Ultrasonic & Megasonic washing and other cleaning techniques seem to have an upper limit in producing cleanliness. Some relevant quotes:
“… washing steps are not able to remove very small particles, such as those having a size of less than 0.5 µm.” [United States Patent 8,182,868 B2, Maxtor Corporation, May 22, 2012]. “
“Some prior systems have tried to minimize particles by cleaning in an aqueous or solvent solution but have not succeeded because the particle reduction plateaus.” [United States Patent 2004/0201926 A1, Seagate Technologies LLC, October 14, 2004]. “
The relationship between encapsulation and cleanliness is well documented. To laminate a component with a layer to contain particles not removable by washing was published as early as 1992 by IBM in its “Technical Disclosure Bulletin”, Vol. 35, Issue 7.
Several patents were filed by HDD manufacturers about immobilizing particulate by encapsulation of mechanical components, for instance, United States Patent 8,182,868 B2, Maxtor Corporation, May 22, 2012.
In order to study and verify the effectiveness of cleanliness by deposition, a laboratory was established. Liquid Particle Counter and relevant necessary equipment were acquired.
Complete LPC equipment.
132 kHz Ultrasonic Extraction Tank.
LPC housed in HEPA enclosure.
18.2 MΩ.cm ultrapure water generator.