Technical Field

[1] The present invention relates to a solder bath, and more specifically to a solder bath using a liquid induction pump so as to prevent the pulsation of molten solder and supply molten solder in the form of a stable wave.

[2]

Background Art

[3] In general, on the printed circuit board used in various kinds of electronic devices are mounted various kinds of chip parts according to the characteristics of the electronic devices, and the parts are soldered and fixed on the circuit board by an automatic soldering apparatus.

[4] A conventional automatic soldering apparatus is provided with a solder processing unit consisting of a fluxer, a heater, a solder bath and a cooler, and a conveyer is installed above the solder processing unit.

[5] Soldering the printed circuit board by the automatic soldering unit will be described briefly. First, the printed circuit board is put on the conveyor and is driven on the solder processing unit, and then flux is applied by the fluxer on the solder surface of the printed circuit board.

[6] Next, the printed circuit board applied with flux is preheated by the heater. Namely, the printed circuit board is preheated by the heater because if flux remains on the printed circuit board there is a danger that molten solder could spatter in the subsequent contact process with molten solder, and if the printed circuit board at room temperature is contacted with molten solder of high temperature there is a problem that heat shock is applied to the printed circuit board or the chip parts mounted on the printed circuit board so as to damage them, and if the printed circuit board at room temperature contacts molten solder of high temperature there is a problem that the temperature of molten solder is lowered so as to lower solderability.

[7] The printed circuit board preheated by the heater is conveyed over the solder bath, and subsequently it goes through the process in which the molten solder supplied from the solder bath contacts the printed circuit board for the chip parts to be soldered.

[8] In general, a first nozzle and a second nozzle are installed in the solder bath of an automatic soldering apparatus, and the printed circuit board has the chip parts soldered while it passes over the first nozzle and second nozzle as it comes into contact with molten solder supplied continuously from the nozzles.

[9] A narrow jet outlet with small diameter is formed in the first nozzle, so that molten solder is ejected in an inclined wave shape. Accordingly, the first nozzle plays a role of soldering by inflowing into the chip parts and the edge portions of the printed circuit board which are difficult for molten solder to inflow into, or the gaps between leads and through holes of the electronic parts.

[10] And in the second nozzle is formed a wide jet outlet with large diameter, so that molten solder is ejected in a gentle wave shape. Therefore, the molten solder ejected in a gentle wave shape from the second nozzle comes into contact with a bridge or icicle shaped protuberance generated from the first nozzle to remove this, so that the printed circuit board has a more cleanly soldered condition.

[11] The solder bath 1 used in the conventional automatic soldering apparatus as described above is shown in Fig. 1.

[12] On the outer circumference of the solder bath 1 are installed heaters 7, and in the solder bath 1 are installed the first nozzle 2 and the second nozzle 3 directed toward the printed circuit board 6 which is conveyed along a conveyor path. In the bottom portions of the first nozzle 2 and the second nozzle 3 are installed impeller ducts 9 for supplying molten solder 8 to the jet outlets of the first nozzle 2 and second nozzle 3, and in the impeller ducts are placed impellers 5 respectively. And the impellors 5 are connected operatively to drive units 4 through impeller shafts respectively.

[13] Below the soldering process will be described.

[14] If the drive units 4 are operated to rotate the impellors 5, with solder in a molten condition by operating the heaters 7 installed on the solder bath 1, the molten solder 8 starts being ejected through the first nozzle 2 and the second nozzle 3. At this time, the molten solder coming out through the narrow jet outlet with a small diameter of the first nozzle 2 is ejected in an abrupt wave shape, and the molten solder 8 coming out through the wide jet outlet with a large diameter of the second nozzle 3 is ejected in an almost flat gentle wave shape so as to be in contact with the printed circuit board conveyed by the conveyor (not shown). As molten solder comes into contact with the printed circuit board 6 that has flux applied in advance, the soldering of the chip parts is carried out.

[15] Since the solder waves are generated by the rotation of the impellor 5, impurities flow back during the wave as oxidation by solder occurs on the impeller shaft, and not only pulsation occurs but also solder waves are unstable. As a result, the flow condition of molten solder is bad, so it is not circulated smoothly.

[16] In particular, there is a problem of excessive oxidation because molten solder comes into excessive contact with air due to pulsation. Due to such excessive oxidation, solder congeals to become dregs, which become a factor of trouble with soldering work.

[17] Disclosure of Invention

Technical Problem

[18] Accordingly, it is an object of the present invention to provide a solder bath provided with liquid induction pumps so as to prevent the pulsation of molten solder and supply molten solder in a stable wave form.

