Data
Overview
Verified Sapphire High Cut-Rates, Long Disc Life
Multiple high-speed wafer abrade tests were made on a 500 rpm lapper machine using 12” vitrified diamond agglomerate island discs to polish groups of 3 each 2” sapphire wafers.
Also, hundreds of sapphire abrade tests were conducted on single 2” sapphire wafers using 6” vitrified diamond agglomerate island discs at 1,000 rpm on a specialty shop milling machine set-up
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Test data from both series of sapphire wafer abrade tests verified the high cut rates of sapphire by the vitrified diamond agglomerate island discs and the island discs long abrade life.
12” Island Disc, 3 Sapphire Wafers, Abrade Test Data
A high-speed lapper machine using 12” vitrified diamond agglomerate island discs was used to polish groups of 3 each 2” sapphire wafers.
The wafers were wax bonded to a 6” wafer disc that was vacuum attached to the wafer head. Both the wafers and disc were rotated at 500 rpm for 2 minutes abrade times.
The 12” discs had 550 each of 0.186” diameter island structures containing 40-50 micron diamond-particle vitrified agglomerates.
The measured sapphire wear ranged from 0.006” to 0.012” with typical island wear of only 0.001 for each 2 minute abrade test.
6” Island Disc, 2” Sapphire Wafer, Abrade Test Data
A shop milling machine with a specialty wafer abrading set-up using 6” vitrified diamond agglomerate island discs was used to polish single 2” sapphire wafers.
This abrade set-up can be used to abrade 2” wafers at high speeds with sample 6” island discs sent to users to explore abrading of their 2” sapphire, SiC and GaN wafers. This can be done at their facilities to verify the high cut rates and explore use of the technology for their customers.
The 6” discs had 162 each of 0.186” diameter island structures containing 30 micron diamond-particle vitrified agglomerates.
The sapphire cut rate averaged 0.0026 inches per minute for 47 one and two minute abrade tests of 10 to 30 runs per test for a total test time of 60 minutes.
A total of 0.160” was abraded from a 0.200” thick sapphire wafer and only a total of only 0.040” was worn off the 0.061” islands.
The cut rate actually increased as the islands were worn down.
These many tests verified the very high sapphire cut rates and the very long island disc abrade life.
Click the image to see details.
Sapphire Wafer Abrade Test #41 Data, Island Disc #41 8-2-23
Keltech Engineering, St Paul MN, www.keltecheng.com
Vitrified diamond 30 um abrasive particles were molded into island structures that were bonded to a flexible 6.25” (50 mm) discs that was PSA attached to a 6” diameter hub wheel driven by a variable speed dc motor. A thick 2” diameter sapphire wafer was attached to the spindle of a standard Bridgeport milling machine. A weight on the mill spindle handle applied a constant abrading force to the wafer. Water spray was supplied to the rotating abrasive disc and a water guard was used to route the water and abrading debris flung radially off the rotating disc into a container. The porous beads between the islands provided a film of coolant water to the surface of the wafer to remove the heat generated by the abrading action. No hydroplaning of the wafer occurred at the high abrading speeds of 1,000 rpm.
The vitrified diamond agglomerate island disc provided very high and consistent sapphire wafer cut rates over the very long 61 minute cumulative abrading time for the island disc.
