Gas separation – Combined or convertible – Involving communication receiving or transmitting apparatus
Reexamination Certificate
1999-02-19
2001-02-27
Simmons, David A. (Department: 1724)
Gas separation
Combined or convertible
Involving communication receiving or transmitting apparatus
C055S428100, C055S442000, C034S077000
Reexamination Certificate
active
06193774
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a reflow solder convection oven with a passive gas decontamination subsystem, and a gas decontamination system useful in environments other than reflow solder convection ovens.
BACKGROUND OF THE INVENTION
Reflow solder convection ovens are used in the production of printed circuit boards employing surface mount technology. Most convection ovens include a number of heating zones spaced along a conveyer which carries the printed circuit boards through the various heating zones. Each heating zone usually includes upper and lower heating elements, and a fan or blower associated with each heater element. The fan blows air, or nitrogen, or some other gas through the heater elements and the heater elements then heat the gas before it moves over and about the printed circuit boards.
After the heated gas passes over the printed circuit boards, various contaminants, for example, alcohol, aldehydes, ketones, acids, rosins and resins are released into the oven and carried by the oven gas flow.
These contaminants often foul the internal components and surfaces of the convection oven to the point that a thick, viscous, tacky paste or fluid or residue is deposited on certain components and surfaces. In some cases, this contamination can cause failure of various oven components. The periodic maintenance required to clean the oven internals reduces productivity.
One attempt to alleviate this problem included the use of a condenser and filter assembly and a fan which urged the contaminated convection oven gas through the condenser and filter. In practice, however, the condenser and filter fouled too quickly and too often, choking off the flow of gas and adversely affecting oven performance, until cleaned.
BRIEF SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a convection oven with an oven gas decontamination subsystem which reduces fouling of the convection oven components and surfaces.
It is a further object of this invention to provide such an oven gas decontamination subsystem which is passive and requires no additional moving parts.
It is a further object of this invention to provide such an oven gas decontamination subsystem which does not require the use of condensers or filters or similar active systems.
It is a further object of this invention to provide such an oven gas decontamination subsystem which itself does not fail or become clogged.
It is a further object of this invention to provide such an oven gas decontamination subsystem which is easy to clean.
It is a further object of this invention to provide an oven gas decontamination subsystem which may be useful in environments other than solder reflow convection ovens.
This invention results from the realization that fouling of a reflow solder convection oven by contaminants present in or carried by the heating gases of the oven which condense or deposit on various components of the oven and that the clogging problem associated with prior art active decontamination systems including condensers and filters can be eliminated by a passive decontamination subsystem which is driven by the pressure and temperature differentials inherent in a convection oven and which uses a network of collision baffles to capture the contaminants instead of condensers and filters which themselves quickly become fouled and clogged This invention features a reflow solder convection oven comprising at least one heating zone with a gas intake and a gas outtake, and a passive gas decontamination subsystem including an intake duct in fluid communication with the gas outtake of the at least one heating zone, and at least one decontamination duct connected on one end to the intake duct. The decontamination duct includes a plurality of collisions baffles therein for collecting contaminants from the gas outtake of the at least one heating zone. Also included is an outtake duct connected to the decontamination duct on an end opposite the intake duct and in fluid communication on an opposite end with the gas intake of the at least one heating zone.
The intake duct is typically vertically disposed and includes a drip tray therein to capture any contaminate condensing in the intake duct. The outtake duct is also usually vertically disposed and includes a drip tray therein to capture any contaminates condensing in the outtake duct. The at least one decontamination duct, however, is preferably horizontally disposed.
The decontamination duct includes a removable wall and the collision baffles are preferably attached to the removable wall for easy cleaning thereof. The removable wall is usually the top cover of the decontamination duct.
The collision baffles are preferably disposed at an acute angle between 40°-80° with respect to the longitudinal axis of the decontamination duct. The collision baffles are preferably disposed at an angle away from the flow direction to create a turbulent flow. The baffles usually have one dimension (e.g. width) with extends across the center line of decontamination duct and another dimension (e.g. length or height) which spans approximately from one side of the decontamination duct to an opposite side of the decontamination duct.
In the preferred embodiment, the decontamination duct is square with a sloped bottom and the baffles are rectangular plates. The decontamination duct and the plates are typically made of aluminum.
The at least one zone which receives the decontaminated gas is preferably a zone other than the reflow zone such as the “pre-flow” or “soak” zone. There typically are n total zones and the intake duct is proximate the n
th
or last zone. This arrangement helps insure that the system processes all the convection oven gas in an effective manner.
In the preferred embodiment, there are two decontamination ducts, one intake duct connected to both decontamination ducts and two outtake ducts, one each connected to a decontamination duct, one each connected to a different gas outtake.
The closed, passive gas decontamination system of this invention includes an intake duct responsive to a gas flow containing contaminants within the convection oven; a decontamination duct connected on one end to the intake duct, the decontamination duct including a plurality of collision baffles therein for collecting contaminants from the gas; and an exhaust duct connected to the decontamination duct opposite the intact duct and terminating at a location within the oven remote from the intake duct.
The passive gas decontamination system of this invention, useful for convection oven and other environments, has a duct assembly including an intake region, a decontamination region, and an exhaust region, the decontamination region including a plurality of collision baffles for collecting contaminates in the gas on the surfaces thereof.
The decontamination region typically includes a duct with a removable wall and the collision baffles are attached to the removable wall for cleaning thereof. The removable wall is preferably the top cover of the decontamination duct.
The collision baffles are preferably disposed at an acute angle (e.g., 40°-80°) with respect to the longitudinal axis of the decontamination region and disposed at an angle away from the flow direction. The baffles also typically have one dimension with extends across the center of the decontamination region and another dimension which spans approximately from one side of the decontamination region to an opposite side of the decontamination region.
REFERENCES:
patent: 3250263 (1966-05-01), Gerjets
patent: 3526970 (1970-09-01), Harrison et al.
patent: 5347103 (1994-09-01), LeMieux
patent: 5611476 (1997-03-01), Soderlund et al.
patent: 5993500 (1999-11-01), Bailey et al.
Durdag Kerem
Sherwin Tom
Silveri Robert
Conceptronic, Inc.
Hopkins Robert A.
Iandioro & Teska
Simmons David A.
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