JP2005175336A - Method and apparatus for forming solder bump - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To satisfactorily remove by reduction an oxide of solder powder and prevent any void from being formed upon forming a bump of an electrode of a substrate using only the solder powder. <P>SOLUTION: A via hole in a mask forming substrate 3 set on a stage 21 is filled with the solder powder under vacuum. At this time, the via hole is filled with the solder powder while the powder is mixed by stirring by making use of a mask printing method using a squeegee 22 while irradiating reducing free radical gas. Then, the solder powder is heated under vacuum with an upper heater 31 and a lower heater 32 and is reflowed while irradiating the reducing free radical gas to the filled solder powder. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for forming solder bumps and an apparatus therefor.

  As is well known, it is widely practiced to form solder bumps on electrode pads of a substrate (for example, a silicon wafer), and various forming methods have been proposed. After heating and melting (reflow) and cooling, there is no need for a post-cleaning step to remove the flux residue, and it is possible to prevent the formation of voids that deteriorate the electrical characteristics (electric conductivity, heat conductivity, etc.) A so-called flackless forming method is emphasized.

As a representative example of such a flackless forming method, solder powder and a flux component (
A method using only solder powder without using a solder paste mixed with rosin, solvent, activator, thickener, etc., that is, as shown in FIG. There is a method in which a mask forming substrate 3 is prepared and heated and melted under irradiation of a reducing free radical gas such as hydrogen radical under vacuum (for example, see Patent Document 1 below).

  However, the above-described flackless forming method supplies the solder powder 2 onto the mask 4 under atmospheric pressure when preparing the mask forming substrate 3 in which the via hole 1 is filled with the solder powder 2, and then The surface of the solder powder layer in the via hole 1 even when heated and melted (reflowed) while irradiating a reducing free radical gas such as a hydrogen radical under vacuum because it is pushed and transferred by the squeegee and filled in the via hole 1 (Or upper layer portion) 2a is prioritized and the inner layer (or lower layer portion) 2b, which is insufficiently reduced, is reflowed as it is, so that it is difficult to form a bump sufficient for reducing and removing the oxide. At the same time, when the solder powder layer is heated only from below the substrate 6 on which the electrode pad 5 is formed, for example, as shown in FIG. 4B, the undissolved upper surface side 7 is spheroidized. Been Void 8 had a disadvantage will be formed on as shown in 4 (c).

JP 2001-58259 A (see FIGS. 1 and 11).

  The present invention was invented in view of the above-mentioned drawbacks, and its first object relates to bump formation using only solder powder, and to form bumps sufficient for reducing and removing oxides of solder powder. Is to be able to.

  In addition, the second object relates to bump formation using only solder powder, and it is possible to form a bump that is sufficient for reducing and removing oxides of the solder powder and to prevent formation of voids. It is.

  In the present invention, in order to achieve the first object described above, the mask-formed substrate in which a mask is formed on the substrate surface on which the electrode pad is formed so as to form a via hole corresponding to the electrode pad. Filling the via hole with the solder powder is performed by a printing method using the mask while irradiating the reducing free radical gas under vacuum, and then the reducing free radical gas is applied under vacuum to the solder powder filled in the via hole. Heating and melting (reflow) is performed while irradiating.

  In order to achieve the second object described above, the solder for the via hole of the mask forming substrate in which a mask is formed on the substrate surface on which the electrode pad is formed so as to form a via hole corresponding to the electrode pad. The powder filling is performed by a printing method using the mask under vacuum, and then the solder powder filled in the via hole is irradiated with reducing free radical gas under vacuum while the mask forming side of the mask forming substrate and Heat is applied from both sides of the mask non-formation side to melt (reflow).

  As described above, in the present invention, the filling of the solder powder into the via hole prior to the reflow is performed by mask printing while irradiating the reducing free radical gas under vacuum. The powder can be filled while being reduced. Therefore, even when only the solder powder is used, bumps sufficient for reducing and removing oxides of the solder powder can be formed.

