Soldering apparatus of a reflow type

Abstract: A soldering apparatus of a reflow type contains a preheating chamber (22,23) and a reflow chamber (24) which are provided with a plurality of heaters (25) for heating printed circuit boards (1) with chips temporarily mounted thereon with solder pastes (3) during conveyance by a conveyor. The heaters (25) are mounted on the side walls of the chamber, extending along a direction of conveyance of the printed circuit boards (1). The chambers are also provided with a screening member (26) respectively so as to prevent direct radiation of radiant heat from the heaters into the chambers and onto the printed circuit boards and to provide a unform air flow so as to be blown uniformly onto the printed circuit boards.

Description: The present invention relates to a soldering apparatus of a reflow type and, more particularly, to a soldering apparatus of a reflow type in which electric parts such as chips temporarily mounted on a printed circuit board are soldered with solder preforms or solder pastes in a reflow chamber of the soldering apparatus after preheating them in a preheating chamber thereof. A soldering apparatus is disclosed in document EP-A-0 325 451 which forms state of the art pursuant to Article 54 (3) and (4) EPC. The apparatus of Claim 1 differs from this state of the art in that the walls on which the heaters are mounted extend not only parallel to the path of travel of the printed circuit boards through the chambers but also laterally to one side of that path of travel. A conventional soldering apparatus of the reflow type is arranged so that printed circuit boards on which chips have been temporarily mounted with solder preforms, solder pastes or adhesives are then exposed to heated air or far infrared rays to fuse or melt the solder preforms or the like, thus soldering the chips on the printed circuit boards. One conventional soldering apparatus of the reflow type is shown in cross-sectional side view FIG. 2 of the accompanying drawings, in which printed circuit boards 101 with chips 102 temporarily mounted thereon with solder paste 103 are placed on a belt conveyor 105 of a metal net being driven through by rollers 105a in a direction shown by the arrow A. The soldering apparatus 104 is provided with a first preheating chamber 106 and a second preheating chamber 107 at positions along the direction of conveyance of the belt conveyor 105 and symmetrically and vertically interposing the belt conveyor 105. The first and second preheating chambers 106 and 107 are provided each with an air inlet 106a and 107a and an air discharge outlet 106b and 107b, respectively. Air is sucked into the chambers 106 and 107 through the air inlets 106a and 107a, respectively, and the air is heated with a heater 109, such as a sheathed heater or a far infrared ray heater, mounted at their respective air discharge outlets 106b and 107b to temperatures as high as approximately 140°C , for example, below the fusion point of the solder paste 103 or the like, thus preheating the printed circuit boards 101 being conveyed in the chambers 106 and 107. The preheated printed circuit boards 101 are then conveyed to a reflow chamber 108 in the soldering apparatus 104, which is provided at a discharge exit 108b thereof with a heater 110, such as a sheathed heater or far infrared ray heater. The printed circuit boards 101 are in turn heated with air sucked from an air inlet 108a by the heater 110 at temperatures as high as 215°C , at the fusion point of the solder paste or the like or higher, thus soldering the chips 102 on the printed circuit boards 101. The heated air is discharged through the discharge outlet 108b. The preheating chambers 106 and 107 and the reflow chamber 108 are further provided each with a fan 111 which is connected through a rotary shaft 112 to each other and to a motor 113. The fans 111 then ventilate heated air in and from the chambers in a direction given by the arrow B. The soldering apparatus 104 is also provided with a cooling fan 114 for cooling the fused or melted solder paste 103 to solidify it and ensure the fixed mounting of the chips 102 to the printed circuit boards 101, and an discharge fan for discharging air inside the soldering apparatus 104. The heater 109 or 110, such as a sheathed heater or a far infrared ray heater, generates radiant heat containing far infrared rays, and the far infrared rays have the advantage that they are likely to heat even the inside of the chips 102 as compared with a heating system applying a thermal conduction of heated air. It is to be noted, however, that, as the solder paste 103 generally has a larger