Soldering apparatus and soldering method

Abstract

To provide technique enabling reduction of the waste loss of a workpiece.SOLUTION: Soldering equipment comprises: a first preheating unit 11 and a second preheating unit 12 as preheating units, each of which heats a workpiece 2 coated with solder paste to a temperature on or less than the melting point of a solder paste; a melting unit 14 which melts the solder paste applied to the workpiece 2 by heating the workpiece 2 to temperature higher than the melting point of the solder paste; an inspection unit 15 which inspects the state of the solder paste during the period of time that the solder paste melts, and determines whether there is any abnormality; and a cooling unit 16 which performs soldering on the workpiece 2 by cooling the workpiece 2 to or less than the melting point of the solder paste when the inspection unit 15 determines that there is no abnormality.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a soldering apparatus and a soldering method.

Background Art

[0002] In general soldering methods, most of them use a liquid flux to remove oxides of solder and electrodes and then join them. However, since the flux has a reducing effect, if the flux remains near the joint, the state where oxides are reduced to generate metal ions is maintained. In a power semiconductor device, it is necessary to ensure electrical insulation at required locations. A power semiconductor device has a function of performing voltage, current, and AC / DC conversion, and for this, so-called power electronics technology that generates and converts a pulsed voltage waveform is applied. At that time, it is necessary to maintain insulation that satisfies the index of the rated withstand voltage, such as a potential difference obtained from the power system between the electrodes in the power semiconductor device or obtained by internal conversion, for example, 600V or 1200V. Also, a characteristic of not being damaged by insulation even when applying AC2500V to the ground for 1 minute is required.

[0003] By the way, when a voltage is applied while the flux adheres to the insulation region around the soldered electrode, migration occurs due to the ionized metal and current leakage occurs, and for avoiding this, the flux is removed. However, there are problems that the cleaning process for flux removal requires a long time or the cleaning liquid becomes industrial waste.

[0004] On the other hand, there is a soldering method that does not require flux cleaning. For example, Patent Document 1 discloses a method of removing oxides of electrodes and solder before soldering using a nitrogen-hydrogen mixed gas containing hydrogen, which is a reducing gas.

[0005] Also, Patent Document 2 discloses a method of introducing a mixed gas containing a carboxylic acid such as formic acid to remove oxides of electrodes and solder before soldering. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2014-157858 [Patent Document 2] International Publication No. 2018 / 096917 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, with conventional technology, inspection is performed after soldering to the workpiece. If a void in the joint of the workpiece exceeds a certain size, the workpiece must be discarded, resulting in waste.

[0008] Therefore, this disclosure aims to provide a technology that can reduce workpiece waste. [Means for solving the problem]

[0009] The soldering apparatus according to this disclosure comprises: a preheating unit that heats a workpiece coated with solder paste to a temperature below the melting point of the solder paste; a melting unit that heats the workpiece to a temperature higher than the melting point of the solder paste to melt the solder paste applied to the workpiece; an inspection unit that inspects the state of the solder paste while it is melting and determines whether there is any abnormality; and a cooling unit that, if the inspection unit determines that there is no abnormality, cools the workpiece to a temperature below the melting point of the solder paste to perform soldering on the workpiece. If an abnormality is detected in the inspection unit, the unit will perform depressurization and repressurization. It is. [Effects of the Invention]

[0010] According to this disclosure, the soldering apparatus inspects the state of the solder paste applied to the workpiece while it is melting, and then performs soldering on the workpiece. By removing voids generated in the solder paste before soldering, the waste loss of the workpiece can be reduced. [Brief explanation of the drawing]

[0011] [Figure 1] This figure shows a cross-sectional view and temperature profile of a soldering apparatus according to Embodiment 1. [Figure 2] This figure shows a cross-sectional view and temperature profile of a soldering apparatus according to Embodiment 2. [Modes for carrying out the invention]

[0012] <Embodiment 1> Embodiment 1 will be described below with reference to the drawings. Figure 1 is a diagram showing a cross-sectional view and temperature profile of the soldering apparatus according to Embodiment 1.

[0013] As shown in Figure 1, the soldering apparatus comprises a tunnel-type reflow oven 4 and a control unit 50 that controls each process within the reflow oven 4. Although Figure 1 shows a tunnel-type reflow oven 4, a batch-type or fixed-type reflow oven may be used as long as it can achieve similar functionality.

