JP2000294915A - Jet solder bath - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent solder failures by covering a part other than a jet nozzle with a cover, setting the installation position of the cover at an upper portion within a specific range from the liquid surface of melted solder, and installing a heater in the liquid of the melted solder within a specific range from the liquid surface of the melted solder, at a part where temperature is reduced other than the jet nozzle. SOLUTION: A throw-in type heater 13 is installed at a depth of 5-40 mm in melted solder 6 in a body 1, the surface is retained at a prescribed temperature, at the same time covers 14A, 14B, and 14C are installed at a position, 5-40 mm above the liquid surface in the upper part of the body 1, and nitrogen gas is supplied from an inert gas inflow port 15 into the cover. Then, in the cover 14A, the parts of a primary jet nozzle 7 and a secondary jet nozzle 8 are opened. In the cover 14B, a shaft 9 and the area between the end parts of two jet nozzles are covered, and at the same time a cover 14C is allowed to cover the area between the shaft 9 and a short-side surface 3 of the body 1, thus preventing soldering failure, such as solder projections and bridges.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a jet solder bath which is installed in an automatic soldering apparatus and solders a printed circuit board.

[0002]

2. Description of the Related Art An automatic soldering apparatus for soldering a printed circuit board is provided with processing devices such as a fluxer, a preheater, a jet solder bath, and a cooler. The soldering of printed circuit boards by this automatic soldering machine involves the steps of flux application with a fluxer, preheating with a preheater, solder adhesion in a jet solder bath, and cooling with a cooler while transporting the printed circuit board on a conveyor. It is done through.

[0003] The quality of the soldering in an automatic soldering apparatus depends on the conditions in each processing apparatus, but the conditions in a jet solder bath have a large effect. For example, if the jet state of the molten solder from the jet nozzle is not stable, poor soldering such as icing and bridges will occur.

[0004] The state of the jet from the jet nozzle is not stable because the rotation speed of the motor for rotating the pump changes due to the heat of the jet solder bath, and the accuracy of the gap between the duct and the pump is poor. However, the most influential factor for the stable jet from the jet nozzle is clogging of foreign matter in the jet nozzle and the flow straightening plate. In other words, the jet solder bath jets the molten solder upward in a wave shape of a predetermined shape,
Soldering is performed by bringing a printed circuit board into contact with the jetted molten solder, but when foreign matter is clogged in the jet nozzle, the jet shape of the jet nozzle changes or the height of the jet wave moves up and down, so-called " Or “breathing phenomena”. As a result, icing, bridges, and the like are generated on the soldered printed circuit board. Also, as a cause of the unstable state of the jet from the jet nozzle, there is a clogging of foreign matters in the current plate. The rectifying plate installed below the jet nozzle is used to make the molten solder pumped in a turbulent state by a large number of holes into a steady flow and jet it from the jet nozzle in a stable state.
The rectifying plate is a plate-like plate having a large number of holes.If foreign matter adheres to the holes, the flow of the molten solder is partially reduced and a stable jet state cannot be obtained from the jet nozzle. This causes defects such as icicles and bridges.

[0005]

The present inventor analyzed foreign matters adhering to a jet nozzle and a flow straightening plate.
As foreign matter, there is an oxide obtained by oxidizing the solder, but it has been found that most of the foreign matter is a sherbet-like solder. Since the oxide is a very fine powder, even if it adheres to the jet nozzle or the flow straightening plate, it takes a long time to change the jet state only by this oxide. Therefore, when the foreign matter adhering to the jet nozzle or the flow straightening plate is only the oxide, cleaning of the oxide by two to three times / day is sufficient, but the sherbet-shaped solder is largely solidified. For this reason, clogging of the jet nozzle and the flow straightening plate is quick, and when the sherbet-like solder is generated in the jet solder bath, the jet nozzle and the flow straightener must be cleaned frequently, for example, once / hour.

[0006] The sherbet-shaped solder is generated even with so-called ordinary solder of tin / lead which has been used more frequently than before, but particularly with lead-free solder which is currently attracting attention due to the problem of lead pollution. And the generation of the sherbet-like solder has often occurred in the conventional jet solder bath. The conventional jet solder bath has a box shape with an open top and is provided with a jet nozzle for jetting molten solder therein.

When the present inventors examined the characteristics of the sherbet-like solder, it was found that when the sherbet-like solder was scooped with a ladle and heated with a gas burner, the sherbet-like solder began to melt, and a small amount of oxide remained thereafter. From this, it was found that the sherbet-like solder was a semi-molten solder. Originally, tin / lead eutectic solder (63Sn-Pb) has a liquidus temperature and a solidus temperature of 183 ° C., which are the same, and does not enter a semi-molten state. However, it has been found that the eutectic solder is in a semi-molten state as described above, but if the temperature is not lowered to the solidus temperature, the air becomes entangled at a temperature close to the solidus temperature to become a sherbet-like solder.

