KR20010077978A - Gas mixing apparatus - Google Patents

Abstract

PURPOSE: A gas mixing apparatus is provided to accurately mix a plurality of gases, to reduce defects such as tombstoning and solder splatter, and to improve soldering performance in the manufacture of a circuit board. CONSTITUTION: The compact gas mixing apparatus comprises a gas panel, pressure control valves(16,18) to regulate differential pressures, flow meters(30,32) and a static mixing chamber(34). The plurality of gases may be a minor gas and a major gas, where, for example, the major gas is nitrogen, and the minor gas is air or oxygen. The major gas and the minor gas is preferably mixed in a proportion of from about 100ppm to about 10,000ppm minor gas in the major gas, more preferably in a proportion of from about 500ppm to about 2,000ppm minor gas in the major gas.

Description

Gas Mixing Device {GAS MIXING APPARATUS}

Technical Field of the Invention

The present invention generally relates to an apparatus for producing a gas mixture. More particularly, the present invention relates to a gas mixing panel capable of generating a controlled atmosphere to improve the performance of the electronic assembly process in a reflow oven.

Background of the Invention

In general, controlled atmospheres containing specific gas characteristics are required to improve the performance of the electronic assembly process in a reflow oven. It would be desirable to provide an economical compact device capable of generating a controlled atmosphere.

Specific gas characteristics in the atmosphere for optimal reflow performance preferably have a concentration of hydrophobic gas in the main gas of about 100 ppm to about 10,000 ppm, more preferably a concentration of hydrophobic gas in the main gas of about 500 ppm to about 2,000 ppm. For the purposes of the present invention, the minority gas may be oxygen or air and the main gas may be nitrogen. The concentration of oxygen or air to this particular range of nitrogen reduces defects such as tombstoning and solder splatters and improves solder performance during the electronic assembly process, especially in the manufacture of circuit boards. If the concentration of oxygen or air in nitrogen is less than about 100 ppm, certain low oxygen defects may occur, and if the concentration of oxygen or air in nitrogen exceeds about 10,000 ppm, certain high oxygen defects will occur. Preferred concentrations of oxygen or air in nitrogen to achieve optimal performance of the reflow oven are known as "sweet spots."

Thus, there is provided a gas mixing device which serves to provide a controlled atmosphere having gaseous properties in which the concentration of oxygen or air in nitrogen is from about 100 ppm to about 10,000 ppm, so that the electronic assembly process has little or no amount of defects. It is desirable to be able to run with.

Conventional gas mixing techniques use expensive mass flow controllers and huge surge tanks. This conventional mixer was used to produce a gas mixture with 1% to 50% oxygen in nitrogen, but not in the ppm range. Recently, larger size gas mixers have been developed and marketed that are considerably more expensive. More recently, a slightly less expensive gas mixer has been developed that uses fixed orifice plates for measuring gas flow and then mixing in a fairly small surge tank. In addition, other conventional mixers have been developed that serve to precisely provide the desired gas composition.

There are also other gas mixing devices in the art which provide mixed gas compositions. US 6,614,655 discloses a combination of test gas and zero gas. The zero gas can be nitrogen or artificial oxygen and no test gas (calibration gas) has been specified. The '655 patent discloses a reduction in the number of critical nozzles necessary to produce different concentrations of feed streams in the product. In the '655 patent, the mixing chamber of the gas mixing device is connected to the outlet of the critical nozzle to ensure that the outlet pressure is above a certain minimum pressure. Each critical nozzle increases in a ratio of 1: 2 from one to the other. Since the outlet pressure is always above the critical pressure, the gas volume is only constant along the cross section of the nozzle. The critical nozzle contains a test gas or zero gas. A valve with two inlets is located above the critical nozzle and the two inlets can alternatively be opened. The four nozzles have a cross section that opens at 1: 2: 4: 8. The largest nozzle is located opposite the mixer outlet. The microprocessor actuates valves, monitors and regulates gas pressure. The gas mixing device of the '655 patent yields 16 linearly graded concentrations of test gas in zero gas.

US Pat. Nos. 5,671,767 and 5,544,674 both disclose mixing two gases together at a controlled rate. Since the mixing device is for a ventilator, the gases of these patents only concern oxygen and air. Since the mixing device achieves high mixing accuracy regardless of the flow rate, the device can be used for high or low flow rates. The first gas stream is controlled by an orifice in a variable region that supplies gas to the mixing chamber. The same applies to the second gas. When the flow rate is reduced, the piston moves toward the valve member. This reduces the size of each orifice, while maintaining the same ratio between orifice flow regions. The passage or orifice area for each of the two gases is increased or decreased by the same amount at each valve, so that the proportion of gases is maintained.

