JPH05263U - Reflow furnace - Google Patents

Abstract

(57) [Summary] [Purpose] To prevent air from entering the reflow furnace in an inert atmosphere, and to carry out soldering without defects such as unsoldered solder balls and solder balls. [Structure] A large number of resistors that obstruct the flow of air are installed at the entrance and exit of the reflow furnace, and a shutter that completely blocks the flow of air is installed at the entrance and exit of the reflow furnace. It is an inert atmosphere reflow furnace that has almost no

Description

[Detailed description of the device]

[0001]

[Industrial applications]

  The present invention is a riff used for soldering a printed circuit board coated with cream solder. The present invention relates to a low furnace, particularly a reflow furnace in which the inside of the furnace is made an inert atmosphere and used.

[0002]

[Prior art]

  Generally, when soldering a printed circuit board coated with cream solder, air is present. I was using a reflow oven. However, soldering cream solder in air If soldering is performed, soldering defects such as unsoldered and minute solder ball formation will occur. There were many occurrences. The cause of such defective soldering is in the air. This is due to the effect of oxygen. In other words, if there is oxygen in the reflow furnace, oxygen will This will oxidize the soldered parts that have reached a high temperature in the furnace, which will prevent the solder from spreading. Powder solder which has a large surface area in cream solder. Oxidize powder solder, which results in the loss of the solder's metallic properties. Becomes a fine solder ball. Therefore, when soldering the cream solder, do not use oxygen. Filled with inert gas such as nitrogen, carbon dioxide, argon, helium, etc. If the solder is heated in an inert atmosphere, the soldering defects will disappear as described above. Knew. Therefore, reflow in an inert atmosphere using nitrogen, which is cheaper than before, Many furnaces were proposed. (Reference: JP-A 64-83395, JP-A 1-118369, 2- No. 44185)

[0003]   In a reflow furnace with an inert atmosphere (hereinafter simply referred to as "reflow furnace"), To eliminate soldering defects with cream solder, which has excellent comparative solderability, use acid The elemental concentration may be around 3%, but RMA (Mildly Activated  Oxygen concentration is 1,000ppm for cream solder using Rosin type flux Hereafter, it is desirable that the concentration is 100 ppm or less if possible.

[0004]

[Problems to be solved by the device]   In a conventional reflow furnace, a large amount of nitrogen is introduced into the furnace to fill the furnace with nitrogen. The surplus nitrogen contained oxygen as it flowed out from the inlet and outlet of the reflow furnace. It was thought that air would not enter the furnace due to the nitrogen outflow. However However, conventional reflow furnaces, especially reflow furnaces that circulate gas in the furnace, Even if a large amount of nitrogen was supplied, the oxygen concentration did not drop below 1,000 ppm.

[0005]   Shutters were installed at the entrance and exit of the reflow furnace to reduce the oxygen concentration in the reflow furnace. An installed reflow oven has also been proposed. (JP-A-62-183960)   However, even in a reflow furnace equipped with this shutter, air from the outside of the furnace will not enter. I couldn't block the entrance enough. Also, a reflow furnace equipped with a shutter Then, when the printed circuit board is put into the furnace for soldering, If the shutter opens and closes longer when you leave it later, wait for the shutter to be installed. Air enters the machine zone and a large amount of nitrogen is supplied to replace it with nitrogen. It has to be done and it takes time, which causes problems in economic efficiency and productivity. It was something.

[0006]   The present invention, in a reflow furnace using a shutter, ensures sufficient oxygen concentration in the furnace. Not only can it be lowered, but the opening and closing time of the shutter will be slightly longer Another object is to provide a reflow furnace in which air does not easily enter the furnace.

