JP2000183511A - Reflow soldering method and its device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflow soldering method for stably operating reflow soldering, even when using lead free solder whose fusing temperature is high, or even to a circuit board on which parts whose heat capacity is much different or a part whose heat-resistance is deteriorated are placed. SOLUTION: In this reflow soldering method, cream solder is printed on a circuit board 1, and parts are placed on the circuit board 1, and the circuit board 1 is carried in a preliminary heating part 2 so as to be heated preliminarily, and carried in a reflow part 3 so as to be heated at a cream solder fusing point or higher, and reflow soldering can be attained and carried in a cooling part 5 to be cooled. In this case, the carrying speed in the preliminary heating part 2, and the carrying speed in the reflow part 3, and the carrying speed in the cooling part 5 can be made different, and are set to be an optimal speed. Thus, a difference between the temperature of a part whose temperature is easily increased and the temperature of a part whose temperature hardly increases can be reduced, and the temperature control of a part whose heat resistance is deteriorated can be ensured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflow soldering method and a reflow soldering apparatus for soldering a surface mount component such as a chip component on a circuit board.

[0002]

2. Description of the Related Art A conventional reflow soldering apparatus and a conventional reflow soldering method will be described with reference to FIGS.

As shown in FIG. 4, in a reflow soldering apparatus B, a preheating zone 22, a reflow zone 23, and a cooling zone 24 are arranged from a loading side to a loading side of a circuit board 21. In the conventional reflow soldering apparatus B, one conveyor 25 disposed from the entrance to the exit of the reflow soldering apparatus mounts the circuit board 21 to be reflowed and transports the circuit board 21 from the entrance to the exit. ing. The preheating zone 22 and the reflow zone 23 are respectively provided with heat from the heater 26 and hot air 27 blown out from the hot air blowing means 27.
a, and the circuit board 21 which has been reflowed in the cooling zone 24 is cooled by the cooling fan 28.

In the conventional reflow soldering method, a circuit board 21 to be reflowed is placed on a conveyor 25 in FIG. 4 and is conveyed at a constant speed in the direction of an arrow.
In the preheating zone 22, the heater 26 and the hot air 27 a blown from the hot air jetting means 27 are heated as a whole to preheat to a predetermined preheating temperature, and in the reflow zone 23, the heater 26 and the hot air jetting means 27 are heated.
Is heated to a predetermined reflow temperature to melt the solder, and the reflowed circuit board 21 is cooled to a predetermined cooling temperature by a cooling fan 28 in the cooling zone 24. Thus, the molten solder is cooled and hardened to complete the reflow soldering.

[0005]

However, in the above-mentioned conventional reflow soldering method, the circuit board 21 is conveyed at a constant speed through the preheating zone 22, the reflow zone 23 and the cooling zone 24 by one conveyor 25. Since each zone is configured to be entirely heated or cooled to a predetermined predetermined preheating temperature, a predetermined reflow temperature, and a predetermined cooling temperature, the temperature on the circuit board 21 rises most as shown in FIG. A temperature difference ΔT of about 40 ° C. to 70 ° C. occurs in the reflow zone between the temperature profile 31 of the hard-to-react portion and the temperature profile 32 of the portion on the circuit board 21 where the temperature is most likely to rise.

The above-mentioned temperature difference ΔT is due to the difference in the size and heat capacity of the components mounted on the circuit board 21.
When the soldering temperature of the lead of a large package IC where the temperature is difficult to rise is raised to the target temperature, the small chip parts where the temperature is easy to rise are heated more than necessary, and are damaged or deteriorated in characteristics. Occurs. Conversely, if the soldering temperature of the electrode part of a small chip component is raised only to the required minimum temperature, a large package IC
In the lead portion, the solder does not reach the melting point of the solder and the solder is in an unmelted state, which causes a problem that an open failure occurs in which electrical connection between the lead portion and the circuit board 21 cannot be obtained.

