JP3700663B2 - Plating film for electronic parts and electronic parts - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lead-free solder plating film formed on a connection terminal for connecting electronic circuits to each other, and an electronic component having a connection terminal provided with a plating film.
[0002]
[Prior art]
An electronic component such as a wiring cable, a wiring board, or an electric element includes a connection terminal for electrically connecting electronic circuits and joining the electronic components. A plating film is formed on the connection terminal, and conduction and joining are simultaneously performed by the plating film. Conventionally, Sn (tin) -Pb (lead) -based solder has been used as the plating film. However, in recent years, the adverse effect of lead on the environment has been pointed out, and Sn-Bi based lead-free solder added with Bi (bismuth) instead of lead has been used.
[0003]
As for this Sn-Bi-based lead-free solder plating, for example, as disclosed in JP-A-11-251503, it is common to use Bi in a concentration of less than 4% by weight. is there.
[0004]
[Problems to be solved by the invention]
However, Sn-Bi solder plating with a Bi concentration of less than 4% by weight has a higher melting point of about 20-30 ° C. than Sn-Pb solder plating, and changes the working conditions in the joining process. In addition, the heat effects on the electronic components due to the temperature increase during the joining work were inevitable.
[0005]
The present invention has been proposed in view of the above-described circumstances, and its purpose is to provide a plating film for electronic parts capable of suppressing the melting point of Sn-Bi solder plating to the level of Sn-Pb solder plating, and an electronic part. It is something to be offered.
[0006]
[Means for Solving the Problems]
The present invention has been proposed in order to achieve the above object. According to the present invention, an Sn-Bi solder plating film formed on the surface of a connection terminal for connecting electronic circuits included in an electronic component is provided. In
The average concentration of Bi is set in the range of 5 to 20% by weight, and the concentration of Bi on the surface of the coating is set in the range of 20 to 35% by segregation to increase the concentration of Bi existing therein. This is a plating film for electronic parts.
[0008]
2. The electronic component according to claim 1, wherein a region having a higher Bi concentration than the inside is segregated on the surface of the coating by controlling a current density at the time of forming the coating. It is a plating film.
[0009]
According to the third aspect of the present invention, the Bi concentration in the final bath is set higher than the Bi concentration in the previous bath in the film forming plating forming step, thereby segregating a region having a higher Bi concentration than the inside on the coating surface. The plated film for electronic parts according to claim 1, wherein the plated film is for electronic parts.
[0010]
An electronic component comprising a connection terminal for connecting electronic circuits to each other, wherein a plating film made of Sn-Bi solder is formed on the surface of the connection terminal,
In the plating film, the average concentration of Bi is set in the range of 5 to 20% by weight, and the concentration of Bi on the surface of the film is set in the range of 20 to 35% by segregation and is higher than the concentration of Bi existing inside. This is an electronic component.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below. As shown in FIGS. 1 and 2, a flexible cable 1 (a kind of electronic component of the present invention) such as a flexible printing circuit (FPC) or a tape carrier package (TCP) has a plurality of connection terminals 2. Is formed. And the plating film 3 is formed in the surface in each connection terminal 2 .... In FIG. 1, only one end is shown, but the other end is configured similarly.
[0012]
The flexible cable 1 has a configuration in which a plurality of linear conductor patterns 5 (a kind of electronic circuit) are formed side by side inside the base films 4 and 4 ′ stacked on each other. Said base film 4 and 4 'are comprised by the film which has electrical insulation, such as a polyimide, for example, and each conductor pattern 5 ... is comprised by Cu layer (copper foil layer).
[0013]
The flexible cable 1 is generally manufactured by the following procedure.
First, a copper foil layer is formed on one entire surface of the base film 4, and this copper foil layer is partially removed by a method such as photolithography. Thus, a plurality of conductor patterns 5 are formed on the base film 4.
If each conductor pattern 5 ... is formed, the substrate film 4 'is bonded to the conductor forming surface of the substrate film 4, and each conductor pattern 5 ... is applied to the substrate film in a state in which the conductor tip portion to be the connection terminal 2 is exposed. Cover with 4 '.
When the base film 4 ′ is joined, the plating film 3 is formed on the surface of each connection terminal 2... (That is, the tip portion of each conductor pattern 5...). The flexible cable 1 is obtained by forming the plating film 3.
[0014]
The plating film 3 is a film made of Sn—Bi solder and has a thickness of about 3 to 10 μm. For example, the plating film 3 has an average Bi content of 5 to 20% by weight, contains at least one component of Ag (silver), Cu (copper), and Zn (zinc) in an amount of less than 3% by weight, and the remainder Sn. As for Ag, Cu, and Zn, only Ag, Cu, or Zn alone may be added, or two or three components may be added. When two or more components are added, the total amount added is less than 3% by weight.
Here, the reason why a trace amount of at least one component of Ag, Cu, and Zn is contained is that a component such as Ag is easily dissolved in Sn. That is, the soldering workability can be improved by adding these additive components. In addition, you may comprise the plating film 3 only by Sn and Bi.
