The manufacturing process for monolayer and multilayer are both the same and quite different. Monolayer is made of one layer of piezoceramic material pressed with up to 1 MN compacting force. Multilayer is made by tape casting very thin layers of piezoceramic material on which thin layers of electrode material is deposited. Approx. 100 layers are then laminated.
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The basic technology for the manufacturing of piezoceramic components is the pressing of shaped bodies using spraydried granular material. This is achieved using high-capacity presses with up to 1 MN compacting force.
The shaped bodies are either manufactured true-to-size, taking into account the sintering contraction, or with machining excesses, which are removed to achieve the required precision.
By using high-production inboard diamond sawing equipment, it is possible to manufacture components (discs, plates, tubes, etc.) with a thickness as low as 0.2 mm.
Multilayer piezoelectric actuators are produced by tape casting very thin layers of piezoceramic material on which are deposited thin layers of electrode material. Several layers are laminated together to form a monolithic ceramic component with internal electrodes.
A flow diagram of the manufacturing processes involved with piezo monolayer and multilayer processing at Noliac is shown below. Each process is described below the diagram.
Depending on the product about to be produced, the relevant piezoceramic powder is taken from stock.
Piezoceramic powder with a specified particle size is mixed with additives and solvents. All is accurately weighed according to a well documented prescription.
The mixed materials are calcinated at 900-1000 °C to remove organics, water or other volatiles left after mixing.
The calcinated materials are milled to achieve a very homogeneous suspension. The suspension is measured for viscosity and approved for tape casting or for monolayer production.
The powder with binder is now granulated by spray drying.
The piezoceramic material is pressed with different pressing tools depending of the shape in production.
The powder is mixed with additives and solvents. The mixed materials are milled to form a homogeneous suspension (slurry).
The suspension is tape casted on a carrier foil. The tape thickness is between 20-40 µm as standard. The green ceramic tape contains binder materials, which makes the tape flexible and easy to handle in the following processes.
Sheet cutting
The tape is cut into sheets and automatically inspected for defects
Printing
Platinum or silver/palladium electrodes with predetermined patterns are printed on the piezoceramic sheets with a suitable electrode paste. A final multilayer item will typically consist of 2-5 different electrode patterns.
Stacking
Layers of ceramic sheets are automatically stacked in the right sequence to the final build-up design. All items are built in 6” x 6” blocks.
The piezoceramic blocks are laminated at defined pressure, temperature and time. At this process the layers are firmly laminated and brought in appropriate contact with each other. This process is very critical as either insufficient lamination or too much lamination has significant influence on the quality of the products.
After lamination, individual components are diced or drilled out of the green piezoceramic blocks. Dicing needs to be accurate matched to the pattern of the internal electrodes. Dicing might also be performed on fired ceramic.
The organic compounds in components, binder materials, additives and remaining solvents are removed by very slowly heating of the green parts to a temperature of 500-700 ºC, where the organic compounds decompose and evaporate from the ceramic.
In order for the piezoceramic grains to grow and merge into a solid polycrystalline structure, the fired parts need to be heated to a temperature above 1000 °C. Several parameters have to be optimized with this process, e.g. temperature ramp rates, holding time and the condition of atmosphere. During sintering the components will shrink approximately 15 %.
All products are machined or tooled in some manner before or after termination depending on the specific product. The surface roughness depends on the grain size of the abrasive used in the slurry.
For multilayer products, external electrodes are applied to make a connection to the internal electrodes inside the component. For monolayer products, the external layer provides external electrodes for connection and polarization.
After careful cleaning, the components are applied with a conductive electrode paste of typically Ag. The screen printing technique is the preferred applying technique. The electrode paste is fired at a temperature between 600-800 °C depending on the material and will form a conductive layer with a good adhesion to the ceramic surface.
Activation of the piezoelectric ceramic properties is called the “poling” process. In order to obtain the piezoelectric effect in the piezoelectric material, the dipoles in the grains must be aligned. This alignment is achieved in the poling process, where a high electrical field, 2-3kV/mm, is applied to the external electrodes at elevated temperatures (100 - 150 °C) for a period of 1-10 minutes.
After poling the components and stacks will go through a final inspection according to customer specifications or internal procedures, which is a combination of statistical method with level AQL 0.65 and 100 % measurements. Various mechanical and electrical parameters might be tested - also according to customer specifications. Mostly capacitance, dielectric loss and mechanical strain level (stroke) are specified for inspection.
Single monolayer as well as single multilayer elements can be stacked. The elements are glued together with epoxy glue. Non-active piezoceramic end-plates are applied to provide electrical insulation. The single stack is typically connected electrically with a bus wire.
Components will be packed properly in plastic trays, plastic bags, foam or placed on tape and then placed in a grey box with the Noliac logo.
We use couriers for shipment of packages and are able to dispatch up to four Noliac boxes in one shipment.
We give you a competitive advantage by using our extensive knowledge to customize and optimize your piezo products. Thus, we will be your long-term piezo partner. Send your request today.
