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HSC™ vs. Doctor Blade Tape Casting — A Comparison

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Improved Ceramic Substrate Density

Shrinkage variability is a constant problem in the production of ceramic substrates. There are many variables contributing to these problems. With the High Shear Compaction™ process green tape density can be controlled and as a result, the shrinkage upon firing and the fired dimensions can be controlled.

To control shrinkage, density of the green substrate is one of the most important factors along with raw material composition and sintering temperature. All three of these factors are interdependent. The following explains the importance of green tape density and how it can be controlled to increase yield or improved product performance.

  • Doctor blade cast tape has a non-uniform density throughout the vertical axis because of particle and binder segregation. Tapes made with the High Shear Compaction™ process have a uniform density throughout all dimensions. This is because the particle and binder distribution is uniform and homogeneous. This is a very important factor since the lack of tape homogeneity always leads to differential shrinkage and camber problems.
  • The green density obtained with the HSC™ process can be considerably higher than the density obtained with a doctor blade tape casting process. This provides the following advantages;
    • Lower overall shrinkage upon firing
    • Less variation in shrinkage upon firing
    • Higher fired density
    • Lower firing temperatures are possible
  • The HSC™ process gives the user the technology to adjust the green density of the ceramic tape to a predetermined value on line. This monitoring function allows easier and more precise control of the ceramic tape or substrate manufacturing.
  • Since HSC™ allows control of the green density; the means exists to compensate for other variations. For example, controlling the process density at about 5% below the maximum achievable green density, allows some process latitude so that firing shrinkage adjustments can be made. These adjustments can compensate to a large degree for powder raw material, lot-to-lot variations so the fired dimensions can be controlled.
  • Higher green density in the ceramic tape results in a higher fired density. Higher fired density will provide improvements in physical and electrical properties of the finished substrate.
  • The variation in density and ceramic tape non-homogeneity of the traditional casting process leads to warping or camber problems during sintering. These problems are eliminated with the HSC™ process. One client has reported that re-firing steps needed to assure flat alumina substrates could be eliminated with the use of the HSC™ process.

Smoother Surface Finish

With the HSC™ process, both substrate surfaces are the same, unlike cast tapes, which have a controlled surface on one side, and a dull surface on the topside. The ability to control both surfaces is a result of the forming process in the tape fabrication step. Both sides are high quality printable surfaces. As an alternative option, different surface finishes can easily be produced on each side of the ceramic tape.

With the HSC™ process, surface roughness can be controlled. Subject to limitations of the powder particle size and sintering environment, the surface of the ceramic thick tape can be controlled from 1 to about 50 micro inches. The machinery imparts the surface finish on both sides of the tape.

Tape Casting Process Stability and Reliability

The HSC™ process is a more stable and reliable process than tape casting;

  • It is independent of humidity, unlike the tape casting process, which is highly sensitive to humidity.
  • The HSC™ process is self-contained and is not affected by temperature extremes.
  • No specialized knowledge is required to monitor the process. The process is automated and reduces problems associated with human error when producing ceramic tapes.

Increased Tape Casting Yield

The HSC™ process will produce in excess of 95% usable ware. The edge trim is 100% reusable. Long test runs of many feet are not needed when the process is restarted at the beginning of a shift.

The process allows much tighter thickness control. Tolerances of +/-5 microns are typical, even at thicknesses of 250 to 500 micron tapes.

As mentioned previously, batch-to-batch variations in raw materials, which can cause shrinkage variations, can, to a high degree, can be compensated for with this process.

Increase Tape Casting Productivity

During the forming process, the HSC™ process can be three to four times faster than the tape casting process. The speed of this process is not dependent on thickness to the degree the tape casting process is. Very long drying ovens are not required such as with tape casting.

Ceramic tapes are formed at full thickness so multiple sheets do not need to be stacked and laminated to form a substrate.

Post Tape Forming

The process is tailored for your application so that ceramic tapes can be scribed or vacuum formed, deep drawn, perforated, and rule-die cut. Ceramic tapes can also be formed into complex three-dimensional shapes. The ceramic tape can be made so that it is easily via-punched and laminated into multi-layer structures suitable for manufacturing complex electronic devices.

Reduced Floor Space Requirements

The HSC™ process does not require a long drying oven. As a result it is a compact, energy efficient machine occupying about half of the space of a comparable tape casting machine.