1. Field of the Invention
This invention relates to fixtures of the bed of nails type used to electrically connect a printed circuit board to be tested with an automatic test system.
2. Description of the Prior Art
As is well known, it is becoming a routine matter among manufacturers to test circuit boards which they intend to use in producing products such as televisions, electronic organs, and many, many others. These tests can be conducted with so-called "bare" boards and with "loaded" boards. A bare board is one not having components mounted thereon while a loaded board is one having these components in place.
In conducting such tests, it is, of course, necessary to have a device commonly called a "fixture" which serves to make an electrical connection between the nodal points in the circuit to be tested and the test system. A standard approach is to use a "bed of nails" fixture. This device derives its name from the fact that it is comprised of a great number of nail-like test probes having tips to make electrical contact with the nodal points of the circuit to be tested. These probes are individually connected through one or more interfacing devices to the test system.
It has been the practice for manufacturers to purchase one fixture for each type of board to be tested. This has been primarily due to the fact that fixtures have largely been custom-made. One would lay out the pattern of nodal points to be used in a test and an array of test probes would be provided in that pattern in one fixture. As the number of boards one must test grows, this becomes an expensive proposition. The expense is due primarily to the high number of probes involved. Test probes are typically spring-loaded and gold-plated and are manufactured to fairly close tolerances. It is not difficult to imagine, then, that a substantial investment is involved if a manufacturer, as is now the practice, is required to maintain an inventory of several fixtures, each containing many such probes.
It would, therefore, be advantageous to provide a universal fixture which could be used to test many different types of circuit boards. It can be expected that such a fixture would represent a relatively large initial investment because it would need to contain more probes than would ordinarily be required to test a single board. In the long run, however, this approach would prove to be a more economical one for manufacturers who are required to test many types of boards.