JP4033191B2 - Electronic component mounting apparatus, electronic component mounting method, and flux transfer method - Google Patents

Description

  The present invention relates to an electronic component mounting apparatus, an electronic component mounting method, and a flux transfer method used for soldering an electronic component to a substrate.

  Conventionally, a soldering method has been widely used as a joining method for mounting electronic components on a substrate, and as a soldering form, metal bumps are formed as soldering electrodes provided on the electronic component by soldering. How to do is known. In recent years, as the size of bumps for solder joints has become smaller due to the miniaturization of electronic components and the increase in mounting density, bump size variation cannot be avoided in the same electronic component, and the electronic component is mounted on the board. In the state mounted on the board, a gap is likely to be generated between the bump having a smaller size than the others and the circuit electrode of the substrate.

  If heating for soldering is performed in a state where such a gap is generated, the solder that has become liquid due to melting of the bumps may cause a soldering failure that cools and solidifies without reaching the surface of the circuit electrode. is there. In order to prevent such a soldering failure, a solder for supplying a solder paste with a metal paste containing metal powder of a metal such as silver having a melting point higher than the melting point temperature of the solder composing the bump when soldering the bump. A joining method is known (for example, Patent Document 1).

According to this method, there is a case where there is a gap as described above by spreading the molten solder along the surface of the metal powder that remains solid when the bump is melted in the heating process. However, there is an advantage that the molten solder can be guided to the surface of the circuit electrode, and bonding failure due to the gap between the bump and the circuit electrode can be prevented.
JP 2000-114301 A

  In the method shown in the above patent document example, in order to guide the solder in which the bump is melted with the metal powder, an active ingredient for removing the oxide film on the bump surface is contained in the metal paste to ensure the solder wettability of the bump. Although it is necessary, when using a flux having a strong active action, the following problems may occur.

  From the viewpoint of environmental protection and process simplification in recent years, the mainstream is the no-cleaning method that eliminates the conventional post-soldering cleaning process, that is, the process of cleaning and removing the flux used in the soldering process using a cleaning agent. It has become. For this reason, the flux supplied at the time of soldering remains as it is in the solder joint. At this time, if the active action of the residual flux is strong, the circuit electrode of the substrate is likely to be deteriorated in the insulation characteristics due to corrosion by the residual flux. As described above, the conventional soldering method has a problem that defects such as poor bonding and deterioration of insulating characteristics are likely to occur.

  Accordingly, an object of the present invention is to provide an electronic component mounting apparatus, an electronic component mounting method, and a flux transfer method capable of obtaining a high-quality solder joint without causing poor bonding or deterioration of insulation characteristics.

An electronic component mounting apparatus according to the present invention is an electronic component mounting apparatus for mounting an electronic component on which a solder bump is formed on a substrate, and includes a stage having a transfer surface on which a convex portion is formed and a squeegee, and transferring the squeegee to the above A thin film forming mechanism that spreads a flux containing flaky metal powder on the transfer surface in a thin film shape by moving the surface relative to the surface, and the solder bumps are pressed against the portion on the transfer surface where the thin film is formed Thus, the metal powder is pressed against the solder bumps by the convex portions, the pressurizing mechanism for breaking through the oxide film covering the surface of the solder bumps and biting into the solder bumps, and the solder bumps in the state where the metal powder has bitten in the electrode of the substrate Equipped with a mounting mechanism for positioning and mounting.

The electronic component mounting method of the present invention is an electronic component mounting method for mounting an electronic component on which a solder bump is formed on a substrate, and includes a flaky metal powder on a stage having a transfer surface on which a convex portion is formed. A thin film forming step of spreading the flux into a thin film , and pressing the solder bump against the portion on the transfer surface where the thin film is formed, thereby pressing the metal powder against the solder bump by the convex portion to cover the surface of the solder bump It includes a metal powder biting process for breaking through the oxide film and biting into the solder bump, and a mounting process for mounting the solder bump in a state where the metal powder bites into the electrode of the substrate.

The flux transfer method of the present invention is a flux transfer method for transferring a flux containing metal powder to a solder bump of an electronic component, and includes a flaky metal powder on a stage having a transfer surface on which a convex portion is formed. A thin film forming step of spreading the flux into a thin film , and pressing the solder bump against the portion on the transfer surface where the thin film is formed, thereby pressing the metal powder against the solder bump by the convex portion to cover the surface of the solder bump And a metal powder biting process for breaking through the oxide film and biting into the solder bumps .