[19]

Technical Solution

[20] In accordance with the present invention, there is provided a solder bath comprising: a storage tank around which heaters are installed; a first nozzle and a second nozzle which are installed at a location raised to a predetermined height from the floor of the storage tank by fixing means arranged in the storage tank; and liquid induction pumps having thrust ducts installed so as to communicate with said storage tank, induction coils placed so as to enclose the outer circumference of said thrust ducts, and internal iron cores installed in separation from the inner wall of said thrust duct to be connected to said first nozzle and second nozzle respectively.

[21] Preferably, a plurality of said induction coils are wound in three-phases and placed sequentially in separation at predetermined intervals from each other in the vertical direction, and three-phase current is supplied to said plurality of induction coils, and said internal iron cores are formed so as to have a space to provide separation from the bottom of said thrust ducts.

[22] Preferably, the solder bath of the present invention further comprises pump heaters installed around the lower portion of said thrust ducts.

[23] Preferably, the solder bath of the present invention further comprises drain valves installed in the lower end portions of said thrust ducts and drain ports connected to said drain valves.

[24] Preferably, a first temperature sensor is installed on one side of said storage tank and second temperature sensors are installed on one side of said thrust ducts.

[25] Preferably, electricity is supplied sequentially to said heaters, said induction coils and said pump heaters.

[26] Preferably, the area between the inner wall of said thrust duct and the outer wall of said internal iron core is smaller than the area defined by the inner wall of said internal iron core.

[27] Preferably, the thickness of said thrust duct is in a range between 1.5 and 2.0 mm and the thickness of said internal iron core is in a range between 4.5 and 5.0 mm.

[28] Preferably, a first nozzle filter and a second nozzle filter are installed respectively in said first nozzle and said second nozzle.

[29] Preferably, said first nozzle and said second nozzle are formed monolithically. Advantageous Effects

[30] According to the present invention, it is possible to prevent the pulsation of molten solder and supply molten solder in a stable wave form, so product rejection rate is reduced so as to improve soldering quality and ensure product reliability.

[31] Also, the quantity of oxidized solder is decreased so as to reduce the equipment required for removing oxidized solder, so equipment operating costs and production costs can be decreased.

[32] Also, it can meet the soldering quality of the printed circuit board that is diversified.

[33]

Brief Description of Drawings

[34] The above objects, features and advantages of the present invention will become more apparent to those skilled in the related art in conjunction with the accompanying drawings. In the drawings:

[35] Fig. 1 is a front view schematically showing a solder bath of prior art;

[36] Fig. 2 is a front view schematically showing a solder bath according to the present invention;

[37] Fig. 3 is a plan view of the solder bath shown in Fig. 2; and

[38] Fig. 4 is a schematic view for describing the operation principle of the liquid induction pump of the solder bath shown in Fig. 2. Best Mode for Carrying out the Invention

[39] Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. When inserting reference numerals into the constituents in the respective drawings, although the constituents are illustrated in different drawings, so far as the constituents are the same, they are described to have the same reference numeral, where possible. The detailed description for the well-known function and constitution, judged to make the gist of the invention obscure, will be omitted.

[40] Fig. 2 is a front view schematically showing a solder bath according to the present invention, and Fig.3 is a plan view of the solder bath shown in Fig. 2.

[41] The solder bath of the present invention generally comprises a storage tank 10 and a first nozzle 26 and a second nozzle 42 which are installed at a location raised to a predetermined height from the floor of the storage tank 10 by a fixing means arranged in the storage tank 10.

[42] The storage tank 10 is supported by a frame 12 which, and the frame 12 is fixed at a location raised to a predetermined height from ground through vertical support members 14 and a horizontal support member 16.

[43] The horizontal support member 16 can have mobility improved by further comprising moving means 18 such as casters, which are mounted, on the rear surface thereof.

[44] As the fixing means, first nozzle supporters 28 and second nozzle supporters 44 composed of brackets and clamping bolts are used, as shown in Fig. 2 and Fig. 3.

[45] Respectively in the first nozzle 26 and the second nozzle 42 are mounted a first nozzle filter 62 and a second nozzle filter 64 for molten solder to be uniformly distributed and raised.

[46] The first nozzle filter 62 and the second nozzle filter 64 may be made in a mesh structure to remove impurities included in molten solder.

[47] And it is preferable that the first nozzle 26 and the second nozzle 42 are constructed in one structure.

