surface texture - bruker...surface texture metrology why filtering and what does it do? 3/26/2015 21...

Surface TextureNon-contact Metrology for Industrial Applications

Outline

3/26/2015 2Bruker Confidential

• Introduction

• Brief overview of 3D microscopes based on interference

• Application to surface texture metrology

• Summary + Q&A section

• Tactile/stylus system users interested in exploring non-contact solutions

• Users looking for repeatable, reproducible metrology for surface texture from nm to µm scales

• Those unfamiliar with 3D optical microscopes based on interferometry and the capability of these tools for non-contact measurements

• Anyone who wants to make comparison to 2D tactile results when using 3D non-contact metrology for surface texture

Who Will Benefit?Intended Webinar Audience


IntroductionBruker Stylus and Optical Metrology


• Technology Leadership• 60+ Patents• 4 R&D 100 Awards• 6 Photonics Circle of

Excellence Awards

• Manufacturing Excellence• Lean, six sigma-based process• Rapid production ramp

capability• 10,000+ global installed base

Bruker Stylus and Optical Metrology is Part of Bruker Nano Group

IntroductionSpeaker

Matt Novak, Ph.D.Director, Technology and Applications Stylus and Optical [email protected]

• Joined Bruker March 2011 (4 years)

• Industry experience (~18 years) optical and systems engineering, fabrication and metrology

• Earned Ph.D. working in private sector metrology capital equipment (instrument design/assembly/test)


Outline


• Introduction





• Microscope with special objective used to provide sample height data• Optics scanned vertically, sample passed through focus• Computer system computes height from this scan data (image stack)

Bruker 3D Optical MicroscopesProduce Accurate 3D Image of Areas of Interest

Fundamental TechnologyPhase Shifting, White Light, or Coherence Scanning Interferometry


~

VSI

3D Microscope (Vertical Scanning) Image acquisition for VSI - example

Feature of

Interest

3/26/2015 Bruker Confidential 9

Live Video View


~ 40 µm

~ -110 µm

~ 150 µm range

Images can be displayed as a color look up table (e.g., red high, blue low)

…or displayed in greyscales to look like SEM as well

3D Microscope Surface ImagingWhat do 3D Images Look Like?

Outline


• Introduction




Surface Texture OverviewIllustrated by a walk over Picacho Peak, AZ, USA


Generally thought of as texture (deviation from ideal form)

Roughness 2D and 3D DescriptionsWell Defined…But No Spatial Information

3/26/2015 13

X

YZ“Surface Roughness”, Ra (Sa) is the average of the absolute

value of profile heights over a given length (area).

dxdyyxZA

SLxLy

a 00

),(1

LdxxZ

LR

L

a 0

)(12D

3D

Surface Texture (Surface Roughness, Waviness and Lay)ANSI/ASME B46.1, 2009, American Society of Mechanical Engineers, NY, New York 10017.

Bruker Confidential

3/26/2015 14

TextureSurfaces Have Different Characteristics and Scales

Histogram shows preponderance of surface is at lower heights Areal parameters to describe this surface property are useful

Texture: “The composite of certain deviations that are typicalof the real surface. It includes roughness and waviness…”

Bruker Confidential

3/26/2015 15

Roughness - Not Necessarily EnoughSurfaces Have Different Characteristics and Scales

These two surfaces have identical Ra (Sa)

Surfaces are different functionally

3D areal parameters (S-parameters) have been developed to capture the differences in a quantifiable way

Bruker Confidential

Machining Influence on TextureExample 3D Areal Images – NB Directionality

• Flat lapping/Reaming • Grinding

3/26/2015 16

• Horizontal Milling

• Vertical Milling

• Turning

Bruker Confidential

Texture ApplicationsConsiderations for When to Use 3D Areal Data


2D and 3D Roughness InspectionWhy 2D vs. 3D, Why Now?

