JP2005353719A - Wave soldering tub - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wave soldering tub in which oxides and intermetallic compounds are prevented from adhering to a soldering portion by blocking movement thereof from the side where a jet stream nozzle is arranged to the side where a jet stream pump is installed. <P>SOLUTION: The wave soldering tub is provided with a partition plate having the upper part projecting from the level of molten solder and the lower part immersed into molten solder, and a dam board having the upper part immersed into molten solder. Phase of oxides having a specific gravity smaller than that of lead free solder is blocked by the partition plate, stream of intermetallic compounds having a specific gravity slightly larger than that of lead free solder is directed downward by the partition plate to sink below the molten solder, and movement of the sinking intermetallic compounds is blocked by the dam board. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a jet solder bath for soldering printed circuit boards, and more particularly to a jet solder bath suitable for soldering using lead-free solder.

  As a method for soldering the printed circuit board, there is an immersion method in which the printed circuit board is brought into contact with molten solder for soldering. In this dipping method, soldering is performed by applying flux to a printed circuit board with a fluxer installed in a soldering device, preheating with a preheater, adhering molten solder in a jet solder bath, cooling with a cooling device, etc. . Molten solder is put in a jet solder tank installed in the soldering apparatus, and a jet pump for jetting the molten solder to contact the printed circuit board is installed. The jet pump is composed of a pump, a shaft, a sprocket, a motor, and the like. The pump is fixed to the lower portion of the shaft, and the sprocket is fixed to the upper portion of the shaft. The sprocket is linked with a motor sprocket placed outside the main body by a belt.

  The operation of the jet pump in the jet solder bath rotates the motor by rotating the motor, and the rotation of the motor is interlocked with the sprocket of the shaft from the motor sprocket. As the pump rotates, molten solder in the vicinity of the pump is sucked into the pump and jetted from the jet nozzle at the pump pressure.

  Conventionally, the solder used for soldering a printed circuit board is a solder containing Pb made of Sn and Pb. When electronic equipment using this Pb-containing solder became old and became unusable or failed, many were disposed of without function upgrades or repairs. Of the materials used in electronic equipment, case plastic, display glass, frame metal, etc. are recovered and reused. Since the substrate could not be completely separated, it could not be reused and was inevitably disposed of in landfills. When acid rain comes into contact with the landfilled printed circuit board, the Pb component in the solder is eluted, and the acid rain containing the Pb component is mixed into the groundwater. And if humans and livestock drank groundwater containing Pb components for many years, there is concern about lead poisoning, and the use of Pb has been regulated on a global scale. Therefore, lead-free solder that does not contain Pb at all has appeared instead of Pb-containing solder, and is currently used in many fields.

  Lead-free solder is composed of Sn as a main component, and Ag, Cu, Bi, In, Zn, Cr, Fe, Ni, Co, P, or the like added thereto as appropriate. Lead-free solders that are widely used in the electronics industry today are Sn-3.5Ag (melting point: 210 ° C), Sn-0.7Cu (melting point: 220 ° C), Sn-3Ag-0.5Cu (melting point: 217 ° C) It is. When these lead-free solders are used in a jet solder bath, the temperature of the molten solder is as high as about 240 ° C. or higher.

  By the way, in the jet solder bath, there are many oxides generated by oxidizing the solder. This is because the solder is melted at a high temperature, and the molten solder is jetted from the jet nozzle, and the jetted molten solder falls on the surface of the molten solder and stirs the molten solder. Because it touches the air. This oxide has a specific gravity smaller than that of the molten solder and floats on the surface of the molten solder. However, when the oxide generated by the jet nozzle moves to the side where the jet pump is installed, it is caught in the rotation of the pump shaft. It is sucked into the pump together with the molten solder. The oxide sucked by the pump is jetted from the jet nozzle together with the molten solder and adheres to the printed board. When the oxide adheres to the printed circuit board, if the oxide is large, not only short-circuiting and lowering of insulation resistance occur between adjacent soldered portions, but also the appearance is deteriorated and the commercial value is lowered.

  When conventional solder containing Pb (63Sn-Pb solder: melting point 183 ° C) is used in a jet solder bath, it naturally oxidizes, but the temperature of the molten solder at the time of soldering is about 220 ° C, and it is easy to oxidize Sn Therefore, the amount of oxide generated is not so large. However, when the above lead-free solder is jetted into a jet solder bath, the melting point of lead-free solder is high, so the temperature of the molten solder in the jet solder bath is higher than that of Sn-Pb solder, which is 250 ° C or higher during soldering. Because of the high temperature, oxides are generated much more than Pb-containing solder. In addition, lead-free solder contains more than 90% by mass of Sn that is easily oxidized, and therefore more oxides are generated.