And the component composition of the plating film 3 in this embodiment is Sn of 82 weight%, Bi is 16 weight%, and the mixed component of Ag, Cu, and Zn is 2 weight%.
[0015]
This plated coating 3 is characterized in that the Bi concentration on the coating surface 3a is higher than the Bi concentration on the inside 3b by segregation. In this embodiment, the average Bi content in the entire coating is 16% by weight, whereas the Bi concentration on the coating surface 3a is increased to 30% by weight.
In addition, since the average content of Bi in the plating film 3 can be changed by 5 to 20% by weight as described above, the Bi concentration on the coating surface 3a also changes according to the average content. For example, when the average content of Bi changes from 5 to 20% by weight, the Bi concentration on the coating surface 3a changes in the range of 20 to 35% by weight.
[0016]
In this plating film 3, since the Bi concentration on the film surface 3a side is higher than the concentration in the inner part 3b, the melting point of the film surface 3a can be made lower than the melting point defined by the average content of Bi. For example, it can be lowered by about 10 to 20 ° C. as compared with a plating film that is not segregated.
In the composition of the present embodiment, since the Bi concentration on the coating surface 3a is about 30% by weight, the coating surface 3a melts at 200 ° C., which is about the same as the Sn—Pb plating coating. When the coating surface 3a is melted, the interior 3b is also melted in a chain. Therefore, the connection work of components can be performed at the heating temperature comparable as a Sn-Pb type plating film.
[0017]
The plating film 3 is formed by, for example, an electroplating method or an electroless plating method.
[0018]
In the film formation method by the electrolytic plating method, it is possible to change the component ratio in the thickness direction of Bi by adjusting the current density, and by reducing the current value in the final stage of film formation, the film surface 3a A region having a higher Bi concentration than the interior 3b can be segregated on the side.
[0019]
For example, by setting the current value to 1.5 A at the final stage of film formation and setting the current value to 2.5 A before that, it is possible to segregate a region having a higher Bi concentration than the inside 3 b on the film surface 3 a side. it can.
[0020]
Moreover, in the film formation method by the electroless plating method, the film thickness is sequentially increased by passing through the plurality of bathtubs using an electroless plating apparatus provided with a plurality of plating baths. By setting it higher than the Bi concentration of the previous bath, it is possible to segregate a region having a higher Bi concentration than the inside 3b on the coating surface 3a side.
[0021]
For example, by setting the Bi concentration in the final bath to 30% by weight and setting the Bi concentration in the previous bath to 5% by weight, a region having a higher Bi concentration than the inside 3b can be segregated on the coating surface 3a side. .
[0022]
Next, the connection operation | work of electronic components (namely, electronic circuits) using the flexible cable 1 in which this plating film 3 was formed is demonstrated. Here, FIG. 3 is a diagram illustrating an ink jet recording head 11 (hereinafter, referred to as recording head 11) in which the flexible cable 1 is used.
[0023]
First, the structure of the recording head 11 will be briefly described. The recording head 11 includes a vibrator unit 12 including a plurality of piezoelectric vibrators 12, a fixed plate 13, a flexible cable 1, and the like, and a case 15 that can store the vibrator unit 14. A flow path unit 16 joined to the front end surface of the case 15 and a wiring board 17 disposed on the mounting surface side of the case 15 are provided.
[0024]
The case 15 is a block-shaped member made of synthetic resin that has a housing empty part 18 formed therein, the front and rear ends of which are both open. The vibrator unit 14 is housed and fixed in the housing empty part 18.
[0025]
The vibrator group 12 is a kind of electronic component, and an external electrode pattern (a kind of electronic circuit, not shown) is electrically connected to each conductor pattern 5 of the flexible cable 1. The vibrator group 12 is constituted by a plurality of piezoelectric vibrators that are cut into comb teeth having an extremely narrow width of about 30 μm to 100 μm, for example. The vibrator group 12 is joined to the fixed plate 13 with a free end protruding outward from the edge of the fixed plate 13. Further, a connection end portion of the external electrode pattern is formed on the surface opposite to the fixing plate 13, and a contact surface 12a is constituted by this connection end portion. One end of the flexible cable 1 is joined to the vibrator group 12 on the contact surface 12a.
[0026]
The flow path unit 16 is a member in which a nozzle opening 20, a pressure chamber 21, a common ink chamber 22, and the like are formed, and is configured by, for example, a silicon substrate or a stainless steel plate. The flow path unit 16 is bonded to the front end surface of the case 15.
[0027]
The wiring board 17 is also a kind of electronic circuit, and is constituted by a so-called printed wiring board provided with a connector and a conductor pattern (one kind of electronic circuit, neither of which is shown).
[0028]
When the recording head 11 is assembled, the vibrator unit 14 is manufactured. In producing the vibrator unit 14, the flexible cable 1 is joined to the subunit in which the vibrator group 12 and the fixing plate 13 are joined.
[0029]
At the time of this joining operation, as shown in FIG. 3B, one end of the flexible cable 1 is placed and positioned on the contact surface 12 a of the vibrator group 12, and is opposite to the vibrator group 12. The thermocompression terminal 25 is pressed from the cable surface. The plating film 3 is heated and remelted (reflowed) by the pressing of the thermocompression terminal 25. Furthermore, the plating film 3 is solidified by separating the thermocompression terminal 25 from the cable surface, and the flexible cable 1 and the vibrator group 12 are joined.
