Silicone contamination

Abstract—The adhesion of pyromellitic dianhydride-oxydianiline (PMDA-ODA) polyimide to fluorine-contaminated silicon dioxide (F-SiO,) with y-aminopropyllriethoxysilane (APS) adhesion promoter has been studied as a function of the peel ambient humidity. The peel strength was not affected by the change in peel ambient relative humidity (RH) from 11-17% to 35-60% when APS was used at the interface. Without APS, the adhesion degraded significantly with this change in RH. It was found that although the dip application of APS caused the removal of about 80% of the initial atomic percentage of fluorine on the surface, it could not be totally removed even after several days in water at elevated temperature. 

Figure 2 - Baman mlciq robe qpectrum of a contaminated silicon wafer (loNer trace) compared with a epectrum of teflon (upper trace). Acquisition coidltlons are dii li ed at the bottom of the figure. Note that laser power at the sanple is 10% of the value displayed.

Silicon nitride as a passivation layer on top of an electronic circuit or a metal structure is an excellent diffusion barrier against water and protects the electronic device from organic and metallic (e.g., Na, K) contaminants. Silicon nitride is also used as a masking layer for wet anisotropic etching of silicon (in KOH), as part of a dielectric membrane, and for mechanical protection in micromechanics during face-down handling of the front of electronics while processing the back of the wafer, a silicon nitride passivation layer prevents defects and scratches on the sensitive front side. 

Dirt repellence is a desirable property for a large number of textile products used in outdoor applications. It can be obtained by finishes or coatings, although the smoothing of the textile surface by calender rolls is also known to be an effective method. For the repellence of oily contamination, silicon compounds, carboxymethyl celluloses and fluorocarbon finishes are applied to the fibres or to the textile material. 

The ultrasonic sprayer can be used to deposit a layer of nanoparticles over a surface to detect and characterize contaminants. Contaminated silicon plates were generated by depositing 10 pL of a dilute solution of test an ytes... 

In order to achieve fuUy dense silicon nitride monolithic bodies, it is necessary to employ either the hot pressing (HP) or hot isostatic pressing (HIP) of sihcon nitride powder, with the addition of metal oxides (for a previous review, see Maccagno, 1989). At temperatures above 1550°C, these additives form with contaminant silicon dioxide films present around individual silicon nitride grains a liquid silicon oxynitride phase in which the silicon nitride may be readily dissolved. 

Both the Toth and Alcoa processes provide aluminum chloride for subsequent reduction to aluminum. Pilot-plant tests of these processes have shown difficulties exist in producing aluminum chloride of the purity needed. In the Toth process for the production of aluminum chloride, kaolin [1332-58-7] clay is used as the source of alumina (5). The clay is mixed with sulfur and carbon, and the mixture is ground together, pelletized, and calcined at 700°C. The calcined mixture is chlorinated at 800°C and gaseous aluminum chloride is evolved. The clay used contains considerable amounts of silica, titania, and iron oxides, which chlorinate and must be separated. Silicon tetrachloride and titanium tetrachloride are separated by distillation. Resublimation of aluminum chloride is requited to reduce contamination from iron chloride. 

Sihcone products dominate the pressure-sensitive adhesive release paper market, but other materials such as Quilon (E.I. du Pont de Nemours Co., Inc.), a Werner-type chromium complex, stearato chromic chloride [12768-56-8] are also used. Various base papers are used, including polyethylene-coated kraft as well as polymer substrates such as polyethylene or polyester film. Sihcone coatings that cross-link to form a film and also bond to the cellulose are used in various forms, such as solvent and solventless dispersions and emulsions. Technical requirements for the coated papers include good release, no contamination of the adhesive being protected, no blocking in roUs, good solvent holdout with respect to adhesives appHed from solvent, and good thermal and dimensional stabiUty (see Silicon COMPOUNDS, silicones). 

The implanted ion can be singly or multiply charged and can be any isotope. The mass separation system is used to avoid contamination. As an example, when implanting silicon the isotope is often used instead of to avoid contamination from the signals. After mass... 

In the first reconstruction [27] of road slabs contaminated with CL, silicon iron anodes were embedded in a layer of coke breeze as shown in Fig. 19-4a or the current connection was achieved with noble metal wires in a conducting mineral bedding material. Slots were ground into the concrete surface for this purpose at spacings of about 0.3 m (see Fig. 19-4b). This system is not suitable for vertical structures. 

Multielement analysis, excellent detection limits for heavy metals quantitative measurement of heavy-metal trace contamination on silicon wafers... 

InP, in the range 10 —10 cm . Boron, phosphorus, and other shallow impurities can be detected in silicon in concentrations approaching 10 cm . Copper contamination at Si surfaces has been detected down to 10 cm levels. ... 

Applications of ISS to polymer analysis can provide some extremely useful and unique information that cannot be obtained by other means. This makes it extremely complementary to use ISS with other techniques, such as XPS and static SIMS. Some particularly important applications include the analysis of oxidation or degradation of polymers, adhesive failures, delaminations, silicone contamination, discolorations, and contamination by both organic or inorganic materials within the very outer layers of a sample. XPS and static SIMS are extremely comple-mentar when used in these studies, although these contaminants often are undetected by XPS and too complex because of interferences in SIMS. The concentration, and especially the thickness, of these thin surfiice layers has been found to have profound affects on adhesion. Besides problems in adhesion, ISS has proven very useful in studies related to printing operations, which are extremely sensitive to surface chemistry in the very outer layers. 