That is, when the molten solder is jetted from the jet nozzle, the sherbet-shaped solder is brought into contact with air at the time of jetting, and falls vigorously onto the molten solder in the jet soldering bath. At this time, the molten solder is cooled or entrained in air to form a sherbet-like solder. This sherbet-like solder floats at a part other than the jet nozzle,
It is sucked into the pump and adheres to the jet nozzle and the flow straightening plate.

A jet solder bath for preventing the surface of molten solder from being oxidized has been proposed (see Japanese Unexamined Patent Publication (Kokai) No. 61-286058).
issue). These jet solder baths cover parts other than the jet nozzles with a cover, and try to prevent oxidation of the molten solder by preventing the surface of the molten solder from coming into contact with air by flowing an inert gas into the cover. Things.

[0010]

The conventional anti-oxidation jet solder bath has an effect of suppressing oxides generated at portions other than the jet nozzle, but is not sufficient for preventing sherbet-like solder. In other words, the sherbet-like solder is generated because, as described above, when the molten solder is jetted from the jet nozzle and falls into the molten solder, it is cooled and entrained by air. In the jet solder bath, it is impossible to completely cover the jet nozzle with the cover, so that air is entrapped at the jet nozzle portion, so that the generation of sherbet-like solder cannot be prevented.

[0011]

In a conventional anti-oxidation jet solder bath, if the jet nozzle can be covered with a cover, even if it vigorously falls into the molten solder from the jet nozzle, air will not be entrained, and the sherbet will not be entrained. Although it is possible to eliminate the generation of solder-like solder, if the jet nozzle is covered with a cover, the cover prevents contact between the jet solder and the printed circuit board, so that soldering cannot be performed. However, since the sherbet-like solder can be easily returned to the molten solder by increasing the temperature as described above, the present inventor does not prevent the occurrence of the sherbet-like solder in the jet solder bath, The inventors of the present invention have conducted intensive studies on the restoration of the solder-like solder and completed the present invention.

According to the present invention, there is provided a jet soldering bath for jetting molten solder from a jet nozzle and bringing a printed circuit board into contact with the jetted molten solder for soldering.
The part other than the jet nozzle is covered with a cover, and the installation position of the cover is 5 to 40 mm above the liquid level of the molten solder. This is a jet solder bath in which a heater is installed in a solder liquid.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a portion other than the jet nozzle is covered with a cover. The installation height of the cover (H in FIG. 4) is 5 to 40 mm. If the height is lower than 5 mm, the pump stops operating and the molten solder jet stops, so that the liquid level of the molten solder rises and lifts the cover. If the height is higher than 40 mm, the cover keeps heat. The effect is lost and the sherbet-shaped solder cannot be returned to the original molten solder.

Further, in the present invention, the main body is covered with the cover and a heater is provided in the liquid level of the molten solder. This heater is provided in a portion other than the jet nozzle where the temperature tends to decrease. The depth at which this heater is installed in the molten solder liquid is 5 to 40 mm. If the depth is less than 5 mm and the height of the molten solder jet is increased, the liquid level of the molten solder drops and the heater is exposed from the molten solder. Would. On the other hand, if the depth is greater than 40 mm, the liquid surface temperature of the molten solder cannot be increased, and the effect of returning the sherbet-shaped solder to the original state is reduced.

In the present invention, the low-temperature portion is kept warm by immersing the cover and the heater in order to prevent the sherbet-like solder. However, when an inert gas such as nitrogen gas is introduced into the cover, the molten solder is melted. Can also be prevented from being oxidized. For the inert gas, an inlet is attached to the cover, and the inlet is connected to an inert gas generator.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. 1 is an exploded perspective view of the jet solder bath of the present invention, FIG. 2 is a plan view of the jet solder bath of the present invention, FIG. 3 is a cross-sectional view taken along line AA of FIG. 2, and FIG. FIG. 5 and FIG. 5 are plan views of another embodiment.

The main body 1 of the jet solder bath has a box shape composed of a pair of long side surfaces 2 and 2 and a pair of short side surfaces 3 and 3 and a bottom surface 4. A heater (not shown) is provided near the long side surfaces 2 and 2 inside the main body 1 and a heater 5 is provided on the bottom surface. The heater 5 melts the solder put into the main body and keeps the molten solder 6 at a constant temperature.

In the main body 1, a primary jet nozzle 7 and a secondary jet nozzle 8 are provided. The primary jet nozzle 7 jets the molten solder having a rough wave to infiltrate the soldered portion of the printed circuit board where the molten solder is difficult to invade. Would. The printed circuit board then contacts the wave of the secondary jet nozzle that jets a quiet wave to correct the icicles and bridges generated by the contact with the primary jet nozzle. The primary jet nozzle and the secondary jet nozzle are connected to a jet pump (not shown) in the molten solder 6 by a duct.

