Precise determination of inclinations is a critical requirement for Seagate Inc. (Bloomington, MN), a vertically integrated builder of hard disk and tape drives for data storage.
An outside vendor manufactures wafer substrates by a unique hot-pressing process and then supplies them to Seagate, which builds up its recording head structures on them. Seagate's own ceramic-grinding operation on the finished wafer is extremely sensitive. The 4.5-inch square wafers each worth thousands of dollars are ground down to 1,250 microns. If the sensitive wafer grinder used in the process is not set at precisely the required angle, the work becomes too costly, and time-consuming adjustments are required. This might take as many as 3 hours. Also, the labor costs for highly trained technicians becomes unsupportable.
Seagate's technology produces a variety of hardware and provides business intelligence, and storage and network management services. But, at the heart of its activities is the ability to make zero-defect recording heads assembled at plants in various domestic and overseas locations.
When the company purchased Fred V. Fowler Company's (Newton, MA) new Wyler Zerotronic sensor system, it substantially increased the efficiency of its tightly controlled and fine-tolerance processing operations. This digitized inclination sensor fulfills the critical function of accurately measuring the relative angle between the chuck holding the wafer and the grind wheel axis.
"The spindle angle", said Mike Kwilinski, a manufacturing engineer at Seagate, "is important because of the type of grinding used to produce the wafers. We must use a minimum spindle angle that best complements the hardness of the self-dressing grinding wheel. One of the keys in setting up the grinders is to measure a precise angle between the grind spindle and the work chuck."
If the spindle angle is too small, the wheels won't break down and will dull. When a 60-pound force on the machine is reached, the grinder stops and manual unloading is required for rectification. If the angle is too large, the wheel breaks down too quickly.
"With wheels costing $1,100 each, the ability for them to function correctly becomes a big factor". "The spindle angle also determines wafer thickness uniformity, which is absolutely necessary" said Kwilinski. He described the long and complex operation of adjusting a grinding machine, which takes it out of production for 3 hours and requires the attention of highly trained personnel. The 3-hour savings for each of the six or eight trials needed for each experiment is a critical factor in managing Seagate’s wafer production system.
"The Zerotronics sensors basically let us know where we're at, and this is a vital bit of information we need to set up the grinders correctly and to know where the wheel spindle is in space." said Kwilinski. The wheels are 11 inches in diameter with a band of abrasive 1/8-inch wide. Tolerance for every point on every wafer is ±8 microns. The wafers measure 4 1/2 inches square and 1 1/4 millimeters thick. It takes about 45 days to produce a wafer and requires more than 100 operations.
· Increased efficiency of tightly controlled
· Fine-tolerance processing operations
· Complete measurement accuracy
· Savings of 3 hours
The device handles both small angles with a high resolution as well as large angles. A temperature sensor mathematically compensates for changing environmental conditions, which improves measurement results.