GB2324058A

GB2324058A - Reflow soldering

Info

Publication number: GB2324058A
Application number: GB9805394A
Authority: GB
Inventors: Hiroaki Aiura
Original assignee: Alps Electric Co Ltd
Current assignee: Alps Alpine Co Ltd
Priority date: 1997-04-10
Filing date: 1998-03-16
Publication date: 1998-10-14
Anticipated expiration: 2018-03-16
Also published as: CN1197366A; CN1091567C; GB9805394D0; JP2812675B2; KR100270764B1; GB2324058B; JPH10284832A; KR19980081217A; JP2812675B1; MY142253A

Abstract

In a reflow soldering apparatus outside air is supplied by a fan member (8) into a heat exchange member (7) in which heat exchange is performed between the outside air and the inside air discharged from a heating member (4), thereby heating the outside air being supplied to the heat exchange member. Then the outside air thus heated is further heated to a high temperature by the heating member to reflow solder a printed circuit board (P).

Description

REFLOW SOLDERING METHOD, AND REFLOW SOLDERING EQUIPMENT FOR SOLDERING BY REFLOW SOLDERING METHOD The present invention relates to a reflow soldering method and a reflow soldering equipment using the reflow soldering method for conveying, to a heating member, a printed board mounted with a circuit component and coated with cream solder, on a conveying member such as belt conveyor. At the heating member the printed board is heated to melt the cream solder, to thereby perform soldering.

A conventional reflow soldering equipment which has been proposed in Japanese Patent Application No. Hei 6-175657 by the applicant of the present invention will be explained. The reflow soldering equipment, as shown in Fig. 7, is equipped with a conveying member 1 which carries an unillustrated printed board mounted with an unillustrated circuit component and coated with cream solder, inwardly from the FEED side A and then towards the DISCHARGE side B.

The conveying member 1 comprises an endless chain conveyor la, a driving motor lb for driving the chain conveyor la, and a conveyor rail lc for guiding the chain conveyor la so that the chain conveyor la will not slack downwardly with the weight of the printed board and others. With the rotation of the driving motor ib the printed board moves in the direction of the arrow C, that is, from the upstream side to the downstream side.

On the upstream side of the interior of the conventional reflow soldering equipment in which the chain conveyor la passes, a first preheating furnace 2 and a second preheating furnace 3 are arranged as preheating members. In a casing 2a of the first preheating furnace 2 are mounted a pair of fans 2b. Above the pair of fans 2b are disposed six infrared ray heater 2d.

In the first preheating furnace 2 in the casing 2a is fed upwardly by the fan 2b into the infrared heater 2d, in which the air is heated. The heated air hits on the upper inner surface of the casing 2a and is reflected to go downwardly, circulating inside the casing 2a to thereby preheat an unillustrated printed board that has been mounted with a circuit component and coated with cream solder.

The second preheating furnace 3 located on the downstream side of the first preheating furnace 2 is of the same constitution as the first preheating furnace 2 and therefore will not be described.

On the downstream side of the second preheating furnace 3 is disposed a reflow furnace 14. The reflow furnace 14 has a heater box 14a located immediately below the chain conveyor la. In the upper part of this heater box 14a, a multitude of heating nozzles 14b are arranged along the direction of travel of the chain conveyor la.

A plurality of unillustrated heaters are built inside the heater box 14a, whereby the air fed therein will be heated to a high temperature.

In the upper part of the reflow furnace 14 is disposed an exhaust cover 15, to which an exhaust duct 6 and a circulation duct 16 are connected. From the exhaust duct 6 a part of high-temperature heated air after the melting of cream solder coated on the printed board is taken in the direction of the arrow D, and is discharged out of the reflow soldering equipment.

The residual heated air not drawn into the exhaust duct 6 is taken in by a fan 17 from the circulation duct 16 in the direction of the arrow E, being fed back into the heater box 14a of the reflow furnace 14 from the inlet port 17a through an exhaust port 17b.

Then, the fan 17 is disposed below the reflow furnace 14, and the circulation duct 16 is extended and connected to the exhaust cover 15.

Above the chain conveyor la the cooling fan 9 having a plurality of flow straightening plates 9a is disposed for cooling the soldered printed board.

