JP2004281522A - Automatic soldering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automatic soldering device which carries out soldering in an inert gas atmosphere, is capable of lowering oxygen in concentration in a jet flow solder tank and a pre-heater, and is capable of cooling quickly in a cooling device simultaneously. <P>SOLUTION: An exhaust device is provided near the inlet of the automatic soldering device, and inert gas of low temperatures is blown out. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an automatic soldering apparatus for soldering a printed circuit board in an inert atmosphere.
[0002]
[Prior art]
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 cooling device, and a conveyor of a transfer device runs on these processing devices.
[0003]
When soldering a printed circuit board by this automatic soldering apparatus, the printed circuit board is held by a nail of a conveyor and then run on the processing apparatus, and the processing is performed by each processing apparatus to perform soldering.
[0004]
First, a flux is applied to a soldering surface of a printed circuit board by a fluxer on a printed circuit board run on a conveyor. This flux application is performed by contacting the printed circuit board with the flux foamed by the foam tube, or by spraying the atomized flux on the printed circuit board with a spray nozzle. The fluxer may be installed in the automatic soldering device or may be installed outside the automatic soldering device. When the fluxer is installed outside the automatic soldering apparatus, the present invention is an automatic soldering apparatus for soldering a printed circuit board in an inert atmosphere intended by the present invention. The automatic soldering apparatus in an inert atmosphere is installed outside the automatic soldering apparatus because if the fluxer is installed in a chamber where the fluxer is in an inert atmosphere, the chamber is contaminated by the flux.
[0005]
Next, the printed circuit board coated with the flux is preheated by a preheater. The pre-heating of the printed circuit board on which the flux is applied is because if the solvent remains in the flux, the molten solder will scatter and become dangerous when it comes into contact with the next molten solder. If the printed circuit board is brought into contact with the molten solder that has rapidly become hot, the printed circuit board and the electronic components mounted on the printed circuit board will be damaged by the heat shock. This is because the contact lowers the temperature of the molten solder, and the low temperature of the printed circuit board deteriorates the solderability.
[0006]
The printed circuit board preheated by the preheater is conveyed to a jet solder bath where it comes into contact with the molten solder to be soldered. A jet solder bath for soldering a printed board is provided with a primary jet nozzle for jetting a rough wave and a secondary jet nozzle for jetting a gentle wave. At the time of soldering, the printed circuit board first spreads the molten solder into the corners and through holes of the soldered portion by the rough waves of the primary jet nozzle to eliminate unsoldered. Next, bridges, icicles and the like generated by soldering of the primary jet nozzle are corrected by gentle waves of the secondary jet nozzle.
[0007]
Conventionally, Pb-63Sn solder has been used for soldering printed circuit boards. This Pb-63Sn solder has an excellent feature that the melting point is relatively low, so that the temperature of the molten solder at the time of soldering can be lowered, or the solderability is good, so that there are few defects and the cost is low. ing. However, when the printed circuit board soldered with the Pb-63Sn solder is landfilled and acid rain comes in contact with the landed printed circuit board, Pb in the solder is eluted and mixed into the groundwater. When humans and livestock drink groundwater containing Pb for many months, lead poisoning is caused, and the use of solder containing Pb has been regulated. Therefore, recently, a so-called lead-free solder containing no Pb has been used.
[0008]
The lead-free solder has Sn as a main component, to which Ag, Cu, Bi, Zn, In, Cr, Mo, Co, Fe, P, Ge, Ga, and the like are appropriately added. Lead-free solder has poor solderability and is easily oxidized as compared with conventional Pb-63Sn solder. Poor solderability to a printed circuit board causes poor soldering such as unsoldering, bridges, and dewetting. In addition, lead-free solder, which is easily oxidized, generates a large amount of oxide in the jet solder bath, not only wastes expensive lead-free solder, but also causes the oxide to adhere to the printed circuit board and deteriorate the appearance, It may cause a short circuit or a decrease in insulation resistance. The reason why the lead-free solder is easily oxidized is that lead-free solder, which is mainly composed of Sn which is easily oxidized and has a high melting point, is further oxidized because the soldering temperature is increased.