Conventionally, many means for preventing the oxide generated in the jet solder bath from moving from the direction where the jet nozzle is installed to the direction where the jet pump is installed have been proposed (Patent Documents 1 to 3). This means for preventing oxide migration is a partition plate. The partition plate is one in which the upper part protrudes from the surface of the molten solder and the lower part is submerged below the surface of the molten solder between the one where the jet nozzle is installed and the one where the jet pump is installed . In a jet solder bath with a partition plate, the oxide generated by the jet nozzle floats on the surface of the molten solder, and even if you try to move from the side where the jet nozzle is installed to the side where the jet pump is installed, Oxide movement is hindered by the partition plate installed on the liquid surface.
Japanese Utility Model Publication No.55-171473 Japanese Utility Model Publication No.58-76375 Japanese Utility Model Publication No. 6-66863

  Moreover, when a printed circuit board is soldered in a large amount in a jet solder bath, the copper foil of the printed circuit board gradually melts into the molten solder in the jet solder bath, and needle-like intermetallic compounds composed of Sn and Cu are generated. When a large amount of this intermetallic compound is generated in the molten solder in the jet solder bath, the acicular intermetallic compound adheres between adjacent soldering portions of the printed circuit board, causing a short circuit. Intermetallic compounds are generated when the molten solder adheres to the copper foil of the printed circuit board, Sn in the solder and Cu of the copper foil are alloyed and the melting point of the Cu alloy part is lowered, so the Cu is molten solder. Melt in. As the amount of Cu dissolved in the molten solder increases, it precipitates as an intermetallic compound of CuSn. In other words, the higher the Sn content in the solder and the higher the temperature of the molten solder, the greater the amount of Cu dissolved from the printed circuit board into the solder. Therefore, in lead-free solder with Sn as the main component and high melting temperature, the amount of Cu that melts into the molten solder increases, and as a result, a large amount of intermetallic compounds are generated, causing defects such as short circuits. It is.

  CuSn intermetallic compound has a lower specific gravity than Pb-containing solder, so in a jet solder bath using Pb-containing solder, it floats on the surface of the molten solder, but it has a higher specific gravity than the aforementioned lead-free solder, so it is lead-free. In the jet solder bath using solder, it is in a state of sinking below the molten solder. Therefore, the intermetallic compound cannot be prevented from moving from the direction in which the jet nozzle is installed to the direction in which the jet pump is installed in the partition plate, and is sucked into the jet pump and jetted from the jet nozzle to the printed circuit board. It was attached.

  By the way, it is inevitable that an oxide or an intermetallic compound is generated in a jet solder bath. However, when lead-free solder is used in a jet solder bath, not only is there much oxide generation, but there are also many intermetallic compounds, and intermetallic compounds have a higher specific gravity than lead-free solder. It sank and was difficult to remove. In other words, the aforementioned partition plate could prevent the oxide from flowing from the direction where the jet nozzle was installed to the direction where the jet pump was installed, but could not prevent the intermetallic compound from moving. . The present invention provides a jet solder bath that prevents the oxide and intermetallic compound from moving from the direction in which the jet nozzle is installed to the direction in which the jet pump is installed, and does not adhere to the soldering portion. is there.

  Oxide is often generated in the vicinity of the jet nozzle because the molten solder is jetted from the jet nozzle, and the intermetallic compound melts when the printed circuit board contacts the molten solder jetted from the jet nozzle. It dissolves in the solder and is also generated near the jet nozzle. In other words, oxides and intermetallic compounds move from the jet nozzle to the jet pump and are sucked into the jet pump together with the molten solder, and they are jetted from the jet nozzle and adhere to the printed circuit board. Yes. Hereinafter, since there are many descriptions of these movements, the direction in which the jet nozzle is installed is referred to as the nozzle side, and the direction in which the jet pump is installed is referred to as the pump side.

  The inventors of the present invention have completed the present invention by intensively studying to simultaneously block these movements when an oxide having a specific gravity lighter than that of solder and an intermetallic compound having a higher specific gravity are mixed.

  The present invention relates to a jet solder bath in which a jet pump and a jet nozzle are installed in a main body. The main body is divided into an upper chamber and a lower chamber by a base plate, and the jet nozzle and the jet pump are installed in the base plate. In addition, the upper chamber is separated from the nozzle side and the pump side by a weir plate whose upper part is submerged in molten solder, and further, the upper part protrudes from the liquid level and the lower part is the liquid level. The jet solder bath is characterized in that a partition plate is provided so as to be immersed below.

