Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
phoebe
POSITIONING UNIT FOR TESTING PRINTED CIRCUIT BOARDS,
PARTICULARLY CERAMIC PRINTED CIRCUIT BOARDS
Background of the Invention
The present invention relates to a unit for positioning printed
circuit boards relative to a printed circuit board testing
apparatus.
The practice of electronically testing industrially fabricated
5 printed circuit boards has gained wide acceptance. Thus, the
quality of the boards may be judged prior to further processing
- such as the installation of comparatively expensive
electronic components on the boards. If a printed circuit
board has one thousand contacts, about 500,000 individual tests
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10 must be yo-yo on two-point connections to ensure that the
board has been reliably tested. It has been found that the
overall testing cannot be performed economically and in a
justifiable time period unless it is done electronically by
15 means of a computer.
computer-controlled printed circuit board testing apparatus
of this kind is programmed by placing a faultless master
circuit board in a mount provided to receive the printed
circuit boards. Then all possible combinations of two-point
connections are automatically tested and the computer memorizes
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the results of each possible connection on the master circuit
board. Thereafter, production circuit boards are fed into such
apparatus for testing. In the testing process, each individual
two-point connection is compared with the memorized
information, and in the absence of identity between the
measured information, and in the absence of identity between
the measured information and the information memorized, an
error output is generated and, if desired, the defective
circuit board is automatically ejected.
10 Each test point on the printed circuit board requires a test
contact. The test contacts of the testing are
generally arranged in a regular array while the test points on
the printed circuit board are quite irregularly arranged.
To accommodate this, the regular grid pattern of testing
15 contacts provided on the printed circuit board testing
apparatus is modified by a so-called customizable adaptor which
has contact pins arranged in a specific pattern corresponding
to the pattern of the connection points on the circuit board to
be tested. In other words: each contact on the printed
circuit board is connected by one contact pin in the
customizable adaptor with a selected contact in the regular
grid of connection points of the printed circuit board testing
apparatus.
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A suitable customizable adaptor is disclosed in German
Laid-Open Application DEMOS 29 33 862 (laid open March 12, 1981).
To precisely and repeatahly position the printed circuit board
to be tested on the adaptor, a plurality of locating pins is
provided to engage complementary locating openings in the printed
circuit board. Having been properly positioned relative to
the contact pins of the customizable adaptor, the printed circuit
board is then pressed on the aforesaid contact pins by suitable
pressure means so that the computer-controlled printed circuit
board testing apparatus may execute its testing routine.
Of course, suitable automatic means may be provided for
feeding and placing the printed circuit boards in the test
position so that the testing process may take its course without
human intervention.
Conventional printed circuit boards usually have a
minimum contact spacing of 2.54 mm (0.10 inch). Normally, each
contact has a drilled hole associated therewith which extends
through the circuit board and which is designed to receive the
lead of an electronic component to be connected by soldering
to the contact. To obtain higher contact densities, ceramic
printed circuit boards have been used increasingly in recent
years: on
it
these ceramic printed circuit boards, the contact spacing or
pitch is as little as 1.27 mm (0.05 inch). Also, the contacts
themselves are not provided with drilled holes, but rather, are
merely small conducting areas or pads on the surface of the
5 ceramic substrate to which the leads of components are
soldered. Since such printed circuit boards are not provided
with drilled component lead holes, they are also usually not
provided with drilled positioning holes. Testing of such
ceramic printed circuit boards in an assembly-line fashion may
10 cause difficulties because such printed circuit boards lack
positioning holes. Also, it is not generally feasible to
visually inspect the circuit board surface to be contacted with
the customizable adaptor because it has to be pressed onto the
contact pins of the customizable adaptor which tends to conceal
15 the test points from view.
It is an object of the invention to provide an apparatus which
enables the ceramic printed circuit boards under test to be
aligned rapidly and precisely on a specific customized adaptor
even if they have no positioning holes therein. It is a
20 further object of the invention to provide a method for setting
up the positioning unit.