[48] Conventionally the first nozzle and the second nozzle are constructed in mutually separated structures, giving rise to a problem that solderability was lowered because the temperature of molten solder is lowered between the first nozzle and the second nozzle. In order to solve this problem, the present invention provides a construction that the first nozzle 26 and the second nozzle 42 are made monolithically to narrow the separation between the first nozzle 26 and the second nozzle 42, so as to prevent the temperature of molten solder between the first nozzle 26 and the second nozzle 42 from being lowered.

[49] A first nozzle block 66 of a mask is mounted at the upper end of the first nozzle 26.

Preferably, the first nozzle block has holes of a predetermined shape so that molten solder can generate waves uniformly.

[50] As shown in Fig. 2, at the upper portion of the second nozzle 42, a second nozzle adjusting guide 68 and a second nozzle adjusting plate 70 are mounted so as to regulate the shape of second waves. The second nozzle adjusting guide 68 has one end bent down toward the first nozzle 26 and the other end bent so as to form the neck portion of the second nozzle 42. The second nozzle adjusting plate 70 has its maximum height formed lower than that of the second nozzle adjusting guide 68, and is directed vertically upward.

[51] And under the storage tank 10 are installed liquid induction pumps 29 and 45 for imparting waves to molten solder.

[52] The liquid induction pumps 29 and 45 include thrust ducts 30 and 46 installed so as to communicate with the storage tank 10, induction coils placed around the thrust ducts 30 and 46, and internal iron cores 32 and 48 installed in separation from the inner walls of the thrust ducts 30 and 46 and connected respectively to the first nozzle 26 and the second nozzle 42.

[53] The thrust ducts 30 and 46 preferably have a cylindrical shape, but the shape of the cross section is not specially limited.

[54] As shown in Fig. 4, a plurality of induction coils 451, 452 and 453 are placed and vertically separated each other around the thrust ducts 30 and 46 at predetermined intervals so as to enclose the thrust ducts 30 and 46.

[55] The plurality of induction coils are wound in three-phases and placed sequentially in separation at predetermined intervals from each other vertically, and three-phase current is supplied from a power source to the plurality of induction coils.

[56] Six induction coils comprising three same or different kinds are used in the embodiment of the present invention.

[57] And in order for molten solder to rise smoothly, it is preferable that the internal iron cores 32 and 48 are formed in such a way that they correspond with the shapes of the cross sections of the bottom end portions of the first nozzle 26 and the second nozzle 42.

[58] As mentioned above, the internal iron cores 32 and 48 are placed in separation from the inner circumferential walls of the thrust ducts 30 and 46, and it is preferable that they are made concentric with the thrust ducts 30 and 46 as the rising force of molten solder can be improved.

[59] It is also preferable that the internal iron cores 32 and 48 have cylindrical shapes and are placed in such a way that their bottom ends are separated from the bottom of the thrust ducts 30 and 46.

[60] The reason for making the internal iron cores 32 and 48 in a cylindrical shape is to raise molten solder effectively.

[61] Therefore, the internal iron cores 32 and 48 and the first nozzle 26 and the second nozzle 42 communicate with each other, and the storage tank 10 communicates with the space between internal cores 32 and 48 and thrust ducts 30 and 46 to flow the molten solder.

[62] In addition, pump heaters 36 and 50 for heating molten solder are installed at the lower portion of the thrust ducts 30 and 46.

[63] In order to improve the performance of the liquid induction pumps 29 and 45, it is preferable to reduce the thickness of the thrust ducts 30 and 46 so as not to impede the magnetic force due to an induction coil. However, since liquid solder of high temperature should be stored, the lowest limit of thickness exists. Namely, it is preferable that the thickness of the thrust ducts 30 and 46 is in a range between 1.5 to 2.0 mm.

[64] And for the thrust ducts 30 and 46, nonmagnetic material should be used so that there is no problem wherein the magnetic flux generated from a three-phase wound induction coil influences (interlinks) the liquid solder. Therefore, the thrust ducts 30 and 46 play a role like the air gap in an induction motor. If magnetic material is used instead of nonmagnetic material, the magnetic flux generated from the induction coil flows out through the thrust ducts 30 and 46 so as to reduce the quantity of interlinkage with solder, negatively influencing the efficiency of liquid induction pumps 29 and 45. [65] The internal iron cores 32 and 38 are made from magnetic materials, and they are the parts playing the same role as back iron in a linear induction motor. The magnetic flux generated from the three-phase winding of the induction coil influences (interlinks) the liquid solder between the internal nonmagnetic material and the internal magnetic material of the liquid induction pumps 29 and 45, so that solder can flow smoothly through the internal magnetic material.

