Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
1997-12-22
2001-10-23
Brown, Glenn W. (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S761010
Reexamination Certificate
active
06307389
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a test device of the type having a probe movable over an electronic board assembly by a controllable drive for testing the electronic board assembly.
BACKGROUND OF THE INVENTION
Test devices of this kind are used for checking electronic board assemblies of the most diverse type. Board assemblies of this kind may, for example, be circuit boards, either with or without components, or, for example, highly integrated circuits, of which a plurality are disposed on a wafer, for IC manufacture. The probes may also be of the most diverse kind, for example electric contact points adapted to be connected via relay banks to stimulus sources or measuring amplifiers of a suitable electronic measuring device, or other probes used for other test methods, such as, for example, inductive or capacitive sensors or optical scanners, e.g. cameras or microscopes.
For the rapid testing of relatively large board assemblies, such as, for example, computer motherboards, a plurality of probes are usually provided, which can be positioned independently of one another. A plurality of probes are frequently also necessary so that when a plurality of electric junction points are to be contacted simultaneously it may be possible, for example, to apply a voltage to two junction points and tap off a voltage at a third junction point. Control of the probes is usually effected by means of sequence programs compiled individually for a specific board assembly.
Known test devices of this type are always so constructed that all the probes can be positioned over the total area of the maximum board assembly which can still be tested on the test device. In the conventional construction, the probes are disposed on slides which are adapted to move over the surface of the board assembly by means of spindles in the X-direction and the Y-direction. In the case of raisable and lowerable contact points, vertical drives operating in the Z-direction are provided on the slides.
In the known test devices, the slide guides and drives have to be movable over the entire length of the board assembly for testing, i.e. over considerable lengths which, in the case of a typical PC circuit board, amount to 30×40 cm for example. With these considerable traversing distances high spatial resolutions are required. For example, the individual contact pins of modern ICs must be controlled with a length resolution of much less than {fraction (1/10)} mm. Consequently, extremely stable and heavy mountings and drives are required for the slides, resulting in high moving masses.
A disadvantage of such test devices is the low speed of travel from one point to another, due to the high moving masses. High masses have to be continually accelerated and stopped. Decay times also have to be taken into account.
In modern production lines, for example for electronic equipment, board assemblies are, however, produced at a speed such that known test devices of the type according to the preamble are too slow. Consequently, only individual selected board assemblies can be tested, or else a plurality of test devices have to be used in parallel.
In contrast, test devices having a separate probe for each grid point of the board assembly, i.e. those operating with stationary probes and which do not have the above-mentioned speed problems, have advantages in terms of speed. These test devices, however, are disadvantageous in terms of circuitry and cost, and particularly in respect of the fixed arrangement of the items under test. They are therefore suitable only for a specific board assembly manufactured on a large scale, while the test devices with their movable probes, are suitable for rapid changeover to different board assemblies, i.e. for testing small-scale production runs.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a test device for testing electronic board assembles with a higher test speed.
With this construction, the advantage of the test devices of the type described above, i.e. to be able to test even larger board assemblies with just one probe or just a few movable probes, is retained. Compared with the known test devices in this area, the advantage lies in the fact that a probe can be driven by a probe drive over just a sub-area of the total board assembly area. The traversed distances are thus reduced and the moving masses can be reduced by several orders of magnitude with the same or better control accuracy. This results in a traversing speed which can be correspondingly increased by several orders of magnitude. For specific applications, e.g. a large board with just one IC, it is sufficient to provide the sub-area in the size of the IC. The other few test points of the board can be tested in some other way. If a plurality of probes are provided with corresponding sub-areas, the probe drives can, for example, be provided to be movable between different sub-areas of the board assembly or be provided in a plurality so as to be stationary covering the total area. With only a slightly increased mechanical outlay, the test speed is considerably increased as a result of reducing the driven masses, and this test speed is sufficient even for the most up-to-date production lines. This construction also gives the possibility of considerable further increase of the speed by increasing the number of probes and probe drives.
Electronic circuit boards which are already equipped with components, the most commonly encountered testing situation, are today predominantly equipped with ICs of standard size. If the sub-areas are adapted to the ICs, it is sufficient to position probe drives over all the ICs or move one or more probe drives from one IC to the next, in order to be able to approach all the test points to be covered.
Advantageously, for example, a plurality of probe drives can be disposed in one line and be moved by a main drive successively transversely to the direction of the line over a larger board. Probe drives can also be arranged to be stationary so as to cover the entire area of a board assembly for testing, and this may be of advantage particularly for smaller assemblies for testing. In the case of the latter construction, the test speeds which can be achieved are very high and hitherto unthinkable.
Probe drives can be provided on the slides of known test devices instead of the probes which were hitherto arranged to be stationary there, and be moved in relatively large steps by the main drives. Even if the main drives are very slow, as is usual in the prior art, this does not appreciably slow down the total testing time, since, with an optimised test sequence program, care can be taken to ensure that the main drive makes only a few steps while the far larger number of test steps is made by the very fast probe drives.
If the probe is disposed on a pivotable needle, it can also be moved beyond the base area of the probe drive. Probe drives can thus be disposed adjacent one another, with the probes able to operate so as to overlap in the boundary zone of two probe drives. In the present state of the art, pivoting drives can be constructed very easily and rapidly for the required control electronics. They offer the additional advantage of enabling difficultly accessible locations to be reached with an inclined needle, for example locations of the kind which are accessible only from the side but not directly from above.
The provision of two transverse drives as the probe drive is advantageously provided. With this construction, the pivoting of the needle can be achieved very easily with two linear drives. Test rigs have proved very rugged and extremely rapid.
Probes can, for example, operate optically, capacitively or without contact in some other manner, the distance from the surface location for testing on the board assembly being uncritical. In that case a vertical drive would not be required for the probe. However, at least in the case of electrically contacting probes constructed as a contact point a vertical drive is necessary to set down and raise the contact point
Buks Manfred
Krueger Jens
Schaller Peter
Brown Glenn W.
Farley Walter C.
Scorpion Technologies AG
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