• Roughness has been measured for decades via 2D cross section• What industrial surfaces lend themselves to 3D vs. 2D inspection?


Directional surface, small holes 3D regular surface Random surface elementsdue to turning, grinding, milling (e.g., honed cylinder) (e.g., bound abrasives)

2D: profile OK 3D: measurement provides 2D: position dependentMeasure 90°to texture additional information 3D measurement is required to characterize regarding hone, volume required to characterize

3D Image and Areal ParametersMore Information than 2D Cross Section, Faster


3D Areal Example Applications3D Data Relate to Properties of Interest


There are ISO norms for 3D parameters, filters (various parts, numbers):

There are analogous norms for 2D:

- 2

Surface Texture MetrologyWhy Filtering and What Does it Do?

3/26/2015 21

• A measurement system build a “representation” of the surface

• Must keep different instrument effects in mind when analyzing results (mechanical stylus filtering, FOV, lateral resolution, etc.)

• After surface is measured....• Data are reduced to a series of parameters (e.g. Ra, Sa)• The value of the parameters may/will depend on the instrument• Filtering defined according to “the rules” provides for standardized

analyses and best repeatability, reproducibility, and correlation

Bruker Confidential

FilteringRobust Gaussian Filter – Why?


Non-Robust

Robust

Filtered surface

Filtered surface Roughness data

Roughness data

Robust Filter Removes Filter Artifacts from Roughness Data

Raw 3D surface data


Filtering2nd Order Gaussian – Why?

0th Order

2nd Order

Filtered surface

Filtered surface Roughness data

Roughness data

2nd Order Filter Removes Edge Artifacts from Roughness Data

Raw 3D surface data

Consistent Filtering, Industry NormsAllows Proper Comparison Across Computations

3/26/2015 24

Unfiltered data UH

NISTBruker

Bruker Confidential

Many Manufacturers, Software ChoicesEmphasizes Need for Standardization


ISO norms filtering for computations

Enables good match across methods, materials

2D and 3D Surface Measurements 2D is Reliable, 3D is Data + Information Rich

• 2D amplitude and statistical parameters are great metrology tools, used since 1930’s to compute from tactile profilers• Reach into small bores, tight spaces (with limitations)• Many applications these work very well• For soft coatings, thin metals, polymers, can make impressions

• 3D areal (S-parameters) have been developed to take advantage of computational power and describe structure• Fast, non-contact

• Structural information has been shown to relate to functional surface performance (shafts, friction plates, seals, etc.)


ApplicationConsiderations When Comparing 2D to 3D Data

• Consider: Must compare, or is new metric which is repeatable, reproducible enough?

• In wide range of cases, 3D WLI data provides analogous results to 2D tactile profile data (Ra to Sa comparison)

• Scientific research show some differences seen –(Pavlicek, Vorburger, Leach, others)• Speckle, diffraction effects• Noise at edges, steep slopes• Slightly increase systematic noise due to

coherence3/26/2015 27Bruker Confidential

ApplicationConsiderations When Comparing 2D to 3D Data

• If one must compare between 2D and 3D for process reasons or to match current methodology

• Mitigation 1 - Use proper filtering, sampling

• Mitigation 2 – Use high magnification, proper evaluation area (stitching as needed, phase correct imaging – for Bruker – VXI in limit cases)

• Mitigation 3 – Use correlation function to bridge differences (values are highly repeatable)



New Computational MethodologiesPhase improves roughness accuracy

• Improved Computational Solutions for WLI• Combined use of amplitude and phase

information for improved center of mass computation

• Examples – CCI, SWLI algorithms, Bruker’s VXI, others…??

