SOLDERING APPARATUS

Abstract: A soldering apparatus of a type in which printed circuit boards having temporarily mounted thereon chip parts with solder paste are heated with in a heating chamber to cause the solder paste to reflow. The heating chamber is partitioned into preheating chamber or chambers and a reflowing chamber, with each preheating chamber being divided into gas flow channels and center space through which the board is transferred and in which a heater, flow control plates and a fan are provided so that the hot air heated with the heater in each preheating chamber is forcibly recirculated within each chamber to preheat the board uniformly. The preheated board is transferred to the reflowing chamber provided with far infrared radiation lamps to cause the solder paste to reflow.

Description: This invention relates to apparatus for soldering printed circuit boards and, more specifically, to a soldering apparatus of a type in which printed circuit boards having temporarily mounted thereon electric parts with solder preforms or solder pastes are heated with hot air to cause the preforms to melt or reflow. One known soldering apparatus of the above-mentioned type is schematically shown in cross-section in Fig. 4, in which designated as 1 is a printed circuit board having chip parts 2 temporarily mounted thereon with a solder paste 3. The board 1 is transferred through a housing 4 by means of a belt conveyor 5 in the direction shown by the arrow A. The inside of the housing 4 is divided by a partition plate 4a into a heating chamber 6 and a cooling chamber 7. Disposed in the heating chamber 6 are sheathed heaters 8 for heating the air therewithin. Fans 10 are provided for causing the heated air to blow on the printed circuit board 1 travelling through the heating chamber 6. Infrared radiation lamps 9 are provided in the chamber 6 adjacent to an inlet portion of thereof to facilitate the heating of the printed circuit board 1. The board 1 is heated in the heating chamber 6 to a temperature sufficient to cause the solder paste 3 to melt or reflow. The resulting board 1 with molten solder is then introduced into the cooling chamber 7 where it is cooled by the action of a cooling fan 11 so that the molten solder is solidified to provide the firm bonding of the chip parts 2 to the board 1. With the above soldering apparatus, since the stream of the heated air in the heating chamber is not uniform, the printed circuit board 1 is not uniformly heated. Therefore, when the board 1 has a large size, there is a risk of a soldering failure. This risk could be avoided if the residence time of the board 1 within the heating chamber 6 was to be increased by, for example, slowly transferring the board 1 through the heating chamber 6. However, such increase of the residence time tends to cause thermal damage to the chip parts 2 on the board 1. The present invention has been made with the foregoing problems of the conventional soldering apparatus in view. In EP-A-0237151 there is disclosed an infrared soldering apparatus for soldering printed circuit boards and which comprises an axially elongated housing through which the circuit boards to be soldered are conveyed and which is partitioned so as to form successively, in the path of travel of the circuit boards, a preheat chamber, a heat stabilizing chamber, a main or reflow heating chamber and, finally, a cooling chamber. Infrared lamps form the heating means in the preheat, heat stabilizing and main heating chambers. DE-A-2928156 shows a soldering furnace for heating and soldering large heat exchangers which are moved through the furnace on a conveyor. The interior of the furnace includes opposed, longitudinally extending air conduction elements between which is defined the heating and soldering chamber and which are constructed so as to permit the direction of flow of heating air over a heat exchanger within the chamber to be varied. In accordance with the present invention there is provided apparatus for soldering printed circuit boards having electric parts temporarily mounted thereon with solder preforms, comprising: an axially elongated housing member; conveying means providing a path along which the printed circuit boards are conveyed through said housing member in the direction parallel to the axis of said housing member; one or more laterally extending partition means provided within said housing member for partitioning the inside space thereof into a reflowing chamber and one or more preheating chambers, with said reflowing chamber being located downstream of said one or more preheating chambers with respect to the direction of the travel of said printed circuit