[0014] The reflow oven 4 is divided into six regions by five partition walls 4a. The six regions are the first preheating section 11, the second preheating section 12, the temperature equalization section 13, the melting section 14, the inspection section 15, and the cooling section 16. Each partition wall 4a is provided with an opening 4b through which the workpiece 2 can pass.

[0015] Inside the reflow oven 4, the workpiece 2 is transported on a pallet 1, and each process is basically carried out in a nitrogen atmosphere. A belt-type transport unit 3 is provided inside the reflow oven 4. The control unit 50 drives the transport unit 3, moving the workpiece 2 placed on the pallet 1 in steps, that is, by a predetermined distance each time, to carry out each process. Specifically, the control unit 50 moves the workpiece 2 in the order of the first preheating unit 11, the second preheating unit 12, the temperature equalization unit 13, the melting unit 14, the inspection unit 15, and the cooling unit 16 to carry out each process. Multiple workpieces 2 are fed in sequentially, and soldering is performed on the workpieces 2 after going through each process in order.

[0016] Now, let's describe Workpiece 2. Workpiece 2 has solder paste (not shown) applied to it before being placed in the reflow oven 4. Workpiece 2 consists of an object to be joined and an object to be joined. Taking the example that Workpiece 2 is a power semiconductor device, the object to be joined is an electronic component such as a chip (not shown), and the object to be joined is a substrate (not shown) on which a pattern has been formed. Therefore, Workpiece 2 placed in the reflow oven 4 is a substrate with electronic components arranged via solder paste. In Embodiment 1, a solder paste containing flux is used.

[0017] The reflow oven 4 requires at least three areas for processing the workpiece 2. Specifically, areas are needed for preheating, melting, and cooling. Figure 1 shows a case where the reflow oven 4 has six areas. Each area, excluding the inspection section 15, is provided with one set each of multiple heat sources 5 and fans 6, one above and one below the transport section 3. The control unit 50 controls the multiple heat sources 5 and fans 6 in each area, circulating hot air so that each area reaches a predetermined temperature. The control unit 50 is, for example, a CPU (central processing unit) or a microcontroller. The lower part of Figure 1 shows a temperature profile illustrating an example of the temperature change of the workpiece 2.

[0018] The first preheating unit 11 and the second preheating unit 12 perform preheating by heating the work 2 coated with the solder paste to a temperature below the melting point of the solder paste. The temperature equalization unit 13 equalizes the temperature of the entire work 2 to improve the quality of the work 2. The melting unit 14 melts the solder paste applied to the work 2 by heating the work 2 to a temperature higher than the melting point of the solder paste.

[0019] The inspection unit 15 includes chambers 7a, 7b, a chamber drive unit 7c, an X-ray source 8, an X-ray camera 9, a gas introduction unit 10a, and a decompression unit 10b. The chambers 7a, 7b are provided above and below the transport unit 3 to airtight the inside of the inspection unit 15. The chamber drive unit 7c includes a drive motor (not shown), and switches the chambers 7a, 7b between an open state and a closed state by moving the chamber 7a in the vertical direction. When the chambers 7a, 7b are in the closed state, the pallet 1 is sandwiched by the chambers 7a, 7b to obtain airtightness. For example, by providing a rubber-like seal portion on the mating surface of the chambers 7a, 7b, these seal portions are brought into close contact to obtain airtightness.

[0020] The X-ray source 8 is provided above the chamber 7a, and the X-ray camera 9 is provided below the chamber 7b. The control unit 50 causes the X-ray source 8 and the X-ray camera 9 to perform transmission X-ray imaging (X-ray inspection) on the work 2 conveyed from the melting unit 14 to the inspection unit 15 through the chambers 7a, 7b. The work 2 conveyed to the inspection unit 15 is in a molten state with the solder paste not cooled. The control unit 50 causes the X-ray source 8 and the X-ray camera 9 to perform X-ray inspection on the state of the solder paste during melting of the solder paste, and determines whether there is any abnormality based on the inspection result.

[0021] The decompression section 10b is an exhaust pipe connected to a vacuum pump (not shown). The gas introduction section 10a is a supply pipe connected to a gas supply source (not shown). Both the decompression section 10b and the gas introduction section 10a are provided with, for example, on-off valves (not shown). By the control unit 50 opening the on-off valve, gas is discharged from the chambers 7a and 7b, and gas is introduced into the chambers 7a and 7b.

[0022] When the control unit 50 determines that there is an abnormality in the state of the solder paste, it causes the decompression section 10b to discharge gas from the chambers 7a and 7b to decompress the inside of the chambers 7a and 7b. Thereafter, the control unit 50 causes the gas introduction section 10a to introduce gas into the chambers 7a and 7b to revenge pressurize the inside of the chambers 7a and 7b.

