SMT007 Magazine

SMT007-Jan2019

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82 SMT007 MAGAZINE I JANUARY 2019 Thermal Profile Group 2 Group 2 is a much more realistic profile than Group 1 that shows the effect of the flux residues left behind on the analysis when the temperatures are only 10° below the recommended limits. However, 10° vari- ability is not out of the question for larger thermal mass boards and components and emphasizes the importance of profiling the assembly as well as the equipment. The equipment must also be tested to ensure that all heating elements are functioning properly. See Figure 5 for the thermal profile, Table 2 for IC data, and Figure 6 for SIR data. Group 1 IC Results The raw paste IC sample shows that acetate, chloride, lithium, sodium, ammonium, and potassium are the ions of highest concentra- tion, and also of highest concern after each reflow profile variation. This worst-case profile shows highly elevated levels of acetate, chlo- ride, lithium, and sodium. The ammonium and potassium levels depreciate greatly with this profile (Table 1). Group 1 SIR Results Group 1 SIR results show that all samples fail the IPC limits of 1.0e8 ohms of resistance (Figure 4). Figure 4: SIR results for Group 1. Figure 5: Group 2 thermal profile.

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