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40 SMT Magazine • September 2016 Assembly Processes Each assembler was provided an identical kit with eight bare boards, together with the com- ponents needed to populate them. The processes employed by each of the as- semblers was recorded and are summarized in Table 3. X-Ray Fluorescence Measurements Evaluation of the extent of solder coverage of component terminations was performed us- ing X-ray fluorescence (XRF). All XRF measure- ments were performed using the production XRF instrument and a 97% by weight tin ma- terials standard. This instrument's principal fea- tures include a PIN diode solid state X-ray de- tector, a capillary tube collimation for 3-micron X-ray beam size, a fine position controlled au- tomatic sample stage, a 50 Kilo-electron-volt X- ray source, and X-ray fundamental parameters based quantitative analysis software. Data col- lected at each measurement location included: thickness of coating, weight fraction of tin and of lead in the coating, and count rate. Measurements were performed in identical locations on each of the test vehicles. Measure- ments were performed on two leads from each of the leaded devices. For each lead analyzed, measurements were taken in three locations: at the toe of the lead adjacent to the pad, at the midpoint of the lead, and at the very top of the lead where it protrudes from the package. For the non-leaded passive devices, measurements were performed at the pad and on the top of the device where the termination finish was far- thest from the pad. X-Ray Fluorescence Results Raw data was collected at each measurement location for: weight percent tin, weight percent lead, and coating thickness. Information on the x-ray count rate for tin lead were also recorded. Results of the XRF measurements for boards from Assembler A are summarized in Appen- Table 3. Summary of assembly process details. MITIGATION OF PURE TIN RISK BY TIN-LEAD SMT REFLOW