  Furthermore, in addition to the above filling, the solder powder is reflowed by heating from both the mask forming side and the mask non-forming side of the mask forming substrate while irradiating the reducing free radical gas under vacuum. As a result, it is possible to form bumps that are sufficient to reduce and remove oxides, and to prevent formation of voids.

  As described above, according to the present invention, when bumps are formed using only solder powder, it is possible to form bumps that are sufficient for reducing and removing oxides of solder powder, and to prevent formation of voids. it can.

  In FIG. 1 which is a front view of a bump forming apparatus according to the present invention and in FIG. 2 which is a plan view of FIG. 1, a reducing free radical gas generator 10 includes a microwave generator 11 and a microwave oscillated therefrom. And a waveguide 12 for transmission. Although not shown, the waveguide 12 is provided with an inlet for introducing the microwave into the plasma chamber 13. In addition, a conduit 14 is provided for supplying a reducing gas (for example, hydrogen gas) to be converted into plasma to the plasma chamber 13.

  Therefore, the reducing gas can be converted into plasma by the microwave to generate reducing free radical gas, and the reducing free radical gas can be introduced into the vacuum chamber 15. Reducing free radical gas (for example, hydrogen radical) passes through the gas dispersion plate 16 and is introduced into the vacuum chamber 15.

  Further, a stage device 17, a printing device 18, a heating device 19 and a substrate transfer device 20 are installed in the vacuum chamber 15. As shown in the figure, the stage device 17 and the printing device 18 are installed below the dispersion plate 16 for introducing reducing free radical gas.

  The above-described stage device 17 includes a circular stage 21 that is mounted so as to be movable up and down and rotatable, and a pin jig (for example, mask formation) for positioning the mask forming substrate 3 is not shown on the stage 21. A pin) to be inserted into the hole of the substrate 3 is attached. Further, as shown in FIG. 4, the mask forming substrate 3 has a mask 4 formed on a substrate 6 (for example, a silicon wafer) with a photosensitive resin or the like. The mask 4 has a plurality of via holes 1 (for example, a diameter of 150 μm and a depth of 50 μm) corresponding to the electrode pads 5 of the substrate 6. The via hole 1 is preferably provided with a diameter larger than that of the electrode pad 5, but may be provided with the same diameter or a smaller diameter as necessary.

  Further, the printing device 18 includes a squeegee 22 that is mounted so as to be movable up and down and rotatable. Therefore, the solder powder 2 (for example, Sn—Ag—Cu solder powder) on the powder supply stage 23 installed in the vacuum chamber 15 is pushed onto the mask 4 of the mask forming substrate 3 with the squeegee 22. The solder powder 2 transferred and pushed onto the mask 4 can be further pushed and transferred to fill the via hole 1. Thus, the fine solder powder 2 having a diameter of about 10 μm can be filled in the via hole 1 by a printing method using the mask 4. The pin jig described above is provided at a position that does not interfere with the movement of the squeegee 22.

  Further, during the above filling, the squeegee 22 is lowered from the upper standby position and positioned at a predetermined level suitable for pushing and transferring the solder powder 2, and then, as indicated by the arrow in FIG. Move horizontally to a predetermined angle. Filling by the above-described printing method is usually performed while the stage 21 is stationary, but if necessary, the stage 21 may be rotated while the squeegee 22 is moved. In the middle of printing, the stage 21 supporting the mask forming substrate 3 is rotated by a predetermined angle and moved to a position suitable for printing the solder powder 2 on the mask 4 and then printing is continued. You may do it.