Vapor-phase decomposition and collection (Figs 4.16 to 4.18) is a standardized method of silicon wafer surface analysis [4.11]. The native oxide on wafer surfaces readily reacts with isothermally distilled HF vapor and forms small droplets on the hydrophobic wafer surface at room temperature [4.66]. These small droplets can be collected with a scanning droplet. The scanned, accumulated droplets finally contain all dissolved contamination in the scanning droplet. It must be dried on a concentrated spot (diameter approximately 150 pm) and measured against the blank droplet residue of the scanning solution [4.67-4.69]. VPD-TXRF has been carefully evaluated against standardized surface analytical methods. The user is advised to use reliable reference materials [4.70-4.72]. 

Another important application area for PSAs in the electronic industry focuses on the manufacturing, transport and assembly of electronic components into larger devices, such as computer disk drives. Due to the sensitivity of these components, contamination with adhesive residue, its outgassing products, or residue transferred from any liners used, needs to be avoided. Cleanliness of the whole tape construction becomes very critical, because residuals like metal ions, surfactants, halogens, silicones, and the like can cause product failures of the electronic component or product. Due to their inherent tackiness, acrylic PSAs are very attractive for this type of application. Other PSAs can be used as well, but particular attention has to be given to the choice of tackifier or other additives needed in the PSA formulation. The choice of release liner also becomes very critical because of the concern about silicone transfer to the adhesive, which may eventually contaminate the electronic part. 

Weak boundary layer. WBL theory proposes that a cohesively weak region is present at the adhesive-substrate interface, which leads to poor adhesion. This layer can prevent the formation of adhesive bonds, or the adhesive can preferentially form bonds with the boundary layer rather that the surface it was intended for. Typically, the locus of failure is interfacial or in close proximity to the silicone-substrate interface. One of the most common causes of a WBL being formed is the presence of contaminants on the surface of the substrate. The formation of a WBL can also result from migration of additives from the bulk of the substrate, to the silicone-substrate interface. Alternatively, molecular... 

The selection of the cure system in these applications is directed by constraints such as location of the adhesive in terms of confined space, speed and depth of cure, etc. The volumes of silicones typically applied are relatively small. In general, the uncured adhesive needs to be dispensed in a well-defined and limited area, and needs to stay in place without flowing during cure. No by-products of the cure reaction are acceptable as they may contaminate other sensitive areas of the devices. These constraints often direct the choice to the platinum-catalyzed hydrosilylation cure system that is relatively expensive. 

Fig. I. Silicone contamination, as measured by XPS, as a function of distance from the edge of a silicone tape after a heal treatment to simulate a curing cycle. The dashed line represents the silicone level that would produce delamination. Adapted from Ref. [11).

Fig. 35. OSEE response and peel strength of NBR rubber on steel for HD2 grease (data from Ref. [162]) and silicone release agent contamination (data from R.L. Cause, unpublished work and Ref. [10]). The HD2 grease is slightly photoemitting so the OSEE signal does not decrease to zero at high contamination levels.

Hermetically sealed electrical devices must be verified by a testing laboratory to meet mechanical abuse and to withstand aging and exposure to expected chemicals. Devices potted with common silicones and similar materials by an end user or even a manufacturer, without testing, and devices merely provided with O-rings seldom meet acceptable criteria. Normally, hermetically sealed devices must be sealed through metal-to-metal or glass-to-metal fusion. Many electrical relays, switches, and sensors are available as hermetically sealed devices for common oil and gas producing facility applications. Hermetically sealed devices are often desirable to protect electrical contacts from exposure to salt air and other contaminants. 

Steel is essentially iron with a small amount of carbon. Additional elements are present in small quantities. Contaminants such as sulfur and phosphorus are tolerated at varying levels, depending on the use to which the steel is to be put. Since they are present in the raw material from which the steel is made it is not economic to remove them. Alloying elements such as manganese, silicon, nickel, chromium, molybdenum and vanadium are present at specified levels to improve physical properties such as toughness or corrosion resistance. 

The fluorine concentration in hydrofluorides of tantalum and niobium is an extremely important issue. Fluorine that separates into the gaseous phase interacts with the construction elements of the furnaces, leading to additional contamination of the final product by silicon, aluminum, etc. Thus, it is recommended to perform diying in crucibles made of Teflon or polypropylene with appropriate temperature limitations. Use of crucibles made of carbon-glass ensures high quality and a broad working temperature range, at least up to 300-350°C. 

The residue consists of the impurities, and the loss in weight of the crucible gives the amount of pure silica present, provided that the contaminants are in the same form before and after the hydrofluoric acid treatment and are not volatilised in the operation. Although silicon is not the only element that forms a volatile fluoride, it is by far the most abundant and most often encountered element consequently the volatilisation method of separation is generally satisfactory. 

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