JPH1093232A - Reflow soldering equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent defects by thermal stress in a printed wiring board by an excessive difference in temperatures between a reflowed surface of the printed wiring board and an opposite surface, when applying a temperature difference to the two surfaces. SOLUTION: A furnace body 22 of a heating furnace 21 is constituted of a preheating section 23 and a reflowing section 28. Below a carrying conveyor 3 which passes through the reflowing section 28, a heating chamber 43 is installed to blow hot air against a printed wiring board 1. And, a cooling equipment 51 to flow inert gas for cooling against the printed wiring board 1 is installed above the carrying conveyor 3. A temperature sensor 48 is installed at the exit of hot air of the heating chamber 43, and the temperature of the hot air is controlled to be a target temperature by a temperature controller 49. A gas exhaust nozzle 58 for cooling of the cooling equipment 51 is provided with a temperature sensor 59, and the temperature of an inert gas heating chamber 54 is so controlled by a temperature controller 60 that the chamber temperature controlled to a target temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of soldering by heating and melting solder previously supplied to a surface to be soldered of a work to be soldered such as a printed wiring board on which electronic components are mounted. The present invention relates to a reflow soldering apparatus for performing the following.

[0002]

2. Description of the Related Art When a printed wiring board is subjected to reflow soldering, an electronic component having heat resistance to a reflow temperature (for example, about 250 ° C.) is mounted on one reflow surface side, which is a surface to be soldered. However, the heat resistant temperature is low (for example, about 12
0 ° C.) In some cases, electronic components are mounted.

In order to perform such reflow soldering of a printed wiring board, it is necessary to suppress an increase in the temperature of the electronic component on the other anti-reflow surface side while heating the reflow surface side.

As one example of such a technique, Japanese Patent Laid-Open No.
The technology disclosed in Japanese Patent No. 212033 is shown in FIGS.

FIGS. 4A and 4B show a conventional "reflow device". FIG. 4A is a side sectional view of the reflow device, and FIG. It is a figure showing a heating profile of a reflow device.

In these figures, 1 is a printed wiring board, 2 is an electronic component, 3 is a conveyor, 4 is a motor, 5
Is a heating furnace, 6 is a furnace body, 7 is a preheating zone, 8 is a soaking zone, 9 is a reflow zone, 10, 11, 12, and 13 are heaters, 14, 15, and 16 are fans, and 17 is a nozzle.

In this technique, before the printed wiring board 1 is carried into the reflow zone 9, the nozzle 17 is provided on the other side of the printed wiring board 1 on the opposite side of the reflow surface, which is not desired to be heated. (For example, a low-temperature nitrogen gas of about −10 to 5 ° C. after vaporization of liquid nitrogen), thereby sufficiently lowering the temperature initial value on the anti-reflow surface side, and then the printed wiring board 1 is reflowed. Even when the reflow soldering is performed by being carried into the zone 9 and being heated by the heaters 12 and 13 as heating means, the temperature rise on the anti-reflow surface side where the cold air is blown is reduced to a low temperature within a desired temperature. The temperature is controlled.

In FIG. 4B, a temperature difference of about 120 ° C. is applied between the soldering surface side of the printed wiring board 1 and its anti-reflow surface side in the preheating zone 7, and thereafter, in the reflow zone 9. It is disclosed that a temperature difference of about 90 ° C. is maintained.

[0009] By the way, an inert gas (for example, nitrogen gas) is supplied into the furnace body 6 of the reflow soldering apparatus to form a low oxygen concentration atmosphere, and an apparatus for performing reflow soldering in this atmosphere (described in the same publication). Nitrogen reflow equipment). With this device, it is possible to prevent oxidation on the reflow surface side, reduce the surface tension of the molten solder, increase its fluidity, and perform good reflow soldering even on a fine soldered part. .

[0010] Therefore, in such a reflow soldering apparatus, since the low-temperature nitrogen gas immediately after the liquefied nitrogen is vaporized can be used as the cold air, the advantage of two birds per stone is obtained.

