Solder bump formation method and solder bump formation apparatus

Abstract

Even with tiny solder balls, the goal is to form solder bumps in precise locations. [Solution] In the solder bump formation method, in the positioning step, solder balls 32 are positioned on the land 61 provided on the connection surface of the substrate 2 using a solder ball fixing jig 14a, and the solder balls 32 are fixed to the solder ball fixing jig 14a. In the heating step, the solder balls 32 are heated with a laser irradiation device while still fixed to the solder ball fixing jig 14a to form solder bumps on the land 61.

Description

Technical Field

[0001] The present invention relates to a solder bump forming method and a solder bump forming apparatus, and more particularly to a solder bump forming method and a solder bump forming apparatus in which solder balls are not displaced even in a fine BGA.

Background Art

[0002] Conventionally, in a semiconductor package, in order to mount a semiconductor substrate having a large number of connection terminals on the bottom surface, there is a BGA (Ball Grid Array) having a large number of solder bumps which are projections of a large number of connection solders.

[0003] For example, Patent Document 1 describes a manufacturing apparatus for a BGA in which minute solder balls are mounted on a pattern formed on such a substrate. A holding table for holding the substrate is provided, and a mask having introduction holes for solder balls corresponding to the pattern of the substrate is provided above the substrate. A spacer is provided between the mask and the substrate, a blade is provided so that the upper surface of the mask can be horizontally moved, and free solder balls are placed on the upper surface of the mask. By horizontally moving the flexible blade, the solder balls are dropped one by one into the introduction holes of the mask, and while scraping off the excess solder balls, the solder balls are collected on one side of the mask and mounted only on the necessary portion.

[0004] In such a method, the solder balls can be easily mounted only on the necessary portion. After the solder balls are positioned and mounted only on the necessary portion in this way, even if the mask is removed, the solder balls are temporarily fixed at the predetermined positions by the adhesiveness of the flux. In this state, the solder balls are melted in a reflow furnace to form solder bumps.

[0005] Figure 1 is a schematic cross-sectional view of a substrate 2 mounted on a semiconductor package 1, which is an example of a product covered by this embodiment. The main substrate 21 of the semiconductor package 1 has the main semiconductor chip mounted on it. A BGA 3a for mounting the semiconductor package 1 is formed on the bottom surface of this main substrate 21. In recent years, semiconductor devices have become smaller and more complex, and for example, a large circuit that was previously integrated on a single semiconductor chip is sometimes divided into multiple small chips called chiplets. These chiplets 4a and 4b are connected by an interposer 5. The interposer 5 is an intermediate substrate that connects the main substrate 21 and the chiplets 4a and 4b. The components are mounted on this interposer 5 and enlarged to fit into a single package. In this case, a BGA 3b is also used for the connection between the interposer 5 and the chiplet 4a. Similarly, a BGA 3c is also used for the connection between the interposer 5 and the chiplet 4b. Such BGA 3b and 3c have solder bumps called microbumps that are smaller than the BGA 3a for mounting the semiconductor package 1.

[0006] Furthermore, in order to increase the integration density within the semiconductor package 1, speed up processing, and suppress electrical losses, three-dimensional mounting is sometimes performed in which chiplets 4c and 4d, such as SRAM and DRAM, are stacked vertically in close proximity to the chiplet 4b. In such cases as well, the chiplets 4c and 4d are connected by BGA3d and 3e on which microbumps are formed.

[0007] Note that Figure 1 is a schematic diagram, and the actual size, combination, quantity, and configuration can vary considerably. In any case, such solder bumps 31 are extremely dense, and the solder balls 32 used are small, with a diameter of φ = 100 [μm] or less, or even 50 [μm] or less. Therefore, in these configurations, the number of solder bumps 31 placed on the microbumps of BGA 3b to 3e within a single semiconductor package 1 can range from tens of thousands to hundreds of thousands. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 10-126046 [Overview of the project] [Problems that the invention aims to solve]

[0009] In such a semiconductor package 1, for example, it is necessary to form solder bumps by precisely and reliably placing tens of thousands to hundreds of thousands of extremely small solder balls, each tens of micrometers in size, in the correct positions.

[0010] However, with conventional methods, because the solder balls are so small, the solder balls that are temporarily fixed with flux can be lifted by the molten flux in the reflow oven, and their position can shift due to the flow of the flux. Furthermore, because they are so small, inspection is also difficult. In such a semiconductor package 1, if even one solder bump 31 among the tens of thousands to hundreds of thousands of solder bumps 31 in each chiplet 4a to 4d is missing, the entire semiconductor package becomes a defective product. This has resulted in a significant decrease in the yield of the final product.

