Fixture wiring is a critical work in the manufacturing process.
The typical number of electrical joints in a fixture varies between few wires in a Function Test Fixture up to a few thousand in an ICT Fixture. Most of the wiring work in the fixture is done using the wire wrap technique. The Wire Wrap technique makes strong and reliable joints quickly and it is easy to use in plates densely packed with test probes.
T-9 Photo of a Genrad full bank with the top side open and showing the wiring
Wire wrap technique uses pneumatic, electrical or hand-operated tools. All of them use the same principle of wrapping the wire around the pin by a rotation movement. As the wire is wrapped, the corners of the pin penetrate the surface of the wire producing a reliable electrical contact.
T-10 Photo showing Probes wired
A solid, round wire usually between 0,25 mm (AWG30) to 1 mm (AWG18) is used for wire wrapping. Due to the tension raised during the wrapping process, the wire must have a good elongation before reaching the breaking point. They should also have plastic insulation elastic enough to support stretching out and of a material that can be easily piled out and torn off with knives blades.
T-11 Photo showing an Agilent test fixture being wired
A good wire wrap wiring has the following attributes:
5 or 6 tightly spaced turns around the pin. Wire turn on top of each other or wide-spaced is a sign of wrong wrapping technique. By overturning too much back force have been applied to the wrapping tool; by spiraled turns, the wrapping tool has been pulled out to fast.
T-12 Close-up photo showing wired probes
1 1/2 to 2-1/2 turns of insulated wire wrapped around the post. Insulated wire wrapped around the terminal greatly increases the ability to withstand vibration.
T-13 Close-up photo showing a double wired probe
No bare wire extending away from the post (pigtail). Pigtails occur when the last turn of the wire is not completely wrapped around the terminal. This is a sign of using a wrong size wrapping bit or ware out or broken wrapping bit.
T-14 Photo showing an Agilent probe plate with wired probes
Wires with different colors are used to “visually” separate probes groups such as the wires of the single board in a multi-board panel or electrical signals such a power and GND signals. Using wire with different colors helps to identify probes or signal during a fixture check and the test program debug process.
T-15 Photo showing a long wire interface with groups of cable with different colors
Well distributed and pull relief wiring layout. Wires must me bundle, guided and fixed in a tidy manner. Wires must be long and pull relief fixed to avoid stress on the wired terminals
T-16 Photo showing a fixture bundle, guided and fixed wiring
We wire our fixture with semiautomatic machines that assist the operator during the wiring process. Wiring machines are automatic XY positioning tables that, in a sequential movement, position the wire wrap tool precisely in front of the two terminals to be connected, leaving the operator only with the task of wiring the terminals. In our Fixture Wiring Process, the fixture wiring Information or Wire Files are read with dedicated software and loaded into the PC that controls the automatic XY positioning table. In a sequential process, the PC runs the automatic XY positioning table to each terminal that needs to be wired.
T-17 Close up Video showing a Keysigh fixture being wired
We have developed and incorporated a special tool into our Fixture Wiring Process the allows us to use the Wiring Machines to wire fixtures for any commercial or custom made test system. By recreating the test system interface layout and developing the corresponding translation table we generate consistent and accurate Wire Files for any interface and wiring sequence including daisy-chain wiring.