[0009]
When lead-free solder is used in an automatic soldering apparatus, it has been known that soldering should be performed in an inert atmosphere in order to eliminate soldering defects and prevent solder oxidation. An automatic soldering device that performs soldering in an inert atmosphere (hereinafter, referred to as an inert soldering device) covers a preheater, a jet solder bath, a cooling device, and the like with a chamber, and places an inert gas such as nitrogen in the chamber. It is filled with an active gas, and many have been proposed in the past. (See Patent Documents 1 to 3)
[0010]
The conventional inert soldering apparatus is provided with a slope that becomes higher from the inlet side to the outlet side, and has an inflow port through which an inert gas flows into the chamber above each processing apparatus. In this soldering device, the inert gas flowing into the chamber fills the chamber and then flows out from the outlet side. The reason why the inert gas flows out from the outlet side is that the conveyor of the transfer device is inclined upward by 3 to 5 degrees in the traveling direction, and the inert gas in the chamber is heated by the preheater or the jet solder bath. This is because the inert gas heated and lightened by the chimney effect of the chamber flows out from the outlet located at a high position.
[0011]
When the inert gas in the chamber flows out of the outlet side due to the chimney effect, air enters the chamber from the inlet, and the oxygen concentration in the chamber increases. In particular, the oxygen concentration in the vicinity of a preheater or a jet solder bath which requires an atmosphere having a low oxygen concentration increases. In order to prevent an increase in the oxygen concentration due to such a chimney effect, there has been proposed a soldering apparatus in which an opening having a suction device is provided in the vicinity of the inlet, and an inert gas in the chamber is sucked from the opening. (See Patent Document 4)
[0012]
[Patent Document 1] JP-A-5-200538 (FIG. 2 on page 5)
[Patent Document 2] Japanese Patent Laid-Open No. 5-235530 (FIG. 2 on page 7)
[Patent Document 3] JP-A-6-29655 (FIG. 1 on page 4)
[Patent Document 4] JP-A-7-36951 (FIG. 1 on page 3)
[0013]
[Problems to be solved by the invention]
By the way, an inert soldering apparatus having an opening near the inlet can surely prevent the chimney effect and eliminate the flow of the inert gas from the outlet. However, soldering equipment with an opening near the entrance does not sufficiently reduce the oxygen concentration in preheaters or jet soldering baths that require a reduction in the oxygen concentration. It was not possible to completely eliminate defects such as unsoldering and bridges in the soldered portion of the substrate, and to sufficiently suppress the generation of oxides in the jet solder bath.
[0014]
In addition, with the conventional inert soldering equipment that has an opening near the entrance, the cooling effect of the printed circuit board in the cooling device is not sufficient, and cracks and cracks occur in the solder after soldering in the jet solder bath. was there. The present invention not only reduces the oxygen concentration in the preheater or the jet solder bath where the oxygen concentration needs to be reduced in the inert soldering apparatus, but also cracks and cracks after soldering in the jet solder bath. It is an object of the present invention to provide a soldering device that does not cause any problems.
[0015]
[Means for Solving the Problems]
The present inventor has conducted intensive research on reducing the oxygen concentration in the preheater portion and the jet solder bath portion, further utilizing the chimney effect preventing means used in the conventional inert soldering apparatus, The present inventors have found that the use of a cooling device for inflow of an inert gas is effective in lowering the oxygen concentration in a necessary portion and preventing cracks and cracks in a soldered portion.
[0016]
The present invention is directed to an automatic soldering apparatus for covering a preheater, a jet solder bath, and a cooling device with a chamber and performing soldering of a printed circuit board by setting the inside of the chamber to an inert atmosphere, wherein a low-temperature inert gas is supplied to the cooling device. An automatic soldering apparatus characterized in that an outlet for blowing onto a printed circuit board is provided, and an exhaust device is provided near an entrance of the printed circuit board.
