JP4962197B2 - Jet solder bath - Google Patents

Description

  The present invention relates to a jet solder bath that is installed in an automatic soldering apparatus and solders a printed circuit board.

  In the automatic soldering apparatus, processing devices such as a fluxer, a pre-heater, a jet solder bath, and a cooler are sequentially installed, and a conveyor conveys on these processing devices. The printed circuit board is soldered by being fluxed by a fluxer, preheated by a pre-heater, solder is attached in a jet solder bath, cooled by a cooler while being run on a conveyor.

  In the automatic soldering apparatus, all the processing apparatuses affect the quality of soldering, but the jet solder bath is particularly important. For example, the required conditions for the jet solder bath are that the top of the jet should be horizontal, that there should be no pulsation that the jet height will move up and down, and that the printed board should have a high jet height if the lead is long. The jet can be made sufficiently high when it is not.

  The jet solder bath is for soldering the printed circuit board by jetting the molten solder upward and bringing the printed circuit board into contact with the jetted molten solder. To that end, the jet solder that sends the molten solder to the jet solder tank A pump and a jet nozzle that jets the molten solder sent by the jet pump upward are required.

  In general, a jet solder tank is provided with a primary jet nozzle for jetting molten solder in a rough state and a secondary jet nozzle for jetting in a quiet state. Since the molten solder jetted from the primary jet nozzle is rough, it easily penetrates into narrow through holes and corners of square chip parts to eliminate unsolder. However, the rough molten solder jetted from the primary jet nozzle causes poor soldering such as bridges and wiggles. Therefore, these soldering defects are corrected with a secondary jet nozzle. The molten solder jetted from the secondary jet nozzle is gentle, which corrects bridges and wiggles.

  In the jet solder bath, the jet pump and the jet nozzle are connected by a duct. That is, a jet pump is arranged at one end of the duct, and a jet nozzle is installed at the other end of the duct. The jet pump is installed in a casing formed at an end of a duct, and sends molten solder sucked by the jet pump to the jet nozzle through the duct, and jets the molten solder upward from the jet nozzle.

  Examples of the jet pump used in the jet solder bath include an impeller pump and a screw pump. An impeller pump is one in which a large number of plate-like blades are radially attached around a shaft. The casing of the impeller pump is formed at one end of the duct, and the shape thereof is substantially snail-shaped. The shaft of the impeller pump projects to the molten solder liquid level through a shaft hole drilled in the upper part of the casing. An inlet for sucking molten solder into the casing is formed in the lower part of the casing.

  The impeller pump is a device in which a large number of blades rotate so that the molten solder between the blades is blown by its centrifugal force, which is sent to a jet nozzle through a duct. In this impeller pump, since the molten solder is blown off by centrifugal force, the impeller pump needs to rotate to some extent. Therefore, in the jet solder bath using the impeller pump, the molten solder that has exited the impeller pump flows quickly through the duct, and when it exits from the jet nozzle, the flow velocity differs between the location near and far from the impeller pump. As a result, the jet height is higher at the higher flow velocity than at the lower flow velocity, and there is a problem that the molten solder does not become horizontal at the jet top and does not uniformly contact the printed circuit board.

  In the impeller pump, the jet from the jet nozzle sometimes pulsated. The cause of the pulsation by the impeller pump is that the molten solder feed becomes discontinuous. In other words, in the impeller pump, after the molten solder is blown between a pair of blades, the molten solder is then blown between a pair of adjacent blades. There is a moment. This causes pulsation in the impeller pump.