  The introduction of the reducing free radical gas and the filling of the solder powder 2 described above are performed in a state where the inside of the vacuum chamber 15 is kept under a predetermined reduced pressure, that is, a vacuum (for example, 13.3 Pa to 133 Pa). The gate 27 is opened to set the mask forming substrate 3 on the stage 21 and the gate 26 is opened to supply the solder powder 2 onto the powder supply stage 23. Next, after the gates 26 and 27 are closed, the vacuum pump 28 is operated to exhaust from the vacuum chamber 15 and depressurize to a predetermined level. The operator performs the supply of the solder powder 2 onto the powder supply stage 23 and the setting of the mask forming substrate 3 to the stage 21.

  Therefore, the solder powder 2 on the mask forming substrate 3 is pushed and transferred by the squeegee 22 under vacuum, and is stirred and irradiated with a reducing free radical gas (for example, hydrogen radical). Things are not perfect, but can be reduced to some extent (preliminary reduction). Irradiation with the reducing free radical gas is continued during the filling of the solder powder 2.

  The above-mentioned solder powder 2 is a flackless material, can be filled into the via holes 1 having various hole diameters, and is a material suitable for utilizing the reducing action. However, on the other hand, when the reducing free radical gas is irradiated after filling the via hole 1, the reduction of the surface layer or the upper layer portion 2a of the solder powder layer formed in the via hole 1 is given priority as described above. Alternatively, the reduction of the lower layer portion 2b becomes insufficient, causing non-uniform reduction. This is caused because the reducing power is gradually lost as the reducing free radical gas flows into the inner layer portion of the solder powder layer. In addition, voids are easily formed unless filled under vacuum. Therefore, by filling the via hole 1 with the solder powder 2 by a printing method using the mask 4 under vacuum, and filling the via hole 1 while irradiating with a reducing free radical gas, the above-mentioned disadvantages are reduced. I try to eliminate it all at once.

  Hereinafter, when the filling of the solder powder 2 is completed by the above-described printing, the squeegee 3 is moved to the upper standby position, and then the mask forming substrate 3 is gripped by the substrate transfer device 20 and the heating device 19 is placed on the stage 21. Transfer to

  The substrate transfer device 20 transfers the mask forming substrate 3 on the stage 21 by holding it with a pair of chucks 30a, 30b. At this time, when the mask forming substrate 3 is gripped by the pair of chucks 30a and 30b, the stage 21 moves downward. As a result, the pins (the jig for positioning the mask forming substrate 3) mounted on the stage 21 are extracted from the holes of the mask forming substrate 3 and detached.

  Next, the pair of chucks 30a and 30b are moved toward the heating device 19, and the mask forming substrate 3 is positioned at the heating position. The heating device 19 includes an upper heater 31 and a lower heater 32, and the mask forming substrate 3 is held by the pair of chucks 30 a and 30 b at the heating position between the upper heater 31 and the lower heater 32. Positioned by appearance (indicated by a dashed line in FIG. 2).

  Therefore, the solder powder 2 filled in the via hole 1 of the mask forming substrate 3 is uniformly heated (for example, 200 ° C.) from the upper and lower surfaces of the substrate, that is, the both surfaces of the mask forming side and the mask non-forming side. be able to. Such heating temperature varies depending on the type of solder powder, but is generally a predetermined temperature selected from a range of 180 ° C. to 260 ° C. suitable for reflow (heating and melting) of the solder powder 2. The heating time can also be selected.

  In addition, irradiation of a reducing free radical gas is continued also during the above-mentioned heat melting (reflow). The reducing free radical gas irradiated onto the stage device 17 also flows into a region between the upper heater 31 and the lower heater 32 and has a reducing action. Therefore, generation of voids (bubbles) can be effectively prevented in such reflow.

  When the above-described reflow is completed, the mask forming substrate 3 is subsequently moved above the stage 21 while being held by the pair of chucks 30a and 30b. Therefore, the mask forming substrate 3 being heated can be cooled while irradiating the reducing free radical gas.

  At this time, when the mask forming substrate 3 is moved above the stage 21, the lowered stage 21 is raised, and the pin jig is inserted into the hole of the mask forming substrate 3 held by the chucks 30a and 30b. Inserted. Next, the chuck 30a is moved to the left and the chuck 30b is moved to the right, and then moved to the upper standby position.