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Brief Description of the Invention
The invention provides an assembly for locating printed
circuit boards to be tested in a printed circuit board testing
apparatus such that connection points of the printed circuit boards
are aligned with an array of test contacts of the testing apparatus,
said assembly comprising: a support unit having opposite first
and second surfaces including respective means for holding respect
live printed circuit boards to be tested means mounting said
support unit for rectilinear movement toward and away from the
testing apparatus between a testing position and a spaced position,
and for, when said support unit is in said spaced position, rotary
movement about an axis extending transverse to the direction of
said rectilinear movement, and thereby directing a selected one of
said first or second surfaces and the respective printed circuit
board held thereon toward the testing apparatus, thereafter said
support unit is moved to said testing position, and directing the
other of said first or second surfaces away from the testing
apparatus, whereat a previously tested printed circuit board may
be removed from said other surface and a new printed circuit board
to be tested may be positioned thereon; and positioning means for
aligning the new printed circuit board -to be tested in a precise
positional relationship on said other surface to enable alignment
thereof with the array of test contacts of the testing apparatus
upon subsequent rotary movement of said support unit about said
axis to direct said other surface and the new printed circuit board
to be tested toward the testing apparatus, said positioning means
~1.2~Çi7~3
comprising at least one light marker projector for projecting a
light mark toward and aligning with an alignment mark on the new
printed circuit board to be tested.
The invention also provides a method of testing printed
circuit boards in a printed circuit board testing apparatus while
locating said printed circuit boards such that connection points
of said printed circuit boards are aligned with an array of test
contacts of the testing apparatus, said method comprising the
steps of: providing a support unit having opposite first and
second surfaces including respective means for holding respective
printed circuit boards to be tested; rotating said support unit
about an axis extending parallel]. to the plane of said array of test
contacts of said testing apparatus to thereby direct said first
surface away from said testing apparatus; positioning a first
printed circuit board to be tested on said first surface to be held
by said respective holding means thereof while projecting a light
mark from at least one light marker projector toward said first
printed circuit board and aligning an alignment mark on said first
printed circuit board with said projected light mark, thereby
positioning said first printed circuit board in precise predator-
mined positional relationship on said first surface as. a function
of the position of said array of test contacts; rotating said
support unit about said axis to thereby direct said first surface
and said first printed circuit board toward said testing apparatus
and to direct said second surface away from said testing apparatus;
moving said support unit in a rectilinear direction transverse to
- pa -
fix
said axis toward said testing apparatus until connection points of
said first printed circuit board to be tested contact said array
of test contacts, and then testing said first printed circuit
board; during said testing, removing a previously tested printed
circuit board from said second surface, and repeating said post-
toning and aligning steps to thereby position a second printed
circuit board to be tested on said second surface in a precise pro-
determined positional relationship as a function of the position
of said array of test contacts; after said testing, moving said
support unit in a rectilinear direction transverse to said axis
away from said testing apparatus; and sequentially repeating the
above recited steps.
Brief Description of the Drawings
To facilitate a better understanding of the invention,
an exemplary embodiment thereof will now be described below and
reference will be made to the attached drawings, wherein:
Figure 1 is a schematic view of a positioning unit
including the two light marker projectors, and
- 5b -
Figure 2 ~ff9 a side view of the apparatus depicted in Figure
1.
Detailed Description of a Preferred Embodiment
A support unit 4 is rotatable mounted above a customizable
adaptor 30 on a horizontal shaft 2 and for movement in a
vertical direction. The phantom lines depict support unit 4 in
a raised position while the solid lines depict support unit 4
in a lowered position. Support unit 4 has two opposite
surfaces 6 and 8, each adapted to receive a (ceramic) printed
circuit board 10, which can be retained thereon by pneumatic
or other means.
Since ceramic printed circuit boards typically have no holes
therein, they can be easily retained in place by applying a
vacuum to their rear surfaces. Vacuum applying equipment is
15 well known and therefore it is not described here in detail
although it is schematically depicted at numeral 20 in Figure
2. Alternatively, mechanical or electromechanical devices may
be used to retain printed circuit boards 10 in place on
surfaces 6, 8, if desired.
The support unit 4 is mounted on a printed circuit board
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testing apparatus of which the contact array base grid plate is
indicated by the lowermost solid line 36 in the drawings. Placed
on this base grid plate 36 is customizable adaptor 30 which may
rest on a reducing adaptor 32 and an intermediate adaptor 34, as
illustrated in the embodiment shown in the drawings. The latter
two adaptors 32, 34 are preferably used to convert the relatively
wide-spaced basic grid contact array of a conventional printed
circuit board testing apparatus to a much denser base grid suited
for testing ceramic printed circuit boards.
lo The support unit 4 is mounted on a horizontal mounting
frame 14 which is coupled to the printed circuit board testing
apparatus (not shown) by vertically extending bolts 16. The mount-
in frame has thereon brackets 18 supporting horizontal shaft 2 of
the pressure unit. The horizontal shaft supports the support unit
4, which may be of rectangular boxlike shape, for vertical movement
luff
and 180 degree pivot able movement en the aforesaid shaft above the
customizable adaptor 30. The pivoting and
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vertical movements of support unit 4 towards the customizable
adaptor 30 are provided in order to alternatingly urge the
ceramic printed circuit boards lo attachable to and fixable on
opposite surfaces 6, 8 of the pressure block against the
5 customizable adaptor 30 so as to create the necessary contact
pressure. jig. l shows support unit 4 in its uppermost
position in phantom lines; in that position, it may be pivoted
on horizontal shaft 2 and the previously tested circuit board
lo may be replaced by a circuit board yet to be tested.