  According to the present invention, the solder bump is pressed into the surface of the solder bump by pressing the solder bump against the portion where the thin film is formed on the flat surface, and the solder bump is in a state where the metal powder is bitten in the electronic component mounting. By positioning and mounting to the electrodes on the board, it is possible to spread the molten solder, which has melted the solder bumps by heating, through the surface of the metal powder that has penetrated into the solder bumps. A high-quality solder joint can be obtained without deteriorating characteristics.

(Embodiment 1)
FIG. 1 is a front view of an electronic component mounting apparatus according to Embodiment 1 of the present invention, FIGS. 2 and 3 are process explanatory diagrams of the electronic component mounting method according to Embodiment 1 of the present invention, and FIG. FIG. 5 is an explanatory diagram of a solder transfer process in the electronic component mounting method according to the first embodiment of the present invention, and FIG. 6 is a solder solder according to the first embodiment of the present invention. It is sectional drawing of the metal powder mixed in the flux in an attaching method.

  First, the configuration of the electronic component mounting apparatus will be described with reference to FIG. This electronic component mounting apparatus has a function of mounting an electronic component on which a solder bump is formed on a substrate. The component supply unit 1, the flux transfer unit 2, and the substrate holding unit 3 are arranged in series, and each of these units is arranged. The component transfer mechanism 4 is disposed above the head.

  The component supply unit 1 includes a component tray 5. A plurality of electronic components 6 having solder bumps 7 (hereinafter simply referred to as “bumps 7”) formed on the lower surface of the component tray 5 are mounted on the component tray 5. Is placed. The bumps 7 are formed by soldering fine-grained solder balls to external connection electrodes. The size of the bump 7 after bump formation is not uniform due to causes such as variations in the size of the solder balls, and the height of the lower end of each bump varies. Here, the bump 7 is in a state where the surface is oxidized by exposure to the atmosphere (see the oxide film 7a shown in FIGS. 2 and 3).

The flux transfer unit 2 disposed adjacent to the component supply unit 1 includes a transfer stage 8 having a transfer surface 8a that is a flat surface on the surface, and a squeegee 9 is disposed above the transfer surface 8a. (Not shown) is disposed so as to be horizontally movable along the transfer surface 8a. In a state where the flux 10 is supplied onto the transfer surface 8a, the squeegee 9 is moved relative to the transfer stage 8 in parallel, so that the squeegee 9 spreads the flux 10 in a thin film shape on the transfer surface 8a to form the flux thin film 10a. A thin film forming operation is performed.

  Here, the composition of the flux 10 will be described. The flux 10 is obtained by mixing an active agent and metal powder 16 (see FIG. 2) as an additive component with a liquid base having a high viscosity obtained by dissolving a resin component such as rosin in a solvent. The activator is added for the purpose of removing the oxide film 7a of the solder formed on the surface of the bump 7, and an organic acid or the like having such an oxide film removing ability is used. In this case, an activator having a low activity that does not require cleaning after soldering is used.

  The material of the metal powder 16 has a melting point higher than that of the solder used for the bump 7 and does not generate an oxide film on the surface of the metal powder 16 in the atmosphere. A material (for example, a noble metal such as gold, silver, palladium or the like having a purity of 90% or more) is selected that has good wettability with respect to the solder, and the solder in a fluid state in which the bumps 7 are melted easily propagates through the surface of the metal powder 16. And the addition to the flux 10 is performed by mixing what processed these metals into scale-like (flaky shape) metal foil in a base material. Here, the size of the metal powder 16 is desirably a representative size in the range of 0.05 μm to 20 μm, and the mixing ratio in the base is desirably in the range of 1 to 20 vol%.

  By pressing the bump 7 against the transfer surface 8a on which the flux thin film 10a containing the metal powder is formed in this way, the flux 10 is transferred to the lower end portion of the bump 7. At this time, by appropriately setting the pressing load of the lifting / lowering pressing mechanism 14, the lower end portion of the bump 7 is somewhat crushed by the pressing load, and flattening is performed to align the heights of the plurality of bumps 7. The solid metal powder 16 partially penetrates the oxide film 7 a covering the surface of the bump 7 by the pressing force during flattening and bites into the solder material of the bump 7.