Japanese Patent No. 11,033,382 discloses a miniaturized and simplified gas mixing unit. This patent uses a pressure equalizer that adjusts two gases to the same pressure. The two gases are mixed in the gas passage region at a ratio corresponding to a preset mixing ratio. The flow rate can be regulated by a control valve.

Although there are a number of devices for mixing gases, it is not believed that economical compact devices can be produced that can mix gases to produce nitrogen products having about 100 ppm to 10,000 ppm of oxygen. Therefore, it is desirable to have a gas mixing device having these characteristics.

It is an object of the present invention to provide a compact gas mixing device for precisely mixing a plurality of gases.

1 is a general schematic diagram of a gas mixing device utilizing a pressure differential gauge, a flow meter, and an electrostatic mixing chamber.

* Description of the main parts of the drawings *

12: nitrogen stream 14: air stream

20, 22: pressure regulator 16, 18: pressure relief valve

24: differential pressure gauge 26, 28: flow meter

30, 32: flow valve 36, 38: check valve

34: gas mixer 40: sample valve

Summary of the invention

One aspect of the present invention relates to a compact gas mixing device for precisely mixing a plurality of gases. The apparatus includes a gas panel, a pressure control valve to adjust the pressure differential, a flow meter, and an electrostatic mixing chamber. The plurality of gases may consist of a minority gas and a main gas, for example the main gas is nitrogen and the minor gas is air or oxygen. The main gas and the hydrophobic gas are mixed to obtain a gas mixture which preferably has a concentration of oxygen in nitrogen of about 100 ppm to about 10,000 ppm, more preferably a concentration of oxygen in nitrogen of about 500 ppm to about 2,000 ppm.

The pressure control valve regulates the pressure differential to approximately ± 5 inches of the water column. The device is integrated with the reflow oven.

As used herein, oxygen is sometimes interchangeable with air. Note that oxygen makes up about 20% of air.

Advantages of the present invention will become apparent from the following description of the invention with reference to FIG. 1, which is a schematic diagram of a gas mixing device utilizing a pressure differential gauge, a flow meter and an electrostatic mixing chamber.

Detailed description of the invention

The invention consists of hydrophobic and plural gases, preferably oxygen or air as hydrophobic gases, nitrogen as plural gases, using an electrostatic mixing chamber, and the concentration of oxygen or air in nitrogen is from about 100 ppm to about 10,000 ppm, and more preferably To provide a compact gas mixing device that can produce a mixture having a concentration of oxygen or air in nitrogen from about 500ppm to about 20,000ppm. The apparatus consists of a fixed in-line baffle in which the gas shears and swirls to provide uniform production.

The present invention provides a stable oxygen concentration in the gas mixture obtained by mixing nitrogen and air or oxygen in a mixing panel in which the pressure difference between the nitrogen supply and the oxygen supply is measured and controlled to be varied by a water column of only about 5 inches or less. do. The mixture is homogenized through an electrostatic helical mixer. This technique provides a sufficient amount of oxygen or air mixed with nitrogen so that the final nitrogen concentration is preferably 100 ppm or 10,000 ppm of oxygen or air in nitrogen, more preferably 500 ppm or 2,000 ppm of oxygen or air in nitrogen. to provide.

The present invention is quite different from the conventional design of measuring two gas streams and mixing the gas streams in the surge tank.

Small pressure variations between the majority and minority gases adversely affect the mixing accuracy. To include the cost, a low cost flow meter was left in the design, but a pressure differential gauge was integrated to measure and adjust the pressure difference between the major and minor gases up to about 5 inches below the water column.

The present invention uses an electrostatic mixing chamber. This electrostatic mixing chamber consists of a fixed in-line baffle where the gas is sheared and swirled to provide uniform production. The use of an electrostatic mixing chamber offsets the cost of the pressure differential gauge and contributes significantly to the compact size of the gas mixing device of the present invention.

