JPH0472001A - Manufacture of fine metallic balls - Google Patents

Abstract

PURPOSE:To easily obtain fine metallic balls by heating and melting a stretched fine metallic wire after stretching the fine metallic wire on upper surface of a heat resistant base plate forming recessed parts on the upper surface. CONSTITUTION:At first, the fine metallic wire 2 is stretched so as to become orthogonal to the grooves 12 on the upper surface of base plate 10 and hung to pins 16 arranged to both end parts in the base plate 10 in order, to stretch the fine metallic wire 2 over on the upper surface of base plate 10. Successively, a pressing cover 20 is laid on the base plate 10 and fixed with holding tools 30, such as clamp, hing. Under this condition, the base plate is charged into a high temp. furnace, e.g., electric furnace, to melt the metallic wire at infinity about 1070 deg.C. At the same time of melting the metallic wire, this is cut with projecting parts 14 among the grooves 12 and dropped into the grooves 12. Therefore, by stilly cooling and only solidifying it, the fine metallic balls can be manufactured, and working efficiency and productivity are improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is a method for manufacturing fine metal balls used as a bonding member when bonding between the t8i of an IC chip and the lead of a TAB tape. It is about the method.

[Conventional technology]

Various methods are used to connect the electrodes of the IC chip and external leads.

There is a method of connecting using ultra-thin wire for wiring (ponding wire), but a method of thermocompression bonding by sandwiching a metal protrusion called a bump between the chip electrode and the lead is also becoming widely used. .

T A B (Tape Automated Bon
ding) method is a technique that is attracting attention as a representative of the latter. In this method, a bump is formed in advance either on the electrode section of the IC chip or on the lead tip section on the TAB tape, and then the IC chip electrode section and the TAB tape containing the leads are stacked via the bump. The two are then joined together. In addition to the TAB method, bumps are also used in the flip-flop method.

Up until now, the method of making bamboo provided for such uses has mainly been the method of making bamboo sticks. In other words, the force is applied by directly plating the metal (mainly high-purity gold) that will become the bump on the electrode part of the IC chip, or by applying the force to form the bump once formed by plating on a glass substrate etc. to the lead tip on the TAB tape side. The mainstream method is to transfer.

However, the method using plating has disadvantages in that it requires large equipment and is also subject to restrictions on the composition of the metal used as the bump. It was also feared that if bumps were to be formed by directly plating the electrodes of IC chips, the IC chips themselves would have to go through the plating process, which would worsen the yield of IC chips. .

As a way to overcome these drawbacks, bump forming methods that do not involve plating have come to be considered. An application was filed for a method for obtaining spherical bumps by cutting the bumps to a specified length and then melting and solidifying the bumps at intervals using surface tension (Japanese Patent Application No. 1-320).
No. 296). The spherical bump made by this method is used by thermocompression bonding to the tip of the lead, etc. (Patent application No. 1-23
No. 4917).

The new method of melting any piece of metal wire to make a hump greatly expands the possibility of using any metal that has properties suitable for a joining member as a hump. In other words, in addition to gold, copper, silver, and various alloys based on these materials can now be easily formed into humps.

[Problem to be solved by the invention]

In the conventional manufacturing method for fine metal balls, after cutting fine metal wires to a predetermined length, the metal wire pieces were manually arranged one by one at regular intervals in a melting tray, etc., and then melted. .

With this method, fine metal spheres of uniform size can be formed by cutting the fine metal wire to a certain length. However, this metal wire piece is 2 to 3 mm long at most.
Since the metal wires are so small, it takes time and effort to arrange the metal wire pieces one by one, resulting in poor work efficiency and a lack of mass productivity.

The present invention has been made based on the above circumstances, and aims to improve work efficiency and provide a method for manufacturing fine metal balls that can be easily mass-produced.

[Means to solve the problem]

In order to achieve the above object, the method for manufacturing a fine metal ball according to the present invention is to stretch a fine metal wire on the upper surface of a heat-resistant substrate having a concave portion formed on the upper surface, and then stretch the fine metal wire It is characterized by obtaining fine metal spheres by heating and melting.