[0030]
In this case, since the Bi concentration of the coating surface 3a is increased to about 30% by segregation, the plating film 3 of the present embodiment has a temperature of about 200 ° C., which is about the same as the Sn—Pb-based plating film as described above. Melts at temperature. Therefore, the temperature of the thermocompression bonding terminal 25 may be adjusted to the same level as in the past, and the flexible cable 1 is damaged, for example, the base films 4 and 4 'are damaged, or the control IC (not shown) mounted on the flexible cable 1 is shown. Can be prevented.
[0031]
Further, after the manufactured vibrator unit 14 is bonded in the case 15, the wiring substrate 17 and the other end portion of the flexible cable 1 are joined.
[0032]
At the time of this joining operation, as shown in FIG. 3C, the other end of the flexible cable 1 is placed and positioned on the contact surface 17a of the wiring board 17, and the cable on the side opposite to the wiring board 17 is positioned. The thermocompression terminal 25 is pressed from the surface. The plating film 3 is reflowed by the pressing of the thermocompression terminal 25, and the plating film 3 is solidified by separating the thermocompression terminal 25 from the cable surface. The flexible cable 1 and the wiring board 17 are joined by the solidification of the plating film 3.
[0033]
Also in this case, since the Bi concentration of the coating surface 3a in the plating coating 3 is increased to about 30% by segregation, the temperature of the thermocompression bonding terminal 25 is the same as that of the conventional (ie, Sn—Pb plating coating). What is necessary is just to adjust to a grade and the damage of the flexible cable 1 can be prevented.
[0034]
Thus, in this embodiment, since the Bi concentration of the coating surface 3a is higher than that of the inner portion 3b by segregation with respect to the plating coating 3 formed on the connection terminal 2, the average of the plating coating 3 is applied to the coating surface 3a. It can be lower than the melting point specified by the Bi content. And about the inside 3b of the plating film 3, it can be made to melt | dissolve with melting of the film surface 3a. Thereby, melting | fusing point of the plating film 3 can be lowered | hung, suppressing Bi density | concentration. Thereby, melting | fusing point in Sn-Bi type | system | group solder can be restrained to the grade of Sn-Pb type | system | group solder plating, and joining work can be implemented on the same conditions as Sn-Pb type | system | group solder plating.
[0035]
【The invention's effect】
As described above, according to the present invention, the average concentration of Bi is set in the range of 5 to 20% by weight, and the Bi concentration on the surface of the coating is set in the range of 20 to 35% by weight by segregation. Since it was higher than the concentration of Bi present, the coating surface melts at a temperature lower than the melting point defined by the average Bi content. When the coating surface melts, the inside also melts in a chain. For this reason, the junction temperature can be lowered to a temperature equivalent to that of a conventional Sn—Pb solder plating film.
Accordingly, it is possible to suppress the thermal influence on the electronic component to the conventional level, and to prevent a significant change in the quality level. In addition, the technology can be diversified.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an end portion of a flexible cable.
FIG. 2 is a partially enlarged cross-sectional view for explaining a plating film.
3A and 3B are diagrams illustrating a recording head using a flexible cable, where FIG. 3A is a cross-sectional view, FIG. 3B is a diagram illustrating the joining of a subunit and a flexible cable in a vibrator unit, and FIG. It is a figure explaining joining of a board | substrate and a flexible cable.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Flexible cable 2 Connection terminal 3 Plating film 3a Coating surface 3b Inside 4, 4 'Base film 5 Conductive pattern 11 Inkjet recording head 12 Vibrator group 13 Fixing plate 14 Vibrator unit 15 Case 16 Flow path unit 17 Wiring board 18 Empty portion 20 Nozzle opening 21 Pressure chamber 22 Common ink chamber 25 Thermocompression bonding terminal

Claims (4)

In the Sn—Bi system solder plating film formed on the surface of the connection terminal that connects the electronic circuits included in the electronic component,
The average concentration of Bi is set in the range of 5 to 20% by weight, and the concentration of Bi on the surface of the coating is set in the range of 20 to 35% by segregation to increase the concentration of Bi existing therein. Plating film for electronic parts.   The plating film for electronic parts according to claim 1, wherein a region having a higher Bi concentration than the inside is segregated on the surface of the film by controlling a current density at the time of forming the film.   In the plating formation process, the Bi concentration of the final bath is set higher than the Bi concentration of the previous bath so that a region having a higher Bi concentration than the inside is segregated on the coating surface. The plating film for electronic components as described. In an electronic component having a connection terminal for connecting electronic circuits to each other, and forming a plating film with Sn-Bi solder on the surface of the connection terminal,
In the plating film, the average concentration of Bi is set in the range of 5 to 20% by weight, and the concentration of Bi on the surface of the film is set in the range of 20 to 35% by segregation and is higher than the concentration of Bi existing inside. An electronic component characterized by that.

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