[0011]

However, as shown in the heating profile of FIG. 4B, the printed wiring board 1 has a temperature difference of about 100 ° C. or more over the preheating zone 7 and the reflow zone 9. Continually applies excessive heat stress to the printed wiring board 1 over a long period of time, and causes a large amount of warpage in the printed wiring board 1 due to the difference in the amount of thermal expansion caused by the temperature difference. Occurs.

Therefore, the mounted electronic component 2 cannot maintain a normal horizontal or vertical mounting state, and the tombstone phenomenon is likely to occur. In addition, stress due to stress is applied to through holes and via holes, and severe cracks may occur.

Further, if the above-mentioned temperature difference exists in the soaking zone 8, the amount of heat moves from the reflow surface side to the cooled anti-reflow surface side, and due to the difference in heat capacity of the mounted electronic components 2, The reflow surface side is not heated uniformly.

A large amount of warpage is caused by the use of the conveyor 3 which places and holds both ends of the printed wiring board 1 and transports the printed wiring board 1. It is also easy to cause an accident of falling off from 3 and falling.

An object of the present invention is to provide an apparatus for performing reflow soldering in an atmosphere of a low oxygen concentration by supplying an inert gas into a furnace, in which a minimum temperature is required only in a heating region where a temperature difference needs to be given. An object of the present invention is to solve the above-mentioned problem by providing a difference.

[0016]

According to the reflow soldering apparatus of the present invention, an inert gas heated in a heating chamber provided with a heater, the temperature of which is controlled by a sensor and a temperature control device is controlled by printed wiring. The feature is that it is configured to spray on the anti-reflow surface side of the plate. Further, a liquefied inert gas is used as a means for supplying the inert gas.

For example, liquid nitrogen as an inert gas has a boiling point of about -195 ° C., and when nitrogen gas, which has not been temperature-controlled immediately after vaporization, is blown onto the printed wiring board, the printed wiring board has an anti-reflow surface side. Temperature drops more than necessary.

For this reason, the reflow is achieved by heating the inert gas to a uniform temperature by a heater provided in a separately provided inert gas heating chamber and blowing the inert gas heated to a required temperature onto the printed wiring board. It is possible to prevent excessive cooling while suppressing the temperature rise on the anti-reflow surface side to a desired value when performing soldering.

Further, since the atmosphere for performing reflow soldering can be a low oxygen concentration atmosphere by using an inert gas, oxidation of the reflow portion can be prevented, and the surface tension of the molten solder decreases. It is possible to improve the wettability of the molten solder in the fine soldered portion.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The flow soldering apparatus of the present invention passes through a conveyor that passes through a heating furnace, and mounts, holds, and conveys a printed wiring board.

The inside of the furnace constituting the heating furnace is divided into a heating section heating chamber of a preheating section, a soaking section heating chamber, and a reflow section heating chamber along the direction of transport of the printed wiring board. The heating temperature can be adjusted to improve the controllability of the heating profile of the printed wiring board.

In the preheating section, infrared heaters provided with a heat insulating material on the furnace wall side are arranged above and below the conveyor, and a temperature sensor is provided on each heater surface, and a separate temperature controller is provided. Can be adjusted to a predetermined target temperature.

In order to circulate the atmosphere inside the furnace of the preheating section along the transport direction of the transport conveyor, a suction port is provided between the heating section and the soaking section, and a suction port is provided on the transport inlet side and the reflow section side, respectively. Air outlets are provided and they are connected to a blower. The drive motor of the blower is controlled by a variable frequency inverter to control the flow rate of the circulating atmosphere.

In addition, the temperature inside the furnace of the preheating unit rises more than necessary by taking in the atmosphere through the on-off valve on the suction port side of the blower or by taking in inert gas such as nitrogen gas from the nitrogen gas supply device. Is configured to be able to be suppressed.

In the reflow section, a heating means for blowing hot air to the printed wiring board is provided below the conveyor, and a cooling device for blowing an inert gas for cooling is provided above.

The heating means is of a hot air circulation type. After the atmosphere supplied from the blower is heated by the heater of the heating chamber, the air is blown out from the outlet as uniform hot air by the rectifying plate, and is blown to the printed wiring board for heating. After that, the air is sucked from the suction port and returned to the blower.

