Locally soldering method

Abstract

To provide a locally soldering method that can prevent poor soldering.SOLUTION: In a locally soldering method, required amount of molten solder is discharged from a nozzle 2 protruding upward, and at the same time at least an environment around a tip part of the nozzle is filled with inactive gas and also the molten solder is contacted with a substrate 13, so as to perform soldering on a desired position of the substrate, where a temperature of inactive gas flowing from an upper end of the nozzle toward a lower surface of the substrate is above a melt temperature of the molten solder discharged from the nozzle.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a local soldering method for performing soldering with a relatively small area and a small amount of solder on a desired location of a substrate.

Background Art

[0002] The local soldering method is a method performed using a local soldering device or the like. Soldering by a soldering device or the like has drawbacks in that since the solder comes into contact with the atmosphere near the ejection port for ejecting the molten solder, the solder is oxidized by oxygen in the outside air and tends to form dross, and the temperature during soldering decreases and the viscosity of the solder increases. To eliminate this drawback, it has been improved so as to cover the vicinity of the ejection port with a high-temperature inert gas.

[0003] Conventional local soldering methods have a function of preventing oxidation of the solder by covering the solder ejected from the nozzle with an inert gas, and have a structure in which the transfer path of the solder from the solder bath through the nozzle to contact with the substrate is sealed, and the space outside the nozzle is filled with a high-temperature inert gas, so that a function of preventing the temperature of the solder from decreasing is adopted throughout the entire solder transfer path from storage in the solder bath to contact with the substrate. And the local soldering device is provided with means capable of heating the internal atmosphere of the heat-insulating chamber to 250°C to 400°C (for example, claim 4 of Patent Document 1). Also, in the conventional local soldering method, when the nozzle of the local soldering device moves to a new substrate location in the substrate and the temperature of the molten solder at the upper end of the nozzle decreases, a waiting time is set until the temperature of the molten solder returns to an appropriate temperature.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] The soldering method of Patent Document 1 is performed by a local soldering device that heats an inert gas in a heat-insulating chamber, circulates it in a solder bath, and causes it to reach the upper end of a nozzle. With such a device structure, it was considered possible to perform soldering that could prevent a temperature drop of the nozzle and the molten solder passing through the nozzle. However, it has been found that even if the inert gas flowing into the heat-insulating chamber is once heated to 350°C or higher, the temperature of the inert gas near the upper end of the nozzle becomes lower than the melting temperature of the molten solder. Therefore, the temperature of the molten solder discharged from the nozzle may drop. Therefore, in the local soldering method, further improvement has been demanded so that the temperature of the inert gas in the ambient atmosphere around the molten solder discharged from the upper end of the nozzle does not become lower than the melting temperature of the molten solder. [Means for Solving the Problems]

[0006] That is, the present invention [1] A local soldering method in which a required amount of molten solder is discharged from a nozzle protruding upward, and at that time, at least the ambient atmosphere around the tip of the nozzle is occupied by an inert gas and the molten solder is brought into contact with a substrate, thereby performing soldering on a desired portion of the substrate, wherein the temperature of the inert gas flowing from the upper end of the nozzle to the lower surface of the substrate is a temperature equal to or higher than the melting temperature of the molten solder discharged from the nozzle, characterized in that it is a local soldering method [2] The local soldering method according to [1], wherein the inert gas is nitrogen gas or argon gas. [3] The local soldering method according to [1], wherein the temperature of the inert gas flowing from the upper end of the nozzle to the lower surface of the substrate is equal to or higher than the melting temperature of the molten solder discharged from the nozzle and is 350°C or lower. [Advantages of the Invention]

[0007] The local soldering method of the present invention can achieve prevention of solder oxidation during soldering and prevention of temperature drop of the molten solder at the upper end of the nozzle by covering the upper end of the nozzle of the local soldering device with an inert gas at a temperature equal to or higher than the melting temperature of the molten solder. Since the viscosity increase of the solder does not occur, the solderability is improved (the height of the solder buildup on the upper surface of the substrate becomes higher), the soldering defects are reduced, and the soldering quality is improved. The local soldering method of the present invention can shorten the waiting time by heating the temperature of the molten solder that has decreased when the nozzle is moved to a new substrate location back to an appropriate temperature, and can improve the soldering speed per location, thereby improving the productivity of soldering.

