The present invention relates to equipment for the testing of printed circuit boards (PCB's) for electronic circuits.
More specifically, the invention pertains to printed circuit test equipment of the type having spring loaded contact fingers distributed on a contact-bearing plate and having a contact selecting plate which, according to the type of circuit to be tested, lets predetermined ones of the contact fingers protrude, whereby the contact fingers can be set to the particular printed circuit board.
Various types of equipment for testing printed circuit boards by establishing an electric contact between certain contact lands and contact fingers which can be connected with test equipment are known from DE-AS 26 57 910, DE-AS 22 43 457, DE-OS 33 11 977, CH-PS 633 403. In these types of equipment, contact-bearing plates are used which, due to their permanent arrangement of the contact fingers, cannot be used except for a single type of printed circuit board, or as in DE-AS 22 43 457 require expensive adaptations for other types of printed circuit boards. The expense for the production of test-specific substitution parts for the adaptation of the equipment is relatively high. This is a prticular disadvantage if a small number of printed circuit boards are to be produced and tested.
A further disadvantage of the above-mentioned conventional equipment is that separate wiring is necessary for each of the contact fingers, which are arranged on the contact-bearing plate according to the requirements of the type of PCB to be tested, with the test equipment or an adapter which connects the test equipment with the PCB. Even utilizing the so-called wire-wrap-technique, such wiring is expensive. Furthermore, large numbers of substitution sets are required for a certain type of printed circuit boards and such sets may in some instances have to be stored for decades for various applications.
Recently equipment of the above-mentioned type has become known, in which the contact fingers are arranged on the contact bearing plate in a pre-determined distribution, i.e. in a regular matrix arrangement with a standardized distance (module). The selection of the contact fingers necessary for the testing of a specific type of printed circuit board is effected via a contact selecting plate which is equipped with fixed selecting fingers. These selecting fingers are also arranged according to the basic matrix, but only at the locations of those contact fingers which are necessary for the respective test. In the assembled state of contact bearing plate and contact selecting plate, the contact fingers necessary for the testing are released from a rest position to contact with a printed circuit board to which the arrangement is set by producing underpressure. The contacting of the contact fingers used for the testing of the printed circuit board with the test equipment or the interface respectively, etc., in these conventional arrangements is effected by the wiring of the respective selecting fingers, which again results in the disadvantages already mentioned.
Thus, the number of substitution parts of the equipment necessary for each kind of printed circuit boards to be tested is reduced, and moreover, the substitution parts are less complicated as well. In addition to the above-mentioned disadvantage of wiring necessity the problems concerning storage of the substitution parts are also similar to those of other equipment already mentioned, because the contact-selecting plate with the selecting fingers--in order to prevent damage--either has to be packed accordingly or stored at a proper distance to the other substitution parts.
A further disadvantage is that the protruding contact fingers at the contact selecting plate make it much more difficult to adapt the equipment automatically for the testing of another type of printed circuit boards or in practice even make it impossible to adapt the equipment accordingly, thus requiring expensive manual adaptation.