1. Wafer Abrade Test Conditions, 7-23-23 Abrade Test Date
a) Sapphire Wafer
1. Wafer thickness at start of abrade test, 0.170” (4.3 mm) approx.
2. Wafer thickness at end of abrade test, 0.010” (0.25 mm) approx.
3. Total wafer thickness worn off during all abrade tests, 0.1569” (3.985 mm)
b) Abrasive Vitrified Diamond Agglomerate Island Disc
1. Island disc diameter, 6.25” (50 mm)
2. Number of islands on disc, 162
3. Island sizes,
a.) 0.186” (4.72 mm) diameter
b.) Island height at start of abrade test 0.061”, ( 1.54 mm)
c.) Island height at end of abrade test 0.021” (0.5333 mm)
d.) Island height worn off during abrade test, 0.040”, (1.02 mm)
4. Annular band of islands, radial width of band on disc: 1.75”, (44.45 mm)
5. Total thickness worn off islands during all abrade tests, 0.040”, (1.016 mm)
c) Vitrified Diamond Agglomerates
1. Diamond Particle Size: 30 microns
d) Abrade Speeds
1. Disc Speed, 1,000 Rpm, CCW
2. Wafer Speed, 1,000 Rpm, CCW
e) Abrade Pressure: 10 psi, 30 lb abrade force on 2” diameter wafer
f) Water Spray Pressure: 12 psi
g) Abrade Test Time Durations
1. 60 second tests: 33 each (13 runs and 20 runs)
2. 120 second tests: 14 each (8 runs and 6 runs)
3. Total abrade time of all sequential abrade tests: 61 minutes
h) A total of 47 individual sapphire wafer abrade tests were made in direct sequence on the same sapphire wafer using the same vitrified diamond abrasive island Disc #41. These were the first wafer abrade tests conducted on the Disc #41. The abrade tests were stopped as the wafer was almost worn off the wafer wheel and the islands were substantially worn down on the Disk #41.
i) The sapphire wafer cut rates were consistently at about 0.0027” per minute ( 68.58 um per minute) for the full duration of all the 47 abrade tests from start to finish.
Likewise the islands wore down (eroded) at about the same rate of about 0.00065”per minute ( 16.51 um per minute) for the full duration of all the 47 abrade tests from start to finish
i) The wafer abrade tests were conducted in four groups over a period of two days. Two groups were for 60-second test runs followed by two groups of 120-second test runs. The island disc remained attached to the island hub disc plate for the whole sequence of 47 wafer abrade tests.
j) A 2” Starrett micrometer was used to measure 6 each ink marked islands around the circumference of the island disc that was PSA bonded to a 6” disc hub attached to a ½ hp dc motor mounted on the milling machine X-Y table carriage. The micrometer measured the top surface of the islands relative to the bottom surface of the disc hub. All measurements were averaged for each abrade test run and compared respectfully with previous test measurements.
A Mitutoyo 1” digital micrometer was used to measure the thickness of the sapphire wafer at 4 circumferential places where the wafer was epoxy bonded to a 2” hub wheel having a nominal hub thickness of 0.500”. The initial thickness of the 2” sapphire wafers was 0.200 “. All measurements were averaged for each abrade test run and compared respectfully with previous test measurements.
2. Wafer, Island Wear During Continuous Sequence Of Abrade Tests
A) First sequence of 60-second abrading tests, run #1 through run #13, (13 runs)
1. Avg. wafer height wear: 0.0354”, (0.090 mm)
2. Total island measured height before test # 1: 1.637”, (41.58 mm)
3. Total island measured height after end of test # 13: 1.627” (41.3 mm)
4. Total island height wear: 0.010”, (0.254 mm)
5. Avg. island wear per run:0.000769”, (19.53 um)
6. Cumulative abrade time at end of test sequence in group, 13 minutes
7. Avg. wafer cut rate per abrade test: 0.0027 inch per min, (68.58 um per min)
8. Remaining height of island after test #13: 0.051 “, (1.295 mm)
B) Second sequence of 60-second abrading tests, run #14 through run #33, (20 runs)
1. Avg. wafer height wear: 0.0490”, (1.245 mm)
2. Total island measured height before test # 14: 1.627”, (41.3 mm)
3. Total island measured height after end of test # 33: 1.614” (41.0 mm)
4. Total island height wear: 0.013”, (0.330 mm)
5. Avg. island wear per run:0.00065”, (16.51 um)
6. Cumulative abrade time at end of test sequence in group, 33 minutes
7. Avg. wafer cut rate per abrade test: 0.0025 inch per min, (63.5 um per min)
8. Remaining height of island after test #33: 0.038 “, (0.965 mm)
C) First sequence of 120-second abrading tests, run #34 through run #41, (8 runs)
1. Avg. wafer height wear: 0.0413”, (1.049 mm)
2. Total island measured height before test # 34: 1.614”, (41.00 mm)
3. Total island measured height after end of test # 41: 1.605” (40.77 mm)
4. Total island height wear: 0.009”, (0.229 mm)
5. Avg. island wear per 120 second run:0.00112”, (28.45 um)
6. Avg. island wear per 60 second run:0.00056”, (14.22 um)
7. Cumulative abrade time at end of test sequence in group, 49 minutes
8. Avg. wafer cut rate per abrade test: 0.0026 inch per min, (66.04 um per min)
9. Remaining height of island after test #41: 0.029 “, (0.736 mm)
D) Second sequence of 120-second abrading tests, run #42 through run #47, (6 runs)
1. Avg. wafer height wear: 0.0352”, (0.8941 mm)
2. Total island measured height before test # 42: 1.605”, (40.767 mm)
3. Total island measured height after end of test # 47: 1.597” (40.56 mm)
4. Total island height wear: 0.008”, (0.203 mm)
5. Avg. island wear per 120 second run:0.00133”, (33.78 um)
6. Avg. island wear per 60 second run:0.000665”, (16.89 um)
7. Cumulative abrade time at end of test sequence in group, 61 minutes
8. Avg. wafer cut rate per abrade test: 0.0029 inch per min, (73.66 um per min)
9. Remaining height of island after test #33: 0.021 “, (0.533 mm)
Liquid Slurry Polish Silicon Wafer Cut Rate Data
Liquid abrasive slurry production data shows that 57 micron boron carbide abrasive slurry particles take 90 minutes to remove only 90 microns (0.0035”) of material from silicon wafers.