On the other hand, the screw pump has one or a plurality of blades formed in a spiral around the shaft, and applies pressure by putting molten solder on the spiral blades. That is, in the screw pump, the molten solder does not flow through the duct as fast as the impeller pump, but is jetted from the jet nozzle by the pressure pushed out by the screw pump. Therefore, in a jet solder bath using a screw pump, there is no discontinuous portion, so it is theoretically assumed that no pulsation occurs, and since molten solder jets from the jet nozzle under pressure, the top of the jet nozzle is horizontal. It has an excellent feature not found in impeller pumps. Many jet solder baths using this screw pump have been proposed for a long time in patents and utility models. (Patent Documents 1 to 5)
Japanese Utility Model Publication No. 48-98520 Japanese Utility Model Publication No. 53-34345 JP-A-62-259665 JP 2006-114555 A JP 2006-114556 A

  As described above, the screw pump is less likely to cause pulsation, but may not be able to sufficiently cope with a printed board having a long lead. That is, in the jet solder bath provided with the screw pump, there is a problem in the pumping efficiency that the jet height does not increase in accordance with the rotational speed when the rotational speed of the screw pump is increased.

  When the present inventors sought the cause of poor pumping efficiency in a jet solder bath equipped with a conventional screw pump, the screw pump is on the spiral blade and the molten solder is sent, and the melt that exits the screw pump The solder is evenly pressured in the duct, but since molten solder already exists in the duct, it will push the molten solder in this duct. Then, the molten solder in the duct tries to push back by applying an opposite pressure to the molten solder from the screw pump. Due to the pressure, the molten solder exiting the screw pump may flow back to the inlet through the screw pump and the inner wall of the casing. It has been found that this causes a reduction in the pumping efficiency of the screw pump.

  In order to prevent this reverse flow, Patent Document 4 solves this problem by making the gap between the blade and the inner wall of the casing as small as possible. According to experiments by the present inventors, it was found that when the gap is 0.5 mm or less, the molten solder that has exited the screw pump does not flow backward through the gap. Therefore, the diameter of the screw pump and the inner diameter of the casing may be precisely processed so as to eliminate the gap, and this processing is sufficiently possible. However, in a jet solder bath with a gap of 0.5 mm or less, it expands and contracts due to the phase transformation between the molten state when solder is used and the solidified state when not used and the temperature change, which causes the pump shaft to be eccentric. As a result, the screw pump and the casing are rubbed. In addition, reducing the gap takes a lot of work to process the casing and screw pump.

  Therefore, as a result of intensive investigations on preventing back flow from between the screw pump and the inner wall of the casing, the present inventors once entered the space if there was a space partitioned by the flow path. It becomes a wasteful flow of going out. Moreover, the present invention has been completed by paying attention to the fact that when there are a large number of them in the flow path, the fluid flowing in the flow path becomes more difficult to flow.

  In the present invention, a screw pump is accommodated in a casing, and an inlet for molten solder is formed in the casing. After molten solder sucked in by the screw pump flows in from the inlet, it is jetted from a jet nozzle. In the jet solder bath, a plurality of annular partitions are formed on the inner wall of the casing so as to be spaced apart from the screw pump in parallel with the horizontal direction, and the space between the partitions is an annular chamber. It is a jet solder bath.

  The jet solder bath of the present invention has a large number of annular partitions installed on the inner wall of a casing that houses the screw pump, and the multiple partitions are installed in parallel in the horizontal direction. That is, the space between adjacent partitions is an annular chamber, and a large number of annular chambers are formed on the inner wall of the casing. Therefore, when the molten solder flows backward between the screw pump and the inner wall of the casing, the molten solder first enters the annular chamber, then passes over the partition of the annular chamber and enters the next annular chamber. Since the molten solder that flows back in this way must flow in the annular chamber, the partition, the annular chamber, the partition,... Sequentially, it does not flow back.

