JPH0997976A - Reflow furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To share as an adhesive curing furnace by providing an openable shutter at the lower heater of a reflow furnace, and so controlling the temperature in the furnace that the surface temperature of a printed board becomes suitable temperature by the shutter. SOLUTION: A printed board 10 temporarily fixed with an electronic component 11 is set to a conveyor 2, conveyed into a furnace body 1, and the component 11 is solder mounted on the front or both the front and rear surfaces of the board 10. In this case, if there is a fear of deteriorating the component 11 mounted on the rear surface (front surface in the previous step) of the board 10 due to the heat emitted directly from a lower heater 3', the heat radiated from the heater 3' is shielded by a shutter 4. Then, the heater 3' disposed at the inlet side (in the direction of an arrow A) and an upper heater 3 disposed at the outlet side are turned OFF, the heater 3' is shielded by the shutter 4, and the temperature in the furnace is so controlled that the surface temperature of the board 10 becomes 140 deg.C. Thus, it can be shared as an adhesive curing furnace.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a reflow furnace.

[0002]

2. Description of the Related Art A conventional reflow furnace is shown in FIG.
Printed circuit board 10 with electronic component 11 mounted in furnace body 1
A conveyor 2 that conveys the above, an upper heater (panel heater or rod-shaped heater) 3, ..., which is sequentially provided along the longitudinal direction of the conveyor 2, and the conveyor 2 is sandwiched between the inlet side and the outlet side of the furnace body 1. Lower heaters (panel heaters or rod-shaped heaters) 3'and 3'opposed to the upper heaters 3 and 3
And the electronic component mounted printed circuit board 10 which is conveyed into the furnace main body 1 by the conveyor 2 is sequentially heated by the upper heaters 3 and 3 and the lower heaters 3 ′ and 3 ′ to melt the solder on the reflow surface, The components are soldered and mounted on the printed circuit board 10. The internal temperature of the reflow furnace is set so that the reflow surface of the printed board 10 is about 200 ° C. (the solder melting temperature is about 180 ° C.).

Recently, in order to mount electronic components on the printed circuit board 10 with high density, electronic components 11 having lead terminals 11 'as shown in FIG. 3 and lead terminals as shown in FIG. 4 are provided. The number of cases in which electronic components 12 and the like that do not exist are mixedly mounted is increasing.

As shown in FIG. 3, the electronic component 11 having the lead terminals 11 'described above is temporarily fixed by inserting the lead terminals 11' into the through holes 10 'provided in the printed circuit board 10 and then reflow soldering. However, the electronic component 12 having no lead terminal shown in FIG. 4 is temporarily fixed on the printed board 10 with an adhesive and then immersed in a molten solder bath for soldering.

To temporarily fix the electronic component 12 having no lead terminal shown in FIG. 4 on the printed circuit board with the adhesive, first, the adhesive is applied on the printed circuit board 10 to form the electronic component 1.
2 is adhered and then heated to 140 ° C. to cure the adhesive. Since a specially designed adhesive curing furnace is used for curing the adhesive, mounting the electronic component 12 on the printed circuit board 10 requires at least two furnaces, which causes a problem that the equipment cost increases. .

Therefore, it is easily conceivable to use the reflow oven as an adhesive curing oven in common. However, if the reflow oven is also used as the adhesive curing oven, there are the following problems.

[0007]

As described above, the furnace temperature of the reflow furnace is set to about 200 ° C, and the furnace temperature of the adhesive curing furnace is set to about 140 ° C. Therefore, the electronic component 12 having no lead terminal in the adhesive curing furnace receives less heat stress. However, if the reflow oven is also used as an adhesive curing oven, the electronic component 12 having no lead terminal is exposed to a high temperature of about 200 ° C. when the adhesive is cured. There is a risk of thermal deterioration.

From the above, the lower heater 3'located on the lower side of the furnace body 1 is turned off and the furnace temperature is controlled so that the surface temperature of the printed circuit board 10 is around 140 ° C.
It is possible to use the reflow oven as an adhesive curing oven. However, in the heater used in the reflow furnace, the surface of the heater is blackened in order to improve the thermal efficiency to increase the heat radiation / heat absorption rate.
Even in the case of F, the lower heater 3 ′ that has absorbed the radiant heat from the upper heater 3 serves as a heat source to radiate heat secondarily, the back surface of the printed circuit board 10 becomes high in temperature, and electronic components vulnerable to thermal stress deteriorate.

An object of the present invention is to provide a reflow oven that can be used as an adhesive curing oven.

[0010]

SUMMARY OF THE INVENTION The present invention is a reflow furnace comprising a conveyer for conveying an electronic component-mounted printed circuit board into a furnace body and heaters provided above and below the conveyor, and at least one heater of the lower heaters. A reflow furnace is configured by providing an openable and closable shutter.

[0011]

At least one of the lower heaters of the furnace body 1, for example, the lower heater 3'provided at the inlet portion shown in FIG. 1 is turned off, and the shutter 4 is moved to the inlet side (arrow A direction). By shielding the lower heater 3 ′ and controlling the temperature inside the furnace so that the surface temperature of the printed circuit board 10 is around 140 ° C., it can be used as an adhesive curing furnace.