[0007] Further, the following problems also exist for weak heat-resistant parts for which the guarantee conditions during reflow are severe. For example, in the case of an aluminum electrolytic capacitor, the peak temperature at the time of reflow is regulated to 230 ° C. or less, and the holding time at 200 ° C. or more is regulated to 30 seconds or less.

However, if the temperature of the lead portion of the large package IC is raised to the melting point of the solder, the guarantee conditions at the time of reflow of the aluminum electrolytic capacitor cannot be satisfied, and after the reflow, the electrolyte in the aluminum electrolytic capacitor leaks out.
There was a problem that the pattern on the circuit board 21 was corroded and disconnected, so it was difficult to reflow solder the large package IC and the aluminum electrolytic capacitor on the same circuit board 21.

The above-mentioned temperature difference ΔT at the time of reflow is caused by the fact that the degree of the temperature rise differs depending on the material of parts due to convection heating by hot air or the like and radiant heating by infrared rays or the like.

When used electronic equipment is discarded outdoors or the like, lead contained in solder used in the electronic equipment may be eluted by acid rain or the like. Therefore, in order to prevent such a problem, use of a solder material (lead-free solder) obtained by removing lead from the solder material has been accelerated in recent years. However, the characteristic of this lead-free solder material is that even materials close to the level that can currently be mass-produced have a higher melting point than conventional eutectic solders containing lead.
It shows a tendency that the wettability is poor. For this reason, when performing reflow soldering, it is required to set more strict heating conditions than the conventional reflow soldering method. In the case of using lead-free solder, depending on the type of the circuit board 21, these conditions must be set. There also arises a problem that the width becomes further smaller and soldering becomes impossible.

[0011] The present invention solves the above-mentioned problems, and when lead-free solder having a high melting temperature is used, the size and heat capacity which cannot be processed by the conventional reflow soldering method and its apparatus are greatly reduced. It is an object of the present invention to provide a reflow soldering method and a reflow soldering apparatus that can stably perform reflow soldering even on a circuit board on which different components or components having poor heat resistance are mounted. .

[0012]

In order to solve the above problems, the present invention provides a method of printing cream solder on a circuit board,
The components are placed thereon, the circuit board is transported in the preheating section and preheated, the solder paste is transported in the reflow section and the cream solder is heated to the melting point or higher and reflow soldered, and the circuit board is transported in the cooling section. In the reflow soldering method for cooling, at least a part of the speed of conveying the inside of the preheating unit, the speed of conveying the inside of the reflow unit, and the speed of conveying the inside of the cooling unit is different.

According to this method, when a lead-free solder having a high melting temperature is used, a component having a size and a heat capacity which cannot be processed by the conventional reflow soldering method and a component having a significantly different heat capacity or a component having poor heat resistance are mounted. Reflow soldering can be stably performed on the placed circuit board.

[0014]

According to the present invention, a cream solder is printed on a circuit board, and a component is placed thereon.
In the reflow soldering method in which the circuit board is conveyed in a preheating section and preheated, the cream solder is conveyed in the reflow section and the cream solder is heated to a melting point or higher and reflow soldered, and the inside of the cooling section is conveyed and cooled. It is characterized in that at least a part of the speed of transporting in the preheating unit, the speed of transporting in the reflow unit, and the speed of transporting in the cooling unit are different.

According to a third aspect of the present invention, there is provided a preheating section for printing a cream solder and preheating a circuit board on which components are mounted, and a melting point of the cream solder of the preheated circuit board. A reflow section for performing reflow soldering by heating as described above, a cooling section for cooling the reflow-soldered circuit board, and a circuit board for reflow soldering, In a reflow soldering apparatus, comprising: a transport unit that transports a circuit board from an inlet to an outlet of the cooling unit; wherein the transport unit transports a circuit board in the preheating unit; and a circuit board in the reflow unit. A second transport unit that transports
It is characterized in that it is divided into a third transport section for transporting the circuit board in the cooling section.