reflectance than the chips 102, the far infrared rays require a longer time for heating the solder paste 103 than for heating the chips 102, whereby the chips 102 are heated earlier than the solder paste 103. Consequently, the chips 102 are likely to be damaged. In a heating system using the heater 109 or 110 it is more difficult to set heating requirements than in a heating system using heated air because there are many varieties and sizes of printed circuit boards 101. Furthermore, when a reflecting plate is provided for reflecting heat from the heater 109, 110, the reflecting surface may become coated by flux scattering from the solder paste 103, thereby decreasing the thermal efficiency of the heater 109, 110. In view of the state of the art it would be desirable to provide a soldering apparatus of a reflow type capable of blocking radiant heat including far infrared rays generated from the heaters and as a consequence removing an impact of radiant heat upon printed circuit boards due to far infrared rays, whilst preheating the printed circuit boards as a whole at uniform temperatures in the preheating chambers and fusing the solder paste in uniform manner in the reflow chamber. The soldering apparatus of a reflow type of the present invention, like that of Fig. 2, comprises a conveyor means for conveying a printed circuit board on which a chip is temporarily mounted with a solder paste successively through at least one preheating chamber for preheating the printed circuit board and a reflow chamber for soldering the chip on the printed circuit board by fusion of the solder paste. Each of the preheating and reflow chambers has a fan for ventilating air in the chamber, one or more heaters for heating air in the chamber, and an air inlet and an air outlet for circulating air heated by the heater. The soldering apparatus of the present invention is characterized in that each of the heaters is mounted on a wall of its respective chamber which extends parallel to and laterally to one side of the path of travel of the printed circuit boards through the chamber. Furthermore, each of the air ventilating fans is located in its chamber downstream of the heater or heaters thereof in the air circulation between air inlet and air outlet, while each chamber includes a screening member mounted around the heater or heaters so as to prevent direct radiation of radiant heat into the chamber and onto a circuit board on the conveyor means. In preferred embodiments of the apparatus of the present invention, the preheating and/or reflow chambers may be provided with a flow transforming member in order to heat the printed circuit boards in uniform manner by transforming a turbulent flow of heated air into a laminar flow. With this preferred arrangement, the radiant heat generated from the heaters can be blocked, preventing the heating of the printed circuit boards by the radiant heat. Furthermore, the air heated in the preheating chamber and in the reflow chamber is blown to the printed circuit boards as a whole in uniform manner by allowing the heated air to pass through the air flow transforming member as a laminar flow, in addition to forcible circulation of the heated air by rotation of the ventilating fans. A preferred embodiment of a soldering apparatus of a reflow type will now be described in detail with reference to Figs. 1(a), 1(b) and 1(c) of the accompanying drawings, in which: Fig. 1(a) is a cross-sectional side view showing the soldering apparatus; Fig. 1(b) is a cross-sectional view taken along the line I-I of Fig. 1(a); and Fig. 1(c) is a cross-sectional view taken along the line II-II of Fig. 1(a). Referring to Figs. 1(a)-(c) of the drawings, the soldering apparatus 21 of the reflow type is shown to comprise a first preheating chamber 22, a second preheating chamber 23, and a reflow chamber 24, each of the first and second preheating chambers 22 and 23 and the reflow chamber 24 each being symmetrically disposed so as to vertically interpose a belt conveyor 5 of a metal net which is driven through rollers 5A. The first preheating chamber 22 is disposed at a position upstream of the second preheating chamber 23 with respect to a belt conveyor 5, and the reflow chamber 24 is disposed at a position downstream of the second preheating chamber 23 with respect thereto. This arrangement permits the heating of a printed circuit board 1 on which a chip 2 is temporarily mounted by means of a solder paste 3 in succession during horizontal movement of the belt conveyor 5 that conveys the printed circuit board 1 in a direction indicated by the arrow A. The conveyor means may be a conveyor chain with holding claws for