the effect of thermal profiles on cleanliness and electrical performance
TRANSCRIPT
The Effect of Thermal Profiles on Cleanliness and Electrical Performance
Eric Camden, Foresite
Overview• Why thermal profiling is important• Methods and equipment• Study on profile variations• Conclusions
Why is Thermal Profiling Important?
Why Profiling is ImportantIt turns out that profiling is NOT wrong.It is actually necessary and important.
…thermal profiling, that is!
Producing Quality Solder Joints
Profiling is Important for ReliabilityProper intermetallic formation that yields a reliable solder joint
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
Best Practices for Profiling
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
Thermocouple AttachmentThermocouple attachment is key
• High thermal mass components• Heavy ground planes for high voltage• Good mix of both
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
Reading a Reflow
A Study on Profile Variations
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
MethodologyTen Umpire2 test boards per group were built and tested with Ion Chromatography, SIR, and Cross-section analysis
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
Results – Group 2
Results – Group 2 (cont.)
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
Results – Group 2 (cont.)
Results – Group 2 (cont.)
Results – Group 2 (cont.)
Results – Group 3
Results – Group 3 (cont.)
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
Results – Group 3 (cont.)
Results – Group 3 (cont.)
Results – Group 3 (cont.)
Results – Group 4
Results – Group 4 (cont.)
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
Results – Group 4 (cont.)
Results – Group 4 (cont.)
Results – Group 4 (cont.)
Conclusions from the Variation Study
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.
Conclusions – Group 3Group 3 shows much better intermetallic formation, but not 100% homogenous, with better IC and SIR results.
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.
