JP3436101B2 - Solder material, printed wiring board and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a solder material, a printed wiring board and a method for manufacturing the same, and more particularly to improvement of solder joint strength of a connecting terminal to a conductor pattern.

[0002]

2. Description of the Related Art Conventionally, as a printed wiring board, there is one in which a solder ball 91 for external connection is joined to a pad 92 as shown in FIG. The pad 92 is formed by coating the surface of the patterned copper layer 920 with the nickel layer 922 and the gold layer 923 on the surface of the insulating substrate 97 by electroless plating. When the printed wiring board is a substrate on which it is difficult to form plated leads, the nickel layer 922 is used.
The gold layer 923 is formed by electroless plating.
The solder balls 91 are joined to the mother board 8.

[0003]

However, in the above-mentioned conventional printed wiring board, the bonding strength of the solder ball 91 to the pad 92 is weak. In particular, when exposed to high temperature conditions for a long period of time, the joint strength further decreases.

The reason is considered as follows. That is, as shown in FIG. 6, the nickel layer 922 containing phosphorus is formed.
When the solder ball 91 is joined to the pad 92 composed of
The components of the solder ball, gold layer and nickel layer diffuse.
In particular, nickel of the nickel layer in the nickel layer 922 quickly diffuses into the gold layer 923.
The phosphorus in the nickel layer 922 is left behind in the upper layer portion 922a of the second layer 922a, and the upper layer portion 922a becomes a layer containing high concentration phosphorus. The formation of this high-concentration P layer reduces the bonding strength of the solder ball 91 to the pad 92.

In view of the above conventional problems, the present invention provides a solder material excellent in solder joint strength, a printed wiring board using the same, and a method for manufacturing the same.

[0006]

According to a first aspect of the present invention, a connection pattern is provided on a surface of a conductor pattern in a printed wiring board, the surface including a nickel layer composed of nickel and phosphorus and a gold layer covering the nickel layer. In the solder material for soldering, the solder material is a solder material in which copper is contained in the solder.

Copper (Cu) is contained in the solder material of the present invention. Therefore, the joint strength between the connection terminal and the conductor pattern made of the solder material is increased. The reason is considered as follows.

When the connection terminal is joined to the surface of the conductor pattern composed of the nickel layer and the gold layer with the solder material, as described above, the high-concentration phosphorus layer which causes the decrease of the solder joint strength is formed on the upper layer of the nickel layer. It is formed. As a result of intensive investigations by the inventors, as in the present invention, Cu is added to a solder material in addition to a solder component (Pb-Sn) to suppress the formation of a high-concentration P layer and to solder-bond a conductor pattern. Invented that the strength can be improved.

First, by adding Cu to the solder material, the diffusion of phosphorus in each component of the nickel layer can be suppressed. Therefore, the thickness of the high-concentration P layer can be reduced, and the decrease in the bonding strength of the solder material to the conductor pattern can be suppressed.

As in the invention of claim 2, it is preferable that the solder material contains 0.1 to 20% by weight of the solder material. As a result, higher solder joint strength can be obtained. The reason is considered that the addition of copper within the above range can suppress the diffusion of the conductor pattern component into the solder material. On the other hand, when the content of copper is less than 0.1% by weight or exceeds 20% by weight, the solder joint strength may decrease.

As in the third aspect of the invention, the solder material is preferably a solder ball. Solder balls are
It can serve as a connection terminal,
It itself joins the conductor pattern as a solder material.

In manufacturing the solder material of the present invention, for example, Pb, Sn, and Cu, which are components of the solder material, are used.
Are mixed in the form of fine powder or in the form of balls larger than them, and if necessary, a flux and a viscosity adjusting agent are added to obtain a paste-like or ball-like solder material.

When the solder material is a solder ball, it can be manufactured by the following method. That is, a solder ball is manufactured by, for example, immersing a copper ball in solder and adding bismuth or iron as needed. The size of the copper spheres is preferably 30 to 85% by volume of the total volume of the solder balls because the content of copper in the above range is added. Further, the soldering of the solder ball to the conductor pattern is performed at a temperature at which copper diffuses into the solder at the surface without melting the copper ball completely, for example, 200 ° C.
It is preferable to heat by the above. For the same reason, the heating time of the solder balls is preferably 30 seconds or more.

