Silicone elastomer mold

To achieve low stress embedding material, low modulus material such as silicones (elastomers or gels) and polyurethanes are usually used. Soft-domain elastomeric particles are usually incorporated into the hard (high modulus) materials such as epoxies and polyimides to reduce the stress of embedding materials. With the addition of the perfect particle size, distribution, and loading of soft domain particles, low stress epoxy molding compounds have been developed as excellent embedding materials for electronic applications. 

Continuous studies were performed in specially prepared microreactors molded from PDMS, designated PDMS (Sylgard 184 silicone elastomer Dow Corning) poured onto silicon wafer molds. The microreactor molds were prepared using 4-in. silicon wafers of Type P, crystal orientation of , resistivity of 1 to 2 Q, and thickness of 457-575 pm from Silicon Quest (Santa Clara, C A). After preparation, mixtures of urease enzyme and PDMS (designated PDMS-E) were poured onto the microreactor mold and allowed to cure at ambient conditions. 

Fluorosilicone compounds can be processed by the same methods used for silicone elastomers based on PDMS. They can be milled, calendered, extruded, and molded. A large proportion of fluorosilicone compounds is used in compression molding. Molded parts produced in large series are made by injection molding, and parts with complex shapes are produced by transfer molding. Calendering is used to produce thin sheets and for coating of textiles and other substrates. 

Silicone elastomers are used to produce numerous molded products which become parts of artificial organs (artificial hearts and assist circulation systems, joint prostheses, etc.). The use of silicone vulcanisates for coating the walls of the artificial ventricle allows it to be used for prolonged assist circulation and prevents the formation of clots on its surface. 

Low-molecular silicone elastomers are a basis for rubber membranes which are used in the production of containers for prolonged storage of fruit, vegetables and other kinds of food. Sealants from low-molecular silicone elastomers are more and more often used to copy articles with complex configurations. The sealant is poured to make a mold which is then filled with molding mixture. This technique is used to copy works of art, in criminalistics (to fix prints), in dentistry (to make models for dentures), etc. 

In consumer markets, keypads, baby bottle nipples, and pacifiers are said to be the applications for molded silicone products with greatest growth potential. Silicone elastomers are particularly well suited for food contact and medical applications. 

Fig. 25 Example of replica molding and imprinting of a surface pattern. Left 3D surface plots of AFM measurements of the original SRG structure generated holographically on compound 9e (top), the replica on the silicone elastomer (middle), and a polycarbonate imprint (bottom). Right corresponding cross-sections. (Adapted with permission from [111]. Copyright Wiley-VCH Verlag GmbH Co. KGaA)...

COHRlastic . [CHR Industries/Furon] Silicone elastomers, some glass-reinforced, aluminum/rubber composites, silicone sponge rubber dimensionally stable, flexible fabric and molded sheet for belting, vacuum blankets, thermal shielding applies. 

Figure 9. Chin implants molded from medical grade silicone elastomer to increase the projection of the mandible.

Figure 12. An ear implant molded from medical grade silicone elastomer and used as artificial cartilage in ear reconstruction.

Storage Store in cool, dry place keep tightly closed Uses Base polymer for addition cure silicone elastomers polymerized prods, provide noncorrosive shield against moisture, dirt, and contaminants for elec, components mold-making elastomers, encapsu-lants, and sealants for elec, components ManufJftistrib. Gelest... 

The silicone elastomers most commonly used for medical applications are the high consistency (HC) and liquid injection molding (LIM) types. The former is most often peroxide cured and the latter platinum cured although there are variations. Both materials are similar in properties. LIM offers greater advantages to the medical device molder and is gaining in popularity. This form of silicone may become the molder s material of choice within the next few years. 

High consistency silicone elastomer consists of methyl and vinyl substituted silicones with aromatic and fluorinated functional groups in some formulations. For the most part, they are peroxide crosslinked. Items are usually compression or transfer molded (Tables 4.8). 

Table 4.9 Typical Properties of Liquid Injection Molding (LIM) Silicone Elastomers...

These new type of resins contain minimum amount of chloride and other mobile ions, such as sodium and potassium, and have become widely used in device encapsulation and molding compounds. The incorporation of fused silica as filler in the epoxy system has drastically reduced the thermal coefficient of expansion of these materials which make them more comparable with the IC die attached substrate materials. The incorporation of a small amount of the elastomeric material (such as, silicone elastomer) to the rigid epoxy has drastically reduced the modulus of the material and reduced the thermal stress of the epoxy material This new type of low stress epoxy encapsu-... 

Silicones have a wide variety of applications (Figure 22.27). Due to the strong Si—O and Si—C bonds, silicones are generally imreactive and can be synthesized to perform in temperature ranges of 75°F to 400°F. Silicone oils can be found in cosmetics, car wax, and hydrauhc fluids. The silicone elastomers are used for medical tubing, heart valve implants, electrical tape, caulk, and gaskets. Silicone resins are used to insulate electrical equipment and in the molding process of electronic circuit boards. These examples represent only a small portion of the uses for silicone compounds. Because of this extensive use, several hundred thousand tons of silicones are manufactured each year. 

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