JP2007227452A - Flexible wiring board, its solder bonding method and optical transmitting package using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flexible wiring board and its solder bonding method by which electrodes can be bonded to each other by solder without producing a corrosive gas, and to provide an optical transmitting package using the same. <P>SOLUTION: The flexible wiring board 1 is comprised of a conductor 3 formed directly on a flexible heat-resistance insulation film 2, a wiring which is formed by covering such a film 41 as a nickel oxide film or the like on the conductor 3 that is difficult to be wetted by solder, and an electrode 5 which is formed by covering the surface of the wiring with such a film 51 that is easy to be wetted by solder such as gold or the like. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a flexible wiring board for connecting electrodes of an electronic component, a soldering method for a flexible wiring board for soldering the flexible wiring board to an electrode, and a light emitting element and an electrode connected using the flexible wiring board. The present invention relates to an optical transmission package.

As a method of arranging a plurality of electronic components in a three-dimensional manner and electrically connecting them, a method of connecting using a flexible wiring board having excellent flexibility is often used.
As a method for connecting electronic components using a flexible wiring board, a method using an anisotropic conductive adhesive film containing conductive particles in an epoxy resin adhesive and a method using solder are usually used.
In the method using the anisotropic conductive adhesive film, since the electrode and the conductive particles are brought into contact with each other by the adhesive force of the epoxy resin, the connection reliability is low. On the other hand, in the method using solder, since the electrodes are metal-bonded with solder, the connection reliability is high and the connection resistance is small.
When joining with solder, by forming solder on the electrodes of the electronic component or the electrodes of the flexible wiring board in advance, aligning the electrodes, and then pressing the electrodes of the flexible wiring board with a heating tool , Solder is melted to realize solder joint. The wiring portion is covered with a polyimide film pasted with a resin called a solder resist or an adhesive so that the solder does not flow along the wiring when the solder is melted.
Therefore, the structure of a conventional flexible wiring board is that a conductor is formed on a polyimide film, and the conductor becomes a wiring for transmitting a signal and an electrode for bonding, and a solder resist is formed on the wiring region excluding the electrode for bonding. Or the polyimide film is affixed with the adhesive agent. (See Patent Document 1)

JP 2002-198643 (pages 4-7, FIG. 1)

By the way, when a flexible wiring board is used for the connection between the electrodes in the package, it is corrosive at a high temperature from the adhesive to which the solder resist and the polyimide film used for preventing the flow of solder from the electrodes to the wiring of the flexible wiring board are attached. Gas may be generated.
Specifically, the amine group used for curing the resin is combined with moisture to become ammonia gas. Or the halogen in the resin is gasified to cause corrosion.
When the gas is generated, other semiconductor elements or electronic components or joints are corroded, and there is a problem that the reliability of the package is lowered.

  The present invention has been made to solve the above-described problems, and is a flexible wiring board capable of solder-bonding electrodes without generating corrosive gas, a solder-joining method thereof, and a light using the same. The purpose is to obtain a sending and receiving package.

  In the flexible wiring board according to the present invention, the conductor formed on the heat-resistant insulating film is composed of an electrode used for bonding and a wiring connecting the electrodes, and a film that does not wet with solder is formed on the wiring. At the same time, a film that gets wet with solder is formed on the electrode.

  In the present invention, as described above, the conductor formed on the heat-resistant insulating film is composed of an electrode used for bonding and a wiring connecting the electrodes, and a film that does not wet with solder is formed on the wiring. At the same time, a film that wets the solder is formed on the electrode, so that the molten solder does not flow out to the wiring at the time of soldering, the electrical characteristics are improved, and the solder is prevented from flowing out to the wiring. It is not necessary to use a solder resist or an adhesive having a low heat resistance temperature, and therefore no corrosive gas is generated.

Embodiment 1 FIG.
1 is a perspective view showing a flexible wiring board according to Embodiment 1 of the present invention.
In FIG. 1, a flexible wiring board 1 includes a conductor 3 formed directly on a heat-resistant insulating film 2, a wiring 4 formed by covering the conductor 3 with a film that is difficult to wet with solder, and a wiring 4. The electrode 5 (substrate side electrode) is formed by covering the surface with a film that easily wets the solder.

2 is a cross-sectional view showing a flexible wiring board according to Embodiment 1 of the present invention. FIG. 2 (a) is a cross-sectional view taken along the line AA in FIG. 1, and FIG. 2 (b) is a cross-sectional view taken along the line B-- in FIG. B sectional drawing and FIG.2 (c) are CC sectional drawings of FIG.
In FIG. 2, 1, 2, and 3 are the same as those in FIG. The conductor 3 is covered with a film 41 that is difficult to wet with solder, and the surface of the wiring 4 is covered with a film 51 that is easily wetted with solder to form an electrode.

