Proper quality control of coating thickness is important to the plating companies and metal finishers that are applying the coatings and also affect the companies that utilize the plated components in their manufactured goods.
Product liability requires quality control to avoid defective coatings and eliminate problems, such as rust, that can lead to production problems or product recalls.
XRF spectrometers can be calibrated for determining both coating thickness and coating quality for many types of material. X-rays achieve superior penetration depths and so can measure coatings that other techniques cannot. If the coatings are predominantly one element, it makes the analysis very easy. Here are a few common coating applications:
- Silicone on Paper, Tissue Paper, and Hygiene products- Silicone is used as a release coating on paper, so that adhesive labels do not stick. Silicone is used on tissue paper like to make it feel softer. Silicone is also used in the liners of diapers and other hygiene products to repel moisture to keep the side next to the skin dry. EDXRF instruments have long been used for these applications.
- Platinum Catalyst in Silicone Resin- Platinum catalysts are used in silicone as a curing agent. It is added at concentration in the 100PPM range and can be analyzed by EDXRF.
- Phosphorus on Steel- Phosphate coatings are used to protect and pre-treat steels. They can be measured along with iron and manganese that is sometimes present. EDXRF is also used for monitoring the baths either by sampling it or by an on-line XRF instrument.
- Sulfur and Phosphorus on Aluminum- Aluminum is coated or anodized by etching the surface with an acid. Acid bonds to the aluminum making it much harder. The coating can be measured by EDXRF by measuring the elemental sulfur or phosphorus on the surface. Alternatively it can be measured by an x-ray absorption technique since the aluminum signal decreases with thicker anodized coatings.
- Copper on Silicon- Now that many silicon wafer fabricators are switching to copper, monitoring them with XRF is easier than ever. EDXRF is usable for on-line process monitoring.
- Capacitors- Modern capacitors like tantalum capacitors are made by coating a thin polymer with a thin layer of metal, then the material is rolled to form the capacitor. Aluminum is the most common metal, with tantalum holding an important niche. A variety of polymers are used including polyester (Mylar), polypropylene, and polycarbonate. EDXRF instruments are ideal for monitoring the metal film thickness. The polymer thickness can also be measured using x-ray absorption techniques.
- Metalized Food Packaging- Many foods are packed in foil pouches made from a polymer coated with metal. The oldest is aluminized Mylar, but titanium and zinc are common, and other polymers can be used. While light transmission is used for many thing coatings, EDXRF instruments are suitable for most applications, particularly with thicker coatings.
- Solar Power Cells- Most solar cells use thin coatings of a metal alloy on a polymer substrate. These coatings can be measured by EDXRF.
- Conductive Coatings on Plastic- In order to comply with regulations on electrical noise, modern plastic cases for electronic equipment must be shielded. Shielding is often achieved by coating the plastic with a conductive layer. In many instances this layer can be analyzed by EDXRF.
- Vapor and e-Beam Deposition Coatings- Numerous elements are deposited in thin films by e-beam or vapor deposition methods. Virtually every element above atomic number 10 can be measured by EDXRF.