boards through said housing member and with said reflowing chamber and one or more preheating chambers being axially aligned ; an aperture provided in each of said one or more partition means to permit the printed circuit boards to pass therethrough; a pair of spaced apart vertical partitions extending axially within each of said one or more preheating chambers for partitioning same into two, outer, air flow channels and a center space; upper and lower openings provided in each of said vertical partitions so that the air flow channels of each chamber are in fluid communication with the corresponding center space; heating means disposed in the center space of each of said one or more preheating chambers for heating the air in said center space, so that the printed circuit boards are preheated with the heated air during their passage through said one or more preheating chambers; heating means disposed within said reflowing chamber for causing the solder preforms of the printed circuit boards to reflow during their passage through said reflowing chamber; fan means provided in the center space of each of said one or more preheating chambers to cause the air in said chamber to circulate through said center space and said air flow channels; and flow control plates provided in the center space of each of said one or more preheating chambers and positioned between the fan and the path of travel of the printed circuit boards for controlling the flow of the circulating air through said center space so as to uniformly heat the printed circuit boards. A preferred embodiment of an apparatus in accordance with the present invention will now be described in detail with reference to the accompanying drawings, in which: Fig. 1 is an elevational, cross-sectional view schematically showing the soldering apparatus; Fig. 2 is a cross-sectional view taken on the line II-II in Fig. 1; and Fig. 3 is a cross-sectional view taken on the line III-III in Fig. 1. Referring now to Figs. 1 through 3, designated generally as 20 is an axially elongated housing member generally rectangular in cross section through which a printed circuit board 1 having electric parts or chip parts 2 temporarily mounted thereon with solder preforms or paste 3 is transferred along a predetermined path of travel, provided by conveying means such as a belt conveyor or a transfer chain 5, in the direction shown by the arrow A. The inside space of the housing member 20 is divided by one or more partition walls (two partition walls in the particular example shown) 21a and 21b into a reflowing chamber 22 and one or more (two in the particular example shown) preheating chamber 23a and 23b. The reflowing chamber 22 is positioned downstream of the preheating chambers 23a and 23b with respect to the direction of the travel of the printed circuit board 1. In the illustrated embodiment, a cooling chamber 24 is also defined downstream of the reflowing chamber 22 by a partitioning plate 25 within the housing member 20. The housing member 20, partition walls 21a and 21b and partition plate 25 are provided with suitable apertures 31a, 31b, 32a, 32b and 33 through which the printed circuit board 1 is passed during its passage through the housing member 20. As best seen from Fig. 2, a pair of spaced apart, vertical, axially extending, partitions 26a are provided within the preheating chamber 23a for partitioning the chamber 23a into two, outer, air flow channels 27a and a center space 28a. Each partition 26a has top and bottom openings 29a and 30a so that the air flow channels 27a are in fluid communication with the center space 28a through the openings 29a and 30a. A fan 34a is provided in the center space 28a. The fan 34a is operable so that the air within the preheating chamber 23a is caused to be circulated as shown by the arrow B in Fig. 2 from the center space 28a into the air flow channels 27a through the bottom openings 30a and then into the center space 28a through the top openings 29a. Flow control plates 35a are disposed in the center space 28a of the preheating chamber 23a at a position between the fan 34a and the conveyor belt 5 for uniformly distributing the flow of the air through the center space 28a. Preferably, the flow control plates 35a are axially spaced apart, downwardly diverging plates extending laterally between and supported by the partitions 26a. The number, structure, orientation of the control plates 35a may be suitably determined so as to obtain optimum results. The preheating chamber 23b and, preferably the reflowing chamber 22, too, are provided with partitions 26b and 26c having top and bottom openings 29b and 29c, and 30b and 30c; fans 34b and 34c; and