Basic Process of High Shear Compaction
High Shear Compaction Tape Fabrication
This process is most commonly used in the production of ceramic substrates for electronic applications, but metal, glass, and even diamond powder tapes and other ceramic tape sheets have been produced.
The High Shear Compaction™ Process is a highly efficient means for high volume production. It is capable of producing tapes of the highest quality, with densities and sheet uniformity far beyond other green sheet forming techniques.
Learn more about RTI's High Shear Compaction Guidelines .
The following describes a typical system for ceramic tape substrates based on a throughput capacity of about 450 kg per day.
Mixing of the proprietary binder and your powder raw material is accomplished by traditional means. The binder content is varied depending on the kind of ceramic used and its characteristics such as particle size and morphology. There is no need to adjust the pH. After mixing, it is dried and made into free flowing granules. At this time it is ready to go into the tape forming process.
The dry powder is fed into a hopper in the tape fabrication machine. The forming machine, unlike traditional single stage roll forming, consists of three process steps. From the hopper the powder is automatically fed at a metered rate into the first stage of the forming machine. The following operations perform several functions in one piece of equipment. These include uniform dispersion, solidification, edge forming, green density, thickness control, and surface finish. The raw material moves continuously through the stages. Its speed is monitored and automatically regulated at each stage. Process monitoring sensors are in place to regulate such parameters as speed, thickness, and green density control.
Unlike the doctor blade tape casting process, the High Shear Compaction™ process has its final effect on thickness at the end of the process line. This is an important advantage because after it is adjusted, there are no further variables, which can cause errors in green tape thickness.
The system can be equipped with thickness sensors at each side of the tape to give a digital readout of the thickness across the tape. Thickness sensors are mounted at the output of the cast tape forming process but before edge trimming.
This technique is more effective than using exotic sensors to measure wet thickness, as is often the case with tape casters. With High Shear Compaction™ the thickness is set at the final stage after the tape is dry. Therefore, it is not necessary to consider the difference in thickness caused by the drying process; it is fixed by the machinery.
Processing time for a 625-micron thick tape will be approximately 20 minutes from hopper to trimming. The width can be chosen from a range of 5 centimeters to over one meter. The tape is fully dry and ready to use as it exits the tape fabrication machine. The polymers used in the binder are stable for good shelf life and are not sensitive to atmospheric humidity.
Trimming, Punching, or Wind-up
The edge slitter is attached to the output of the tape fabrication machine. The tape feeds directly into it and is automatically slit so the rough edges fall away into a container for re-processing.
The ceramic tape sheets can then be punched or slit into individual units. If desired the tape can also be wound onto a take-up spool. Tension is maintained throughout the roll.
Recycling of Scrap
A key advantage of HSC is that tape trimmings can be reprocessed directly back into tape. The scraps are simply chopped up and added back to the virgin material at the same rate they are generated. This allows a near 100% utilization of raw materials and eliminates the need to recycle and reconstitute starting materials.