HSC™ vs. Doctor Blade Tape Casting – A Comparison

Improved Ceramic Substrate Density

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.

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.

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.

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.

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.

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.