The jet pump has its shafts 9 and 9 projecting upward from the liquid surface of the molten solder 6, and upper pulleys 10 and 10 and motors 11 and 11 and a belt 12 attached to the outside of the main body 1. , 12 are linked.

A plurality of throw-in type heaters 13 are provided in the liquid of the molten solder 6. The immersion depth D is 5 to 4 as shown in FIG.
0 mm, and the installation position is where the temperature is low.
What is the low temperature where the throw-in type heater is installed?
For example, as shown by the dotted line in FIG. 2, the main body 1 is parallel to the long side surface between the long side surface 2 and the primary jet nozzle 7, between the primary jet nozzle 7 and the secondary jet nozzle 8, and between the secondary jet nozzle 8 and the long side surface. 5, between one end and the other end of the main body, or between the ends of the two nozzles 7, 8 and the short side 3 of the main body 1 in a state parallel to the short side as shown in FIG. 9, 9 and between the ends of the two jet nozzles 7, 8 and between the two shafts 9, 9 and the short side surface 3.

The body 1 is provided with a cover 14.
The cover 14 does not cover the primary jet nozzle 7 and the secondary jet nozzle 8, and is appropriately divided for easy installation. In the embodiment, a cover 14 having a jet nozzle portion is opened.
A, cover 1 for covering between shafts 9 and 9 and two jet nozzle ends
4B, cover 14 for covering between shafts 9 and 9 and short side surface 3 of main body 1
C consists of three parts.

An inert gas inlet 15 is provided in the cover 14C covering the end portion, and an inert gas supply source (not shown) is connected to the inlet.

Next, an operation state of the jet solder bath of the present invention having the above-described structure will be described.

The surface of the molten solder 6 in the main body 1 is maintained at a predetermined temperature by a cast-in heater 13. A cover 1 is placed on the upper part of the main body 1 at a position 10 mm above the liquid level.
4A, 14B, and 14C are provided, and nitrogen gas is supplied from the inert gas inlet 15 into the cover.

In the above-mentioned jet solder bath of the present invention, 63Sn-P
b), and the internal temperature of the molten solder is set to 23.
The temperature was adjusted to 0 ° C., and the surface temperature was adjusted to 240 ° C. by a cast-in heater immersed in the liquid surface. When the jet solder bath of the present invention in such a state was continuously operated for 8 hours, there was no clogging of foreign matter into the jet nozzle and the rectifying plate, and when the cover was opened, sherbet-like solder and oxides were generated. Was very small.

On the other hand, the 63Sn-Pb eutectic solder was introduced into a jet solder bath in which no cover was provided on the main body and no dipping type heater was immersed near the liquid surface of the molten solder, and the internal temperature was set to 230 ° C. The surface temperature at this time is 220 ° C
Met. When the jet solder bath was operated continuously for 8 hours, the jet state changed after 1 hour, and after 3 hours, the jet height became about half of the initial height.
This was caused by the attachment of the sherbet-like solder to the jet nozzle and the current plate. When the cover was opened three hours later, a large amount of sherbet-like solder was deposited on the surface.

[0027]

As described above, the jet solder bath of the present invention covers the main body with the cover and installs a heater near the liquid surface of the molten solder to maintain the liquid surface of the molten solder at a high temperature. The sherbet-like solder that has been cooled and engulfed by air when jetted from the jet nozzle can be returned to the original clean molten solder. Therefore, in the jet solder bath of the present invention, a stable jet state can be obtained without the sherbet-shaped solder adhered to the jet nozzle or the rectifying plate for a long time, so that reliability of soldering such as icicles and bridges does not occur. An excellent soldered portion can be obtained.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of a jet solder bath according to the present invention.

FIG. 2 is a plan view of a jet solder bath according to the present invention.

FIG. 3 is a sectional view taken along line AA of FIG. 2;

FIG. 4 is an enlarged sectional view of a main part of FIG. 3;

FIG. 5 is a plan view of another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main body 2 Long side 3 Short side 6 Molten solder 7 Primary jet nozzle 8 Secondary jet nozzle 9 Pump shaft 13 Cast-in heater 14 Cover 15 Inert gas inlet

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B23K 31/02 310 B23K 31/02 310F // B23K 101: 42

Claims (2)

[Claims] 1. A jet solder bath in which molten solder is jetted from a jet nozzle and a printed circuit board is brought into contact with the jetted molten solder for soldering. A portion other than the jet nozzle is covered with a cover. The heater is installed 5 to 40 mm above the liquid surface of the molten solder, and a heater is installed in the liquid of the molten solder 5 to 40 mm from the liquid surface of the molten solder except for the jet nozzle where the temperature tends to decrease. And the jet solder bath. 2. The jet solder bath according to claim 1, wherein an inside of the cover is supplied with an inert gas.