CONTROLLING THE LEVEL OF OXYGEN IN REFLOW OVEN

ATMOSPHERE FIELD OF APPLICATION

The present invention belongs to the electronic engineering field for its reference to portable equipment for monitoring and controlling the level of oxygen in reflow ovens atmosphere. STATE OF THE ART

A reflow oven is a heati n g device used for sol de ri ng electronic components on printed circuit boards, through the surface mount technology (SMT).

The use of this technique in the industry of electronics manufacturing enables an easier construction of electronic devices, ensuring that the electronic components are properly mounted and that the electrical connections on the circuit board are guaranteed by reflowed soldering techniques.

The technique of using an inert atmosphere is pretty much applied to control chemical reactions when handled substances present high sensitivity to air.

Several materials used in modern technolog ies such as microelectronics, among others, exhibit unusual and undesired states of oxidation and reactions due to the presence of atmospheric air.

As a solution to this problem, the use of inert gas in, for example, the atmosphere of reflow ovens, made it possible that even at high temperatures, the adverse effects of oxidation are reduced.

Some reflow ovens can operate with an atmosphere of inert gas, although they sometimes have some equipment for monitoring the air quality when related to oxygen levels, and they generally do not make it possible to adjust the quality of the oven atmosphere and it is an integral part of the own reflow oven. In these ovens, without the action of an operator in controlling the flow of nitrogen of this equipment, there may be some waste or lack of nitrogen in the atmosphere of the reflow oven. This lack generates high levels of oxygen in the welding surroundings which can cause welding defects such as open circuits, solder balls, short circuits, among others.

For example, the document JP20100007080 describes a reflow oven capable of controlling the supply of nitrogen and preventing the increase on the concentration of oxygen coming from the outside air. The atmosphere control system is an integral part of the oven, and therefore, it is not a portable device.

The present invention describes a portable equipment for monitoring and controlling the level of oxygen in the atmosphere of reflow ovens, which is portable as its main advantage, and that it can be easily coupled to any conventional reflow ovens using their own outputs of nitrogen and of existing sampling in all reflow ovens, for the connection of collecting and analysis boxes and control of nitrogen injection flow. Therefore, its maintenance is made easier.

The system allows the user to predetermine the desired level of oxygen in the reflow ovens surroundings; it keeps the oxygen levels desired by the user without the need for an operator to control the flow/volume of nitrogen injections in the reflow oven; prevents spending insufficient or excessive nitrogen in reflow ovens processes, and improving the quality of the final product. BRIEF DESCRIPTION OF THE INVENTION

The present invention describes the portable equipment for monitoring and controlling the level of oxygen in atmosphere of reflow ovens.

The device features interface in which the user can preselect the desired values for a given operation. The referred equipment is able to determine the quality of the atmosphere of a reflow oven through parameters predetermined by the user. Therefore, the equipment performs the monitoring of the atmosphere of the reflow oven and controls the oxygen level in the reflow oven by increasing or decreasing the influx of nitrogen through the control that the m icrocontroller has on the control va lve of nitrogen injection, by opening or closing the proportional valve of nitrogen flow control, in order to maintain those predetermined values of oxygen concentration.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic flow diagram of the portable equipment for monitoring and controlling the atmosphere of reflow ovens.

DETAILED DESCRIPTION OF THE INVENTION

This invention descri bes the portable equipment for monitoring and controlling the atmosphere of reflow ovens ( 1) .

The referred equipment is capable of: instantly ascertain the q ua l ity of the atmosphe re of a refl ow oven ( 1 ), to perform its monitoring and control .

According to Figure 1, the portable equipment for monitoring and controlling the atmosphere of reflow ovens ( 1 ) has : a collection and analysis box (3), a control box of nitrogen injection flow (2), a box with programmable controller, electrical power and display with communicative interface (4), connected with one another by electrical cables of power and logic.

The control box of nitrogen injection flow (2) is comprised of ball-type ma n ua l va lves ( 5 ) , nitrogen pressure regu lators with pressure gauge (8), proportional valve of nitrogen flow control (9) located between the nitrogen network and the reflow oven ( 1) . There is a cleaning line (16) that comes out of the box control of nitrogen injection flow (2) which can be used to clean the sampling system using nitrogen. The cleaning line (16) is comprised of a ball-type manual valve of the cleaning line (6) and nitrogen pressure regulator of the cleaning line with pressure gauge (7).

The collecting and analysis box(3) is comprised of line filter (10), solenoid valves (11) to control the input of cleaning sample or nitrogen, a lambda sensor coupled to an analysis chamber (12) which sends electrical signal to the signal converter (13), flow meter with needle valve (14) and a diaphragm-type vacuum pump (15).

The box with the programmable controller, electrical power and display with communicative interface (4) is comprised of a microcontroller and an electrical panel of the control system.

Operation of portable equipment for monitoring and controlling the level of oxygen in reflow oven atmosphere

The portable equipment for monitoring and controlling the atmosphere of reflow ovens (1) can be coupled to reflow ovens (1) of any brand and model for monitoring/controlling the reflow atmosphere.

In the existing communicative interface in the box with programmable controller (4), the user preselects the desired values of oxygen on the reflow surroundings for a given recipe for the oven operation.

Firstly, the equipment evaluates the values if the oxygen amount collected in the sampling collecting and analysis box (3) corresponds to an atmosphere within the desired operating recipe, as predetermined by the user.

The microcontroller performs the control of the oxygen level in the reflow oven (1) by using as an ideal parameter the value preselected by the user. Additionally, the microcontroller informs the oxygen value measured through the equipment display and controls the nitrogen injection flow so that the oxygen level is kept in the reflow surroundings, according to that preselected by the user.

The microcontroller continuously compares the oxygen levels desired predetermined by the oven operator (1) (set point) to real values presented during the operation performed at that time. The information on quality of the reflow atmosphere is obtained by the lambda sensor (12) in the collecting and analysis box (3) connected to the sampling line (17) of the reflow oven (1).

After that comparison performed between the real values at the time of oven operation (1) and the values preset by the user, a command signal is sent from the microcontroller to the nitrogen flow control box (2), which then coordinates if the proportional valve of nitrogen flow control (9) must be open or closed. Therefore, it is possible to control the desired amount of oxygen in the reflow atmosphere.

This system was designed to control oxygen concentrations below 3000 PPM, in the reflow oven surroundings (1). This way, during the monitoring the equipment detects that there is too much oxygen in the reflow oven surroundings (1) (levels above those previously determined by the user), the equipment automatically injects more nitrogen to the reflow oven (1) until the level predetermined by the user is reached.

On the other hand, when the level of residual oxygen in the reflow surroundings is extremely low (below those values predetermined by the user), the equipment automatically reduces the nitrogen flow into the reflow oven (1), by closing the proportional valve of nitrogen flow control. (9).

When the oxygen level is according to what has previously been predetermined by the user, the equipment automatically locks the open position of the proportional valve of nitrogen flow control (9). This way, it is kept a constant nitrogen injection flow into the reflow oven (1) until the moment at which the equipment detects that the oxygen level is no longer as predetermined by the user.

Therefore, the use of a nitrogen amount lower or higher than that required for that oven specific operation (1) is avoided, preventing the waste of nitrogen, improving the quality of the final product of which specification requires low oxygen concentration in the reflow surroundings.

Although the invention has been extensively described, it is obvious to those skilled in the art that several changes and modifications can be made aiming at a design improvement without these changes being not covered by the scope of the invention.