Next, the operation will be described.
The conductor 3 is formed directly on the heat resistant insulating film 2. This forming method includes forming a heat-resistant insulating film on the heat-resistant insulating film 2 by a method such as sputtering, vapor deposition, or plating, and patterning by photolithography, and forming a heat-resistant insulating film on the metal film, and then forming the metal film by photolithography. There is a method of patterning.
Here, as a material of the heat-resistant insulating film 2, a resin film having flexibility and having heat resistance of 200 ° C. or higher is used, and examples thereof include polyimide and liquid crystal polymer. The conductor 3 is preferably made of a material having good heat conduction and low electrical resistance, such as copper.

  The wiring 4 is configured by covering the conductor 3 with a film 41 that is difficult to wet with solder. The material of the film 41 that is difficult to wet with solder may be a metal such as chromium, aluminum, or molybdenum, but a metal oxide film is simple and inexpensive. Here, a nickel oxide film was used. The nickel oxide film is not only difficult to wet with solder but also has corrosion resistance. Specifically, a method was used in which nickel was plated on the conductor 3 to form several μm and oxidized in air.

The surface of the electrode 5 is covered with a film 51 that easily wets the solder. The material of the film 51 that easily gets wet with solder is gold. Specifically, after the nickel plating was applied to the entire surface of the conductor 3, the wiring portion was covered with a resist, the electrode portion was exposed, the gold plating was applied, and the resist was peeled off. Therefore, the film 51 that easily wets the solder of the electrode 5 is formed on the nickel by gold plating.
The wettability to solder is expressed by an angle (contact angle) between the surface of the electrode and a molten solder droplet. In the case of good wettability, the solder spreads well and the contact angle becomes an acute angle. Conversely, if the solder is difficult to wet, the solder does not spread and tends to become a sphere, so the contact angle becomes an obtuse angle.

1 and 2 show the case where the conductor 3 is formed on both surfaces of the heat-resistant insulating film 2, the conductor 3 may be formed on one surface of the heat-resistant insulating film 2.
Moreover, you may provide the through-hole which penetrates the heat-resistant insulating film 2 and connects mutually to the electrode 5 and the wiring 4 of the front and back of the heat-resistant insulating film 2.

According to the first embodiment, since no solder resist or an adhesive having a low heat resistant temperature is used as the material of the flexible wiring board, no corrosive gas is generated at a high temperature of 150 ° C. or higher, and the reliability of the electronic device is improved. Does not deteriorate.
In addition, the electrode surface used for joining is made of a material that easily gets wet by the solder (contact angle is acute), and the surface of the wiring other than the electrode is made of a material that does not get wet with the solder (contact angle is obtuse). The solder melted at the time of soldering does not flow in the wiring direction, so that the conductor thickness of the wiring can be kept constant, and there is an effect that the electrical characteristics are not deteriorated without changing the impedance.

Embodiment 2.
FIG. 3 is a cross-sectional view showing a solder connection method according to Embodiment 2 of the present invention.
In FIG. 3, 2 to 5 are the same as those in FIG. 1, and films similar to those of the first embodiment are formed on 4 and 5. In FIG. 3, the electrode 61 of the electronic component 6 and the electrode 5 of the flexible wiring board 1 are joined by solder 7.
Here, it is assumed that the length A of the wiring 4 of the flexible wiring board is smaller than the length B between the electrodes 61 of the electronic component 6. Further, the contact angle α between the solder 7 and the surface of the electrode 61 forms an obtuse angle.

Next, the operation will be described.
The electrode 61 of the electronic component 6 and the electrode 5 of the flexible wiring board 1 are joined with the solder 7. The length B between the electrodes 61 of the two electronic components 6 is longer than the length of the wiring 4 of the flexible wiring board 1. As a result, the contact angle α between the solder 7 and the surface of the electrode 61 forms an obtuse angle and does not cause stress concentration, so that cracks do not occur in the solder and joint reliability can be improved. Incidentally, when the contact angle α is an acute angle, the solder is likely to crack.

  According to the second embodiment, since the length between the electrodes of the electronic component is longer than the length of the wiring of the flexible wiring board, it is possible to improve the bonding reliability.

Embodiment 3.
FIG. 4 is a sectional view showing a solder connection method according to Embodiment 3 of the present invention.
4, 2, 5, 6, 61 are the same as those in FIG. The flexible wiring board is formed in the same manner as in the first embodiment. The heating tool 8 of FIG. 4 is formed by covering the core material 81 with a film 82 that is difficult to wet with solder. The front and back electrodes 5 are connected by through holes 31 provided in the heat-resistant insulating film 2.

