JP2000200963A - Wiring board and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a wiring board with which a solder bonding operation of high connection reliability is obtained by a method, wherein impurities which obstruct a bonding operation to solder are removed from the region of a nickel- plated film which forms an alloy with the solder. SOLUTION: On an insulating board 4, which contains a copper layer as the uppermost wiring pattern of a multilayer wiring board, the whole face which excludes the external connecting-terminal formation region of a copper layer 3 is coated with a solder-resist insulating layer 2. While the insulating layer 2 is used as a mask, an electroless nickel-plated layer 1 is formed on the exposed copper layer 3. Then, the surface layer part of the nickel-plated layer 1 is etched, and impurities which obstruct a connection to solder are melted and removed selectively. Consequently, a nickel-plated layer 5 not containing the impurities which obstruct the connection to the solder is formed on the surface layer part of the nickel-plated layer 1. An actual external connecting terminal is constituted, a gold plating operation which ensures the prevention of oxidation, and the wettability of solder is executed to the nickel- plated layer 5 which does not contain the impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a wiring board,
The present invention relates to a wiring board provided with external connection terminals requiring connection reliability such as flip-chip bonding of a semiconductor or solder ball bonding of a BGA.

[0002]

2. Description of the Related Art As is well known, a wiring board is provided with hundreds of external connection terminals for mounting and connecting electronic parts and the like, and a wiring pattern is protected on the surface of the board excluding these external connection terminals. For this purpose, a solder resist is generally coated as a heat-resistant insulating film.

An example in which an external connection terminal of the wiring board is connected by soldering to an electroless nickel-phosphorous plating film made of aluminum as a base material is disclosed in, for example, JP-A-63-16695.
No. 5 discloses an example in which copper is used as a base and soldered to an electroless nickel-phosphorus / gold plating film, for example, (American S
society of Mechanical Engineers) 97-WA-EEP-10 (199
7). On the other hand, nickel plating solutions other than phosphorus-based ones are disclosed in JP-A-63-19528.
No. 0 discloses an electroless nickel-boron plating solution, and JP-A-2-500673 discloses an electroless nickel plating solution using hydrazine as a reducing agent.

[0004]

For example, in the connection between a nickel film and a solder containing tin, a nickel / tin alloy is formed and good bonding is obtained. In this type of nickel plating film, a phosphorus component is generally added to an electroless nickel plating solution to improve corrosion resistance, resulting in a nickel-phosphorus plating film. The nickel-phosphorous plating film has a problem that a phosphorus segregation layer is formed simultaneously with a nickel / tin alloy layer at the time of solder connection, and the strength is reduced due to an interface rupture between the two (as pointed out in the literature).

On the other hand, when a nickel-boron-based plating film containing no phosphorus is used, the interface breakage caused by phosphorus does not occur, but the interface breakage occurs due to sulfur segregation of impurities in the film. . Since boron-based alloys generally have higher stress than phosphorus-based alloys, sulfur-based stress relaxation agents must be added to the plating solution, and as a result, sulfur is usually incorporated into the plating film in a small amount.

Further, in the case of a hydrazine-based nickel plating film, the interface breakage also occurs at the interface between the nickel film and the solder due to the segregation of sulfur caused by the stress relaxation agent, and the stability of the plating solution due to the instability of hydrazine is also reduced. Problematic and impractical.

Accordingly, a first object of the present invention is to solve the above-mentioned problems of the conventional electroless nickel plating and to provide a wiring board provided with an electroless nickel plating film as an external connection terminal capable of obtaining good bonding with solder. The second object is to provide a manufacturing method for achieving the first object.

[0008]

The present inventors have analyzed the fracture surfaces of the solder and the nickel-phosphorus plating film by micro Auger in the depth direction, and confirmed the segregation of phosphorus. Further, as a result of analyzing the fracture surface of the solder and the nickel-boron plating film in the depth direction by micro Auger, segregation of sulfur was confirmed. No interface rupture occurred in the bonding between the nickel-boron plating film containing no sulfur and the solder.
From the above experimental facts, it has been found that segregation of at least one of phosphorus and sulfur at the joint interface with the solder may cause interface breakage. The present invention has been made based on such findings.

Therefore, in order to ensure connection reliability, these impurities must be removed from the area of the nickel plating film which forms an alloy with solder. The present inventors first thought of excluding phosphorus from the plating solution components, but for that purpose, it was necessary to find an excellent reducing agent instead of sodium hypophosphite, which is a reducing agent of the source of nickel plating. It was judged that it was very difficult from the viewpoint of time and cost.

