JP3430864B2 - Transfer method of conductive ball - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for transferring conductive balls onto electrodes on a substrate. 2. Description of the Related Art As a method for forming bumps on electrodes on a substrate, a method using conductive balls such as solder balls is known. In this method, a conductive ball is transferred onto an electrode of a substrate, and then the substrate is heated, so that the conductive ball is soldered to the electrode to form a bump. At this time, flux is generally used to perform good soldering of the conductive ball and the electrode, and it is necessary to apply the flux to either the conductive ball or the electrode before transferring the conductive ball onto the electrode. Done. The flux applied at this time also has a role of holding the conductive ball on the electrode due to the adhesiveness of the flux after the conductive ball is transferred onto the electrode. [0003] Conventionally, as a method of applying a flux,
A method has been practiced in which a suction head that vacuum-adsorbs a conductive ball is lowered to the surface of a flux stored in a container, and the flux adheres to the tip of the vacuum-adsorbed conductive ball. In this method, the flux is attached only to the tip of the conductive ball by controlling the descending stroke of the suction head. [0004] In the above method, when the suction head is lowered to cause the flux to adhere to the tip of the conductive ball, the flux adheres not only to the conductive ball but also to the lower surface of the suction head. May be. If the flux adheres to the lower surface of the suction head, the conductive balls adhere to the lower surface of the suction head even after the vacuum suction is released, causing a transfer error. The stroke must be strictly controlled. However, as the diameter of the conductive ball is reduced, it is difficult to completely prevent the flux from adhering to the lower surface of the suction head only by controlling the downward stroke of the suction head during the transfer of the flux. It has become to. In addition, other coating methods also have various problems associated with reducing the diameter of the conductive ball. For example, it is difficult to produce a small-diameter pin for transfer by a method in which a flux is attached to the tip of a pin and the flux is transferred to an electrode of a substrate and applied. Further, in the method of applying the flux to the electrodes of the substrate by screen printing, the opening area of the screen mask is reduced due to the miniaturization of the electrodes of the substrate, so that the flux cannot be applied to the electrodes of the substrate stably. As described above, any of the conventional methods has a problem that it is difficult to perform a stable transfer without a transfer error, particularly in the case of a small-diameter conductive ball. SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of transferring a conductive ball which can stably transfer even a small-diameter conductive ball without a transfer error. [0007] A method for transferring conductive balls according to the present invention is a method for transferring conductive balls onto electrodes of a substrate, the method comprising diluting with a solvent. The flux was applied to a substrate, and the flux was thinned by volatilizing volatile components. Then, the conductive balls were transferred onto the electrodes of the substrate. According to the present invention having the above-mentioned structure, a flux diluted with a solvent is applied to a substrate, and a volatile component is volatilized to thin the flux. By transferring the conductive balls on the electrodes, it is possible to stably transfer the conductive balls without the flux adhering to the suction head and without transferring errors. Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of a flux coating device according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of a coating nozzle unit of the flux coating device, FIGS. 3 (a), (b), and FIG.
(A), (b), (c) is process explanatory drawing of the transfer method of the same conductive ball. First, a flux coating apparatus will be described with reference to FIG. In FIG. 1, a substrate 2 is mounted on a base 1. A plurality of electrodes 3 are formed on the substrate 2. Above the base 1, an X table 4 and a Y table
A movable table 6 composed of a table 5 is provided.
An arm 7 is provided on the movable table 6, and a coating nozzle unit 8 is mounted on a tip of the arm 7. The coating nozzle unit 8 is connected to a flux tank 11 through a pipe 9, and a valve 10 is provided in the middle of the pipe 9.
Is provided. The flux tank 11 has a pressure source 1
2 are connected. Flux tank 11 diluted with a solvent such as isopropyl alcohol
3 is stored, and the flux 13 is pressure-fed to the application nozzle unit 8 by air pressure supplied from a pressure source 12. The coating nozzle unit 8 sprays and applies the flux 13 to the upper surface of the substrate 2 in a mist state. Next, the structure of the coating nozzle unit 8 will be described with reference to FIG. Reference numeral 21 denotes a main body case, which is formed by detachably connecting an upper case 21a and a lower case 21b with a screw portion 22. The nozzle 2 is located at the center of the main body case 21.
3 are erected. The lower end 23a of the nozzle 23 extends below the lower case 21b. A flange 24 is formed below the nozzle 23, and the flange 24 is grounded on a seal 25 provided on the bottom surface of the lower case 21b. The nozzle 23 is screwed to the block 26 with a screw portion 27. Collar 24
, An ultrasonic transducer 28 is provided between the blocks 26. The ultrasonic vibrator 28 has a drive circuit 39 with a cord 29.
It is connected to the. Accordingly, when the ultrasonic vibrator 28 is driven, the nozzle 23 ultrasonically vibrates, and the flux 13 sent to the nozzle 23 is atomized and jets out from the lower end 23a of the nozzle 23 in a mist (see arrow A). 2 is applied to the upper surface. At this time, the flux 1