A temperature sensor is provided at the outlet of the hot air, and a detection signal is input to a temperature control device to control the heater power so as to reach a target hot air temperature instructed to the temperature control device in advance. It is configured as follows.

On the other hand, liquid nitrogen as a cooling source of the cooling means is supplied from a liquid nitrogen cylinder, enters an inert gas heating chamber through an on-off valve, and has a uniform temperature distribution by a heater in the inert gas heating chamber. After heating, the cooling gas is supplied to the cooling gas ejection nozzle through the flow control valve and the flow meter, and the nitrogen gas ejected from the nozzle is blown to the printed wiring board.

Further, a sensor for detecting the temperature of the nitrogen gas ejected from the cooling gas ejection nozzle is provided. This detection signal is inputted to a temperature control device, and the temperature becomes a target temperature previously instructed to the device. The heater power is controlled as described above.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a description will be given of a practical embodiment of a reflow soldering apparatus according to the present invention.

FIG. 1 is a side sectional view showing a first embodiment of the present invention, in which reflow soldering is performed only on the lower surface of a printed wiring board. The supply system and the temperature control system are shown in a symbol diagram, and the same reference numerals as those in FIG. 4 indicate the same parts.

That is, the printed wiring board 1 passes through the heating furnace 21 and passes through a conveyor (chain conveyor) 3, and the side end of the printed wiring board 1 is placed on a pin (not shown) of the chain conveyor 3.・ Hold and transport.

Inside the furnace body 22 constituting the heating furnace 21, along the transport direction A of the printed wiring board 1, the preheating section 23 has a heating section heating chamber 25 as a heating section 24 and a heating section 25 as a temperature equalizing section 26. An equalizing section heating chamber 27 is provided, and a reflow section heating chamber 29 is provided in the reflow section 28 so that the heating temperature can be adjusted for each of the heating chambers 25, 27, 29 so that the printed wiring board 1 can be adjusted. The controllability of the heating profile is improved.

In the preheating section 23, infrared heaters 32 provided with a heat insulating material 31 on the furnace wall side are arranged above and below the conveyor 3, and although not shown, a temperature sensor is provided on the surface of each heater 32. In addition, a temperature adjustment control device is separately provided so that the surface temperature of the infrared heater 32 can be adjusted to a predetermined target temperature.

In order to circulate the atmosphere in the furnace body 22 of the preheating section 23 along the transport direction A of the transport conveyor 3, a suction port 33 is provided between the temperature raising section 24 and the temperature equalizing section 26. Air outlets 35 are provided on the carry-in port 34 side and the reflow section 28 side, respectively, and these are connected to a blower 36. The rotation of a drive motor (induction motor), not shown, of the blower 36 is controlled by a variable frequency inverter so that the flow rate of the circulating atmosphere can be adjusted.

An on-off valve 37 is provided on the side of the suction port 33 of the blower 36, and air is introduced through the on-off valve 37 as necessary, or an inert gas such as nitrogen gas is introduced from a nitrogen gas supply device. The configuration is such that the temperature inside the preheating unit 23 can be prevented from rising more than necessary. Reference numeral 38 denotes a carry-out port.

The reflow section 28 includes a heating device 41 for blowing hot air to the printed wiring board 1 below the conveyor 3.
A cooling device 51 for blowing a liquefied inert gas (nitrogen gas) for cooling is provided as an inert gas supply means on the upper side.

The heating device 41 is of a hot air circulation type. After the atmosphere supplied from the blower 42 is heated by the heater 44 of the heating chamber 43, the air is supplied to the air outlet 46 by the rectifying plate 45 as uniform hot air.
And blows the printed wiring board 1 to heat it, and then sucks it from the suction port 47 and returns to the blower 42.

The hot air outlet 46 is provided with a temperature sensor 48, and this detection signal S _TH is sent to the temperature controller 4
9, the heater power S _PH is controlled so that the target hot air temperature is instructed in advance to the device 49.

