Co-fired ceramic
Low Temperature Co-fired Ceramics ( LTCC, dt: Low temperature co-fired ceramics ) is a technology for the fabrication of multilayer circuits on the basis of sintered ceramic substrates in electronics. Can traces, capacitors, resistors and coils are produced. The elements can be applied by screen printing or photochemical processes. The ceramic green sheets are individually structured, then stacked and laminated. Finally, a defined sintering profile is started with a peak temperature of about 850-900 ° C. The LTCC technology combines the advantages of HTCC ( High Temperature Co-fired Ceramics english ) and the thick-film technology and is especially in small and medium quantities, a cost effective alternative to conventional printed circuit board technology.
Processing
LTCC can with existing thick film devices Print and burn. The ceramic mass with plasticizers (to allow for lamination under temperature and pressure) and solvents provided. Thickness of about 4-12 mils ( mils; 0,1 - 0,3 mm). For indoor location traces and vias silver, and gold Silber/Palladium- pastes have been developed that can be processed on the ceramic film and shrink by almost the same extent as the ceramic layer. The outer layers are preferably baked separately ( post- fired ) to ensure extreme accuracy Pass for Automatic Assembly. Through holes (vias ) are punched or drilled with the laser. Thereafter, 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. Is laminated under heat and pressure (eg, 70 ° C, and 20.6 N/mm2). After lamination, cut to final size. Burning for one hour at 350 ° C in a convection oven, it will be burned out 85% of organic ingredients. Then burning in the normal thick-film oven at 850 ° C.
The shrinkage of the LTCC can be reproduced at about 1 % tolerance when the temperature curve in the kiln will be repeated exactly. The electrical properties of the conductive tracks corresponding to the normal thick film conductor tracks. Relatively poor thermal conductivity compared to aluminum oxide ( thick film technology ), therefore, often use of thermal vias.
Applications
Areas of application are due to the favorable high frequency characteristics in the mobile, satellite, micro- technology and medical technology as well as the auto industry ( ECUs ).
The LTCC ceramics are ideal for printing with resistors. With a screen printing method, a conductive paste is printed on the surface of the LTCC, from which the required resistances in the circuit are generated. These resistors soft all of their desired values from (± 25%) and are therefore printed at large. With the laser trimmer to trim with different cutting styles resistors until they have reached their exact resistance values (± 1%). By this method, no resistance need to be stocked, so that a further miniaturization of the printed circuit board becomes possible.
LTCC stacks are used in the field of microfluidics. This makes you look over glass substrates, the possibility to build three-dimensional structures exploit.