Low Temperature Sputtered Coatings for Plastics
It is widely known that traditional magnetron sputtering thin film deposition lends itself to elevated temperatures. This high temperature environment is not ideal for non-optical applications where a thin film coating is required on soft moldable substrates such as polyamides, ABS and other forms of plastic. Materion Precision Optics has developed low temperature sputtering metallization capabilities that can be applied to most moldable synthetic and semi-synthetic plastics. This technique has been used to enable a number of applications such as conductive flexible membranes, impedance matched layers in acoustic stacks, and reflective / anti-reflective packages for optical focal planes and detectors.
Not all plastics are equal and the material characteristics are important when preparing the coating process. It is important to understand the softening point, melting point, etc. to ensure that there is no damage to the substrate during thin film deposition. Monitoring the substrate temperature is critical. Typical methods used are: optical pyrometers, thermocouples, or something as simple as a thermometer inside the chamber visible to the operator. Depending on the part and its rotation, it can sometimes be very difficult to monitor the temperature and installing an optical pyrometer through a port window may be necessary.
Monitoring the temperature is only one part of the process. Even though you verify the temperature in the chamber, sometimes an undesirable increase is unavoidable. To help control the temperature during deposition multiple between-layer cool downs may be required. The number of pauses is going to be dependent on the coating thickness. Materion Precision Optics has successfully used temperature-monitoring, cool down phases during deposition along with other proprietary processes. This ensures that the plastic substrate material is not damaged during thin film deposition.
Thin is In!
Adhesion of the metallization or thin film coating can also be a challenge when dealing with plastic media. As the adhesion /cleaning guru Kash Mittal from IBM always says, “Thin is In.” The coating layers should be as thin as possible without losing the functionality of the coating. Even though thin coatings would be preferred Materion has coated plastic substrates with coatings as thick as 10,000-12,000 angstroms. A thin coating helps adhesion but also reduces the need for cool downs during the deposition process as explained above. The key to thin film adhesion to plastics begins with substrate preparation. “We would typically perform a water break test (Surface Tension) to determine the best method of pre-clean before coating which may consist of an In-Situ corona clean, plasma treatment or RF back sputter,” according to Thomas Ives, Sales & Technology for Barr Precision Optics.
One last item that needs to be considered is the stress induced by thin film deposition which is generally difficult to control in a sputtering process. The influence of the gas media can change the film properties but can be controlled to a certain extent. Stress has to be taken into consideration when coating plastic films or thin membranes. In general, Materion’s coating process will produce a slightly compressive film vs. a tensile one.
Materion "Can Do" Attitude
We often hear the discouraging phrase, “you can’t coat that!” Our belief is that you can’t unless you try. Materion Precision Optics has been very successful at coating many types of plastics including, PET, PEEK, Kapton, Acrylic, Polycarbonate and more. Even though our heritage is in Optics, we have the technology, engineering and expertise to be your primary supplier for all your coating needs.
For further information on our coating solutions, please contact Andrew Houde, Director of Engineered Films Business, email: Andrew.Houde@Materion.com.