Data
Overview
Island Disc Sapphire Abrading Test Data
Numerous experiments were conducted where vitrified abrasive particle agglomerates were made and molded into island structures bonded to flexible polymer backing substrates to form raised island discs.
Multiple vitrified agglomerate island discs having different diamond abrasive sizes, agglomerates formulations and island disc constructions were used in hundreds of tests to abrade sapphire wafers at high abrading speeds on the abrasive lapper machine.
Verified Sapphire High Cut-Rates
The abrade test results verified very high sapphire cut rates and very long island disc abrade lives without wafer hydroplaning.
Typically, three each 2” diameter sapphire wafers attached to a 6” polymer wafer disc had 0.006” wear in two minutes of abrade time when abraded by a 12” diameter disc having 550 island structures containing agglomerates having 40-50 micron diamond particles when both the wafer disc and the island disc are rotated at 500 rpm and cooled with a water spray.
Other similar abrade tests had 0.012” sapphire wafer wear in two minutes. The 0.186 diameter islands typically only wear about 0.001” during the sapphire polishing test.
Abrade Test Data Graphs
Three 2” sapphire wafers were bonded to a polymer disc , attached to a wafer head and abraded with a 12” diameter disc having 550 vitrified diamond agglomerate islands formed in an annular band.The overall thickness at five positions of each of the wafers were accurately measured before and after abrading.
The material removed at each of the fifteen data points was calculated and plotted to easily visualize the wafer wear.
The floating wafer head was clamped to provide a “rigid mode” during these tests to focus on the wafermaterial removal rate.
Silicon Wafer Slurry Polish Time Data
Past liquid abrasive slurry production data from China shows that 57 micron boron carbide abrasive slurry particles take 90 minutes to remove only 90 microns of material from silicon wafers. In subsequent abrading, 3 micron diamond particles in a slurry take 40 minutes to remove 60 microns from the silicon wafers. The final wafer polishing takes another 180 minutes.
By comparison, the Keltech fixed-abrasive 40-50 micron diamond vitrified agglomerates island discs remove 150 microns (0.006”) of sapphire in only 2 minutes. The 150 microns of material removed far exceeds the amount of material required to polish a wafer.
Also, this very high cut rate occurs even though the sapphire is much harder than silicon.
Substantial wafer material removal is completed in minutes, not hours.
Sapphire Wafer Slurry Polish Time Data
Recent liquid abrasive slurry production data from China shows that 56 micron boron carbide abrasive slurry particles take 120 minutes to remove only 70 microns of material from sapphire wafers. In subsequent abrading, 3-6 micron diamond particles in a slurry take 45 minutes to remove 30 microns and 80 micron SiO2 particles take 120 minutes to remove 15 microns of the silicon material.
By comparison, the Keltech fixed-abrasive 40-50 micron diamond vitrified agglomerates island discs remove 150 microns (0.006”) of sapphire in only 2 minutes.
Again, substantial wafer material removal is completed in minutes, not hours.
Watch Crystal Sapphire Slurry Polish Time
Past liquid abrasive slurry production information from China shows that the typical time to polish the sapphire crystals used as watch crystals can exceed 10 hours.
Again, by comparison, the Keltech fixed-abrasive 40-50 micron diamond vitrified agglomerates island discs remove 150 microns (0.006”) of sapphire in only 2 minutes. The 150 microns of material removed exceeds the amount of material typically required to polish a watch crystal.
Here, sapphire abrasive polishing is completed in minutes, not hours.
100X Faster Sapphire Wafer Polishing
The recent liquid abrasive slurry production data from China shows that 56 micron boron carbide abrasive slurry particles take 120 minutes to remove only 70 microns of material from sapphire wafers.
By comparison, the Keltech fixed-abrasive 40-50 micron diamond vitrified agglomerates island discs remove 150 microns (0.006”) of sapphire in only 2 minutes. The 40-50 micron diamond particles are slightly smaller than the 56 micron boron carbide particles but they are somewhat harder.
The fixed-abrasive agglomerate vitrified diamond particles had a 120X faster sapphire cut rate than the loose-abrasive boron carbide slurry particles. They removed 150 microns in 2 minutes, or 75 microns in 1 minute. It took the boron carbide slurry particles 120 minutes to remove essentially the same amount of 70 microns of sapphire. The cut-rate ratio is 120:1.
For reference, other Keltech sapphire abrade tests using 40-50 micron diamond vitrified agglomerates island discs removed 300 microns (0.012”) of sapphire in only 2 minutes.
User Wafer Abrade Test Of Vitrified Island Disc
Vitrified diamond agglomerate island 6” discs can be supplied to users to conduct their own high speed abrading tests on small 2” sapphire, SiC or GaN wafers with a very simple test apparatus described on the Technology Page of this website.
Vitrified Diamonds Cut 36 Grit Alum Oxide Disc
In other abrading tests, vitrified agglomerate 12”island discs, containing few 40-50 micron (0.002”) diamond particles, quickly ground off all of 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 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. Tests also showed that different types of synthetic glass in the agglomerates were effective in supporting diamond particles against abrading forces.
A wide range of abrading cut rates and disc abrade life can be affected by the percent of diamond particle content in the vitrified abrasive agglomerates, the size of the diamond particles, the island disc and agglomerate manufacturing processes, the abrade speeds, the abrade pressures and the abrade test time duration.
Discs With Erodible Filler Between Islands
Additional abrading tests were also made using agglomerate island discs with and without the added erodible porous layer of material between islands.These tests consistently demonstrated the effectiveness ofthe porous layer to provide substantial improvements in cooling whole abraded surfaces of sapphire wafers during high-speed abrading procedures.It was also shown that the erodible porous layer did not reduce the cut rate of the agglomerate islands.
The white material shown on the worn 3-wafer disc shown in the photo is sapphire debris.