Brief Description of the Drawings

[0008]

Figure 1

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Figure 7

Best Mode for Carrying Out the Invention

[0009] The soldering method of the present invention heats an inert gas with a heater member in an inert gas introduction pipe and / or a heat preservation chamber to increase the temperature of the inert gas introduction pipe and the heat preservation chamber, and has a heating means such that the temperature of the inert gas covering the upper end of the nozzle is equal to or higher than the melting temperature of the molten solder, and is characterized by a soldering method capable of supplying a certain amount or more of heat to the lower surface of the substrate. And a local soldering apparatus (hereinafter also referred to as an apparatus) that can use the method of the present invention is provided. To achieve the method of the present invention, for example, an inert gas, an inert gas heating means for heating the inert gas and maintaining it at a temperature equal to or higher than the melting temperature of the molten solder until it flows from the upper end of the nozzle to the lower surface of the substrate, an inert gas circulation means for forming a flow path of the inert gas that vigorously flows from the upper end of the nozzle to the lower surface of the substrate, a molten solder heating means from the solder bath to the tip of the nozzle, and a solder pressure feeding means are provided. Hereinafter, it will be described together with the specific configuration of an apparatus using the method showing one aspect of the present invention. In one aspect of the configuration of the local soldering apparatus, for example, the apparatus includes a solder bath for storing molten solder, a nozzle for sending the molten solder to the lower surface of the substrate, a heat preservation chamber covering the upper part of the solder bath, an inert gas introduction pipe for introducing an inert gas, and the like.

[0010] <Inert gas> In the present invention, the inert gas is a gas that does not oxidize the solder and does not contain oxygen. For example, nitrogen gas, helium gas, or argon gas can be mentioned, and nitrogen gas or argon gas is preferable in terms of being inexpensive and relatively easy to obtain. The inert gas in the present invention flows into the inside of the heat preservation chamber from a gas supply source such as a high-pressure cylinder via an (heater member-equipped) inert gas introduction pipe. At this time, the inert gas may be at room temperature or pre-heated to a certain temperature, for example, up to about 100°C to 200°C. The inert gas flows into the inside of the heat preservation chamber in a sufficient amount so that the temperature of the molten solder pumped to the nozzle does not decrease, and flows from the upper end of the nozzle to the lower surface of the substrate. The flow rate is approximately 10 liters (L) / minute or more, preferably approximately 20 L / minute or more, and more preferably approximately 30 L / minute.

[0011] <Inert gas heating means> The inert gas heating means refers to means for heating the inert gas by a heater member installed in the heat preservation chamber and / or a heater member installed in the inert gas introduction pipe. The heater member in the heat preservation chamber heats the inert gas in the heat preservation chamber. On the other hand, the heater member installed in the inert gas introduction pipe heats the inert gas before it flows into the heat preservation chamber, and the heated inert gas heats the heat preservation chamber, the solder bath, and the nozzle. Both heater members also heat the transfer path of the molten solder from the solder bath where the molten solder is sealed to the nozzle and then discharged from the upper end of the nozzle toward the lower surface of the substrate, so that oxidation and temperature drop of the molten solder can be effectively prevented.

[0012] In the present invention, it is required that the temperature of the inert gas flowing from the upper end of the nozzle to the lower surface of the substrate (nozzle upper end gas temperature) is higher than the temperature of the molten solder. In a conventional local soldering device, even if there is a means capable of heating the internal atmosphere of the heat preservation chamber to 250 to 400°C, the nozzle upper end gas temperature was 200 to 220°C. Since the melting temperature of the molten solder is generally 250°C or higher, the required nozzle upper end gas temperature is 250°C or higher, which is higher than the melting temperature of the molten solder. Therefore, the ambient temperature of the heater member during heating (the temperature of the internal atmosphere of the heat preservation chamber or the outflow temperature of the inert gas introduction pipe with the heater member) may be 450 to 850°C, preferably 500 to 800°C, and more preferably 600 to 800°C. Also, the nozzle upper end gas temperature is preferably 250 to 350°C, more preferably 260 to 330°C, and even more preferably 280 to 300°C.

