Lab Vacuum FurnacesPosted on:
Thermic Edge Ltd are very pleased to have delivered our latest MK3 2000°C top loading laboratory vacuum furnace, to a Semiconductor Fab in Japan. This latest revision of our 2000°C laboratory vacuum furnace has been improved with the addition of a Mitsubishi touch screen and plc. The touch screen now replaces the old style mechanical push buttons, that were situated on the front panel, giving much greater flexibility over process control, and improved diagnostics with dedicated interlocks screen and mimic screen showing the status of all interlocks, valves and pump.
Lab Vacuum Furnaces
The Thermic Edge lab vacuum furnaces’ greatest assets is its very compact size measuring 1140mm high (lid closed) x 1120mm wide x 720mm deep, light weight (300kg), very safe and very easy to use, even for unskilled operators, with interlocked touch screen, but still boasting high power with 20kw of DC switch mode power, giving fast ramp rates of under 30 minutes to 2000°C. The furnace uses 3 phase mains supply, reducing the need for a very high current supply, the furnace above required 208v 3ph x 95 amp supply. The furnace vacuum chamber is constructed from 304 Stainless Steel, and is fully water cooled, having a double skinned body with water cooled top and bottom flanges, lid and power feedthroughs. This enables the furnace to operate indefinitely without overheating.
Although the furnace is small and light, it still boasts a large all graphite hot zone, with the useable area inside the crucible measuring Ø180mm x 140mm. Access to the top loading hot zone is enabled by an electric lid lift, operated from the touch screen, which effortlessly swings the heavy water cooled lid out of the way, allowing the operator to easily load and unload the furnace.
After the furnace is loaded and the lid closed, the operator starts the pumping sequence by pressing the “Pump” button on the touch screen control. The furnace uses a simple Edwards RV8 rotary pump to pump the chamber to vacuum. To ensure all of the Oxygen is removed from the chamber, the plc runs a pump / purge sequence, using the vent gas to shock, dilute and dislodge oxygen from the internal surfaces of the chamber and hot zone, and then pump it away. The pump / purge sequence is repeated several times to ensure all oxygen is removed from the chamber, protecting the graphite hot zone from oxidation and subsequent degradation.
At all times safety is the number one priority, both safety of the operator and safety of the laboratory vacuum furnace hot zone. Being made entirely from graphite, the hot zone can be easily destroyed if exposed to Oxygen, when it is above 500°C. The PLC ensures that the furnace is fully interlocked, monitoring water cooling flow to all areas, chamber external temperature, process and vent gas connections / pressure, hot zone temperature, vacuum integrity, lid closed position and internal atmospheric pressure. The PLC will not allow the operator to carry out any function that could harm the operator or the furnace.
After the furnace has been successfully pumped to vacuum, processing is then enabled. The furnace uses either an RKC900 or Eurotherm 3504 programmable pid temperature controllers, to control the thermal processing cycles. Recipes can be created and stored, for heating, soaking and cooling cycles. Both controllers come with free OEM software, that allows the operator to easily connect a laptop or PC, so that thermal processing and monitoring can be controlled from a laptop, rather than the small front screens of the controllers.
The Laboratory vacuum furnace above had a maximum operating temperature of 2000C, but this same furnace design can reach a maximum temperature of 3000C if needed.
Gas processing is also enabled, with the VCR gas lines ensuring high quality gas delivery to the hot zone. The furnace shown here was supplied with two gas inlet lines, with needle valves and flow meters to accurately control the gas flow rate into the chamber. The output from the furnace to the pump, is also controlled with an Edwards speedy valve, allowing the pumping speed to be controlled manually. The needle valves and throttle valves enable the operator to easily control the hot zone pressure and gas flow rate. The lid clamp enables processing at slightly over atmospheric pressure (<0.5 bar max), and an automatic pressure relief valve ensures the chamber cannot be over pressurised, for safety.
As our customers always seem to have their own special requirements for gas introduction and handling, our furnaces gas lines and control can be very easily customised to suit our customers’ exact requirements. The flexibility of the Mitsubishi touch screen and PLC, makes it very easy to customise the gas flow control, and the addition of extra gas lines.
The Mitsubishi plc and touch screen software are written by Thermic Edge, enabling the control functions to be easily modified during installation, to provide the exact control method required by our customers.
The simple touch screen control is arranged in three screens:-
The Home screen – contains the furnace control buttons for Pumping, Venting, Gas admission, Power supply enable and Chamber lid operation. This screen also displays the chamber state, Vacuum or Atmosphere, and a list of interlocks and their state.
Indicator lamps below the switches show the state of the process, for that particular switch, or if the switch is enabled for use. Certain switches are interlocked out for safety at certain times. The process lamp indicators show Red if the process has not started, flash red and green when the process is running and green when the process is complete.
This simple interlocked control means the furnace can be operated in total safety by low skilled staff.
The Interlocks Screen – This screen displays all the furnace interlocks and their current state, and gives more information about the application of each interlock.
The Mimic Screen – This screen displays the input and output valves for the gas lines and pumping lines, plus the state of the rotary pump. It shows when valves are open or closed and if the pump is on or off. It also displays a list of interlocks and their state, plus the state of the vacuum chamber.
The mimic screen enables the operator to easily see the state of the laboratory vacuum furnace at any time.
Furnace pressure is displayed on the built in colour screen of the MKS wide range gauge. The operator can easily select the preferred pressure units using the gauge touch screen and can select from Pascal, Torr or Millibar.
The picture below shows the furnace successfully installed in a class 1000 clean room in Japan.