ALIGNMENT AND TEST FIXTURE APPARATUS
This invention relates to test apparatus and, more particularly, to apparatus useful for aligning and testing circuit boards.
Presently there exist many techniques for testing electrical apparatus fabricated in mass production quantities. Such apparatus may include radio and television receivers which utilize signal processing sections operating at relatively high frequencies. An example of such a section is the radio frequency amplifier of the radio and television receiver. The above-noted receiving apparatus is usually fabricated to include a plurality of printed circuit boards or other types of component boards, each individual one of which may be associated with a different receiver signal processing function. Such boards are usually prefabricated on an assembly line prior to insertion into the receiver. For example, the entire radio frequency amplifier for an FM receiver may be fabricated on a single circuit board and prewired by means of a common assembly or production line technique. The circuit board, when completed, is capable of performing RF amplification if suitable operating potentials and input signals are applied thereto. At this stage of the fabrication process, it is desirable to test the circuit board before insertion of the same into the final receiving apparatus.
Accordingly, as indicated, the prior art is replete with many different types of test fixtures which serve to apply signal and operating potentials to such a circuit board assembly. Various measurements are made to determine whether or not the circuit board will adequately respond when placed in its final environment. Such fixtures also enable the operator to adjust coils and capacitors to assure that the respective tuned circuits and other adjustable components are preset at desired values. This then assures proper operation in the final receiving apparatus.
Certain prior art testing fixtures had a plurality of probe or contact points located on a surface of the fixture, which probes would make contact with a certain number of predetermined test points located on the circuit board. The fixture probes would be aligned with the test points when the circuit board was placed in the fixture. The probes would then be activated either with operating potential or signal and measurements taken at various probe positions to determine proper operation. Many such probes were coupled to spring mechanisms to assure that the probe would, in fact, make electrical contact with the test point. In such arrangements, all the necessary probes contacted the plurality of test points simultaneously. In such arrangements, still another factor is that each probe had to contact an appropriate test point on the board with a sufficient amount of contact pressure to assure a good electrical connection. Hence, if a large number of test points were necessary, large contact pressures would flex and bend the boards. In some cases the contact pressures were large enough to prevent board insertion.
Due to the relatively high frequency of operation of certain circuit boards, as for example an RF amplifier board, this simultaneous contact arrangement resulted in placing stray capacitance and inductance on the various points associated with the circuit board. This undesirably affected the correct operating frequency of the various circuitry mounted on the board. The ad
verse effects caused by the external stray reactance introduced by prior art fixtures were precompensated for. The manufacturer would first test a completely operational board by conventional manual means. This
5 board was tested at the requisite operating voltages and signal frequencies and aligned until it was assured that satisfactory operation of the board would be achieved in the final receiver. The board was then placed in a test fixture and, due to the prior art probes and contact
*° arrangements, was undesirably affected by the abovementioned stray reactances. The manufacturer then obtained a second set of readings, which would be different than those desired, due to the inherent loading of
15 the board by the stray reactances. This set of readings would then be utilized to align other boards originating from the assembly line. These other boards would therefore provide incorrect readings when compared to those readings that were obtained under normal opera
20 tion. These incorrect readings took into account the adverse loading effects of the test fixture. In many instances, because of the loading produced and due to the operating frequency of certain of these printed circuit boards, the test procedure was not adequate to
25 determine proper operation of the board in the receiver environment. Therefore, even though many of these printed circuit boards would perform well in the test fixture, they would still require additional trimming in the final receiver assembly.
30 An apparatus for performing circuit board testing embodying the present invention includes a fixture or a base member having a top surface including a predetermined area thereon which is relatively congruent with the circuit board to be tested. Included within the area
are a plurality of holes positioned at predetermined locations, each hole being specified with respect to a particular one of a number of test points associated with said electrical circuit board. Mounted in each hole is a 40 pneumatic cylinder, each of which includes a piston member slideably mounted within said cylinder housing. Coupled to each cylinder is a selectively activated valve which is adapted for coupling to a pneumatic source when activated, and when activated serves to 45 move the piston through the hole in the base member to contact a test point of a circuit board positioned within said predetermined area.
These and other objects of the present invention will become clearer if reference is made to the following 50 specification when read in conjunction with the accompanying figures, in which:
FIG. 1 is a top plan view of a test fixture according to this invention; FIG. 2 is a schematic diagram of the cylinder ar55 rangement shown in FIG. 1;
FIG. 3 is a side cross-sectional view taken through a typical pneumatic cylinder assembly;
FIG. 4 is a cross-sectional view of a typical valve utilized in such apparatus;
FIG. 5 is a top plan view of a test fixture with a circuit board inserted therein;
FIG. 6 is a partial plan view of a cam operated sequencer suitable to activate the cylinder arrange65 ments shown herein.
Referring to FIG. 1, there is shown an electrical test fixture 10 which may be fabricated from an insulating material such as bakelite and is generally of a hollow