JP2008227055A - Circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solder material flow out preventing structure which prevents the flowing out of a solder material, which does not inhibit wire bonding and the mounting of a component after soldering, and which is excellent in terms of mounting property. <P>SOLUTION: An electronic component 5 is fixed with a solder material 4 by use of the solder material 4 in a state in which the electronic component crosses over a conductor pad 13 of an component mounting portion. Then, a solder flow out preventing portion 8 for preventing the solder material from flowing out to a wire bonding pad 7 is provided in order to connect a wire 6 using a wire bonding pad 14. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a circuit board in which electronic components such as capacitors, resistors, and semiconductor elements are placed in a predetermined region and joined with a solder material.

  When electronic components such as capacitors, resistors, and semiconductor elements are mounted on a ceramic circuit board to form an electronic circuit, a solder material is inserted between the circuit board and the electronic component in order to fix the electronic component. . After heating to a temperature at which the solder material melts, the temperature is lowered to cure the solder material, and the electronic component is loaded onto the wiring circuit of the circuit board. Further, when connecting with another circuit board or between the electrode of the electronic component and the wiring circuit, the connection is performed by wire bonding.

  At this time, as the metal that covers the surface of the wiring circuit, a metal that is easy to join a solder material and that is easy to wire bond is used. For example, Au is generally used. However, since the entire surface of the wiring circuit is covered with Au, when the solder material is melted on the substrate, it flows out of the outer periphery of the component to be mounted. At this time, the molten solder material flows on the surface of the wiring circuit continuous with the place where the electronic component is mounted, and flows out to the wire bonding region continuous with the wiring circuit where the electronic component is mounted. As a result, a mounting problem that hinders wire bonding is caused.

  On the other hand, in order to prevent the outflow of the solder material on the circuit, a conventional technique is known in which a damming portion for stopping the outflow of the solder material outside the soldering area is provided on the soldering surface of the conductor (for example, Patent Document 1). The damming portion has a structure in which a solder resist protrudes on the surface to be soldered.

JP 2001-257444 (FIG. 1)

  However, even when a damming portion is provided by projecting a solder resist around a mounting portion of an electronic component such as a semiconductor element or an electrical component, a new problem occurs due to melting of the solder material. For example, the solder material melts the solder resist itself that forms the protrusions, or melts the metal under the solder resist to float the solder resist, causing the solder resist to flow out, resulting in a satisfactory dam effect. There was a problem that it was not possible.

The present invention has been made to solve such a problem, and provides a solder material outflow prevention structure that prevents the solder material from flowing out and does not hinder component mounting or wire bonding after soldering. is there.

A circuit board according to the present invention includes a conductor layer formed on a ceramic substrate, a nickel layer formed on the conductor layer, a conductor pad formed on the nickel layer and made of a gold film layer, and the nickel layer. A wire bonding pad formed of a gold film layer formed on and in close contact with the conductor pad, an electronic component soldered to the conductor pad, and bonded to the wire bonding pad by wire bonding A conductor wire;
A nickel layer is exposed between the soldered portion of the electronic component in the conductor pad and the wire bonding pad, and an oxide film is formed on the surface of the exposed nickel layer.

  According to the present invention, it is possible to prevent the solder from flowing out to the wire bonding region by providing the solder flow-out preventing portion by the nickel oxide layer on the wiring circuit on which the electronic component is mounted.

Embodiment 1 FIG.
FIG. 1 shows a mounting structure using a ceramic circuit board according to Embodiment 1 of the present invention. The substrate constituting the ceramic circuit substrate 2 may be either a single plate or a laminated plate, and an alumina ceramic substrate, a low-temperature fired substrate, or the like is used. In the ceramic circuit board 2, electronic components 5 such as semiconductor elements, capacitor elements, and resistor elements are mounted on a predetermined wiring area of the circuit board, and the components are bonded and fixed by a solder material.

  Here, the semiconductor element means an electronic component generally used in various devices. For example, IC chips such as MIC and MMIC, LSI chips, transistors (bipolar type, field effect type), diodes, optical A semiconductor element such as a semiconductor element. These electronic components are fixed to the ceramic circuit board using a solder material. In addition, the solder material said here says the solder material containing Sn type metals and metals, such as a trace amount Cu and Ag.

  The base plate 1 fixes the ceramic circuit board 2 on which the electronic component 5 is mounted and the ceramic circuit board 3 on which the electronic component 5 is not mounted but used as an electrical lead line. The base plate 1 is not limited to two ceramic substrates as shown in FIG. 1, and a large number of ceramic circuit substrates may be fixed thereon with a solder material or an adhesive. The base plate 1 may be made of an alloy with Al, Cu, Fe, Co, Ni or the like, or may be a sintered ceramic coated with metal plating or the like. There is no particular limitation. In the ceramic circuit boards 2 and 3, the purity of the substrate material is generally 50% to 99.9%. Whether the ceramic circuit board is a single plate or a laminated plate, it does not disturb the circuit structure on the surface.

