JPH08288625A - Method for connecting circuit board and electronic circuit device using it - Google Patents

Abstract

PURPOSE: To prevent the segregation of Pb on the boundary between an electroless-plated Ni-B metallized pad containing Pb and formed on a circuit board and parts by connecting the parts to the metallized pad by forming an Ni-Sn alloy of an Sn-based brazing material. CONSTITUTION: The surface of a conductor substrate is pretreated by soft etching the surface with an alkaline solution, neutralizing the surface with an acid, and activating the surface with a liquid containing a lead compound after degreasing the surface. Then, after an electroless-plated Ni-B film 5 is formed, an electroless-plated Au film 15 is formed and the film 15 is metallized. After the film 15 is metallized, the adhesion between the joined metallic layers 5 and 15 is improved by mutually diffusing the films 5 and 15 to each other. Then I/O pins 17 mounted with Au-20Sn are positioned on the metallic layers formed in the conductor section of the substrate and the pins 17 are heated. Therefore, the segregation of Pb on the boundary between the pins 17 and metallic layer can be prevented, because the Pb can be diffused in the formed intermetallic compound layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for connecting a circuit board and components, and more particularly to a method for connecting a circuit board and an electronic component such as an I / O pin, which is suitable for securing high joint strength and improving reliability. And an electronic circuit device using the same.

[0002]

2. Description of the Related Art Electronic circuit devices such as large-scale computers are equipped with a large number of semiconductor circuit elements such as semiconductor elements and I / O on a printed board or a ceramic board (hereinafter referred to as a circuit board).
An electronic circuit is formed by mounting electronic parts such as pins. The representative method of mounting these parts is as follows. A metallization pad for solder connection is formed on a circuit board, a metal terminal for electrolysis is formed on an electronic circuit component, and a metal layer for joining is formed on other joining members. afterwards,
A solder alloy is formed between the substrate and the electronic component by heating through a solder material to a connection temperature to form a connection with the metallization. As this metallization material, the prior art describes a method of providing a nickel / gold layer on a molybdenum conductor portion of a substrate, as described in JP-A-1-1060. Typical methods for forming this metallization are a sputtering method and a plating method.
A characteristic of the sputtering method is that a dense film having high adhesion to the underlying layer can be obtained, but it has a drawback that the cost is high because a patterning step of metallization is required. The feature of the plating method is that it is possible to form a film at low cost, but it requires a step of obtaining adhesion to the substrate surface. Among the plating methods, electroplating provides a high-purity film, but if electrodes or wiring in place of them cannot be attached to each plated pattern, then an electrically independent pattern cannot be used. There is a drawback that a film cannot be formed. On the other hand, the electroless plating method has a drawback that impurities other than the target metal are deposited at the same time as the plating due to the origin of the additive which is an essential component, but it is uniformly distributed on a complicated and fine independent pattern. Film formation is possible and it is the lowest cost process. For the above reason, the metallization was formed on the fine independent pattern on the circuit board by the electroless plating method. here,
The electroless nickel plating used for electronic parts will be described. Representative platings include electroless nickel-boron alloy plating and electroless nickel-phosphorus alloy plating. By comparing the characteristics of both of them, electroless nickel-boron alloy plating having a high melting point and good solderability and capable of low temperature plating was adopted. The plating film obtained by this method has a boron content of 0.5% by weight or less and a relatively high nickel purity. However, electroless nickel-boron alloy plating (hereinafter referred to as Ni-B plating) has the following drawbacks. Lead (actually as a lead compound) added to the plating solution for the purpose of stabilizing the solution and selectively depositing is taken into the plating film at the same time as the film formation. Similarly, since lead (actually a lead compound) is added to the activation treatment solution for starting the electroless Ni-B plating reaction for the purpose of stabilizing the solution, the activity adsorbed on the plated pattern is The chemical conversion particles also contain Pb, and as a result, the plating film contains Pb. For these reasons, the plating film contains lead derived from the activation treatment solution and electroless Ni-B plating solution. On the nickel layer formed by the electroless Ni-B plating method, electroless gold plating was performed to form a metallization for the purpose of surface protection.