Here, mechanical regulators are used to regulate the nitrogen and oxygen streams, and pressure differential indicators are used to ensure that the two gas streams are controlled within 5 inches of the water column pressure. The regulated gas stream flow was adjusted using a flow meter such as a rotameter to adjust the desired measured gas mixture. The two gas streams were then mixed in an electrostatic mixing chamber and then the final gas mixture was transferred to a reflow oven.

The present invention produces a stable gas mixture with an accuracy of ± 1 ppm with a gas mixture of 100 ppm. Simple pressure differential gauges produce gas mixtures with varying accuracy in flow range and up to about ± 1 ppm. Accuracy was improved by identifying the same transport pressure of the two gas streams at ± 5 inches of the water column. The conveying pressure in the present invention was measured up to about 300 inches of water column.

As an example of the gas mixing panel of the present invention, a "flat plate" design is constructed to facilitate field installation in a reflow oven. The gas mixing panel of the present invention is detailed as follows:

Dimensions Height 24 "x Length 24" x Depth 12 "

(61cm high x 61cm long x 30.5cm high)

Weight 65 lbs (29.2 kg)

Junction Nitrogen Inlet: 1/2 "FPT

Air Inlet: 1/4 "FPT

N ₂ / Air mix outlet: 1/2 "FPT

N ₂ / Air mixed samples: 1/4 "quick-junction

Gas requirements

Clean dry air 50 scfh (100 psig) minimum

Grade Nitrogen 3000 scfh (100 psig) minimum from Praxier

1 provides one embodiment of a flowchart of the present invention. Nitrogen stream 12 (280-2800 scfh, 5-50 scfm) and air stream) 14 (2-20 scfh) enters 75 psig. The pressure difference between the streams is measured by a pressure difference gauge 24. If the pressure differential is too large, the pressure regulators 20 and 22 will adjust the pressure differential until it is within about ± 5 inch water column. The stream will pass through pressure relief valves 16 and 18 (set to 100 psi) before passing through flow meter 26 or 28. Flow valves 30 and 32 monitor the flow of the stream according to the particular composition selected for the final stream. The irradiation valves 36 and 38 regulate the air and nitrogen gas before entering the gas mixer 34 which is an electrostatic mixing chamber. There is a product stream 16 in which the gases are mixed and have an oxygen content of about 10 ppm to about 10,000 ppm, depending on the composition selected. Sample valve 40 induces the following sample gas.

Various aspects of the invention are interchangeable. For example, a pressure differential gauge with a pilot / slave regulator arrangement can be placed on pure nitrogen and a pressure supply. In this design, the nitrogen regulator regulates the pressure of the delivered nitrogen to provide a signal that presets the air regulator at a pressure substantially equal to the nitrogen pressure.

Another variant contemplated by the present invention replaces the electrostatic mixing chamber with a compact surge tank and a diffusion nozzle on the inlet of the surge tank. The diffusion nozzle provides the necessary shearing and swirling to properly mix the nitrogen and oxygen streams.

Features of the invention are shown in one or more drawings for convenience only, as each feature may be combined with other features of the invention. Other embodiments are recognized by those skilled in the art and are intended to be included within the scope of the claims.

The present invention provides a compact gas mixing device for precisely mixing a large number of gases, which serves to reduce defects such as tombstoning and solder splatters and during electronic assembly processes, in particular of circuit boards. Improve solder performance at the time of manufacture.

Claims (10)

a) gas panel; b) a pressure control valve for adjusting the pressure difference; c) flow meters; And d) Compact gas mixing device for accurately mixing a plurality of gases, including an electrostatic mixing chamber. The apparatus of claim 1 wherein the minor gas and the primary gas are mixed. 3. An apparatus according to claim 2, wherein the main gas is nitrogen and the minor gas is air. 3. An apparatus according to claim 2, wherein the main gas is nitrogen and the minor gas is oxygen. 3. An apparatus according to claim 2, wherein the main gas and the hydrophobic gas are mixed to obtain a gas mixture having a concentration of oxygen in nitrogen of about 100 ppm to about 10,000 ppm. 3. The apparatus of claim 2, wherein the control valve adjusts the pressure difference to about ± 5 inches of the water column. The apparatus of claim 1 integrating with a reflow oven. The apparatus of claim 1 wherein the electrostatic mixing chamber comprises a fixed in-line baffle. The apparatus of claim 1 wherein the flow meter is a rotometer. The apparatus of claim 1 wherein the electrostatic mixing chamber is replaced by a surge tank and a dissolution nozzle.