[0023] When it is determined in the inspection section 15 that there is no abnormality, the cooling section 16 cools the work 2 to below the melting point of the solder paste to perform soldering on the work 2. Thereafter, the work 2 is discharged. In a cleaning facility (not shown), by cleaning and removing the flux contained in the solder paste after soldering, a product of good quality can be obtained.

[0024] Next, the processing in the inspection section 15 will be described in detail. In the inspection section 15, the control unit 50 inspects whether voids have occurred in the solder paste applied to the work 2, and calculates the area of the voids if voids have occurred. If the area of the voids is equal to or greater than a specified threshold area, the control unit 50 reduces the pressure of the gas in the chambers 7a and 7b to, for example, 1 / 100 atmospheric pressure, and the volume of the voids becomes 100 times, and the voids are discharged outside the solder paste.

[0025] Thereafter, the control unit 50 causes gas to be introduced from the gas introduction section 10a to pressurize the inside of the chambers 7a and 7b to revenge atmospheric pressure. Preferably, by repeating decompression and revenge pressurization until there are no voids equal to or greater than the threshold area, soldering in a state without defects can be completed.

[0026] In Embodiment 1, the pressure is reduced. revenge The example of repeatedly applying pressure was shown, but if the solder melting time is too long, the electrode material may dissolve into the solder, potentially compromising its quality. Therefore, the pressure should be reduced before the predetermined melting time is reached. revenge The repeated application of pressure may be stopped, and the material may be transported to the cooling unit 16.

[0027] Furthermore, preferably, if a light metal with a small atomic weight of Al is used in the parts of chambers 7a and 7b that overlap with the workpiece 2 when viewed from the vertical direction, the contrast ratio of the X-ray inspection can be increased, thereby improving the accuracy of the inspection.

[0028] Furthermore, a sealing function against air is required between the chambers 7a and 7b and the pallet 1. For example, a heat-resistant packing is suitable for this purpose. By providing a ring-shaped heat-resistant packing at the contact point between the chambers 7a and 7b and the pallet 1, an airtight seal can be efficiently formed. In this case, by providing the heat-resistant packing on the sealing surface between the chambers 7a and 7b and the pallet 1, it is economical because multiple pallets 1 are used while only one set of chambers 7a and 7b is needed. On the other hand, if a heat-resistant packing is provided on each pallet 1, maintainability is improved. It is important to decide where to provide the heat-resistant packing based on the user's frequency of use.

[0029] Furthermore, by providing a partition wall 4a in the reflow oven 4, the temperature in each region can be controlled with high precision, allowing for a smaller and more economical soldering device. By making the partition wall 4a movable and providing a drive mechanism that enables shutter operation, it becomes possible to control the temperature with even greater precision.

[0030] As described above, the soldering apparatus according to Embodiment 1 includes a first preheating section 11 and a second preheating section 12, which serve as preheating sections for heating a workpiece 2 coated with solder paste to below the melting point of the solder paste; a melting section 14 for heating the workpiece 2 to a temperature higher than the melting point of the solder paste to melt the solder paste applied to the workpiece 2; an inspection section 15 for inspecting the state of the solder paste while it is melting and determining whether there are any abnormalities; and a cooling section 16 for performing soldering to the workpiece 2 by cooling the workpiece 2 to below the melting point of the solder paste if the inspection section 15 determines that there are no abnormalities. Specifically, the inspection section 15 inspects the state of the solder paste using X-rays.

[0031] Therefore, since the soldering apparatus inspects the condition of the solder paste applied to the workpiece 2 while it is melting, and then performs soldering on the workpiece 2, it is possible to reduce the waste loss of workpiece 2 by removing voids that occur in the solder paste before soldering.

[0032] Furthermore, if an abnormality is detected in the inspection unit 15, a depressurization process will be performed within the inspection unit 15. revenge Pressure is applied. Conventionally, when voids occurred in the solder paste, workpiece 2 was reheated to melt the solder paste and separate workpiece 2, and then soldering was performed on workpiece 2 again, which was a so-called rework process. However, in Embodiment 1, reduced pressure is applied while the solder paste is melting. revenge By applying pressure to remove voids in the solder paste, it becomes unnecessary to reheat workpiece 2, allowing for economical void removal. Furthermore, the time occupied by the soldering equipment can be reduced compared to conventional methods that required rework.