[0011] The problem that the solder bump forming method and solder bump forming apparatus of the present invention aim to solve is to form solder bumps in precise locations, even with minute solder balls. [Means for solving the problem]

[0012] To solve the above problems, the present invention provides a solder bump forming method for soldering solder balls to a plurality of connection terminals provided on the connection surface of a target product, wherein the solder bump forming method comprises a positioning step of positioning the solder balls to the connection terminals using a solder ball fixing jig, and a heating step of heating the solder balls with a heating means while they are fixed to the solder ball fixing jig to form solder bumps on the connection terminals.

[0013] The solder ball fixing jig can be a plate-shaped member made of a heat-resistant material, which is a mask having through holes through which the solder balls pass, corresponding to the positions of the connection terminals. The heat-resistant material of the solder ball fixing jig may be SUS, metal including steel, glass, or ceramics.

[0014] The aforementioned target product can be a wafer or an interposer, which is a substrate mounted on a semiconductor package. The diameter of the solder ball may be 100 [μm] or less.

[0015] A laser light source may be used in the heating device used in the heating step. A light pulse may be used in the heating device used in the heating step. Furthermore, the solder bump forming apparatus of the present invention is a solder bump forming apparatus that aligns solder balls to a plurality of connection terminals provided on the connection surface of a target product and solders them, and is characterized by comprising a positioning device that fixes the solder balls to the connection terminals using a solder ball fixing jig, and a heating device that heats the solder balls with a heating means while they are fixed to the solder ball fixing jig to form solder bumps on the connection terminals.

[0016] The solder ball fixing jig can be configured as a mask made of a heat-resistant plate-shaped member, having through holes through which the solder balls pass, corresponding to the positions of the connection terminals.

[0017] The heat-resistant material of the solder ball fixing jig may be SUS, metal including steel, glass, or ceramics. The aforementioned target product can be a wafer or an interposer, which is a substrate mounted on a semiconductor package.

[0018] The diameter of the solder ball may be 100 [μm] or less. A laser light source may be used in the heating device. Light pulses may be used in the heating device. [Effect of the Invention]

[0019] According to the solder bump forming method and the solder bump forming apparatus of the present invention, even for fine solder balls, there is an effect that solder bumps can be formed at accurate positions. [Brief Description of the Drawings]

[0020] [Figure 1] It is a schematic cross-sectional view of a substrate of a semiconductor package which is an example of a target product. [Figure 2] It is a bottom view showing an example of a BGA provided on the connection surface of the substrate. [Figure 3] It is a schematic block diagram showing the solder bump forming apparatus of the present embodiment. [Figure 4] It is a flowchart showing the procedure of the solder bump forming method of the present embodiment. [Figure 5] It is a cross-sectional view schematically showing the cross-sectional structure of a substrate on which lands and a solder resist are formed. [Figure 6] It is a cross-sectional view schematically showing the cross-sectional structure of a substrate coated with a flux. [Figure 7] It is a bottom view of a solder ball fixing jig. <00001​​​​​​​​​​​​​​​​​​This is a schematic cross-sectional view showing the cross-sectional structure of a substrate on which lands and solder resist have been formed. [Figure 15] This is a schematic cross-sectional view showing the cross-sectional structure of a substrate coated with flux. [Figure 16] This is a schematic perspective view showing the solder ball positioning jig attached to the circuit board. [Figure 17] This is a schematic cross-sectional view showing the circuit board with the solder ball positioning jig attached. [Figure 18] This is a schematic cross-sectional view showing the circuit board with the solder ball positioning jig removed. [Figure 19] This is a schematic cross-sectional view showing the state of the heating process in a reflow oven. [Figure 20] This is a schematic cross-sectional view showing the state after the formation of solder bumps has been completed. [Figure 21] This is a schematic cross-sectional view illustrating the movement of solder balls due to molten flux during the heating process in a reflow oven. [Figure 22] This is a schematic cross-sectional view showing a state where the formation of solder bumps has been completed in a misaligned position. [Modes for carrying out the invention]

[0021] The solder bump formation method and solder bump formation apparatus of the present invention will be described below with reference to one embodiment. This embodiment should not be construed as limiting the present invention. In this embodiment, the drawings show an example of the basic structure for the convenience of explanation and should not be interpreted as showing the actual size, quantity, shape, or balance.

[0022] (Summary of this embodiment) As described in the background information, the solder bumps 31 are extremely fine, so they tend to come off using conventional methods. Here, we will briefly explain the conventional method for forming solder bumps 31. Then, we will describe the solder bump formation method and solder bump formation apparatus 10 of this embodiment.

[0023] In this description of the embodiment, "substrate 2" broadly includes substrates on which solder bumps 31 can be formed, regardless of their name. For example, it includes the main substrate 21, chiplets 4 (4a to 4d), or interposer 5, which is an intermediate substrate, of a semiconductor package 1 formed on a wafer such as a silicon wafer 60. The interposer 5 is not limited to a silicon wafer 60 and includes substrates made of resin or glass. When describing these in common, they are collectively referred to as substrate 2. Also, in this description of the embodiment, when describing the chiplets 4a to 4d and BGAs 3b to 3e shown in Figure 1 together, they are referred to as chiplet 4 and BGA 3.