Further, the lower heater 3'is turned on, the shutter 4 is moved in the direction of arrow B (see FIG. 2) to open the lower heater 3 ', and the surface temperature of the printed circuit board 10 is about 200.degree. It can be used as a reflow furnace by controlling the temperature inside the furnace so that the melting temperature is about 183 ° C.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. 1 is a sectional view showing an embodiment of the present invention, FIG. 2 is a sectional view showing a state of use, and FIGS. 3 and 4 are explanatory views showing electronic components mounted on a printed circuit board.

In FIGS. 1 and 2, reference numeral 1 is a furnace main body, and 2 is a conveyor such as a chain conveyor that conveys a printed circuit board 10 on which electronic components are mounted. 3.
3 is an upper heater (panel heater or rod-shaped heater) which is sequentially provided along the longitudinal direction of the conveyor 2 3 ', 3'
Is a lower heater (panel heater or rod-shaped heater) provided opposite to each other with the upper heater 3 provided at the inlet portion of the furnace body 1 and the upper heater 3 provided at the outlet portion of the furnace body 1 sandwiching the conveyor 2. . Reference numeral 4 denotes a shutter made of a metal plate such as stainless steel or aluminum. The shutter 4 is attached to the upper surface of the conveyor 5 as shown in the drawing, and by moving the conveyor 5 left and right, a lower portion provided at the entrance of the furnace main body 1 The heater 3'is shielded and opened. The conveyor 5 is moved by a driving device such as a motor or manually. 6 is a positioning switch for detecting that the shutter 4 has closed the lower heater 3'provided at the entrance of the furnace body 1, and 7 is a positioning switch for detecting that the lower heater 3'is opened.

[0015]

EXAMPLES In order to mount the electronic components 11 and 12 on the front surface or both front and back surfaces of the printed circuit board 10 by the reflow furnace of the present invention configured as described above, first, the surface temperature of the printed circuit board 10 is about 200.degree. The temperature inside the furnace is set so that the melting temperature of the solder becomes about 183 ° C., and the printed circuit board 10 on which the electronic component 11 having the lead terminals 11 ′ shown in FIG. Electronic component 1 on the front surface or both front and back surfaces of printed circuit board 10
1 is mounted by soldering. At this time, when the electronic component 11 mounted on the back surface (front surface in the previous step) of the printed circuit board 10 may be deteriorated by direct heat from the lower heater 3 ′, as shown in FIG. The heat deterioration of the electronic component 11 is reliably prevented by shutting off the heat radiation by the shutter 4. Next, the lower heater 3 ′ located on the inlet side and the upper heater 3 located on the outlet side are OF
When the temperature is set to F, the lower heater 3'is shut off by the shutter 4 as shown in FIG. 1, and the furnace temperature is controlled so that the surface temperature of the printed circuit board 10 is around 140 ° C. In this state, the electronic component 1 without the lead terminals shown in FIG.
Conveyor 2 is a printed circuit board 10 in which 2 is adhered to a predetermined position.
And is conveyed to the inside of the furnace main body 1 to cure the adhesive to temporarily fix the electronic component 12 to the front surface or both front and back surfaces of the printed circuit board 10. At this time, the lower heater 3'is attached to the shutter 4
Since the lower heater 3 ′ absorbing the radiant heat from the upper heater 3 serves as a heat source, the secondary heat radiation from the upper heater 3 may cause thermal deterioration of the electronic component bonded to the back surface of the print substrate 10. Not at all. Further, since the upper heater 3 located on the outlet side is turned off, the lower heater 3'does not serve as a heat source. In a device in which the heat capacity of the furnace body 1 is insufficient when the upper heater 3 located on the outlet side is turned off, a shutter is also attached to the lower heater 3 ′ on the outlet side to absorb the radiant heat from the upper heater 3. By blocking the secondary heat radiation when 3 ′ serves as a heat source, it is possible to reliably prevent thermal deterioration of the electronic component 12. After that, the printed circuit board 10 is melted into a solder bath (not shown).
Then, the electronic components 11 and 12 are mounted on the front surface or both front and back surfaces of the printed circuit board 10.

[0016]

As described above, according to the present invention, it is possible to provide a reflow oven which can be used not only as an adhesive material curing oven but also assuredly preventing the deterioration of electronic components due to thermal stress. There is.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a sectional view showing a usage state.

FIG. 3 is an explanatory view showing an electronic component.

FIG. 4 is an explanatory view showing an electronic component.

FIG. 5 is a sectional view showing a conventional reflow furnace.

[Explanation of symbols]

1 furnace body
2 Conveyor 3 Upper heater
3'lower heater 4 shutter

Claims (1)

[Claims] 1. A reflow furnace comprising a conveyer for carrying a printed circuit board on which electronic parts are mounted into a furnace main body, and heaters provided above and below the conveyor, wherein at least one heater of the lower heaters has an openable shutter. A reflow furnace characterized by being provided with.