[0033] Furthermore, workpiece 2 includes a substrate and electronic components arranged on the substrate via solder paste. Because such workpiece 2 has a large soldering area, it has a high heat capacity and poor heat transfer, making it prone to void formation in the solder paste. However, by using the soldering apparatus according to Embodiment 1, voids formed in the solder paste can be removed, reducing the void ratio, which is the ratio of the bonded area to the void-occupied area. This improves the bonding quality of workpiece 2.

[0034] <Embodiment 2> Next, a soldering apparatus according to Embodiment 2 will be described. Figure 2 is a diagram showing a cross-sectional view and temperature profile of the soldering apparatus according to Embodiment 2. In Embodiment 2, the same reference numerals are used for components that are the same as those described in Embodiment 1, and their descriptions are omitted.

[0035] In Embodiment 1, a solder paste containing flux was used to solder to the workpiece 2, but in Embodiment 2, a solder paste without flux is used.

[0036] As shown in Figure 2, the reflow oven 4 is equipped with an oxide film removal unit 23 instead of a temperature uniformization unit 13.

[0037] The oxide film removal unit 23 comprises chambers 21a and 21b, a chamber drive unit 21c, and a reducing gas supply unit 22. Chambers 21a and 21b are positioned above and below the transport unit 3 to ensure airtightness within the oxide film removal unit 23. The chamber drive unit 21c includes a drive motor (not shown) and switches chambers 21a and 21b between an open state and a closed state by moving chamber 21a vertically. When chambers 21a and 21b are in the closed state, airtightness is achieved by sandwiching the pallet 1 between chambers 21a and 21b. For example, airtightness is achieved by providing rubber-like seals on the mating surfaces of chambers 21a and 21b to ensure tight contact between these seals.

[0038] The reducing gas supply unit 22 is a supply pipe connected to a reducing gas supply source (not shown). The reducing gas supply unit 22 is equipped with, for example, an on-off valve (not shown), and the control unit 50 opens the on-off valve to introduce reducing gas into the chambers 21a and 21b.

[0039] The control unit 50 transports the workpiece 2, which has been preheated in the second preheating unit 12, to the oxide film removal unit 23. The control unit 50 drives the chamber drive unit 21c to sandwich the workpiece 2 between chambers 21a and 21b, and introduces a reducing gas from the reducing gas supply unit 22 into chambers 21a and 21b. Suitable reducing gases include, for example, hydrogen gas, a mixture of hydrogen and nitrogen, or nitrogen gas containing formic acid. By pre-removing the oxide film formed on the surface of the workpiece 2 at the preheating temperature, the wettability of the solder paste is improved, enabling soldering with fewer defects such as voids and solder failure.

[0040] Next, the melting section 14 heats the workpiece 2 to a temperature higher than the melting point of the solder paste, thereby melting the solder paste applied to the workpiece 2. Next, the inspection section 15 inspects the state of the solder paste while it is melting and determines whether there are any abnormalities. If the inspection section 15 determines that there are abnormalities, the pressure is reduced within the inspection section 15 and revenge By applying pressure, voids that occur in the solder paste are removed.

[0041] Embodiment 2 shows an example in which formic acid is applied in the reducing gas supply unit 22. The reducing effect of formic acid becomes significantly stronger from around 150°C, but the decomposition of formic acid begins at 180°C or above. In reduction by formic acid, formate is formed where there was once an oxide film, and then the formate is thermally decomposed into unoxidized metal and gas. In other words, after applying nitrogen gas containing formic acid, the formate and formic acid are decomposed at 180°C or above, and the problem of voids further increasing due to the gas generated from formic acid can be resolved.

[0042] As described above, in the soldering apparatus according to Embodiment 2, the solder paste does not contain flux, and the soldering apparatus further includes an oxide film removal unit 23 that, after heating the workpiece 2 in the first preheating unit 11 and the second preheating unit 12 to below the melting point of the solder paste, introduces a reducing gas to remove the oxide film formed on the surface of the solder paste. This improves the wettability of the solder paste and enables soldering with fewer defects such as voids and solder failure.

[0043] Furthermore, in Embodiment 2, since a flux-free solder paste is used, the process of cleaning the flux is unnecessary, and the effect of not generating voids caused by the flux is obtained.

[0044] Furthermore, it is possible to freely combine each embodiment, or to modify or omit each embodiment as appropriate.

[0045] The various aspects of this disclosure are summarized below as an appendix.