In a conventional reflow soldering equipment, there is arranged a falling object receiving net 10 beneath the first and second preheating furnaces 2 and 3 for receiving unnecessary matters such as solder spatter dropping into the irst and second preheating furnaces 2 and 3.

In the above-described reflow soldering equipment, however, because a flux is mixed in the cream solder coated on the printed board for purpose of improving soldering effectiveness, the flux is partly vaporized into a hot gas when the cream solder is melted with the high-temperature heated air discharged from the heating nozzle 14b.

The heated air inclusive of the flux that has turned into a gas, when taken in by the fan 17, lowers in temperature during travel from the circulation duct 16 to the fan 17, making the gaseous flux become a high-viscosity liquid or a solid and attach to the interior of the circulation duct 16, fan 17, or reflow furnace 14.

The intake performance and exhaust performance of the fan 17, therefore, are degraded, to thereby fail in sending the desired amount of heated air into the reflow furnace 14.

Therefore, it will take much time to heat the inside temperature of the reflow furnace 14 to a desired high temperature, resulting in an increased power consumption. Also, the temperature of the high-temperature heated air discharged from the reflow furnace 14 varies with the result that the cream solder coated on the printed board will be melted unevenly and the soldering performance will be degraded.

Furthermore, the circulation duct 16 and the fan 17 require maintenance including disassembly and cleaning in a short period of time in order to remove the flux holding on the interior of the circulation duct 16 and the fan 17; therefore the operation rate of the reflow soldering equipment will lower to degrade the producibility of the equipment.

Since the exhaust cover 15 and the fan 17 are connected through the circulation duct 16 extended, the high-temperature heated air taken in from the exhaust cover 15 lowers while passing through the circulation duct to be recharged to the reflow furnace 14 through the fan 17.

As a first means for solving the above-described problem, a reflow soldering method of the present invention comprises the steps of supplying the outside air by the fan member into the heat exchange member at which heat exchange is taken place between the outside air and the inside air of different temperatures to decrease the temperature difference; heating the heat exchange member supplied with the outside air, by the use of the heated air discharged from the heating member to raise the temperature of the outside air supplied inside the heat exchange member; supplying the thus heated outside air to the heating member; further heating the outside air to a high temperature by the heating member; and discharging the high-temperature heated air out of the heating member, thereby soldering a circuit component to the printed board by the use of the high-temperature heated air thus discharged.

As a secondary means for solving the above-described problems, the reflow soldering method of the present invention aiso includes absorbing the heat of the heated air discharged from the heating member by the outside air in the heat exchange member, to thereby lower the temperature of the heated air present in the vicinity of the heat exchange member outside of the heat exchange member.

Furthermore, as a third means for solving the abovedescribed problems, the reflow soldering equipment of the present invention comprises a conveying member for carrying a printed board mounted with a circuit component and coated with cream solder, a fan member for supplying the outside air into the interior, a heat exchange member for introducing the outside air from the fan member into the interior, and a heating member for heating the outside air being supplied from the fan member through the heat exchange member. The heat exchange member is disposed in a position where the heated air heated at the heating member is discharged.

Furthermore, as a fourth means for solving the abovedescribed problem, the reflow soldering equipment of the present invention is constituted such that the heat of the high-temperature heated air discharged from the heating member is taken away and cooled by the outside air fed into the heat exchange member. To gather and discharge the thus cooled air out, the exhaust member is provided. In the exhaust member is disposed the heat exchange member.

Furthermore, as a fifth means of the present invention for solving the above-described problem, the heat exchange member is disposed on the opposite side of the heating member beneath the conveying member.

Furthermore, as a sixth means of the present invention for solving the above-described problem, the heat exchange member is comprised of an air reservoir, which is formed collectively of a plurality of tubes on both the inlet and outlet sides; the outside air is fed from the fan member, through the air reservoir, being further fed to the heating member.

Furthermore, as a seventh means of the present invention for solving the above-described problem, an air reservoir of the heat exchange member is comprised of a plurality of ridges which form a wavy surface.

Embodiments of the invention will now be described, by way of example only1 with reference to the accompanying drawings, in which: Fig. 1 is a general block diagram of one embodiment of a reflow soldering equipment according to the present invention; Fig. 2 is a sectional view of a major portion of a first preheating furnace of the reflow soldering equipment of Fig.