Next, a fourth aspect of the present invention is a printed wiring board having a conductor pattern in which connecting terminals are joined by a solder material containing copper, wherein the conductor pattern is 3 to 12% by weight of phosphorus and nickel. A nickel layer consisting of the balance and a gold layer covering the nickel layer, and
The printed wiring board is characterized in that a plating lead for forming the nickel layer by electrolytic plating is not formed on the printed wiring board.

What is most noticeable in the present invention is that the connection terminal is soldered to the conductor pattern by a solder material containing copper (Cu). In the present invention, since the solder material contains copper, as described above, the solder joint strength with respect to the conductor pattern of the connection terminal is increased.

Further, when the nickel layer contains phosphorus, the adhesion between the nickel layer and the gold layer becomes high. In addition, the gold forming the gold layer has a high deposition rate, and excellent bonding strength between the connection terminal and the conductor pattern made of the solder material can be obtained.

On the other hand, when the phosphorus concentration in the nickel layer is less than 3% by weight, the deposition rate of gold is high and wire bonding is possible, but on the other hand, the connection terminals made of solder material and the conductor pattern are Bonding strength becomes low. The reason is that when the gold layer is a substitution type formed by electroless plating and has a film thickness, phosphorus does not migrate to the surface of the gold layer and remains at the interface between the nickel layer and the gold layer, and the high concentration P layer is formed. Therefore, the solder joint strength becomes low. Also, on the surface of the gold layer,
Ni transferred from the nickel layer and S transferred from the solder material
It is considered that this is because a Ni—Sn—O alloy composed of n and oxygen (O) in the atmosphere is formed.

When the phosphorus concentration in the nickel layer exceeds 12% by weight, the adhesion between the nickel layer and the gold layer becomes high, but on the other hand, the deposition rate of gold for forming the gold layer is high. Is delayed. In addition, the solder joint strength at room temperature becomes low. The reason is considered to be that the high-density P layer is formed in the upper layer portion of the nickel layer during soldering. Further, the above-mentioned alloy layer on the surface of the gold layer is likely to be oxidized, and the solder joint strength in a high temperature atmosphere may be reduced.

More preferably, the content of phosphorus in the nickel layer is 5 to 9% by weight. As a result, the solder joint strength between the connection terminal and the conductor pattern is further increased.

The surface of the nickel layer is covered with a gold layer. As a result, the connection terminal can be firmly soldered to the surface of the conductor pattern.

The printed wiring board is not provided with a plating lead for forming the nickel layer by electrolytic plating. Therefore, high density and fine wiring can be obtained.

Also, the nickel layer and the gold layer can be formed by electroless plating. As a result, the conductor pattern can be formed very uniformly. In addition, since leads for electroplating are not required, electrical noise is unlikely to occur, and high density and fine wiring can be obtained.

According to a fifth aspect of the present invention, the connection terminals are solder balls, lead pins, flip chip pads, or TCP pads. Among them, the solder ball is joined to the conductor pattern by its own solder. The lead pin is inserted into the through hole of the printed wiring board, and is soldered by a conductor pattern covering the inner wall of the through hole and a solder material. The TCP pad means a tape carrier package.

The conductor pattern is a film formed on the surface or inside of the printed wiring board, the inner wall of the through hole, or the like for joining the connection terminals. The shape of the conductor pattern changes depending on the shape of the connection terminal. For example, the conductor pattern is often a pad, a land of a through hole, or the like.

The connection terminals are, for example, a motherboard,
By connecting to a counterpart member such as a daughter board, a memory module, a multi-chip module, a plastic package, a semiconductor device, a conductor circuit, etc., electricity can be transferred between the printed wiring board of the present invention and the counterpart member.

Next, a sixth aspect of the present invention is the wiring substrate, wherein the entire surface of the insulating substrate is covered with a wiring conductor film, and then a portion of the wiring conductor film where the conductor pattern is not formed is covered with a mask. Electricity for electrolytic plating is applied through the conductor film, and electrolytic Ni plating is applied to the conductor pattern forming portion to form a nickel layer consisting of 3 to 12% by weight of phosphorus and the balance of nickel. Then, the mask is removed, and then, With the surface of the nickel layer covered with a mask, the conductor film for wiring is etched to form a conductor pattern, and the conductor film for wiring that conducts electricity for electroplating is removed. A method for manufacturing a printed wiring board is characterized in that a connection terminal is joined to a surface of a conductor pattern with a solder material containing copper.

