by July 7, 2000 0 comments

After the CPU, the hard disk is perhaps the most vital
component of your computer. Over the years, it has seen significant improvements
in the amount of data it can store, and in how fast it can retrieve the data.
But through all these years, its basic mechanical structure has remained more or
less the same.

Under the case of each hard disk, you’ll see a PCB board.
This houses the electronics that makes the drive do what it is expected to do.
Inside the casing, the bulk of the space is occupied by one or more platters
mounted one on top of the other, on a spindle on a motor. The data is stored on
magnetic material on these platters. And finally, there’s the
reading/recording head, and its drive mechanism. Each face of each platter will
have its own independent head.

Different disk manufacturers could be using different processes. What’s
detailed here is the process followed by Seagate, as seen at their Recording
Media Operations at Ang Mo Kio, Singapore. At Seagate, hard disk manufacturing
is spread across different factories, which are situated in different countries.
The platters are made in one plant, and they’re prepared to hold data in
another. The reading head is produced in another, while the final drive is
assembled in yet another.

Here, we’ll look at how the individual platters are
prepared for holding the data.

The disk platter is a finely balanced piece of work, finished
to microscopic tolerances. Take the smoothness of its surface, for example. The
drive head rides a cushion of air microscopic distances above the surface of the
platter. So, the surface can’t be too smooth, or the drive head will end up
sticking to the platter. It can’t be too rough either, or the head will end up
getting caught in the microscopic bumps on the surface.

Almost all the work takes place in clean rooms, where the amount of dust in
the atmosphere is kept very low, and is strictly controlled and monitored.
Remember the Pentium bunnies in the old Intel ads? Well, in some of the clean
rooms, the workers are similarly dressed, to avoid contamination of the material
they’re working with.

The platters come to the factory, packed in shipping
cassettes. When they get taken in for production, they’re transferred to what
are called process cassettes, which are nothing but carrying cases, as shown
here. They move from one process to another in these cassettes. When the
cassettes have to move from one room to another, they do so on automatic guided
vehicles. This is to prevent contamination due to human contact.

The first step in getting the platter ready to record data is Mechanical
Texturing. Here, roughness and grooves

are applied to the polished surface of the disk. This helps
in depositing magnetic material on the disk later.

During the texturing process, small amounts of nickel get
removed from surface of the disk and remain there. To remove this, the platter
is now washed. This process is called Oliver Wash.

If you look at a platter removed from a finished hard disk,
you’ll see a 2-4 mm band near the center, much like the one you see on the
silver side of a CD-ROM. This is the Laser Texture, the landing area where the
read head comes to rest.

Laser Texturing is done now. The landing area is created by
creating microscopic bumps, using a laser. This prevents the head clinging to
the disk surface when the disk is spinning.

Time for a final cleaning of the platter. This is done using
a series of ultrasonic, megasonic and Quick Dump Rinse (QDR) steps. At the end
of the final clean, the platter has an ultra-clean surface and is ready for
depositing of magnetic media–a process known as sputtering.

The platters now move to a Class10 clean room, in an automatic guided
vehicle, described earlier. Sputtering is perhaps the most critical in the whole
process of creating a recording media.

Magnetic film is coated on to substrates that are then
transferred on to the platter.

There are two types of sputtering–pass-by sputtering and
static sputtering. In pass-by sputtering, disks are passed inside a vacuum
chamber, where they’re bombarded with the magnetic material. Static sputtering
uses smaller machines, and each disk is picked up and sputtered individually.

The sputtering material is prepared in what are called bombs, which are
loaded onto the sputtering machine. The bombs are vacuum chambers with targets
on either side. The platter is lifted into the bomb and is bombarded with the
magnetic material. Though the process uses bombarding, my guess is that the name
bomb comes from the shape of the chamber, rather than the process.

Sputtering leads to some spikes being deposited on the
platter, which need to be removed. To ensure that this doesn’t lead to the
scratching of the platter, lube is applied to the platter surface now.

Once lube has been applied, the platters move to the buffing
stage, which is basically polishing the disk while it spins around. After
buffing, the platter is wiped and clean lube is evenly applied on the surface.

The disk is now ready, and needs to be tested for quality.
This is a three-stage process. First, a burnishing head passes over the surface,
removing any bumps (asperities as the technical term goes). The glide head now
goes over the disk, checking for remaining bumps if any. And finally there is
the Cert head (the certifying head) that checks the surface for manufacturing
defects and also measures the magnetic recording ability of the platter.

Platters that pass the quality test go into final packing.
They’re vacuum packed onto caddies. These are sent to the disk drive
operations plant, where they’re assembled into hard disks.

Next month, we’ll take a quick look at what goes on there.

Krishna Kumar at Segate Recording Media Operations, Singapore with
inputs from Philip J Maher, Vice President, Recording Media Operations,
Seagate

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