Measuring and testing – Vibration – Loose object detection
Patent
1990-01-31
1992-02-25
Chapman, John E.
Measuring and testing
Vibration
Loose object detection
73663, G01H 100, G01M 702
Patent
active
050902440
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a system for detecting free particles in a component housing and to its detection method.
2. Discussion of the Background
The principle of searching for particles in the housings of individual electronic components is known in the art. It is put into practice, at the present time, by the piezo-acoustic detection of the impacts which these particles generate on the walls of the housing when the component is subjected to a vibration of appropriate amplitude and frequency Appliances which generate a sequence of shocks (to free possibly "wedged" particles) and which provide standardized detection periods have been on the market for several years. Particles of a mass of 10.sup.-6 gram can be detected by this method.
This method is, above all, a means for improving the production processes for components; but it is also the last stage in combatting pollution which may be dangerous for the proper functioning of the component and which is generated or trapped during the closing of its housing.
This test is often required for components to be used in space. However, it is carried out before the components are assembled on printed-circuit boards.
When the components are mounted on printed-circuit cards, it becomes difficult to conduct such a test because of the risks of damage to the card during this handling.
The identification of components polluted by particles and assembled on a fully equipped printed card becomes expedient from the moment before one of these components has been involved in a failure process.
It becomes necessary when:
this pollution is found to be of metallic origin,
there is sufficient probability of the presence of an identical source of pollution in the rest of the batch of components,
the function performed in the equipment necessitates exceptional reliability,
the time and financial resources for producing one or more new cards are not available.
The test of components already assembled on printed-circuit cards is made difficult because:
the equipped cards are of different formats,
the cards are difficult to hold mechanically,
the components involved are in metal housings of the type TO99 (8.2 mm in diameter and 4 mm high), and access to some of them is difficult,
the cards are lacquered on both sides,
no mechanical, physical or chemical deterioration of the cards is acceptable,
the detection of the polluted components must
it must be easy for the system as a whole to be used within an industrial context.
SUMMARY OF THE INVENTION
The subject of the invention is a system allowing such a test and avoiding any risk of physical, mechanical or chemical deterioration of the card and its components.
The invention therefore relates to a system for detecting free particles in one or more component housings which are assembled on a printed-circuit card, comprising:
a vibrating stage;
vacuum-generating means fixed to the vibrating stage, carrying the printed-circuit card on one of its faces and holding this card in position as a result of the generated vacuum;
at least one piezo-acoustic detector which can be coupled acoustically to one or more components.
The invention also relates to a method for detecting free particles in one or more components assembled on a printed-circuit card, involving the following steps:
holding the printed-circuit card on a vibrating stage by the generation of a vacuum between the card and the vibrating stage;
measuring possible sound impacts on the walls of each component by the acoustic coupling of at least one piezo-acoustic detector to one or more components.
BRIEF DESCRIPTION OF THE DRAWINGS
The various subjects and characteristics of the invention will emerge more clearly from the following description given as an example with reference to the accompanying figures wherein:
FIG. 1 shows a simplified exemplary embodiment of the detection system of the invention;
FIG. 2 shows a detailed exemplary embodiment of the system according to the invention for the pneumatic fastening of a card
REFERENCES:
patent: 3534589 (1970-10-01), Gibbons et al.
patent: 3916677 (1975-11-01), Isley et al.
Gruau Jean
Lecrivain Albert
Potier Daniel
"Thomson-CSF"
Chapman John E.
Le Centre National d'Etudes Spatiales
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