On the other hand, as a cooling source of the cooling device 51, liquid nitrogen is used. The nitrogen gas supplied from the liquid nitrogen cylinder 52, which is a source of the inert gas, passes through the on-off valve 53, enters the inert gas heating chamber 54, and enters the inert gas heating chamber 54.
After being heated to a uniform temperature distribution by the heater 55 in the inside, it is supplied to a cooling gas ejection nozzle 58 through a flow control valve 56 and a flow meter 57, and the nitrogen gas ejected from the nozzle 58 is blown to the printed wiring board 1. It is a configuration to attach.

Further, a temperature sensor 59 for detecting the temperature of the nitrogen gas ejected from the cooling gas ejection nozzle 58 is provided, and this detection signal _STC is inputted to the temperature control device 60 and the device 60 is instructed in advance. The heater power S _PC is controlled so as to reach a target temperature.

The reason for providing the infrared heater 32 for heating the upper side surface of the printed wiring board 1 in the preheating section 23 described above is that the printed wiring board 1 on which the electronic component 2 having a low heat-resistant temperature is mounted is mounted. Although the upper surface is also at a temperature lower than the heat-resistant temperature, the printed wiring board 1 is heated by heating within the range.
This is to ensure that the whole is heated to a temperature as uniform as possible.

FIG. 2 is a diagram showing an example of a heating profile when the hot air blowing temperature of the reflow section 28 of FIG. 1 is set to about 250 ° C. and the cool air temperature, that is, the nitrogen gas blowing temperature is set to about 100 ° C. is there.

In the preheating section 23, the surface temperature of the infrared heater 32 is adjusted so that the temperature of the lower surface of the printed wiring board 1, ie, the temperature of the portion to be soldered on the reflow soldering surface is about 140 ° C.
, And the temperature of the upper surface, that is, the anti-reflow soldering surface, is set to about 100 ° C. In this case, the on-off valve 37 is opened to supply the atmosphere slightly. Alternatively, a slight amount of nitrogen gas may be supplied. As a result, the ambient temperature of the preheating unit 23 can be reduced, and the temperature on the upper surface side of the printed wiring board 1 can be easily prevented from excessively increasing.

As described above, the difference between the temperature on the reflow surface side of the printed wiring board 1 and the temperature on the non-reflow surface side of the printed wiring board 1 can be maintained within about 40 ° C.

In the reflow section 28, hot air of about 250 ° C. is blown to the reflow surface side of the printed wiring board 1 to
The temperature is raised to 40 ° C., and the solder in the soldered portion is melted and soldering is performed. On the other hand, about 10
Nitrogen gas at 0 ° C. is blown, and the temperature is maintained at about 110 ° C. In other words, the anti-reflow surface side only needs to remove the amount of heat so as not to raise the temperature more than necessary.

Further, since nitrogen gas is supplied to the reflow portion 28, the oxygen concentration in the atmosphere is small, the oxidation of the portion to be soldered is suppressed, and the flowability of the molten solder is improved, and the soldering of the fine portion is reduced. Sex is greatly improved.

As described above, the stress caused by the temperature difference is applied to the printed wiring board 1 only in the reflow portion 28, and the electronic component having low heat resistance is applied to the printed wiring board 1.
Even if it is mounted on the anti-reflow surface side, it can be protected below the heat-resistant temperature.

[Second Embodiment] FIG. 3 is a side sectional view showing a second embodiment of the present invention, showing a case where reflow soldering is performed only on the lower surface of the printed wiring board 1, and the inert gas The supply system and the temperature control system are shown in a symbol diagram, and the same reference numerals as those in FIG. 1 indicate the same parts.

The second embodiment differs from the first embodiment only in the means for blowing an inert gas for cooling the printed wiring board 1 in the reflow section 28. That is, the cooling device 61 of the second embodiment has the same atmosphere circulation structure as the heating means for blowing hot air, and does not include the heating chamber 43 and the heater 44 for heating the atmosphere as shown below. Then, the suction port 47 of the blower 62
It is configured to supply temperature-controlled nitrogen gas to the side.

