Last Updated on March 23, 2023 by You Ling
Piezoelectric ceramics need to be fixed with other electronic components in order to function. Among them, bonding is the best way to fix them. Many customers who purchase piezoelectric ceramics have reported issues with bonding them. Therefore, we are writing this article to help everyone bond piezoelectric ceramics correctly and more easily.
1、Why fix piezoelectric ceramic?
There are three main options for fixing piezoelectric ceramics to a solid surface: bonding, welding, and clamping. Among these three options, the best way to fix piezoelectric components is usually to use glue or epoxy resin for bonding.
Advantages of bonding:
Provides strong, flexible, and non-conductive adhesion
Eliminates fatigue that may occur due to vibration during long-term operation
Can be used at temperatures above 150C
Disadvantages of welding:
Over time, welding may fail because vibration in the ceramic can cause bonding to fail, and the high temperatures used during welding can affect the performance of the ceramic.（More about welding）
Disadvantages of clamping:
The least reliable way to fix piezoelectric components to a solid surface is by clamping, as it may damage the ceramics during fixing. Clamping can also restrict the movement of ceramics.
2、What are the adhesive options for piezoelectric ceramics?
Piezoelectric ceramics have electrodes on their surface and a high voltage electric field inside, so any mechanical or chemical contact with the ceramics can lead to damage. Even slight traces of corrosive substances on the surface of the ceramics can cause a decrease in performance or even damage over time.
Therefore, when using adhesives, sealing and packaging materials, it is important to pay attention: during the processing, do not produce reactive substances with corrosiveness. Do not use standard single silicon compounds, as they will produce acid when exposed to humid air, which will penetrate the surface of the piezoelectric ceramics and corrode the electrode. Therefore, only materials with corrosion resistance can be used.
Epoxy resin glue is mainly used as the adhesive for piezoelectric ceramics, while polyurethane or cyan acrylic esters have also been successfully used.
Quality of adhesive layer
The quality of the adhesive layer is determined by both the quality of the glue and the bonding process.
Generally, bonding quality is achieved by solidifying bonding for more than 30 minutes at room temperature or slightly heated. Quick-drying adhesives can lead to thicker adhesive layers and lower bonding quality.
When it comes to the quality of the adhesive layer, the general idea is that thinner and harder adhesive layers will result in higher bonding quality. However, for piezoelectric ceramics with different deformation modes, specific analysis is needed.
For example, in bonding piezoelectric ceramic sheets: applying voltage to the piezoelectric ceramic sheet will inhibit the transverse d31 displacement of the piezoelectric ceramic sheet, as well as the axial d33 displacement. In the actuation process, high mechanical stresses will be generated within the mechanical structure.
Therefore, for schemes that require large-area bonding, preliminary testing must be carried out to identify suitable adhesives and adhesive layer thicknesses to ensure that the displacement of the piezoelectric ceramics is not hindered.
3、How to secure a piezoelectric ceramic to a solid surface
Today, we will give a brief introduction to bonding and fixing commonly used series of piezoelectric ceramics.
Stacked piezoelectric ceramics
Stacked piezoelectric ceramics are axially driven piezoelectric ceramics, including square and circular shapes, and can be customized with square openings or other shapes.
Precautions for bonding and fixing:
Do not stick the adhesive to the side surface layer;
Ensure that the glue between the piezoelectric ceramic and the bonding surface is thin;
After gluing, gently press to fix it;
The side of the stacked piezoelectric ceramic cannot withstand clamping force.
Piezoelectric ceramic sheet
The thickness of the piezoelectric ceramic sheet is 2-3mm, and the shape is mainly circular and square. Unlike the unpoled ceramic layer on the upper and lower surfaces of the stacked piezoelectric ceramic, the upper and lower surfaces of the piezoelectric ceramic sheet are normal polarized ceramic layers. If a hard adhesive layer and other structures are used for bonding, it will cause unexpected deformation under the driving voltage, so preliminary tests need to be performed to find the bonding layer.
Precautions for bonding and fixing:
Do not stick the glue to the driving area;
The thickness of the adhesive layer needs to be tested beforehand to avoid reducing displacement;
The piezoelectric ceramic sheet cannot directly contact with metal, and a kapton film or insulating pad should be added between the ceramic and metal surfaces.
Precautions for bonding and fixing:
Square bent pieces: the glue should be applied within 3mm of the non-driving area to avoid affecting displacement.
Square bent pieces: the mechanical clamping force should be appropriate, about 5 times the output force.
Circular bent pieces: when fixing the outer diameter, there should be elasticity to avoid reducing the bending effect due to additional clamping force, so the mechanical clamping force should be appropriate.
Circular bent pieces: if glued, an elastic epoxy resin adhesive should be used, and space for displacement should be left at the bottom.
Piezoelectric ceramic shear slice
Piezoelectric ceramic shear slice is a type of piezoelectric ceramic that utilizes the d15 shear mode. It can be combined and stacked in a XY motion platform configuration, and when combined with axially-driven piezoelectric ceramics, can be used to create a mini XYZ three-dimensional micro-motion platform. The electrodes of the piezoelectric ceramic shear slice are on the top and bottom surfaces and can be fixed in place through mechanical clamping or adhesive bonding.
Notes on adhesive bonding and fixing:
The adhesive layer should be uniform.
Epoxy resin adhesive is recommended.
The adhesive layer should be as thin as possible.
Low viscosity adhesive is preferred.
Pressure should be applied during the curing process, with a recommended pressure of 2-3 MPa.
Notes on mechanical clamping and fixing:
The axial force of the shear slice should be controlled when using mechanical clamping, with a recommended pressure of 1-3 MPa.
The load structure in the driving direction should have as low a stiffness as possible to avoid hindering the motion of the shear slice.
The load should be applied uniformly over the entire surface.
The contact surface must be insulated from the connecting structure, which can be achieved through the use of insulating ceramic tiles or polyimide insulation films.
Fixing the shear slice via the side surface through clamping is not recommended.
Piezoelectric ceramic fiber slice
The piezoelectric fiber slice is a piezoelectric fiber composite material made up of piezoelectric fiber rods. When driven by voltage, it can produce various forms of deformation, such as transverse elongation, contraction, and 45° direction elongation and contraction. By adhering and bonding the piezoelectric fiber slice to a metal sheet, the metal sheet can be bent and twisted. Additionally, the deformation of the piezoelectric fiber slice can be used to generate a voltage signal, making it suitable for use as a sensor.
Notes on adhesive bonding and fixing:
We recommend using 3M or Loctite epoxy resin adhesive for the piezoelectric fiber slice.
The adhesive layer should be thin.
Do not apply adhesive to the side with the electrode.
Piezoelectric ceramic tube scanner
The piezoelectric ceramic tube scanner is a device that divides a piezoelectric ceramic tube into four quadrants with 90° electrode segmentation. Each quadrant is then separately controlled and driven to achieve X, Y, and Z axis piezoelectric ceramic scanning, with a scanning range of up to 82μm for the X and Y axes and 15μm for the Z axis.
Notes on adhesive bonding and fixing:
The adhesive layer should be as thin as possible.
Avoid applying adhesive across two electrodes.
The external structure needs to be electrically insulated from the electrode.
4、Case Study: He-shuai company
He-shuai company has accumulated rich experience in piezoelectric ceramic bonding and provides various types of epoxy resin adhesives to meet the diverse needs of customers.
