Circuits Assembly - November 2008 - (Page 40)

Process Doctor Electronics Residues Testing Methods An analysis of four common methods starts with FTIR. B eginning this month, we will discuss the applications of four typical analysis techniques and their pros and cons in regard to understanding electronics residues. The techniques include FTIR (Fourier transform infrared spectroscopy), SEM/ EDX (scanning electron microscopy/ electron dispersive b-ray), XRF and ion chromatography. Eric W. Weisstein explains In its simplest form, a Fourier transform spectrometer consists of two mirrors located at a right angle to each other and oriented perpendicularly, with a beamsplitter placed at the vertex of the right angle and oriented at a 45° angle relative to the two mirrors (Figure 1). Radiation incident on the beamsplitter from one of the two “ports” is then divided into two parts, each of which propagates down one of the two arms and is reflected off one of the mirrors. The two beams are then recombined and transmitted out the other port. When the position of one mirror is continuously varied along the axis of the corresponding arm, an interference pattern is swept out as the two phase-shifted beams interfere with each other. Figure 1. Sample FTIR schematic. FTIR COMPARISON Figure 1. Sample FTIR schematic. 1.21 1.1 1.0 0.9 Abductance, log (T) Figure 2 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.01 4000 3000 0.8 Used (~200 Cycles) solution Fresh solution 2000 1500 1000 400 Frequency, cm-1 Terry Munson is with Foresite Inc. (residues.com); tm_foresite@ residues.com. This column appears monthly. FTIR provides specific information Figure 2. FTIR comparison. about chemical bonding and molecular structures, making it useful for anaThe assessment of unknown visible residues lyzing organic materials and certain inorganic on electronics involves looking at samples from materials. Chemical bonds vibrate at characterthe top of soldermask, laminate and metallizaistic frequencies, and when exposed to IR radiation. When samples are analyzed, they tend to tion, they absorb the radiation at frequencies include these other materials. The analysis shows that match their vibration modes. Measuring the presence of combined materials, and no separadiation absorption as a function of frequency ration is done using this technique; and while it produces a spectrum that can be used to identify can identify a family, it cannot quantify the resifunctional groups and compounds. due amount. Residue assessment will reveal that Applications and limitations include identia white flaky or gooey material around a solder fying the molecular structure of organic comjoint is a flux, but that’s where it stops. With 70% pounds for contamination analysis; identification of the industry using no-clean fluxes, this proof organic particles, powders, films, and liquids vides slightly more information than in known (material identification); and the large (20,000 pretesting. item) library of materials to match material sign natures, which permits observations on the pure material and aged materials (for changes). Circuits Assembly NOVEMBER 2008 circuitsassembly.com 40 http://www.residues.com http://www.residues.com http://www.circuitsassembly.com

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Circuits Assembly - November 2008 Contents Caveat Lector Industry News Market Watch Talking Heads Focus on Business On the Forefront Screen Printing Better Manufacturing RoHS Conversion for Medical Devices Supporting Full-Service Customer Requirements at the Regional EMS Level Speed Thrills Tech Tips Wave Soldering Process Doctor Pb-Free Lessons Learned The Defects Database Getting Lean Materials World Product Spotlight Ad Index Assembly Insider Technical Abstracts

Circuits Assembly - November 2008

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