• VXI renders topography by…• Self-sensing smooth/rough

surface• Producing high accuracy phase

data surfaces• Reducing noise and artifacts on

rougher surfaces

ApplicationExamples Showing Comparison, 2D and 3D Data

• Show examples comparing tactile surface roughness and 3D optical surface roughness

• Show example results on traceable standards on tactile (stylus based) and non-contact (3D microscope based on WLI) systems

• Show result on precision sample deemed to be difficult due to nature of light / surface interaction


Tactile Roughness MetrologyIndustrial Stylus Setup

• Industry Metrology Lab – Calibration Report


NB: ISO CD 11562 – covers phase correct (Spline Gaussian) filtering

3D Microscope Roughness MetrologyOptical System Setup

• 10X objective magnification• 0.55X zoom lens

magnification

• Total magnification of 5.5X (1.2 mm x 0.9 mm for single field of view, 1.8 micron spatial sampling)

• Filtering with cutoff lengths (0.8 mm and 0.0025 mm), phase correct Spline within Vision software Stylus Analysis


3D Optical Result – 209.3 nmIndustrial Stylus Result - 209.4 nm


Average Ra, Vision Stylus Analysis = 209.3 nm

3D Optical Result – 573.4 nmIndustrial Stylus Result - 568.9 nm


Average Ra, Vision Stylus Analysis = 573.4 nm

3D Optical Result – 1.61 μmIndustrial Stylus Result – 1.62 μm


Average Ra, Vision Stylus Analysis = 1.61 μm

3D WLI Microscope and StylusComparison on PTB* certified standards


• PTB = Physikalisch-Technische Bundesanstalt• National Metrology Institute of Germany

PRECISION SAMPLEElectroformed nickel sine wave grating

Nominal Ra=0.100um, Period = 10um, PV=.3 umhttp://www.rubert.co.uk/Reference.htm

Measurements with 115X interferometric objectives

Camera sampling 640x480 pixels

March 26, 2015 Slide 37Bruker Confidential Information© Copyright 2011, Bruker Inc. All Rights Reserved

10um

55um

3D WLI Microscope and StylusComparison on Precision Sample

March 26, 2015 Slide 38Bruker Confidential Information© Copyright 2011, Bruker Inc. All Rights Reserved

Stylus profiler trace

2um tip Single 55 um profile

3D Microscope data section

115X 0.8 NA objective, VXISingle 55 um profile

Method Ra

Nominal 100 nm

Optical 105 nm

Stylus 108 nm

3D WLI Microscope and StylusComparison on Precision Sample

3/26/2015 39

Sa: Surface Average Roughness

Sq: Surface RMS Roughness

Both A and B have:Sa = 16.03nm and Sq= 25.4nm

Bruker Confidential

Example Surface Texture Uses Amplitude Parameters – No Spatial Information

3/26/2015 40

Rvk

Rpk

Rk

Bearing Ratio Curve

Mr1 Mr2

Spk = “Peak Height” .. First Region of contactSk = “Core Height”... “working” Region ..”Base”Svk = “Valley Depth” ... “Lubricant Retention Region”SMr1 = “1st Material Ratio”... “Peak Material”SMr2 = “2nd Material Ratio” ... “Valley Material”

