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I have a HW design with me. Now I need to test it with ICT. But huge cost is associated with ICT and I also assume some changes in my HW Design which will impact the ICT Fixture change. I am confused shall I do ICT setup now or Later on once I have finalized my HW Design?
I also want to know that what kind of changes will not impact the Fixture change for ICT?
Typical ICT uses a 'bed of nails' to make connection. This is an array of spring probes that contact the PCB, usually by pulling the board down on to them with a vaccuum pump although 'flying probe' systems are available. Behind the probes is a multiplexer which routes voltages and test instruments to the desired combination of probes to make two or four wire measurements and sometimes to apply 'guard' potentials to isolate unwanted current paths.
The ICT 'fixture' (the bed of nails) has to be designed so the probes are located where the connections points to the circuit are located on the PCB. For through-hole components the coordinates can be extracted from the PCB drill file but probing the pins of surface mounted devices is a bad idea because the probe pressure could push the pin against the track below it and hide a dry-joint fault. For SMD, small pads joined to the test nodes is a better method but this has to be incorporated at the PCB design stage.
You really have to design with ICT in mind from the start, if you don't, the testability will be limited or impossible.
Brian.
(trained in Fairchild, Genrad and HP ICT systems!)
I reside on the other side of testing in that I design functional test fixtures. Depending on your design, it may be more cost effective to create a functional test rather then an in-circuit. There are trade-offs between both test methods. It's up to you to decide which will meet your needs; effectiveness, cost, versatility, etc.
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