  As described above, the solder powder 2 can be filled, heated and melted (reflowed), and cooled while being irradiated with the reducing free radical gas in a single vacuum chamber 15. The reducing gas is supplied from the pipeline 14 by controlling the gas supply source 34 to a predetermined value by the control device 33. After the cooling, the bump-formed mask forming substrate 3 opens the gate 27 and an operator takes it out of the vacuum chamber 15 from the stage 21. Note that irradiation with the reducing free radical gas is stopped prior to that.

  In the above bump formation, the filling of the solder powder and the heating and melting of the solder powder are performed at different locations in the vacuum chamber 15, but they may be performed at the same location. This aspect is illustrated in FIG. In the figure, a heating stage device 40 includes a stage 21 mounted on a movable carriage 42 guided by a rail 41 so as to be movable up and down, and a lower heater 32 mounted on the stage 21.

  Therefore, in a state where the gate 27 of the vacuum chamber 15 is opened, the stage 21 is lowered, and then the carriage 42 is moved to the left side so that one end side of the stage 21 and the lower heater 32 protrudes outside the vacuum chamber 15. Therefore, an operator can set the mask forming substrate 3 to be filled with the solder powder 2 in the via hole 1 in that portion.

  Thereafter, the carriage 42 is moved to the right side, and then the stage 21 is raised, so that the mask forming substrate 3 can be positioned at the printing level as shown in the figure. The mask forming substrate 3 is positioned by being fitted into the through hole 44 of the mask plate 43 attached in the vacuum chamber 15.

  On the other hand, the printing apparatus 18 includes a filling squeegee 22a and a finishing squeegee 22b. The squeegees 22a and 22b are mounted so as to be movable up and down and horizontally. Therefore, the solder powder 2 on the mask plate 43 can be filled into the via hole 1 by being pushed and transferred by both squeegees 22 a and 22 b and printed on the mask 4 of the mask forming substrate 3. At that time, the solder powder 2 is pushed and transferred under vacuum, and is stirred and irradiated with a reducing free radical gas (for example, hydrogen radicals). Therefore, the oxide film of the solder powder 2 is not perfect, but is reserved to some extent. Can be reduced.

  Thereafter, when the filling of the solder powder 2 is completed by the above-described printing, the solder powder 2 is subsequently heated and melted. This is performed by energizing the upper heater 31 and the lower heater 32 after the upper heater 31 is swung and brought into contact with the upper surface of the mask forming substrate 3. The upper heater 31 is swingably attached to the mask plate 43 as shown by the arrow in the figure. Further, the filling of the solder powder 2 and heating and melting are performed under irradiation with reducing free radical gas under vacuum. Then, after heating and melting (after reflow), heating is stopped, but irradiation with reducing free radical gas is continued, and cooling is performed for a predetermined time.

  As described above, filling of the solder powder 2 and heating and melting of the solder powder layer can be performed at the same location in the vacuum chamber 15. Then, after the cooling is completed, in a state where the gate 27 is opened, the stage 21 is lowered, and the cooled bump-formed mask forming substrate 3 is extracted from the through-hole 44 of the mask plate 43 to the lower side. Then, the carriage 41 is moved to the left and taken out of the vacuum chamber 15. Note that irradiation with the reducing free radical gas is stopped prior to that.

  The above-described reducing free radical gas is a gas obtained by converting a reducing gas into plasma by microwaves, and representative examples thereof include hydrogen radicals, but other gases can be used as long as they are gases that generate free radicals by plasma formation. For example, hydrogen-containing plasma may be used. Reducing free radical gas has a significantly stronger reducing power than reducing gas such as hydrogen gas. As the plasma excitation power source, for example, a high frequency 13.56 MHz or microwave 2.45 GHz power source can be used. The plasma irradiation time is the filling time of the solder powder 2 in the initial reduction, and is about 1 minute after heating and melting (after reflowing). The heating stage device 40 is preferably provided in a horizontal movable type, but may be provided in a fixed type as necessary. The solder powder is not limited to a lead-free solder powder such as Sn—Ag—Cu or Sn—Cu, but may be a lead-containing solder powder such as Pb—Sn.