In subsequent abrading, 3 micron diamond particles in a slurry take 40 minutes to remove 60 microns (0.0024”) from the silicon wafers. The final wafer polishing takes another 180 minutes.
These very slow wafer cut rates occur even though silicon is much softer than sapphire.
Substantial wafer material removal completed by the Keltech vitrified diamond agglomerate island discs occurs in minutes, not hours.
Liquid Slurry Polish Sapphire Wafer Cut Rate Data
Liquid abrasive slurry production data shows that 56 micron boron carbide abrasive slurry particles take 120 minutes to remove only 70 microns (0.0035”) of material from sapphire wafers.
Other data shows that 56 micron boron carbide abrasive slurry particles take 120 minutes to remove only 70 microns (0.0028”) of material from sapphire wafers.
In subsequent abrading, 3-6 micron diamond particles in a slurry take 45 minutes to remove 30 microns (0.0012”).
And, 80 micron SiO2 particles take 120 minutes to remove 15 microns (0.0006”).
By comparison, the Keltech fixed-abrasive 30 micron diamond vitrified agglomerates island discs remove 150 microns (0.005”) of sapphire in only 2 minutes.
Again, substantial sapphire wafer material removal is completed in minutes, not hours.
Watch Crystal Sapphire Liquid Slurry Polish Time Data
Past liquid abrasive slurry production information shows that the time to polish sapphire watch crystals can exceed 10 hours.
Again, by comparison, the Keltech fixed-abrasive 30 micron diamond vitrified agglomerates island discs remove 127 microns (0.005”) of sapphire in only 2 minutes.
Here, sapphire abrasive polishing is completed in minutes, not hours.
Vitrified Diamonds Cut 36 Grit Alum Oxide Disc
In other abrading tests, vitrified agglomerate 12”island discs, containing 40-50 micron diamond particles, quickly ground off the large 36 grit (0.019”) aluminum oxide particles on a 6” abrasive disc mounted on the wafer head of a lapper machine with less than 0.002” island structure wear.
The 36 grit aluminum oxide abrasive particles coated on the 6” discs are hard like the sapphire wafer’s aluminum oxide material.
These 36 grit abrasive disc abrading tests also verify the high aluminum oxide cut rates and the long abrade lives of the vitrified diamond agglomerate island discs.
The 6” abrasive discs in these tests are periodically mounted to the wafer head to quickly regrind the disc island surfaces to maintain precision-flat islands.
Percent Diamond Particles In Agglomerates
Other abrading tests with 30 micron diamonds were conducted with similar sapphire cut rate results as the 40-50 micron diamond discs.
A wide range of abrading cut rates and disc abrade life can be affected by many variables. These include: the percent of diamond particle content in the vitrified abrasive agglomerates, the quantity of agglomerates in the islands, the porosity of the islands, the size of the diamond particles, the island disc and agglomerate manufacturing processes, the abrade speeds and the abrade pressures.
Discs With Porous, Erodible Filler Between Islands
Additional abrading tests were also made using diamond abrasive agglomerate island discs with and without the added erodible porous layer of material between islands.
These tests consistently demonstrated the effectiveness of the porous layer between he islands to provide effective cooling of the whole abraded surfaces of sapphire wafers during high-speed abrading procedures.
It was also shown that the erodible porous layer between the islands does not reduce the cut rate of the diamond agglomerate islands and does not affect the prevention of wafer hydroplaning.