[0024] Figure 2 shows an example of a BGA3 provided on the connection surface 2a of substrate 2. As shown in Figure 2, the substrate 2 has BGA3 (3a-3e) formed on its bottom surface, which is the connection surface 2a (mounting surface). The BGA3 has solder bumps 31 arranged in a matrix, as shown in Figure 2. While the actual number of solder bumps 31 constituting a BGA3 varies, they are generally more numerous and finer than the number schematically shown in Figure 2.

[0025] <Conventional solder bump formation method> Figure 12 is a schematic block diagram showing a conventional solder bump forming apparatus 110. As shown in Figure 12, the conventional solder bump forming apparatus 110 includes a substrate manufacturing apparatus 111, a coating apparatus 112, a mask attachment / detachment apparatus 113, a solder ball positioning apparatus 114, and a reflow oven 115 as a heating apparatus.

[0026] Figure 13 is a flowchart showing the procedure for a conventional solder bump formation method. The conventional solder bump formation method is completed through the following steps: substrate manufacturing (S101), land formation (S102), flux application (S103), mask mounting (S104), solder ball alignment (S105), mask removal (S106), and reflow oven heating (S107).

[0027] <Substrate manufacturing (S101)> First, in the substrate manufacturing process (S101), the substrate 2 is manufactured using the substrate manufacturing apparatus 111. There are various types of substrate manufacturing processes (S101), but here we will explain one example. In the substrate manufacturing process (S101), first, an oxide film is formed on the silicon wafer 60 (Figure 14), and then a resist is applied. Then, in the lithography (exposure and development) process, the circuit pattern is exposed onto the silicon wafer 60 through a photomask to draw the circuit. Next, in the etching process, unnecessary films are removed to create a three-dimensional circuit. Finally, impurities are implanted to adjust the electrical properties of the semiconductor, or the silicon wafer 60 is heat-treated, using ion implantation or heat treatment.

[0028] <Land formation (S102)> Figure 14 is a schematic cross-sectional view showing the cross-sectional structure of the substrate 2 on which lands 61 and solder resist 62 have been formed. In land formation (S102), after the lands 61, which are circuits and terminals, are formed in substrate manufacturing (S101), a layer of solder resist 62 is formed on top of them. The formation of solder resist 62 involves a process in which resist ink is applied to the substrate 2, followed by exposure, development, and curing, and then the unwanted parts are removed. Application methods include screen printing, spray printing, curtain coating, roll coating, and dry film bonding. After that, the ink is cured by light (UV) or heat to form an insulating film, which prevents short circuits and protects the circuits. Once the solder resist 62 on the lands 61 is removed and the process is complete, measuring instruments are connected to each land 61 to inspect the state of the circuits created on the silicon wafer 60.

[0029] <Flux application (S103)> Figure 15 is a schematic cross-sectional view showing the cross-sectional structure of the substrate 2 to which flux 63 has been applied. In the flux application (S103) process, flux 63 is applied to the formed lands 61 by the application apparatus 112. The most important component of flux 63 is resin (or rosin), which is an acidic substance. By applying flux 63, the invisible oxide film on the lands 61 is removed, making it easier to bond the metals.

[0030] The coating device 12 applies flux 63 to the lands 61 only using a dispenser (not shown). In the prior art, such as Patent Document 1, the position of the solder balls 32 was temporarily fixed using the adhesive force of the flux 63, so the flux 63 was applied to the lands 61 only in a matrix pattern.

[0031] <Wearing a mask (S104)> Figure 16 is a schematic perspective view showing the solder ball positioning jig 114a being mounted on the substrate 2. Figure 17 is a schematic cross-sectional view showing the solder ball positioning jig 114a mounted on the substrate 2. In the mask mounting (S104) procedure, flux 63 is applied to the land 61, and then the solder ball positioning jig 114a is mounted. A mask attachment / detachment device 113 (not shown) can attach or remove the solder ball positioning jig 114a from the substrate 2 by well-known methods such as gripping with a robot hand or magnetic attraction.

[0032] The conventional solder ball positioning jig 114a has a solder ball introduction hole 114b for introducing the solder ball 32 to a predetermined position corresponding to the land 61. The solder ball fixing jig 14a of this embodiment also has a similar solder ball fixing hole 14b, but its function is different. This will be described in detail later in the description of this embodiment.

[0033] As shown in Figure 17, there is a gap G between the solder ball positioning jig 114a and the solder resist 62 on the substrate 2, resulting in a non-contact state. Therefore, the flux 63 is less likely to adhere to the solder ball positioning jig 114a.