  The jet solder bath of the present invention has a partition plate between the pump side and the nozzle side, the upper part protruding above the molten solder liquid level, the lower part submerged in the liquid level, and the upper part below the molten solder liquid level, Since the lower plate is installed with a dam plate standing up from the base plate of the main body, the partition plate prevents the oxide from moving from the nozzle side to the pump side, and the combination of the dam plate and the partition plate Directs the intermetallic compound below the molten solder and also prevents it from moving from the nozzle side to the pump side. In other words, the jet solder bath of the present invention can perform highly reliable soldering because it does not adhere to the printed circuit board because oxides and intermetallic compounds are not sucked into the jet pump.

  In the jet solder bath, since the molten solder flows from the nozzle side to the pump side, oxides and intermetallic compounds also ride on the flow of the molten solder and the molten solder flows from the nozzle side to the pump side. However, since the jet solder bath of the present invention has a partition plate and a weir plate installed between the nozzle side and the pump side, the movement of oxide is blocked by the partition plate, and the flow of intermetallic compounds is blocked by the partition plate and the weir plate. The Therefore, if a large amount of oxide accumulates in the vicinity of the partition plate, it is scraped off with a net or handle, and the scraped oxide is discarded in a predetermined disposal can.

  On the other hand, an intermetallic compound generated using lead-free solder in a jet solder bath has a specific gravity slightly larger than that of lead-free solder, and therefore accumulates below the molten solder in a state where there is no convection. However, in a place where convection constantly occurs like a jet solder bath, it does not sink below the molten solder as it is. That is, the intermetallic compound generated at the jet nozzle rides on the flow of the molten solder and exceeds the top of the dam plate. However, in the present invention, since the partition plate is provided in front of the barrier plate, the intermetallic compound is forcibly moved downward by the partition plate. That is, the intermetallic compound part sinks below the molten solder due to the downward movement by the partition plate and the heavy specific gravity. Thus, the intermetallic compound collected in the lower part of the molten solder cannot be scooped off with a net or a handle. Therefore, it is better to attach a drain to the body where the intermetallic compound is sinking. That is, when a large amount of printed circuit board is soldered and an intermetallic compound accumulates in the lower part of the molten solder, the drain is opened and the intermetallic compound is allowed to flow out of the bath together with the molten metal.

  Hereinafter, the jet solder bath of the present invention will be described with reference to the drawings. 1 is an AA line cross-sectional perspective view of FIG. 3, FIG. 2 is an inventive jet solder bath, FIG. 3 is a cross-sectional view of FIG. 3 AA line, and FIG. It is a top view.

  The main body 2 of the jet solder bath 1 has a box shape with an upper part opened. A molten solder 3 is placed inside the main body 2 and is maintained at a predetermined melting temperature by an electric heater (not shown). The main body 2 is divided into an upper chamber 5 and a lower chamber 6 by a base plate 4 stretched laterally, and a jet pump 7 and a jet nozzle 8 are installed in the upper chamber 5.

  Between the pump side 9 and the nozzle side 10 of the upper chamber 5, a dam plate 11 and a partition plate 12 are installed. The dam plate 11 is erected on the base plate 4 so as to cross between the pump side 9 and the nozzle side 10 and is fixed between the opposite side walls 13 and 14 of the main body. The upper part of the dam plate 11 is submerged from the liquid surface of the molten solder 3, and the molten solder cannot flow from the nozzle side 10 to the pump side 9 unless it passes through the upper part of the dam plate.

  A partition plate 12 is installed on the nozzle side 10 adjacent to the dam plate. The upper part of the partition plate 12 protrudes upward from the liquid level of the molten solder 3, and the lower part is submerged below the liquid level of the molten solder 3. Accordingly, the molten solder 3 cannot pass over the partition plate 12 when flowing from the nozzle side 10 to the pump side 9 and flows from the lower portion of the partition plate, that is, the molten solder liquid level does not move. It is designed to flow under the liquid level. Engagement pieces 15 and 15 are formed at both ends of the partition plate 12, and the engagement pieces are detachably installed by engaging with opposing wall surfaces 13 and 14, respectively.

  The jet pump 7 includes a cylinder 16, a pressure pump 17, a shaft 18, a shaft sprocket 19, a belt 20, a motor 21, and a motor sprocket 22. The cylinder 16 is a block in which a cylindrical hole is formed, and is installed on the base plate 4. A pressure pump 17 is disposed in the hole of the cylinder 16, and a shaft 18 is fixed to the pressure pump. A shaft sprocket 19 is attached to the upper portion of the shaft 18, and is linked to a sprocket 22 of the motor 21 via a belt 20. The motor 21 is attached to a bracket 23 having an L-shaped cross section, and the bracket is attached to a plurality of leg posts 24 fixed to the cylinder 16.