[0013] <Inert gas flow means> The inert gas flow means is a means for flowing an appropriate inert gas at an appropriate flow rate through an appropriate flow path in the path from when the inert gas flows into the inert gas introduction pipe until it flows to the lower surface of the substrate. The flow path of the inert gas flows from an inert gas cylinder or the like into the heat-insulating chamber through the inert gas introduction pipe from the side of the heat-insulating chamber, and flows into the side surface of the chamber inner wall from a plurality of holes in the lower inner side of the heat-insulating chamber while heating the lower part of the nozzle, generates an upward flow from the bottom to the top along the side surface of the chamber inner wall, then flows out from the gap between the upper end of the nozzle and the cap, and reaches the lower surface of the substrate vigorously from the upper end of the nozzle. Through these flow paths, it is possible to more reliably heat the heat-insulating chamber, the nozzle, the molten solder passing through the nozzle, and the lower surface portion of the substrate. The cap opening around the upper end of the nozzle is sized so that air does not flow into the inside of the cap, while being adjusted to a size that does not disturb the molten solder discharged from the upper end of the nozzle. According to the above inert gas flow means, when discharging a necessary amount of molten solder from the upper end of the nozzle, the ambient atmosphere around the tip of the nozzle can be occupied by an inert gas at a temperature equal to or higher than the melting temperature of the molten solder.

[0014] <Molten solder heating means> The molten solder heating means is a heating means from when the solder is melted and stored in the solder bath until it reaches the lower surface of the substrate from the upper end of the nozzle. The solder in the solder bath is maintained at 250°C or higher in the solder bath by heaters installed on the side surface, bottom surface, etc. of the solder bath. Then, the solder in the nozzle after being pumped is heated by heat radiation from a heat-insulating chamber heated by an inert gas or the like. Further, the solder when contacting the upper end of the nozzle and the lower surface of the substrate is heated by an inert gas. The temperature of the inert gas at the upper end of the nozzle and the lower surface of the substrate is heated to approximately 250°C to approximately 350°C. Therefore, the temperature of the molten solder discharged from the nozzle is a temperature of approximately 250°C to approximately 300°C or higher than the melting temperature of the solder.

[0015] <Solder pumping means> The solder pumping means discharges the molten solder in the solder bath through the inside of the solder tower from above the nozzle. This solder pumping means generally consists of an impeller, a shaft attached to the impeller, and a power source for rotating the impeller via the shaft, and is adjusted so that the amount of molten solder discharged from above the nozzle becomes the required amount. In a particularly preferred embodiment of the present invention, the molten solder is lead-free solder.

