Silicone coated film has seen increased use in the electronics industry as a release liner for films applied as protective layer during circuit board processing. For sensitive and complex PCB processing, silicone coated films must meet published specifications, such as the level of temperature resistance and release characteristics.
Release films for electronics applications are made of a polymer layer, such as polyethylene terephthalate (PET) to which a very thin silicone coating is applied. The polymer itself will depend on the final properties of the film, such as the ability to withstand temperatures over 200ºC, but in all cases, it’s important that the film has high strength, is chemically inert and sticks well to the PCB. In terms of the silicone layer, it’s important that no silicone residue is left on the sticky layer after release. This is especially crucial for semiconductor electronics, where silicone could migrate into the device and impair performance. The thickness of the silicone layer must be within a given range to ensure the film has right flexibility to completely cover features on the substrate, and the silicone layer must have the right release profile to work with the process tooling system.
As mentioned above, the release characteristics of the liner can be changed depending on the application - and this characteristic is an important part of the liner’s specification. The release characteristics are determined by the quality of the silicone layer coverage, the completeness of the silicone curing process and the silicone formula itself. It’s important to control these parameters carefully during release liner production to ensure the final product meets the specified release characteristics.
XRF helps to control the quality of the silicone layer by returning a value for coat weight. For the very thin layers applied, there is a linear relationship between the XRF silicon signal and the coat weight, provided the instrument has the right calibration. This makes it a very simple exercise to determine the thickness of the layer as you can take a single, rapid measurement on a sample of coated film. There’s no chemical processing or manual calculations involved, unlike other methods such as atomic absorption spectroscopy (AAS). This simple coat weight measurement is useful during process engineering when determining the curing level of the silicone layer. Here, you simply measure the coat weight with XRF before and after extracting the excess silicone to determine the effectiveness of the curing process.
Hitachi’s LAB-X5000 is a benchtop XRF analyzer that’s ideal for silicone coat weight analysis. Rugged, compact and powerful, the LAB-X5000 is designed for constant use in a production environment. Once a sample has been prepared (simply by cutting a small disc of coated film and placing it in a sample holder), the operator presses the start button and within seconds results are displayed on the screen.
The instrument parameters are optimized for this application, and it’s simple to set up a pass / fail value within the software, removing the need for the operator to interpret the results.
Also, the LAB-X has a built-in sample spinner–rotating the sample during the analysis to provide a repeatable coat weight result.
You can find more information on the LAB-X5000 for release liners here. Alternatively, get in touch to arrange a demo.
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