[Means for Solving the Problems]

  The present inventor applies the reflow furnace proposed by the applicant of the present invention in Japanese Patent Application No. 3-17855. If the existing outside air ingress prevention device is applied to a reflow furnace with a shutter, these phases The present invention was focused on the fact that air does not enter the reflow furnace further due to the riding action. Completed

[0007]   The present invention is applied to a reflow furnace in which an inert gas is introduced to make the inside of the furnace an inert atmosphere. In addition, a resistor that can block the flow of gas is installed at the inlet and outlet of the reflow furnace. At the same time, a shutter that can be opened and closed is installed at the entrance of the reflow furnace. It is a reflow furnace.

[0008]   The resistor used in the present invention should be one that obstructs the passage of gas. Although it may be one, flexible heat-resistant resin (trade name: Kapton) is convenient to use In addition, it is effective in preventing air from entering the furnace. When using a heat-resistant resin piece The electronic components mounted on the printed circuit board were moved even when they contacted the traveling printed circuit board. Will not be dropped. The resistors may be installed irregularly, but the printed circuit board progresses. If a large number of goodwills are lined up in the same direction, the turbulence of the gas will subside and air intrusion will be prevented. The stopping effect becomes remarkable.

[0009]   Since the shutter is a plate-like one and can block the entrance and exit, the flow of gas The effect of preventing the above is remarkable. Shutters installed at the entrance and exit of the reflow furnace Is most effective in preventing air intrusion if it is installed on both sides of a number of resistors, Experimental results show that there is considerable effect on either the front side or the rear side of the antibody are doing.

[0010]

【Example】

  The reflow furnace of the present invention will be described below with reference to the drawings.   FIG. 1 is a front center sectional view of a reflow furnace of the present invention, and FIG. 2 is an enlarged perspective view of a main part. .

[0011]   The reflow furnace 1 includes a preheating zone P, a main heating zone R, a cooling zone C and an air. A printed circuit board (not shown) consisting of the intrusion prevention zones K, K is placed in the furnace in the direction of arrow A. The conveyor 2 that is being transported to is running.

[0012]   The upper and lower parts of the main heating zone R and the preheating zone P have a pair of surface blows. Output type heaters 3 are installed. The surface blowing type heater 3 blows hot air The mouth 4 and the gas suction port 5 are on the same plane, and the gas is sucked from the gas suction port 5 by the internal fan 6. That sucks in, heats it with an electric heater 7, and blows it out from the hot air outlet 4 Is. As a surface blowing type heater, a porous metal plate and electric If you install a heater and use a porous surface coated with ceramic, From the hot air outlet, hot air can be blown out and far infrared rays can be emitted, When soldering the printed circuit board, the printed circuit board and cream solder are heated uniformly at the same time. Come to do.

[0013]   Surface blowing type heaters installed above and below the main heating zone R and the preheating zone P Are arranged so that they are offset from each other in the opposite direction. The gas flow passages formed between the die heaters include the upward passage region X, the collision region Y, and And the downward passage area Z.

[0014]   In the cooling zone C, cooling devices 8 are installed in the upper and lower parts with the conveyor 2 interposed therebetween. It The cooling device 8 has the same structure as the surface blowing type heater, but is provided with an electric heater. Not placed. In the vicinity of the cooling device 8, a fan for applying external cold air to the cooling device 8 is provided. 9 is installed. Therefore, the cooling device is cooled by the outside air, and cool air circulates between the upper and lower parts. It is designed to ring. Nitrogen is supplied to the reflow furnace at appropriate points. The cheat 10 is attached.

[0015]   Inlet / outlet of the reflow furnace, that is, in front of the preheating zone P (in the traveling direction of the printed circuit board). 2) and behind the cooling zone C are air intrusion prevention zones K, K. The air A large number of resistors 11 ... Are installed in the intrusion prevention zone. The values shown in the examples Antibodies are made of heat-resistant resin pieces in the shape of a hot-spot and are installed in the upper and lower parts. It The heat-resistant resin piece is not deformed by the hot air in the reflow oven and is flexible Therefore, even if it comes in contact with the traveling printed circuit board, it will be mounted on the printed circuit board. Conveying device in the air intrusion prevention zone that does not drop the electronic parts There is no hindrance to the movement when moving according to the width of the printed circuit board.