[0034] <Solder ball positioning (S105)> As shown in Figure 17, the flux-coated land 61 on the substrate 2 to which the solder ball positioning jig 114a is attached is exposed through the solder ball introduction hole 114b. The inner diameter of the solder ball introduction hole 114b is φ IN The outer diameter of the solder ball 32 is φ OUTThe holes are slightly larger and there are no large gaps. As a result, the solder balls 32 are positioned within a predetermined error range by the solder ball introduction holes 114b. Furthermore, at room temperature when the substrate 2 is not heated, the flux 63 has high viscosity and tackiness. As a result, the solder balls 32 can be temporarily fixed in place by the tackiness of the flux 63.

[0035] In this state, numerous solder balls 32 are placed on top of the solder ball positioning jig 114a, and the solder balls 32 are introduced into each solder ball introduction hole 114b. By vibrating and tilting the substrate 2, the solder balls 32 are introduced into all of the solder ball introduction holes 114b. Once all of the solder balls 32 have been introduced into all of the solder ball introduction holes 114b, any remaining solder balls 32 are completely removed and collected using a doctor blade or similar tool.

[0036] <Mask removal (S106)> With solder balls 32 introduced into all solder ball introduction holes 114b, the solder ball positioning jig 114a is removed by the mask attachment / detachment device 113.

[0037] Figure 18 is a schematic cross-sectional view showing the substrate 2 with the solder ball positioning jig 114a removed. Each solder ball 32 is fixed in position because it is adhered to the flux 63 applied to the land 61.

[0038] <Reflow oven heating (S107)> Figure 19 is a schematic cross-sectional view showing the state of the heating process by the reflow oven 115, which is a heating device. Each solder ball 32 is fixed in position by adhering to the flux 63 applied to the land 61, and is then heated by the reflow oven 115a.

[0039] First, the flux 63 melts, and the solder ball 32 comes into contact with the land 61 due to gravity. In the next stage, the solder ball 32 melts through the molten flux 63, and the soldering between the solder ball 32 and the land 61 is completed.

[0040] <Completion of Solder Bump 31> Figure 20 is a schematic cross-sectional view showing the state after the formation of the solder bump 31 is complete. In the reflow oven 115, the solder balls 32 melt via the molten flux 63, and the soldering between the solder balls 32 and the land 61 is completed. After cooling, the solder bump 31 of the BGA3 is completed.

[0041] <Problems with conventional technology> Conventionally, the solder balls 32 were relatively large, with an outer diameter exceeding 100 [μm]. As a result, the solder balls 32 sank vertically in the molten flux 63 due to gravity, and their position did not shift from the land 61. The molten flux 63 then removed the oxide film on the land 61, allowing the molten solder balls 32 to be soldered to the land 61.

[0042] However, as mentioned in the background technology section, the density of BGA3 has increased in recent years, and the outer diameter φ of the solder balls 32 has often been 100 [μm] or less. In particular, the following problems arose when the outer diameter φ of the solder balls 32 was 50 [μm] or less.

[0043] Figure 21 is a schematic cross-sectional view showing the movement of solder balls 32 due to molten flux 63 during the heating process in a conventional reflow oven 115. Figure 22 is a schematic cross-sectional view showing the state in which the formation of solder bumps 31 has been completed at a shifted position.

[0044] As shown in Figure 21, when the solder balls 32 become smaller, the solder balls 32' may float on the surface of the molten flux 63 due to its surface tension. In the reflow oven 115, the inside of the oven is heated by hot air 115a. As a result, the solder balls 32' that were floating due to the surface tension of the molten flux 63 may deviate from the position of the land 61 along with the molten flux 63, as indicated by the arrows.

[0045] Therefore, as shown in Figure 22, on the substrate 2 that has passed through the reflow oven 115, solder bumps 31' may be formed in a position shifted from the land 61, unlike the solder bumps 31 in the correct position. With solder bumps 31' in a shifted position, misalignment with the terminals to be mounted may occur, potentially leading to poor connections. Also, with solder bumps 31' in a shifted position, if they lie on the solder resist 62, conductivity with the land 61 may not be ensured.

[0046] (Configuration of this embodiment) Conventional technologies have the problems described above. The solder bump forming method and solder bump forming apparatus 10 of the present invention solve these problems and forms solder bumps 31 in precise positions, even for minute solder balls 32.

[0047] The following describes a solder bump formation method and solder bump formation apparatus 10, which are embodiments of one invention. In this description, since there are parts that are common with the prior art described above, the explanation of the common parts will be omitted, and the parts that differ from the prior art will be explained.

[0048] <Comparison of solder bump forming apparatus 10 with conventional technology> Figure 3 is a schematic block diagram showing the solder bump forming apparatus 10 of this embodiment. As shown in Figure 3, the solder bump forming apparatus 10 of this embodiment includes a substrate manufacturing apparatus 11, a coating apparatus 12, a mask attachment / detachment apparatus 13, a solder ball position fixing apparatus 14, and a laser irradiation apparatus 15 as a heating apparatus.