On the other hand, in order to make full use of the nickel-boron plating solution, it is essential to use a stress-reducing agent containing no sulfur, but no sulfur-free and effective stress-releasing agent has been found. Since the sulfur-containing stress relieving agent is also added to the hydrazine-based nickel plating solution, it has the same problems as the boron-based stress reduction agent, and is unsuitable for mass production because the plating solution has a short life.

The present inventors have tried not to improve the nickel plating solution itself but to improve the quality of the plating film, and have reached the present invention. That is, this is a method of removing phosphorus or sulfur in a film surface layer by etching from an electroless nickel plating film formed as an external connection terminal of a wiring board. This is based on the idea that good solder joints can be obtained by removing these impurities that inhibit solder joints from the plating film surface layer that serves as a diffusion front with the solder.

As a result of a detailed experimental study, it was found that this idea was in fact almost correct and that it could be put to practical use. The preferred etching depth from the surface from which impurities that inhibit solder bonding are selectively removed by etching from the electroless nickel plating film is 0.05 to 0.2 μm, and more preferably 0.08 to 0.12 μm. Since the surface layer of the nickel plating film, which serves as a diffusion front with the solder, is a region having a depth of about 0.1 μm from the surface, usually, the surface layer of the film which serves as a diffusion front with the solder is etched as a guide. It is practical and preferable.

Since the thickness of the electroless nickel plating film is usually on the order of several μm, most of the nickel plating film used in the present invention contains impurities introduced from the plating solution except for the surface layer. I do. Therefore, the characteristics of the impurities that were positively introduced (for example, the corrosion resistance of phosphorus,
The effect of sulfur as a stress relaxation agent) is substantially retained.

As described above, for example, gold plating is applied as an antioxidant film on the electroless nickel plating film whose surface layer has been etched to form a final external connection terminal.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. In this figure, one of the hundreds of external connection terminals 7 provided on a wiring board is taken out, and an impurity that inhibits bonding with solder is removed from the surface layer of electroless nickel plating (nickel-phosphorus) by etching. FIG. 4 is an enlarged cross-sectional view illustrating a process of removing the hologram.

That is, FIG. 1A shows that an insulating substrate 4 including an uppermost wiring pattern (copper layer) 3 of a multilayer wiring board is
A solder resist (insulating layer) 2 is coated on the entire surface of the copper layer 3 except for the external connection terminal forming region, and the copper resist 3 is selectively electrolessly exposed on the exposed copper layer 3 using the solder resist (insulating layer) 2 as a mask. 1 shows a cross-sectional structure in which a nickel plating layer 1 is formed. FIG. 1 (B) shows that the surface layer of the plating layer 1 which is a feature of the present invention is etched to selectively dissolve and remove impurities which hinder the solder connection. 2 shows a cross-sectional structure in which a plating layer 5 containing no impurity that hinders formation is formed.

First, an etchant is used. When a phosphorus-containing electroless nickel plating film is used for bonding with a solder, the phosphorus etchant dissolves phosphorus without damaging nickel. Regardless of the type. Among them, the aqueous solution containing barium ion was particularly effective for dissolving phosphorus. As the barium ion concentration,
It is preferably 0.02 to 0.5 mol / L, and if the concentration is less than 0.02 mol / L, the phosphorus etching reaction is extremely slow, so that it is not efficient. If it is more than 0.5 mol / L, the etching reaction rate does not increase and the reagent is wasted.

The processing temperature is preferably from 30 to 90 ° C., and below 30 ° C., the etching reaction becomes very slow.
On the other hand, if the temperature is 90 ° C. or higher, the oxidation of the nickel surface proceeds remarkably in a short time, so that the adhesion to the gold plating film in the next step is reduced. The pH of the treatment liquid is preferably from 6 to 13, and if the pH is 6 or less, the etching rate becomes extremely slow.
If the pH is 13 or more, nickel hydroxide is likely to be generated on the surface of the nickel plating film. Therefore, a separate treatment for removing nickel hydroxide is required after the etching treatment, which increases the number of steps.

On the other hand, when an electroless nickel plating film containing sulfur in a plating film is used for solder bonding, the etching of sulfur is not particularly limited as long as it can etch sulfur without damaging nickel. Absent. Among them, the effect of the aqueous solution containing sulfite ions was remarkable. As the sulfite ion concentration, 0.01 to 0.9 mol
L / L is preferable, and if it is less than 0.01 mol / L, the sulfur etching reaction is very slow, so that it is not efficient. 0.9mol
Above / L, the etching reaction rate does not increase and the reagent is wasted.