[0016]   Shutters 12, 12 are installed in the air intrusion prevention zones K, K. Implementation In the reflow furnace shown in the example, a set of shutters sandwiches the resistor 11 ... The shutter is installed later, and the shutter is moved up and down by the cylinders 13 and 13 as shown by arrow B. It is designed to move. A transfer device 14 is installed in the air intrusion prevention device. It The transfer device runs independently, but the speed is the same as that of the conveyor 2 in the furnace. It is almost the same.

[0017]   Next, the usage state of the reflow furnace of the present invention will be described.   The surface blowing type heater in the reflow furnace is heated to remove nitrogen from the nozzle 10. Supply into the flow furnace. Nitrogen discharged from the nozzle was present in the reflow furnace Pre-heating zone P, main heating zone R, cooling zone for expelling air C and the entrance air entrance prevention zones K, K are filled. Fill the furnace with nitrogen. When filling, keep the outer shutter closed and the inner shutter open. Keep it. This will ensure that the nitrogen penetrates well into the air ingress zone. Become.

[0018]   When all the places in the furnace are filled with nitrogen and the oxygen concentration reaches the specified value, After closing the inner shutter, open the outer shutter at the entrance, The substrate is carried into the air intrusion prevention zone K. The printed circuit board has a When you enter the printer, close the outer shutter and open the inner shutter to print. The plate is transferred to the conveyor 2. When the outer shutter is open, the outside air is Easily penetrate the air intrusion prevention zone by being disturbed by many resistors in the air intrusion prevention zone. I do not come in.

[0019]   After the printed circuit board enters the air intrusion prevention zone, close the outer shutter at the entrance. After opening the inner shutter, transfer the printed circuit board to the conveyor 2, and after transfer Close the inner shutter.

[0020]   The printed circuit board transferred to the conveyor 2 is preheated to around 150 ° C in the preheating zone P. It is heated and heated in the main heating zone to the melting temperature of the solder (190 ℃ or more), And is cooled in the cooling zone C to be soldered. From this preheating to cooling The printed circuit board is exposed to extremely low oxygen during Cream solder does not oxidize and can be soldered with few defects.

[0021]   After cooling the printed circuit board, the inner shutter of the outlet is opened and the printed circuit board is The carrier 14 is transferred to enter the air intrusion prevention zone K at the exit. Printed circuit board is empty After entering the air intrusion prevention zone, the inner shutter is closed and the outer shutter is opened. The printed circuit board is carried out of the furnace. Many times when this outer shutter is open Due to the number of resistors, air does not enter the air intrusion prevention zone.

[0022]

[Effect of device]

  The reflow furnace of the present invention has the effect of preventing air intrusion by the resistor installed at the entrance and exit. In addition, since the shutter has a gas flow prevention effect, these synergistic effects Air hardly enters the furnace, and the oxygen concentration in the furnace should be extremely low. This enables reliable soldering without defects.

[Brief description of drawings]

FIG. 1 is a front center sectional view of a reflow furnace of the present invention.

FIG. 2 is an enlarged perspective view of a main part.

[Explanation of symbols]

1 reflow furnace 2 conveyors 3-sided blowing heater 11 resistor 12 shutters 13 cylinders P preheating zone R Main heating zone C cooling zone K Air intrusion prevention zone

Claims (3)

[Scope of utility model registration request] 1. In a reflow furnace in which an inert gas is introduced to make the inside of the furnace an inert atmosphere, a resistor capable of impeding the flow of gas is installed at the inlet and outlet of the reflow furnace, and at the inlet and outlet of the reflow furnace. A reflow oven that has a shutter that can be opened and closed. 2. The reflow furnace according to claim 1, wherein the shutter is installed in front of and behind the resistor with a resistor interposed therebetween. 3. The shutter is installed on either the front side or the rear side of the resistor.
Reflow oven as described.