Thickness control

Cake Thickness Control Sometimes the rate of cake formation with bottom feed-type filters is rapid enough to create a cake too thick for subsequent operations. Cake thickness may be controlled by adjusting the bridge-blocks in the filter valve to decrease the effective submergence, by reducing the slurry level in the vat, and by reducing the vacuum level in the cake formation portion of the filter valve. If these measures are inadequate, it may be necessaiy to use a toploading filter. 

StiTJCtural adhesives are also available in paste form. Bondline thickness control and void elimination are more difficult with paste materials but they can be very useful for unusual designs and innovative manufacturing methods. 

After a satisfactory verification film is produced, an assembly may be fabricated specifically for destructive inspection to validate that the verification film was accurate. This correlation allows the use of verification film rather than more expensive destructive inspection for future changes such as duplicate tool fabrication and tool or detail modification. Simple assemblies are usually not destructively inspected because of high confidence that the verification film is entirely representative of the expected bondlines. Complex or large parts may not be destructively inspected because of the cost of the details and assembly time. In these cases other means of validating the verification film are used. Meticulous pre-bond detail and post-bond assembly thickness measurements may be sufficient to prove bondline thickness control. Ultrasonic inspection and X-ray photography (discussed previously) may be sufficient to prove that details are in the correct places and bonds are good. 

Strand of glass fiber colored differently from the remainder of the roving package. It allows a means of determining whether equipment used to chop and spray glass fibers is functioning properly and provides a check on quality and thickness control. 

A SiC buffer layer was grown on a silicon wafer at 1150-1300°C from one to 45 minutes using C3Hg and H2 as reactant gases. The thickness of the film increased gradually by diffusion of Si into the deposit until a thickness controlled by temperature and silicon etching was reached. 

The properties of thermal-sprayed coatings vary as a function of processing parameters such as temperature and particle velocity. Generally, such coatings have greater porosity than CVD or PVD coatings and thickness control is more difficultto achieve. Yet the process is economical and undemanding. It can be applied in any location. 

Modeling studies have shown that when the bed is not monosized and the difference in particle sizes is great enough, it is possible that the large particles will not reach a lower settling velocity than the small particles hence the large particles will remain in the bottom of the bed (Myska and Svec, 1994). If biofilm thickness control is desired, removal of particles at a location other than the free surface would have to be implemented in this case. 

This basic operation utilises a two-bowl calender in horizontal or vertical configuration. The feed material, either in strip or pig form, is fed into one side of the nip and is squeezed by the bowls, thereby emerging as a sheet which is pulled from the bowl by some manual or mechanical means or supported by a liner cloth. Because of their versatility, three-bowl calenders are now more widely used for sheeting as well as other basic calendering operations. Thickness control is accomplished by use of the adjustable nips and may be further refined by automatic control systems using thickness sensors. It should be noted here that the force required in the nip to flatten the feed material causes deflection of the bowls, however slight. If some corrective steps are not taken, the product thickness will vary across the sheet, resulting in excessive variations of the product and possibly excessive use of expensive materials. In order to overcome these problems, three basic techniques are used to achieve uniform product thickness ... 

Early thickness control systems relied on the calender operator setting up the machine correctly by the use of hand-held thickness gauges, with the consequent slowness of response time during set-up and running before any desired modification to gauge could be achieved. It was usual to run the calender at a low speed to set-up the required dimensions for the product and then to speed up the... 

Spin 10nm-5pm Uniformity, reproducibility, excellent thickness control, low cost Requires flat substrate, high material loss Photoresists, dielectric layers, flat panel displays... 

Atomic layer deposition is a high vacuum process where small amounts of the precursors are leaked into the system sequentially with intermittent evacuations. The ALD enables the conformal deposition of atomically thin layers with precise thickness control at low temperatures without the typical aggregate formation in the gas-phase. 

B. Kloeck, S.D. CoUins, N.F. de Rooij, and R.L. Smith. Study of electrochemical etch-stop for high-precision thickness control of silicon membranes , IEEE Transactions on Electron Devices 36 (1989), 663-669. 

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