It is a front view of a bump forming apparatus. FIG. 2 is a plan view of FIG. 1. It is a front view of another bump forming apparatus. FIG. 4 (a) is a view showing a state where a via hole is filled with solder powder, FIG. 4 (b) is a view showing a spheroidized state of the solder powder, and FIG. c) is a diagram showing the appearance of voids.

Explanation of symbols

1: Via hole 2: Solder powder 3: Mask forming substrate 4: Mask 5: Electrode pad 6: Substrate 8: Bubble 10: Reducing free radical gas generator 17: Stage device 18: Printing device 19: Heating device 20: Substrate transfer Device 31: Upper heater 32: Lower heater 40: Heating stage device

Claims (12)

Solder powder is filled in the via hole of the mask forming substrate in which a mask is formed on the substrate surface on which the electrode pad is formed so as to form a via hole corresponding to the electrode pad, and then the solder powder is vacuumed In the method of forming a solder bump which is heated and melted while irradiating a reducing free radical gas, the solder powder is filled by a printing method using the mask while irradiating the reducing free radical gas under vacuum. Forming solder bumps. 2. The method for forming solder bumps according to claim 1, wherein the heating and melting is performed by heating from both sides of the mask forming substrate on the mask forming side and the mask non-forming side. The method for forming solder bumps according to claim 2, wherein the filling and the heating and melting are performed in one vacuum chamber. The method of forming a solder bump according to claim 3, wherein the reducing free radical gas is a hydrogen radical. The method for forming solder bumps according to claim 4, wherein the filling and the heating and melting are performed at different locations in a vacuum chamber. The method for forming solder bumps according to claim 4, wherein the filling and the heating and melting are performed at the same place in a vacuum chamber. The method of forming a solder bump according to claim 5 or 6, wherein after the heating and melting, cooling is performed while irradiating with hydrogen radicals in the vacuum. A free radical gas generator for introducing a reducing free radical gas into a vacuum chamber, and a mask forming substrate in which a mask is formed on the substrate surface on which the electrode pad is formed so as to form a via hole corresponding to the electrode pad A stage device for supporting the solder, a printing device for pushing and transferring the solder powder on the mask with a squeegee to fill the via hole, a heating device for heating and melting the solder powder filled in the via hole, and the mask forming substrate A substrate transfer device for transferring from the stage device to the heating device or transferring from the heating device to the stage device; and the stage device, the printing device, the heating device and the substrate transfer device for the vacuum An apparatus for forming solder bumps, characterized by being installed in a chamber. The free radical gas generator is installed so as to introduce reducing free radical gas from above the stage device, and the heating device is installed on the mask forming side of the mask forming substrate and the mask is not formed. The solder bump forming apparatus according to claim 8, wherein the solder bump forming apparatus is configured with a lower heater installed on the side. A free radical gas generator for introducing a reducing free radical gas into a vacuum chamber, and a mask forming substrate in which a mask is formed on the substrate surface on which the electrode pad is formed so as to form a via hole corresponding to the electrode pad A heating stage device that supports the mask, a printing device that pushes and transfers the solder powder on the mask with a squeegee to fill the via hole, and a heater that heats from the mask forming side of the mask forming substrate, and the stage device A solder bump forming apparatus, wherein a printing apparatus and a heater are installed in the vacuum chamber. 11. The solder bump forming apparatus according to claim 10, wherein the heating stage device is provided so as to be horizontally movable so that the mask forming substrate can be moved from the inside of the vacuum chamber to the outside of the chamber. 12. The solder bump forming apparatus according to claim 8, wherein the reducing free radical gas is a hydrogen radical.

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