[0017]
In the soldering apparatus of the present invention, a low-temperature inert gas is blown from a cooling device to a soldering surface of a printed circuit board immediately after soldering in a jet solder bath to rapidly cool the board. When the soldered portion immediately after the soldering is rapidly cooled, the molten solder attached to the printed circuit board is rapidly solidified, so that cracks and cracks do not occur even if vibration or impact is applied due to conveyance. In particular, since lead-free solder has a high melting temperature, it does not quickly solidify under conventional fan cooling, and cracks and cracks often occur, but soldering a low-temperature inert gas as in the present invention Spraying on the surface can prevent these occurrences.
[0018]
In the present invention, when the cooling device is connected to the refrigerator, a low-temperature inert gas can be blown to the printed circuit board immediately after soldering, so that the molten solder adhering to the printed circuit board can be quickly cooled and solidified. Therefore, the inert soldering apparatus of the present invention can rapidly cool even a material having a high melting point, such as lead-free solder, so that cracks and cracks can be prevented, and the strength of the solder can be improved by making the structure of the solder fine.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described with reference to the drawings. FIG. 1 is a front sectional view of the inert soldering apparatus of the present invention.
[0020]
In the inert soldering apparatus of the present invention, the conveyor 1 is installed so as to be inclined upward in the traveling direction (arrow A). Below the conveyor, processing devices such as a preheater 2, a jet solder bath 3, and a cooling device 4 are installed in the traveling direction, and these processing devices are housed in a chamber 5.
[0021]
A fluxer (not shown) and a preheater are installed outside the chamber 5 adjacent to the fluxer. The reason why the fluxer is installed outside the chamber is that the flux is scattered when the flux is applied by the fluxer, thereby contaminating the chamber, and the flux application does not require a low oxygen concentration. The pre-heater (not shown) installed adjacent to the fluxer volatilizes the solvent of the flux applied to the printed circuit board and performs pre-heating of the printed circuit board. Since the heating temperature is not too high, again, a low oxygen concentration is not necessary. Therefore, the fluxer and the preheater adjacent to the fluxer are installed outside the chamber.
[0022]
The pre-heater 2 installed before the jet solder bath 3 installed before the jet solder bath 3 in the drawing is used for soldering a printed circuit board preheated by a pre-heater (not shown) installed outside the chamber. The preheating is performed to a temperature suitable for mounting. Here, since the preheating is performed at a temperature higher than the preheating temperature of the preheater, a low oxygen concentration is required.
[0023]
In the conveyor 1, a pair of endless chains are rotating, and the opposing chains on the inner side run in the same direction (arrow A). The printed circuit board is held between a large number of claws (not shown) attached to these inner opposing chains and travels on each processing apparatus.
[0024]
The pre-heater 2 is a panel heater, and pre-heats a printed circuit board with radiant heat. When a panel heater is used as the pre-heater, the flow of gas in the chamber can be reduced due to radiant heat, and there is no increase in oxygen concentration by inflow of air from the outside.
[0025]
The jet solder bath 3 is provided with a primary jet nozzle 6 for jetting a rough wave and a secondary jet nozzle 7 for jetting a gentle wave. A lead-free solder 8 is placed in the jet solder bath, melted by a heater (not shown), and maintained at a predetermined temperature.
[0026]
The cooling device 4 is connected to an inert gas supply device (not shown), and an inert gas is ejected from the cooling device. If the refrigerator 9 is provided between the cooling device and the inert gas supply device, the inert gas can be discharged at a low temperature. When the inert gas can be sufficiently cooled by the inert gas supply device, the refrigerator need not be provided.
[0027]
The chamber 5 houses the pre-heater 2, the jet solder bath 3, and the cooling device 4 and is sealed so that gas cannot flow in and out of ports other than the entrance and exit. A number of labyrinth tapes 10 are suspended in the chamber. Is established. The labyrinth stabilizes the gas in the chamber and prevents outside air from entering through the entrance. A glass plate 11 is fitted into the upper part of the jet solder bath 3 so that the state of the molten solder jet in the jet solder bath 3 can be observed from outside through the glass plate. Further, in the upper chamber of the jet solder bath 3, inflow pipes 12, 12 for an inert gas are provided.
