Laser subtractive structuring

There are more process steps involved in laser subtractive structuring (LSS) than in the additive or semiadditive processes (Fig. 3.2). Injection molding is followed by short surface activation to permit electroless copper or nickel plating. This chemical premetallization is followed by a galvanic process to build up the plating to target thickness. The next step is structuring as such, by application of an activatable etch resist. 

The main laser-structuring techniques for MID are derivatives from the world of printed-circuit board engineering. For this reason the various techniques are commonly classified as additive, semiadditive, or subtractive. Laser direct structuring is an additive technique, and its most important manifestations are LPKF-LDS and ADDIMID. MIPTEC, a process developed by Panasonic, is one of the semiadditive techniques. Subtractive laser structuring techniques are commonly used on ceramic substrate materials. Figure 3.2 is an overview of the individual structuring techniques and the steps involved. 

Using time-resolved crystallographic experiments, molecular structure is eventually linked to kinetics in an elegant fashion. The experiments are of the pump-probe type. Preferentially, the reaction is initiated by an intense laser flash impinging on the crystal and the structure is probed a time delay. At, later by the x-ray pulse. Time-dependent data sets need to be measured at increasing time delays to probe the entire reaction. A time series of structure factor amplitudes, IF, , is obtained, where the measured amplitudes correspond to a vectorial sum of structure factors of all intermediate states, with time-dependent fractional occupancies of these states as coefficients in the summation. Difference electron densities are typically obtained from the time series of structure factor amplitudes using the difference Fourier approximation (Henderson and Moffatt 1971). Difference maps are correct representations of the electron density distribution. The linear relation to concentration of states is restored in these maps. To calculate difference maps, a data set is also collected in the dark as a reference. Structure factor amplitudes from the dark data set, IFqI, are subtracted from those of the time-dependent data sets, IF,I, to get difference structure factor amplitudes, AF,. Using phases from the known, precise reference model (i.e., the structure in the absence of the photoreaction, which may be determined from... 

Pump-probe patterns are obtained by exciting the molecule of interest to an excited state, and subtracting the diffraction pattern with the pump-laser off from a pattern with the pump-laser on. The ultrashort pulsed nature of the laser and the electron pulses allows us to probe structural dynamics by measuring the pump-probe diffraction patterns as a function of the delay time between the laser pulse and the electron pulse. 

Fig. 2 Experimental arrangement for time-resolved FSRS (femtosecond stimulated raman spectroscopy). The femtosecond actinic pump pulse excites the sample electronically. After a delay the femtosecond probe pulse and picosecond Raman pump pulse arrive together to interrogate the instantaneous molecular structure. The self-heterodyned signal is emitted in the probe direction, dispersed, and detected by a kHz readout CCD. Data collection is best performed by division of subsequent Raman pump-on by Raman pump-off laser shots (lower trace), however this has been performed by other groups as a subtraction of subsequent pulses (upper trace). Reproduced from ref 2 with permission from the PCCP Owner Societies (2012).

An examination of the above equations shows that the intermodulated DFM technique realizes an FM Differential Interferometer which produces a locking signal similar to conventional FM laser locking, but in which the optical tuning parameter A=(0Q-2tr n c/2L is replaced by the radio frequency (differential) tuning parameter 5=(0j-2tr c/2L. The DFM sideband structure creates an optical subtraction in the photodiode of the (n+l)-th cavity resonance curve from the (n-l)-th curve and thus permits accurate, low noise measurements of the cavity mode spacing. 

FIGURE 3.2 Process steps in additive, semiadditive, and subtractive laser structuring as in [48]... 

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