Maintaining an ultra clean environment is the primary priority in areas such as the fabrication of semiconductors. The enclosed spring of the Turcon Variseal Ultra-Clean from Trelleborg Sealing Solutions eliminates dead space and the consequential risk of contamination. Specifically in semiconductor manufacture, it is proven to solve the problem of ion extractables in wafer processes.
Variseal is commonly used in processing systems. One of the main reasons for this is that Turcon, the Trelleborg Sealing Solutions proprietary PTFE based material, offers compatibility with virtually all chemical media. It also has superior wear resistance, unrivalled friction characteristics and can withstand extreme operating temperatures. PTFE, though, has no elasticity, which means that Turcon Variseal is energized with a spring fitted into the seal profile.
In most applications the open spring of the standard Turcon Variseal is acceptable. However, where cleanliness is paramount, the area of dead space around the spring where bacteria can potentially be caught can pose a risk of contamination. Specifically in semiconductor fabrication there is the possibility of metal extractables entering the system. These can migrate into the wafer and cause short circuits, which alter the optical or electrical properties of a semiconductor.
Trelleborg Sealing Solutions recognized the need to offer an enclosed Turcon Variseal design. Considerable research and development work has resulted in the Turcon Variseal Ultra-Clean. In this unique design, the spring required to activate the seal is fully enclosed within a Turcon case. This for manufacturers of food, beverage and pharmaceutical products ensures there is no dead space within the seal, guaranteeing that bacteria cannot accumulate, avoiding the risk of contamination.
Numerous tests were undertaken to establish the best material for the Turcon Variseal Ultra-Clean. This proved to be Turcon MF, a material which has been specially engineered for super clean environments. Based on ultra clean technology, Turcon MF compounds are produced from high purity PTFE grades and additives. Their smooth finish, with high gloss and low porosity, avoids the risk of contamination build up and reduces particle shedding.
It also withstands high pressures and has a vacuum capability of 10-9mbar x l/s in air.
Specifically to semiconductor manufacture tests show that Turcon MF compounds have extremely low ion extractables. Test samples of Turcon MF1 were immersed in ultra-pure de-ionised (UPDI) water at a temperature of 85degC (185F) for a duration of one week. According to SEMI standard F57-0301 the leach out of 20 of the most hostile cations was measured. In terms of parts per billion (ppb), Turcon MF1 demonstrated a leach out of 80 percent less than that of a standard perfluoroelastomer (FFKM) material.
"Turcon Variseal Ultra-Clean is a revolutionary seal," says Stuart Moares, Product Manager for Trelleborg Sealing Solutions Bridgwater, where the seal was developed. "We know that it will provide real benefits to processing companies globally. It offers the ultimate in cleanability and cleanliness for a spring-energized PTFE based seal and solves the problem of ion extractables from seals contaminating wafer processes."
