Newton, MA--Better, faster, cheaper. Like most everything, attaining this goal comes with a price. Take the computer hard drive industry for example. Technological gains in recent years--such as the use of magnetorestrictive (MR) head technology--have enabled greater memory capacity. The tradeoff: increased potential for contamination. (see sidebar)
Prompted in part by a growing industry concern with microcontamination, the Santa Clara, CA-based International Disk Drive Equipment and Materials Association (IDEMA) is establishing standards aimed at eliminating microcontamination in hard disk drive (HDD) assemblies.
IDEMA's Microcontamination Committee, in existence for two years, receives input from members and volunteers in the hard drive industries in Japan, Singapore, and the U.S. The Committee comprises two sub-committees--one focused on terms and definitions, another on test and methodology.
"You have to be realistic when setting standards," says Arnold Toxen, consultant and Chair of IDEMA's Terms and Definitions Committee.
"It's important to define what 'contaminant' means, types of contaminants, what harmful effects they might have, and units. Plus, specifying contaminant levels means nothing unless you also define the test procedure by which you make the measurement," he says.
The Committee currently has several proposals addressing such issues up for vote. Down the line, IDEMA hopes to set specifications on specific contaminants. "It's an on-going process," acknowledges Toxen.
One thing is certain, microcontamination is not new, and it isn't disappearing any time soon. "As disk drives get more sophisticated, the problems get exacerbated," Toxen says. "And as microcontamination becomes more of a problem, disk drive manufacturers will set more stringent specifications on products made for them--from disks to motors."
Moving ahead. Even without definitive standards, some suppliers are already taking steps to end microcontamination. Take the Glen Rock, PA-based adhesive manufacturer Adhesives Research Inc., for example.
The company's pressure-sensitive adhesives (PSAs) are widely used to bond components on or in HDD assemblies. Components fabricated with PSAs include environmental seals, such as warranty and clockhead seals; identification labels; and bar code parts. PSAs also bond various filters within the hard drive housing, as well as flexible circuit cables, vibration insulators, and magnets.
Industrial-grade pressure-sensitive adhesives have performed satisfactorily for many years in HDD applications. Now, "cleaner" adhesives are required.
Specifically, very low outgassing characteristics and minimal ion contamination are musts, says William Stratton, market development manager at Adhesives Research. The problem: industrial-grade PSAs typically contain between 0.5 and 2.5% volatile organic content by weight, which contributes to high outgassing, which in turn leads to corrosion.
In addition, many industrial-grade PSAs use acrylic acid in the adhesive polymer backbone. It increases adhesion to polar surfaces such as metals and glass, and can be used to cross-link the adhesive polymer to increase the cohesive strength of the PSA, Stratton explains. Despite its benefits, however, acrylic acid causes head corrosion and media fogging. Plus, some industrial-grade PSAs incorporate release liners catalyzed by organotins, which have been cited as a cause of hard drive failures.
Potential solution. Adhesives Research has developed an acrylic acid-free, low-outgassing PSA technology that employs a PSA polymer known as AS-123. A proprietary alternative chemistry is used to achieve peel adhesion and cohesive strength. And the polymer contains minimal anion content, reducing potential corrosion.
Pressure-sensitive transfer adhesives and label stocks that use this new acrylic acid-free polymer typically exhibit outgassing values of 0.15 to 0.20% when measured after a 2 hour exposure at 100C in a vacuum oven. "This compares favorably with industrial-grade PSAs often specified into hard drive assemblies," says Stratton.
In addition, transfer adhesives and label stocks manufactured using the AS-123 technology use no organotin catalysts in either adhesive or release coating curing. And the technology withstands the environmental conditions associated with electronic applications with no degradation in performance, Stratton says.
Overall benefits, he claims: Eliminating acrylic acid from the entire PSA manufacturing process reduces potential media fogging and head corrosion. Minimizing volatile organic content decreases failures related to chemical contamination due to outgassing. And the use of chemistries with minimal ion content and no organotin prevents other sources of chemical contamination from affecting drive performance. "Each of these factors helps extend the Mean Time Between Failure for the HDD assembly, increasing reliability," Stratton says.
So far, the AS-123 PSA technology has been used to reduce microcontamination hard disk drives that use MR head technology. Applications include tape seals and HSA barcode labels. It is currently being evaluated for flexible circuit bonding and filter bonding inside the HDD assemblies.
While the PSA technology is a step in the right direction, IDEMA knows it has a long way to go. "Everyone in the industry is aware of the problems. Once there's a sanctioned standard, there will be more pressure on them to conform," says Toxen. "For now, I think we're heading in the right direction."
For more information Call 1-800-828-6344 x011 and enter the product code.
Microcontamination and IDEMA Product Code 4269
PSA technology from Adhesives Research: Product Code 4270