JP3683247B2 - Micro joint metal joining method and conductive tape - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fine joint metal joining wire to be joined to a base metal such as a terminal of an electronic component and a joining method using the same.
[0002]
[Prior art]
With the reduction in energy and weight of electronic devices, individual electronic components have become very small. These electronic components require electrical connection as in the past. In order to easily and accurately perform electrical connection to such a minute portion, various devices are required.
[0003]
As means well known as a micro joint, there is a non-contact type means such as micro laser welding or micro arc welding. Examples of contact means include micro spot welding and pulse heat welding.
In these conventional welding methods, when a non-contact type means is used, a joint metal is brought into contact with the base metal, and heat joining is applied to the base metal to perform fusion bonding. In other words, since a small joint metal is brought into contact with a base metal having a small area and heat energy is applied in a fixed state, there is a risk of causing a displacement due to an energy shock or poor bonding due to floating. It is necessary to finely adjust the amount of energy applied by the laser and arc so that the minute joint metal is not melted.
In the case of contact-type means, since the minute joint metal is brought into contact with the base metal and pressed, problems such as misalignment can be solved. However, if the applied pressure and applied force are not finely adjusted, the minute joint metal is energized. It melts during heating.
[0004]
As a means for solving this problem, Japanese Patent Application Laid-Open No. 11-333561 discloses a fine joining apparatus. A base metal and a micro joint are formed by placing a micro joint metal on a micro base metal, pressing a heating head having a micro gap from above, and heating a resistance heating element interposed between the workpiece and the heating head. It joins metal. The resistance heating element is in the form of a ribbon, and the ribbon is shifted for each joining and a new ribbon is always heated. Therefore, a change with time due to repeated joining is excluded. If this apparatus is used, it is easy to adjust the applied pressure and applied force, and the positional displacement between the objects to be joined hardly occurs.
[0005]
[Prior art documents]
JP-A-11-333561 (second page, right column (0009) to page 3, right column (0016)).
[0006]
[Problems to be solved by the invention]
The device has effectiveness as a device. However, when the micro joint metal is further miniaturized, it is expected that the joint force is reduced after joining due to the deformation of the joint metal due to the applied pressure, the joint portion is broken, and the like. Therefore, as a means for reducing the applied pressure at the time of joining the base metal or the minute joint metal and preventing the deformation of the joint metal, a means for coexisting the solder in the joint portion and assisting the applied pressure by welding the solder was searched.
[0007]
[Means for Solving the Problems]
The present invention is one means for solving the above problems. That is, solder is added to the minute joint metal, and the solder has a role of assisting in joining at the time of joint. Specifically, it is a fine joint metal bonding wire comprising a conductive core material for electrical connection and solder covering the core material. The conductive core material of the wire is intended for electrical connection and can be used as long as it is conductive. However, the conductive core material is Cu, Ti, W, Mo, AI, Cu alloy, iron alloy, nickel A simple material made of an alloy or an aluminum alloy, or a multilayer material made of a Cu clad product, a nickel clad product, a gold clad product or a platinum clad product is preferable. In particular, it is more preferable that it is one kind selected from Cu, Cu alloy, Cu clad product, and Al, which are relatively easily available.
[0008]
The solder covering the core material may be a conventionally used Pb—Sn solder, but it is preferable to use Pb-free solder. As the Pb-free solder, Sn—Ag—Cu solder is preferably used, but Sn—Zn—Bi solder and Sn—Zn—Al solder can also be used.
[0009]
In addition, if the outer periphery of the wire is covered with an electrical insulating resin, even if the wire is connected to another base metal after being connected to the base metal, It is preferable because a compact connection is possible without causing problems such as static leakage. In particular, since the core material is coated with solder, the electrical insulating resin is decomposed and removed by heat at the time of connection rather than the heat resistant electrical insulating resin such as heat resistant polyimide or polyamideimide. It is preferable to use polyurethane.
[0010]
The cross-sectional shape of the wire may be polygonal or plate-like as well as circular. In the case of a plate shape, one side may be a core material and one side may be solder. In this case, the solder surface may be opposed to the base metal side. However, since the object of the invention is a minute joint metal, it is preferable that the cross-sectional shape is substantially circular in consideration of convenience when used in the form of a wire. In this case, the core material having a circular cross section, that is, the core wire can be coated with solder, and then the resin for electrical insulation can be coated using a method of manufacturing a winding. Of course, even if the wire is polygonal or plate-shaped, it is possible to coat the resin for electrical insulation.
[0011]
Thus, although the cross-sectional shape can be selected as necessary, for the purpose of use in a micro joint, the cross-sectional diameter ((maximum diameter + minimum diameter) / 2) of the wire is in the range of several μm to 300 μm. preferable.