[0016] <Local soldering device (device)> As described above, in one aspect of the configuration of the local soldering device, the device may be provided with a solder bath for storing molten solder, a nozzle for sending the molten solder to the lower surface of the substrate, a heat-insulating chamber covering the upper part of the solder bath, an inert gas introduction pipe for introducing an inert gas, and the like. An example of one aspect of the device will be further described. The solder bath is equipped with heaters on the bottom surface, side surfaces, etc., and stores the required amount of molten solder. The nozzle is provided at the upper part of the solder tower. The lower part of the solder tower is equipped so as to be immersed in the molten solder in the solder bath. The molten solder sent from the lower part of the solder tower reaches the nozzle, discharges the solder from the upper end of the nozzle, and brings the solder into contact with the substrate. By making the shape of the upper end of the nozzle a thin cylindrical shape, it is ensured that the discharged molten solder contacts only the desired location on the substrate. The "required amount of molten solder" is the amount of molten solder that can solder a part of the substrate, and is the amount of molten solder that ensures reliable soldering of the parts to be soldered to the substrate. A heat-insulating chamber is installed above the solder bath. The heat-insulating chamber is composed of a lid member, an inner wall of the heat-insulating chamber, a cap, etc. The lid member seals the upper part of the solder bath and supports the heat-insulating chamber. The inner wall of the heat-insulating chamber is a member that partitions the opening in the center of the heat-insulating chamber and is arranged around so as not to contact the nozzle. The cap serves to narrow the flow path when the inert gas flows out of the device and is installed in the heat-insulating chamber and the like. For example, the "nozzle protruding upward" means that when there is a cap, it is a nozzle protruding from the upper end of the cap, and when there is no cap, it is a nozzle protruding from the upper end of the heat preservation chamber. Note that it is desirable that the molten solder has a structure that can be completely blocked from the atmosphere, the inside of the heat preservation chamber is also a space substantially blocked from the atmosphere, and the entire device has a structure that does not allow the atmosphere to flow in. With the above device, a required amount of molten solder is discharged from the nozzle protruding upward, and at least the ambient atmosphere around the tip of the nozzle is occupied by an inert gas and the molten solder is brought into contact with the substrate, so that a local soldering method for soldering a desired portion of the substrate can be used.

[0017] <Heat quantity index> In a conventional local soldering device, when the flow rate of the inert gas flowing out of the device is reduced, there has been a problem that the quality of soldering deteriorates. In the present invention, it is considered that the cause is that when the flow rate of the inert gas is reduced, the amount of heat supplied from the inert gas is reduced, and an index corresponding to the amount of heat is provided and its lower limit is set. That is, when soldering, the method of soldering above the lower limit is also included in the present invention. The method of soldering above the lower limit is also included in the present invention. The relational expression between the flow rate of the flowing gas / liquid and the amount of heat is shown below. Heat quantity = P × t = k × c × ρ × q × ΔT × t Formula (11) P represents electric power (W), t represents time (min), k represents a constant (which changes depending on whether the unit of heat quantity is selected as J or cal), c represents specific heat (kJ / (kg·°C)), ρ represents density (kg / m3), q represents flow rate (m3 / min (standard state)), ΔT represents temperature difference (°C) = target temperature T (°C) - initial temperature T0 (°C). Here, if we consider the amount of heat per unit time in Formula (11), Amount of heat per unit time / k (heat quantity index) = c × ρ × q × ΔT Formula (12) As a result, Equation (12) can be used as a heat quantity index.

Example

[0018] Hereinafter, an aspect of the present invention will be described more specifically with reference to examples. However, the scope of the present invention is not limited to these examples only.

[0019] (Device Example 1) Regarding the local soldering device of the present invention, the local soldering device 1 shown in FIGS. 1 to 3 will be described as an example. The local soldering device 1 includes a nozzle 2, a solder column 3, a solder bath 6, a cap 9, an inert gas introduction pipe 10 with a heater member, a heat insulation chamber 25, a heater member 26, an inert gas heating means (the inert gas introduction pipe 10 with a heater member and the heater member 26), an inert gas circulation means 20, a solder pumping means 30, and the like.

[0020] A plurality of heaters 7 are installed at the bottom of the solder bath 6 so that the solder 4 in the solder bath 6 can be maintained at approximately 250°C or higher to 300°C. The solder bath 6 is configured in a box shape via a lid member 15 that covers the upper part and a packing 11. The nozzle 2 is installed at the upper part of the solder column 3, and the upper end of the nozzle 2 protrudes from the heat insulation chamber 25 and further from the cap 9. The length of the upper end of the nozzle 2 is adjusted so that when the solder 4 is pumped to the upper end of the nozzle 2, it can be maintained at a temperature (approximately 250°C or higher) that can prevent a significant increase in viscosity. The solder column 3 is equipped such that the lower part is immersed in the solder 4 and the upper nozzle 2 stands upright through the through hole 16 of the lid member 15 and the opening of the heat insulation chamber 25 (the space partitioned by the inner wall 21 of the heat insulation chamber). Since the solder column 3 has a tapered structure from bottom to top, it ensures that the solder 4 is pumped to the upper end of the nozzle 2. The solder column 3 is attached to the solder bath 6 by a fixture 8.

