Noncontact Testing
The concurrent reduction of printed wiring board (PWB) features and utilization
of many embedded signal layers is rendering the application of mechanical
(pin contact) electrical testers obsolete. Fragile interconnections on
high input/output (I/O) boards now require the application of nondestructive,
nonloading technologies for electrical testing of PWB's. Laser-based non-contact
testing (NCT) can potentially access these fine structures via a photoionization
plasma, which is used to complete the required electrical signal pathways.
Other testing technologies, however, possess characteristics that are important
to an optimal test system. Mechanical probing provides a long access time
in which measurements can be made on the PWB. The small spatial resolution
possible with e-beam technologies is also very desirable. An accurate visual-mode,
computer-controlled positioning system would also assist the tester. Signal
injection would allow the user to overdrive a circuit or to analyze a single
path on a large board. These characteristics were all considered in the
design of an optimal NCT workstation.
The NCT method has been shown to provide a nonloading, nondestructive electrical
pathway, which could potentially enable very high speed (>1GHz) dynamic
electrical measurements. In addition, the NCT system is an excellent complement
to the expensive hardware (i.e. digital testers, oscilloscopes, computers)
that is already in use on the manufacturing floor.
The noncontact test process is being developed under contract
from the Department of Defense for use at
Tobyhanna Army Depot to test SINCGARS.
These are pictures of the Noncontact Test Workstation.
This is a picture of
the other Noncontact Test Bench. Here we are developing a fiber optic delivery
system. This is quite tricky for the Nd:YAG laser produces a pulse in the
fiber with a peak power density in excess of
1 Gigawatt per square centimeter!
The graduate students involved in the development of
Noncontact Testing:
Karl R.
Umstadter, Ph.D.
Engineering Physics
At this point you can view some images of laser-induced
plasmas, essential to noncontact testing, or you can go
to RPInfo.