  In the jet solder bath of the present invention, a large number of partitions are installed between the inner wall of the screw pump and the casing, and the space between the partitions is a large number of annular chambers. Even if an attempt is made to reversely flow between the screw pump and the inner wall of the casing, the partition and the annular chamber prevent the reverse flow. Thus, if the partition is installed in the inner wall of the casing, the backflow of the molten solder is prevented even if the gap between the screw pump and the inner wall of the casing is somewhat wide. Therefore, the jet solder bath of the present invention does not require precise processing for the manufacture of screw pumps and casings, and not only can be manufactured at low cost, but also does not require accurate dimensional accuracy during casing cleaning and maintenance. This presents an excellent effect not found in a jet solder bath using a conventional screw pump that can be assembled very easily.

  As a partition used in the present invention, a thick casing inner wall is formed by cutting a large number of annular chambers, or a large number of washer-like annular plates are attached to the inner wall of the casing by welding. An annular chamber, an annular plate having a large inner diameter and an annular plate having a small inner diameter are alternately arranged.

  The casing is formed with a circular inlet for sucking molten solder into the casing. The inner diameter of the inlet is preferably equal to or less than the diameter of the screw pump, and 2/3 or more of the diameter of the screw pump. When the inner diameter of the inlet is larger than the diameter of the screw pump, the molten solder that has flowed backward easily flows out of the inlet, and when the diameter is smaller than 2/3 of the diameter of the screw pump, the amount of suction by the screw pump is reduced. End up.

Hereinafter, the jet solder bath of the present invention will be described with reference to the drawings.
FIG. 1 is a front sectional view of a jet soldering bath according to the present invention, FIG. 2 is an enlarged sectional view of an essential part, FIG. 3 is a perspective view of FIG. 2, and FIG. 5 is an enlarged cross-sectional view of a main part of another embodiment.

  The jet solder bath of the present invention has a box 1 with a body 1 having no lid, and a molten solder 2 is placed inside, and the molten solder is maintained at a predetermined temperature by a heater (not shown). ing. A duct 3 is installed in the main body 1. A casing 4 is disposed at one end of the duct, and a jet nozzle 5 is attached to the upper end of the other end. The jet nozzle 5 is a primary jet nozzle, and a rough wave plate 6 for roughing the molten solder jetted is attached to the upper part.

  A screw pump 7 is accommodated in the casing 4. The casing 4 has a cylindrical shape, and a circular inflow port 8 is formed in the lower part. The inner diameter of the inlet is not more than the diameter of the screw pump and is not less than 2/3 of the diameter of the screw pump. A number of partitions 9 are formed on the inner wall of the casing 4. The partition 9 has an annular shape, and an annular chamber 10 is formed between adjacent partitions. The partition of the casing shown in FIGS. 1 to 3 is formed by machining a thick casing by machining. The gap between the inner periphery of the partition 9 and the screw pump 7 is a sufficient distance so that the partition 9 and the screw pump 7 are not rubbed even if the screw pump is slightly misaligned.

  The screw pump 7 has four blades 11 spirally formed on a shaft 12. The shaft 12 is held by a shaft holder 13, protrudes above the liquid surface of the molten solder 2, and a pulley 14 is fixed to the upper end thereof. The pulley 14 is interlocked by a belt 16 and a pulley 16 of a motor 15 attached to the outside of the main body 1.

FIG. 5 shows another embodiment of the casing used in the jet solder bath of the present invention. A large number of annular plates 18 are joined to the inner wall of the casing 4 by welding. Accordingly, the annular chamber 10 is formed between the adjacent annular plates. In the screw pump of FIG. 5 as well, the molten solder that has come out above the screw pump does not flow back between the screw pump and the inner wall of the casing, similar to the casing in which the annular chamber is formed.

Next, the operation state in the jet solder bath of the present invention having the above structure will be described.
When the motor 15 is operated, the rotation rotates the shaft 12 via the pulley 16, the belt 17, and the pulley 14. Then, the screw pump 7 fixed to the shaft 12 rotates, and the molten solder 2 on the blade 11 of the screw pump is carried and comes out above the screw pump 7. Then, the molten solder 2 at the lower part of the duct 3 is sucked from the inflow port 8 and is conveyed upward by the blades 11 of the screw pump 7, and is pumped through the duct 3 from above the screw pump 7 as indicated by arrows.