[0021] The heat insulation chamber 25 is installed on the lid member 15. The heat-insulating chamber 25 covers the periphery of the nozzle 2 above the lid member 15. The cap 9 is attached to the heat-insulating chamber 25 so as to cover the periphery of the nozzle 2 (the space 14 around the nozzle). The gap between the upper end of the nozzle 2 and the cap 9 is adjusted to be large so that when the inert gas flows out, the pressure is applied and the discharge of the solder 4 from the upper end of the nozzle 2 is not disturbed, and small so that air can be prevented from flowing into the inside of the heat-insulating chamber 25 and the cap 9.

[0022] A heater member 26 is installed to heat the atmosphere inside the heat-insulating chamber 25. The inert gas flows into the side of the heat-insulating chamber 25 from a high-pressure cylinder through the inert gas introduction pipe 10 with a heater member. The inert gas is heated to approximately 450 to 850 °C by the inert gas introduction pipe 10 with a heater member and the heater member 26, hits the side surface of the inner wall 21 of the heat-insulating chamber after passing through the hole below the heat-insulating chamber 25, then rises along the side surface, rises toward the top of the opening of the heat-insulating chamber 25 while heating the space 14 around the nozzle, and goes from the gap of the cap 9 toward the upper end of the nozzle 2 (see the arrow in Fig. 2). The upward flow 28 causes the inert gas to rise along the side surface after flowing into the side surface of the inner wall 21 of the heat-insulating chamber. The inert gas circulation means 20 includes the above upward flow 28, and is means for flowing the inert gas into the inert gas introduction pipe 10 with a heater member, then flowing it out from the heat-insulating chamber 25 and the cap 9 installed at the upper end thereof, and further flowing it from the upper end of the nozzle 2 to the lower surface of the substrate.

[0023] The local soldering device 1 is provided with a solder pumping means 30 including an impeller 34 provided in the solder bath 6, a shaft 32 attached to the impeller 34, and a power transmission means 31 for transmitting the driving force of the motor 33 to the shaft 32. By the solder pumping means 30, the solder 4 in the solder bath 6 passes through the inside of the solder column 3 and is discharged from above the upper end of the nozzle 2. And this local soldering device 1 can prevent the formation of dross by preventing contact with oxygen in the atmosphere during soldering and local soldering operations. Also, since the local soldering device 1 heats the entire transfer path of the solder 4 from within the solder bath 6 until it is soldered to the substrate 13, it can prevent the temperature drop of the solder 4 and thus prevent the increase in its viscosity. Furthermore, the local soldering device 1 can maintain the temperature of the inert gas flowing from the upper end of the nozzle to the lower surface of the substrate above the melting temperature of the molten solder by means of the inert gas heating means using the heater member 26 and the inert gas introduction pipe 10 with a heater member. Based on the above, Device Example 1 in which the inert gas introduction pipe 10 with a heater member and the heater member 26 inside the heat preservation chamber 25 are installed was fabricated. (Device Example 2) Device Example 2 in which the inert gas introduction pipe 10 with a heater member is installed was fabricated, which is the same as Device Example 1 except that the heater member 26 inside the heat preservation chamber 25 is not installed. (Device Example 3) Device Example 3 in which the heater member 26 inside the heat preservation chamber 25 is installed was fabricated, which is the same as Device Example 1 except that no heater is installed in the inert gas introduction pipe 10 with a heater member or the heater of the inert gas introduction pipe 10 with a heater member is not used.

[0024] (Soldering Method) Soldering in the local soldering device 1 is performed by discharging the molten solder 4 from the upper end of the nozzle 2 (cylindrical; overall length approximately 80 cm; outer diameter approximately 3 to 20 mm) and bringing it into contact with a desired location on the substrate 13. The amount of the solder 4 discharged from the nozzle 2 was adjusted to an appropriate amount for soldering.