holding printed circuit boards. The first preheating chamber 22 is provided with a heater 25a, such as a sheathed heater, far infrared ray heater or the like, on a side wall 22A which extends along the conveying direction of the printed circuit board 1, namely along the direction indicated by the arrow A, so that air therein can be heated to approximately 160 °C for heating the printed circuit boards 1 to rapidly raise their temperature to approximately 140 °C , below the fusion point of the solder paste 3. The first preheating chamber 22 is further provided with a screening plate 26a, for example, of a metal plate, in parallel to an inner surface of the side wall 22A so as to block radiation of radiant heat containing far infrared rays generated from the heater 25a into the first preheating chamber 22. The screening plate 26a forms a heating sub-chamber 27a in association with the side wall 22A on which the heater 25a is mounted and the provision of the screening plate 26a prevents radiant heat from radiating onto the printed circuit boards 1 with the chips 2 mounted thereon. In the first preheating chamber 22 is mounted a ventilating fan 28a, such as multiblade fan or the like, for circulating the heated air in the chamber, and a flow passage 35a is provided for communicating the heating sub-chamber 27a with the inside of the ventilating fan 28a, through which the air heated in the heating sub-chamber 27a by the heater 25a is passed into the ventilating fan 28a operated by a motor 29 so that the heated air is circulated in the first preheating chamber 22. The first preheating chamber 22 is provided with an air outlet 30a at a lower end thereof, and the air outlet 30a in turn is provided with an flow transforming plate 32a at a position adjacent to the passage along which the printed circuit board 1 with the chips 2 is conveyed. The air flow transforming plate 32a serves to transform a turbulent air flow in the chamber into a laminar flow. Thus, the heated air withdrawn from the first preheating chamber 22 through the air flow transforming plate 32a is caused to flow as a laminar flow in a direction shown by the arrow B and is blown uniformly onto the printed circuit boards 1 conveyed by the belt conveyor 5. The second preheating chamber 23 has substantially the same structure as described immediately hereinabove for the first preheating chamber 22. As shown in FIG. 1, identical elements are provided with identical reference numerals but to which reference symbol "b" is added. More specifically, for example, the second preheating chamber 23 is likewise provided with a heater 25b for heating air therein at temperatures as high as 140°C so as to heat the printed circuit boards 1 and retain them at 140 °C in stable manner while they are conveyed by the belt conveyor 5. The printed circuit boards 1 are then conveyed to the reflow chamber 24 which in turn is substantially the same as the first preheating chamber 22, so that identical elements are provided with identical reference numeral but with reference symbol "c" after the reference numeral. The air heated in the heating sub-chambers 27a, 27b, and 27c of the preheating chambers 22 and 23 and the reflow chamber 24 is introduced through the flow passage 35 therefrom to the ventilating fans 28a, 28b, and 28c, respectively, and blown by them onto the printed circuit boards 1 in the direction as shown by the arrow B. More specifically, the heated air withdrawn through the air flow transforming plates 32a, 32b, and 32c at the air outlets 30a, 30b, and 30c is allowed to arise in the soldering apparatus 21 for circulation and then sucked again through air inlets 31a, 31b, and 31c defined at both side portions in the widthwise direction perpendicular to the conveying direction (indicated by the arrow A) of the printed circuit boards 1, into the heating sub-chambers 27a, 27b, and 27c, respectively. A passage of the heated air in a form of a turbulent flow caused by the fans 28a, 28b, and 28c leads eventually to a laminar flow as the heated air passes through the flow transforming plates 32a, 32b, and 32c, thus blowing the air in uniform manner and as a consequence heating the printed circuit board 1 uniformly in a widthwise direction of the printed circuit board 1. The uniform heating of the printed circuit board 1 in the widthwise direction in the respective first preheating chambers 22 and 23 and in the reflow chamber 24, respectively, permits a uniform fusion of the solder paste 3, thereby avoiding irregularity of soldering and providing printed circuit boards 1 of higher quality. The printed circuit boards 1 with the chips 2 soldered thereon are then conveyed