  Here, the transfer surface 8a of the transfer stage 8 is not a completely smooth surface, but is provided with fine convex portions 8b (see FIG. 4) on the surface and processed to a predetermined surface roughness. In the pressing process of the bump 7, the metal powder 16 in the flux 10 is pressed against the bump 7 by the convex portion 8 b. As a result, the flaky metal powder 16 that hardly breaks through the oxide film 7a as it is can be made to bite into the bumps 7. In this way, the presence of the metal powder 16 that penetrates through the oxide film 7a at the lower end of the bump 7 causes the bump 7 to melt and be soldered to the electrode 12a of the substrate 12 as will be described later. The bondability can be improved.

  In the above configuration, the flux transfer unit 2 includes a transfer stage 8 having a transfer surface 8a which is a flat surface and a squeegee 9, and the metal powder 16 is placed on the flat surface by moving the squeegee 9 relative to the flat surface. It is a thin film formation mechanism that spreads the flux 10 containing slag into a thin film shape. The component transfer mechanism 4 including the elevation pressing mechanism 14 includes a pressure mechanism that causes the metal powder 16 to bite into the surface of the bump 7 by pressing the bump 7 against a portion of the transfer surface 8a where the flux thin film 10a is formed. It has become.

  The substrate holding unit 3 disposed adjacent to the flux transfer unit 2 includes a substrate holding table 11. On the substrate holding table 11, a substrate 12 having an electrode 12a formed thereon is held. The component transfer mechanism 4 includes a lifting and lowering pressing mechanism 14 that is moved in the horizontal direction by a moving table 13, and a component holding head having a function of sucking and holding the electronic component 6 on the lower surface of the lowering and pressing mechanism 14. 15 is installed. By driving the elevation pressing mechanism 14 with the component holding head 15 positioned above the component supply unit 1, the component holding head 15 moves up and down with respect to the component tray 5 and picks up and picks up the electronic component 6.

  Then, the component holding head 15 is moved to the flux thin film 10a formed on the transfer surface 8a by driving the elevation pressing mechanism 14 with the component holding head 15 holding the electronic component 6 moved to the flux transfer unit 2. On the other hand, the bump 7 is pressed against the transfer surface 8a. As a result, the flux 10 is transferred to the lower end of the bump 7, and the metal powder 16 bites into the bump 7. At the same time, the lower end portions of the bumps 7 are crushed by the pressing load, and flattening is performed so that the heights of the plurality of bumps 7 are almost uniform.

  Then, the component holding head 15 holding the electronic component 6 after the flux transfer is moved onto the substrate holding unit 3, and the bump 7 is aligned with the electrode 12 a of the substrate 12 and moved up and down with respect to the substrate 12. 6 is mounted on the substrate 12. Therefore, the component transfer mechanism 4 is a mounting mechanism that positions and mounts the bumps in which the metal powder 16 is biting into the electrodes of the substrate. In this case, the mounting mechanism also serves as the pressure mechanism described above.

  Next, an electronic component mounting method for mounting the electronic component 6 on which the bumps 7 are formed on the substrate 12 will be described with reference to FIGS. In this electronic component mounting method, after flux transfer is performed on the bump 7, the electronic component 6 is mounted on the substrate 12 and reflowed to melt the bump 7 and solder it to the electrode 12 a of the substrate 12. 4 and 5 show the details of the A portion in FIG. 2B and the details of the B portion in FIG. 3B, respectively.

  In FIG. 2A, a flux 10 containing metal powder 16 is spread in a thin film on a transfer stage 8 having a flat transfer surface 8a to form a flux thin film 10a (thin film forming step). Next, the component transfer head 15 holding the electronic component 6 is moved onto the transfer stage 8, and the bumps 7 are pressed against the portion on the transfer surface 8a where the flux thin film 10a is formed, as shown in FIG. As a result, the metal powder 16 is bitten into the surface of the bump 7 (metal powder biting process).

  In this metal powder encroaching step, as shown in detail in FIG. 4A, the flaky metal powder 16 is broken through the oxide film 7a by the projections 8b formed on the transfer surface 8a, and bites into the bumps 7.

  Thereafter, by raising the component holding head 15 from the transfer stage 8, the lower end portion of the bump 7 is partially crushed and flattened as shown in FIG. The flux 10 is transferred. The metal powder 16 and the metal powder 16 in the transferred flux 10 are present at the lower end portion of the bump 7 in a state where the metal powder 16 has digged into the electrode 12a together with the bump 7 in the mounting process described below. To be transferred.