I; Fig. 3 is a sectional view of a major portion of a heating member of the reflow soldering equipment of Fig. 1; Fig. 4 is a schematic perspective view of a heat exchange member of the reflow soldering equipment of Fig. 1; Fig. 5 is a schematic perspective view of another embodiment of the heat exchange member of Fig. 4; Fig. 6 is a perspective view explaining the heated state of a printed board heated by the heating member of Fig. 3; and Fig. 7 is a general block diagram of a conventional reflow soldering equipment.

The reflow soldering equipment of the present invention will be explained by referring to Fig. 1 to Fig. 6. The same members as those used in the above-described related art reflow soldering equipment will be designated by the same reference numerals and explained.

Fig. 1 is a general block diagram of one embodiment of the reflow soldering equipment according to the present invention, in which a conveying member 1 is disposed for carrying a printed board P from the FEED side A to the DISCHARGE side B.

The conveying member 1 is comprised for instance of the endless chain conveyor la, the driving motor lb for driving the chain conveyor la, and a conveyor rail lc for guiding the chain conveyor la from below so that the chain conveyor la will not be slackened downwardly with the weight of a part being carried, and is so designed as to travel, with the rotation of the driving motor lb, in the direction of the arrow C, that is, from the FEED side A on the upstream side to the DISCHARGE side B on the downstream side.

The chain conveyor la is once directed out of the reflow soldering equipment at the FEED side A and the DISCHARGE side B, and then directed back into the reflow soldering equipment after being guided by a plurality of guide rollers le. The chain conveyor la is further routed in the lower part of the interior of the reflow soldering equipment, and then wound on the pulley of the driving motor lb so as to repeat running with the rotation of the driving motor lb.

In the reflow soldering equipment in which the chain conveyor la runs, the first preheating furnace 2 and the second preheating furnace 3 are disposed on the upstream side to preheat the printed board P. The first preheating furnace 2 is housed in the casing 2a, the interior of which is separated into two chambers. In either chamber are mounted a pair of fans 2b, each having a rotating shaft 2c projecting downwardly.

Above either of the pair of fans 2b, six infrared heaters 2d are disposed.

In the first preheating furnace 2, as shown in Fig. 2, the air in the casing 2a is fed upwardly with the rotation of the fan 2b. The air heated at the infrared heater 2d is about 150 OC. After the preheating of the printed board P mounted with a circuit component P1 and coated with cream solder, the preheated air of about 1500C hits on the upper wall surface of the casing 2a, being reflected to circulate at about 150"C uniform temperature within the casing 2a.

Therefore, the air in the interior of the casing 2a is kept at a uniform temperature; that is, there exists no temperature difference between the upper part and the lower part, so that the printed board P can be heated at a uniform temperature.

Below the conveying member 1 on the downstream side of the second preheating furnace 3 there is disposed the heating member 4. The heating member 4 has a heater box 4a disposed immediately below the chain conveyor la. In the upper part of the heater box 4a a multitude of heating nozzles 4b are arranged at a predetermined spacing, for instance with a pitch of about 20 mm, along the direction of travel, in the direction of the arrow C, of the chain conveyor la.

The heating nozzle 4b having an about 50 mm x 5 mm opening is longitudinally arranged at right angles with the direction of travel of the chain conveyor la.

In the heater box 4a, as shown in Fig. 3, a plurality of heaters 4c and a plurality of spray nozzles 4d with a number of unillustrated small-diameter holes formed face down, in the upper part of the heaters 4c, are embedded in order from below in one side wall of the heater box 4a. Also, a thermocouple 4e for measuring the temperature in the heater box 4a is embedded in the other side wall opposite to the one side wall in which the heater 4c and the spray nozzle 4d are embedded.

An air filter 4g is mounted between the thermocouple 4e and an upper cover 4f for covering the upper part of the heater box 4a in which a multitude of heating nozzles 4b are formed, to thereby reduce air flow turbulence when the air blown out of the spray nozzle 4d and heated to a high temperature in the heater 4c flows into the heating nozzle 4b.

Directly above theheatingnozzle4bof theheatingmember 4 is disposed the chain conveyor la. Also above the chain conveyor la a box-shaped exhaust member 5 which is open in the lower part is disposed at a predetermined space. The exhaust member 5 is connected to the exhaust duct 6 through which the high-temperature heated air from the heating nozzle 4b is collected and discharged out.