Japanese Unexamined Patent Publication No. 1-124304 discloses a method of assembling an electronic circuit device by mounting a large number of electronic components on a circuit board having metallization formed by this method. According to this description, the circuit board is assembled by connecting the I / O pin semiconductor device and the sealing cap to the board in this order. The brazing material that connects the I / O pins, the brazing material that connects the semiconductor elements, and the brazing material that connects the sealing cap are used in this order.The materials with the highest melting points are used. Au-Ge brazing filler metal is shown as an I / O pin connecting brazing filler metal that satisfies the above conditions. 356 ℃ ~
An Au-Ge brazing material having a melting point of 450 ° C was mounted.
The I / O pin is heated above the melting point of the brazing material, and the melt wets and spreads on the metallization and at the same time reacts with nickel to form a Ni-Ge intermetallic compound. According to this joining method, low residual stress, high strength connection, and high reliability of the multilayer ceramic circuit board can be obtained.

Combining conventional technologies, I / O pin brazing filler metal
I / O pin bonding was performed by using an electroless Ni-B plating film containing Pb as a metallization material of u-Ge solder.
As a result of evaluating the bonding state, the I / O pin bonding strength was extremely low, and a failure phenomenon frequently occurred at the bonding interface between the electroless Ni—B plating metallization and the intermetallic compound generated during bonding. This multilayer ceramic substrate cannot withstand the attachment and detachment with the circuit substrate performed in the subsequent assembling process, correction and repair.

In the present invention, in order to solve the above-mentioned drawbacks of the prior art, when bonded to an electroless Ni-B plating metallization containing Pb, sufficient bonding strength can be obtained without causing Pb segregation at the bonding interface. A suitable brazing material was selected to solve the problem.

[0006]

According to the above conventional technique,
Electroless Ni-B plating film metallization containing Pb is formed on the circuit board and I / O is performed using Au-Ge brazing material.
Pinned. After joining, a tensile test of the I / O pin was performed to evaluate the joined state. As a result, the bonding strength is low,
A failure phenomenon frequently occurred at the bonding interface between the electroless Ni-B plating metallization and the intermetallic compound generated during bonding. Therefore, sufficient strength cannot be obtained for insertion / removal into / from the connector of the electronic circuit device having the I / O pin, which is an obstacle during the assembly process and during use. The following experiment was conducted to investigate the cause. Micro Auger analysis was performed on the pin-side and substrate-side fractured surfaces of the I / O pin that caused the bonding failure, and the types of the elements existing on the cross-sectional surface were confirmed. As a result, I / O
The existence of the Ni-Ge compound layer and Pb was confirmed from the outermost surface of the fracture surface on the pin side, and the existence of only the Ni plating layer was confirmed from the substrate side. The outermost surface of the fracture surface on the I / O pin side was removed by sputter etching to remove about 150 Å in the depth direction, and the same analysis was performed. As a result, Pb was not present. From this result, it was found that the disconnection of the I / O pin occurred at the interface between the metallization and the intermetallic compound, and the segregated Pb existed in a thin layer at the bonded interface. Also, as a result of analyzing the bonding material, Pb was found to be other than electroless Ni-B plating metallization, that is, in the brazing material, in the I / O pin,
Since it was not contained in the Au plating film and the substrate surface, the origin of segregated Pb was determined to be an electroless Ni-B plating film. From the above analysis, it has been found that the deterioration of the bonding strength is caused by segregation of the bonding interface of lead contained in the electroless Ni-B plating film.

An object of the present invention is to electroless Ni-containing Pb.
By selecting a suitable brazing material that does not cause Pb segregation at the bonding interface, which is the cause of the reduction in bonding strength of parts such as I / O pins, for B plating film metallization, a circuit board having sufficient bonding strength can be obtained. An object is to provide a method for joining parts and an electronic circuit device using the same.

[0008]

SUMMARY OF THE INVENTION The above object is to provide a component for connecting on the circuit board to an electroless Ni-B plating metallization pad containing Pb formed on the circuit board.
This is achieved by a joining method characterized by connecting with an n-based brazing material mainly by forming a Ni—Sn alloy.

[0009]

The operation of the present invention will be described with reference to the drawings.