Preferably, the substrate is formed with a large number of recesses having the same opening size at least in the portion where the fine metal wire is stretched.

Further, it is desirable to heat and melt the fine metal wires after placing a heat-resistant presser lid on the upper surface of the substrate on which the fine metal wires are stretched.

[Effect]

With the above-described configuration, the present invention heats the fine metal wire stretched over the upper surface of the substrate to cut the fine metal wire into metal wire pieces having the size of the opening of the recess, and the cut metal wire pieces. By holding and melting the metal wire by the bottom of the recess, the metal wire piece is spheroidized using the surface tension of the molten metal. Thereafter, it is gently cooled and solidified to form fine metal spheres.

By forming a large number of recesses in the substrate, at least the portions where the fine metal wires are stretched, the openings have the same size, so that the large number of melted metal wire pieces all have the same length. Therefore, fine metal spheres of uniform size can be easily mass-produced.

In addition, by placing a heat-resistant presser lid on the top surface of the substrate on which the fine metal wires are stretched, and then heating and melting the fine metal wires, the metal wires are generated by thermal expansion when heating the fine metal wires. This prevents the melting point from shifting due to the deformation of the piece, and also ensures that the fine metal wires are cut in each recess precisely, even if there are differences in the timing of fusing the fine metal wire in each recess when a large number of recesses are formed on the board. Can cut metal wires.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 1 to 4. FIG. 1(a) is a schematic diagram of a substrate and a holding lid used in an embodiment of the present invention; Fig. 1 (b) is a schematic side view of the substrate and the presser lid together, Figs. 2 and 3 are diagrams for explaining the method of applying fine metal wires to the substrate, and Fig. 4 is a diagram showing the method. It is a schematic diagram when a substrate covered with a fine metal wire and a presser lid are fixed. In this example, a gold wire (fine metal wire) with a wire diameter of 20 μm is used, and a gold wire with a diameter of 80 μm is used. A case of manufacturing a sphere (fine metal sphere) will be explained.

A large number of grooves (concave portions) 12 having a constant width are formed in a heat-resistant substrate 10 shown in FIGS. 1(a) and 1(b). The substrate 10 is desirably made of a heat-resistant material such as carbon or ceramics. Although the dimensions of the substrate 10 are not particularly limited, they are length A-30 mm and width B-50 mm.

Further, the cross section of the groove 12 is formed in a semicircular shape, the width of the opening of the groove 12 D=Q, 8 mm, the width E of the protrusion 14 between the ills 12=0°1 mm, and the depth of the groove 12 H=0. .35m
Let's start with m. In practice, there are no restrictions on the shape of the grooves 12. The cross section of the groove 12 is not limited to a semicircular shape, but may be rectangular or V-shaped. However, if the cross-sectional shape is V-shaped,
The bottom part must be rounded to a radius o of 35 mm or more. Further, it is desirable that the width E of the protrusion 14 between the grooves is as narrow as possible.

The width of the opening of the groove is determined by the wire diameter of the fine metal wire and the size of the fine metal sphere to be manufactured. Also,
In the case of this example, the diameter of the groove opening is ±0.1 m.
If manufactured with an accuracy of m, the variation in the length of the cut metal wire piece will be within about 10%, and when formed into a metal sphere, the error in the radius will be about 5%, making it possible to achieve uniformity with high precision. Fine metal spheres can be manufactured. therefore,
When cutting a fine metal wire, which will be described later, the gold wire on the protrusion 14 between the grooves does not have a large effect on the accuracy of the obtained metal ball, regardless of which groove of the protrusion 14 the gold wire falls into.

Further, a large number of pins 16 are provided at both ends of the substrate 10 at intervals approximately equal to the diameter of the bottle, and the pins 16 at one end are arranged at intervals approximately equal to the diameter of the bottle.
is located between the pins 16 at the other end. This allows the fine metal wires to be stretched almost parallel to the upper surface of the substrate IO.

