Measuring and testing – Gas content of a liquid or a solid
Reexamination Certificate
2000-06-26
2001-09-18
Williams, Hezron (Department: 2856)
Measuring and testing
Gas content of a liquid or a solid
C073S031020, C073S863230, C073S863120, C095S018000, C095S054000
Reexamination Certificate
active
06289715
ABSTRACT:
BACKGROUND OF THE INVENTION
(I) Field of the Invention
The present invention relates to the field of gas analysis systems and pertains more particularly to systems for analyzing the content of at least one element of the atmosphere in an enclosure used for soldering or tinning by means of a metal alloy, these soldering or tinning operations using the assistance of a chemical flux which conventionally comprises one or more components among acids, alcohols, or resins, especially rosins.
(II) Description of the Related Art
Soldering and tinning operations are carried in particular in electronics. Examples include soldering of electronic components on a circuit, soldering of circuits in module backplanes, or else termination tinning of electronic components.
The role of the fluxing is then to clean the metal surfaces to be soldered or tinned (degreasing, deoxidation, decontamination of absorbed layers, etc.), the purpose of this being to facilitate the subsequent wetting of these surfaces by the solder.
This fluxing operation is therefore, most commonly, carried out by means of chemical fluxes, often obtained from a resinous base to which, in particular, acid components are added.
It will therefore be noted that two of the most commonly used methods for carrying out such soldering operations in electronics are called “wave soldering” and “reflow soldering.”
In the first case of wave-soldering machines, the design of these machines is such that the parts to be soldered or tinned are brought into contact with one or more liquid solder waves obtained by making the solder bath contained in a tank flow through a nozzle. The parts (circuit, component) have generally been fluxed beforehand in a zone upstream of the machine, by means of a flux spray or foam, the fluxing operation being followed by a preheating operation which is done to activate the fluxes deposited beforehand on the circuit and to preheat the circuits or components before their arrival in the hot soldering zone.
In the case of the second type of method, called reflow soldering, which moreover combines several techniques under this name, it is not a bath of liquid solder that is used but a solder paste containing the solder alloy, in which paste formulation the chemical flux is included, which paste is deposited on the substrate and to which paste a certain amount of heat allowing the metal alloy to melt is supplied; usually, this heat transfer is carried out in a continuous oven.
It is becoming increasingly commonplace for industrial gas users (electronics, heat treatment, food, etc.) to be required to analyze one or more components of the atmosphere that they employ at a given user station, so as to be in a position to carry out a complete quality control of the parts treated, complete quality control assuming, in particular, that it is possible to know under which atmosphere conditions each part has been treated.
Depending on the intended application, safety conditions (risks of explosion) also apply.
Gas consumers therefore usually want to be able to know these atmosphere conditions, or indeed to display them, to archive them, to have traceability and even to process these values thus archived.
It is therefore considered necessary to be able to be in a position to offer industrial gas consumers analytical methods and equipment allowing gas samples to be taken at the various analysis points monitored in the enclosure used for the treatment, making it possible to minimize the response time of the analyzer or analyzers in question and to ensure that the analytical bay is provided with gas samples which are representative of the atmosphere in the enclosure.
By way of illustration, reference may be made to the following documents in the name of the Applicant, which also relate to this field of atmosphere analysis or of atmosphere regulation in soldering or tinning enclosures: FR 98-07498 or EP-A839,599.
The work that Applicant has conducted in this field has raised questions about the reliability of the analytical systems currently present in such soldering or tinning plants, and especially the information in terms of residual oxygen content of the atmosphere in the enclosure for operations carried out under nitrogen.
These uncertainties raise serious doubts regarding the production quality from the soldering or tinning machines in question.
SUMMARY AND OBJECTS OF THE INVENTION
One of the objectives of the present invention is therefore to provide a solution to the above-mentioned technical problems, and therefore especially to improve the reliability of gas analysis systems operating on such processes for soldering or tinning by means of a metal alloy and in the presence of chemical fluxes.
The system according to the invention for analyzing the content of at least one element of the atmosphere in an enclosure for soldering or tinning by means of a metal alloy, comprises the following elements:
at least one sampling line for taking a gas sample from the enclosure;
at least on analyzer capable of analyzing the element;
at least one coalescence filter located on the sampling line upstream of the analyzer;
a means for allowing that portion of the sampling line which is located between the enclosure and the coalescence filter to be devoid of cold spots which could cause precipitation of solid or pasty compounds in the line portion;
a means for detecting any blockage in the sampling line between the enclosure and the analyzer.
Moreover, the system according to the invention optionally comprises one or more of the following characteristics:
several coalescence filters of different grades, placed in series on the sampling line upstream of the analyzer;
at least two coalescence filters placed in series, offering increasing retention performance along the gas sampling path;
the at least one coalescence filter is positioned in the immediate vicinity of the wall of the enclosure where the sampling line is connected;
the at least one coalescence filter is positioned near the wall of the enclosure where the sampling line is connected and the sampling line portion going from the wall to the coalescence filter has been thermally insulated;
the system includes a heater for the sampling line portion located between the enclosure and the coalescence filter, which is capable of heating this line portion to a temperature above the temperature below which precipitation phenomena in compounds (i.e., solid, semisolid, liquid or pasty compounds) may occur;
the system includes a pressure controller located downstream of the analyzer, on its gas removal line, and upstream of a pumping device;
the system includes a pressure controller or a flow meter located upstream of the analyzer;
the system includes a device for cooling the at least one coalescence filter, such as a fan.
One of the merits of the present invention is that it can demonstrate the lack of reliability of the current atmosphere analysis systems in such plants for soldering or tinning with a metal alloy, especially those concerned with analyzing the residual oxygen content in nitrogen-based soldering or tinning atmospheres. This lack of reliability is specially associated with the sampling methods in these analysis systems.
The Applicant has especially been able to demonstrate that the analytical results provide, for example, an extremely low residual oxygen content in the nitrogen-based atmosphere, leaving the operator to believe that his soldering process is perfectly inerted, but not reflecting the actual residual oxygen content conditions in his soldering enclosure.
In fact, it should be emphasized that the chemical soldering or tinning fluxes normally used in these operations are resin-based formulations, especially rosins, in which there is also, in particular, the presence of alcohol and of acid.
In this context, the following comments may therefore be made:
a) because of the presence of alcohol in the atmosphere analyzed, a measurement technology which uses a zirconium oxide probe proves difficult to employ since the high temperature of the measurement cell causes oxidation b
Gilbert Chevalier
Marc Leturmy
Burns Doane Swecker & Mathis L.L.P.
L'Air Liquide, Societe Anonyme pour l'Etude et l'
Wiggins David J.
Williams Hezron
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