When applying 3, the application nozzle unit 8 does not require precise position control, so that a rough positioning mechanism and control method can be used. This flux coating apparatus has the above-described configuration, and its operation will be described below. First, the substrate 2 is placed on the base 1, and the application nozzle unit 8 is positioned with respect to the substrate 2. Next, when the valve 10 is opened, as shown in FIG. 3A, the flux 13 diluted with the solvent is ejected in a mist form from the lower end 23a of the nozzle,
It is applied on the surface of the substrate 2. At this time, the application conditions such as the magnitude of the air pressure and the application time are adjusted so that the film thickness T of the applied flux 13 becomes a predetermined film thickness (for example, about 100 microns). Next, the volatile component of the solvent is volatilized from the flux 13 applied to the substrate 2 by a volatilizing means. It is possible to simply evaporate the volatile components spontaneously. However, as a volatilizing means for accelerating the volatilization, the time required for volatilizing the volatile components by heating the substrate 2 or by placing the substrate 2 under a reduced pressure atmosphere such as in a vacuum chamber. Can be shortened. When the volatile components evaporate, the flux 13 becomes thin. At this time, the film thickness is greatly reduced, and the film thickness is made uniform in the process of evaporating the volatile components.
As shown in (b), a thin and uniform film of the flux 13 having a thickness t of about 10 microns is formed on the surface of the substrate 2. Next, solder balls 30 which are conductive balls are transferred to the substrate 2 on which the thin film of the flux 13 is formed. As shown in FIG. 4A, the solder balls 30 vacuum-sucked on the suction head 31 are
, And the solder ball 30 is positioned on the electrode 3 of the substrate 2.
Transfer to the top. FIG. 4B shows a state in which the solder balls 30 have been transferred onto the electrodes 3. At this time, the thin film of the flux 13 on the electrode 3 has sufficient viscosity because the volatile component evaporates and the viscosity increases, so that the conductive ball 13 can be held on the electrode 3 with a sufficient fixing force. it can. Here, the component ratio of the flux 13 before and after the volatile component is volatilized will be described with reference to (Table 1). [Table 1] In Table 1, flux A is a flux according to an embodiment of the present invention, and flux B indicates a component ratio after the volatile components of flux A have volatilized.
The flux C is a flux used in a conventional method for transferring conductive balls. As shown in Table 1, the component ratio of the rosin and the activator of the flux B after volatilization is equal to or higher than that of the conventional flux C, and has sufficient tackiness. The flux A at the time of application has a much higher solvent ratio than the flux C, and has a component ratio suitable for application by spraying with a lower viscosity. Next, the substrate 2 is sent to a reflow furnace and heated. Thereby, the solder balls 30 on the electrodes 3 are melted,
By cooling and solidifying on the surface of the electrode 3, the solder bump 3
0 'is formed. At this time, since the thin film of the flux 13 completely covers the electrode 3, the molten solder 30 is uniformly joined to the electrode 3. According to the present invention, a flux diluted with a solvent is applied to a substrate, and the flux is thinned by removing volatile components, and then the conductive balls are transferred onto the electrodes of the substrate. Therefore, even in the case of a small-diameter conductive ball, flux does not adhere to the suction head, and therefore a stable transfer of the conductive ball without a transfer error due to the conductive ball adhering to the lower surface of the suction head can be achieved. It can be carried out. In addition, since the thinned flux has sufficient adhesiveness due to volatilization of volatile components, the transferred conductive balls can be stably held on the electrodes. Furthermore, since the flux is completely applied to completely cover the electrodes, it is possible to perform uniform soldering without uneven bonding when soldering the conductive balls onto the electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a flux coating device according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of a coating nozzle unit of the flux coating device according to an embodiment of the present invention. (A) Process explanatory view of a method for transferring conductive balls according to an embodiment of the present invention (b) Process explanatory view of a method for transferring conductive balls according to an embodiment of the present invention a) Process explanatory view of a conductive ball transfer method according to one embodiment of the present invention (b) Process explanatory view of a conductive ball transfer method according to one embodiment of the present invention (c) One embodiment of the present invention Process explanation drawing of conductive ball transfer method of embodiment [Description of reference numerals] 1 base 2 substrate 3 electrode 6 movable table 8 coating nozzle unit 10 valve 11 flux tank 12 pressure source 13 flux 23 nozzle 28 ultrasonic vibration Child 30 Solder ball 31 Suction head

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H05K 3/34 B23K 3/00 B23P 21/00

Claims (1)

(57) [Claim 1] A method of transferring conductive balls to transfer conductive balls onto electrodes of a substrate, wherein a flux diluted with a solvent is applied to the substrate and volatilized. A method for transferring conductive balls, comprising transferring a conductive ball onto an electrode of a substrate after thinning a flux by volatilizing a component.