The presser M2C is also made of ceramics, and this
It plays the role of fixing the fine metal vA2 stretched over the groove 12. The surface of the presser M2C facing the substrate 10 is processed to be flat. Further, a hole 22 corresponding to the bottle 16 is formed in the holding lid 20. Note that it is desirable that the gap created when the substrate 1O and the presser lid 20 are overlapped is as small as possible.
Finish 0. By sandwiching the fine metal vA2 between the thus processed substrate 10 and the presser M2C, the fine metal wire is fixed.

In order to manufacture fine metal balls, first, a fine metal wire 2 is stretched on the upper surface of a substrate 10 so as to be perpendicular to the groove 12. In this embodiment, as shown in FIG. 2, the fine metal wires 2 are successively hooked onto bins 16 provided at both ends of the substrate 10, thereby stretching the fine metal wires over the upper surface of the substrate 10. Alternatively, as shown in FIG. 3, the pins may not be provided on the substrate 10, and a plurality of fine metals vA2 may be arranged in parallel on the substrate 10. When a plurality of fine metal wires 2 are arranged in this way, in particular, a presser lid 2 for fixing the fine gold i-wires 2 is used.
There is great significance in using 0.

After stretching the fine metal wire (gold wire) 2 on the substrate 10, presser M
2C is placed on the substrate 10 and fixed with a stopper 30 such as a clamp or a hinge as shown in FIG.

In this state, the substrate is placed in a high temperature furnace, such as an induction heating furnace, and the gold wire is melted at 1060°C. At the same time as the gold wire melts, it is fused and cut at the protrusion 14 between the grooves 12 and falls into the groove 12. In this embodiment, the width of the groove 12 is formed to be 0.8 mm, so that the gold wire also melts. Cut into lengths of 0.8 mm. In this way, the fused gold wire pieces are placed at appropriate intervals (
(approximately equivalent to the diameter of the pins 16).

Generally, molten metal has a large surface tension, and when a fine solid material of an appropriate shape is heated above the melting temperature, it tends to change into a spherical shape by itself in the molten state. therefore,
Fine metal spheres can be produced simply by melting a metal having the same mass as the metal sphere and then gently cooling and solidifying it.

Therefore, the metal wire pieces arranged at regular intervals in the grooves 12 are melted in the furnace and formed into fine metal spheres of the same size. Finally, the substrate 10 is removed from the furnace and slowly cooled to obtain fine metal spheres of the desired dimensions.

As described above, in the method for manufacturing fine metal balls of this embodiment, the cutting process of fine metal wires and the process of melting metal wire pieces can be performed in one step, so that the process of arranging metal wire pieces after cutting can be performed in one step. is no longer necessary, and it is possible to improve work efficiency in the manufacturing process of fine metals. Moreover, by forming a large number of grooves 12 or by forming the grooves 12 to be long, mass productivity can be improved.

Further, in this embodiment, heat-resistant materials are used for the substrate 10 and the presser cover 20, so that they can be used semi-permanently if they are manufactured several times.

FIGS. 5 and 6 are views showing other examples of the presser lid used in this embodiment. The holding lid 20a shown in FIG. 5 has a width F"0 at the portion corresponding to the protrusion 14 of the groove 12 of the substrate 10.
A recessed portion 24 of 2 mm, depth G=O, and 1 mm is formed. By forming the presser lid 20a in this manner, there is no need for finishing between the recessed portions 24 of the presser lid 20a, and processing of the presser lid 20a becomes easy.

The holding lid 20b shown in FIG. 6 has a corrugated cross-section on the surface that meets the substrate 10. Each wave-shaped convex portion 26 is formed to correspond to the guide 12 of the substrate 10. 6th
By using the holding lid 20b shown in the figure, the holding lid 20b presses the fine metal wire at the center of the good conductor 12 toward the lower side of the figure during fusing.
When fusing a fine metal wire, the fine gold r/X-ray can be reliably cut at each protrusion 14, so that the size of the metal wire piece after fusing becomes uniform.

