ARCS EXTINGUISHED WITHIN MICROSECONDS
22/06/2011 TRUMPF Ltd
-€¦ the key to high quality plasma coatingPlasma coating is growing in popularity but it does have one significant drawback. The application of thin layers inside a plasma chamber is susceptible to electrical discharge or arcing and this can severely compromise the efficiency of the coating process. However, thanks to the development of a new arc switch by HÃœTTINGER Electronics, part of the TRUMPF Group, quicker detection of arcing by the power supply will soon be possible, enabling the condition to be suppressed more efficiently.
Plasma-based coating processes employ a mixture of gases to create plasma inside a vacuum chamber, inducing chemical reactions within the plasma. The by-products of this reaction are then deposited as a thin layer on the substrate. Often, and without any warning, arc strikes occur between the electrodes and these can damage the coating layers that have already been applied as well as the material that is being sprayed.
Arcs typically appear 40 to 50 times per second, but in extreme cases, they can occur several thousand times per second. To protect the surface being coated, the power supply needs to be able to detect arcing as fast as possible, so that the energy input can be interrupted and the discharge extinguished.
To detect arcs, an integrated electronic detector monitors the incoming electric current and voltage applied to the plasma inside the processing chamber. When a sudden drop in voltage and an increase in current beyond a set limit occur, it is safe to assume that an arc is occurring. In this case, the energy supply to the process is interrupted by deactivating the generator. However, the power supply cannot shut off its output instantaneously.
Even after being shut off, the generator will supply some residual energy to the plasma chamber, sustaining the discharge. Indeed, a few microseconds can pass before the arc is completely extinguished. And in this short time span significant damage can be inflicted on the substrate.
To optimise arc prevention HÃœTTINGER Electronics is developing a new electronic arc management system with the support of the German Government. This system is intended to interrupt up to 8,000 arcs per second.
The most significant innovation is the reduction of the residual power down to values that have not been attained before by the use of an electronic shut-off switch to disconnect the generator from the plasma chamber. Arcs will therefore be detected with improved sensitivity and extinguished within a few microseconds. This in turn will guarantee the highest levels of safety for the process and provide optimal coating results.
TRUMPF Ltd
President Way
Airport Executive Park
Luton
Bedfordshire
LU2 9NL
Tel: 01582 725335
Fax: 01582 399250
Email: sales@uk.trumpf.com
Web: www.trumpf.com
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