Next, the operation will be described.
FIG. 4 shows a state in which the electrode 61 of the electronic component 6 and the electrode 5 of the flexible wiring board 1 are joined by solder. Solder bumps are formed on the electrodes 61 or the electrodes 5 of the electronic component 6 in advance, and after the electrodes are aligned, the heating tool 8 is pressed against the electrodes 5 to melt the solder 7 and perform solder joining.
In this case, when the heating tool 8 is covered with a material that gets wet with the solder, the solder that has crawled up through the through-hole 31 of the flexible wiring board 1 flows along the heating tool 8, so that adjacent electrodes A short circuit occurs between them. On the other hand, when the heating tool 8 is covered with the film 82 that is not wetted by solder as in the third embodiment, the flow of solder is suppressed and a short circuit between adjacent electrodes does not occur.
Since the heating tool 8 needs to melt the solder, it needs to have good heat conduction and rigidity, and since it is necessary not to get wet with the solder, copper is used for the core material 81 to wet the surface solder. Chromium plating was used as the non-film 82.

  According to the third embodiment, when the electrode of the flexible wiring board and the electrode of the electronic component are soldered together, a heating tool in which a metal film that is difficult to wet with solder is formed on a metal surface with good thermal conductivity is used. There is an effect that the soldering can be realized without deteriorating the heat inflow amount, the solder does not adhere to the heating tool, and the soldering short circuit between the adjacent electrodes and the bonding failure are not generated.

Embodiment 4.
FIG. 5 is a plan view showing an optical transmission package according to Embodiment 4 of the present invention.
In FIG. 5, 1, 4, and 5 are the same as those in FIG. 1, and films similar to those in the first embodiment are formed on 4 and 5. The package 9 includes a flexible wiring board 1, an external terminal 91 that is a connection terminal to the outside, an electrode 92 that is connected to the external terminal 91, a light emitting element 93, a support block 94 that is die bonded to the light emitting element 93, A wire 95 is provided to connect the electrode 5 of the flexible wiring board 1 and the electrode of the light emitting element 93, and the electrode 92 and the light emitting element 93 are connected via the flexible wiring board 1.

Next, the operation will be described.
In the optical transmission package, a support block 94 having a ground potential is formed in the package 9, and a light emitting element 93 is die-bonded thereon. The electrode 5 of the flexible wiring board 1 is joined to the electrode 92 and the support block 94 with solder, and further from the electrode 5 of the flexible wiring board 1 on the opposite side via the heat-resistant insulating film and the electrode 5 soldered to the support block 94. The wire 95 is connected to the electrode of the light emitting element 93.
Thus, by using the flexible wiring board 1 for the connection between the electrode 92 connected to the external terminal 91 and the light emitting element 93, no corrosive gas is generated, and the impedance of the wiring is reduced as described above. Since control is easy, a high-performance and highly reliable optical transmission package can be realized.

  According to the fourth embodiment, by using a flexible wiring board for connection between the electrode connected to the external terminal and the light emitting element, a signal with impedance matching can be transmitted, and an optical transmission / reception package with good electrical characteristics can be obtained. be able to.

It is a perspective view which shows the flexible wiring board by Embodiment 1 of this invention. It is sectional drawing which shows the flexible wiring board by Embodiment 1 of this invention. It is sectional drawing which shows the solder connection method by Embodiment 2 of this invention. It is sectional drawing which shows the solder connection method by Embodiment 3 of this invention. It is a top view which shows the optical transmission package by Embodiment 4 of this invention.

Explanation of symbols

1 flexible wiring board, 2 heat-resistant insulating film, 3 conductors,
31 Through-holes that connect the front and back conductors, 4 wires,
41 Film that does not easily get wet with solder, 5 electrode, 51 Film that easily gets wet with solder,
6 Electronic components, 61 Electrode electrodes, 7 Solder, 8 Heating tool,
81 Core material, 82 Solder resistant film, 9 package,
91 external terminals, 92 electrodes connected to external terminals, 93 light emitting elements,
94 support block, 95 wires.

Claims (4)

  The conductor formed on the heat-resistant insulating film is composed of an electrode used for bonding and a wiring connecting the electrodes. A film that does not wet with solder is formed on the wiring, and a solder is formed on the electrode. A flexible wiring board, wherein a film that gets wet is formed.   In a method of connecting electrodes in an electronic component with a flexible wiring board, a flexible wiring board having a wiring length shorter than a distance between the electrodes of the electronic component is used. A method for soldering a flexible wiring board, characterized in that the solder is joined with solder.   A flexible wiring board having an electrode and a wiring connected to the electrode, and a film that does not wet with solder is formed on the wiring, and a film that wets with solder is formed on the electrode; and After the electronic component having an electrode corresponding to the electrode is disposed so that the electrode and the electrode of the electronic component face each other through the solder, heating in which a film that does not wet the solder is formed on a material having good heat conduction A soldering method for a flexible wiring board, wherein the electrode is pressed with one of the flexible wiring board and the electronic component with a tool and the electrodes are joined with the solder.   The flexible wiring board according to claim 1, comprising: an electrode connected to an external terminal and joined to the electrode of the flexible wiring board by solder; and a light emitting element connected to the electrode via the flexible wiring board. Features optical transmission package.

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