A quest for improved disk drive cleanliness standards
Santa Clara, CA — The International Disk Drive Equipment and Materials Association (IDEMA) is on a quest for better microcontamination control standards. Just how much will be gained by increased cleanliness, however, is hard to judge because it`s difficult to uncover the impact of today`s microcontamination.
“How many companies want to say we lose 10 percent of the drives during build or 20 percent or whatever? Those are not the kinds of things people want to talk about,” notes Arnold Toxen, an independent consultant to the disk drive industry and co-chairman of the IDEMA microcontamination committee.
Since mid-1995, the microcontamination committee has been meeting about every six weeks. As is the case in many trade organizations, the committee members are volunteers and the meetings are open to interested parties. During the last 2.5 years, nine standards have been hammered out. These range from definition of microcontamination terms to recommended reporting and testing practices to explanations of the effects of contamination.
The committee is also working on six new standards that cover such topics as correlating non-volatile residue tests between independent labs. Such standardization is important if test results are to be compared. The challenge is made more difficult because IDEMA is an international organization, with offices in the United States, Japan, and Singapore. Member companies are just as far-flung. The widespread nature of the industry is one reason why committee members don`t approve standards blindly.
“It`s not required, but if they`re going to approve the standard, most of the people involved with the committee will take the test back and try to run it or compare it to a test that they`re already running,” explains Seth Ayers, standards manager for IDEMA.
Ayers reports that of the six new standards in development, one is close to final approval. The others, which include special cations analysis, ionic contamination analysis, general outgas test procedure by dynamic headspace analysis, SEM-based particle analysis, and aqueous cleaning systems, are in various stages of writing or balloting.
While IDEMA was founded in 1986, it`s only in the past few years that the organization has had a microcontamination committee. This increased interest is being driven by two factors. One is the need to increase product reliability and hence the meantime before product failure. The other is the ever-decreasing flying height of the read/write head above the magnetic media and the disk surface. Closer contact leads to faster data transfer and improved data storage, but this is not without a price.
“We`re talking about microinches and going down to contact or pseudo-contact recording,” remarks Toxen. “We`re really down in the micron range and in fact we`re heading toward the submicron range there in terms of the particles that are a problem.”
Toxen reports that unlike other cleanroom products, larger particles are not always a problem for disk drives. That`s because if a particle is too big the flying head will push it out of the way. Conversely, if a particle is too small, the head will not be affected by it.
However, also unlike other cleanroom products, a disk drive is made up of a number of components. There`s the disk itself, which is a platter coated with magnetic recording media and a thin layer of lubricant. There are mechanical motors that spin up the disk and move the head. There are plastics and other polymers that are in the disk casing and body. As a result, there are a number of sources for particulates and contaminants. These can come from flakes of magnetic material, from polymer outgassing, or from the various lubricants used.
Such a wide variety of contaminant sources leads to an array of failure mechanisms. These range from corrosion of components due to molecular contaminants to loss of data due to magnetic flakes. For the most part, Toxen believes, these problems do not show up during initial testing. It`s only after the drives are in the field that the failures occur.
While IDEMA has been creating industry specific standards, other organizations have also been at work on cleanroom criteria. Among these are the efforts by the Institute of Environmental Sciences and Technology (IEST/Mount Prospect, IL). While there are disk drive companies that are part of both IDEMA and IEST, there is little overlap between the documents produced by the two groups. That may not be a bad thing.
“They deal with the process. We don`t necessarily deal with the process of producing product,” says Bob Spector, technical vice president for the contamination control division of IEST. “You can get your specifics from one place but if you need a detail about the whole cleanroom environment you may have to go some place else [like the IEST].”
For disk drive manufacturers, such generic documents could be quite helpful. For IEST, industry specific standards can be valuable supporting information. Such an arrangement may be part of what`s needed to produce cleaner disks.