The reason why the bonding strength of the brazing material to be bonded to the electroless Ni-B plating metallization pad containing Pb formed on the circuit board is different depending on the difference between Ge-based and Sn-based will be explained. First, according to the conventional technique, Au-
FIG. 1 shows a schematic cross-sectional view of the I / O pins when they are joined with a Ge brazing material. No. 1 is I / O pin, No. 2 is circuit board, No.
No. 3 is Au-Ge brazing filler metal, No. 4 is Au-Ge intermetallic compound layer, No. 5 is electroless Ni-B plating metallization, No. 6 is electrode pad on substrate, No. 7 is through-hole.
It is. An enlarged view of the bonded interface portion in FIG. 1 is shown in FIG. As a result of the analysis, in the Ni—Ge intermetallic compound layer 4, Ni ₃ Ge intermetallic compound 8 is generated at the interface with the metallization. Similarly, the Au-Sn brazing material is replaced with electroless Ni.
FIG. 3 shows an enlarged view of the joining interface portion of the joining portion when joined to the -B plating metallization. From the result of the analysis, it was confirmed that the intermetallic compound Ni ₃ Sn was generated at the interface with the metallization in the Ni—Sn intermetallic compound layer 9. Therefore, attention was paid to the intermetallic compounds Ni ₃ Sn and Ni ₃ Ge generated at the bonding interface, and the diffusion behavior of Pb metal with respect to each compound at the bonding temperature was examined by the following experiment. Intermetallic compound Ni with mirror-polished surface
Pb was vapor-deposited with a thickness of several microns on ₃ Sn and Ni ₃ Ge, and the test pieces were held at the respective brazing temperatures for 1 hour to diffuse Pb. Then, the Pb metal remaining on the surface without being diffused is removed by chemical etching, and the presence of Pb in the depth direction of the intermetallic compound surface is confirmed by SIMS (Seco
ndary Ion Mass Spectroscopy). Table 1 shows the results.

[0011]

[Table 1]

It can be seen that the diffusion behavior of Pb is completely different for both intermetallic compounds. When I / O pin bonding is performed using an Au-Ge brazing material, Pb does not diffuse at all to the Ni ₃ Ge intermetallic compound generated at the bonding interface, whereas Au does not diffuse.
-Ni ₃ G generated at the bonding interface when Sn brazing material is used
ePb diffuses as much as 25 nm for the intermetallic compound. In addition, the cause of deterioration of the I / O pin joint strength due to Pb segregation was examined by the phase diagram of the alloy for the compatibility between the metals involved in the joint and Pb. 4 and 5 show Ni-
Pb binary system phase diagram and Ni-Ge binary system phase diagram (Thad
deus B. Massalski, Ed .; BINARY ALLOY PHASE DIAGRAMS
1986). As can be seen from the Ni-Pb phase diagram, Pb dissolves in a very small amount of Ni near the joining temperature of 400 ° C, but does not dissolve at all at room temperature. Similarly, from the Ni-Ge phase diagram, Pb does not form a solid solution with Ge at room temperature to around the bonding temperature. Therefore, Pb does not exist as a stable intermetallic compound or alloy with Ni and Ge under the temperature condition of circuit board assembly. Therefore, G in the brazing material
e forms a Ni—Ge alloy (intermetallic compound) at the time of joining and does not form a Pb—Ge—Pb alloy.

From the above consideration and experimental results, the formation of Ni ₃ Ge intermetallic compound at the time of I / O pin joining is caused by electroless Ni-B.
It acts as a diffusion barrier for Pb contained in the plating metallization, and P between the metallization and the intermetallic compound.
It became clear that b segregation occurs. In addition, voids, cracks, etc. were generated at the bonding interface due to Pb segregation, and the deterioration of the bonding state caused the I / O pin bonding strength to decrease. In contrast, in the case of Au-Sn based brazing material bonding, the Ni ₃ Sn intermetallic compound that generates at the bonded interface Pb can diffuse. Therefore, even if the electroless Ni-B metallization contains Pb using the Sn-based brazing filler metal, the I / O pin bonding is sufficient because the Pb does not segregate at the bonding interface and the bonding state is not deteriorated. Has excellent I / O pin bonding strength.

Thus, by selecting the combination of the metallization and the brazing material so that Pb in the electroless Ni-B plating metallization can diffuse the intermetallic compound layer formed at the time of joining, It is possible to eliminate Pb segregation at the interface and prevent a decrease in the bonding strength of the I / O pin.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the method of joining a circuit board and an I / O pin with reference to the drawings.