[0012]
The manufacture of the micro joint metal joining wire is preferably performed as follows. A conductive material to be a core material is stretched to a predetermined size, and solder is clad, vapor-deposited or plated. The resulting multi-layered wire is drawn to the required dimensions with a wire drawing machine or the like. In the case of a plate-like cross section, it can be produced by forming a core material on a sheet, clad, vapor-depositing or plating solder on the core, rolling it to a required thickness, and then cutting it into a slit shape. Furthermore, in order to coat | cover resin for electrical insulation, in the case of a cross-sectional circle or a polygon, it can process by using the manufacturing method of a coil | winding. That is, it is possible by dipping the solder-coated core material on an enamel varnish such as urethane varnish, squeezing it with a felt or the like and then curing the resin in a baking furnace. Of course, depending on the selection of the resin for electrical insulation, electrodeposition coating and powder coating are possible, and depending on the solvent of the resin, there are means for drying at room temperature. In addition, recently, means utilizing a gas phase reaction such as reactive vapor deposition can be used. In the case of a plate shape, it may be coated with a resin solution for electrical insulation in the form of a foil, and then cut into a slit shape to form a plate shape.
[0013]
In the joining method using the micro joint metal joining wire, the micro joint metal joining wire is placed on the object to be joined, and the conductive tape is pressed from above with a heating head to heat the conductive tape. Thus, the solder covering the core material of the wire is melted, and the object to be joined and the fine joint metal joining wire are joined by the melted solder. The apparatus to be used can be used as long as the electrode portion of the fine bonding apparatus described in JP-A-11-333561 is different, and even another apparatus is not particularly specified as long as the requirements are met.
[0014]
The conductive tape used here is preferably composed of a heat-resistant resin layer and a conductive metal layer, with the heat-resistant resin layer side facing the object to be joined. The base metal may have solder bumps, but may not be particularly pretreated like lead frame terminals. In the case of the micro joint metal joining wire of the present invention, since the solder exists in the joining portion, it can be sufficiently joined by melting the solder without applying a large pressure to the joining portion. Since solder exists in the joining portion, it is better not to use a material that attracts molten solder at the time of joining on the heating head side. For this reason, the conductive tape has a conductive metal layer necessary for heating on the heating head side, and the opposite side, that is, the bonded side, is a layer of a material that is unsuitable for solder such as a heat-resistant resin layer. It is preferable to use a multilayer tape using If it does in this way, it will work as solder effectively, without taking out solder from a joined part.
[0015]
More preferably, the heat-resistant resin layer of the conductive tape is polyimide, and the conductive metal layer is Cu or stainless steel. Since polyimide does not fit well with solder, molten solder does not easily adhere to the conductive tape. When Cu is used for the conductive metal, it is highly conductive and sufficiently flexible when it is made into a tape, so that when the heating head holds the object to be bonded, it is covered with the object to be bonded. The shape may be followed. When stainless steel is used, since it has rust prevention properties, the tape can be used for a long time without maintenance, but it is difficult to follow the shape of Cu.
When a polyimide and Cu are combined, if a rust preventive film such as Sn or Sn alloy is previously provided on the surface on the Cu side, long-term stability of the tape itself can be added to suppress rusting.
[0016]
When a tape coated with a low melting point metal is used on the conductive metal side of the conductive tape, it improves the adhesion between the electrode and the conductive tape and protects the electrode and the conductive tape from rust and the like. Hold and preferred. If the low-melting-point metal is Sn or Sn alloy, it is particularly preferable because it melts during energization heat generation and improves the electrical connection between the electrode and the conductive tape.
[0017]
The heating head is preferably an offset electrode. The offset electrode is particularly preferable because it can be more easily pressed so as to surround the workpiece from both sides when the workpiece is pressed.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments will be described below with reference to the drawings, but the present invention is not limited to the following embodiments.
FIG. 1 is an enlarged view of a heating head portion of a fine bonding apparatus described in JP-A-11-333561. The present invention can be used if the electrodes of this fine bonding apparatus are different. The heating head 2, the electrodes 22a and 22b called the parallel electrodes attached thereto, and the insulator 21 are not used in the present invention. Preferably, the electrode portion is an offset electrode shown in FIG. Further, it is not necessary to change the supply reel 23a and the take-up reel 23b protruding from the left and right in FIG. Another change in the present invention is the tape 24. As shown in FIG. 2, the tape 24 is composed of a conductive metal layer 24a on the electrode side and a heat-resistant resin layer 24b on the opposite side, which is unsuitable for solder. The foreign matter removing means 26 may not be used in the present invention.
[0019]
Moreover, although the point which pushes down and uses the heating head 2 of FIG. 1 is the same also in this invention, the to-be-joined object which is the target object pressed differs. Here, a micro joint metal joining wire (abbreviated as a wire) 51 comprising a core wire 51a made of a conductive metal and a solder layer 51b according to the present invention is used. In FIG. 2, the wire 51 is described in a two-layer structure, but it is preferable that there is an electrical insulating resin on the outer periphery of the solder layer 51 b. If the electrical insulating resin is a urethane resin, it is decomposed and removed when the bonded portion is heated by the heating head. However, since electrical insulation is maintained in the non-joined portion, electrical leakage does not occur when contacting with other wirings, devices, etc., which is advantageous in use.