[0025] (Example 1) Using Device Example 2, the flow rate of the inert gas was 0.03 m 3As the minimum, it was confirmed that when heating to 700 °C or higher with the inert gas introduction pipe 10 with a heater member and allowing the inert gas to flow out from the gap between the nozzle 2 and the cap 9, the gas temperature at the upper end of the nozzle could be maintained at 280 °C or higher. Thereafter, using Apparatus Example 2, soldering of the 10-pin connector was performed. After soldering, the connector portion of the 10-pin connector was removed, and a photograph showing the swelling of the solder is shown in Fig. 4(b), and a schematic diagram of the photograph is shown in Fig. 5(b).

[0026] (Comparative Example 1) Using Apparatus Example 2, with the inert gas being nitrogen, when allowing the inert gas to flow out from the gap between the nozzle 2 and the cap 9, the gas flow rate was 0.03 m 3 / min. Heating was carried out to 350 °C or higher with the inert gas introduction pipe 10 with a heater member, and when allowing the inert gas to flow out from the gap between the nozzle 2 and the cap 9, it was confirmed that the gas temperature at the upper end of the nozzle could be maintained at 220 °C or higher. Thereafter, using Apparatus Example 2, soldering of the 10-pin connector was performed. After soldering, the connector portion of the 10-pin connector was removed, and a photograph showing the swelling of the solder is shown in Fig. 4(a), and a schematic diagram of the photograph is shown in Fig. 5(a).

[0027] (Measurement of solder swelling amount) The measurement results of a1 to a6 in Fig. 5(a) and b1 to b6 in Fig. 5(b) are shown in Table 1.

Table 1

[0028] (Nitrogen gas flow rate) Using Apparatus Example 2, with the inert gas being nitrogen, while maintaining the gas temperature at the upper end of the nozzle at 280 °C or higher when allowing the inert gas to flow out from the gap between the nozzle 2 and the cap 9, the flow rate of the inert gas flowing out from the apparatus and flowing from the upper end of the nozzle to the lower surface of the substrate (inert gas flow rate) was set at 0.005, 0.01, 0.015, 0.02, 0.03, 0.045, 0.06 m 3 / min in 7 steps, and soldering of 10 or more substrates was performed at each step. When checking the quality of the soldered substrate, it was found that there was no problem with the substrate soldered with an inert gas flow rate of 0.01 m 3 / min or more. However, for the substrate soldered with an inert gas flow rate of 0.005 m 3 / min, although there was no soldering defect, something close to a soldering defect was found. Here, the heat quantity indexes for the cases of inert gas flow rates of 0.005 m 3 / min and 0.01 m 3 / min were calculated. Heat quantity index = c × ρ × q × ΔT Equation (1) (In Equation (1), c is the specific heat of nitrogen gas, 0.25 (kcal / (kg·°C)), ρ is the density of nitrogen gas, 1.211 (kg / m 3 ), q is the inert gas flow rate, 0.005 or 0.01 (m 3 / min), ΔT is the temperature difference, which is the nozzle upper end gas temperature of 280 (°C) - the initial ambient temperature of 25 (°C) When the inert gas flow rate is 0.005 m 3 / min, the heat quantity index = 0.386 When the inert gas flow rate is 0.01 m 3 / min, the heat quantity index = 0.772 Therefore, in the local soldering device, if the heat quantity index exceeds 0.386, it is considered that the soldering of the substrate can be carried out normally and with high quality. Figure 6 is a graph showing the relationship between the (required average) heat quantity index and the inert gas flow rate when the nozzle upper end gas temperature is maintained at 220°C, 240°C, 260°C, 280°C, and 300°C and the inert gas flow rate is changed from 0.005 to 0.075 m 3 / min. Note that the minimum value of the (required average) heat quantity index is set to 0.77, which exceeds 0.386. From the above examples, when the inert gas is nitrogen, a soldering method can be proposed in which the heat quantity index calculated from the nozzle upper end gas temperature of the inert gas flowing from the nozzle upper end to the substrate lower surface and the flow rate of the inert gas is 0.77 or more.