The present invention is a method of manufacturing a printed wiring board according to the invention of claim 5.

This will be specifically described with reference to FIG. First, a mask 6 is formed on a portion of the wiring conductor film 300 such as a copper foil, which is not formed on the conductor pattern, formed on the entire surface of the insulating substrate 7.
1 (FIG. 3 (a)), and the conductive pattern forming portion is subjected to electrolytic Ni plating to form a nickel layer 31 (FIG. 3 (b)). At this time, the wiring conductor film 300 arranged on the entire surface functions as an electrolytic plating lead. Then, the mask 61 is removed (FIG. 3C). Next, the surface of the nickel layer 31 having the shape of the conductor pattern is covered with the mask 62 having the shape of the conductor pattern (FIG. 3D), and the conductor film 300 for wiring is etched to form a copper layer having the shape of the conductor pattern. 30 (Fig. 3 (e)).
At this time, the electroplated leads are removed by etching. After that, the mask 62 is removed. As a result, as shown in FIG. 3 (f), the printed wiring board 8 having the conductor pattern 301 can be obtained without leaving the plating lead for forming the nickel layer.

[0029]

DETAILED DESCRIPTION OF THE INVENTION

Embodiment 1 A printed wiring board according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. Printed wiring board 8 of this example
As shown in FIG. 1, has a pad 3 formed by solder-bonding a solder ball 1 for external connection. The pad 3 is a part of the conductor pattern, which is a copper layer 30 and a nickel layer 31.
And a gold layer 32. The tops of the solder balls 1 are bonded to the pads on the motherboard (see FIG. 5).

The nickel layer 31 contains 5 to 9% by weight of phosphorus,
It consists of the balance nickel. Solder ball 1 is copper 0.1-0.1
It consists of 15% by weight and the balance of the solder. Solder is lead (P
b) 10 to 70% by weight and tin (Sn) 30 to 90% by weight
Consists of. The insulating substrate 7 around the pad 3 is covered with a solder resist.

In manufacturing the printed wiring board of this example, as shown in FIG. 2, epoxy type, polyimide type,
An insulating substrate 7 made of a resin such as bismaleimide triazine and glass cloth or glass fiber is prepared, and a copper foil is attached to the surface thereof. Then, the copper foil is etched to form a pad-shaped copper layer 30. Then, on the surface of the patterned copper layer 30 by electroless plating,
The nickel layer 31 and the gold layer 32 are formed to form the pad 3. The thickness of the nickel layer 31 is 0.1 to 30 μm,
The thickness of the gold layer 32 is 0.01 to 10 μm. Further, a conductor circuit (not shown) is formed on the surface of the insulating substrate 7.

Next, a copper ball 11 is prepared and immersed in a solder bath. As a result, the solder ball 1 in which the periphery of the copper ball 11 is covered with the solder 12 is obtained. Copper ball 11
Is 30 to 85% by volume with respect to the entire volume of the solder ball 1. The bottom of the solder ball 1 is a flat surface 19. This is for stabilizing the position when the solder ball 1 is placed on the pad 3.

Next, the solder ball 1 is placed on the pad 3 and the solder ball 1 is melted by heating. Heating
The temperature is 200 ° C. or higher for 30 seconds or longer. As a result, the copper of the copper ball 11 diffuses into the solder 12. The high-concentration P layer generated by the conventional solder ball bonding was not formed on the upper portion of the nickel layer 31 (see FIG. 6).

In this example, the nickel layer 31 is formed by electroless plating, but it may be formed by electrolytic plating (see FIG. 3). Further, in this example, the solder ball 1 is formed by immersing the copper ball 11 in a solder bath (FIG. 2). However, each fine powder of solder and copper is mixed with a flux and a viscous agent. It can also be formed by forming a paste into a ball shape.

Embodiment 2 In this example, as shown in Table 1, the relationship between the solder ball and nickel layer components and the solder ball bonding strength was investigated. A printed wiring board was manufactured in the same manner as in Embodiment 1 by changing the contents of Cu in the solder balls and P in the nickel layer. Samples 1 and 2 (invention products) and samples C1 and C were prepared.
It was set to 2 (comparative example). In addition, the solder (Pb
-Sn) was kept constant at 37% by weight of Pb and 63% by weight of Sn.