[0046] (Note 1) A preheating unit that heats a workpiece coated with solder paste to a temperature below the melting point of the solder paste, A melting section is provided in which the solder paste applied to the workpiece is melted by heating the workpiece to a temperature higher than the melting point of the solder paste, An inspection unit that inspects the state of the solder paste while it is melting and determines whether there are any abnormalities, If the inspection unit determines that there is no abnormality, the cooling unit cools the workpiece to below the melting point of the solder paste, thereby performing soldering on the workpiece. Equipped with a soldering device.

[0047] (Note 2) The soldering apparatus described in Appendix 1, wherein the inspection section uses X-rays to inspect the state of the solder paste.

[0048] (Note 3) If an abnormality is detected in the inspection unit, the pressure will be reduced within the inspection unit. revenge A soldering apparatus described in Appendix 1 or Appendix 2 that applies pressure.

[0049] (Note 4) The aforementioned solder paste does not contain flux. The soldering apparatus according to Appendix 1, further comprising an oxide film removal unit that, after heating the workpiece in the preheating unit to below the melting point of the solder paste, introduces a reducing gas to remove the oxide film formed on the surface of the solder paste.

[0050] (Note 5) The soldering apparatus according to Appendix 1, wherein the workpiece includes a substrate and an electronic component arranged on the substrate via the solder paste.

[0051] (Note 6) (a) A step of heating a workpiece to which solder paste has been applied to a temperature below the melting point of the solder paste, (b) A step of heating the workpiece to a temperature higher than the melting point of the solder paste, thereby melting the solder paste applied to the workpiece, (c) A step of inspecting the state of the solder paste while it is melting and determining whether there is any abnormality, (d) If it is determined that there is no abnormality in step (c), the step of soldering to the workpiece by cooling the workpiece to below the melting point of the solder paste, Prepare, soldering method. [Explanation of Symbols]

[0052] 2 workpiece, 11 first preheating section, 12 second preheating section, 14 melting section, 15 inspection section, 16 cooling section, 23 oxide film removal section.

Claims

1. A preheating unit that heats a workpiece coated with solder paste to a temperature below the melting point of the solder paste, A melting section is provided in which the solder paste applied to the workpiece is melted by heating the workpiece to a temperature higher than the melting point of the solder paste, An inspection unit that inspects the state of the solder paste while it is melting and determines whether there are any abnormalities, If the inspection unit determines that there is no abnormality, the cooling unit cools the workpiece to below the melting point of the solder paste, thereby performing soldering on the workpiece. Equipped with, A soldering apparatus that, if an abnormality is detected in the inspection section, performs depressurization and repressurization within the inspection section.

2. A preheating unit that heats a workpiece coated with solder paste to a temperature below the melting point of the solder paste, A melting section is provided in which the solder paste applied to the workpiece is melted by heating the workpiece to a temperature higher than the melting point of the solder paste, An inspection unit that inspects the state of the solder paste while it is melting and determines whether there are any abnormalities, If the inspection unit determines that there is no abnormality, the cooling unit cools the workpiece to below the melting point of the solder paste, thereby performing soldering on the workpiece. Equipped with, The aforementioned solder paste does not contain flux. A soldering apparatus further comprising an oxide film removal unit that, after heating the workpiece in the preheating unit to below the melting point of the solder paste, introduces a reducing gas to remove the oxide film formed on the surface of the solder paste.

3. (a) A step of heating a workpiece to which solder paste has been applied to a temperature below the melting point of the solder paste, (b) A step of heating the workpiece to a temperature higher than the melting point of the solder paste, thereby melting the solder paste applied to the workpiece, (c) A step of inspecting the state of the solder paste while it is melting and determining whether there is any abnormality, (d) If it is determined that there is no abnormality in step (c), the step of soldering to the workpiece by cooling the workpiece to below the melting point of the solder paste, Equipped with, A soldering method that, if an abnormality is detected in step (c) above, reduces pressure and restores pressure.

4. (a) A step of heating a workpiece to which solder paste has been applied to a point below the melting point of the solder paste, (b) A step of heating the workpiece to a temperature higher than the melting point of the solder paste, thereby melting the solder paste applied to the workpiece, (c) A step of inspecting the state of the solder paste while it is melting and determining whether there is any abnormality, (d) If it is determined that there is no abnormality in step (c), the step of soldering to the workpiece by cooling the workpiece to below the melting point of the solder paste, Equipped with, The aforementioned solder paste does not contain flux. (e) A soldering method further comprising the step of heating the workpiece to below the melting point of the solder paste in step (a), and then introducing a reducing gas to remove the oxide film formed on the surface of the solder paste.

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