out of the reflow chamber 24 and cooled by a cooling fan 33. Exhaust air and gases in the soldering apparatus 21 are withdrawn by an exhaust fan 34 mounted on an upper wall of the soldering apparatus 21. In this embodiment, since the heating sub-chambers 27a, 27b, and 27c are formed along the both side walls 22A, 23A, and 24A arranged in the conveying direction of the printed circuit boards 1 (indicated by the arrow A), as mentioned above, the printed circuit boards may be heated only by the air heated by the heaters 25a, 25b, and 25c without direct heating due to radiation of radiant heat containing far infrared generated from the heater 25a, 25b and 25c. Therefore, damage to the chips due to the radiant heat can be effectively prevented. However, since no radiant heat from the heater 25 is used to heat the solder paste it will take a longer time to fuse or melt the solder paste 3. This time may be shortened, however, by increasing the flow velocity of the heated air. Still further, in the above preferred embodiment, although the soldering apparatus comprises a pair of similarly constructed upper and lower first preheating chambers, a pair of similarly constructed upper and lower second preheating chambers and a pair of similarly constructed upper and lower reflow chambers, either one of the upper and lower chambers may be omitted if desired. An important feature of the illustrated soldering apparatus is that it is provided with heaters on side walls of the preheating chambers and of the reflow chamber extending along the conveying direction of the printed circuit board, for heating air therein, and also with screening plates along the heaters in order to prevent radiation of radiant heat from the heaters into the preheating chambers and the reflow chamber. Furthermore, the preheating chambers and the reflow chamber of the soldering apparatus are provided each with an air inlet and an air outlet in order to allow the heated air to be circulated in the chamber with the ventilating fan. With the arrangement of the soldering apparatus according to the illustrated embodiment, the printed circuit boards and chips are heated only by the air heated, so that such arrangement can prevent damage of the chips due to direct heating by radiant heat which might otherwise be caused by a fusion of the solder paste prior to the heating of the printed circuit boards, whereby the invention can provide printed circuit boards with chips of higher quality, and also permit an easy adjustment of the temperatures in the chambers because the air in the chambers is heated by heaters mounted within the chambers. Thus also productivity can be improved.

Claims: A soldering apparatus of a reflow type, comprising: a conveyor means (5), for conveying a printed circuit board (1) on which a chip (2) is temporarily mounted with a solder paste (3) successively through a preheating chamber (22;23) for preheating the printed circuit board and a reflow chamber (24) for soldering the chip on the printed circuit board by fusion of the solder paste, each of said chambers (22;23;24) having a fan (28a;28b;28c) for ventilating air in the chamber, one or more heaters (25a;25b;25c) for heating air in the chamber, and an air inlet (31a;31b;31c) and an air outlet (30a;30b;30c) for circulating air heated by the heater, wherein; each of said heaters (25a;25b;25c) is mounted on a wall of its respective chamber (22;23;24;) which extends parallel to and laterally to one side of the path of travel of said printed circuit boards (1) through the chamber, each of said fans (28a;28b;28c) is located in its chamber (22;23;24) downstream of the heater or heaters (25a;25b;25c) thereof in the air circulation between air inlet (31a;31b;31c) and air outlet (30a;30b;30c), and each chamber (22;23;24) includes a screening member (26a;26b;26c) mounted around the heater or heaters (25a;25b;25c) so as to prevent direct radiation of radiant heat into the chamber and onto a circuit board (1) on the conveyor means (5). A soldering apparatus as claimed in Claim 1, wherein the preheating chamber (22;23) is provided at an air outlet portion with an air flow transforming member (32a;32b) for providing a uniform flow of heated air in the preheating chamber. A soldering apparatus as claimed in Claim 1 or Claim 2, wherein the reflow chamber (24) is provided at an air outlet portion with an air flow transforming member (32c) for providing a uniform flow of heated air in the reflow chamber.

Inventors: KONDO KENSHI, KONDO, KENSHI
Applicants: NIPPON DENNETSU KEIKI KK, NIHON DEN-NETSU KEIKI CO., LTD.
Application year: 1989
Main classification: B23K1
IPC codes: B23K1, H05K3, B23K31