JP2004207645A - Method and device for reflow soldering - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and device for maintaining rapid and high quality soldering in a reflow soldering using a cream solder. <P>SOLUTION: The method comprises steps of: vacuum drying for defoaming and drying foam, solvent component, moisture or the like included in the cream solder; and partially heating a soldering part of a circuit board for a short period of time at not less than a solder melting point on the circuit board. The vacuum drying is conducted at a temperature not more than heat-resistant temperature of a heat-resistant component which comes under the influence of temperature limit in the circuit board before the heating step. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a reflow soldering method and a soldering apparatus for soldering electronic components to a printed circuit board.
[0002]
[Prior art]
Conventionally, as a reflow soldering method for soldering electronic components to a printed circuit board, hot air or infrared light is used as a heat source, and the printed circuit board is heated uniformly from preheating to reflow heating. After vacuum drying at room temperature, there is a method of uniformly heating the entire circuit board by reflow main heating.
[0003]
FIG. 3 shows a conventional method of uniformly heating the entire substrate by reflow main heating after vacuum drying at room temperature (see Patent Document 1). 3, the soldering apparatus includes a printed circuit board 100, a board transport unit 101, a vacuum drying unit 102, a vacuum pump unit 103, a reflow heating furnace unit 104, and a cooling unit 105.
[0004]
In such a configuration, the air in the sealed container is sucked by the vacuum pump unit 103 while the entire printed circuit board 100 is carried into the vacuum drying unit 102, and is maintained in a vacuum state. During this time, the cream solder on the substrate 100 is dried uniformly at room temperature. After the drying process, the vacuum is broken, the printed circuit board 100 is taken out, and the printed circuit board 100 is carried into the reflow heating furnace unit 104. In the reflow heating furnace unit 104, the entire printed circuit board 100 is uniformly heated to a temperature equal to or higher than the solder melting temperature, and the electronic components are reflow soldered to the printed circuit board 100 through a temperature profile process shown in FIG. Attached.
[0005]
[Patent Document 1]
JP-A-3-207573
[Problems to be solved by the invention]
However, the above-mentioned conventional reflow soldering method has the following problems.
[0007]
First, there is a problem that productivity is poor because the processing is performed over 60 seconds or more for the vacuum drying processing time and 60 seconds or more for the reflow heating time.
[0008]
Second, in the reflow heating section, the heat-resistant temperature of components that are limited by the heating temperature, such as CCD image sensors, camera modules, crystal oscillators, and optically mounted components, is determined by the solder melting point in order to uniformly heat the entire circuit board. There is a problem that weak heat-resistant components having a temperature lower than the temperature cannot be simultaneously packaged by reflow mounting.
[0009]
Third, if the vacuum drying step and the reflow heating step are performed in a short time, the solvent, moisture, and air bubbles remaining in the cream solder are rapidly heated during the reflow heating because the drying is completed in an insufficient state. There is a problem that bumping occurs due to an increase in temperature, and soldering defects such as solder balls and chip standing occur.
[0010]
In view of the above problems, the present invention sufficiently dries and defoams the solvent, moisture, and air bubbles remaining in the cream solder in advance by heating and vacuuming the printed circuit board on which the electronic components are mounted on the cream solder. Accordingly, even when the temperature is rapidly increased in the case of performing the reflow heating bonding process in a short time, bumping of the solvent, moisture, and bubbles in the cream solder can be suppressed. As described above, an object of the present invention is to provide a soldering method and apparatus capable of suppressing the cause of the occurrence of standing of a solder ball or a chip, performing reflow soldering in a short time while maintaining high quality, and realizing high productivity. It is another object of the present invention to provide a soldering method and apparatus capable of performing reflow soldering by performing local reflow heating and joining in a short time while protecting weak heat-resistant parts of a component that is restricted by temperature.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, the reflow soldering method of the present invention, a circuit board, air bubbles contained in cream solder, solvent component, defoaming, etc., a vacuum drying step of drying, drying the circuit board, A heating step of heating the soldered portion partially, for a short time, to a temperature equal to or higher than the melting point of the solder; The method is characterized in that the vacuum drying step is performed.