[0028]
An exhaust device 14 is provided near the inlet 13 of the inert soldering device. The exhaust device is connected to a blower 15 so that a gas near the inlet 13 of the inert soldering device is forcibly sucked from the exhaust device 14.
[0029]
Subsequently, the soldering of the printed circuit board in the inert soldering apparatus of the present invention having the above configuration will be described. First, an inert gas (nitrogen) is flown into the chamber 5 from the cooling device 4 and the inert gas inflow pipes 12 and 12 in the chamber to lower the oxygen concentration in the chamber to 1000 ppm or less.
[0030]
When the oxygen concentration in the chamber drops to 1000 ppm or less, flux application and preheating are performed on the printed circuit board by a fluxer and a preheater (not shown). Thereafter, the printed circuit board is conveyed by the conveyor 1 in the direction of arrow A, enters the chamber 5 from the entrance 13 of the inert soldering apparatus, and is preheated to a predetermined temperature by the preheater 2. This predetermined temperature is about 150 ° C. when the solder in the jet solder bath is Sn-3Ag-0.5Cu lead-free solder (melting point: 217 ° C.).
[0031]
The printed circuit board preheated by the preheater 2 is transferred to the jet solder bath 3, where soldering without unsoldering is performed by the primary jet nozzle 6, and then a bridge or an icicle is corrected by the secondary jet nozzle 7.
[0032]
The printed circuit board soldered in the jet solder bath 3 is carried to the cooling device 4. A low-temperature inert gas is blown from the cooling device 4 onto the soldering surface of the printed circuit board to cool the molten solder attached to the printed circuit board. The inert gas blown from the cooling device 4 is cooled to below zero (about −10 ° C.) by the refrigerator 9 to rapidly cool the soldering surface of the printed circuit board. Due to this rapid cooling, the lead-free solder attached to the printed circuit board solidifies rapidly, so that even if vibrations or impacts are applied to the printed circuit board, not only cracks and cracks do not occur but also the structure is made finer and the mechanical strength is improved. .
[0033]
The inert gas flowing into the chamber 5 from the cooling device 4 flows toward the inlet 13 as shown by the arrow B. Since the exhaust device 14 is installed near the inlet 13 and the gas near the inlet 13 is forcibly sucked from the exhaust device 14, the inert gas in the chamber 5 flows toward the inlet 13. Accordingly, the inert gas supplied from the cooling device 4 and the inlet 12 flows into the jet solder bath 3 and the preheater 2 which require an inert gas during soldering, so that the oxygen concentration is low. .
[0034]
【The invention's effect】
As described above, the inert solder bath of the present invention is a jet solder bath in which the inert gas flowing out of the cooling device, which is the final processing device, flows toward the inlet against the chimney effect and requires an inert gas. Since the preheater is kept at a low oxygen concentration, unsoldered, poor appearance due to oxides, short circuit, reduced insulation resistance, loss of expensive lead-free solder, etc. are eliminated, and low-temperature inert gas is supplied from the cooling device. The conventional method of spraying the printed circuit board immediately after soldering and rapidly solidifying the solder attached to the printed circuit board not only does not cause cracks or cracks, but also improves the mechanical strength by making the solder structure finer. It has excellent effects not found in the inert soldering apparatus.
[Brief description of the drawings]
FIG. 1 is a front sectional view of an inert soldering apparatus of the present invention.
REFERENCE SIGNS LIST 1 Conveyor 2 Preheater 3 Jet solder bath 4 Cooling device 5 Chamber 8 Molten solder 9 Refrigerator 12 Inert gas inlet 13 Inlet 14 Exhaust device 15 Blower

Claims (2)

A preheater, a jet solder bath, and a cooling device are covered with a chamber, and the inside of the chamber is made into an inert atmosphere to perform soldering of a printed circuit board. An automatic soldering device having an outlet and an exhaust device near an entrance of a printed circuit board. The automatic soldering apparatus according to claim 1, wherein the outlet is connected to an inert gas supply device via a refrigerator.

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