What are the tolerances for Ferroperm™ Piezoceramic materials?

Our customers specify more than 95% of all piezoceramic production in Meggitt A/S. 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 all parameters, since over-specification often leads to an unnecessarily difficult part to produce, and therefore also becomes very expensive. We have therefore a set of standard tolerances that we use if nothing else is specified. This list is separated into several different categories. For most of these categories the customer however have the opportunity to specify other tolerances for the specific parameters which are most critical for that certain application.
If this is the case it should however always be discussed with Meggitt A/S and incorporated into the quotation and ordering as soon as possible in the dialog.

First of all there is of course the material itself, where a list of tolerances must be fulfilled in order to qualify as a "Pz21", "Pz27" or any of the other materials in our programme. A set of tolerances has therefore been defined for this. 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 then be a list of parameters regarding the size, geometrical parameters and electric behaviour, which have to be fulfilled. The standard tolerances on these parameters can be summarised as follows:

Standard
tolerance

Minimum
tolerance
Diameter of Discs, Rings,
or Tubes
OD ≤ 10 mm± 0.3 mm0.01 mm
OD > 10 mm± 3 %0.01 mm
Length and width of Plates
L, W ≤ 10 mm± 0.3 mm0.01 mm
L, W > 10 mm± 3 %0.01 mm
Thickness of Rings, Discs
or Plates


T ≤ 1 mm0.03 mm 0.01 mm
T > 1 mm± 3 %0.01 mm
Focussing Bowls
Radius of curvature
(R1 and R2)

± 3 % or ±3 mm
whichever is largest
1 mm,
(dependent on total size)
Diameter± 3 % or ±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 material1 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.