The heat exchange member 7 is mounted within the exhaust member 5, above the conveying member 1 and oppositely to the heating member 4 beneath the conveying member 1.

The heat exchange member 7 is so designed that heat exchange is done between the outside air and the inside air which are at different temperatures, thereby reducing the temperature difference between the outside air and the inside air.

The heat exchange member 7 is of such a constitution that, as shown in Fig. 4, a plurality of round tubes 7a are assembled with a predetermined clearance provided therebetween to form the air reservoir 7b; and the round tubes 7a are collected on either of the inlet side 7c and the outlet side 7d. The inlet side 7c is connected to the air supply duct 8a while the outlet side 7d is connected to the supply duct 7e. The supply duct 7e, as shown in Fig. 1, is connected to the heating member 4 rom the heat exchange member 7.

The air supply duct 8a connected to the inlet side 7c of the heat exchange member 7 is extended from the fan member 8 comprising the fan and others disposed beneath the heating member 4 and connected. In the fan member 8 the air inlet port 8b is fitted with the filter 8c to take in clean outside air with dirts removed, then sending the outside air from the discharge port 8d to the heat exchange member 7 through the air supply duct 8a.

Furthermore, on the downstream side of the reflow furnace 4, the cooling fan 9 having a plurality of flow straightening plates 9a is disposed above the chain conveyor 1. Also the falling object receiving net 10 is disposed in the first and second preheating furnaces 2 and 3 to receive unnecessary objects such as solder spatter dropping from the chain conveyor That is, the reflow soldering equipment of the present invention comprises a conveying member 1 for carrying a printed board P mounted with a circuit component and coated with cream solder, a fan member for supplying the outside air into the interior, a heat exchange member for introducing the outside air from the fan member 8 into the interior, and a heating member 4 for heating the outside air being supplied from the fan member 8 through the heat exchange member 7. The heat exchange member 7 is disposed in a position where the heated air 11 heated at the heating member 4 is discharged.

In the reflow soldering equipment of the present invention of the above-described constitution, the printed board P mounted with a circuit component P1 and coated with cream solder is carried by the conveying member from the FEED side A; when the printed board P is preheated in the first and second preheating furnaces 2 and 3, the temperature of the printed board rises to about 120 to 1500C.

The preheated printed board P is carried to over the multitude of heating nozzles 4b of the heating member 4, the heated air 11 heated to so high in a temperature, about 300"C at center, is applied from the heating nozzles 4b to the lower surface side of the printed board P as shown in Fig. 5, thereby raising the temperature of the printed board P to about 200 to 250"C on the lower surface side.

Then, the cream solder coated on the lower surface of the printed board P is melted to produce an electrically conductive condition between the circuit component P1 and an unillustrated circuit pattern on the printed board P.

The printed board P with the molten cream solder, when carried by the carrying member 1 to the downstream side, is sent from the heating member 4 to the cooling fan 9, at which the printed board P is cooled with the air from the flow straightening plates 9a. Thus the cream solder is set to connect the circuit component P1 to the circuit pattern not illustrated.

The heated air 11 that has been discharged upwardly from the heating nozzles 4b and melted the cream solder is cooled by heat absorption by the outside air being fed into the heat exchange member 7. The air thus cooled is collected and discharged by the exhaust member 5 out of the reflow soldering equipment. In the exhaust member 5 is disposed the heat exchange member 7.

In the heat exchange member 7 there is formed the air reservoir 7b having a plurality of tubes 7a. The heat of the heated air 11 being discharged upwardly from the heating nozzle 4b of the heating member 4 is absorbed by the outside air supplied from the fan member 8 in the air reservoir 7b of the heat exchange member 7, lowering the temperature of the heated air 11 outside of the heat exchange member 7.

The outside air supplied from the fan member 8 in the heat exchange member 7 takes heat from the heated air 11, thus rising in temperature to 100 to 1500C in the air reservoir 7b.

The outside air in the air reservoir 7b that has risen to 100 to 1500C is forced, by fresh outside air coming from the fan member 8 through the air duct 8a, from the supply duct 7e to the heater box 4a of the heating member 4.

The thus heated outside air that has been sent into the heater box 4a is blown out towards the heater 4c from a plurality of unillustrated holes of the spray nozzle 4d.