[0012]
Further, the reflow soldering apparatus of the present invention encloses the circuit board on which the electronic components are mounted in a closed space, in a vacuum atmosphere, and at a temperature equal to or lower than the heat-resistant temperature of the weak heat-resistant component subjected to the temperature limitation in the circuit board. A vacuum drying unit for defoaming and drying air bubbles, solvent components, moisture, etc. contained in the cream solder, and partially heating the vacuum-dried circuit board at a temperature equal to or higher than the melting point of the cream solder for a short time. A heating unit, a first substrate transport unit that transports the circuit board to the vacuum drying unit, and a second substrate transport unit that transports the circuit board from the vacuum drying unit to the heating unit. I do.
[0013]
According to the reflow soldering method and the soldering apparatus of the present invention, by performing the vacuum drying process in a heated state, the solvent contained in the cream solder, the saturated vapor pressure of moisture is increased, and drying is promoted, and in several tens of seconds. The necessary drying is completed. In the drying step, a constant degree of vacuum is maintained for a predetermined time, so that the cream solder is sufficiently dried and bubbles contained in the paste can be sufficiently defoamed. This eliminates the problem of soldering defects such as solder balls and chip standing caused by bumping of the solvent, moisture, and bubbles remaining in the cream solder due to sudden heating by reflow heating. Rapid reflow heating can be performed in a short time of not more than ten seconds. Therefore, both the vacuum drying step and the reflow heating step can be performed in a short time, and high productivity can be realized.
[0014]
Furthermore, in the reflow heating section, the component soldering section can be heated rapidly, so that the parts that are limited by the heating temperature, such as CCD image sensors, camera modules, crystal oscillators, optical mounting parts, etc. The soldered portion in the printed circuit board can be simultaneously reflow-soldered while the weakly heat-resistant part of the weakly heat-resistant component having a temperature equal to or lower than the melting point of the solder is suppressed to a temperature equal to or lower than the restriction temperature.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a representative embodiment of the present invention will be described.
[0016]
(Embodiment 1)
In FIG. 1, 1 is a printed circuit board (hereinafter, referred to as a circuit board), 2 is a first board transfer section for transferring the circuit board 1, and 3 is a transfer board for heating and drying the circuit board 1 to a vacuum drying section 4. The second substrate transport unit 5 is a third substrate transport unit that transports the circuit board 1 to the local reflow heating unit 6, and the cooling unit that cools the circuit board 1 heated by the local reflow heating unit 6. The heating vacuum drying unit 4 includes an entrance shutter 4a, an exit shutter 4b, a positioning stopper 4c, a vacuum circuit unit 4d, a vacuum suction unit 4e, a vacuum breaking unit 4f, and an infrared heater 4g. The local reflow heating section 6 includes a laser oscillation section 6a and a mirror section 6b.
[0017]
The reflow soldering apparatus configured as described above will be described with reference to FIG. A circuit board 1 mounted with a weak heat-resistant component formed of a component having a heat-resistant temperature of a part lower than the solder melting point of a part constituting an electronic component is on standby in the first substrate transport unit 2. When the entrance shutter 4a of the heating vacuum drying unit 4 opens the substrate carrying-in port, the circuit board 1 waiting in the first carrying unit 2 is sent to the second substrate carrying unit 3, and the circuit board 1 reaches the positioning stopper 4c. Then, the entrance shutter 4a and the exit shutter 4b are closed, and the heating vacuum drying unit 4 is closed. The vacuum circuit unit 4d senses that the airtightness has been closed, and sucks air in the heating vacuum drying unit 4 from the vacuum suction unit 4e. During this time, the circuit board 1 is heated by the infrared heater 4g. The vacuum circuit section 4d detects that a predetermined degree of vacuum has been reached and the required processing time has elapsed, and air or an inert gas is injected into the heating vacuum drying section 4 from the vacuum breaking section 4f to break the vacuum. After the vacuum circuit section 4d detects that the pressure has returned to substantially the atmospheric pressure, the outlet shutter 4b is opened, and the circuit board 1 is carried out of the heating vacuum drying section 4 and delivered to the third substrate transport section 5. The circuit board 1 is stopped at a predetermined position in the local reflow heating section 6 by the third board transport section 5. Then, the laser is oscillated for a predetermined time from the oscillator of the laser oscillating unit 6a toward a predetermined soldering position on the stopped circuit board 1, and is radiated to the predetermined position by the mirror unit 6b.