Example 1 FIG. 6 shows electroless Ni containing Pb.
-Using Sn-based brazing material for B plating metallization
FIG. 2 is a cross-sectional view of a joint portion showing an embodiment of the present invention with I / O pins attached, in which 11 is a multilayer ceramic substrate and 12 is Sn2.
A brazing material having a composition of 0% by weight Au and 80% by weight, 9 is an intermetallic compound layer, 5 is electroless Ni-B plating metallization, 6 is a conductor portion on the surface of the circuit board, and 7 is a through hole. FIG. 8 is a perspective view showing an outline of an electronic circuit device in which a circuit board as an embodiment of the present invention in which I / O pins are connected by Au20Sn brazing material is assembled. In the electronic circuit device of this embodiment, a plurality of semiconductor elements 18 are arranged on the multilayer wiring board 11 having the I / O pins 1 connected by the above method, and the heat conduction relay member 19 is placed on the semiconductor elements. A cap 20 that covers the multilayer wiring board 11 is placed on the relay member, and the cooling plate 2 is placed on the upper surface of the cap 20.
1 is laminated. This electronic circuit device wiring board is I / O
It is connected to the wiring board 22 via pins and constitutes an electronic circuit.

Next, the circuit board used in the present invention and the method for producing the I / O pin connection electrode metallization. Figure 7
Will be described with reference to a schematic view of the production process of. FIG. 7A is an enlarged view of a conductor portion and a through hole section of the substrate, and a ceramic circuit substrate is used as the substrate. As a pretreatment, the conductor surface is soft-etched with an alkaline solution and neutralized with an acid.
Degreasing was performed. Next, activation treatment was performed using a liquid containing a lead compound as a stabilizer (FIG. 7 (b)). After that, an electroless Ni-B plating film 5 was formed (FIG. 7C), and an electroless Au plating film 15 was formed for the purpose of surface protection (FIG. 7D) to obtain metallization. After film formation, heat treatment of the substrate causes mutual diffusion between the conductor surface / electroless Ni-B plating film / electroless Au plating film to improve adhesion between the joining metal layers.
(FIG. 7 (e)). After the heat treatment, the I / O pin on which the Au-20Sn brazing material was previously mounted was positioned on the metal layer formed on the substrate conductor portion (FIG. 7 (f)), and then heated to 320 ° C. At the same time that the Au-Sn brazing material wets and spreads on the surface of the joining metal layer, it diffuses into the electroless Ni-B plating layer and N
The i-Sn metal compound is formed and the I / O pins are connected to the substrate.

The tensile strength of the I / O pin was measured in order to evaluate the bonding state between the I / O pin connected in this step and the conductor portion on the substrate. The evaluation criteria are as follows. When the joining condition is good, the I / O pin joint (brazing part) does not break, and the I / O pin itself breaks at a certain strength or higher.
That is, the condition is that the joint strength of the brazed portion per I / O pin is higher than the tensile strength of the material of the I / O pin shaft portion. In order to evaluate the bonding state of the I / O pin bonded using the Au20Sn brazing material, a tensile test was conducted, and all the pins were broken, and sufficient bonding strength was obtained. Observation of the cross-sectional shape of this bonded portion revealed that the bonded state was normal without the occurrence of voids, cracks and the like.

For comparison, the same applies to the electroless Ni-B plating metallization formed by the above method using the conventional technique and the I / O pin bonding using Au13Ge at the bonding temperature of 400 ° C. A tensile test was performed. As a result, 90% or more of the I / O pins caused a joint failure that fractured between the intermetallic compound and the metallization. From this, it was verified that the joining using the Au20Sn brazing filler metal, which is one embodiment of the present invention, is a brazing filler metal that gives a sufficient bonding strength to the electroless Ni-B plating metallization containing Pb. In this way, when I / O pin bonding is performed using a Sn-based brazing material, Pb can diffuse in the intermetallic compound layer to be formed, so that high I / O pin bonding strength can be achieved without causing Pb segregation at the bonding interface. Was obtained.

As described above, by using the present invention,
With respect to electroless Ni-B plating metallization containing Pb formed on a circuit board, a good circuit board having high bonding strength and high reliability without causing segregation of Pb at the bonding interface that causes deterioration of bonding strength The connection method of / O pin was achieved, and the electronic circuit device using this was realized.

(Example 2) Electroless Ni-B on a circuit board
An example in which a semiconductor element having an Au-plated electrode terminal portion is bonded to the metallization by using a solder material having a composition of Ag3 wt% Sn97 wt% will be described. As shown in FIG. 9, Example 1 was formed on the electrodes of the circuit board.
Sn3Ag fine solder balls 23 are interposed between the metallization formed by the same method as described above and the electrode terminal portion of the semiconductor element, and brazing is performed at a bonding temperature of 240 ° C. At this time, Pb contained in the metallization can diffuse into the compound layer with respect to the Ni-Sn intermetallic compound formed at the bonding interface between the metallization and the Sn3Ag brazing material. Therefore, by connecting the Sn-based Sn3Ag solder material to the electroless Ni-B metallization containing Pb, a bond having sufficient strength and high reliability can be obtained without segregating Pb at the bonding interface.