[0049] Of these, the substrate manufacturing apparatus 11, coating apparatus 12, and mask attachment / detachment apparatus 13 of the solder bump formation apparatus 10 have basically the same configuration as the conventional substrate manufacturing apparatus 111, coating apparatus 112, and mask attachment / detachment apparatus 113 shown in Figure 12, so their explanation will be omitted.

[0050] On the other hand, the solder ball positioning device 14 and laser irradiation device 15 of this embodiment have fundamentally different configurations from the conventional solder ball positioning device 114 and reflow oven 115. Therefore, the differences between the solder ball positioning device 14 and laser irradiation device 15 will be explained in detail.

[0051] <Comparison of solder bump formation procedure with conventional techniques> Figure 4 is a flowchart showing the procedure for the solder bump formation method of this embodiment. In the solder bump formation method of this embodiment, the process is completed as shown in Figure 11, through the steps of substrate manufacturing (S1), land formation as shown in Figure 5 (S2), flux application as shown in Figure 6 (S3), mask mounting (S4), solder ball fixing (S5), laser heating (S6), and mask removal (S7).

[0052] The conventional technology includes the following steps: substrate manufacturing (S101), land formation (S102) as shown in Figure 14, flux application (S103) as shown in Figure 15, and mask mounting (S104). These are similar to the steps of substrate manufacturing (S1) as shown in Figure 13, land formation (S2) as shown in Figure 5, flux application (S3) as shown in Figure 6, and mask mounting (S4). On the other hand, the steps of solder ball fixing (S5), laser heating (S6), and mask removal (S7) differ from the steps of solder ball alignment (S105), mask removal (S106), and reflow oven heating (S107) in the conventional technology. In addition, a different method from the conventional one can be used for flux application (S3).

[0053] In the solder bump formation method of this embodiment, after aligning the solder balls (S5), the solder balls 32 are fixed with the solder ball fixing jig 14a still attached and heated by the laser irradiation device 15, which is a heating device (S6). Then, after the solder bump 31 is completed, the solder ball fixing jig 14a is removed (S7). For this reason, the procedures of solder ball fixing (S5), laser heating (S6), and mask removal (S7), which differ from the conventional technology, will be explained in detail. First, the flux application method (S3), which is possible in this embodiment and differs from the conventional method, will also be explained.

[0054] <Flux application in this embodiment (S3)> In the flux application (S3) of this embodiment, methods that would cause problems in the prior art can be carried out as follows. In the conventional flux application (S103), flux 63 was applied only to the land 61 using a dispenser. However, with the miniaturization of solder balls 32 in recent years, it has become difficult to accurately apply a very small amount of flux only to the land 61. Therefore, instead of applying flux only to the land 61 using a dispenser, it is also possible to apply flux 63 to the entire connection surface 2a, wipe off the flux 63 from the solder resist 62 with a doctor blade or the like, and then apply flux 63 to the land 61. In the prior art, there was a problem that the solder balls 32 would easily move when flux 63 was applied to the entire surface, but in this embodiment, the position is fixed by the solder ball fixing jig 14a, so such a problem does not occur.

[0055] <Solder ball fixing (S5) and solder ball position fixing device 14 of this embodiment> Next, the differences between the solder ball positioning device 14 of this embodiment and the conventional solder ball positioning device 114 will be described in detail. The solder ball positioning device 14 differs in function from the conventional solder ball positioning device 114.

[0056] In other words, the mask attachment / detachment device 13 attaches and detaches the solder ball fixing jig 14a to the substrate 2. In the prior art, the solder ball positioning device 114 attaches and detaches the solder ball positioning jig 114a to the substrate 2 using the mask attachment / detachment device 113. Both devices share the commonality of attaching and detaching a mask.

[0057] However, in the conventional solder ball positioning device 114, after the solder balls 32 are aligned (S105), the solder ball positioning jig 114a is immediately removed by the mask attachment / detachment device 113 (S106). Then, after removing the solder ball positioning jig 114a, the solder balls are heated in the reflow oven 115 (S107). In other words, the reflow oven heating process (S107) is performed while the solder balls 32 are not being held in position by the solder ball positioning jig 114a.

[0058] On the other hand, the solder ball position fixing device 14 of this embodiment not only positions the solder balls 32 like the conventional solder ball positioning jig 114a, but also keeps the position of the positioned solder balls 32 fixed throughout the laser heating (S6) process.

[0059] <Solder ball fixing jig 14a> Figure 7 is a bottom view of the solder ball fixing jig 14a. The solder ball fixing jig 14a in this embodiment has a shape that corresponds to the shape of the BGA3 formed on the substrate 2 shown in Figure 2.