Initial bonding strength of each sample and 125 ° C. 1
The joint strength after heating for 00 hours, and the Sn-Ni alloy layer thickness and the high-concentration P layer thickness were measured. The results are shown in Table 1. As is known from the table, the samples 1 and 2 had higher bonding strength than the other samples C1 and C2. In the case of the nickel layer containing phosphorus (Sample C1), the bonding strength was lower than that in the case of the nickel layer not containing phosphorus (Sample C2).

When the solder material containing copper is bonded to the nickel layer containing phosphorus (Samples 1 to 5 and C1), the bonding strength is higher than that when the solder material containing no copper is bonded (Samples C2 to C4). It was

When the joint strength of the solder material increases, Sn-
It was recognized that the Ni alloy layer thickness and the high-concentration P layer thickness tended to become smaller. It is considered that this is because the amount of nickel transferred to the solder balls in the nickel layer decreased.

[0039]

[Table 1]

Embodiment 3 In the printed wiring board 8 of this embodiment, as shown in FIG. 4, the bonding wires 2 as connecting terminals are soldered to the pads 3. The bonding wire 2 has a pad 3 and
The semiconductor device mounted on the printed wiring board 8 is electrically connected. When soldering the bonding wire 2 to the pad 3, the cream-shaped solder material 10 is applied to the surface of the pad 3, and the solder material 10 is heated and melted. The components of the solder material 10 are the same as those of the solder ball used in the first embodiment. Others are the same as those in the first embodiment. Also in this example, the same effect as that of the first embodiment can be obtained.

[0041]

According to the present invention, it is possible to provide a solder material excellent in solder joint strength, a printed wiring board using the same, and a method for manufacturing the same.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a printed wiring board according to a first embodiment.

FIG. 2 is an explanatory view showing a method for manufacturing a printed wiring board according to the present invention.

FIG. 3 is an explanatory view showing a method of manufacturing a printed wiring board having a conductor pattern without leaving an electroplating lead in the present invention.

FIG. 4 is a sectional view of a printed wiring board according to a third embodiment.

FIG. 5 is a cross-sectional view of a conventional printed wiring board.

FIG. 6 is an explanatory diagram showing a problem of the conventional example.

[Explanation of symbols]

1. ． ． Solder balls, 10. ． ． Solder material, 3. ． ． pad, 30. ． ． Copper layer, 31. ． ． Nickel layer, 32. ． ． Gold layer, 7. ． ． Insulating substrate,

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H05K 3/34

Claims (6)

(57) [Claims] 1. A solder material for solder-bonding a connection terminal to a surface of a conductor pattern in a printed wiring board, the surface comprising a nickel layer composed of nickel and phosphorus and a gold layer covering the nickel layer. The solder material is characterized in that the solder contains copper in the solder. 2. The solder material according to claim 1, wherein the copper content in the solder material is 0.1 to 20% by weight. 3. The solder material according to claim 1, wherein the solder material is a solder ball. 4. A printed wiring board having a conductor pattern formed by joining connecting terminals with a solder material containing copper, wherein the conductor pattern has a nickel layer consisting of 3 to 12% by weight of phosphorus and a nickel balance. The printed wiring board comprises a gold layer covering the nickel layer, and
A printed wiring board having no plating lead for forming the nickel layer by electrolytic plating. 5. The printed wiring board according to claim 4, wherein the connection terminal is a solder ball, a lead pin, a flip chip pad, or a TCP pad. 6. An electrolytic plating electroplating method is performed through the wiring conductor film in a state where the entire surface of the insulating substrate is covered with the wiring conductor film, and then a portion where the conductor pattern is not formed in the wiring conductor film is covered with a mask. Is subjected to electrolytic Ni plating on the conductor pattern forming portion to form a nickel layer composed of 3 to 12% by weight of phosphorus and the balance of nickel.
The mask is removed, and then, with the surface of the nickel layer covered with the mask, the conductor film for wiring is etched to form a conductor pattern, and at the same time, the conductor for electricity for conducting the electroplating is conducted. A method for manufacturing a printed wiring board, comprising removing a film and then joining a connection terminal to the surface of the conductor pattern with a solder material containing copper.