flow control plates 35b and 35c, respectively. These parts are similar to those in the preheating chamber 23a and the detailed explanation thereof is not repeated here. First heating means, such as electric heaters, preferably sheathed heaters 36a and 36b, are provided in the center spaces 28a and 28b, respectively, for heating the air therewithin. Thus, the printed circuit board 1 is preheated by the heated air during its passage through the preheating chambers 23a and 23b. It is preferred that an auxiliary heating means, preferably far infrared radiation lamps 37 be provided in the preheating chamber 23a at a position adjacent to the inlet aperture 31a in order to reduce the preheating time. Designated as 38 are reflecting plates to increase the heating efficiency of the lamps 37. Second heating means, preferably far infrared irradiation lamps 39 with reflecting plates 40 are provided in the center space 28c of the reflowing chamber 22 for causing the solder pastes 3 to melt or reflow during the passage of the printed circuit board 1 through the reflowing chamber 22. If desired, auxiliary air heaters such as sheathed heaters similar to the heaters 36a and 36b may be provided in the reflowing chamber 22 to facilitate the reflowing operation. The above-described soldering apparatus is typically operated as follows. First, the temperatures within the upstream end preheating chamber 23a and the the succeeding preheating chamber 23b are maintained at about 160 °C and 140 °C, respectively. The printed circuit board 1 bearing chip parts 2 is first introduced through the inlet aperture 31a into the preheating chamber 23a where it is heated to about 140 °C with the heated air recirculating through the center space 28a by the operation of the fan 34a. Since the heated air in the chamber 23a is about 160 °C, the heating of the board 1 to about 140 °C can be effected within a relatively short period of time. The board 1 is then transferred through the aperture 32a to the succeeding preheating chamber 23b where it is contacted with the heated air at about 140 °C. This step serves to effect a fine adjustment of the temperature of the board and to minimize the temperature fluctuation of the board 1. The preheating in the chambers 23a and 23b is generally performed for about 60-80 seconds. The preheated board 1 is then fed through the aperture 32b to the reflowing chamber 22 where it is heated with the lamps 39 quickly (generally at 215 °C for 15-20 seconds) to cause the solder paste or preforms to melt. Thereafter, the board 1 is discharged from the reflowing chamber 22 and is introduced through the aperture 33 into the cooling chamber 24 where it is cooled by means of a cooling fan 41 to solidify the molten solder and to provide firm bonding of the parts 2 to the board 1. The resulting board 1 is withdrawn out of the housing member 20 through the outlet aperture 31b. Thus, in the illustrated soldering apparatus according to the present invention, since one or more, preferably two, preheating chambers 23a and 23b are provided upstream of the reflowing chamber 22, heating of the board 1 can be sufficiently effected without involving thermal damages of the chip parts mounted thereon. Moreover, since the air within the preheating chambers 23a and 23b and, if desired, the reflowing chamber 22 is forcibly recirculated in each chamber and since flow control plates 35a, 35b and 35c are provided above the board transfer path, the flow of the heated air in each chamber is uniformly distributed so that the entire printed circuit board 1 can be heated uniformly.

Claims: Apparatus for soldering printed circuit boards (1) having electric parts (2) temporarily mounted thereon with solder paste or preforms (3), comprising: an axially elongated housing member (20); conveying means (5) providing a path (A) along which the printed circuit boards (1) are conveyed through said housing member (20) in the direction parallel to the axis of said housing member; and heating means (39) disposed within said housing member (20) for causing the solder paste or preforms (3) of the printed circuit boards (1) to reflow; characterized in that: one or more laterally extending partition means (21 a ,21 b ) are provided within said housing member (20) for partitioning the inside space thereof into a reflowing chamber (22) in which is disposed said heating means (39) for causing the solder paste or preforms (3) of the printed circuit boards (1) to reflow, and one or more preheating chambers (23 a ,23 b ), with said reflowing chamber (22) being located downstream of said one or more preheating chambers (23 a ,23 b ) with respect to the direction of the travel (A) of