Then, the outside air further rises in temperature to about 300"C, becoming the high-temperature heated air 11 as shown in Fig. 6. The heated air 11 is discharged out upwardly from the heating nozzle 4b.

Subsequently, the printed board P that has been carried in on the conveying member 1 is heated by the high-temperature heated air 11 up to about 200 to 250CC at the lower surface of the printed board P, to thereby melt the cream solder coated on the lower surface of the printed board P.

Furthermore, since the heat exchange member 7 is arranged on the opposite side of the heating member 4 which is below the conveying member 1 in the exhaust member 5, the heat of the heated air 11 that has been discharged out of the heating member 4 and melted the cream solder is efficiently absorbed, thereby lowering the temperature of the heated air 11 present outside of, and in the vicinity of, the heat exchange member 7. The circuit component P1 on the printed board P, therefore, can be protected from getting hot and damaged.

In the embodiment of the present invention, the air reservoir 7b of the heat exchange member 7 comprising an assembly of a plurality of round tubes 7a has heretofore been explained; the tubes 7a, however, are not limited to the round ones but may be formed in other form, for instance an oval form.

Furthermore, it is to be noticed that the air reservoir 7b of the heat exchange member 7 is not limited to the plurality of tubes 7a, but the air reservoir 7b as shown in Fig. 5 may be comprised of a plurality of wavy-surface ridge portions and formed hollow inside.

According to the present invention heretofore described, a reflow soldering method comprises supplying the outside air by the fan member into the heat exchange member at which heat exchange is taken place between the outside air and the inside air of different temperatures to decrease the temperature difference; heating the heat exchange member supplied with the outside air, by the use of the heated air discharged from the heating member; supplying the thus heated outside air to the heating member; further heating the outside air to a high temperature by the heating member; and discharging the high-temperature heated air out of the heating member, thereby soldering a circuit component to the printed board with the high-temperature heated air thus discharged. Therefore, the heat of the high-temperature heated air discharged from the heating member is efficiently absorbed at the heat exchange member, thereby raising the temperature of the outside air supplied into the heat exchange member in a short period of time. Thus it becomes possible to supply the hot outside air to the heating member.

The outside air to be supplied to the heating member, being hot, can be easily heated to a high temperature by the heating member in a short time, thereby uniformly melting the cream solder coated on the printed board and accordingly ensuring a high-reliability soldering result.

Furthermore, the heat of the heated air discharged from the heating member is absorbed by the outside air in the heat exchange member, to thereby lower the temperature of the heated air outside of the heat exchange member; it is, therefore, possible to prevent the circuit component loaded on the printed board from getting hot and thermally damaged.

Furthermore, the reflow soldering equipment comprises a conveying member for carrying a printed board mounted with a circuit component and coated with cream solder, a fan member for supplying the outside air into the interior, a heat exchange member for introducing the outside air from the fan member into the interior, and a heating member for heating the outside air being supplied from the fan member through the heat exchange member. The heat exchange member is disposed in a position where the heated air heated at the heating member is discharged.

Therefore, the heat of the high-temperature heated air being discharged from the heating member is absorbed, to thereby efficiently heat the outside air being fed into the heat exchange member and feed the thus heated outside air into the heating member. Therefore it is possible to provide a lowpower consumption reflow soldering equipment which can decrease the electric capacity of the heater for heating the heating member.

Furthermore, it is possible to provide a reflow soldering equipment having an improved time efficiency and high producibility, in which the outside air to be supplied from the fan member is clean air and therefore neither flux nor dust will attach on the interior of the fan member and the heating member. It is, therefore, possible to prolong the maintenance period of the equipment.

The high-temperature heated air discharged from the heating member is cooled by heat absorption by the outside air fed into the heat exchange member. To gather and discharge the cooled air out, the exhaust member is provided. In the exhaust member is disposed the heat exchange member. It is, therefore, possible to efficiently absorb heat from the high-temperature heated air, and to heat the outside air fed into the heat exchange member to a high temperature in a short period of time.

Furthermore, the heat exchange member, being disposed on the opposite side of the heating member below the conveying member, can efficiently absorb the heat from the hightemperature heated air after melting the cream solder coated on the printed board, to thereby cool the high-temperature heated air, thus preventing the circuit component loaded on the printed board from getting hot and thermally damaged.

