What are the effects of oil vapor reflux in PVD vacuum evaporation coating equipment？
During the vacuuming of vacuum evaporation coating equipment, the backflow of oil vapor often exists. In fact, any coating machine vacuum system equipped with a mechanical pump and a diffusion pump for vacuum is usually affected by the backflow pollution of oil vapor.
In general, for the diffusion pump of the vacuum system without oil blocking device, the backflow rate is approximately equal to 10⁻²mg/(cm²·min)~10⁻³mg/(cm²·min). The increase of oil-retaining measures such as water-cooled cap and water-cooled baffle can reduce the oil return rate by 100 to 1000 times.
The low-temperature vacuum chamber has a larger space volume and a larger material surface area. From the time of vacuuming to 15 Pa, until the end of the pumping of the coating equipment, there is always a directional flow of oil vapor in this process. This "directional" refers to Is the direction from the pumping unit to the container. At this time, the container of the vacuum chamber of the coating machine is like a pump that selectively traps oil vapor.
The return flow in the vacuum chamber of the vacuum evaporation coating equipment is directly proportional to the conductance of the pumping pipe, the pumping time, and the oil return rate of the unit. Therefore, the oil return rate of domestically made vacuum pumps is generally higher. This is because the longer the pumping time of the low-temperature vacuum chamber, the greater its return flow.
The recirculating oil vapor from the vacuum evaporation coating equipment has a stronger affinity with the adsorbent, which means it is easier to be adsorbed. Furthermore, after it adsorbs more oil vapor molecules, it will affect N₂, H₂, etc.