[0029] (Argon gas flow rate) Using apparatus example 2, with the inert gas being argon, while maintaining the gas temperature at the upper end of the nozzle at 280 °C or higher when the inert gas flows out from the gap between nozzle 2 and cap 9, the inert gas flow rates were set at 0.005, 0.01, 0.015, 0.02, 0.03, 0.045, and 0.06 m 3 / min in seven steps, and soldering of 10 or more substrates was performed at each step. The quality of the soldered substrates was checked. Substrates soldered at an inert gas flow rate of 0.015 m / min or higher had no problems. However, substrates soldered at an inert gas flow rate of 0.01 m 3 / min or lower were not defective in soldering, but those close to soldering defects were found. 3 Here, the heat quantity indexes for the cases of inert gas flow rates of 0.01 m / min and 0.015 m 3 / min were calculated. 3 Heat quantity index = c × ρ × q × ΔT Equation (1) (In Equation (1), c is the specific heat of argon gas, 0.124 (kcal / (kg·°C)), ρ is the density of argon gas, 1.784 (kg / m ) 3 ) q is the inert gas flow rate, 0.01 or 0.015 (m 3 / min), ΔT is the temperature difference, which is the gas temperature at the upper end of the nozzle, 280 (°C) - the initial ambient temperature, 25 (°C). Heat quantity index for an inert gas flow rate of 0.01 m 3 / min = 0.564 Heat quantity index for an inert gas flow rate of 0.015 m 3 / min = 0.856 Therefore, in the local soldering apparatus, if the heat quantity index exceeds 0.564, it is considered that the soldering of the substrate can be performed normally and with high quality. Figure 7 shows that when the gas temperature at the upper end of the nozzle is maintained at 220 °C, 240 °C, 260 °C, 280 °C, and 300 °C, the inert gas flow rate is 0.005 - 0.075 m 3It is a graph showing the relationship between the (required average) heat quantity index and the inert gas flow rate when it is changed to / min. The minimum value of the (required average) heat quantity index was set to 0.77, which is a value exceeding 0.564. From the above embodiment, when the inert gas is argon gas, a soldering method can be proposed in which the heat quantity index calculated from the nozzle upper end gas temperature of the inert gas flowing from the upper end of the nozzle to the lower surface of the substrate and the flow rate of the inert gas is 0.77 or more.

[0030] In the local soldering apparatus of the present invention, the heat quantity index of the inert gas (nitrogen or argon gas) provided for performing high-quality soldering may be 0.77 or more, preferably 1.00 or more, and more preferably 1.5 or more.

Explanation of reference numerals

[0031] 1: Local soldering apparatus 2: Nozzle 3: Solder tower 4: Solder 6: Solder bath 7: Heater 8: Fixture 9: Cap 10: Inert gas introduction pipe with heater member 11: Packing 13: Substrate (position) 14: Space around the nozzle 15: Lid member 16: Through hole 20: Inert gas flow means 21: Inner wall of heat insulation chamber 25: Heat insulation chamber 26: Heater member 28: Upward flow 30: Solder pressure feeding means 31: Power transmission means 32: Shaft 33: Motor 34: Impeller

Claims

1. A local soldering method for soldering a desired location on a substrate by discharging a required amount of molten solder from a nozzle protruding upward, and at this time, filling at least the atmosphere around the tip of the nozzle with an inert gas and bringing the molten solder into contact with the substrate, wherein: The local soldering method is characterized in that the temperature of the inert gas flowing from the upper end of the nozzle to the lower surface of the substrate is equal to or higher than the melting temperature of the molten solder discharged from the nozzle.

2. The local soldering method according to claim 1, wherein the inert gas is nitrogen gas or argon gas.

3. The local soldering method according to claim 1, wherein the temperature of the inert gas flowing from the upper end of the nozzle to the lower surface of the substrate is equal to or higher than the melting temperature of the molten solder discharged from the nozzle and is equal to or lower than 350°C.

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