Example Surface Texture Uses Functional Parameters – Derived via Abbott Curve

Bruker Confidential

3/26/2015 41

Sbi: Surface Bearing Index

)05.0(1

)05.0( hTrueheightqbi SS

For Gaussian, Sbi=0.61 , High Sbi = good bearing surface

Bruker Confidential

Example Surface Texture Uses Functional Parameters, Surface Bearing Index - Sbi

3/26/2015 42

Sci: Core Fluid Retention Index

qA

hVhVci SS vv

)()( 80.005.0

Vv(h) is the void Volume at h

Svi: Valley Fluid Retention Index

qAhVi SSv v

)( 80.0

For Gaussian, Sci = 1.56, smoother = smaller Sci

For Gaussian, Svi = 0.11, Good Fluid Retention = larger Svi

Bruker Confidential

Example Surface Texture Uses Functional, Fluid Retention Properties – Sci, Svi

3/26/2015 43

Honed SurfaceAngular Power Spectrum

Honed SurfacePower Spectrum

Std: Texture Direction of SurfaceAPSDFromDerivedLayofdirectionMajortdS

Honed Surface

Std Major = -70 degStd Minor = 71 deg

70 deg

Bruker Confidential

Example Surface Texture Uses Spatial Surface Parameters – Std

3/26/2015 44

Str: Texture Aspect Ratio

directionanyinACFofdecayslowestofLengthdirectionanyinACFofdecayfastestofLength

trS )2.0(

)2.0(

Sal: Fastest Decay Autocorrelation LengthDirectionAnyIntoACFofdecayfastestoflengthalS 2.0

LithoplateBrake Rotor

Bruker Confidential

Example Surface Texture Uses Spatial Surface Parameters – Sal, Str

3/26/2015 45

Sa for two surfaces within 10%

Sdr (Developed Interfacial Area) is different by 200%

Sdr is particularly useful for study of adhesion and coatings for functional surfaces

Bruker Confidential

Example Surface Texture Uses Hybrid Parameters – Sdr

3/26/2015 46

Svi can be target value for proper performance during manufacturing process

Bruker Confidential

Application – Honed CylinderFunctional Parameters

3/26/2015 47

Sbi 0.69

Sci 1.29

Svi 0.15

Sm 2.5 x 10-5

Sc 8.0 x 10-4

Sv 1.1 x 10-4

Unworn Bore Worn Bore

Sbi 0.70

Sci 1.32

Svi 0.11

Sm 8.3 x 10-6

Sc 1.5 x 10-4

Sv 1.8 x 10-5

1 mm

Note similar functional surface parameters for both cases

Bruker Confidential

Application – Wear of Cylinder BoreFunctional Parameters

3/26/2015 48

Shaft- UnwornSa 368nm

Sds 1130 /mm2

Ssc 49 mm-1 (radii 20m)

Sa 769 nm

Sds 247 /mm2

Ssc 6 mm-1 (radii 166 m)

Shaft- worn600 m

Bruker Confidential

Application – Journal Sealing SurfaceAmplitude, Hybrid Parameters

3/25/2015 49

Application – Bearing Wear Amplitude Parameters

• Roller bearings are investigated for end thrust wear

• Interferometry will easily measure the surface texture of 1-4 micro-inches (25 nm – 100 nm)

Bruker Confidential


Flexible Φ automation and cylinder stitching supported

Auto-locate measurement sites and“stitch” images to make larger format

Cylinder stitch showing sealgroove ~ 4 µm depth

Available on Contour with horizontal sample roller stage or NPFLEX Products

Application – Sealing SurfaceSpatial, Amplitude Std, Sz

51

• Crosshatch texture of machined surface affects lubrication and motion of piston within the cylinder bore

• Fold mirror bends optical axis to analyze sidewall surface textures

The Bruker fold mirror bends the light path to image the honed bore sidewall - the honing process results in a cross hatch texture shown here in 3D

Application – Cylinder Bore 3D Imaging for Spatial, Std, Hone Angle, Svi


Application – Cylinder LinerFold Mirror 3D Imaging

Views of fold mirror optics cover larger and smaller bores

9.11”

1.34”

Max Distance Inner Bore ~ 7.75”


Application – Cylinder Bore, LinerLong Reach Objective, 3D Imaging

Outline


• Introduction




Summary

• Introduced Bruker, SOM within Bruker Nano Group

• Overview, 3D microscopes based on WLI technique• Discussed surface texture, measurement

• 2D tactile systems compared to 3D non-contact• Discussed considerations when comparing techniques• Discussed methods, mitigations to make best comparisons

• Showed examples of 3D S parameters, applications• Questions? [email protected]

3/26/2015 Slide 55Bruker Confidential Information© Copyright 2011, Bruker Inc. All Rights Reserved

surface texture - bruker...surface texture metrology why filtering and what does it do? 3/26/2015 21...

Documents