The temperature of the atmosphere containing nitrogen gas blown to the anti-reflow surface side of the printed wiring board 1 is detected by a temperature sensor 59 provided at the outlet 46, and the temperature control device 60 uses the detection signal _STC to control the temperature. Inert gas heating chamber 54
Controlled to a predetermined temperature by controlling the heater power S _PC. That is, by adjusting the temperature of the supplied nitrogen gas, the temperature of the atmosphere blown to the anti-reflow surface side of the printed wiring board 1 is adjusted.

As described above, by adjusting the temperature of the supplied nitrogen gas to adjust the temperature of the atmosphere blown to the printed wiring board 1, the temperature of the printed wiring board 1 on the side opposite to the reflow surface can be reduced. The temperature can be adjusted to a desired value, and the atmosphere in the reflow section 28 can have a low oxygen concentration.

The oxygen concentration in the atmosphere can be adjusted by adjusting the flow rate of the nitrogen gas.
The blower 62 (the motor is an induction motor)
The flow rate of the atmosphere blown to the printed wiring board 1 can be adjusted by adjusting the number of revolutions by the variable frequency inverter. Therefore, the amount of heat taken away from the anti-reflow surface side of the printed wiring board 1 is adjusted by the air volume. You can also. That is, by adjusting the flow rate of the nitrogen gas and the heating temperature of the nitrogen gas in the heating chamber while maintaining the oxygen concentration at the target value by controlling the flow rate of the nitrogen gas, the temperature on the side opposite to the reflow surface is within the target temperature. Can be maintained.

[0054]

As described above, according to the present invention, the reflow soldering is performed only on the reflow surface side while minimizing the stress applied to the printed wiring board, and the anti-reflow surface side is set to a desired temperature, for example, below the heat resistance temperature of the mounted electronic component. Can be maintained. Of course, it is possible to prevent the reflow of the solder on the surface of the printed wiring board which is mounted and designed to be reflow-soldered on both sides of the printed wiring board and which has already been reflow-soldered.

Further, the atmosphere in which the reflow soldering is performed is maintained at an atmosphere having a low oxygen concentration, so that good solderability can be ensured. Further, by using the liquefied inert gas, the energy of the gas can be used without waste.

Since the inert gas is heated by the heater in the inert gas heating chamber and is sprayed on the printed wiring board with a uniform temperature distribution, it is possible to maintain a uniform temperature distribution on the anti-reflow surface side of the printed wiring board. become able to.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing a first embodiment of the present invention.

FIG. 2 is a diagram showing an example of a heating profile of FIG.

FIG. 3 is a side sectional view showing a second embodiment of the present invention.

FIG. 4 shows a conventional “reflow device”;
4A is a side sectional view of the reflow device, and FIG.
It is a figure which shows the heating profile of the reflow apparatus of (a).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Printed wiring board 3 Conveyor 21 Heating furnace 22 Furnace body 23 Preheating section 24 Heating section 25 Heating section heating chamber 26 Equalizing section 27 Equalizing section heating chamber 28 Reflow section 29 Reflow section heating chamber 41 Heating device 42 Blower 43 Heating chamber 44 Heater 48 Temperature sensor 49 Temperature control device 51 Cooling device 52 Liquid nitrogen cylinder 54 Inert gas heating chamber 55 Heater 56 Flow control valve 58 Cooling gas ejection nozzle 59 Temperature sensor 60 Temperature control device 61 Cooling device 62 Blower

Claims (2)

[Claims] 1. A reflow process, comprising: heating one reflow surface side of a plate-like work to be soldered by a heating means while blowing an inert gas to the other anti-reflow surface side by an inert gas supply means to cool; An apparatus for reflow soldering by melting solder supplied in advance to a surface side soldering portion, wherein a sensor for detecting a temperature of the inert gas sprayed on the soldering work, An inert gas heating chamber provided with a heater for heating the inert gas sprayed on the work to be soldered; and comparing the temperature detected by the sensor with a previously designated temperature so that the two temperatures match. A reflow soldering device, comprising: a temperature controller for adjusting electric power supplied to a heater. 2. The reflow soldering apparatus according to claim 1, wherein the inert gas supply means supplies a liquefied inert gas.