Thin Film Measurement on Angled Surfaces

In the past, the precise analysis of coatings placed on a surface that is curved has proved to be problematic in the absence of witness samples. Problems can come to light because coatings are often located on surfaces that are curved. For example, the coatings located within syringes (and various tubes), medical equipment that is polymer coated, or the protective polymer layer found on automotive headlights.

The MProbe system aids in the simple and quick analysis of films on surfaces that are curved utilizing a manual probe (CSH) or a microscope.

Microscopes are often utilized when analyzing the coatings of medical equipment. They are recommended when analyzing smaller parts (less than 25 mm in size) due to the lesser spot size of the microscope which is smaller than 40 μm, meaning that the surface curve has no excessive effect on measurement.  

There are a couple of manual probes which can be utilized, and both are different in their spot size. CSH has a measurement spot of 2 mm, whereas CSHF has a measurement spot of 200 μm. When selecting which probe to utilize, the size of the sample and the degree of the curve should both be considered. Both CSH and CSHF probes align to the curvature of the sample. They are designed with a tactile bottom made from rubber which can be directly fixed onto a point of curvature, which makes it easy to take dependable and accurate measurements.

Measuring Coatings on Automotive Lights

Throughout the manufacturing of automotive lights, there are various levels where the thickness of coatings utilized needs to be analyzed for QC.

Coatings are utilized to shield the light casing from any outside damage and scratches that may arise, and to make sure reflectors (hard-coatings) are protected. Meanwhile, anti-fog coatings must be used to protect polycarbonate lenses. In each of the coating applications, there can be problems with analysis. For example, there are colored surfaces underneath the films to consider, along with the use of reflective surfaces, and there can be a small optical contrast between the polycarbonate and the coating.

The MProbe Vis system can help researchers to alleviate each of these particular problems when used with Semiconsoft’s TFCompanion software. The software uses algorithms that are FFT (Fast Fourier Transform). The FFT algorithms can be designed to precisely analyze hard and non-traditional samples using an easy method that can be used by operators with not much experience.

The MProbe Vis makes it simple for operators to analyze components with ease, and straight after the method of coating.

Clear headlight with hardcoat: Measurement of reflectance spectra. (see results Fig. 1b)

Figure 1a. Clear headlight with hardcoat: Measurement of reflectance spectra. (see results Fig. 1b)

Results of the measurement of clear headlight with hardcoat. Hardcoat thickness- 15.2 μm; IPL (interface layer) thickness - 1.85 μm (First peak aligns to the hard coat layer; the second peak refers to the total thickness hardcoat+IPL)

Figure 1b. Results of the measurement of clear headlight with hardcoat.
Hardcoat thickness- 15.2 μm; IPL (interface layer) thickness - 1.85 μm
(First peak aligns to the hard coat layer; the second peak refers to the total thickness hardcoat+IPL)

Red headlight with hardcoat (on textured surface): Reflectance spectra measurement. (see results Fig. 2b)

Figure 2a. Red headlight with hardcoat (on textured surface): Reflectance spectra measurement. (see results Fig. 2b)

Outcomes of the measurement of the red headlight with hard coat. The hard coat thickness - 8.7 μm, IPL (interface layer) thickness - 1.4 μm

Figure 2b. Outcomes of the measurement of the red headlight with hard coat.
The hard coat thickness - 8.7 μm, IPL (interface layer) thickness - 1.4 μm

Measuring Coatings Inside of Transparent Tubes

In various applications, coatings can be found on the inside of a transparent tube such as in medical syringes, which utilize a coating to lessen friction with the plunger, or bottles for drinks can use an inside coating to preserve the drink held inside of the bottle.

Each tubing application can each have their problems, and some of these are common to all tubing applications, for example there can be lesser degrees of reflectivity, and there can be light scatter because of the friction and imperfections of the material utilized.

Figure 3 outlines the measurement utilizing the MProbeVis-Micro (measurement spot of 40 µm) of a polymer coating located on the inside surface of a syringe. The syringe was created from a transparent polymer, with a whitish appearance and a diameter of approximately 15 mm.

Measurement of the polymer layer inside the syringe tube. Measured vs. model data, scattering and surface roughness correction is applied. Thickness: 288 nm

Figure 3. Measurement of the polymer layer inside the syringe tube.
Measured vs. model data, scattering and surface roughness correction is applied. Thickness: 288 nm

Measuring Coatings on Medical Devices

To prevent the possibility of medical devices degrading within the body or to prevent the body rejecting the implant, medical devices must be coated with biocompatible materials and/or polymers.

The most frequent problems arising when analyzing these types of coatings include scattering from the metallic coating of the implant, and analysis can be made difficult due to the lesser size and steep curves of the devices. When analyzing coatings that are non-polymer, the optical coefficients, n and k, need to also be analyzed, as they are affected by the conditions of deposition.

To solve the challenges of measuring a steep curvature, the analysis is run utilizing a small spot of 40 µm, and light scattering is aligned for surfaces that are metallic.

Figure 4 outlines the outcomes for the coating measurement of a Ti/Al oxide coating on a Ti nail of approx. 6 mm diameter.

Outcomes of the measurement (measurement vs. model) of the coating on Ti nail. Oxide coating material dispersion is represented using Tauc-Lorentz approximation. Light scattering is corrected. Thickness: 115 nm

Figure 4. Outcomes of the measurement (measurement vs. model) of the coating on Ti nail. Oxide coating material dispersion is represented using Tauc-Lorentz approximation. Light scattering is corrected. Thickness: 115 nm

Measuring Coatings In-Line

The MProbe Vis can also be utilized for in-line coating measurement, along with being perfect for QC processes to be undertaken in the laboratory.

The process utilizes a fiber optical probe which means that precise measurements can be taken at a distance. Semiconsoft has a Modbus (TCP) system which can communicate with factory controllers to make in-line measurement methods simple to set-up, with customized integration available if necessary. This system creates quality control on a pass or fail basis.

This information has been sourced, reviewed and adapted from materials provided by SemiconSoft.

For more information on this source, please visit SemiconSoft.

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