The processing temperature is preferably from 30 to 90 ° C. If it is lower than 30 ° C., the etching reaction becomes extremely slow, which is not efficient. At 90 ° C. or higher, the oxidation of sulfite ions proceeds remarkably, and the etching efficiency decreases due to the production of sulfate ions. The pH of the treatment liquid is preferably 2 to 11, and if the pH is 2 or less, sulfur dioxide is likely to be generated due to decomposition of sulfite ions. If the pH is 11 or more, the etching reaction rate does not increase and there is no special effect.

FIG. 2 shows the flow of the plating process of the present invention incorporating the above-described etching step, and FIG. 3 shows the flow of a general plating process of the prior art as a comparative example. Note that the type of impurity that causes interface breakage may differ depending on the type of solder, the combination of plating metals to be joined, and the like. However, in the process of the present invention, if the impurities to be removed from the solder joint interface can be specified not only to the above phosphorus and sulfur but also to other substances, an etching solution suitable for etching the impurities may be selected, and the process is omitted. If it is incorporated after electrolytic nickel plating and only locally etches the plating surface layer impurities in the diffusion front part with the solder, good solder joints can be obtained, so it is not limited to the nickel plating solution and the type of impurities. .

The actual configuration of the external connection terminal is shown in FIG.
Gold plating is applied on the plating layer 5 which is formed on the surface layer of the plating layer 1 and does not contain impurities which hinder solder connection, in order to prevent oxidation and ensure solder wettability. The gold plating is usually thinned by substitution type electroless plating, and thicker reduction type electroless plating is applied thereon.

Here, substitutional electroless plating is a plating method in which a metal film is formed by utilizing the difference in ionization tendency. In this process, nickel dissolves into ions and simultaneously generated electrons are converted into gold. The ions are received and deposited. Although it is indispensable to obtain adhesion to the base, it cannot be thickened due to the reaction mechanism. On the other hand, thick reduction electroless plating is electroless plating in which a metal film is formed using a plating solution containing a reducing agent, and can be thickened. After the plating process, for example, 150 ° C in air
And heat-dry.

[0024]

An embodiment of the present invention will be described below with reference to the drawings. <Embodiment 1> An outline will be described first with reference to the drawings. Using five double-sided copper-clad laminates 6 according to the normal process,
A zero-layer multilayer wiring board is formed, and a solder resist (insulating layer) 2 is coated on the entire surface except for a region where an external connection terminal is formed on the outermost wiring pattern. Thus, FIG.
(A) As shown in FIG.
Are exposed to prepare a wiring board, and an electroless nickel-phosphorous plating film 1 is formed on the exposed copper layer 3 according to the plating process shown in FIG.

Next, as shown in FIG. 1 (B), the electroless nickel-phosphorous plating film 1 has a nickel plating layer 5 in which phosphorus has been removed from the surface layer through an etching step of selectively dissolving and removing phosphorus. Obtain the structure of the external connection terminal. Eventually, a gold plating film (not shown) is formed on the nickel plating layer 5 to become the external connection terminals 7. In addition,
In an actual wiring board, this kind of external connection terminal 7 has several tens of
0 are formed.

Hereinafter, the present embodiment will be described in more detail in accordance with the steps shown in FIGS. 1A and 1B and the plating process shown in FIG. First, in order to wash the surface of the external connection terminal formation region (copper layer) 3 exposed from the solder resist (insulating layer) 2, an acidic degreasing solution (a degreasing solution manufactured by World Metal Corporation: Z-200, 40 ° C., 1 minute).

After two minutes each of primary and secondary water washing, light etching of the copper surface (ammonium persulfate: 100 g / L,
Room temperature, 1 minute). After 1 minute each of primary and secondary washing,
Acid treatment (10% sulfuric acid, room temperature, 1
Min), and after 1 minute each of primary and secondary water washing, in order to activate the copper surface for electroless nickel plating,
Pd activation treatment (catalyst solution manufactured by Hitachi Chemical Co., Ltd .: SA-1
00, room temperature, 5 minutes).

After 1 minute each of primary and secondary water washing, electroless nickel-phosphorus plating (plating solution: NIPS-100, manufactured by Hitachi Chemical Co., Ltd., 85 ° C., 20 minutes) is performed, and a 7 μm-thick electroless film is formed. A nickel-phosphorus plating film was formed. One minute after each of the primary and secondary water washing, in order to remove phosphorus in the surface of the electroless nickel-phosphorous plating film 1 from the surface layer, a phosphorus etching solution (a 0.1 mol / L barium hydroxide aqueous solution: 85 ° C.) Ten
Min). Thus, the electroless nickel-phosphorous plating film 1 having a thickness of 7 μm was etched from the surface layer portion to a depth of 0.15 μm to form an electroless nickel layer 5 in which phosphorus was selectively dissolved and removed.