  The molten solder pumped in the duct 3 jets from the rough wave plate 6 of the jet nozzle 5 with the pumping direction facing up. The molten solder jetted from the rough wave plate 6 is rough and penetrates into the through-holes of the printed circuit board and the corners of the chip parts to eliminate unsolder, but causes defects such as tsura and bridge. Therefore, the printed circuit board soldered by the primary jet nozzle corrects these defects with the molten solder of the secondary jet nozzle that gently jets.

  In the duct 3, the molten solder 2 that has come out above the screw pump 7 tries to push out the molten solder that already exists in the duct 3, but is pushed back toward the screw pump 7 by the reaction of the molten solder in the duct 3. It is. At this time, in the jet solder bath using the conventional screw pump, when the space between the screw pump and the inner wall of the casing is wide, the motor flows backward from the gap and flows out from the inlet, or sufficient pressure does not come out. In spite of the faster rotation, the jet height could not be increased. However, since the jet solder bath of the present invention has a large number of partitions on the inner wall of the casing and the space between the partitions is an annular chamber, the molten solder that flows back between the screw pump and the inner wall of the casing is annular. Since it enters into the room and enters the next annular chamber again after exiting the annular chamber, it will be difficult to flow, so there is no back flow. Further, when the inner diameter of the inlet is smaller than the diameter of the screw pump, the backflow prevention effect is improved.

Here, in the jet solder bath of the present invention, the principle that the partition plate formed on the inner wall of the casing and the annular chamber prevent the backflow of the molten solder will be described with reference to FIG.
When the molten solder exiting the screw pump is pushed back by the molten solder in the duct, the molten solder flows into the gap between the casing 4 and the screw pump 7 and flows backward. The molten solder flowing backward through the gap enters the uppermost annular chamber. At this time, the molten solder that has entered the annular chamber changes direction or hits the wall of the annular chamber, so that the flow velocity and pressure are weakened. Then, the molten solder that has entered the annular chamber enters the next annular chamber beyond the partition. Here again, the flow rate and pressure of the molten solder are weakened, and further enter the next annular chamber. In this way, the molten solder that flows backward through the gap gradually loses its flow velocity and pressure, and eventually stops flowing at all.

  In the embodiments, the primary jet solder bath for roughing the waves has been described. Needless to say, the jet solder bath of the present invention can also be used for a secondary jet nozzle for jetting a quiet wave. In particular, the Sn-based lead-free solder with a small specific gravity could not be produced with a lead-containing solder with a large specific gravity even though the jet flow could be increased. The height can be increased.

FIG. 1 is a front sectional view of a jet solder bath according to the present invention. Expanded sectional view of the main part Perspective view of FIG. Explanatory drawing in which partition plate and annular chamber prevent fluid flow The principal part expanded sectional view of another Example

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Body of jet solder tank 2 Molten solder 3 Duct 4 Casing 5 Jet nozzle 7 Screw pump 8 Inlet 9 Partition 10 Annular chamber

Claims (4)

Are screw pump is housed in the casing, wherein the casing is an inlet of the molten solder is formed, after the molten solder which is sucked by the screw pump flows into from the inlet to the jet from the jet nozzle the jet solder bath,
Wherein the inner wall of the casing is formed in a state that the partition of the plurality of annularly spaced apart from the screw pump is parallel to the horizontal direction, jet solder bath between the partition switching is characterized that it is annular chamber . The jet solder bath according to claim 1 , wherein the partition is formed by carving an inner wall of a casing. The jet solder bath according to claim 1, wherein the partition is formed by joining an annular plate to an inner wall of a casing. The jet solder bath according to claim 1, wherein an inner diameter of the inflow port is equal to or less than a diameter of the screw pump and is equal to or more than 2/3 of a diameter of the screw pump.

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