According to the reflow soldering method and the reflow soldering apparatus, the speed of transporting in the preheating section, the speed of transporting in the reflow section, and the speed of transporting in the cooling section are set to optimal speeds. By that
Since the difference between the temperature of components that tend to increase in temperature and the temperature of components that do not tend to increase in temperature can be reduced and the heating or cooling control of the components can be performed finely, the temperature regulation of components with poor heat resistance is restricted. It can be guaranteed for sure.
For example, the peak temperature during reflow is 230 ° C.
The temperature regulation of the aluminum electrolytic capacitor in which the holding time at 0 ° C. or more is 30 seconds or less can be reliably ensured. In this case, the circuit board on which the aluminum electrolytic capacitor is mounted is conveyed in a preheating unit controlled to 200 ° C. or less by the first conveying unit having a low speed, and is heated to a temperature close to 200 ° C. with time, It is sufficient that the aluminum electrolytic capacitor is passed through the reflow unit in which the top surface temperature of the aluminum electrolytic capacitor is controlled to 230 ° C. or lower in 30 seconds or less in the second conveying unit having a high speed. As a result, it is always possible to guarantee the temperature regulation of the reflow soldering of various components such as an aluminum electrolytic capacitor, which has been difficult to guarantee by the conventional reflow soldering method and the reflow soldering apparatus.

According to a second aspect of the present invention, in the reflow soldering method according to the first aspect, the calorific value of the convection heating and the radiant heating at a location near the transfer route of the circuit board is measured by a calorimeter. The measured data of convection heating and radiant heating are compared with calorific value data of convective heating and radiant heating corresponding to a preset temperature, and data for correcting the deviation so as to be smaller is fed back to the heating source. Soldering is performed while controlling the amount of heat in an optimal balance.

According to a fourth aspect of the present invention, in the reflow soldering apparatus according to the second aspect, the convection heating and the radiant heating are performed at positions where the preheating section, the reflow section, and the cooling section do not come into contact with the conveyed circuit board. A calorimeter to measure the temperature, compare the measured data of the calorimeter with the calorie data of convection heating and radiant heating corresponding to the preset temperature, and heat the data to correct the deviation so as to reduce the deviation. By providing feedback to the source, control means is provided for performing soldering while controlling the amount of heat of convection heating and radiant heating to an optimal balance.

According to the reflow soldering method according to the third aspect and the reflow soldering apparatus according to the fourth aspect, the amounts of convective heating and radiant heating in the preheating section, the reflow section, and the cooling section are optimized. Soldering can be performed while controlling the balance. And in this way, especially in a circuit board having an aluminum electrolytic capacitor or the like in the preheating section of the circuit board, the amount of radiant heating by infrared rays is made larger than the amount of convective heating, thereby reducing the temperature rise of the aluminum electrolytic capacitor body. Since the temperature difference can be suppressed, the temperature difference on the circuit board in the preheating unit can be reduced. For this reason,
The temperature regulation of the reflow soldering of the aluminum electrolytic capacitor is always guaranteed, and the reflow soldering can be performed.

An embodiment of the reflow soldering method and the reflow soldering apparatus according to the present invention will be described below with reference to FIGS. As shown in FIG. 1, in a reflow soldering apparatus A of the present embodiment, a preheating unit 2 divided into first and second zones from a loading side to a loading side of a circuit board 1 and a cream solder A reflow section 3 for heating the material to a temperature equal to or higher than its melting point and performing reflow soldering, and a cooling section 5 having a cooling fan 4 are sequentially arranged. The pre-heating unit 2 and the reflow unit 3 are heated by infrared rays from the infrared panel 6 and hot air 7a blown from the hot air blowing means 7, respectively.

A conveyer for conveying the circuit board 1 includes a first conveyer 8a for conveying the circuit board 1 in the preheating section 2 and a circuit board 1 for conveying the circuit board 1 in the reflow section 3.
And a third conveyor 8c for transporting the circuit board 1 in the cooling unit 5. The speeds of the first, second, and third conveyors 8a, 8b, 8c can be freely set, and can be set to be equal speeds, to set higher or lower speeds, or to set one speed at a time. You can also stop it.

