The Effect of Thermal Profiles on Cleanliness and Electrical Performance
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Transcript of The Effect of Thermal Profiles on Cleanliness and Electrical Performance
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The Effect of Thermal Profiles on Cleanliness and Electrical Performance
Eric Camden, Foresite
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Overview• Why thermal profiling is important• Methods and equipment• Study on profile variations• Conclusions
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Why is Thermal Profiling Important?
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Why Profiling is ImportantIt turns out that profiling is NOT wrong.It is actually necessary and important.
…thermal profiling, that is!
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Producing Quality Solder Joints
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Profiling is Important for ReliabilityProper intermetallic formation that yields a reliable solder joint
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Profiling is Important for Cleanliness• Fully complexed no-clean flux residues
that are benign and non-conductive• Lower amounts of conductive residues
lower the risk of electrical leakage
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Best Practices for Profiling
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Equipment Choices• Equipment choices include real time
and recorded data acquisition • Recorded data method is most
common around the world with RF becoming more prevalent
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Thermocouple AttachmentThermocouple attachment is key
• High thermal mass components• Heavy ground planes for high voltage• Good mix of both
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Reading the Data• Profile for individual assemblies and not
for individual paste types• Limit the number of times a profile board
is used• Profile a board and not an oven• Understand how to read the results and
what they mean to your assembly
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Reading a Reflow
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A Study on Profile Variations
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Focus Groups• Group 1 - 20o below manufacturer
recommendation (This produced garbage results without useful data, so those results are not included here.)
• Group 2 - 10o below manufacturer recommendation
• Group 3 - recommended thermal profile from manufacturer
• Group 4 - 10o above manufacturer recommendation
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MethodologyTen Umpire2 test boards per group were built and tested with Ion Chromatography, SIR, and Cross-section analysis
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Methodology• Lead-free, no-clean paste • Recommended peak of 25-45o above
liquidus. For this study we used 250o (35o above) as ideal.
• Ramp rate of 0.5o-2.0oC/second
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Results – Group 2
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Results – Group 2 (cont.)
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Results – Group 2 (cont.) Averages
C2H2O2 CH2O2 Cl- Li+ Na+ NH4+ K+
273.44 39.06 61.02 248.49 10.26 23.57 64.659.11 2.59 1.98 12.72 2.24 5.49 1.389.79 3.38 2.35 11.39 6.38 7.88 1.059.95 3.19 2.04 11.55 4.46 5.26 1.260.99 1.22 0.93 2.01 1.02 2.19 0.72
Group 2Raw Solder Paste
TQFPLCCBGA
Header
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Results – Group 2 (cont.)
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Results – Group 2 (cont.)
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Results – Group 2 (cont.)
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Results – Group 3
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Results – Group 3 (cont.)
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Results – Group 3 (cont.)C2H2O2 CH2O2 Cl- Li+ Na+ NH4
+ K+
273.44 39.06 61.02 248.49 10.26 23.57 64.651.73 2.64 1.48 1.67 1.82 1.24 1.321.42 2.32 1.20 2.53 1.84 1.38 2.191.88 2.01 1.06 1.79 1.41 1.08 1.960.61 0.85 0.80 0.74 0.83 1.05 0.97
Group 3Raw Solder Paste
TQFPLCCBGA
Header
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Results – Group 3 (cont.)
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Results – Group 3 (cont.)
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Results – Group 3 (cont.)
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Results – Group 4
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Results – Group 4 (cont.)
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Results – Group 4 (cont.) Averages
C2H2O2 CH2O2 Cl- Li+ Na+ NH4+ K+
273.44 39.06 61.02 248.49 10.26 23.57 64.651.55 2.52 1.56 1.03 1.04 1.23 1.161.61 1.71 1.30 1.22 1.39 1.14 1.291.66 1.60 1.48 1.28 1.11 1.18 1.250.55 0.82 0.54 0.65 0.51 0.55 0.76
Group 4Raw Solder Paste
TQFPLCCBGA
Header
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Results – Group 4 (cont.)
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Results – Group 4 (cont.)
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Results – Group 4 (cont.)
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Conclusions from the Variation Study
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Conclusions – Group 2Group 2 shows poor intermetallic formation, as well as failing IC and SIR tests.
This was only at 10oC below the recommended limit.
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Conclusions – Group 3Group 3 shows much better intermetallic formation, but not 100% homogenous, with better IC and SIR results.
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Conclusions – Group 4Group 4 shows the best level of intermetallic formation, as well as acceptable IC and SIR results.
This is not necessarily the best option when considering upper allowable temperatures for components.