Parylene films are created via a Chemical Vapor Deposition (CVD) process.
As part of this process there normally are four stages. These are:
- Stage 1: Vapourisation
- Stage 2: Pyrolysis
- Stage 3: Coating Deposition
- Stage 4: Cold Trap
Stage 1: Parylene Vapourisation
Dimer is placed in the glass tube at the opposite end from the deposition chamber in an aluminum foil cup called a “boat”.
The volume of dimer placed in the boat will determine the final coating thickness deposited on the product.
The boat is inserted into the vaporizer stage of the Parylene system and the process started.
The vaporizer radiant heater heat the dimer to between 100-180ºC.
The dimer changes from a solid to a vapor
The molecules move down the tube by virtue of the reduced pressure at the opposite end.
Stage 2: Parylene Pyrolysis
At this time the vapor is pulled under vacuum into the pyrolizer furnace zone.
The pyrolysis zone is typically at temperatures of 650-700°C.
This high temperature cleaves the dimer by sublimation into monomers.
The monomer is now ready for transfer to the coating deposition chamber.
Stage 3: Parylene Coating Deposition
The monomer molecular gas continues to be drawn by vacuum one molecule at a time into the coating chamber.
The monomers are collectively re-aligned and reform into polymer chains on all surfaces within the chamber.
The monomer deposits on the desired substrate at ambient temperatures in the coating chamber.
The coating forms slowly and uniformly over surfaces with both sharp edges and deep crevices with no pinholes.
Stage 4: Cold Trap
The final stage of the parylene deposition process is the cold trap.
This is between the Coating Chamber and the pump.
The cold trap is cooled to between -90ºC and -120ºC.
It is responsible for removing all residual parylene materials pulled through the coating chamber.
Key Elements of the Process
There are many key points to the process.
- Dimer vaporized at ~180°C
- Pyrolized to Monomer at ~700°C
- Polymerization occurs on product surface at room temperature
- Deposition process – occurs only at vapor level, no liquid phase throughout
- Low vacuum pressure (30-50 mtorr)
- Process in non-toxic from start to finish
- No volatile effluents (VOC’s)
- Minimal impurities (99% pure)
- Controlled process – beginning to end.
- Polymerization process is slow, can take 4 hours, or 20+ hours.
- Deposition at the molecular level…one at a time, on all surfaces (even chamber walls)
- No initiators or curing required
- Controlled film thickness (nanometers, microns or mils)
- Completely 3-dimensional process
- Thin film…no weight added to target substrate
The Total Parylene Process
The actual Parylene coating process involves a complex sequence of stages.
- Masking (as required)
- Surface Preparation or Promotion
- Coating Application Process
- De-masking (as required)
- Final Inspection
Understanding that this is a complete process and good process development is critical is the key to a great solution. Thin film Partners can take the pain away from this process development.