How is your hard disk made?

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