10 Support unit 4 is shown in solid lines in its lowermost
position in which the ceramic printed circuit board is pressed
on the customizable adaptor 30. This position also allows for
a replacement of the previously tested circuit board by a fresh
untested circuit board.
15 Hydraulic or pneumatic mechanisms (not shown) inside support
unit 4 provide the aforesaid vertical reciprocating movement
and the required pressures. The mechanism used for rotating or
pivoting the support unit 4 by 180 degrees in each operating
cycle is not shown in detail, either, as such mechanisms are
20 well known in the art.
The ceramic circuit board lo is held in a stationary position
on the opposite surfaces of the pressure block by pneumatic
means 20. In other words, as indicated schematically in Figure
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2, these two support surfaces are constructed in the form of
vacuum plates 20, which are well known in the art. By properly
timed application of vacuum to suitable openings in suction
plate 20, the ceramic printed circuit board 10 may readily be
5 retained in position on the suction plate 20.
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-4~Yb~ light marker projectors 12 are mounted by a frame or
uprights 22 above the pressure block. These light marker
projectors cooperate with two alignment marts on the surface of
the ceramic printed circuit board 10 for optically adjusting
10 the position of the latter on the upwardly facing suction plate
20.
In operation, a ceramic printed circuit board to be tested 10
is placed on surface 6 with the side having the contacts
thereon turned upwards facing the operator. As will be seen,
the board is provided with preferably two alignment marks
which the operator will adjust to two corresponding light
markers projected by projection lamps 12 and which are
positioned during apparatus set-up. This way, the ceramic
printed circuit board 10 to be tested can be positioned in a
20 rapid and precise manner for subsequent pneumatic retention,
thereafter the support unit 4 is pivoted about its horizontal
axis and moved vertically downward, such movement being
preferably effected by suitable hydraulic elements provided in
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the interior of the support unit 4, causing the precisely
positioned ceramic printed circuit 10 to be pressed onto the
array of test contacts of the customizable adaptor 30 of the
test apparatus. The ceramic printed circuit board 10
5 previously examined and situated on the identical opposite
support surface 8 is exchanged by the operator for another
circuit board to be tested, the latter being positioned by the
operator with the aid of the alignment markers on the circuit
boards and the light markers imaged by the projector lamps 12.
10 Thereafter, support unit 4 will again be raised from the
customizable adaptor 30 and will be rotated 180 degrees on
horizontal shaft 2 so that the operator can now remove the
circuit board 10 just tested and replace it by yet another new
one, as explained above. The operating cycle described above
15 will then be repeated.
As mentioned before, during the set up of the testing apparatus
the light marker projectors 12 must be correctly positioned to
cast their light markers on the proper points on surfaces 6, 8.
To this end, a relatively thin and ductile sheet of plastic or
20 metallic material is held on one of receiving surfaces 6, 8 by
the vacuum apparatus 20 and pressed onto the customizable
adaptor 30, the contact pin positions of which have previously
been arranged to correspond precisely to the contact array
pattern on the ceramic printed circuit board 10 to be tested.
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This operation embosses the thin sheet of material with a
pattern corresponding to the arrangement of the contact pins.
The support unit 4 is thereafter rotated and the impressions
the contact pins leave in the thin sheet are utilized to adjust
5 the projectors 12 to project their light markers to convenient
positions on the thin sheet. Such positions may be generally
or specifically identified before the embossing operation. the
projectors 12 are then fixed in place and, if not already done,
the projected markers are marked as alignment marks on the thin
10 sheet using a Corey other convenient tool. The vacuum can
thence be released, the thin sheet removed from surface 6, 8
and, if not already made, it can be used to make masks which
are used during the manufacture of printed circuit boards loo
In either event, the proper relationship between the positions
15 of the test points and the alignment marks is carried over to
the mask. Thus, the manufactured printed circuit boards will
include alignment marks which need only be aligned with the
light markers projected by lamps 12 to ensure subsequent proper
alignment with the test pins of the testing apparatus.
20 Having described the invention in connection with specific
embodiments thereof, modification may now suggest itself to
those skilled in the art. Such modification can be made
without departing from the spirit and scope of the invention.
Accordingly, it is not intended that the invention be limited
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to the disclosed embodiment except as required by the appended
claims.
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