JPH074469Y2 - Thick film firing furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a thick film baking furnace used for baking, for example, a gold (Au) paste into an Au thick film.

(B) Conventional Technology As one of methods for forming a wiring pattern on a printed circuit board, a method is known in which an Au paste or a copper (Cu) paste is printed on an insulating substrate and the paste is baked. For this firing, a thick film firing furnace as shown in FIG. 4 is used.

In this thick film firing furnace, 22 is a muffle, which is made of metal such as Inconel 601 and has a cylindrical shape extending in the left-right direction in the plane of FIG. At the entrance and exit of the muffle, gas curtains 23a and 23b for shutting off outside air are provided.

A belt 30 for transporting the substrate 28 passes through the muffle 22, and the belt 30 slides on the muffle bottom surface 22c from the left side to the right side in FIG.

The inlet side of the muffle 22 is surrounded by a heat insulating material 26.
It is heated by a heater 27 installed on the inner surface. This heated part is burned out from the entrance side in order of burnout zone B.
Z, called the firing zone FZ. 24a, 24b
Are gas inlets for introducing the furnace atmosphere gas into the burnout zone BZ and the firing zone FZ, respectively.
A forced exhaust port 25 is provided between the burnout zone BZ and the firing zone FZ.
The gas in the muffle 22 is forcibly discharged to the outside by the forced exhaust means such as the Venturi method. The exit side of the muffle 22 has a cooling zone CZ for cooling the substrate 28.
It is said that

FIG. 5 shows the temperature distribution (profile) in the muffle 22. In the case of the Au thick film, the burnout zone BZ shifts to the firing zone FZ at about 500 ° C. The burnout zone BZ is a zone where the resin component in the Au paste burns, and the firing zone FZ is a zone where the unburned Au and binder are sintered. It is a problem that the gas flowing in the burnout zone BZ, that is, the burnout gas, flows out to the firing zone FZ, so the forced exhaust port 25 is provided at the position where the burnout zone BZ moves to the firing zone FZ. .

(C) Problems to be Solved by the Invention In the above-mentioned conventional thick film firing furnace, it is inevitable that metal dust is generated due to friction between the belt 30 and the muffle bottom surface 22c. However, since the forced exhaust port 25 is provided on the muffle top surface 22d, when the furnace atmosphere gas and the burnout gas are sucked into the forced exhaust port 25, the metal dust soars and adheres to the surface of the substrate 28. There was a problem that the wiring pattern was broken.

In addition, as the burnout gas soars, there is a problem that carbon components in the burnout gas are condensed and flow out to the firing zone FZ.

The present invention has been made in view of the above, and an object thereof is to provide a thick film firing furnace capable of preventing metal dust from adhering to a substrate, condensation of burnout gas, and outflow of burnout gas to a firing zone.

(D) Means and Actions for Solving the Problems The configuration of the thick film baking furnace of the present invention will be described with reference to FIG. 1 corresponding to one embodiment. The muffle 2 and the muffle 2 are heated from the outside. Heater 7 and the muffle bottom surface 2c
A belt that slides on and conveys the substrate 8 in this muffle 2.
10 and a forced exhaust port 5 which is opened in the muffle 2 and forcibly discharges the burnout gas in the muffle 2, the forced exhaust port 5 is opened in the muffle bottom surface 2c. It has a feature.

In the thick film baking furnace of this invention, the belt 10 and the muffle bottom surface 2c
The metal dust generated by the friction with is carried along the bottom surface 2c of the muffle and is discharged to the outside through the forced exhaust port 5. Therefore, it is possible to prevent metal dust from flying up and adhering to the substrate.

Burnout gas also flows on the substrate 8 along the muffle bottom surface 2c and is immediately discharged to the outside from the forced exhaust port 5. Therefore, the burnout gas does not soar, and the condensation of the burnout gas and the inflow of the burnout gas into the firing zone FZ can be prevented.

(E) Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

FIG. 3 is a diagram showing the entire thick film firing furnace 1 of the embodiment.
Reference numeral 10 denotes a belt, which is composed of a mesh or a chain so as to allow gas to pass therethrough. The belt 10 is guided by guide rollers 11, 12, and 13 and is driven and driven by a drive roller 14. 15 belt 10
Is a cleaner.

