ANALYTICAL APPROACH nantly molecular ion at 62 amu. This observation is evidence of a stable resonance intermediate state that does not dissociate in competition with ionization. Despite the inefficient two-photon absorption, the final ionizing photon was very efficient. Performance
Polymeric Materials for Electronics Packaging and Interconnection
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hile there has been a number of books addressing packaging, and to some extent polymers, virtually none has emphasized the synthetic and physical chemistry of these systems. This new volume fills that gap, addressing the many aspects relating to the development of novel polymeric materials and processes. The emphasis is on chemistry and materials science, rather than circuitry, its electrical capabilities, or its design characteristics. Covering a broad spectrum of subjects, this 38-chapter book focuses on four general areas: • physical chemistry of materials • properties and applications of encapsulants • properties and applications of gels • printed circuit board substrates and materials for circuit board substrates.
A major objective of our work was to quantitate the sensitivity, selectivity, and response time for the detection of chemical warfare agent-type molecules. Our working definition of sensitivity is the concentration of a target molecule that gives a detectable signal. A detectable signal, in this case, is one that exceeds the fluctuation of the background signal. The detectable concentration C0 is determined by recording the signal strength, Sref, for a calibrated reference sample concentration, Cref, and comparing it to the background fluctuation level S0 (the detection limit is Co = CrefSo/Sref). A model was also developed to relate the experimentally measured detection levels and response time. Basically, there is the usual trade-off in which sensitivity improves the longer one collects signals. We define re as the response time required for the signal to grow to within 1/e of its final value and TO as the response time required for the detected signal to exceed the back-
ground fluctuation level So. We consider T 0 to be the response time for detection and Te the response time for the measurement of concentration. In addition, T 0 can be considerably smaller than Te for target molecule concentrations well above the detection limit (6). The response of our detection system to a 60-ppb sample of dimethyl sulfide in water-saturated air (i.e., 100% relative humidity, 17,000 ppm) is presented in Figure 5. An enlargement of the baseline region and a sensitivity scale are included. The ratio of the reference sample signal to background signal, (Sref/So), is > 200, corresponding to a detection limit for dimethyl sulfide of < 300 parts per trillion (ppt). The measurement response time Te is 8 s; however, the detection response time T 0 at 60 ppb is much less than a second. Finally, by varying the time for collecting the ion signal and averaging the signals over the background fluctuation, a trade-off between T 6 and Co can be made to enhance one parameter at the expense of the other. Summary
Molecular beam MPI is a powerful research tool that has contributed enormously to our fundamental understanding of the spectroscopy and dynamics of excited-state molecules. It is only natural that the benefits of high
Also included is a review of the marketing trends which drive packaging technology. This unique volume will be helpful to scientists engaged in materials development for electronic packaging, electronic packaging engineers, and to technologists who monitor developments in the electronics industry and related fields. John H. Lupinski, Editor, General Electric Company Robert S. Moore, Editor, Eastman Kodak Company Developed from a symposium sponsored by the Division of Polymeric Materials: Science and Engineering and of Polymer Chemistry of the American Chemical Society ACS Symposium Series No. 407 512 pages (1989) Clothbound ISBN 0-8412-1679-9 0 • R • D • E • R
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Figure 5. Sensitivity determination for a 60-ppb sample of dimethyl sulfide in watersaturated air.
508 A • ANALYTICAL CHEMISTRY, VOL. 62, NO. 8, APRIL 15, 1990