[66] If the material of internal iron cores 32 and 38 is made of nonmagnetic material instead of magnetic material, the magnetic flux generated from the three-phase winding influences liquid solder to negatively influence thrust. In other words, since the direction of the current generated from liquid solder in the inner walls of the internal iron cores 32 and 38 and the direction of the current generated from the liquid solder between internal iron cores 32 and 38 and thrust ducts 30 and 46 is identical, thrust is generated in the identical direction.

[67] And if the thickness of the internal iron cores 32 and 38 is small, the magnetic flux generated from the three-phase winding is so saturated that the magnetic flux can influence the liquid solder inside, so it is preferable that the internal iron cores have dimensions above the range in which the magnetic force is not saturated. On the other hand, if the thickness is large, saturation of magnetic force may be prevented, but the space for liquid solder to flow is narrowed, which could negatively influence thrust.

[68] Therefore, the performance of liquid induction pumps 29 and 45 cannot be maximized unless dimensions within an adequate range are adopted. It is preferable that the thickness of internal iron cores 32 and 38 is in a range between 4.5 and 5.0 mm.

[69] And, at the lower end portions of the thrust ducts 30 and 46 are installed drain ports

40 and 54 and drain valves 38 and 52 for discharging solder liquid later such as in a case of maintenance.

[70] Also, a first temperature sensor 20 for detecting the temperature of the solder is further installed on one side of the storage tank 10, so it is possible to control the heating value of side heaters 23 and a bottom heater 24 based on the temperature of solder detected by the sensor.

[71] Also, second temperature sensors 56 and 58 for detecting the temperature of the solder are installed on one side of the thrust ducts 30 and 46, so it is possible to control the heating value of pump heaters 36 and 50 based on the temperature of solder detected by the sensors.

[72] Therefore, it is preferable to construct the side heaters 23, bottom heater 24 and pump heaters 36 and 50 as electric heaters.

[73] For operation, electricity is supplied sequentially to the heaters 23 and 24, the induction coils 451, 452 and 453 and the pump heaters 36 and 50. [74] And, in order to raise molten solder smoothly in the internal cores 32 and 48, it is preferable that the area B between the inner wall of thrust ducts 30 and 46 and the outer wall of internal cores 32 and 48 is made smaller than the area A defined by the inner wall of the internal iron cores 32 and 48.

[75] Therefore, the velocity energy of molten solder passing the area B can be converted into velocity energy in area A, and at the same time the interval between the induction coil and internal iron cores 32 and 48 can be reduced to improve the rising force by induced magnetism, so it is possible to prevent overload from being applied to induction coil.

[76] Basically, the configuration of the solder bath according to the embodiment of the present invention is as described above. Below the operation principle of solder bath will be described.

[77] The liquid induction pumps 29 and 45 have a structure as shown in Fig. 4.

[78] Accordingly, when three-phase alternating current is supplied to induction coils 451,

452 and 453, magnetic flux that is variable in terms of time according to Faraday s law is generated. And the generated magnetic flux that is variable in terms of time generates induced current in internal iron cores 32 and 48. Due to the inter action of the current and the magnetic flux generated like this, thrust is generated, so that molten solder in the internal iron cores 32 and 48 flows upward or downward.

[79] At this time, if the direction of magnetic flux of induction coils 451, 452 and 453 is made in the upward right screw direction as shown in Fig. 4, molten solder flows upward.

[80] Accordingly, the liquid induction pumps 29 and 45 can function as pumps that move liquid linearly upward.

[81] Therefore, the molten solder that rises in the internal iron cores 42 and 48 by liquid induction pumps 29 and 45 is ejected upward through the first nozzle 26 and the second nozzle 42 that are communicated with the internal iron cores 32 and 48, and solder liquid that is ejected and flows out from the first nozzle 26 and the second nozzle 42 passes the storage tank 10 again to enter into the internal iron cores 32 and 48 through the space between internal iron cores 32 and 48 thrust ducts 30 and 46.

[82] As a result of this, the molten solder in the liquid bath according to the embodiment of the present invention can be circulated in the arrow direction marked in Figs. 2 to 4.

[83] And as shown in Fig. 2, such molten solder of a wave shape generated by the liquid induction pumps 29 and 45 is contacted with the printed circuit board 60 conveyed by a conveyor (not shown), while the flux is already applied to the printed circuit board 60 that the chip parts to be soldered to are mounted thereon.

[84] Although the present invention has been described in connection with the exemplary embodiments illustrated in the drawings, it is only illustrative. It will be understood by those skilled in the art that various modifications and equivalents can be made to the present invention. Therefore, the true technical scope of the present invention should be defined by the appended claims.