[0018]
For example, when a semiconductor laser is used, 4 W of energy is irradiated to one soldering location for 60 ms to melt the solder, and local reflow heating of 166 soldering locations can be performed in 10 seconds.
[0019]
As described above, according to the present embodiment, the circuit board 1 on which the weak heat-resistant component formed of a component having a lower heat-resistant temperature of a part of the electronic component than the solder melting point is mounted is first replaced with the heat-resistant temperature of the part. By performing vacuum processing while heating with the infrared heater 4g to the following level, the saturated vapor pressure of the solvent and water contained in the cream solder increases, and the cream solder dries in a shorter time.
[0020]
In addition, degassing of gas contained in the cream solder is also promoted. In this way, the cream solder can be completely dried in a short period of time, preventing the solvent, moisture, and bubbles in the cream solder from bumping even if the temperature rises sharply due to local reflow heating by laser. It is possible to suppress the occurrence of standing of solder balls and chips, and to finish reflow soldering of the circuit board in a short time of several tens of seconds while maintaining high quality. Further, by performing local heating in a very short time, reflow soldering can be performed while maintaining the heat resistant temperature of the weak heat resistant component.
[0021]
(Embodiment 2)
In the first embodiment, the configuration is described in which the laser is used as the heating medium in the local reflow heating unit, but a light beam may be used as the heating medium. FIG. 2 shows an example. The components having the same functions as those of the first embodiment will be described using the same reference numerals.
[0022]
In FIG. 2, 1 is a circuit board, 2 is a first board transfer section, 3 is a second board transfer section, 5 is a third board transfer section, 4 is a heating vacuum drying section, and 6 is local reflow. The heating unit 7 is a cooling unit. The heating vacuum drying unit 4 includes an entrance shutter 4a, an exit shutter 4b, a positioning stopper 4c, a vacuum circuit unit 4d, a vacuum suction unit 4e, a vacuum breaking unit 4f, and an infrared heater 4g. The local reflow heating unit 6 includes a light beam irradiation unit 6c.
[0023]
The reflow soldering apparatus configured as described above will be described with reference to FIG. A circuit board 1 on which a weak heat-resistant component formed of a component having a lower heat-resistant temperature than a solder melting point of a part of the electronic component is waiting in the first substrate transport unit 2. When the entrance shutter 4a of the heating vacuum drying unit 4 opens the substrate carrying-in port, the circuit board 1 waiting in the first carrying unit 2 is sent to the second substrate carrying unit 3, and the circuit board 1 reaches the positioning stopper 4c. Then, the entrance shutter 4a and the exit shutter 4b are closed, and the heating vacuum drying unit 4 is closed. The vacuum circuit unit 4d senses that the airtightness has been closed, and sucks air in the heating vacuum drying unit 4 from the vacuum suction unit 4e. During this time, the circuit board 1 is heated by the infrared heater 4g. The vacuum circuit section 4d detects that a predetermined degree of vacuum has been reached and the required processing time has elapsed, and air or an inert gas is injected into the heating vacuum drying section 4 from the vacuum breaking section 4f to break the vacuum. After the vacuum circuit section 4d detects that the pressure has returned to substantially the atmospheric pressure, the outlet shutter 4b is opened, and the circuit board 1 is carried out of the heating vacuum drying section 4 and delivered to the third substrate transport section 5. The circuit board 1 is stopped at a predetermined position in the local reflow heating section 6 by the third board transfer section 5. Then, the light beam is irradiated from the light beam irradiation unit 6c to a predetermined position for a predetermined time toward a predetermined soldering position on the stopped circuit board 1.
[0024]
For example, when using a light beam condensed by a xenon lamp, the soldering points existing in the area having a diameter of about 20 mm are collectively locally irradiated, and if the solder is melted, the soldered part is locally irradiated in about 10 seconds. Reflow heating can be performed. When there is a component that the user does not want to raise the temperature in the irradiation area, the temperature rise can be partially suppressed by applying a mask that blocks light even in the irradiation area due to the straightness of the light beam.