In the reflow soldering apparatus A, one or more (a plurality of cases are shown) calorimeters 9 for measuring convection heat and radiant heat are installed. One of the purposes of providing the first, second, and third conveyors 8a, 8b, 8c is to assure temperature regulation during reflow of parts having poor heat resistance. For example, the temperature regulation of the aluminum electrolytic capacitor in which the peak temperature at the time of reflow is 230 ° C. or less and the holding time at 200 ° C. or more is 30 seconds or less is to be surely guaranteed. In this case, the circuit board 1 on which the aluminum electrolytic capacitor is mounted is conveyed in the preheating unit 1 controlled to 200 ° C. or less by the first conveyor 8a having a low speed, and it takes time to reach a temperature close to 200 ° C. It may be heated and passed through the reflow section in which the top surface temperature of the aluminum electrolytic capacitor is controlled to 230 ° C. or less by the second conveyor 8b having a high speed in 30 seconds or less. As a result, even in the case of lead-free solder having a high melting point, the temperature regulation of the reflow soldering of the aluminum electrolytic capacitor, which was difficult to assure with the conventional reflow soldering method and its apparatus, can always be guaranteed.

Further, according to the reflow soldering apparatus A of the present embodiment, as shown in FIG. 2, components having significantly different dimensions and heat capacities mounted on one circuit board 1 have small temperature differences. Heating can be performed with the temperature profiles 11 and 12. A component having a small size or heat capacity is heated in a state indicated by a temperature profile 11, and a component having a large size or heat capacity is heated in a state indicated by a temperature profile 12. Comparing this with the conventional reflow soldering method shown in FIG. 5 and the temperature profile 13 of a component having a large size and heat capacity in the apparatus, the conventional reflow soldering method produces large temperature differences Δt ₁ and ΔT ₁ . However, according to the reflow soldering method in the present embodiment, the temperature differences Δt ₂ and ΔT ₂ can be reduced.

A reflow soldering method by the reflow soldering apparatus A for an example of a combination of various components mounted on the circuit board 7 will be described below with reference to FIGS.

Pattern 1: When only components having substantially the same heat capacity and heat resistance are mounted on the circuit board 1 (a general case), the first, second, and third conveyors 8a,
The speeds of 8b and 8c are set equal. The preheating unit 2
Control is performed so that the circuit board 1 is heated to a temperature of 200 ° C. or less. The reflow unit 3 controls the circuit board 1 to be heated to a melting point of 230 ° C. or lower. That is, reflow soldering is performed by the same operation as the conventional reflow soldering method. In this case, since the heat capacity and the heat resistance of the components mounted on the circuit board 1 are almost equal, even if the speeds of the first, second, and third conveyors 8a, 8b, 8c are set to be equal. As shown in FIG. 3, all the lands of the circuit board 1 are heated to a predetermined temperature of 200 ° C. or lower in the preheating unit 2 and heated to a melting point of the solder or higher in the reflow unit 3. Then, cooling is completed in the cooling unit 3 within a predetermined time, and soldering is performed.

Pattern 2: When a small component, a large package IC and an aluminum electrolytic capacitor are mounted on the circuit board 1, the speed of the first conveyor 8a is set to be low, and the circuit board 1 is preheated. It is set so that it is transported for a relatively long time in the section 2 and the circuit board 1
The second conveyor 8b is set at a higher speed so that the second conveyor 8b passes through the reflow unit 2 within about 30 seconds. That is, the preheating unit 2 controls so that the small components of the circuit board 1 and the aluminum electrolytic capacitor are heated to a temperature of 200 ° C. or less over time. The reflow unit 3 controls the small components of the circuit board 1 and the aluminum electrolytic capacitor so that the top surface temperature of the aluminum electrolytic capacitor is heated to 230 ° C. or less. At this time, the data from one or more convection and radiant calorimeters 9 installed in the reflow soldering apparatus A is corrected while comparing it with a preset temperature, and the temperature rise of the aluminum electrolytic capacitor is always suppressed. While heating.

