Comparisons with Single-Point Diamond Machining — Part 1 ...1 Surface Studies for Electrodischarge Machining(EDM) with Electropolishing and Comparisons with Single-Point Diamond

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Surface Studies for Electrodischarge Machining(EDM) with Electropolishing and

Comparisons with Single-Point Diamond Machining — Part 1

PJChou- Note/ 96-001

July 10, 1996

I. Vendor information

1. Job shop= Ron Witherspoon, Inc. (RWI)., 430 Industrial St., Campbell, CA.

SLAC P.O. No.= US 550700-M.

Engineering drawing prepared by Mike Copeland(file= TESTDETAIL001 E1).

The geometric layout of the workpiece is depicted in the appendix.

Process= wire EDM with 4 mil brass wire coated with zinc.

2. Material= OFC, K= 264.3, from Chris Pearson.

II. Summary

The machining accuracy RWI held over a cutting length of 0.262" is about 1.5 µm.

For a longer cutting length of 0.744", the accuracy is about 9 µm. The smallest corner

radius RWI can machine is about 0.003", which is adequate for our project. It is apparent

that RWI can not give us the kind of machining accuracy required for making 90 GHz

structures.

The electropolishing process gives a mirror finish surface( 4 minutes processing

time ), also pits on the polished surface. Longer processing time( over 8 minutes ) does

not prove to be beneficial to us. The surface smoothness does not get improved, especially

near the step edge where the current density is higher. Some waviness on the metal surface

has developed due to excessive electropolishing treatments. The metal removal rate does

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not increase in proportion to the processing time of EP. Further tests with different

settings of electropolishing are needed in order to reduce the number of pits and eliminate

the surface waviness. The effects of pits under high RF power has yet to be understood.

III. Test Results

1. Summary of QC results from Eric Lundahl(metrology dept.) for the machining

accuracy achieved by RWI:

workpiece actual value nominal value deviation

TEST001- A 0.74439" 0.74400" 0.00039" ( 9.9 µm )

0.26205" 0.26200" 0.00005" ( 1.3 µm )

TEST001- B 0.74440" 0.74400" 0.00040" ( 10.2 µm )

0.26206" 0.26200" 0.00006" ( 1.5 µm )

TEST001- C 0.74442" 0.74400" 0.00042" ( 1.1 µm )

0.26208" 0.26200" 0.00008" ( 2.0 µm )

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TEST001-C

processing time= 4 min.

metal removal rate= 3 µm/ 4 min.

2. Metal removal rate of the electropolishing process:

• All workpieces are immersed in a 30-gallon tank with little agitation in the polishing

solution. The parameters used for all workpieces are given in SPEC. No. EP4( refer to

A. Farvid for details ). The voltage setting is 8 volts for all workpieces.

TEST001-B


metal removal rate= 4.5 µm/ 4 min.

TEST001-A



TEST001-A



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Appendix:

Stanford Linear Accelerator CenterEngineering Sketch

Engr: P.J. Chou

SK- PJ- TEST001

5- 8- 96'

Unless otherwise specified:all dimensions in inches. Tolerances: .X± .02, .XX ± .01, .XXX ± .005.XXXX± .0001Surfs finishes 32 max

ARDBHIGH GRADIENT STRUCTUREEDM + ELECTROPOLISHING TEST

Approvals

.7440 .744

.2620

~.5

~.5

.744

~1

~.5 ~.5

Top View Side View

End View

.744

NOTES:

This module is meant to answer the following questions:1) how much material has to be etched out for a class 8 surface after the EDM process?2) can we hit the 2 µm tolerance for EDM at SLAC?

ATTENTION : The EDM parameters used for this module have to be documented for the latter surface studies with electropolishing process.

~2 R .002

MATERIAL: OXYGEN-FREE COPPER (OFC)

this surface beenused for SEM pictures

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Part 2— After EDM but before electropolishing(EP)


July 10, 1996

• One damaged piece of Damped detuned Structure(DDS) for the NLCTA has been

used to compared with the EDM'ed workpiece. No surface polishing is performed on

both DDS component and the EDM'ed workpiece. The following results are for

workpiece "TEST001-C".

• scan001.tiff= 3-D surface profile scan by using a dynamic focusing optical

scanner(using red laser), provided by UBM, Co. in Sunnyvale. The height accuracy of

the scanner is ± 0.1 µm. The picture depicts the surface finish of EDM'ed copper.

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• scan002.tiff= 3-D surface profile scan provided by UBM. The picture depicts the

surface finish of single-point diamond machined copper. The sample piece is a

damaged X-band DDS component.

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• scan004.tiff= A close-up picture of the corner radius machined by wire EDM. We

asked for a radius of 0.002", and RWI achieved a radius of 0.003".

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• scan006.tiff= The cut edge of damping slot of the DDS component machined by

single-point diamond machining. The picture is taken by an optical microscope. The

burrs caused by the single-point diamond machining is clearly shown.

• scan007.tiff= Energy-dispersive X-ray analysis for a EDM'ed copper surface. There is

some zinc embedded on the surface.

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• scan008.tiff= A close-up look at scan007.tiff. The small bump indicates the existence

of zinc.

• scan009.tiff= SEM micrograph of EDM'ed copper surface.

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• scan010.tiff= SEM micrograph of EDM'ed copper surface. Note that two scraping

lines caused by the stylus of profilometer. Copper is too soft to be scanned by doing

contact measurements.

• scan011.tiff= SEM micrograph of single-point diamond machined copper surface.