[0025]
As described above, according to the present embodiment, the circuit board 1 on which the weak heat-resistant component formed of a component having a lower heat-resistant temperature of a part of the electronic component than the solder melting point is mounted is first replaced with the heat-resistant temperature of the part. By performing vacuum processing while heating with the infrared heater 4g to the following level, the saturated vapor pressure of the solvent and water contained in the cream solder increases, and the cream solder dries in a shorter time. In addition, degassing of gas contained in the cream solder is also promoted. In this way, sufficient drying of the cream solder can be completed in a short period of time, preventing the solvent, moisture, and bubbles in the cream solder from bumping even if the temperature rises sharply due to local reflow heating with a light beam. It is possible to suppress the occurrence of standing of solder balls and chips, and to finish reflow soldering of the circuit board in a short time of several tens of seconds while maintaining high quality. Further, by performing local heating in a very short time, reflow soldering can be performed while maintaining the heat resistant temperature of the weak heat resistant component.
[0026]
In the above-described embodiment, a configuration is described in which a laser or a light beam is used as a heating medium in the local reflow heating unit. However, the same effect is exerted by using hot air from a nozzle as the heating medium.
[0027]
【The invention's effect】
As described above, according to the reflow soldering method and the soldering apparatus of the present invention, a printed circuit board on which electronic components are mounted on cream solder is first heated and vacuum-processed at a temperature not higher than the heat-resistant temperature of a weak heat-resistant component subject to temperature restrictions. By drying and defoaming, it is possible to prevent bumping of the solvent and moisture in the cream solder, even if the temperature rises sharply when heating and joining at a temperature equal to or higher than the melting point of the solder. The occurrence of chip standing can be suppressed. Furthermore, since reflow soldering can be performed in a short time while maintaining high quality, the thermal influence on weak heat-resistant parts can be reduced as much as possible, and productivity is improved.
[Brief description of the drawings]
FIG. 1 is a schematic explanatory view of a reflow soldering apparatus according to a first embodiment of the present invention, in which (a) is a top explanatory view of the configuration, (b) is a side explanatory view of the configuration, and (c). FIG. 3 is an explanatory diagram of a temperature profile of the same device.
FIGS. 2A and 2B are schematic explanatory diagrams of a reflow soldering apparatus according to a second embodiment of the present invention, wherein FIG. 2A is a top explanatory diagram of the configuration, FIG. 2B is a lateral explanatory diagram of the configuration, and FIG. FIG. 3 is an explanatory diagram of a temperature profile of the same device.
3A and 3B are schematic explanatory views of a conventional reflow soldering apparatus, in which FIG. 3A is an explanatory view of the configuration, and FIG. 3B is an explanatory view of a temperature profile of the same apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Circuit board 2 1st board conveyance part 3 2nd board conveyance part 4 Vacuum drying part (heating vacuum drying part)
4g infrared heater 6 heating unit (local reflow heating unit)
6c Light beam irradiation unit

Claims (5)

In the method for reflow soldering a circuit board on which electronic components are mounted, for the circuit board, air bubbles contained in cream solder, a solvent component, moisture and the like are defoamed and dried, and a vacuum drying step of drying the circuit board, Partially, for a short time, having a heating step of heating to a temperature equal to or higher than the melting point of the solder, and before the heating step, at a temperature equal to or lower than the heat-resistant temperature of the weak heat-resistant component subjected to the temperature limitation in the circuit board. A reflow soldering method, wherein the vacuum drying step is performed. Air bubbles and solvents contained in the cream solder on the circuit board at a temperature lower than the heat resistance temperature of the weak heat-resistant parts that are confined to the circuit board on which the electronic components are mounted in a closed space in a vacuum atmosphere and at a temperature within the circuit board A vacuum drying unit for defoaming and drying components, moisture, etc., a heating unit for partially heating the vacuum-dried circuit board at a temperature equal to or higher than the melting point of cream solder, and a heating unit for heating the circuit board, A reflow soldering apparatus, comprising: a first substrate transport unit that transports a circuit board to a vacuum drying unit; and a second substrate transport unit that transports the circuit board from the vacuum drying unit to the heating unit. 3. The reflow soldering apparatus according to claim 2, wherein the heating in the vacuum drying unit includes placing an infrared heater above, below, or both above and below the circuit board. 4. The reflow soldering apparatus according to claim 2, wherein a light beam obtained by condensing light of a laser or a lamp is used as a heat source of the heating unit. The reflow soldering apparatus according to claim 2, wherein local heating by hot air from a nozzle is used as a heat source of the heating unit.

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