Next, after 1 minute each of primary water washing and secondary water washing, an acid treatment (10% hydrochloric acid, room temperature, 1 hour) was carried out to remove an oxide film on the surface.
Min). After each minute of primary and secondary washing, replaceable electroless gold plating (plating solution manufactured by Hitachi Chemical Co., Ltd .: HGS-500, 85) to ensure wettability with solder
℃), and after 1 minute each of primary and secondary water washing, reductive electroless gold plating (plating solution: HGS-2000, 65 manufactured by Hitachi Chemical Co., Ltd.)
(° C., 50 minutes) to form a gold plating film having a thickness of 0.7 μm.

Next, after 2 minutes each of primary and secondary water washing, blow drying was performed, followed by heat treatment drying in air at 150 ° C. for 4 hours. And solder reflow (eutectic solder, 200 ° C or higher, 1 minute)
Thereafter, a breaking mode by a shear test was observed. The results are shown in Table 1 together with Comparative Examples.

<Embodiment 2> In the present embodiment, the first embodiment is used.
In place of the electroless nickel-phosphorous plating solution described above, an electroless nickel-boron plating solution (plating solution manufactured by World Metal Co., Niboron-KOM, pH6.7, 65 ° C, 60 minutes) is used instead of the phosphorus etching solution A sample was prepared and evaluated in the same manner as in Example 1 except that the etching solution was changed to a sulfur etching solution (sodium sulfite: 0.5 mol / L, pH 5.0, 60 ° C., 10 minutes). The results are shown in Table 1 together with Comparative Examples.

<Comparative Example 1> As Comparative Example 1, a copper-clad laminate processed in the same manner as in the above embodiment was used and plated according to the conventional process shown in FIG. 3 without an impurity etching step. That is, first, an object to be plated (copper layer 3) was acidified with a degreasing solution (degreasing solution manufactured by World Metal Co., Ltd .: Z-200,
Min).

After 2 minutes each of primary and secondary water washing, light etching of the copper surface (ammonium persulfate: 100 g / L,
Room temperature, 1 minute). After 1 minute each of primary and secondary washing,
An acid treatment (10% sulfuric acid, room temperature, 1 minute) is performed, and after 1 minute each of primary water washing and secondary water washing, Pd activation treatment (catalyst solution manufactured by Hitachi Chemical Co., Ltd .: SA-100, room temperature, 5 minutes) )did.

One minute after each of the primary water washing and the secondary water washing, electroless nickel-phosphorus plating (plating solution manufactured by Hitachi Chemical Co., Ltd .: NIPS-100, 85 ° C., 20 minutes) was performed. Further primary washing,
One minute after each secondary washing, substitutional electroless gold plating (plating solution manufactured by Hitachi Chemical Co., Ltd .: HGS-500, 85 ° C), and again one minute after each primary washing and secondary washing, thickened reduction type Electroless gold plating (plating solution manufactured by Hitachi Chemical Co., Ltd .: HGS-2000, 65
C., 50 minutes).

Next, two minutes after each of the primary and secondary water washing, blow drying was performed, followed by heat treatment drying in air at 150 ° C. for 4 hours. And after solder reflow (eutectic solder, 200 ° C or more, 1 minute)
The breaking mode by the shear test was observed. Table 1 shows the results.
It was shown to.

<Comparative Example 2> Instead of the electroless nickel-phosphorous plating solution of Comparative Example 1, an electroless nickel-boron plating solution (plating solution manufactured by World Metal Corporation: Niboron-K) was used.
OM, pH 6.7, 65 ° C., 60 minutes), and a sample was prepared and evaluated in the same manner as in Comparative Example 1 above. The results are shown in Table 1.

[0037]

[Table 1]

Table 1 shows the presence or absence of the "solder ball falling mode" in the breaking mode. In the table, “Solder ball falling off” means that among the hundreds of external connection terminals formed on the sampled multilayer wiring board, at least one of the external connection terminals has a 100% breakage of the solder at the interface with the nickel film. This indicates the mode in the case of performing.

[0039]

As described in detail above, the present invention has achieved the intended purpose. That is, by removing impurities that hinder solder connection from the nickel plating surface layer, a wiring board having external connection terminals capable of obtaining solder connection with high connection reliability was realized.

Further, even if there is an impurity to be removed other than phosphorus or sulfur which hinders this kind of solder connection, it can be dealt with by changing an etching solution suitable for the impurity. There is an effect that can be applied to the process of the present invention without limitation.

