Hard disc makers demand more from cleaning

Key changes in hard disc specifications - such as GMR heads and a reduction in flying height from 1 micron to near contact - put pressure on cleaning system developments.

The hard disk industry has just celebrated its 50th anniversary.

While their capacity has steadily increased over the years, their size has dramatically reduced.

A key technology which has contributed to this improvement is the development of GMR heads and a reduction in flying height from 1 micron to near contact.

This change in specification has placed even greater emphasis on the effectiveness of cleaning systems and their ability to satisfy not only low levels of ionic contamination but also to remove particulates down to sub micron level and to remove organic residues.

Levels for both organics and ionics now approach the detection limit for head space and ion chromatographic equipment.

Now future developments could be claimed are as dependent on the quality of cleaning as technological advances.

Guyson asks: imagine what sort of cleaning system you would have to use to remove solid particulates and both volatile and non-volatile organic residues down to ppb (parts per billion) levels, working around the clock on a 97% up time and cleaning around 40 million hard drive components including base castings and top covers per month for one of the world's largest technology companies? The answer would be a Guyson 'Supercleaner'.

These high volume, high quality aqueous precision cleaning systems have been designed to meet the rigorous quality standards laid down by the 'International Disk Drive Equipment and Materials Association' (IDEMA).

These standards include the removal of sub-micro contamination from disk drive components.

This with the ever higher storage densities involved means that such high levels of cleanliness quality are proving critical to the performance success of the disk drives.

Aqueous washing of precision disc drive components has been the industry standard for the last ten years; therefore, the cleaning process is well established and normally includes an ultrasonic immersion cleaning tank designed for use with water based cleaning solutions followed by deionised water rinsing and with hot air and vacuum drying.

This type of multi-stage cleaning process is fully automated to ensure total control of all critical process parameters.

* The Supercleaner - all Guyson Supercleaners have to pass exhaustive testing to ensure continuous running for 23 out of 24h/day - one hour is set aside for machine clean down.

This aqueous precision cleaning system will remove organic residues down to ppb (parts per billion) levels and particulate contamination to 0.1 micron from computer hard disk drive (HDD) components.

To achieve these extreme standards of cleanliness, the Supercleaner provides a multi-stage aqueous wash and high purity deionised water rinse process using high frequency ultrasonics selectable at 35kHz, 70kHz, 130kHz and 200kHz, and a high throughput in-line tunnel type hot air dryer.

* Ultrasonic frequency - the original operating frequency of 40kHz is now considered to be too low for sub micron work, as it results in a degree of cavitation or resonance which may cause damage to sensitive components such as GMR heads.

Effective removal of sub-micron particles at 40kHz has also been questioned.

It can be proved mathematically that particles smaller than 0.5 micron require frequencies >100kHz to dislodge them.

Whilst some laboratory scale trials claim improved sub-micron particle removal at higher frequencies, the practical difficulty is to identify a single frequency which will remove a wide range of particles, say 0.5 micron to 50 micron, which would typify production conditions.

Therefore new Guyson microprocessor controlled Primewave generators have been developed to provide switchable frequencies and power levels 70 or 130kHz with frequency sweep and fully adjustable power output (Watts), all programmable within a single cleaning or rinsing cycle.

* Dynamic tank features - whilst it is essential to remove contamination both particulate and soluble from a batch of parts, it is just as important to maintain the cleaning and rinse tanks at a controlled level of cleanliness compatible with preset component and water cleanliness standards.

Guyson Supercleaner wet tanks are crevice free, full 30mm radius corner construction with four-sided flat weir overflow.

The 316L stainless steel is electro polished with chrome plated ultrasonic tank base to eliminate sub-micron entrapment and the possibility of secondary particulate generation due to cavitation erosion.

Filtration systems are sized to allow the total tank volume to be filtered down to 0.1 micron at high flow rates equivalent to the tank volume every two minutes.

A specially designed sparge pipe return determines the most effective flow characteristics to eliminate liquid dead spots.

All pipework is polypropylene with IR welded joints to ensure the highest chemical compatibility and again avoiding crevices.

Vertical agitation, typically 50mm x 30 strokes/min of batch load parts during the cleaning cycle, provides improved flushing of the cleaning and rinse solutions.

* Operation sequence - a typical Guyson eight-stage Class 10 cleaning system will process components with tanks one and two pre-washing and rinsing with Primewave 35/70kHz or 70/130kHz ultrasonics and micro filtration.

Tanks three, four, five and six comprise the final rinse with cascade rinsing also including Primewave 70/130kHz and 130/200kHz ultrasonics and micro filtration.

Stage seven is a three stage hot air tunnel dryer, double basket capacity with HEPA filtration and dynamic air flow control, perfect for high throughput on robust mechanical components.

A variation is available with double hot air dryer and vacuum dry which is more suited to delicate components or with difficult to dry blind holes.

The whole process is fully automated using up to three Autotrans two-axis work transporters.

The transporter heads are cantilever mounted, include servo type motors and are fully programmable with intelligent automatic program selection feature.

Particular attention has been paid to mechanical design for Class 10 cleanroom use.

To complete the Supercleaner specification a windows PC based supervisory control and data acquisition (SCADA) system monitors all critical process parameters such as temperature, flow rates and water quality.

These are displayed in spreadsheet format and may be recorded for batch traceability purposes.

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