Tape casting production

In many cases the powder is the one ingredient over which the materials engineer or scientist has the least control, since it is usually selected to provide specific properties in the final product. In other cases, it is selected for its ability to be processed or sintered under specified conditions. In our laboratory, about 80% of the materials we are asked to process into tape-cast products are preselected by our clients. In the rare cases where we have the liberty to select the starting powder (s), we can define several powder properties to make the tape casting formulation more forgiving and easier to process. These powder characteristics will be reviewed in the sections that follow. It is often, but not always, necessary to combine different powder chemistries in order to achieve the desired strength, resistivity, dielectric constant or dielectric strength, chemical resistance, porosity, or other fired property or characteristic. 

The optimized slip is now ready to be moved to the casting equipment for forming the tape-cast product. The tape casting process is discussed in Chapter 4. 

This same type of slitter is also used to cut a wider piece of tape into narrower sections at the exit end of the machine. For example, a 200-mm-wide tape may be slit into four 50-mm strips. Each of the 50-mm strips would then be rolled as a separate entity onto the take-up roller(s). Another type of slitter used to cut a wide tape into sections is based upon the scissors principle—that is, it has two cutter wheels or block knives that overlap each other and shear the tape like a pair of scissors. The block knives on each of these systems are driven and are synchronized with the movement of the tape-cast product. When a wide tape is slit into two or more narrower widths, there are usually two take-up axles. As the slit tape moves from the slitter, alternating strips are diverted to different take-up axles, thus eliminating the possibility of overlap or interference between adjacent rolls. 

If the tape is to be slit into narrower strips, the carrier is almost always removed from the tape prior to the slitting operation. This is usually accomplished by having the carrier make a 180° bend around either a knife edge or a roller. The tape-cast product continues in a straight path once it is stripped from the carrier, and the bare carrier is rolled onto a take-up roller. The tape-cast product then passes into the slitter section. 

If the product is being stripped from the carrier, the take-up system is a bit more complex. The speed control to provide constant speed during the cast is actually on the take-up roll for the carrier, and this speed is maintained by the tachometer feedback loop described previously The product, on the other hand, must be handled with a tensionless take-up system, since there is no carrier to provide the mechanical strength needed in a system under tension. This is accomplished by using a proximity sensor with a loop of tape where a servo-motor accelerates and decelerates the take-up roller, depending on where the loop is with respect to the sensor. This system provides a tensionless take-up system for the tape-cast product. Many different types of proximity sensors have been used in these systems. The main requirement is that the sensor detects the tape that is being speed controlled. At times, especially when the tape-cast product "blocks —that is, sticks to itself—a paper or other material must be interwoven between the layers on the roll. Machines have been built with all of these features added as options. 

Once the tape-cast product has been fabricated in either sheet or roll form, it is ready for evaluation and characterization before being processed into a useful shape or part. This chapter will cover the green tape characterization techniques and procedures that are used in industry as well as procedures we have instituted in our laboratory. The remainder of the chapter will address the downstream processing steps followed in the final shaping procedures to produce parts for specific products. These procedures include blanking, punching, calendering, and lamination. First we will review the tape characterization procedures and techniques. 

Automated equipment is now manufactured for production punching of micro-holes in tape-cast product. Most of these machines use a computer-controlled punch head with reported punching speeds of up to 10 holes per second on 2.54 mm (0.100 in.) movements. The reported hole sizes range from 0.102 mm to 9.525 mm (0.004 to 0.375 in.). Square holes, triangular holes, and oval-shaped holes are also within the capability of these machines. The reported positional resolution is 2.54 pm (0.0001 in.) and the positional accuracy is 5 pm (0.0002 in.).io... 

Stack the metallized parts in the exact order desired using alignment pins. Make sure that the tapes are stacked top surface to bottom surface, since there is some binder segregation in most tape-cast products, and this will prevent binder-poor side to binder-poor side bonding, which can cause delamination. 

Apply a low pressure and allow the stack to preheat for a long enough time to reach equilibrium. This can range from seconds to minutes, depending upon the thickness of the stack. Standard temperatures used for most of the organic systems in tape-cast products range from room temperature to 100°C. 

In the manufacture of MLCCs today, as many as 300 layers are being laminated to produce a monolithic structure with excellent electrical properties. Lamination is definitely one of the most important downstream processing steps in the manufacture of tape-cast products today. 

The procedure must be followed exactly to yield the best possible tape-cast product. This procedure is as follows ... 

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