As described above, by using the present invention,
A good circuit board and a semiconductor device having a bonding strength and high reliability without causing segregation at the bonding interface Pb that causes a decrease in bonding strength with respect to an electroless Ni-B plating metallization pad containing Pb on the circuit board. The method of connecting to the terminal electrode of 1 was achieved, and an electronic circuit device using this was obtained.

(Example 3) Electroless Ni-B on a circuit board
For plating metallization, Pb37 wt% Sn63
An example in which a cap that seals the periphery of the semiconductor element is joined using a solder alloy having a composition of wt% will be described. As shown in FIG. 10, the Sn37Pb solder material 24 is interposed between the metallization formed in the peripheral portion of the circuit board by the same method as in Example 1 and the peripheral edge portion on the sealing cap side, and the bonding temperature is 200 ° C. Connect with. In this case, Pb contained in the electroless Ni-B plating metallization can diffuse into the compound layer, with respect to the Ni-Sn intermetallic compound formed at the bonding interface between the metallization and the Sn37Pb brazing material. Therefore, electroless Ni containing Pb
-Sn-based Sn37P for B metallization
By connecting with the b solder material, a good bonding state can be obtained without Pb segregation at the bonding interface, and bonding with sufficient strength and high reliability can be obtained.

Thus, by using the present invention,
For an electroless Ni-B plating metallization pad containing Pb on a circuit board, a good circuit board having good bonding strength and high reliability without causing segregation at the bonding interface Pb that causes a decrease in bonding strength is formed. A cap connecting method was achieved, and an electronic circuit device using the same was obtained.

[0025]

As described above, according to the present invention, an Sn-based brazing material is used for a Ni-S alloy for an electroless Ni-B plated metallization pad containing Pb formed on a circuit board.
By connecting the parts by forming the n-alloy, the segregation of the joint interface Pb, which causes a decrease in the joint strength, does not occur.
A good method of connecting a circuit board and parts, which can obtain high bonding strength and high reliability, and an electronic circuit device using the same have been realized.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a joint in which an I / O pin is connected to a metallization formed on a circuit board by a conventional technique.

FIG. 2 is an enlarged view of the bonding interface of FIG.

FIG. 3 is a cross-sectional view of a bonding interface in which I / O pins are connected to metallization formed on a circuit board by using the connection method of the present invention.

FIG. 4 is a state diagram of a Ni—Pb binary system according to the present invention.

FIG. 5 is a Ge-Pb binary system state diagram according to the present invention.

FIG. 6 is a cross-sectional view of a joint portion in which a circuit board and an I / O pin are connected by using the connection method of the present invention.

FIG. 7 is a diagram showing a method of connecting a circuit board and components of the present invention,
Explanatory drawing which shows the process of connecting a circuit board and an I / O pin.

FIG. 8 is a perspective view showing a configuration of an electronic circuit device according to an embodiment of the present invention.

FIG. 9 is a cross-sectional view of a joint portion in which a circuit board and a semiconductor element are connected by using the connection method of the present invention.

FIG. 10 is a cross-sectional view of a joint portion in which a circuit board and a sealing cap are connected by using the connection method of the present invention.

[Explanation of symbols]

 1 ... I / O pin, 7 ... Ni-Ge intermetallic compound layer, 20 ... Sealing cap, 21 ... Cooling plate, 22 ... Wiring board.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kiyoshi Matsui 1 Horiyamashita, Hadano-shi, Kanagawa Hitachi General Computer Division (72) Inventor Toshihiko Ota 1 Horiyamashita, Hadano, Kanagawa Hitachi Ltd. General Computer Division

Claims (2)

[Claims] A metallization pad is formed on the circuit board by electroless nickel-boron alloy plating containing lead, and the metallization pad is formed on the circuit board by a connection method using a brazing material on the circuit board. A method for connecting circuit boards, characterized in that parts are connected mainly by forming a nickel-tin alloy using a tin-based brazing material. 2. An electronic circuit device using the connection method according to claim 1.