Hi, We need help from specialists on vacuum evaporation, your advice will be very appreciated.
We use a vaccum metalizer for Al coating, recently, its evaporating current tends to be unstable(under the same parameters setting) and the Al melting status was uneven on each tungsten wire. we are trying to find the reason.
We have done:
a. Cleaned all parts in the evaporating chamber but the status had no improving.
b. Measured the both voltages of input and output on the evaporation transformer, they were meeting the set ratio and were always stable.
c. Separately measured (with mOhm meter)the both resistances on each tungsten wire and each section on the holder in chamber, they were roughly consistent.
The questions are:
1. What probable factors led to uneven distribution of evaporation current on each parallel branches of the tungsten wires.
2. What probable factors led to evaporation current sometime high or low.
3. When begining evaporation, the current ratio was proportional with the control ratio, but maybe due to the resistivity on tungsten wires rised along with temp rising, finally caused current only having a low-proportional increasing or no increasing. How to control the evaporating ratio and time to get a balance point between the variable parameters?