg containing epoxy resin containing glass cloth sandwiched between the two substrates, and the two substrates are bonded to each other.

Then, through holes are formed by drilling at predetermined positions so as to penetrate all of the four wiring layers, and electroless copper plating and, if necessary, electrolytic copper plating are performed to form the four layers. The divided wiring layers are electrically connected. Thereafter, a solder resist 22 is printed and formed on the side on which the BGA package 1 and the like are mounted, that is, on the side to be the surface of the multilayer printed wiring board 4. This solder resist 22
Is a wiring which protects the wiring formed on the surface of the printed wiring board 4 and is opened at a portion where the electrode 3 is arranged.

Thereafter, electroless gold plating or electrogold plating is performed using the solder resist 22 as a mask, thereby forming a gold plating layer on the electrode nickel plating layer of the electrode 3. Thereby, the solder wettability of the electrode 3 can be improved.

The BGA package 1 and the QFP 2 are placed on the multilayer printed wiring board 4 completed through these steps.
After positioning and mounting the solder balls 9 and QF
The solder provided on the connection pin 10 of P2 is melted. As a result, the BGA package 1, the QFP 2, and the like are mounted on the multilayer printed wiring board 4.

FIG. 5 shows the bonding state of the solder ball 9 with the electrode 3 and the circuit wiring 16 of the interposer 15 at this time. As described above, the electrode 3 and the circuit wiring 16 to which the solder balls 9 are melted and joined have the electric nickel plating layer and the gold plating layer formed on the copper lands. The gold plating layer improves the wettability when the solder is melted, but gradually melts into the melted solder. Therefore, the molten solder reaches the electric nickel plating layer 35. At this time, like the gold, the nickel contained in the electro-nickel plating layer 35 dissolves in the molten solder to form a Ni-Sn alloy with tin contained in the solder.

However, the electric nickel plating layer 35
Does not contain a large amount of phosphorus unlike the electroless nickel plating layer, so even if nickel dissolves in the molten solder, an impurity layer such as a phosphorus-enriched layer may be formed on the surface layer. There is no.

Therefore, even if there is a change in the environmental temperature in which the device on which the printed wiring board 4 is mounted is used, the adhesion between the solder balls 9 and the electrodes 3 and the circuit wiring 16 is not weakened. Therefore, even if a stress is generated between the solder ball 9 and the electrode 3 or the circuit wiring 16 due to the warpage of the printed wiring board 4 or the like, it is possible to prevent a crack from being generated at the joint interface therebetween. As a result, the bonding reliability between the solder balls 9 and the electrodes 3 and the circuit wirings 16 can be greatly improved, and poor contact between them can be prevented.

The soldering of the connection pins 10 of the QFP 2 to the electrodes 3 is the same as that of the soldering of the solder balls 9 to the electrodes 3 and the circuit wirings 16. The solder and the electrode 3 are firmly joined.

As described above, the printed wiring board 4 in this embodiment can effectively prevent poor contact with elements mounted by soldering. The effect is particularly great when used for a mobile phone or the like.

The present invention is not limited to the above-described embodiment, but can be variously modified without departing from the gist of the invention.

For example, although the multilayer printed wiring board 4 having multiple wiring layers has been described as the printed wiring board, a single-layer printed wiring board composed of a single wiring layer may be used.

Further, it is not necessary to form the electric nickel plating layer 35 on the electric copper plating layer 34 with respect to all the wiring layers 20 of the multilayer printed wiring board 4, and at least the electric wiring layer on the surface side of the printed wiring board is not required. It is sufficient that a nickel plating layer is formed.

That is, with respect to the lower substrate, a wiring having a predetermined pattern is formed on the core material 30 by using a conventional subtractive method or a full additive method, and the wiring and electrodes formed through the above-described steps are formed. May be bonded to a substrate on which an electric nickel plating layer is formed.

In the above-described embodiment, the wirings and electrodes are formed by the electroplated copper layer 34. However, the electroless copper plating having a predetermined thickness is performed by performing electroless copper plating with the plating resist 33 formed in advance. A plated layer may be formed and used as a wiring and an electrode. In this case, the electric nickel plating is performed while applying a voltage to the electroless copper plating layer. Further, a copper foil may be pasted on the core material in advance, the copper foil may be etched into a predetermined pattern to form electrodes and wirings, and an electric nickel plating layer may be formed thereon.

Further, in the above-described embodiment, the electroless copper plating is performed to form the electroless copper plating layer 32 on the entire surface of the core material 30. However, the electroless copper plating layer 32 only needs to function as an electrode for subsequent electrolytic copper plating, and conductivity may be imparted to the core material 30 with another conductive material. That is, a conductive metal such as palladium or a conductive organic substance such as carbon may be coated on the core material, and direct plating of electrolytic copper plating may be performed. The core material can be coated with a conductive metal or an organic substance by, for example, applying it to the surface of the core material via a negatively charged surfactant.

