Alternate Systems has over 35 years of experience with XRF coating thickness measurement and energy-dispersive X-ray micro analysis. In addition to surface finishing and electronics applications, we have supported projects including special coatings on flight systems, detonator bridge characterizations, and neutron tube manufacturing. We have even developed a novel method to determine the density of PETN pellets in very small volumes. Alternate Systems has supported special component manufacture for the Z Machine pulsed power project.
The most common coating process is conventional electroplating. Other processes include electroless plating, galvanized coating (typically applied to steel, iron, and aluminum), physical and chemical vapor disposition, anodizing, mechanical coating, pickling, etching, and sputtering.
Coatings impart valuable properties to metal: corrosion resistance, wear-resistance, solderability, machinability, hardness, brightness, adhesive qualities, and lubricity (reduced friction in moving parts). Industries that rely on coatings include automotive, aerospace, medical device, construction, and electronics. Metal is coated with a variety of substances, including chrome, nickel, and zinc.
Chrome works well with many substrates. Decorative chrome is used to improve appearance, while hard, or industrial, chrome offers excellent corrosion-, wear- and friction-resistance. Hard chrome is used in the nuclear, aerospace, and automotive industries as well as in the manufacture of many tools and medical devices.
Nickel is a multi-purpose coating material; it’s aesthetically pleasing, corrosion-resistant, wear-resistant, stress-resistant, and magnetic. According to an article on Product Finishing, nickel can be made to plate with little or no stress so it’s especially useful for electroforming or aerospace applications. Nickel is used for engineering applications to promote durability, and it provides a barrier layer on coins, jewelry and circuit boards. On strip steel and in aerospace applications, nickel is used for low stress or for resizing. In electronics, nickel is used as a layer to prevent the intermetallic migration of copper into a precious metal top coat like gold, silver, palladium, and rhodium.
Zinc works with a variety of substrates but is most often used to coat steel for protection against corrosion. There are many ways to apply zinc coating to steel but the most common are hot-dip galvanizing and continuous galvanizing.
Precious metals like gold, silver, palladium, platinum, and rhodium are used as both decorative coatings in jewelry, and as functional coatings in electronic products to provide low contact resistance and other special surface functions. Because of the high expense of these materials, measurement is critical. Enough coating must be present to provide durability and desired function, but not so much that costs are too high.
Why Is Coating Thickness Measurement Important?
Coating materials must be applied in certain thickness specifications in order to express the desired characteristics. Metals that are either over or under plated won’t perform as expected. Over-plating also wastes expensive coating material. If coating thickness inaccuracies aren’t detected, entire pieces may end up being scrapped. X-ray fluorescence technology was originally developed as a measurement device because the instruments can identify and differentiate elements and allow XRF to measure coatings that other techniques cannot.
While the application reach of the non-destructive testing technology has grown, the measurement of coatings and thin films continue to be an ideal, and popular, use of XRF. This critical quality control technology is relied upon in a wide range of facilities – from general plating shops to aerospace, automotive, and military manufacturing plants.
Potential coating thickness applications can range from single-layer measurements (Au/Cu, etc.) to very complex multi-layer alloy coatings with compositional analysis. It is possible, for instance, to analyze a three-element alloy coating on an intermediate layer of a five element base material (Au-Cu-Cd over Ni on a Stainless Steel base).
Common Coating Thickness Applications Include:
- Single Layer Coatings; one metal coating (Au, Ni, Zn, Zr, Ni, Cr, Cu, etc) over a substrate
- Binary Alloy Coatings, SnPb
- Multiple Layer (multilayer) Coatings; two or more layers over a substrate (Cr/Ni/Cu)
- Common applications in electronics are ENIG and ENEPIG per IPC 4552 and IPC 4556
- Composite coatings over a substrate (Hard Au/Ni/Cu and ZnNi/Cu)
- composition of the alloy coating can be identified as well
- Thin film measurements (i.e. wafer fab quality control in semiconductor industry)
- Solution analysis of plating baths
- Measurement methods according to ASTM standards when applicable
- Common standard: ASTM B568 for Coating Measurements
Alternate Systems is able to offer a number of options for fast, accurate, and reliable accredited coating thickness measurements and specialized applications for proprietary products.