[0060] Figure 8 is a schematic perspective view showing the solder ball fixing jig 14a being attached to the substrate 2. Figure 9 is a schematic cross-sectional view showing the solder ball fixing jig 14a attached to the substrate 2. A mask attachment / detachment device 13 (not shown) is a device for attaching or removing the solder ball fixing jig 14a from the substrate 2. As shown in Figure 8, when the solder ball fixing jig 14a is attached to the substrate 2 by the mask attachment / detachment device 13, the solder ball fixing holes 14b are positioned at the locations of the lands 61 to which flux 63 has been applied, as shown in Figure 9.

[0061] The solder ball fixing jig 14a has the same function as the conventional solder ball positioning jig 114a. That is, as described above, with the solder ball fixing jig 14a mounted on the substrate 2, a number of solder balls 32 are placed on top of the solder ball fixing jig 14a, and the solder balls 32 are introduced into each ball fixing hole 14b. By vibrating and tilting the substrate 2, the solder balls 32 are introduced into all the ball fixing holes 14b. Once all the solder balls 32 have been introduced into the solder ball fixing holes 14b, any remaining solder balls 32 are removed and collected using a doctor blade or the like.

[0062] Furthermore, the solder ball fixing jig 14a of this embodiment has the following functions in addition to the functions of the conventional solder ball positioning jig 114a. Figure 10 is a schematic cross-sectional view showing the state of laser heating (S6) by the laser irradiation device 15. That is, as shown in Figure 10, the positioned solder ball 32 is fixed in the solder ball fixing hole 14b of the solder ball fixing jig 14a. Therefore, even if the flux 63 melts and flows out during laser heating (S6), the solder ball 32 will not be displaced by the molten flux 63 as shown in Figure 21.

[0063] To effectively perform these functions, as shown in Figure 10, a gap G is provided between the surface of the substrate 2 and the molten flux 63 and molten solder balls 32, as shown in Figure 9.

[0064] The inner diameter φ of the solder ball fixing hole 14b shown in Figure 9 IN The outer diameter of the solder ball 32 is φ OUT The diameter is slightly larger. This difference is small enough to allow the solder ball 32 to be easily inserted into the solder ball fixing hole 14b. If this difference is too large, the positioning accuracy of the solder ball 32 will decrease.

[0065] <Laser heating (S6) and laser irradiation device 15 in this embodiment> Next, we will describe the laser irradiation device 15, which is a heating device using a laser light source used in the laser heating (S6) process of this embodiment. The laser irradiation device 15 of this embodiment irradiates the solder balls 32, which are fixed to the position of the lands 61 on the substrate 2 by the solder ball positioning jig 114a, with laser light 15a. Although not shown in the figures, a well-known laser irradiation device can be used for the laser irradiation device 15 of this embodiment. The laser irradiation device 15 has a laser light source and, for example, has a galvanometer mirror to selectively scan and irradiate the laser light 15a so that the contact points between the solder balls 32 and the lands 61 are heated. The laser light 15a may be continuous light or pulsed light. It may also be an irradiation line that passes continuously through each solder ball 32, or it may be configured to selectively irradiate only each solder ball 32. The laser beam 15a melts the flux 63 and the solder ball 32 in contact with the land 61, causing the solder ball 32 to physically and electrically bond with the land 61. On the other hand, the upper part of the solder ball 32 does not melt and maintains its shape, forming a solder bump 31. Furthermore, the laser beam 15a does not irradiate the solder ball fixing jig 14a and therefore does not heat it. Even if the laser beam 15a irradiates the solder ball fixing jig 14a, the solder ball fixing jig 14a is made of a heat-resistant material. For example, SUS can be used as the heat-resistant material in this embodiment.

[0066] <Mask removal in this embodiment (S7)> After irradiation with the laser beam 15a, the solder ball fixing jig 14a is removed by the mask attachment / detachment device 13. It is desirable to cool the solder ball fixing jig 14a with cold air or the like while it is still attached after irradiation with the laser beam 15a. This cooling allows the solder ball fixing jig 14a to be removed only after the solder bumps 31 have sufficiently hardened, thus reducing the likelihood of misalignment. The solder ball fixing jig 14a itself can also be cooled. Of course, it is also acceptable to leave it for a certain period of time to allow for natural cooling without active cooling.

[0067] (Operation of this embodiment) The solder bump formation method and solder bump formation apparatus 10 of this embodiment have the following effects. In the conventional technology, when forming solder bumps 31 for fine BGA3, misalignment occurred in the reflow oven 115, leading to a decrease in product yield. In contrast, the solder bump formation method and solder bump formation apparatus 10 of this embodiment use a solder ball fixing jig 14a to fix the solder balls 32 so that they do not shift from a predetermined position, and then heat them in a short time with a laser irradiation device 15 to form solder bumps 31.