2 is a muffle, and the belt 10 slides on the bottom surface 2c. The muffle 2 is a tubular body made of metal such as Inconel 601 and the entrance 2a and the exit 2b are provided with gas curtains 3a and 3b for shutting off outside air, respectively.

The inlet half of the muffle 2 (the left half in the drawing of FIG. 3) is covered with a heat insulating material 6. A far-infrared heater 7 is provided on the inner surface of the heat insulating material 6 to heat the muffle 2 from the outside (see FIGS. 1 and 2). This heated portion corresponds to the burnout zone BZ and the firing zone FZ in order from the inlet 2a. The outlet half of the muffle 2 (right half on the plane of FIG. 3) is the cooling zone CZ.

An enlarged cross section of the burnout zone BZ and the firing zone FZ of the muffle 2 is shown in FIGS. 1 and 2. 4a, 4b
Are inlets of the furnace atmosphere gas which are respectively opened on the inner wall surface of the muffle 2, and supply the furnace atmosphere gas of the burnout zone BZ and the firing zone FZ. Further, a forced exhaust port 5 is opened on the bottom surface 2c of the muffle, which is a transition portion from the burnout zone BZ to the firing zone FZ. The forced exhaust port 5 is connected to a Venturi type forced exhaust means (not shown) by a pipe 5a. Since the gas in the furnace is forcibly discharged from this forced exhaust port 5, a gas flow in the same direction as the feeding of the belt 10 occurs in the burnout zone BZ, and in the firing zone FZ,
Gas flow occurs in the opposite direction to the belt 10 feed.

Next, the operation of the thick film firing furnace 1 of the embodiment will be described. A substrate 8 on which a thick film paste such as Au paste is printed and dried is placed on the belt 10. This board 8 is a muffle entrance
It is introduced into the muffle 2 from 2a, passes through the gas curtain 3a, and is guided to the burnout zone BZ.

In the burnout zone BZ, the resin component in the paste is
It burns by reacting with the atmosphere gas in the furnace. The burnout gas generated at this time is from the surface of the substrate 8 to the bottom surface 2c of the muffle.
And is immediately discharged from the forced exhaust port 5 to the outside. Therefore, the burnout gas does not rise,
It is possible to prevent the carbon component in the burnout gas from condensing and flowing out to the firing zone FZ.

Next, the substrate 8 moves from the burnout zone BZ to the firing zone FZ. In the firing zone FZ, the remaining components of the paste, for example, in the case of Au paste, Au and binder are sintered and changed into an Au thick film. Further, the substrate 8 moves from the firing zone FZ to the cooling zone CZ, is cooled, and is carried out of the muffle 2 through the outlet 2b.

Since the belt 10 slides on the muffle bottom surface 2c, metal dust is generated by friction at this time. However, since the forced exhaust port 5 is opened to the muffle bottom surface 2c, the metal dust is carried by the gas flow along the muffle bottom surface 2c, and the forced exhaust port 5 is discharged.
More discharged to the outside. Therefore, metal dust does not fly up and adhere to the surface of the substrate 8, and disconnection of the wiring pattern can be prevented.

(F) Effect of device As described above, the thick film baking furnace of this device is characterized in that the forced exhaust port is opened on the bottom surface of the muffle, so that metal dust floats and adheres to the substrate. It has the advantage of being prevented. Further, it has an advantage that the carbon component in the burnout gas and the like and the outflow of the burnout gas to the firing zone can be reduced.

[Brief description of drawings]

FIG. 1 is a sectional view of a main part of a thick film baking furnace according to an embodiment of the present invention, FIG. 2 is a sectional view taken along line II-II in FIG. 1 of the thick film baking furnace, and FIG. FIG. 4 is a diagram for explaining the overall configuration of the thick film firing furnace, and FIG.
FIG. 5 is a diagram explaining a temperature profile of a conventional thick film firing furnace. 2: Muffle, 2c: Muffle bottom, 5: Forced exhaust port, 7: Far infrared heater, 8: Substrate, 10: Belt.

Claims (1)

[Scope of utility model registration request] 1. A muffle, a heater for heating the muffle from the outside, a belt for sliding a substrate on the bottom of the muffle to convey a substrate in the muffle, an opening in the muffle, and a burnout gas in the muffle is forced. In the thick film firing furnace, the forced exhaust port is provided with a forced exhaust port for exhausting the gas, and the forced exhaust port is opened on the bottom surface of the muffle.