Thermal profiling during the reflow soldering process is important for producing reliable solder joints with low residue levels. A study examined the effects of varying the reflow thermal profile above and below the manufacturer's recommendations. Groups that were 10 degrees Celsius below or at the recommended profile showed poorer intermetallic formation and some failures. The group 10 degrees above produced the best intermetallic formation and acceptable cleanliness and reliability test results, though exceeding component limits. Proper thermal profiling is key for joint quality and cleanliness.

1. The Effect of Thermal Profiles
on Cleanliness and
Electrical Performance
Eric Camden, Foresite

2. Overview
• Why thermal profiling is important
• Methods and equipment
• Study on profile variations
• Conclusions

3. Why is Thermal Profiling
Important?

4. Why Profiling is Important
It turns out that profiling is NOT wrong.
It is actually necessary and important.
…thermal profiling, that is!

5. Producing Quality Solder Joints

6. Profiling is Important for
Reliability
Proper intermetallic formation that yields a
reliable solder joint

7. 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

8. Best Practices for Profiling

9. 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

10. Thermocouple Attachment
Thermocouple attachment is key
• High thermal mass components
• Heavy ground planes for high voltage
• Good mix of both

11. 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

12. Reading a Reflow

13. A Study on Profile Variations

14. 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

15. Methodology
Ten Umpire2 test boards per group were built and
tested with Ion Chromatography, SIR, and Cross-
section analysis

16. 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
-2.0o
C/second

17. Results – Group 2

18. Results – Group 2 (cont.)

19. Results – Group 2 (cont.) Averages
C2H2O2 CH2O2 Cl-
Li+
Na+
NH4
+
K+
273.44 39.06 61.02 248.49 10.26 23.57 64.65
9.11 2.59 1.98 12.72 2.24 5.49 1.38
9.79 3.38 2.35 11.39 6.38 7.88 1.05
9.95 3.19 2.04 11.55 4.46 5.26 1.26
0.99 1.22 0.93 2.01 1.02 2.19 0.72
Group 2
Raw Solder Paste
TQFP
LCC
BGA
Header

20. Results – Group 2 (cont.)

21. Results – Group 2 (cont.)

22. Results – Group 2 (cont.)

23. Results – Group 3

24. Results – Group 3 (cont.)

25. Results – Group 3 (cont.)
C2H2O2 CH2O2 Cl-
Li+
Na+
NH4
+
K+
273.44 39.06 61.02 248.49 10.26 23.57 64.65
1.73 2.64 1.48 1.67 1.82 1.24 1.32
1.42 2.32 1.20 2.53 1.84 1.38 2.19
1.88 2.01 1.06 1.79 1.41 1.08 1.96
0.61 0.85 0.80 0.74 0.83 1.05 0.97
Group 3
Raw Solder Paste
TQFP
LCC
BGA
Header

26. Results – Group 3 (cont.)

27. Results – Group 3 (cont.)

28. Results – Group 3 (cont.)

29. Results – Group 4

30. Results – Group 4 (cont.)

31. Results – Group 4 (cont.) Averages
C2H2O2 CH2O2 Cl-
Li+
Na+
NH4
+
K+
273.44 39.06 61.02 248.49 10.26 23.57 64.65
1.55 2.52 1.56 1.03 1.04 1.23 1.16
1.61 1.71 1.30 1.22 1.39 1.14 1.29
1.66 1.60 1.48 1.28 1.11 1.18 1.25
0.55 0.82 0.54 0.65 0.51 0.55 0.76
Group 4
Raw Solder Paste
TQFP
LCC
BGA
Header

32. Results – Group 4 (cont.)

33. Results – Group 4 (cont.)

34. Results – Group 4 (cont.)

35. Conclusions from the
Variation Study

36. Conclusions – Group 2
Group 2 shows poor intermetallic formation,
as well as failing IC and SIR tests.
This was only at 10o
C below the
recommended limit.

37. Conclusions – Group 3
Group 3 shows much better intermetallic
formation, but not 100% homogenous, with
better IC and SIR results.

38. Conclusions – Group 4
Group 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.

39. Thanks for reading!
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