[0020]
FIG. 2 is an enlarged view when the electrode portion of FIG. 1 is different, that is, when an offset electrode is used. Bumps 42 are placed on the input / output terminals 41a of the IC 41, and the wires 51 are placed thereon. At the time of FIG. 2A, the wire cross section maintains a two-layer state. The electrodes 22a and 22b descend from above the objects to be joined through the tape 24. The electrodes 22a and 22b are offset electrodes that move up and down and also move left and right. As shown in FIG. 2 (a), it is preferable that the tip portion is partially cut away so that a space is formed between the two electrodes. 2B, the wire 51 placed on the bump 42 is fixed on the bump 42 by the lowering of the heating heads 22a and 22b. At this time, the heating heads 22 a and 22 b are lowered and approach each other, so that the wire 51 is sandwiched via the tape 24. The tape 24 surrounds the wire 51 in a fixed state. As a result, since the heat from the heating head is easily transmitted to the bonded portion and the bonded side of the tape 24 is the heat-resistant resin layer 24b which is not well suited to solder, the solder layer 51b of the wire 51 surrounds the core wire 51a. It selectively flows toward the bump 42. As a result, as shown in FIG. 2C, the core wire 51a is fixed in a state of being half-fitted into the bump 42, and further, the solder layer 51b is joined so as to cover the upper portion of the core wire. Thus, the method of joining using the micro joint metal joining wire of this invention can obtain reliable joining, without crushing a core wire.
[0021]
(Example 1) A copper wire having a diameter of 2 mm was prepared for a magnet wire. A 1 mm thick lead-less solder (Ag 3.5%, Cu 0.75%, Sn balance) plate was prepared, and the copper wire was clad to obtain a solder clad copper wire having a diameter of 4 mm. It was drawn down by drawing with a die and thinned to a diameter of 20 μm. The obtained solder clad copper wire was supplied to an enamel baking furnace, and a urethane enamel varnish was applied and baked to obtain a wire for bonding a small joint metal covered with an electrically insulating resin. The finished wire had a diameter of 25 μm. The cross section of this wire is circular, the copper portion of the core wire is 10 μm in diameter, the solder layer is 5 μm, and the urethane enamel layer is 2.5 μm.
[0022]
This wire was used to joint the solder bump of the IC. The apparatus used was a micro-joining apparatus whose electrode part is an offset electrode. And the tape which hits a heating head part was produced as follows. A polyimide varnish was applied and dried on a 18 μm thick copper film to form a 25 μm thick polyimide film. The copper side of this film was coated with 25 μm of Sn alloy by plating. This film was cut into a width of 0.5 mm with a slitter to obtain a tape.
The finished tape was mounted on the supply reel of the fine joining apparatus and used. The connection conditions were a voltage of 1.3 V, a current of 27 A, and a power of 20 W. The core wire was pushed down, half-embedded in the bumps of the IC, and the upper part was covered with the solder of the wire.
[0023]
【The invention's effect】
The electronic device using the micro joint metal joining wire according to the present invention can be joined to the micro terminal more reliably and more reliably, and can be connected without leaving any dirt due to extra solder.
[Brief description of the drawings]
FIG. 1 is an enlarged view of a heating head portion of a fine bonding apparatus used in the present invention.
FIG. 2 is an operational diagram showing an example of the method of the present invention. (A) is before bonding, (b) is during pressure bonding, and (c) is in a state of pressure removal after bonding.
[Explanation of symbols]
1. Base 2 Heating head 21. Insulator 22. Electrode 22a. Electrode left 22b. Electrode right 23a. Supply reel 23b. Take-up reel 24. Tape 24a. Conductive metal layer 24b. Heat resistant resin layer 25. Motor 26. Foreign matter removing means 41. IC
41a Input / output terminal 41b. Fixed terminal 42. Bump 51. Wire 51a. Core wire 51b. Solder layer d. Distance between electrodes

Claims (8)

On the object to be joined, a fine joint metal joining wire used for forming an electric circuit between electrodes, consisting of a conductive core material for electrical connection and solder covering the core material, The conductive tape is pressed with a heating head from above, and the conductive tape is heated to melt the solder covering the core material of the fine joint metal joining wire, and the solder is joined by the molten solder. In a joining method for joining an object and a wire for joining a minute joint metal, the conductive tape is composed of a heat-resistant resin layer and a conductive metal layer, and the heat-resistant resin layer side faces the object to be joined. A method for joining micro-joint metal, characterized in that :   2. The method of joining a micro joint metal according to claim 1, wherein an outer periphery of the micro joint metal joining wire is coated with an electrical insulating resin.   The method for bonding a minute joint metal according to claim 2, wherein the resin for electrical insulation is polyurethane.   4. The micro joint according to claim 1, wherein a cross-sectional diameter ((maximum diameter + minimum diameter) / 2) of the micro joint metal joining wire is in a range of several μm to 300 μm. Metal bonding method.   A conductive tape comprising a heat-resistant resin layer and a conductive metal layer and used in the method for joining a micro joint metal according to claim 1.   6. The conductive tape according to claim 5, wherein the heat-resistant resin layer is polyimide and the conductive metal layer is made of Cu or stainless steel.   The conductive tape according to claim 5 or 6, wherein a low melting point metal is coated on the conductive metal layer side.   The conductive tape according to claim 7, wherein the low melting point metal is Sn or an Sn alloy.

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