Fused silica mold

More details on fused silica mold fabrication can be found elsewhere [80]. In general, a resist is patterned using electron-beam lithography and then transferred to a thin (between 8 and 20 nm) chromium layer with a CI2/O2 plasma. Afterwards, fused silica is etched in a fluorocarbon plasma using the chromium layer as a hard mask. Finally, this hard mask is removed in a wet or dry process. 

The ability to prepare monoliths within a mold of any shape was used by Lee et al. [128] who prepared monolithic ST-DVB microbeads within pulled fused silica needles and used them for the reversed-phase separation and on-line electrospray ionization mass spectrometry (ESI-MS) detection of proteins and peptides. As illustrated by Fig. 18, these monolithic microcolumns separated proteins far better than capillaries packed with commercial C18 silica or polymeric beads. 

Instead of using a planar molding master, a fused silica capillary tube (50 pm i.d. and 192 pm o.d.) was used as a template for casting PDMS channels, and as the fluid inlet/outlet tubes. After PDMS curing, the middle pre-scored section (4 cm) of the capillary was removed to reveal the PDMS channel (192 pm wide and deep) [817]. Similarly, a capillary was used to mold a PDMS channel, and to produce an electrospray emitter. In this case, after PDMS curing, the last 0.5-cm section of the capillary was removed to create a channel [821]. 

In addition, Vycor can be shaped and/or formed while in its borosilicate state before it is transformed into Vycor. Thus, molded, pressed, tapered, and other shapes that would otherwise be very difficult, expensive, and/or impossible in fused silica can be done (relatively) easily with the pre-Vycor material with much less energy. Once the manufacturing is complete, the glass can then be processed to Vycor. 

Epoxy polymers (including epoxy novolacs) have been designed to meet most of these requirements and are almost universally used in such encap-sulant applications. Epoxy polymers exhibit superior adhesion that in many cases eliminates the need for a barrier or junction coating. They have a low coefScient of thermal expansion low shrinkage and low injection velocity, which means that low transfer or injection pressures can be used. These polymers also possess excellent mechanical properties coupled with low moisture and gas permeability. Above all, they are cheap and readily available. Other transfer-molding materials used to a limited extent include silicones, phenolic materials, and even polyesters. Most molding formulations are highly filled (70-75%) with materials such as quartz, fused silica, short... 

Siltex. [Kat lite] Fused silica for plastics, elec, molding and potting comjxlSn epoxy compds., sealants. 

The dried powder is placed in a mold and subjected to a gradually increasing pressure of 25 t.s.i. over a period of three minutes and the pressure then gradually reduced over a period of one minute. The coherent, molded bar is further dried in air at 50°C and then placed in an electrically heated muffle and heated to 800°C, while supported on a fused silica plate. Another electric muffle, adjacent to the first, is heated to a temperature of 1050°C. The silica bar, not yet sintered at 800°C is quickly transferred to the muffle at 1050°C and left for 15 min. It is observed that the specimen shrinks perceptibly in dimensions, and becomes more translucent. As soon as this change occurs, which requires 15 min at 1050°C, the specimen is removed from the furnace and cooled by dropping it into water. 

CAS 68439-86-1 EINECS/ELINCS 215-145-7 Uses For casting of refined copper, copper alloy, and aluminum as protective coating on ladles, troughs, etc. made from fused silica ceramic fiber, calcium silicate, castable all metal equip, and tools exposed to molten metal (ladles, sow molds, ingot molds, metal troughs) floor areas around mold stations, furnaces, ladles Features High heat transfer resist. 

Physical forms. The molding compound will consist of 20 to 25% resin (phenyl and methyl siloxanes), 75% filler (glass fiber and fused silica mix), a lead-based catalyst pigment, and lubricants. The compounds are free-flowing granular in form and are available in opaque colors (mostly red). They are readily moldable in compression, transfer, and injection molding processes. 

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-... 

Fig. 31. Comparison of the profile of the apparent mean viscosity vs, time for the silica filled epoxy molding compound, measured by RPA. (O denotes conventional crushed fused silica and denotes spherical fused silica)...

---