Hot Plate Ettiquette
Hot Plates are widely used pieces of equipment at LNF. They are used for curing photoresist, polymers, suspensions, wafer dehydration, chemical processes, heat chemicals, etc. At the LNF, hot plate processes that will produce volatiles are vented inside laminar flow hoods or with snorkels. Hot plates that are used in chemical processes such as, wet etching, plating, chemical reactions, etc., MUST be located inside the wet chemical benches.
There are two type of hot plates used at LNF: chemical hot plates and wafer hot plates. Chemical hot plates have a ceramic, enamel or aluminum top, wafer hot plates have a flat top, made of aluminum or anodized aluminum. All new hot plate as well as the wafer hot plates are explosion proof. They can't heat to temperatures above 400C. Chemical hot plates have stirring and temperature control capabilities. The temperature is controlled via the feedback provided by a probe inserted in the liquid.
Users should observe the following common sense rules:
- Hot Plates are part of a bench ancillary equipment, they belong on a bench they should not be moved to other bench
- Protect the surface of the hot plate or your sample from contamination by covering the surface with aluminum foil found at the supply rack at LNF. Make sure you DO NOT cover the vent holes on the sides of the hot plate
- Make sure hot plate is a safe distance from combustibles.
- Never expose to high temperature a material on a hot plate that is NOT exhausted
- Always make sure the material or materials on the sample do not decompose or damages at the temperatures planned for the process (a.k.a temperature budget)
- New temperature probes are made of Inconel, be aware of this when using it in corrosive solutions, though this Ni/Fe alloy is used mostly because it is resistant to oxidation and corrosion
- If the process requires precise control of the temperature. It will be necessary to let the hot plate equilibrate at the desired temperature.
- Heating rate is affected by the heat conductance between the beaker (for example) and the surface of the hot plate. Make sure beaker is clean, the Al foil is flat. Al foil is not the ideal heat conductor but it is a good projection for the equipment and a barrier to cross contamination
- Most of the hot plates are equipped with proportional controller, before reaching equilibrium the temperature will oscillate around the set point. The overshoot will depend on difference of temperature between the initial value and the set point. Again, let it stabilize before placing your sample on the hot plate
- At the end of the process, let the hot plate cool down, remove the Aluminum foil and clean the hot plate.