An electronic component 5 is fixed to the surface of the wiring circuit formed on the surface of the ceramic circuit board 2 using a solder material 4.
FIG. 1 shows an example in which a chip capacitor, which is a capacitor element, is used as the electronic circuit 5. Since the chip capacitor is provided with electrodes at both ends and the chip size is somewhat large, a solder fillet is formed at the end of the electrode as shown in the figure when soldering. Each electrode of the electronic circuit 5 is joined by a solder material 4 at a component mounting portion in two different wiring lines formed on the surface of the ceramic circuit board 2. That is, the electronic circuit 5 is mounted across two different wiring lines. A conductor pad 13 on which the electronic circuit 5 is placed is configured in the component mounting portion.

  A wire bonding pad 7 that is a conductor pad for connecting one end of the wire 6 is provided on the surface of the wiring circuit formed on the surface of the ceramic circuit board 2. Also on the surface of the wiring circuit formed on the surface of the ceramic circuit board 3, conductor pads 9 for connecting the other end of the wire 6 are provided.

  Further, when the solder material 4 is melted on the conductor pads 13 of the component mounting portion, the molten solder material 4 flows into the wire bonding pads 7 on the surface of the wiring circuit formed on the surface of the ceramic circuit board 2. A solder flow-out prevention unit 8 is provided to prevent this.

  The wire 6 used to connect the ceramic circuit board 2 and the ceramic circuit board 3 is used as a conductive wire for connection for transmitting an electric signal, and the material thereof is generally Au or Al, for example, a diameter of φ25 μm to φ200 μm. In addition, as a conductive wire for connection instead of a wire, for example, a conductor ribbon, which is a ribbon-like strip having a thickness of 20 μm to 50 μm, which is a single piece of Au or Au and Ag, and has an arbitrary width exceeding 0.1 mm. The method used may be used.

  FIG. 2 is a cross-sectional view showing details of the solder flow prevention structure of ceramic circuit board 2 according to Embodiment 1 of the present invention.

  In FIG. 2, a bonding layer 10 for improving the adhesion between the ceramic material 9 and the circuit conductor is formed on the ceramic material 9, and a conductor layer made of Cu which is an electrically good conductor is formed on the bonding layer 10. 11 is formed. The metal used for the bonding layer 10 is generally composed of Cr, Ni—Cr, W, Ta, Ti, or an alloy thereof. For example, when the film thickness is 10 nm to 500 nm, the ceramic material 9 and the conductor are formed. Bonding force with Cu constituting the layer 11 is improved. The conductor layer 11 is preferably made of Cu for the purpose of minimizing electrical loss. However, the conductor layer 11 is not limited as long as it is a good electrical conductor such as Ag, Au, Pt, Pd, and alloys thereof in addition to Cu. The film thickness of the conductor layer 11 is preferably, for example, standard 0.5 μm to 10 μm.

  A Ni (nickel) layer constituting the conductor layer (nickel conductor layer) 12 must be formed on the conductor 11. Although there are various Ni purities and manufacturing methods for the conductor layer 12, any of vapor deposition, sputtering, ion-assisted vapor deposition, etc. may be used, and even with phosphorus-containing Ni plating formed by electrolytic plating or electroless plating I do not care. For example, in the case of a Ni film formed in vacuum such as vapor deposition or sputtering, the standard film thickness is 0.1 μm to 5 μm, and 2 μm to 10 μm is preferable according to the plating method.

  The wire bonding pad 7 is a bonding layer with one end of the wire 6, and is preferably a gold film layer made of, for example, Au. The conductor pad 13 is a bonding layer with the electronic component 5 and is a metal having both solderability and wire bonding properties, and is preferably a gold film layer made of, for example, Au. The Au film thickness of both the wire bonding pad 7 and the conductor layer 13 is preferably 0.5 μm to 2 μm, for example, from the bondability by the solder material 4 and the bondability of the wire 6.

  In FIG. 2, the solder flow-out prevention unit 8 is provided in a shape that partitions a portion where the conductor pad 13 and the wire 6 of the component mounting unit are joined. The solder flow-out preventing portion 8 is formed of a portion where the Ni film 12 is exposed. An oxide film is formed on the surface of the Ni film 12 to form a nickel oxide layer. The conductor pad 13 adjacent to the solder flow-out prevention part 8 is a part on which the electronic component 5 is mounted and fixed with a solder material. In the illustrated example, one electrode of the chip capacitor is fixed with a solder material as the electronic component 5, and a solder fillet is formed around the outside of the electrode, and the bonding strength of the electronic component 5 is secured by the fillet. ing. The wire bonding pad 7 is connected in a state where one end of the wire 6 is crushed by wire bonding.