The present invention is not limited to the electroless nickel plating film. In addition, the present invention is not limited to the electroless nickel plating film. Needless to say, it can also be applied to copper and the like.

[Brief description of the drawings]

FIG. 1 is a sectional view schematically showing an embodiment of the present invention.

FIG. 2 is a process chart of a plating process according to an embodiment of the present invention.

FIG. 3 is a diagram showing a conventional plating process.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Nickel-phosphorous plating layer, 2 ... Insulating layer (solder resist), 3 ... Copper layer (wiring pattern), 4 ... Insulating substrate, 5 ... Nickel plating layer after phosphorus etching, 6 ... Copper clad laminated board, 7 ... External connection terminal.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yuko Takehara 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside the Hitachi, Ltd. Production Technology Research Institute (72) Inventor Yasunori Narizuka 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Inside Hitachi, Ltd. Production Technology Research Laboratories (72) Inventor Satoshi Akazawa 1500 Odai Ogawa, Shimodate City, Ibaraki Prefecture Inside Hitachi Chemical Co., Ltd. Shimodate Plant (72) Inventor Hiroshi Yamamoto 1500 Odai Ogawa Shimodate City, Ibaraki Prefecture Hitachi Chemical Co., Ltd. F-term in Shimodate factory (reference) 4K022 AA42 BA14 BA16 BA19 CA04 DA01 EA04 4K057 WA07 WB03 WB11 WE03 WN01 5E319 AC01 AC17 GG03

Claims (12)

[Claims] An electroless nickel plating film formed on an external connection terminal of a wiring board has a lower layer portion containing impurities mixed during plating and a surface layer portion from which impurities which inhibit bonding with solder are selectively removed. And a wiring board composed of: 2. The method according to claim 1, wherein the depth of the surface layer portion from which impurities that inhibit the bonding with the solder are selectively removed is equivalent to the depth of the nickel plating film serving as a diffusion front at the time of bonding with the solder. The wiring board as described. 3. The depth of the surface layer portion from which impurities that inhibit the bonding with the solder are selectively removed is 0.5 to 0.2 μm.
The wiring board according to claim 1, wherein 4. The wiring board according to claim 1, wherein the impurity that inhibits the bonding with the solder is sulfur or phosphorus. 5. An external connection terminal having a gold plating layer formed on an electroless nickel plating layer from which impurities that hinder the bonding with the solder are selectively removed. The wiring board according to any one of the above. 6. A method of manufacturing a wiring board, comprising the step of selectively removing, by etching, impurities that inhibit bonding with solder from a surface layer of an electroless nickel plating film formed on external connection terminals of the wiring board. Method. 7. A step of selectively removing, from the surface layer of the electroless nickel plating film, an impurity which inhibits bonding with the solder by etching, to a depth of the nickel plating film serving as a diffusion front at the time of bonding with the solder. 7. The method for manufacturing a wiring board according to claim 6, comprising a step of etching. 8. The step of selectively removing the impurities that inhibit the bonding with the solder by etching, the step of etching to a depth of 0.5 to 0.2 μm from the surface of the electroless nickel plating film. Item 8. The method for manufacturing a wiring board according to Item 6 or 7. 9. An electroless nickel plating film, wherein the impurity contained in the electroless nickel plating film is sulfur or phosphorus, and the electroless nickel plating film formed on the surface of the external connection terminal of the wiring board is
A step of contacting the impurity with an etchant capable of selectively dissolving the impurity for a predetermined time, controlling the contact time to etch to a depth that becomes a diffusion front with solder, and selectively removing the impurity by etching. 8. The method for manufacturing a wiring board according to claim 6, wherein the wiring board is configured. 10. The method according to claim 1, wherein the impurity contained in the electroless nickel plating film is sulfur, and the method further comprises the step of selectively removing the sulfur on the surface layer of the electroless nickel plating film by an etching solution containing barium. Claims 6 to 9
The method for manufacturing a wiring board according to any one of the above. 11. The method according to claim 1, wherein the impurity contained in the electroless nickel plating film is phosphorus, and the method further comprises a step of selectively etching away phosphorus on the surface layer of the electroless nickel plating film with an etching solution containing sulfite ions. Claims 6 to 9 comprising
The method for manufacturing a wiring board according to any one of the above. 12. A process for selectively removing impurities contained in a surface layer portion of an electroless nickel plating film, which inhibits bonding with a solder, by a method for manufacturing a wiring board according to claim 6. Forming a thin gold plating layer on the surface of the etched plating film by substitutional electroless gold plating; and forming a thin gold plating layer on the thin gold plating layer surface by reduction electroless gold plating. Forming a thick gold plating layer.