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JANUARY 2019 I SMT007 MAGAZINE 81 humidity within 3%. A calibrated automatic switching measurement system was used for the electrical measurements taken once every 10 minutes. Thermal Profile Group 1 The first thermal profile group was processed at a worst-case temperature of 20° below what is recommended by the solder paste manufac- turer. This is a profile that barely achieves liqui- dus state of the paste and could be a function of multiple failing heating sources, an improper recipe being used (possible a standard leaded profile), or other unknowns (Figure 3). technique. The parts were all mechanically removed, and the samples were taken from the board level. Localized extractions are of utmost importance as they do not normalize out pock - ets of contamination across the full surface area of the assembly like other extraction and test methods do. A raw sample of the chosen solder paste was tested with IC to determine the main constituents of the paste activator. All samples were compared to the raw paste IC data when determining the level of ionic cleanliness. The SIR testing was performed in a standard environmental chamber capable of maintain- ing a temperature within ±1°C and relative Figure 3: Group 1 thermal profile. Table 1: IC data for Group 1.

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