Introduction to LTCC technology

6-4-2012

Last week was my first week in Dr. Eitel's lab. I began my research project, which is to design a ceramic chip with microfluidic channels for biodetection. The material used to make these ceramic chips is Heraus Herlock Low Temperature Co-fired Ceramic tape (LTCC tape). LTCC tape can be purchased in bulk and allows for easy assembly of small ceramic devices. The tape can be cut into a variety of shapes and layered to form a 3-D object. In Dr. Eitel's lab we use a laser cutter, which was originally designed to engrave trophies, to shape the ceramic tape. After cutting out all the required pieces for a given object, and perhaps printing circuits or otherwise modifying them, the pieces are assembled on a form and pressed in a uniaxial press. The form used to assemble LTCC ceramic tape has holes in the corners that line up with holes cut into each piece. This allows for shapes on one layer that line up perfectly with the tape below. After pressing the tape together (the tape is not actually tacky, so it requires pressure to stick), the layered pieces are trimmed, vacuum-sealed, and placed in an isostatic press. The isostatic press allows for uniform compression around the ceramic and the vacuum bags protect the ceramic from the oil used in the isostatic press. The isostatic press contains an oil solution, which can be pressurized to thousands of pounds per square inch. When removed from the isostatic press, the ceramic is completely devoid of air between layers and is ready for firing. After being fired in a ceramic oven for about 12 hours, the LTCC ceramic product is ready to use.

The remarkable thing about Herlock LTCC ceramics is the lack of shrinkage in the lateral directions. Normal ceramic shrinks in all directions and is typically created from a uniform mixture. The Herlock LTCC is layered with different ceramic powders, each of which has a unique sintering point. One layer will shrink, but because it is attached to a layer that is not also sintering, it will be limited to vertical shrinkage. Then the next layer will be limited to vertical shrinkage by the previous layer, and so on. Therefore, with Herlock LTCC there is a large loss of thickness, but virtually no loss in length or width. This allows for the creation of objects to scale without having to factor in the shrinkage parameters.