Low Temperature Cofired Ceramics
Low Temperature Cofired Ceramics (LTCC, dt .: low temperature single-fired ceramics ) isa technologyin electronics for the production of multilayer circuits on the basis of sintered ceramic carriers. Conductor tracks, capacitors , resistors and coils can be created. The elements can be applied by screen printing or photochemical processes. The unfired ceramic foils are structured individually, then stacked and laminated. Finally, a defined sintering profile with a peak temperature of 850 to 900 ° C is run. The LTCC technology combines the advantages of HTCC ( English High Temperature Co-fired Ceramics ) and the thick film technology and is particularly important for small and medium quantities an economical alternative to conventional printed circuit board technology .
processing
LTCC can be printed and burned with existing thick film equipment. The ceramic mass is provided with plasticizers (to enable lamination under temperature and pressure) and solvents. The thickness is between 4 and 12 mils (milli- inches ); H. between 100 and 300 µm. Silver , silver / palladium and gold pastes have been developed for inner layer conductor tracks and vias , which can be processed on the ceramic film and shrink to almost the same extent as the ceramic layer. The outer layers are preferably burned in separately ( post-fired ) in order to ensure extreme accuracy of fit for automatic assembly. Through holes (vias) are punched or punched with the laser . Then the holes are filled with a conductive paste. After drying, the conductor tracks are printed. The individual layers are aligned and stacked in a press mold. Laminating takes place under heat and pressure (e.g. 70 ° C and 20 N / mm 2 ). After lamination, cut to final dimensions. Burning out for one hour at 350 ° C in a convection oven, during which 85 percent of the organic components are burned out. Then firing in a normal thick-film furnace at 850 ° C.
The shrinkage of the LTCC is reproducible with a tolerance of about 1% if the temperature curve in the furnace is repeated exactly. The electrical properties of the conductor tracks correspond to the normal thick-film conductor tracks. Relatively poor heat conduction compared to aluminum oxide (thick-film technology), so thermal vias are often used .
Applications
Due to the favorable high-frequency properties, areas of application are in mobile communications , satellite , microsystem and medical technology as well as the automotive industry (control devices).
The LTCC ceramics are ideal for printing with resistors. A conductive paste is printed on the LTCC surface using a screen printing process, from which the resistors required in the circuit are generated. These resistances all deviate from their nominal values (± 25%) and are therefore printed too large. With the laser trimmer , the resistors are trimmed with different cuts until they have reached their exact resistance values (± 1%). This process means that no resistors need to be fitted, which enables further miniaturization of the circuit boards .
LTCC stacks are also used in the field of microfluidics . In contrast to glass substrates, this makes use of the possibility of building three-dimensional structures.
Individual evidence
- ↑ Proceedings microelectronics conference ME 08, . 2008. Retrieved January 11, 2011.