said printed circuit boards (1) through said housing member (20) and with said reflowing chamber (22) and one or more preheating chambers (23 a ,23 b ) being axially aligned; an aperture (32 a ,32 b ) is provided in each of said one or more partition means (21 a ,21 b ) to permit the printed circuit boards (1) to pass therethrough; a pair of spaced apart vertical partitions (26 a ,26 b ) extend axially within the or each of said one or more preheating chambers (23 a ,23 b ) for partitioning same into two, outer, air flow channels and a center space (28 a ,28 b ); upper and lower openings (29 a ,30 a ;29 b ,30 b ) are provided in each of said vertical partitions (26 a ,26 b ) so that the air flow channels (27 a ,27 b ) of each chamber are in fluid communication with the corresponding center space (28 a ,28 b ); heating means (36 a ,36 b ) are disposed in the center space (28 a ,28 b ) of each of said one or more preheating chambers (23 a ,23 b ) for heating the air in said center space, so that the printed circuit boards (1) are preheated with the heated air during their passage through said one or more preheating chambers; fan means (34 a ,34 b ) are provided in the center space (28 a ,28 b ) of each of said one or more preheating chambers (23 a ,23b) to cause the air in said chamber to circulate through said center space and said air flow channels (27 a ,27 b ); and flow control plates (35 a ,35 b ) are provided in the center space (28 a ,28 b ) of each of said one or more preheating chambers (23 a ,23b) and positioned between the fan (34 a ,34 b ) and the path of travel (A) of the printed circuit boards (1) for controlling the flow of the circulating air through said center space (28 a ,28 b ) so as to uniformly heat the printed circuit boards (1). Apparatus as set forth in claim 1, further comprising a cooling chamber (24) provided adjacent to and downstream of said reflowing chamber (22) with said path (A) of the printed circuit boards (1) extending through said cooling chamber, and a cooling fan (41) provided in said cooling chamber (24) and operable for cooling the printed circuit boards during their passage through said cooling chamber. An apparatus as set forth in claim 1 or claim 2, wherein said heating means (36 a ,36 b ) disposed in said one or more preheating chambers (23 a ,23 b ) includes one or more electric heaters. Apparatus as set forth in any preceding claim, further comprising an auxiliary heater (37) provided in the, or the upstream end, preheating chamber (23a) to expedite the heating of the printed circuit boards (1). Apparatus as set forth in claim 4, wherein said auxiliary heater (37) includes one or more far infrared radiation lamps. Apparatus as set forth in any preceding claim, wherein said heating means (39) for causing said reflow of said solder paste or preforms (3) includes one or more far infrared radiation lamps. Apparatus as set forth in any preceding claim, further comprising: a pair of spaced apart vertical partitions (26c) extending axially within said reflowing chamber (22) for partitioning same into two, outer, air flow channels (27 c ) and a center space (28 c ), with said heating means (39) for causing said reflow of said solder paste or preforms (3) being disposed within the center space (28c) of said reflowing chamber; upper and lower openings (29 c ,30 c ) provided in said second pair of vertical partitions (26 c ) so that the air flow channels (27c) of said reflowing chamber are in fluid communication with the center space (28 c ) of said reflowing chamber; fan means (34c) provided in the center space (28c) of said reflowing chamber to cause the air in said reflowing chamber to circulate through the center space and the air flow channels (27 c ) of said reflowing chamber; and flow control plates (35 c ) provided in the center space (28 c ) of said reflowing chamber and positioned between the fan means (34 c ) thereof and the path of travel (A) of the printed circuit boards (1) for controlling the flow of the circulating air through the center space (28 c ) of said reflowing chamber so as to uniformly heat the printed circuit boards. Apparatus as set forth in claim 7, further comprising an auxiliary air heater provided in said reflowing chamber (22) for heating the air therewithin. Apparatus as set forth in any preceding claim, wherein said flow control plates (35 a ,35 b ) in said preheating chambers (23 a ,23 b ) are axially spaced apart plates extending laterally between and supported by said pair of vertical partitions (26 a ,26 b ).

Inventors: KONDO, KENSHI
Applicants: NIHON DEN-NETSU KEIKI CO., LTD.
Application year: 1988
Main classification: B23K1
IPC codes: B23K1