Since the speed of the first conveyor 8a is low, the small components on the circuit board 1 and the aluminum electrolytic capacitor are heated to a predetermined temperature close to 200.degree. Large package I
C is also heated to a predetermined temperature close to 200 ° C. of the preheating unit 2, but since this temperature range is outside the temperature regulation of the aluminum electrolytic capacitor, there is no problem even if heating is performed over a long time. As described above, the small component heated to a predetermined temperature close to 200 ° C. and the aluminum electrolytic capacitor can be moved within 30 seconds within the reflow unit 3 in which the top surface temperature of the aluminum electrolytic capacitor is set to 230 ° C. or less. A large package IC that has sufficiently reached the solder melting temperature when passing therethrough and has a large heat capacity heated to a predetermined temperature close to 200 ° C. at the same time passes through the inside of the reflow unit 3 where the top surface temperature of the aluminum electrolytic capacitor is set to 230 ° C. or less. When it passes within 30 seconds, it sufficiently reaches the solder melting temperature storage.

In the case of an aluminum electrolytic capacitor, the infrared ray is used as a heating source, and the temperature of the aluminum electrolytic capacitor body is raised by utilizing the property that aluminum, which is the case of the aluminum electrolytic capacitor body, reflects infrared rays. It is possible to lower it. Therefore, if there is an aluminum electrolytic capacitor,
In this case, by increasing the ratio of radiant heating by infrared rays to the ratio of convective heating by hot air, it is possible to raise the electrode portion of the aluminum electrolytic capacitor to the soldering temperature while suppressing a rapid rise in the temperature of the aluminum electrolytic capacitor body.

In any case, at least one calorimeter 9 is placed at a position of the pre-heating unit 2, reflow unit 3, and cooling unit 5 where the conveyors 8a, 8b, and 8c do not contact the conveyed circuit board 1. In the installed state, the temperature preset in the apparatus for each circuit board 1 is compared with data obtained by measuring the amount of heating by convection heating and radiant heating in each zone, and the temperature variation is corrected, The corrected data is fed back to the heating source while controlling so that the convection heating and the radiant heating calorie have the optimal balance with respect to the temperature of the day mark, and the infrared panel 6 as the heating source and the hot air blowing means 7 are connected to each other. Adjust the heating amount. Thereby, the entire surface of the circuit board 7 can be soldered in a uniform state.

The aluminum electrolytic capacitor is connected to the circuit board 1
When mounted above, aluminum, which is the case of the aluminum electrolytic capacitor body, has the property of reflecting infrared rays, so if this property is used, the temperature rise of the aluminum electrolytic capacitor body will be suppressed and other temperatures will be reduced. It is possible to secure a soldering temperature for a portion that is difficult to rise. In other words, if there is an aluminum electrolytic capacitor, the electrode heating is suppressed while suppressing the rapid temperature rise of the aluminum electrolytic capacitor main body by increasing the radiant heating ratio by infrared rays in the preheating unit 2 to be higher than the convective heating ratio by hot air. Can be raised to temperature.

Further, since the cooling rate can be changed, it is possible to prevent the formation of a low melting point alloy layer at the interface between the component electrode and the solder and the interface between the substrate electrode and the board during the cooling of the solder when the lead-free solder is used. As a result, soldering using lead-free solder can be performed favorably without lowering the joining strength of components, and joining reliability can be increased.

The number of calorimeters 9 for measuring the amount of convective heat and the amount of radiant heat can be measured more precisely and the actual control can be performed more precisely if provided in large numbers. However, the present invention is not limited to this. Only one may be used, and in this case, control processing and the like can be performed relatively easily. Further, in the above embodiment, the case where the conveyor is divided into three parts has been described, but it is also possible to further divide the conveyor.

