Equipment for Production of Multilayer Based Components in LTCC Production
The Low Temperature Cofired Ceramic (LTCC) technology can be defined as a way to produce multilayer circuits with the help of single tapes, which are used to apply conductive, dielectric and / or resistive pastes on.
These single sheets have to be laminated together and fired in one step all. This saves time, money and reduces circuits dimensions. Because of the low firing temperature of about 850°C, it is possible to use the low resistive materials silver and gold instead of molybdenum and tungsten (which have to be used in conjunction with the HTCCs).
Keko equipment can offer lab scale production lines as well as fully automatic lines for processing green tapes with or without carrier film. LTCC production steps consist of:
LTCC producers usually use tapes shipped on a roll. For those customers who would like to develop LTCC tape or produce it by themselves.
A tape is unrolled and cut into individual pieces.
For this purpose, our Tape blanker SC-series can be used. It can process either a ceramic tape cast on carrier PET film or tapes whiteout carrier film; it depends on the type. A sheet dimension is adjustable. It is preferred to rotate the single sheets in turns 90° to compensate the different x/y-shrinking of the LTCC.
Vias may be punched or drilled with a laser. Most of available lasers have problem to punch white, thick, green ceramic tape, especially if the ceramic tape is on the carrier film. For punching vias, Keko can offer single or multiple pin high speed punching machines, such as PAM-series, with or without automatic tape handling. In case the tape is cut into individual sheets on the punching machine, a slitting machineis not necessary.
Vias can be filled with a conventional thick film screen printer or an extrusion via filler. In the first case, the tape has to be placed on a sheet of paper that lies on a porous plate; a vacuum pump holds the tape on its place and it is used as an aid for via filling. The second possibility to fill the vias is to use a special extrusion via filler that works with pressures of about 4 to 4.5 bar.
Both methods need to have a mask; this mask should be made of a 150-200mm thick stainless steel. An alternative to that is to use the (Mylar-) foil, on which the tape is usually applied. For a via filling operation we can offer a P-200AVF printer with a via filling option, with or without an automatic sheet handling.
Cofireable conductors etc are printed on the green sheet using a thick film screen printer. The screens are standard (250 – 400) emulsion or foil type thick film screens. Just like the via printing process, a porous plate is used to hold the tape in place. Printing of the conductor tends to be easier and of higher resolutionthan standard thick film on alumina.
This is due to the flatness and solvent absorption of the tape.
After printing, the vias and conductors have to be dried in an oven at 80 to 120°C for 5 to 30 minutes (depends on material); some pastes need to level at room temperature for a few minutes before drying. With the help of our P-200A screen printer, it is possible to print conductors with a 50mm line resolution.
Opposite to the process where each layer is placed in turns over tooling pins or where some processors use heat pliers to fix the sheets in turns one on top of the other, we stack one by one sheet by CCD vision alignment or by positioning pins. For this process, developed by Keko LTCC production technology, no special tools are needed. According to required productivity, we offer different possibilities.
There are two possibilities of laminating the tapes in the process of LTCC production. The first one is uniaxial lamination; the tapes are pressed between heated plates at 70°C, 200 bar for 10 minutes (typical values). This method requires a 180° rotation after half the time. The uniaxial lamination could cause problems with cavities / windows.
This method causes higher shrinking tolerances than the isostatic lamination. The main problem is the flowing of the tape; that results in high shrinkage tolerances (especially at the edge of the part) during the firing and varying thickness of single parts of each layer (it causes serious problems on the high frequencies sector). A suitable press would be our TPR-series.
The second way is to use an isostatic press. The stacked tapes are vacuum packaged in a foil and pressed in hot water (temperature and time are just the same like using the uniaxial press). The pressure is about 350 bar. We recommend our ILS-series model.
After laminating, the parts are usually cut into the individual pieces. For this purpose, our manual or automatic CM-series model-cutting machine can be used.
It cuts up to 5mm thick green ceramic bars on a vacuum table with a hot blade. For those customers who would like to do half cut of the stack, a modified versionof standard cutting machine is available. If the fired parts have to be cut into smaller pieces or other shapes, there are three different possibilities.
The first one is to use a post fire dicing saw, which holds tight outside dimensional tolerances and allows high quality edges.
9. Cofiring
Laminates are fired in one step on a smooth, flat setter tile.
The firing should follow a specific firing profile, which causes the need of a programmable box kiln. A typical profile shows a (slow) rising temperature (about 2-5°C per minute) up to about 450°C with a dwell time of about one to two hours, where the organic burnout (binder) takes place; then the temperature has to be risen up to 850 to 875°C with a dwell time of about 10 to 15 minutes.
The whole firing cycle lasts between three and eight hours (depends on the material; large / thick parts cause the need of a modification of the firing profile). For further information on Low Temperature Cofired Ceramic production equipment please contact us (click here).
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