What are the tolerances for Ferroperm™ Piezoceramics materials?

At Ferroperm Piezoceramics, more than 95% of our piezoceramic production is specified by our customers. This means that most orders will come with a list of individual parameters and tolerances that will have to be fulfilled before the final inspection unit can approve the production, and parts can be shipped.

In most cases, it is not necessary to specify every single material parameter. Over-specification can lead to an unnecessarily difficult part to produce, making it more expensive than it has to be. To avoid this, we have developed a set of standard tolerances that we use if nothing else is specified. This set is separated into several different categories for most of which, our customers have the opportunity to specify so they meet the requirements of the application in question.
We advice that you bring up specific tolerance and parameter requests as early as possible in our dialogue so we can incorporate into the quotation and ordering in a timely manner.

For each individual material type in our portfolio, a set of tolerances has been defined. These tolerances are also used to verify any new material batches before it is released for regular production.

Dielectrical Properties	± 10%
Relative dielectric constant
Dielectric loss factor

Electromechanical Properties	± 5%
Coupling factors
Charge coefficients
Voltage coefficients
Frequency constants

Mechanical Properties	± 2.5%
Density
Elastic compliances

Note:
Catalogue values are based on measurements on standard geometries fulfilling recommended geometrical conditions. When parts differ from optimum geometrical conditions, one or more parameters may be affected, and larger variation than allowed for by the standard tolerances must therefore be expected. A very thin disc will for example have a lower dielectric constant than a standard geometry whereas very thick parts for example have thickness frequency constants in-between Nt and N33.

For the specific production, there will be a list of parameters regarding the size, geometry and electric behaviour which have to be fulfilled. The standard tolerances on these parameters can be summarized as follows:

	Standard tolerance	Minimum tolerance
Diameter of Discs, Rings, or Tubes
OD ≤ 10 mm	± 0.3 mm	0.01 mm
OD > 10 mm	± 3 %	0.01 mm
Length and width of Plates
L, W ≤ 10 mm	± 0.3 mm	0.01 mm
L, W > 10 mm	± 3 %	0.01 mm
Thickness of Rings, Discs or Plates
T ≤ 1 mm	0.03 mm	0.01 mm
T > 1 mm	± 3 %	0.01 mm
Focusing Bowls
Radius of curvature (R1 and R2)	± 3 % or ± 0.3 mm whichever is largest	1 mm, (dependent on total size)
Diameter	± 3 % or ± 0.3 mm whichever is largest	0.01 mm
Thickness uniformity	Max variation 2,5% or 0,025 mm whichever is largest	0.03 mm (dependent on total size)
Resonance frequency
Resonance ≤ 4 MHz	± 5%	± 0.5%
Resonance > 4 MHz	± 10%	± 1%
Capacitance	Fulfil dielectric constant for material	1 pF

Finally, other more subjective parameters will be measured and documented when relevant. Among these parameters are for example, internal cracks, solderability, electrode adherence, surface roughness, and edge resistance in wrap-around electrodes.

Based on these measurements, the final QA-Unit will document all productions on a Final Inspection sheet as shown below. With this sheet, a print-out of an impedance curve will be made and saved as a "finger-print" of that specific production, showing resonances, spurious modes etc.