Defects contact printing

DUV contact printing offers a potential for delineating submicrometer features with high aspect ratio (Figure 3.19), but suffers from mechanical defects caused by the intimate contact between a mask and a resist film. In contrast. 

Unfortunately, contact printing was plagued by a number of practical and technical difficulties. Bringing the mask and the wafer into direct contact causes damage to the mask and creates defects, which are reproduced in subsequent exposures. In addition, nonflatness of the wafer and mask results in alignment... 

However, due to the defectivity problem associated with contact printing, as discussed above, the first noncontact aligners, called proximity aligners, were introduced in 1973 by Kasper Instruments. In proximity printing mode, the mask does not come into direct physical contact with the wafer [see Fig. 13.24(a)]. Rather, it is held 10-25 p.m above the upper surface of the resist-coated wafer. This gap, however, limited resolution on account of diffraction. The theoretical resolution limit of proximity printing is given by the expression... 

Contact or proximity printing is no longer widely used because of defects caused by mask/wafer contact. It is still used in non-critical situations when such defects can be tolerated, or when the resolution required is low enough to allow an adequate gap to be left between mask and wafer. 

The coarse texture of the fibrous gas diffusion media can further amplify the contact stress exerted on the MEA. Figure 3 shows the relative size of a carbon fiber with respect to the typical thickness of the electrode and the electrolyte membrane. It can be seen that the diameter of the carbon fiber in the gas diffusion media is comparable to the thickness of the electrode. The rigid carbon fiber pressed onto the porous electrode layer can produce in-prints which can later become a stress-concentration and defect-initiation sites at the electrode-electrolyte interface. A microporous layer, if used, tends to smooth out the surface of the GDM and reduces fiber inprint. Thicker electrode layer also offers protection against fiber in-prints. 

Reported volume resistivities for printed patterns formed from commercial silver-based inks are higher than that of bulk silver. This occurrence reflects the fact that sintered ink patterns contain non-ideal defects such as incomplete particle-to-particle contact, incomplete sintering between contacting particles, residual porosity, and the presence of non-conductive additives. The morphology and extent of void formation in two representative sintered silver nanoparticle inkjet inks are illustrated in Fig. 1. 

In proximity printing spacing the mask away from the substrate minimizes defects that result from contact, but increases the diffraction of the transmitted light which reduces the resolution. The degree of reduction in resolution and image distortion depends on the mask to substrate distance which may vary across the wafer. For proximity printing, equation (3.1) can be rewritten as... 

Uses Surfactant, emulsifier, pigment wetting agent/dispersant, color acceptance agent for industrial coating systems, esp. latex paints, and for solvent-borne architectural paints, printing inks, adhesives, latexes food pkg. adhesives defoamer in food-contact paper coatings Features Low-foam remedies defoamer-induced film defects suitable for PVAc, acrylics, S/B, PVC/PVdC, alkyds, HC resins, NC, PU, epoxy, polyesters... 

Just like visual inspection, automated inspection systems do not require physical contact with the printed circuit assembly to generate the desired images. Unlike visual inspection, however, automated inspection removes human subjectivity from defect detection, thereby increasing repeatabihty rates typically by an order of magnitude. Many of the automated inspection systems also provide accurate, repeatable, quantitative measurements that directly correspond to process parameters, thus providing the means for process control and improvement. ... 

The corrosion property of contact interface between the conductive polymer with 40 wt% carbon particle and Au plated printed circuit board was examined under a corrosive environment of H2S 3 ppm for 1000 hours at 40 c and 80 % relative humidity. The specimen arrangement is shown in Figure 1 two printed circuit boards hold the conductive polymer in a sandwich configuration at a deformation rate of 20 % in compression. After 1000 hours test, to evaluate the air - tight property of the polymer on the Au plated circuit board, discoloration and contact resistance for the surface of Au plate were examined. The contact resistance was measured by using Au probe with 1 mm/ as the other contact member under flowing a current of 0.15 mA and a contact load of 10 g. Corroded parts due to defects in the Au plate show a high level contact resistance because of contaminant films. On the contrary, for the uncorroded part, contact resistance is maintained at a low level. Therefore, contact resistance measurements can be used to evaluate the corrosion of the contact surface. 

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