  Thereafter, the electronic component 6 after the flux transfer coating is mounted on the substrate 12. First, as shown in FIG. 3B, the bumps 7 in which the metal powder 16 has digged in are positioned and mounted on the electrodes 12a of the substrate 12 (mounting process). Then, the substrate 12 after mounting the components is heated in a reflow furnace, and the molten solder in which the bumps 7 are melted by the heating is transferred to the surface of the metal powder 16 transferred to the electrodes 12a in a state where the bumps 7 are bitten. Spread wet (solder melting process).

  This solder melting step will be described with reference to the details of part B in FIG. FIG. 5 shows the contact surface between the surface of the electrode 12a and the bump 7 at the start of solder bonding. Since the bump 7 is flattened in the flux transfer process, the lower end portion of all the bumps 7 is the electrode. It abuts almost uniformly on the surface of 12a.

At this time, when the active action of the flux 10 is weak, the oxide film 7 a is not completely removed and remains on the surface of the bump 7. For this reason, the solder bump 7 does not directly contact the surface of the electrode 12a but contacts the electrode 12a through the oxide film 7a on the surface. The metal powder 16 digging into the lower end of the bump 7 while breaking through the oxide film 7a is in direct contact with the surface of the electrode 12a, or the metal powder 16 contained in the flux 10 and transferred together. And in contact with the electrode 12a. Further, even when the metal powder 16 in the state of biting is not in contact with the electrode 12a, the contact state of the bump 7 with the electrode 12a is uniform by flattening, so that the metal powder 16 is applied to the surface of the electrode 12a. It is in close proximity at close range.

  When the bump 7 is melted in this state, the molten solder breaks through the oxide film 7a and spreads downwardly through the surface of the metal powder 16 in a state where the bump 7 and the surface of the electrode 12a are connected. And it reaches the surface of the electrode 12a directly through the surface of the electrode 12a or through the surface of the metal powder 16 interposed between the oxide film 7a, and then spreads in the horizontal direction along the surface of the electrode 12a, The molten solder of the bump 7 covers the entire bonding surface of the electrode 12a. Thereafter, the molten solder is cooled and solidified, whereby the bumps 7 are soldered to the electrodes 12a.

  In this solder bonding process, the activator contained in the flux 10 exerts an action of removing the oxide film 7a of the bump 7. However, the molten solder that has broken through the oxide film 7a as described above follows the metal powder 16. As a result of wetting and spreading, good solderability is ensured even when the oxide film 7a is only partially removed, so that the activator contained in the flux 10 is not required to have a strong active action.

  In other words, it is possible to use a low activity flux having a weak active action by causing the metal powder 16 to bite into the oxide film 7a on the surface of the bump 7 in advance, and the circuit electrode even in a state where the flux remains after soldering. Is less likely to be corroded by active ingredients. Therefore, even in a non-cleaning method in which cleaning for flux removal is not performed after soldering, a high-quality solder joint can be obtained without causing poor bonding or deterioration of insulating characteristics.

  Instead of using a single metal species as the metal powder mixed in the flux 10, as shown in FIG. 6A, the core metal 16a serving as the core and the surface metal 16b covering the surface of the core metal 16a You may make it use the metal powder 16A comprised by these. In this configuration, a metal species used as the core metal 16a is selected from tin (Sn), zinc (Zn), lead (Pb), and indium (In), and a flaky metal foil is formed by the metal species. Then, a gold (Au) or silver (Ag) film having good wettability with solder is formed on the surface of the metal foil by a method such as electroplating to form the surface metal 16b.

  Here, in the combination of the metal species used for the core metal 16a and the surface metal 16b, diffusion (see FIG. 6B) from the surface metal 16b to the core metal 16a inside easily occurs due to heating during reflow, and reflow At the end of the process, a combination is selected that achieves such diffusion characteristics that the diffusion of the surface metal 16b into the core metal 16a is completed and is almost taken into the core metal 16a. That is, in this configuration, the surface metal 16b is formed of a metal that has good wettability with solder, and the core metal 16a is formed of a metal that can be dissolved into the surface metal 16b by heating by reflow and incorporated therein. Has been.

