Vapor phase processing apparatus

A vapor phase processing apparatus of the type wherein an article is heated to a preselected temperature for vapor phase processing, comprises a vessel containing a liquid having a boiling point at least equal to the preselected temperature, into and out of which the article is transported, and a heating device for boiling the liquid in the vessel to produce vapor. The heating device is provided, as the sole source of heat, at a base wall of the vessel in such a manner that the heating device is not exposed to the liquid in the vessel.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an apparatus for vapor phase processing such as 
soldering, fusing or brazing. 
An article on which the vapor phase processing is to be performed is heated 
to a preselected temperature appropriate for the vapor phase processing by 
condensing hot saturated vapor of liquid on the article. Although the 
present invention is not to be construed as limited to soldering, it is 
most readily understood in the context of soldering. 
2. Description of the Prior Art 
U.S. Pat. No. 3,904,102 discloses a vapor phase processing apparatus of the 
type wherein an article is heated to a preselected temperature for vapor 
phase processing comprising: a vessel containing a liquid having a boiling 
point at least equal to the preselected temperature, into and out of which 
the article is transported; heating means for boiling the liquid to 
produce vapor; and cooling means for condensing the vapor. In this 
apparatus, the heating means is provided inside the vessel. Although an 
external source of heat such as a hot plate may be applied to the vessel 
as a supplemental heating means, the main heating means remains inside the 
vessel. This apparatus has several disadvantages. 
Since the heating means inside the vessel must be submerged in the liquid 
to prevent overheating, a quantity of liquid is always needed in the 
vessel so that the liquid level is maintained above the heating means. 
Conventionally, flux is used with elements to be soldered in the soldering 
operation, and the flux merged in the liquid is deposited on the external 
surface of the heating means to degrade the thermal conductivity of the 
heating means. 
Moreover, the existence of the heating means inside the vessel prevents 
easy cleaning of the interior of the vessel. 
The other prior art listed below also has the above disadvantages: 
U.S. Pat. No. 3,866,307; 
U.S. Pat. No. 4,389,797; 
U.S. Pat. No. Re. 30,399. 
SUMMARY OF THE INVENTION 
It is, accordingly, an object of this invention to overcome the above 
disadvantages of the prior art. 
The above disadvantages are overcome by providing a vapor phase processing 
apparatus in accordance with this invention wherein heating means for 
boiling the liquid to produce vapor is provided, as the sole source of 
heat, at a base wall of the vessel in such a manner that the heating means 
is not exposed to the liquid in the vessel. 
In this construction, since there is no heating means inside the vessel, 
the apparatus needs only a small quantity of liquid in the vessel during 
operation, and the flux merged in the liquid is prevented from being 
deposited on the surface of the heating means. Further, the interior of 
the vessel is easy to clean. 
In the preferred embodiment, the heating means is provided on an outer 
surface of the base wall of the vessel. 
The inner surface of the base wall of the vessel may be inclined with 
respect to the horizontal, and the heating means may include at least two 
heating elements disposed along the direction of the inclination of the 
inner surface of the base wall. The heating elements may be capable of 
being individually temperature-controlled by temperature controlling means 
associated with temperature sensor means. 
In the preferred embodiment, the apparatus may include trough means for 
receiving condensed vapor, which is inclined in the direction opposite to 
the inclination of the inner surface of the base wall, and which is 
provided at a lowermost portion thereof with aperture means for permitting 
the condensed vapor received in the trough means to drop therethrough onto 
the uppermost portion of the inclined inner surface of the base wall.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, there is shown an apparatus for performing the vapor 
phase processing on a single article 2 or on a batch of articles. The 
apparatus includes a vessel 3 having at the upper end thereof an opening 
through which the article 2 is transported into and out of the vessel, and 
a base wall 3a at the lower end thereof. The vessel 3 contains a liquid 1 
having a boiling point at least equal to a temperature appropriate for the 
vapor phase processing. In the case of the soldering operation, the 
temperature may be preselected at the melting point of the solder which is 
placed on the article 2 with elements to be soldered thereon. 
Plate-like heating elements 4 together with respective temperature sensors 
7 are provided on the outer surface of the base wall 3a of the vessel 3. 
The inner surface of the base wall 3a is inclined in only one a single 
direction with respect to the horizontal as shown in FIG. 1, and the 
heating elements 4 and the sensors 7 are spaced from each other in the 
direction of the inclination of the inner surface of the base wall 3a. The 
heating elements 4 may be individually temperature controlled by a 
temperature controller 10 associated with the sensors 7. 
The apparatus includes a cooling coil 6 located in the upper region of the 
vessel 3. 
An annular trough 8 may be provided below the cooling coil 6. The trough 8 
may have a rectangular configuration in general which corresponds to the 
shape of the cooling coil 6. The trough 8 is inclined in the direction 
opposite to the inclination of the inner surface of the base wall 3a of 
the vessel 3, and has an aperture 9 or apertures such as slits, holes, 
notches or the like at its lowermost portion. 
The liquid 1 in the vessel 3 may be circulated through a pump 11, a filter 
device 12, the trough 8 and the aperture 9 for removing the flux and the 
other material from the liquid. 
In operation, the heating elements 4 boil the liquid 1 in the vessel 3 to 
produce vapor. A portion of the hot saturated vapor is condensed on the 
article 2 transported into the vessel 3, and the article 2 is heated to 
the desired temperature by transfer of the heat. At this stage, the vapor 
phase processing (e.g., soldering, fusing or brazing) is performed on the 
article 2, and then the article 2 is transported out of the vessel 3. 
The temperature controller 10 associated with the temperature sensors 7 
individually controls the temperature of the heating elements 4 so as to 
effectively boil a small quantity of liquid in the vessel 3 without 
overheating the heating elements 4. 
The condensed vapor received in the trough 8 and the filtered liquid pumped 
from the lower portion of the vessel 3 through the filter device 12 into 
the trough 8 drop through the aperture 9 onto an uppermost portion of the 
inner surface of the base wall 3a. When there is only a very small 
quantity of liquid in the vessel 3 and the upper portion of the inner 
surface of the base wall 3a is not submerged in the liquid 1 in the vessel 
3, the drops of the liquid which have fallen from the aperture 9 onto the 
uppermost portion of the inner surface of the base wall 3a flow downwards 
thereon while being partially vaporized. 
The embodiment shown in FIG. 2 is combined with a continuous conveyor 
system. In this embodiment, the articles 2 are continuously transported 
into and out of the vessel 3 by a belt conveyor system 14 through conduits 
15 provided on the opposed side walls of the vessel 3. The conduits 15 are 
provided with cooling coils 16. The construction and the operation of the 
other parts are similar to those of the embodiment in FIG. 1. 
The embodiments shown in FIGS. 3 and 4 are similar to the embodiments shown 
in FIGS. 1 and 2, respectively, but are different from them in that the 
heating elements 4 are in a cylindrical form and are located in pipes 17 
which are secured on the outer surface of the base wall 3a by means of, 
for example, welding. The heating elements 4 may be removable from the 
respective pipes 17 for maintenance purposes. 
The construction and the operation of the other parts of the embodiments in 
FIGS. 3 and 4 are similar to those of the embodiments shown in FIGS. 1 and 
2, respectively.