  The jet nozzle 8 is a primary jet nozzle 25 that jets rough waves and a secondary jet nozzle 26 that jets gentle waves. The lower chamber 6 is divided between the primary jet nozzle 25 and the secondary jet nozzle 26 by a partition wall (not shown). Therefore, when the jet pump of the primary jet nozzle 25 is operated, the molten solder pumped by the jet pump is jetted from the primary jet nozzle, and when the jet pump of the secondary jet nozzle 26 is operated, the molten solder pumped by the jet pump is secondary. It jets from the jet nozzle. However, since the primary jet nozzle and the secondary jet nozzle are not separated in the upper chamber, the molten solder jetted from the respective jet nozzles is mixed in the upper chamber.

  A drain 28 is attached to the wall surface 27 of the main body, which is the lowermost part of the upper chamber 5 and is the upper part of the base plate 4.

  Here, the operating state of the jet solder bath of the present invention having the above-described configuration will be described. When the motor 21 is driven, the rotation of the motor rotates the pressure pump 17 from the sprocket 22, the belt 20, the shaft sprocket 19, and the shaft 18 of the motor. Then, the molten solder 3 on the pump side 9 in the upper chamber 5 is sucked into the pressure pump 17 by the rotation of the pressure pump 17 and pressure is applied to the molten solder in the lower chamber 6. With this pressure, the molten solder in the lower chamber 6 is pushed up and jetted from the jet nozzle 8.

  A printed circuit board (not shown) is also conveyed by a conveying device (not shown), and first contacts the rough wave jetted from the primary jet nozzle 23, and the solder adheres to the soldering portion of the printed circuit board. The primary jet nozzle is designed to prevent unsolder from entering through the corners of the through-holes and chip parts. However, since the waves are rough, defects such as wiggles and bridges are generated. Then, the printed circuit board is brought into contact with a gentle wave jetted from the secondary jet nozzle to correct soldering defects such as wigs and bridges.

  Since the molten solder jetted from the jet nozzle 8 is always in a clean state, it is oxidized to oxide S when it comes into contact with air, and a large amount of oxide is generated in the vicinity of the jet nozzle. Since this oxide S has a specific gravity smaller than that of the molten solder, it floats on the liquid surface of the molten solder 3. In the jet solder bath, Cu melted from the printed circuit board is alloyed with Sn in the solder to form an intermetallic compound K and sinks below the molten solder. In the jet solder bath, the molten solder jetted from the jet nozzle is circulated to the pump side, sucked into the jet pump, and jetted again from the jet nozzle, so that the oxides and intermetallic compounds generated on the nozzle side are also It flows from the nozzle side to the pump side and is sucked into the jet pump. However, in the jet solder bath of the present invention, since the weir plate 11 and the partition plate 12 are installed between the pump side 9 and the nozzle side 10, the small-specific gravity oxide S floating on the liquid surface of the molten solder 3 is separated from the partition plate. The flow is blocked at 12, and the intermetallic compound K having a large specific gravity that sinks below the molten solder is blocked by the dam plate 11. Therefore, the jet solder bath of the present invention allows molten solder with very little oxide or intermetallic compound to flow into the pump side 9, and when the printed circuit board is soldered, The adhesion of oxides and intermetallic compounds is extremely small.

  The jet solder bath of the present invention exhibits an excellent effect when lead-free solder is used, but it can prevent adhesion of oxides and intermetallic compounds even when Pb-containing solder is used.

FIG. 4 is a cross-sectional perspective view taken along line AA of FIG. FIG. 4 is a cross-sectional view taken along line AA of FIG. It is a top view of this invention jet soldering bath.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Jet solder tank 2 Main body 3 Molten solder 4 Base plate 5 Upper chamber 6 Lower chamber 7 Jet pump 8 Jet nozzle 9 Pump side 10 Nozzle side 11 Weir plate 12 Partition plate
S oxide
K intermetallic compound

Claims (2)

In a jet solder bath in which a jet pump and a jet nozzle are installed in the main body, the main body is divided into an upper chamber and a lower chamber by a base plate, and the jet nozzle and jet pump are installed on the base plate. The chamber is separated from the nozzle side and the pump side by a weir plate whose upper part is submerged in molten solder, and further, the upper part protrudes from the liquid surface and the lower part is submerged below the liquid surface. A jet solder bath, characterized in that a partition plate is installed. 2. A jet solder bath according to claim 1, wherein a drain is installed in a lower part of the upper chamber on the nozzle side.

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