INSTRUMENTATION
Polymeric Materials for Electronics Packaging and Interconnection
W
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 re lating 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.
emission, 5t in Equation 2 could ap proach unity and δΒ could also be large as a result of the narrow bands. Upconversion would appear to be preferable to pump/probe measurements for Ra man spectroscopy, although it has not yet been used. For resonance Raman, the resonance enhancement would be approximately offset by the inefficien cy of upconversion, but fluorescence would be eliminated in the process. Effects of temporal dispersion. Emission spectroscopy is not the same game on ultrafast time scales as it is in nanosecond spectroscopy. If you are holding this paper 12 in. away, it takes 1 ns for the photons reflected from the paper to reach your eyes. The relation ship between time and distance is cru cial to ultrafast spectroscopy because the speed of light is comparatively slow on these time scales. An optical pulse is lengthened in time if any part of it trav els a different optical distance than the rest of the pulse. This effect is called temporal dispersion. Despite short la ser pulses and fast detection, the time resolution in an experiment can be de stroyed by temporal dispersion from the optical layout of the experiment. For any ultrafast emission method, temporal dispersion must be carefully diagnosed and eliminated. There are three causes of temporal dispersion. First, collecting light over a nonzero
solid angle with a lens or mirror results in a distribution of optical pathlengths (Figure 4a). Furthermore, passage through a thick lens can have a much greater effect than this distribution of pathlengths (Figure 4b). Either a larger /-number or reflective optics should be used; implementing both would give the best results. Second, for excitation over a finite pathlength, molecules on one end of the path are excited at a different time than those on the other end (Figure 4c). This is a severe problem in an emission experiment but is absent in a pump/ probe experiment. Finally, the refrac tive index of any material is wave length dependent. A short pulse has frequency components greater than a few hundred nanometers, and the red wavelengths move faster than the blue wavelengths through typical optical materials (Figure 4d). The result is called pulse chirping because of what this signal would sound like if these were audio frequencies. Figure 4 illus trates that the temporal profile of the ultrafast pulse is easily lengthened by passage through commonly used op tics. A careful study of temporal disper sion in an upconversion measurement was recently detailed (32). From this study, one can appreciate that the reso lution of 200 fs is a noteworthy accom-
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.
Also included is a review of the marketing trends which drive packaging technology. This unique volume will be helpful to scien tists engaged in materials development for electronic packaging, electronic packaging en gineers, and to technologists who monitor de velopments in the electronics industry and re lated fields. John H. Lupinski, Editor, General Electric Company Robert S. Moore, Editor, Eastman Kodak Company Developed from a symposium sponsored by the Divi sion 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 Ο · R · D · Ε · R
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Figure 4. Pulse dispersion. (a) Collection of light causes dispersion resulting from a distribution of pathlengths, (b) passage through a thick lens causes severe dispersion, (c) a long pathlength and perpendicular detection cause dispersion, and (d) passage through a material causes frequency chirp. Note that chirp would also be severe in part b but is neglected for clarity.
274 A · ANALYTICAL CHEMISTRY, VOL. 62, NO. 4, FEBRUARY 15, 1990
