With the current trends in hard disk drive design, contamination control of all components, including pressure-sensitive adhesives (PSAs), is more critical. Design engineers must address several key questions when specifying a PSA into components for hard disk drive assemblies. William Stratton, market development manager at Adhesives Research Inc. (Glen Rock, PA) offers these guidelines:
What to ask
- How clean is the PSA?
- What is the level of outgassing under conditions typically experienced in the drive? What are the outgassing components?
- Is the PSA polymerized using acrylic acid as one of its monomers, or is it acrylic acid-free?
- What are the levels of extractable anions?
- Is organotin present?
- Is this an "industrial-grade" PSA or one designed specifically for hard disk drive assemblies?
- How is the PSA cleanliness controlled by the manufacturer?
- Are all production lots tested for total outgassing?
- Does the component supplier demand Certified Test Reports from the PSA manufacturer?
- Do these reports include outgassing data?
Why it's important
"Cleaner" adhesives are now required. Low outgassing and minimal ion contamination are musts. High volatile organic content by weight contributes to higher outgassing, which leads to corrosion. Acrylic acid, causes head corrosion and media fogging. Plus, release liners catalyzed by organotins, have been cited as a cause of hard drive failures.
Industrial-grade PSAs were not designed with the needs of the hard disk drive industry in mind. For example, many were developed for applications in the automotive, appliance, consumer, or other general industrial assembly applications.
Most PSA manufacturers do not measure the outgassing characteristics of industrial-grade adhesives on a lot-to-lot basis. While an individual industrial-grade PSA sample may pass the outgassing specification at an HDD manufacturer, there is no guarantee that all lots will pass.