[0033]

As described above, according to the reflow soldering method of the present invention, the speed of transporting in the preheating section, the speed of transporting in the reflow section, and the speed of transporting in the cooling section are made different. , Components with small heat capacity mounted on circuit board, large package IC with large heat capacity,
Reflow soldering of parts that could not be reflow-soldered in the past, which can stably heat aluminum electrolytic capacitors, etc., which have poor heat resistance, with a small temperature difference and above the solder melting temperature within the range of temperature regulation of each part. The effect of enabling attachment is obtained. Furthermore, because the cooling rate can be changed, when using lead-free solder,
It is possible to prevent the formation of a low-melting alloy layer at the interface between the component electrodes and the solder and the interface between the board electrodes during solder cooling, and it is possible to perform good soldering with lead-free solder without lowering the joint strength of the components Thus, the joining reliability is increased.

According to the reflow soldering apparatus of the present invention, the conveying means includes a first conveying section for conveying the circuit board in the preheating section, and a second conveying section for conveying the circuit board in the reflow section. And a third transfer unit for transferring the circuit board in the cooling unit, so that the speed for transferring the inside of the preheating unit, the speed for transferring the inside of the reflow unit, and the speed for transferring the inside of the cooling unit are different. Can be easily performed.

[Brief description of the drawings]

FIG. 1 is a schematic side view of a reflow soldering apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a temperature profile by a reflow soldering method according to the embodiment of the present invention.

FIG. 3 is a diagram showing a temperature profile by a separate reflow soldering method of the reflow soldering apparatus according to the embodiment of the present invention.

FIG. 4 is a schematic side view of a conventional reflow soldering apparatus.

FIG. 5 is a diagram showing a temperature profile according to a conventional reflow soldering method.

[Explanation of symbols]

 A Reflow soldering apparatus 1 Circuit board 2 Preheating section 3 Reflow section 5 Cooling section 8a First conveyor (first transport section) 8b Second conveyor (second transport section) 8c Third conveyor (third transport section) 9) Calorimeter

Claims (4)

[Claims] 1. A solder paste is printed on a circuit board, a component is placed thereon, and the circuit board is transported in a preheating section and preheated. In the reflow soldering method of heating and performing reflow soldering and transporting and cooling in the cooling unit, the speed of transporting in the preheating unit, the speed of transporting in the reflow unit, and the speed of transporting in the cooling unit A reflow soldering method characterized in that at least a part of the speed is made different. 2. A calorimeter for measuring the amount of heat of convection heating and radiant heating at a location near the transfer route of the circuit board,
The measurement data of the calorimeter is compared with the calorie data of the convection heating and the radiant heating corresponding to the preset temperature, and the data for correcting the deviation to be small is fed back to the heating source, so that the convection heating and the convection heating are performed. The reflow soldering method according to claim 1, wherein the soldering is performed while controlling the amount of heat of the radiant heating with an optimal balance. 3. A preheating unit for printing a cream solder and preheating a circuit board on which components are mounted, and a reflow solder by heating the cream solder of the preheated circuit board to a melting point or higher. A reflow section for performing mounting, a cooling section for cooling the reflow-soldered circuit board, and a circuit board on which the reflow soldering is to be performed, and an exit of the cooling section from an entrance of the preheating section. And a transfer unit for transferring the circuit board in the preheating unit, and a second transfer unit for transferring the circuit board in the reflow unit. A reflow soldering device, wherein the reflow soldering device is divided into a unit and a third transfer unit that transfers a circuit board in the cooling unit. 4. A calorimeter for measuring the amount of heat of convection heating and radiant heating at a position not in contact with the circuit board conveyed in the preheating section, reflow section, and cooling section, and the measurement data of the calorimeter is Comparing with the calorific value data of convective heating and radiant heating corresponding to the preset temperature, and feeding back the data to correct so that the deviation becomes smaller to the heating source, the optimal amount of heat of convective heating and radiant heating is balanced. 4. The reflow soldering apparatus according to claim 3, further comprising control means for performing soldering while controlling.