Quality analysis of high value components relies on precision non-destructive analytical instruments. X-Ray Fluorescence (XRF) provides a quick method for elemental materials analysis that is both non-destructive and non-contact. It is a powerful, quantitative, and qualitative analysis tool that is well suited for film thickness measurements, determination of elemental concentrations,and identification of specific and trace elements in complex sample structures.

XRF uses scattering events between a collimated x-ray beam and the atomic electrons of the irradiated area of the sample. The x-rays have sufficient energy to ionize the atoms that they interact with, which leads to the emission of an x-ray spectrum from the sample. Each element has its own unique x-ray spectrum, which serves as a fingerprint for that element. Analysis (by the data acquisition system within a modern XRF instrument) will determine both the elements that are present and their concentrations. The operation of an XRF is quite straightforward. The sample or specimen is simply placed into the measuring chamber, and after the press of a button, results can be obtained in minutes. The test is completely non-destructive and no sample preparation is required.

Quantitative analysis from an XRF tool is dependent on the use of high quality standards for specific applications. These can be either empirical calibration standards or they can utilize mathematical models to enhance the physical standards. The application of a mathematical model to the data analysis often leads to a significant reduction in the number of calibration standards needed for a specific application. Calibration standards and data analysis packages for specific applications are commonly purchased with the XRF equipment. It is important that the operator be knowledgeable about the range of the calibration standards and the mathematical models. Quantitative analysis outside of these ranges can lead to substantial errors in the conclusions drawn from the data.

XRF is a primary non-destructive test method to ensure compliance to Restriction of Hazardous Substances (RoHS), Waste from Electrical and Electronic Equipment (WEEE), and other directives. RoHS compliance by component suppliers is neither universal, nor standardized, and a part number or descriptor alone may not specify whether or not the part meets the RoHS directive; use of XRF can help alleviate such an uncertainty. Furthermore, XRF measurements can quickly and reliably provide screening results for the concentrations of many other materials of concern. Figure 6-1 shows a sample spectrum of a component using the Fischer Scope XRF. Note that for the sample shown in Figure 6-1, the peak for Pb is large, and thus may exceed the RoHS maximum concentration limit.

XRF can also be utilized in determining reliability of electronic assemblies by the application of material analysis and coating thickness measurements. For instance, solder embrittlement can be a result of a gold coating that is in excess of its thickness specification. For component plating, XRF is capable of providing thickness measurements of as many as three coating layers, with up to four metal ion constituent elements. XRF software can also output the material composition of as many as 24 elements at a time, thus providing a very comprehensive analysis of a particular material. In addition, XRF units are capable of analyzing the following:

• Multi-layer electronic components and assemblies.
  
  
• General material testing analysis of plating bath solutions.
  
  
• Micro-hardness measurements
  
  
• Ferrite content
  
  
• Porosity testing

The EMPF can assist with X-Ray Fluorescence analysis. For more information on XRF, or for demonstration of the Fischer XRF please contact the EAB coordinator, Ken Friedman at (610) 362-1200 x279, or kfriedman@aciusa.org. For more
information regarding lead-free manufacturing, failure analysis, or other classes available from the EMPF, including IPC certifications, please contact the registrar at (610) 362-1295, via email at registrar@empf.org or find course descriptions on the web at http://www.aciusa.org/courses.