In the above-described embodiment, the electric nickel plating layer 35 is formed on the entire surface of the electric copper plating layer 34.
Electro nickel plating and electroless or electro gold plating may be formed on the copper lands to be the electrodes 3. in this case,
After the solder resist 22 having an opening in the electrode 3 is formed, electric nickel plating and electroless or electric gold plating may be performed while applying a voltage to the electrode 3.

Further, in the above-described embodiment, copper is used as the conductive metal for forming the electrodes 3 and the wiring. However, when the core material to be the substrate is made of ceramic, tungsten, silver, and palladium may also be used as the conductive metal. Can be.

[Brief description of the drawings]

FIG. 1 is a mounting diagram showing a state where elements are mounted on a printed wiring board according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a detailed mounting structure of the BGA package 1 on a printed wiring board 4;

FIG. 3 is a schematic diagram showing an arrangement pattern of electrodes 3 provided on a printed wiring board 4;

FIG. 4 is a manufacturing process diagram showing a manufacturing process of the printed wiring board 4;

FIG. 5 is an explanatory view showing a bonding state of a solder ball 9;

FIG. 6 is a cross-sectional view showing a mounting structure of a conventional BGA package 101 on a printed wiring board 109.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... BGA package, 2 ... QFP, 3 ... Electrode, 4 ... Printed wiring board, 9 ... Solder ball, 30 ... Core material, 3
2 ... Electroless copper plating layer, 34 ... Electric copper plating layer, 35 ...
Electric nickel plating layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tetsu Mizuno 1-1-1 Showa-cho, Kariya-shi, Aichi F-term in Denso Corporation (reference) 4E351 AA03 BB33 CC06 CC07 DD06 DD19 GG02 GG15 5E319 AA03 AB05 AC17 AC18 BB04 CC33 GG11

Claims (13)

[Claims] An insulating substrate; a wiring made of a conductive metal formed on the insulating substrate; a nickel plating layer formed on the wiring at least at a location where the wiring is to be soldered; A wiring board, comprising: a gold plating layer formed on at least a part of a plating layer; wherein the nickel plating layer is formed by electric nickel plating. 2. An insulating substrate; a wiring made of a conductive metal formed on the insulating substrate; a nickel plating layer formed on the wiring at least at a location where soldering is performed on the wiring; A gold plating layer formed on at least a part of the plating layer, and when soldering is performed on a predetermined portion of the wiring, the gold plating layer dissolves in the solder, and the solder and the nickel plating layer are A wiring substrate, which is directly bonded without passing through an impurity layer included in a nickel plating layer. 3. The wiring board according to claim 1, wherein the conductive metal is copper. 4. The wiring board according to claim 1, wherein the wiring board is a motherboard on which at least a package component is mounted. 5. The wiring board according to claim 1, wherein the wiring board is used for mounting an electronic element used in a portable device. 6. A wiring forming step of forming a wiring of a predetermined pattern made of a conductive metal on an insulating substrate, and forming a nickel plating layer on the wiring by electric nickel plating at least at a location where the wiring is to be soldered. A method of manufacturing a wiring board, comprising: a nickel plating layer forming step of forming; and a gold plating layer forming step of forming a gold plating layer on at least a part of the nickel plating layer. 7. The wiring forming step includes: providing a conductive substance to the insulating substrate by forming a conductive substance on the surface of the insulating substrate; and providing a conductive property formed by the conductive providing step. 7. The method according to claim 6, further comprising an electroplating step of electroplating the conductive metal using a substance as an electrode. 8. The wiring forming step includes: forming a conductive material on the entire surface of the insulating substrate to impart conductivity to the insulating substrate; and forming the wiring of the predetermined pattern. A plating resist forming step of forming a plating resist having a pattern on the conductive substance, and using the conductive substance formed in the conductivity providing step as an electrode, performing electroplating of the conductive metal, and performing the plating with the plating resist. An electroplating step of forming an electroplating layer of the conductive metal in a predetermined pattern; a stripping step of stripping the plating resist; and an etching step of etching the conductive material immediately below the plating resist. The method for manufacturing a wiring board according to claim 6. 9. The conductive metal formed in the electroplating step is thicker than the conductive material formed in the conductivity providing step.
Or the method for manufacturing a wiring board according to 8. 10. The electroconductive plating step of forming the conductive metal on the surface of the insulating substrate by electroless plating.
The method for manufacturing the wiring board according to the above. 11. The nickel plating layer forming step is performed between the electroplating step and the stripping step, and the plating resist is shared by the electroplating of the conductive metal and the electroplating of nickel. 9. The method for manufacturing a wiring board according to claim 8, wherein: 12. The method for manufacturing a wiring board according to claim 6, wherein the wiring board is a mother board on which at least a package component is mounted. 13. The method of manufacturing a wiring board according to claim 6, wherein the wiring board is used for mounting an electronic element used in a portable device.