Generators info

A bed of nails tester is a traditional electronic test fixture comprised of numerous pins inserted into holes in an acrylic plate which are aligned to make contact with test points on a printed circuit board and are also connected to a measuring unit by wires.

Typically, four to six weeks are needed for the manufacture and programming of such a fixture. Fixture can either be vacuum or press-down. Vacuum fixtures give better signal reading versus the press-down type. The bed of nails or fixture as generally termed is used together with a in-circuit tester such as i3070, 3070 from Agilent (USA), Teradyne Spectrum Series and continuation of the old Genrad Teststation series under the Teradyne flag (USA), IFR 4200 series, was Marconi Test prior to acquisition by IFR (USA), TRI (Tiawan), Digitaltest(Germany), Okano (Japan), Checksum (USA).

The Checksum system is an entry level machine selling for approx. USD$10K and finding approximately 95-98% of manufacturing defects. The Teradyne system is a system designed for high end manufacture and military use, and sells for approx. USD$200K plus.

“During board layout, one of the primary concerns is that accurate tooling holes and appropriate test pad size and location are all critical to increasing the probability that the spring-loaded probes in a bed-of-nails test fixture will reliably make contact and transfer signals to and from the board under test.” Blackwell, The Electronic Packaging Handbook

This technique of testing PCB’s is being slowly superseded by Boundary Scan techniques (Silicon Test Nails) and Automatic Optical Inspection, due to shrinking product sizes and lack of space on PCB’s for test pads.

Example of In-Circuit Test Product