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• scan012.tiff= SEM micrograph of the cut edge of DDS damping slot. The burrs

caused by the single-point diamond machining are clearly shown.

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Part 3— After EDM and EP( workpiece TEST001-C, 4 minutes EP )


July 10, 1996

• All pictures were taken for the workpiece "TEST001-C".

• scan013.tiff= Photograph of EDM'ed copper surface with EP. The small shining dots

are craters caused by oxygen bubbles created during EP. The large crater near the

bottom of the picture is artificial due to the inappropriate handling of workpiece.

Picture taken by an optical microscope.

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• scan015.tiff= Wire EDM cut corner radius after EP. The deformation seen in the

upper right corner of the picture is caused by the wire. The projection light was turned

off for a better edge definition. Picture taken by an optical microscope.

• scan017.tiff= Energy-dispersive X-ray analysis of EDM'ed copper surface after EP.

No residual zinc is found on the surface after EP.

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• scan018.tiff= Energy-dispersive X-ray analysis of EDM'ed copper surface after EP. A

close-up picture of scan017.tiff. Comparing with scan008.tiff, the bump indicating the

existence of zinc is gone. This means no zinc on the surface.

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• scan019.tiff= SEM micrograph of EDM'ed copper surface after EP. Those surface

debris are probably dust particles. Those pin holes were caused by oxygen bubbles

formed during the electropolishing process.

• scan020.tiff= SEM micrograph of EDM'ed copper surface after EP.

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• scan021.tiff= SEM micrograph of EDM'ed copper surface after EP.

• scan022.tiff= A close-up picture of the pin hole on the EDM'ed copper surface after

EP.

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Part 4 — After EDM and EP + AFM scan


July 10, 1996

• AFM scan was done by B. Kirby, 06/20/96', Job ID# 313.

• Workpiece= TEST001-C.

• Analysis summary: XPS surface analysis(< 4 nm information depth) of the EDM-

only piece shows zinc from the EDM wire and fairly high carbon level. The EP piece,

however, has no zinc left and a low carbon level. The surface topography was

examined with the AFM. There is an overall marked improvement in surface

roughness although there is still evidence of the EDM wire groves in the EP'ed surface.

Also apparent were shallow depressions in the EP'ed sample, of various diameters.

There are probably from surface bubbles formed during the EP process which were

not removed by proper agitation.

• 13122401.eps= 2-D topography of EDM'ed copper surface before EP, span 70 x 70

(µm)2.

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• 13122410.eps= 2-D topography of EDM'ed copper surface after EP, span 70 x 70

(µm)2.

• Line02.pict= Cross-sectional profile of EDM'ed copper surface before EP ( for

13122401.eps).

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• Line01.pict= Cross-sectional profile of EDM'ed copper surface after EP( for

13122410.eps)

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• 13122431.pict= 3-D topography of EDM'ed copper surface before EP, span 70 x 70

(µm)2.

• 13122430.eps= 3-D topography of EDM'ed copper surface after EP, span 70 x 70

(µm)2.

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central area

edge

Top ViewSide View

Part 5 — After EDM and EP( 8, 12 minutes EP )


July 11, 1996

I. Workpiece TEST001-B( 4 minutes EP ):

• Workpiece TEST001-B was treated with EP for 4 minutes, the same processing time

as TEST001-C. The only difference is that TEST001-B was not cut in half before EP.

After EP treatments, workpiece TEST001-B was cut away and examined by SEM.

We looked at areas depicted in the sketch below:

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• Scan035.pict= SEM micrograph of central area( 4 minutes EP ). Two deep holes

along the crystal grain boundary of copper were observed which may be caused by the

removal of hydrogen during the EP process.

• Scan037.pict= A close-up view of scan035.pict.

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• Scan038.pict= SEM micrograph of the central area of another half of TEST001-B( 4

minutes EP ). The crystal grain boundary is clearly shown.

• Scan039.pict= A close-up view of scan038.pict, the magnification increased by two

times.

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• Scan040.pict= A close-up view of scan038.pict, the magnification increased by 10

times. Five crystal grains of copper are counted in the micrograph.

• Scan041.pict= SEM micrograph of the edge area( 4 minutes EP ).

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TEST001-A step edge

side edge

Top View

• Scan042.pict= A close-up view of scan041.pict on the crystal grain boundary.

2. Workpiece TEST001-A( 8 minutes EP )



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• Scan023.pict= SEM micrograph of the step edge area( 8 minutes EP ). Notice the

surface waviness due to excessive EP treatments.

• Scan023a.pict= An inverted view of scan023.pict which gives a better view of those

holes.

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• Scan025.pict= A close-up view on the hole seen in scan023.pict. No sharp spikes

were observed. The magnification was increased by 10 times.

• Scan026.pict= SEM micrograph of the side edge area( 8 minutes EP ). No surface

waviness was observed.

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TEST001-A step edge

side edge

Top View


times. No sharp spikes were observed.

3. Workpiece TEST001-A( 12 minutes EP )



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• Scan029.pict= SEM micrograph of the step edge area( 12 minutes EP ). Surface

waviness due to excessive EP treatments is clearly shown.

• Scan029a.pict= An inverted view of scan029.pict which gives a better view of those

holes on the surface.

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times.

• Scan034.pict= SEM micrograph of the side edge area( 12 minutes EP ). No surface

waviness was observed.

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• Scan033.pict= A close-up view of scan034.pict.

Documents

Comparisons with Single-Point Diamond Machining — Part 1 ...1 Surface Studies for Electrodischarge Machining(EDM) with Electropolishing and Comparisons with Single-Point Diamond