FIGS. 7 and 8 are diagrams showing other examples of the substrate used in this embodiment. The feature of the substrate 10a shown in FIG. 7 is that a partition wall 18 is provided in the groove 12 of the substrate 10 shown in FIGS. 1 and 2.
By providing this, a12 is divided into small rooms 12a each having a length J=4 mm. Note that the thickness of the partition wall 18 is L=1 mm. Further, the substrate 10b shown in FIG.
The feature is that a hole 19 with a diameter M of about 4 mm is provided instead of a groove. By using the substrate shown in FIG. 7 or 8, when the fine metal wire is fused, each metal wire piece falls into each small part M12a or hole part 19 one by one, so a plurality of metal wire pieces It is possible to prevent large-sized defective products from being formed due to overlapping melting. Therefore, by using the substrate shown in FIG. 7 or 8, it is possible to improve the yield.

Incidentally, in the above embodiment, the case where one substrate is used has been described, but a plurality of substrates may be stacked and used. For example, as shown in FIG. 9, three substrates 10 may be stacked and placed in a heating furnace. However, in this case, the bottom surfaces of the upper and middle substrates 10 must be finished with the same precision as the presser lid. . By giving the substrate 10 the function of a presser lid in this way, the presser M2O is the topmost substrate]
Since it is only necessary to cover the metal balls 2o, the number of presser lids 2o can be reduced, and a large amount of fine metal balls can be easily manufactured in the step.

In addition, in the above embodiment, the case where the fine metal vA2 is a straight line has been described, but the fine metal wire is not limited to a straight line.
For example, it may be formed into a waveform as shown in FIG. By using the bendable fine metal wires 2a, the fine metal wires 2a are cut at each top 2az at the time of fusing, so precise finishing of the protrusions 14 is not required, and the manufacture of the board becomes easy. However, in this case, the length of the metal wire piece is the length of the circular arc of each waveform.

Further, in the above embodiment, a case was explained in which a holding lid is used during fusing, but it is also possible to omit the holding lid by forming fine metal wires as shown in FIG. 10. It goes without saying that if the precision of the fine metal balls is not required, the holding lid can be omitted.

Furthermore, in the above embodiments, the case where the grooves, holes, etc. of the substrate are formed to have a constant size has been described, but the present invention is not limited to this, and the size can be changed in one substrate. By forming and using several types of grooves, holes, etc. with different sizes, it is also possible to manufacture fine metal spheres of different sizes in a step.

〔Effect of the invention〕

As explained above, according to the present invention, by placing fine metal wires on the upper surface of a substrate and heating the substrate to a high temperature,
A method for manufacturing fine metal balls that can improve work efficiency and mass productivity in the manufacturing process of fine metal balls, since cutting the fine metal wire and melting the cut metal wire pieces can be performed in one step. can be provided.

[Brief explanation of the drawing]

FIG. 1(a) is a schematic diagram of a substrate and a presser lid used in an embodiment of the present invention, FIG. 1(b) is a schematic side view of the substrate and presser lid combined, FIGS. The figure is a diagram for explaining the method of stretching fine metal wires on the substrate, Figure 4 is a schematic diagram of the substrate on which the fine metal wires are stretched and the holding lid is fixed, and Figures 5 and 6 are Figures 7 and 8 are diagrams showing other examples of the holding lid used in this embodiment, Figures 7 and 8 are diagrams showing other examples of the substrate used in this embodiment, and Figure 9 is a diagram showing another example of the substrate used in this embodiment. FIG. 10, which is an explanatory diagram in the case of heating, is a diagram showing an example of a fine metal wire. 2.2a...Fine metal wire 10.10a, 10b--one substrate, 12 =-groove, 14
... Protrusion, 16... Bin, 18... Partition wall, 19... Hole, 20.20a,
20b---Pressure lid, 30...stopper

Claims (3)

[Claims] (1) On the top surface of a heat-resistant substrate with a recess formed on the top surface,
A method for producing a fine metal sphere, which comprises stretching a fine metal wire and then heating and melting the stretched fine metal wire to obtain a fine metal sphere. (2) The method for manufacturing a fine metal ball according to claim 1, wherein the substrate has a large number of recesses having the same opening size at least in the portion where the fine metal wire is stretched. (3) The method for manufacturing fine metal balls according to claim 1 or 2, wherein the fine metal wire is heated and melted after a heat-resistant presser lid is placed on the upper surface of the substrate on which the fine metal wire is stretched.