  By adopting such a configuration as the metal powder mixed in the flux 10, excellent effects as described below can be obtained. First, at the stage where the solder bumps 7 are melted in the solder melting process described above, the surface metal 16b of the metal powder 16A plays a role of guiding the molten solder that has contacted the surface while wetting and spreading along the surface. Here, the metal powder 16A uses an expensive noble metal such as gold or silver as the surface metal 16b that covers the surface of the inexpensive core metal 16a. Compared with the method used, the cost can be significantly reduced.

  Then, by continuing the heating in the solder melting step, as shown in FIG. 6B, the surface metal 16b is gradually taken into the core metal 16a by diffusion. Depending on the metal type of the core metal 16a and the heating temperature, the surface metal 16b may be diffused into the liquid-phase core metal 16a or may be diffused into the solid-phase core metal 16a. The metal 16b is gradually taken into the core metal 16a. When the surface metal 16b is completely taken in and the surface of the core metal 16a is exposed, as shown in FIG. 6C, an oxide film 16c in which the core metal 16a is oxidized by heating is formed on the surface of the metal powder 16A. It is formed. The oxide film 16c has an effect as described below in improving the insulation after soldering.

  In the non-cleaning method in which the cleaning for removing the flux is not performed after the solder joining process, the metal powder 16A contained in the solder paste remains as a flux residue around the solder joint. When a metal such as gold or silver is used as it is as a metal powder mixed in the flux, migration may occur depending on the residual amount, causing electrical corrosion between the circuit electrodes of the substrate and lowering the insulation. For this reason, conventionally, it has been necessary to keep the blending ratio of the metal powder low in consideration of ensuring insulation, and as a result, there has been a situation where the effect of guiding the molten solder is not realized well.

  On the other hand, by using the metal powder 16A having the above configuration, the surface of the metal powder 16A is electrically stable even when a considerable amount of the metal powder 16A remains around the solder joint after the solder joining process. Since it is covered with the oxide film 16c, no migration occurs and good insulation is ensured. Therefore, by using the metal powder 16A having the above-described structure, a sufficient amount of metal powder is mixed in the solder paste to improve solder jointability, and also ensure insulation after solder joint to improve mounting reliability. It is possible to make it.

(Embodiment 2)
FIG. 6 is a front view of the electronic component mounting apparatus according to the second embodiment of the present invention. In the second embodiment, the flux transfer operation to the electronic component 6 and the mounting operation of the electronic component 6 on the substrate 12 performed by the single component transfer mechanism 4 in the first embodiment are respectively dedicated components. It is configured to be performed by a transfer mechanism.

  In FIG. 6, the component supply unit 1, the flux transfer unit 2, and the substrate holding unit 3 are the same as the units shown in FIG. 1 in the first embodiment. A first component transfer mechanism 4A is disposed above the component supply unit 1 and the flux transfer unit 2, and a second component transfer mechanism 4B is disposed above the flux transfer unit 2 and the substrate holding unit 3. It is arranged.

  The first component transfer mechanism 4A and the second component transfer mechanism 4B include a first lifting and lowering pressing mechanism 14A and a second moving mechanism 13A, which are moved in the horizontal direction by the first moving table 13A and the second moving table 13B, respectively. A first component holding head provided with a lifting and lowering pressing mechanism 14B and having a function of sucking and holding the electronic component 6 on the lower surface of each of the first lifting and lowering pressing mechanism 14A and the second lifting and lowering pressing mechanism 14B. 15A and a second component holding head 15B are mounted.

  The first component holding head 15A moves up and down with respect to the component tray 5 by driving the first lifting / lowering pressing mechanism 14A with the first component holding head 15A positioned above the component supply unit 1. The electronic component 6 is picked up and picked up. The first component holding head 15A is moved to the transfer surface 8a by driving the first raising / lowering pressing mechanism 14A in a state where the first component holding head 15A holding the electronic component 6 is moved to the flux transfer unit 2. It descends with respect to the flux thin film 10a formed thereon.

  Thereby, similarly to the example shown in the first embodiment, the transfer of the flux 10 to the bump 7, the biting of the metal powder 16 into the bump 7, and the flattening of the bump 7 are performed. That is, the first component transfer mechanism 4A is a pressurizing mechanism that causes the metal powder 16 to bite into the surface of the bump 7 by pressing the bump 7 against the portion of the transfer surface 8a where the flux thin film 10a is formed.