[0068] Therefore, the solder bump forming method and solder bump forming apparatus 10 of this embodiment have the effect of suppressing the displacement of the solder balls 32 that occurs in the conventional method. (Effects of this embodiment) (1) The solder bump forming method and solder bump forming apparatus 10 of this embodiment have the effect of forming solder bumps 31 in the precise position without any omissions, even with fine solder balls 32. This has the effect of improving product yield and reliability. In addition, since displacement of solder balls 32 can be reliably suppressed, the inspection process can also be simplified.

[0069] (2) In the positioning step, the solder balls are positioned on the land 61 using the solder ball fixing jig 14a. In the heating step, the solder balls 32 are heated with the laser irradiation device 15 while still fixed to the solder ball fixing jig 14a to form solder bumps 31 on the land 61. This has the effect of preventing the solder balls 32 from shifting from their predetermined positions during the heating step.

[0070] (3) The solder ball fixing jig 14a is a plate-shaped member made of a heat-resistant material and is configured as a mask having through holes corresponding to the positions of the lands 61. Therefore, the solder ball fixing jig 14a has durability in the heating process and can be used repeatedly.

[0071] (4) The heat-resistant material of the solder ball fixing jig 14a is made of SUS. Therefore, it has high mechanical strength and high heat resistance, which has the effect of being able to align the solder balls 32 with high precision. Furthermore, because it has low wettability to solder, it has the effect that molten solder from the heating process does not adhere to it.

[0072] (5) The target product is a silicon wafer 60 or interposer 5, which is a substrate 2 mounted on a semiconductor package 1. Even with such a fine BGA, this has the effect of forming solder bumps 31 in the correct positions without any omissions.

[0073] (6) The diameter of the solder ball 32 is 100 [μm] or less. Even with such a fine BGA3, this has the effect of forming solder bumps 31 in precise positions without any omissions.

[0074] (7) The heating device is a laser irradiation device 15 that uses a laser light source. As a result, solder bumps 31 can be formed in a short time. Therefore, the production efficiency is significantly more efficient compared to a conventional reflow oven 115. In addition, since the entire substrate 2 is not easily heated, the thermal impact on the substrate 2 is extremely small.

[0075] (Another example) Although the present invention has been described above with reference to one embodiment, the present invention is not limited to the above embodiment. For example, it can be implemented by the following alternative examples.

[0076] 〇Although a laser irradiation device 15 has been given as an example of a heating device in this embodiment, the heating device is not limited to this. The present invention can be implemented as long as the solder balls 32 are heated while fixed to the solder ball fixing jig 14a during the heating process in which they are positioned on the land 61 by the solder ball fixing jig 14a, thereby forming solder bumps 31 on the land 61. For example, if the solder ball fixing jig 14a has sufficient heat resistance and mechanical strength, the reflow oven 115 is not excluded. Furthermore, the present invention can be implemented as long as the solder bumps 31 can be formed using high frequency, high electric field, high magnetic field, infrared lamp, etc.

[0077] For example, by precisely controlling the irradiation light of a high-power xenon lamp as "light pulses," it is possible to instantaneously heat, dry, and sinter only the surface of the material. With high-power, short-pulse irradiation, even substrates with low heat resistance (substrate 2) can be soldered without damage, and conventional lead-free flux can be used. Specifically, examples include the "PulseForge" light sintering device manufactured by PulseForge, Inc.

[0078] The products to which the present invention applies are not limited to BGA3s of semiconductor substrates 2 or chiplets 4 formed on silicon wafers 60, or BGA3s formed on interposers 5 made of silicon, organic materials, glass, etc., as long as they form solder bumps 31. Furthermore, although a matrix-shaped BGA3 is illustrated in this embodiment, other patterns such as staggered patterns may also be used. Moreover, the invention may also apply to forms solder bumps 31 scattered on, for example, general printed circuit boards.

[0079] Alternatively, the main board 21 may be omitted, and a BGA 3a may be provided on the interposer 5, with multiple chiplets 4a and 4b arranged on the interposer 5. Furthermore, the solder ball 32 is not limited to pure solder, but may be composed of a brazing material or the like.

[0080] In this embodiment, flux 63 is applied and the solder ball 32 is soldered, but the application of flux 63 (S3) is not an essential step in the present invention. Therefore, the solder bump 31 may be formed without applying flux 63.

[0081] The flux 63 in this embodiment is made of resin, but is not limited to this. For example, a solder paste containing powdered solder may also be used. If the solder paste has a lower melting point than the solder ball 32, the melting and deformation of the solder ball 32 can be suppressed.

[0082] In this embodiment, the solder ball fixing jig 14a is attached after the flux 63 is applied, but it is also possible to apply the flux 63 over the solder ball fixing jig 14a after it has been attached. In this case, the flux may be applied only to the land 61 using a dispenser, or the flux 63 may be applied to the entire surface of the solder ball fixing jig 14a and any excess flux 63 may be removed with a doctor blade or the like.

