Vacuum Chamber Care

By Ian Livingstone - Queensland Manager

Most operators of vacuum systems are aware of the significance of proper component handling and assembly practices; however, there are a few basic hints that can be applied to further ensure optimum system performance:

• Keep the system dry – Venting your vacuum chamber with dry Nitrogen will minimize the absorption of water vapour within the chamber. Keeping the chamber door closed unless absolutely necessary will prevent the ingress of moist air into your chamber reducing the adsorption. Other than a leak, moisture in your vacuum system is the biggest “killer” of pump down time.
• Keep the system clean – When carrying out any work inside your chamber it is important that you wear gloves. Correctly sized Latex or Nitrile gloves will still allow you a sense of feel to carry out your tasks without dropping small parts. If there is a need to wipe the chamber out, use Isopropyl Alcohol and a lint free cloth making sure you turn and/or replace the cloth regularly to avoid spreading contaminants. Fingerprints and sweat left in the chamber will outgas and add a considerable gas load during your pump down cycle. If you’re “lucky” enough to have a chamber that you have to physically get inside – treat it like you would a clean room. Overshoes, gloves and disposable overalls……and if you get out of the chamber, replace them before you go back in.
• Watch your Surface Area – Some operators of deposition systems cover their chamber shields (as well as other items) with aluminium foil to protect the shields from condensate build-up with the view to saving time in cleaning the shields. This practice is fine so long as pump down time is not critical. Remember, 1 square metre of surface covered with aluminium foil = 3 square metres of total surface area. An increase in surface area = an increase in gas to be desorbed from the chamber surfaces = increased pump down time. In addition, there’s the torturous path for the gasses trapped between the aluminium foil and what it is covering. If pump down time is critical, obtain a second set of condensate shields and rotate them through during your maintenance cycle – you can then clean the used ones at your leisure and have them ready for the next change.
• Modifications Matter – If you need to modify the internals of your chamber pay particular attention to your choice of materials and methods of fixing. Treat all plastics with caution – there are plastics well suited to vacuum applications (PEEK is a good one) but their suitability will depend on what pressure you wish to achieve in your system as well as any temperature issues. The best material choice is stainless steel grades 316 or 304 (NOT 303). If your budget is tight and you do not have any corrosive or aggressive processes you can consider aluminium or brass. Steel is best avoided as it will corrode over time. When drilling and tapping holes for fasteners, avoid “blind” holes whenever possible. If you cannot avoid this, make sure the end of the hole is vented by either drilling a small hole through the centreline of the fastener or drilling a small hole into the base of the blind hole. Leaving blind holes un-vented with a fastener inserted creates a trapped pocket of gas (AKA ~ virtual leak) which could leave you tearing your hair out!

The above is merely scratching the surface regarding chamber care and to cover all possible topics would take many pages. If you have any questions or would like assistance with your vacuum system care, please don’t hesitate to contact your nearest AVT office on 1800 55 99 88.