Ionic contamination surface

During the last two decades, pressure-driven membrane processes namely reverse osmosis (RO), nanofiltration (NF), and ultrafiltration (UF) have found increased applications in water utilities and chemical industries. Unlike RO, NF, and UF, the Donnan membrane process (DMP) or Donnan dialysis is driven by an electrochemical potential gradient across an ion-exchange membrane. Theoretically, the DMP is not susceptible to fouling because particulate matter or large organic molecules do not concentrate on the membrane surface, as commonly observed with pressure-driven membrane processes. DMP has been used in the past in hydrometallurgical operations [19,20], for concentration of ionic contaminants [21,22] and for separation of... 

A number of integrated circuit (IC) failure mechanisms are related to the presence of water and impurities at device surfaces. The most catastrophic failures are open or short circuits resulting from electrochemical attack on substrate metallization. Other, more subtle maladies include increased capacitive coupling between conductors (1.), reduced bipolar current gain (2), shifted MOS threshold voltages (3.4), and parasitic MOS devices (5.6). These problems arise from spurious electrical conduction processes in the presence of moisture and ionic contaminants. Polymer encapsulants, such as silicone rubber, provide barriers that prevent the formation of conductive water films on IC surfaces. 

Hicks, 1993 Acar et aL, 1994 Eykholt and Daniel, 1994 Hicks and Tondorf 1994 Shapiro, Probstein, and Hicks, 1995 Alshawabkeh and Acar, 1996 Electorowicz and Boeva, 1996 Yeung, Hsu, and Menon, 1996 Dzenitis, 1997 Reddy and Parupudi, 1997). While electroosmosis is analogous to soil washing, ion migration is probably the primary mechanism of mass transport when the contaminants are ionic or surface charged. 

Most silicone polymers act as very good insulators. Polarity of the slloxane backbone apparently is shielded by methyl groups. In addition, the hydrophobic nature of the surface helps to repel water (and dissolved ionic contaminates) which assures the retention of insulation properties under difficult conditions. One application where these properties have found recent importance has been for insulator sheds. Even after repeated exposure to salt fog and high voltage stress, the materials retain their resistance to conductive and arc failure (33). 

BFGoodrich Specialty Chemicals produces a family of thermoplastic alloys that are inherently conductive. Alloys with 15% of the active conductive polymer differ little in surface resistivity from alloys with 25% active polymer. Further, the conductive polymer content remains relatively constant through processes such as injection molding, extrusion, and thermoforming, unlike resins containing conductive fillers. In contrast to chemical antistats, the conductive polymers are active at all humidity levels, do not lose their potency over time, and add no ionic contaminants to the surrounding atmosphere. 

Cleaning agents based on aUcoxypropanols show extremely satisfying cleaning results due to their chemical structure. The lipophilic part of the molecule is capable of removing organic soils such as greases or oils from the substrate surface, whereas the hydrophilic part is able to remove the ionic contaminations. 

The phase transition produces a cleaning mixture that exhibits die properties of bodi solvent-based and water-based cleaners. Water-like properties allow die cleaning agent to effectively dissolve ionic contaminants and remove them from the substrate s surface. 

Most organic residues on assemblies are not detected by ionic contamination meters. However, such residues do change the surface tension of assemblies, thereby influencing the adhesion of subsequent coatings. This method determines the surface tension by iterative use of corresponding testing inks. 

Surfaces exposed to the atmosphere are generally contaminated. Any unwanted material and/or energy on a surface are regarded as a contaminant. Surface contamination can be gaseous, liquid, or sohd in its physical state and may be present as a film or in particulate form. Furthermore, it can be ionic or covalent and inorganic or organic in its chemical character. Most scientific and technical investigations and applications, however, require clean surfaces. 

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