Using optical correlation to measure leak rates in sealed packages.
An optical correlation technique has been shown to accurately measure leak conduction rates from 10(-1) to 10(-6) atm cc/sec. Using hybrid microcircuit packages with glass capillary leakers, dimensional changes were detected as the packages were exposed to a small increase in external pressure. The rate at which the package returns to its original dimensions is measured and used, along with the internal free volume, to compute the leak rate. Because of its several advantages, the technique has the potential to become a useful nondestructive quality-control technique.
Optical system for fast inspection of hermetic seals in electronic packages
Microelectronic devices and components require hermetic packaging for mechanical protection and thermal dissipation. A hermetic packaging also prevents the intrusion of atmospheric contaminants such as moisture and airborne particles, thereby mitigating their attack on the enclosed delicate electronic components. Imperfect hermetic sealing, however, allows moisture and other impurities to migrate into the package and cause microcircuit malfunctions. This malfunction is often experienced in automobiles where the microchips and microelectronic devices are exposed to hostile environments. To date, testing of hermetic seals of microelectronic packages is achieved primarily through fluorocarbon fluid, helium and even radioisotope leak detection, which are cumbersome and risky in operation, therefore unemployable on production lines. In this paper, a laser based optical system is presented for rapid evaluation of hermetic seals. The proposed system is composed of a partial vacuum chamber and a shearographic camera. During testing, the electronic packages are placed inside the chamber and the shearographic camera is used to monitor the packages through a transparent glass window. The package under test is then stressed by an air pressure change. With the pressure change maintained, the lid of a perfectly sealed package will remain deformed while a leaky package will not hold the deformation and recover gradually, which can be monitored by shearography. Hence, by measuring the deformation of the packages' surface as a function of time, package leaks and the extent of leakage can be revealed in seconds. This leak testing is fast and practical and can be extended for testing of pharmaceutical packages, food packages, etc.
PULSE: a high-repetition-rate linac driver for x-ray FELs
We describe a staged concept for a linac-based freeelectron laser providing coherent tuneable VUV and soft X-ray output with pulse lengths down to 10 fs or less. Use of 1.3 GHz cryomodules operated with CW RF will allow flexible pulse patterns at potentially very high repetition rates up to 1 MHz. We consider the options for FELs that may be included in a facility of this type.