Also the heat exchange member is composed of an air reservoir, comprising an assembly of a plurality of tubes which are collected at the inlet and outlet sides to make the outside air being supplied from the van member pass to the heating member through the air reservoir. It is, therefore, possible to efficiently absorb the heat from the high-temperature heated air to thereby heat to a high temperature the outside air fed into the air reservoir within a short time.

The air reservoir of the heat exchange member is comprised of a plurality of ridge portion having a wavy surface; the air reservoir, therefore, can be increased in a surface area to efficiently absorb the heat of the high-temperature heated air, thereby heating, in a short period of time, to a high temperature the fresh air supplied into the air reservoir.

Claims

1. A reflow soldering method, comprising the steps of: supplying the outside air by a fan member into a heat exchange member at which heat exchange is taken place between the outside air and the inside air of different temperatures to decrease a temperature difference; heating said heat exchange member supplied with the outside air, by the use of the heated air discharged from a heating member to raise the temperature of the outside air supplied inside said heat exchange member; supplying the thus heated outside air to said heating member; further heating the outside air to a high temperature by said heating member; and discharging the high-temperature heated air out of said heating member, thereby soldering a circuit component to a printed board by the use of the high-temperature heated air thus discharged.

2. A reflow soldering method according to claim 1, wherein the heat of the heated air discharged from said heating member is absorbed by the outside air in said heat exchange member, to thereby lower the temperature of the heated air present in the vicinity of said heat exchange member outside of said heat exchange member.

3. A reflow soldering equipment, comprising: a conveying member for carrying a printed board mounted with a circuit component and coated with cream solder; a fan member for supplying the outside air into the interior; a heat exchange member for introducing the outside air from a fan member into the interior; and a heating member for heating the outside air being supplied from said fan member through said heat exchange member, said heat exchange member being disposed in a position where the heated air heated by said heating member is discharged.

4. A reflow soldering equipment according to claim 3, wherein the high-temperature heated air discharged from said heating member is cooled by heat absorption by the outside air -ea into said heat exchange member; an exhaust member is further provided for gathering and discharging che thus cooled air out; and said heat exchange member is disposed in said exhaust member.

5. . < reflow soldering equipment according to claim 4, wherein so said heat exchange member is disposed on the opposite side of said heating member below said conveying member.

s. A reflow soldering equipment according to claim 5, wherein said heat exchange member comprises an air reservoir, which is formed collectively of a plurality of tubes on both the inlet and outlet sides; and the outside air is fed from said fan member, through said air reservoir, being further fed to said heating member.

7. A reflow soldering equipment according to claim 6, wherein said air reservoir of said heat exchange member comprises a plurality of ridge portions having a wavy surface.

8. A reflow soldering equipment according to claim 4, wherein said heat exchange member comprises an air reservoir, which is formed collectively of a plurality of tubes on both the inlet and outlet sides; and the outside air is fed from said fan member, through said air reservoir, being further fed to said heating member.

9. A reflow soldering equipment according to claim 8, wherein said air reservoir of said heat exchange member comprises a plurality of ridge portions having a wavy surface.

10. A reflow soldering equipment according to claim 3, wherein said heat exchange member is disposed on the opposite side of said heating member below said conveyor member.

11. A reflow soldering equipment according to claim 10, wherein said heat exchange member comprises an air reservoir, which is formed collectively of a plurality of tubes on both the inlet and outlet sides; and the outside air is fed from said fan member, through said air reservoir, being further fed to said heating member.

12. A reflow soldering equipment according to claim 11, wherein said air reservoir of said heat exchange member comprises a plurality of ridge portions having a wavy surface.

13. A reflow soldering equipment according to claim 3, wherein said heat exchange member comprises an air reservoir, which is formed collectively of a plurality of tubes on both the inlet and outlet sides; and the outside air is fed from said fan member, through said air reservoir, being further fed to said heating member.

A A reflow soldering equipment according to claim 13, wherein said air reservoir of said heat exchange member comprises a plurality of ridge portions having a wavy surface.

15. A reflow soldering equipment substantially as hereinbefore described with reference to, and as illustrated by the accompanying drawings

16. A reflow soldering method substantially as hereinbefore described with reference to the accompanying drawings.