  In this way, by providing a nickel oxide layer (a layer in which an oxide film is formed on the surface of the portion where the Ni film 12 is exposed) on the wiring circuit on which the electronic component 5 is mounted, the solder flow-out prevention unit 8 is configured, thereby forming a wire. It is possible to prevent the solder from flowing out to the bonding area.

  Here, a process of forming the solder flow-out preventing portion 8 by exposing the Ni film 12 will be described. In this step, a photoengraving method generally used for semiconductor production is used. Hereinafter, the pre-process and the post-process for forming the solder flow-out prevention unit 8 will be described in order.

First, the pre-process for forming the solder flow-out prevention part 8 will be described.
First, the parts other than the solder flow-out prevention part 8 are protected by a photosensitive resin.
Next, in the region where the solder flow-out preventing portion 8 is formed, Au on the surface in the region is removed by an etching method using an ion milling method or a chemical etching method using an etching solution, and partially exposed Ni A film 12 is formed.
Here, the ion milling method is an etching method in which dilute argon gas is introduced in a vacuum, ionized by glow discharge, and irradiated onto a conductor. Further, in the chemical etching method, for example, an aqueous potassium iodide solution is generally used as an etching solution, but is not limited thereto.

  Note that the pre-process for forming the solder flow-out prevention unit 8 is not limited to the etching method described above. For example, after the Ni film 12 is formed, only the solder flow-out prevention part 8 is protected by a photosensitive resin, and then the conductor pads 13 and the wire bonding pads 7 of the component mounting part are selectively Au-plated.

Subsequently, a post-process for forming the solder flow-out prevention unit 8 will be described.
In this post-process, after forming the conductor pad 13 of the component mounting portion, the wire bonding pad 7 and the exposed portion of the Ni film 12, an oxide film is formed on the surface of the Ni film 12 exposed by heating in the air. Thus, the solder flow-out preventing portion 8 is formed.
At this time, the air means a living environment atmosphere, and it is not necessary to form a special atmosphere. The heating device may be a heat gun or hot plate that can be heated locally, or a drying furnace that can heat the entire substrate, and does not limit the heating method or means. However, the heating temperature is preferably 200 ° C. to 300 ° C., for example, when the heating temperature is 250 ° C., the heating time is 6 to 8 hours, and when the heating temperature is 300 ° C., the heating time is 3 hours to 5 hours.

  If the heating temperature and time are both small, the thickness of the oxide film formed on the surface of the Ni film of the solder flow-out prevention unit 8 becomes thin, and the solder flow-out prevention function may not be satisfied. For this reason, when forming an oxide film on the surface of the Ni film, a good solder flow preventing function can be realized by applying the heating time and the heating temperature.

  In the first embodiment, the electronic component 5 is mounted on the wiring circuit on the ceramic circuit board having the above-described structure, and the electronic component 5 is fixed to the conductor pad 13 by the solder material 4. At this time, even if the molten solder material 4 is about to flow out, the solder flow-out preventing portion 8 made of an oxidized Ni film repels the solder material. For this reason, when the electronic component 5 is soldered, the solder does not flow out to the surface of the oxidized Ni film, and the solder does not adhere to the adjacent conductor (wire bonding pad 7). Component mounting of the electronic component 5 can be carried out reliably.

1 is a perspective view showing a wiring structure of a ceramic circuit board according to a first embodiment. FIG. 3 is a cross-sectional view showing a structure of a solder flow-out prevention unit according to the first embodiment.

Explanation of symbols

  1: Base, 2: Ceramic circuit board, 3: Ceramic circuit board, 4: Solder material, 5: Parts, 6: Wire (conductive wire), 7: Wire bonding pad, 8: Solder flow prevention part, 9: Ceramic material 10: bonding layer, 11: conductor layer, 12: Ni layer (nickel layer), 13: component mounting part (conductor pad).

Claims (2)

A conductor layer formed on a ceramic substrate;
A nickel layer formed on the conductor layer;
A conductor pad formed on the nickel layer and made of a gold film layer;
A wire bonding pad comprising a gold film layer formed on the nickel layer and disposed in close contact with the conductor pad; and
Electronic components soldered to the conductor pads;
Conductive wires joined to the wire bonding pads by wire bonding;
With
A circuit board, wherein a nickel layer is exposed between a soldered portion of the electronic component in the conductor pad and the wire bonding pad, and an oxide film is formed on the surface of the exposed nickel layer. The circuit board according to claim 1, wherein the electronic component is a chip capacitor.

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