[0083] In this embodiment, the solder ball fixing jig 14a is exemplified by SUS as a heat-resistant material, but is not limited to this. Examples of heat-resistant materials include steel, metals including cast iron, glass, and ceramics. However, any material that can withstand short-duration laser light 15a may be used, such as other metals, such as aluminum alloys or titanium, or resins with high heat resistance. In particular, ceramics can be used to create a solder ball fixing jig 1a with high heat resistance.

[0084] Furthermore, materials with low wettability that repel molten flux 63 and molten solder are desirable. In this respect, materials such as SUS, Al, and Ti, which form a strong oxide film, are also desirable. ○The solder ball fixing hole 14b of the solder ball fixing jig 14a in this embodiment has an inner diameter of φ INThe holes are cylindrical through-holes of equal size. The solder ball fixing hole 14b is not limited to this, and the inner diameter φ on the introduction side of the solder ball 32 is also φ IN The inner diameter φ on the substrate 2 side is increased. IN The size can be reduced. This allows for easy introduction of the solder ball 32, and enables high-precision positioning and fixing.

[0085] ○The flowchart shown in Figure 4 is an example of the present invention, and the steps can be added, deleted, rearranged, or rearranged to carry it out. ○The drawings are provided for understanding the invention, but may not accurately reflect an actual secondary battery due to omissions, exaggerations, or schematics, and do not limit the present invention.

[0086] The drawings are for illustrative purposes only and may omit numbers or exaggerate dimensional balances for ease of explanation; however, they are not limited to these drawings.

[0087] ○The numerical values, numerical ranges, compositions, etc., in this embodiment are illustrative and do not limit the present invention. They can be appropriately optimized and implemented by those skilled in the art. ○The present invention can be implemented by those skilled in the art with additions, deletions, and modifications, without departing from the scope of the claims. [Explanation of Symbols]

[0088] 1… Semiconductor package 2 (21, 4, 5) ... Circuit board (Target product) 2a…Connection surface 21…Main board 3, 3a~3e…BGA (Ball Grid Aray) 31... Solder bump 32... Solder ball φ…Diameter, outer diameter, inner diameter [μm] 4, 4a~4d... Chiplets 5…Interposer 60…Silicon wafer 61...Land (connection terminal) 62...Solda Resist 63... Flux (solder paste) 10, 110... Solder bump forming device 11, 111...Substrate manufacturing equipment 12, 112... Coating device 13, 113... Mask attachment / detachment device 14... Solder ball position fixing device 14a... Solder ball fixing jig 14b... Solder ball fixing hole G... Gap 114... Solder ball positioning device 114a... Solder ball positioning jig 114b...Solder ball introduction hole 115…Reflow oven (heating device) 115a…hot air 15…Laser irradiation device (heating device) 15a…Laser light

Claims

1. A solder bump formation method comprising aligning solder balls on multiple connection terminals provided on the connection surface of a target product and soldering them, A positioning step of introducing the solder ball into a through hole of a solder ball fixing jig to position it on a plurality of connection terminals provided on the connection surface of the target product, The heating step includes heating the solder ball with a heating means while it is still fixed to the solder ball fixing jig at the position where the positioning step was performed, thereby forming a solder bump on the connection terminal. The solder ball fixing jig is a plate-shaped member made of a heat-resistant material, and is configured as a mask having through holes through which the solder balls pass, corresponding to the positions of the connection terminals. The heating device used in the aforementioned heating process uses a laser light source or optical pulses. The diameter of the solder ball is 100 [μm] or less. A solder bump formation method characterized by the following.

2. The solder bump forming method according to claim 1, characterized in that the heat-resistant material of the solder ball fixing jig is a metal including SUS or steel, glass, or ceramics.

3. The solder bump formation method according to claim 1, characterized in that the target product is a wafer or interposer which is a substrate mounted on a semiconductor package.

4. A solder bump forming apparatus for aligning solder balls on multiple connection terminals provided on the connection surface of a target product and soldering them, A positioning device that fixes the aforementioned solder ball to a plurality of connection terminals provided on the connection surface of the target product by introducing the solder ball into a through hole of a solder ball fixing jig, The system includes a heating device that, at the position where the positioning step has been performed, heats the solder ball with a heating means while it is still fixed to the solder ball fixing jig to form a solder bump on the connection terminal, The solder ball fixing jig is a plate-shaped member made of a heat-resistant material, and is configured as a mask having through holes through which the solder balls pass, corresponding to the positions of the connection terminals. The heating device uses a laser light source or light pulses, The diameter of the solder ball is 100 [μm] or less. A solder bump forming apparatus characterized by the following.

5. The solder bump forming apparatus according to claim 4, characterized in that the heat-resistant material of the solder ball fixing jig is SUS, a metal including steel, glass, or ceramics.

6. The solder bump forming apparatus according to claim 4, characterized in that the target product is a wafer or interposer which is a substrate mounted on a semiconductor package.

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