  The electronic component 6 after the flux transfer is held by the first component holding head 15 </ b> B and moves onto the substrate holding unit 3. Then, the electronic component 6 is mounted on the substrate 12 by driving the second lifting and lowering pressing mechanism 14 </ b> B to raise and lower the electronic component 6 relative to the substrate 12. Therefore, the second component transfer mechanism 4B is a mounting mechanism that mounts the bumps in a state in which the metal powder 16 is biting in alignment with the electrodes of the substrate.

  As described above, the first component transfer mechanism 4A having the function of pressing the bumps 7 against the transfer surface 8a and causing the metal powder 16 to penetrate, and the second component having the function of mounting the electronic component 6 after the flux transfer on the substrate 12 are provided. By separately providing the component transfer mechanism 4B, each component transfer mechanism can be provided with an appropriate mechanism characteristic corresponding to a required function.

  That is, for the first lifting / lowering pressing mechanism 14A and the first component holding head 15A, a large component having a large number of bumps is required to perform a work requiring a pressing load such as biting of the metal powder 16 into the bump 7 or flattening of the bump 7. The second elevating and pressing mechanism 14B and the second component holding head 15B have high positional accuracy and fine load control in a mounting operation such as a thin flexible substrate. It is possible to obtain a high-accuracy type structure that can accommodate a required type of substrate.

  The electronic component mounting apparatus, the electronic component mounting method, and the flux transfer method of the present invention have the effect that a high-quality solder joint can be obtained without causing poor bonding or deterioration of insulation characteristics, and solder bumps are formed. This is useful in the field of electronic component mounting where the electronic component is mounted on a substrate.

The front view of the electronic component mounting apparatus of Embodiment 1 of this invention Process explanatory drawing of the electronic component mounting method of Embodiment 1 of this invention Process explanatory drawing of the electronic component mounting method of Embodiment 1 of this invention Explanatory drawing of the flux transcription | transfer process in the electronic component mounting method of Embodiment 1 of this invention Explanatory drawing of the solder joint process in the electronic component mounting method of Embodiment 1 of this invention Sectional drawing of the metal powder mixed in the flux in the soldering method of Embodiment 1 of this invention The front view of the electronic component mounting apparatus of Embodiment 2 of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 Flux transfer part 4 Component transfer mechanism 6 Electronic component 7 Solder bump 8 Transfer stage 8a Transfer surface 9 Squeegee 10 Flux 10a Flux thin film 12 Substrate 12a Electrode 14 Lifting press mechanism 15 Component holding head 16A Metal powder 16a Core metal 16b Surface metal 16c Oxide film

Claims (5)

An electronic component mounting apparatus for mounting an electronic component on which a solder bump is formed on a substrate, comprising a stage having a transfer surface on which a convex portion is formed and a squeegee, and moving the squeegee relative to the transfer surface a thin film forming mechanism to spread the flux containing flaky metal powder on the transfer surface into a thin film, said metal powder by the protrusions by pressing the solder bump thin film is formed partially on said transfer surface Press mechanism against the solder bump, break through the oxide film covering the surface of the solder bump and bite into the solder bump, and mounting mechanism that aligns and mounts the solder bump with the metal powder biting into the electrode of the board An electronic component mounting apparatus characterized by comprising:   The electronic component mounting apparatus according to claim 1, wherein the mounting mechanism also serves as the pressure mechanism. An electronic component mounting method for mounting an electronic component on which a solder bump is formed on a substrate, and forming a thin film that spreads a flux containing flaky metal powder on a stage having a transfer surface on which convex portions are formed. A step of pressing the solder bump against the portion where the thin film on the transfer surface is formed, pressing the metal powder against the solder bump by the convex portion , breaking through the oxide film covering the surface of the solder bump and biting into the solder bump An electronic component mounting method comprising: a metal powder engraving step, and a mounting step of aligning and mounting a solder bump in a state in which the metal powder has encroached on an electrode of a substrate. A flux transfer method for transferring a flux containing metal powder onto a solder bump of an electronic component, and spreading the flux containing a flaky metal powder into a thin film on a stage having a transfer surface on which convex portions are formed. Forming step , pressing the solder bump against the portion of the transfer surface on which the thin film is formed, and pressing the metal powder against the solder bump by the convex portion, breaking through the oxide film covering the surface of the solder bump and forming the solder bump A flux transfer method comprising: a metal powder encroaching step for encroaching. The flux transfer method according to claim 4, wherein the metal powder contains any one of gold, silver, and palladium having a purity of 90% or more .

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