Microstructural Evolution of SAC305 Solder Joints in Wafer Level Chip-Scale Packaging (WLCSP) with Continuous and Interrupted Accelerated Thermal Cycling

Quan Zhou, Bite Zhou, Tae Kyu Lee, Thomas Bieler

Research output: Contribution to journalArticle

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Abstract

Four high-strain design wafer level chip scale packages were given accelerated thermal cycling with a 10°C/min ramp rate and 10 min hold times between 0°C and 100°C to examine the effects of continuous and interrupted thermal cycling on the number of cycles to failure. The interruptions given two of the samples were the result of periodic examinations using electron backscattered pattern mapping, leading to room temperature aging of 30 days–2.5 years after increments of about 100 cycles at several stages of the cycling history. The continuous thermal cycling resulted in solder joints with a much larger degree of recrystallization, whereas the interrupted thermal cycling tests led to much less recrystallization, which was more localized near the package side, and the crack was more localized near the interface and had less branching. The failure mode for both conditions was still the same, with cracks nucleating along the high angle grain boundaries formed during recrystallization. In conditions where there were few recrystallized grains, recovery led to formation of subgrains that strengthened the solder, and the higher strength led to a larger driving force for crack growth through the solder, leading to failure after less than half of the cycles in the continuous accelerated thermal cycling condition. This work shows that there is a critical point where sufficient strain energy accumulation will trigger recrystallization, but this point depends on the rate of strain accumulation in each cycle and various recovery processes, which further depends on local crystal orientations, stress state evolution, and specific activated slip and twinning systems.

LanguageEnglish (US)
Pages1-12
Number of pages12
JournalJournal of Electronic Materials
DOIs
StateAccepted/In press - Feb 2 2016

Profile

Microstructural evolution
Thermal cycling
solders
packaging
Soldering alloys
Packaging
chips
wafers
cycles
Chip scale packages
Cracks
cracks
Recovery
Twinning
Strain energy
Crystal orientation
Failure modes
Crack propagation
recovery
thermal cycling tests

Keywords

  • Accelerated thermal cycling
  • crack growth
  • crack nucleation
  • electron backscattered diffraction mapping
  • lead-free solder
  • recovery
  • recrystallization
  • slip systems
  • twinning

ASJC Scopus subject areas

  • Electrical and Electronic Engineering
  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Materials Chemistry

Cite this

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title = "Microstructural Evolution of SAC305 Solder Joints in Wafer Level Chip-Scale Packaging (WLCSP) with Continuous and Interrupted Accelerated Thermal Cycling",
abstract = "Four high-strain design wafer level chip scale packages were given accelerated thermal cycling with a 10°C/min ramp rate and 10 min hold times between 0°C and 100°C to examine the effects of continuous and interrupted thermal cycling on the number of cycles to failure. The interruptions given two of the samples were the result of periodic examinations using electron backscattered pattern mapping, leading to room temperature aging of 30 days–2.5 years after increments of about 100 cycles at several stages of the cycling history. The continuous thermal cycling resulted in solder joints with a much larger degree of recrystallization, whereas the interrupted thermal cycling tests led to much less recrystallization, which was more localized near the package side, and the crack was more localized near the interface and had less branching. The failure mode for both conditions was still the same, with cracks nucleating along the high angle grain boundaries formed during recrystallization. In conditions where there were few recrystallized grains, recovery led to formation of subgrains that strengthened the solder, and the higher strength led to a larger driving force for crack growth through the solder, leading to failure after less than half of the cycles in the continuous accelerated thermal cycling condition. This work shows that there is a critical point where sufficient strain energy accumulation will trigger recrystallization, but this point depends on the rate of strain accumulation in each cycle and various recovery processes, which further depends on local crystal orientations, stress state evolution, and specific activated slip and twinning systems.",
keywords = "Accelerated thermal cycling, crack growth, crack nucleation, electron backscattered diffraction mapping, lead-free solder, recovery, recrystallization, slip systems, twinning",
author = "Quan Zhou and Bite Zhou and Lee, {Tae Kyu} and Thomas Bieler",
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AU - Bieler,Thomas

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AB - Four high-strain design wafer level chip scale packages were given accelerated thermal cycling with a 10°C/min ramp rate and 10 min hold times between 0°C and 100°C to examine the effects of continuous and interrupted thermal cycling on the number of cycles to failure. The interruptions given two of the samples were the result of periodic examinations using electron backscattered pattern mapping, leading to room temperature aging of 30 days–2.5 years after increments of about 100 cycles at several stages of the cycling history. The continuous thermal cycling resulted in solder joints with a much larger degree of recrystallization, whereas the interrupted thermal cycling tests led to much less recrystallization, which was more localized near the package side, and the crack was more localized near the interface and had less branching. The failure mode for both conditions was still the same, with cracks nucleating along the high angle grain boundaries formed during recrystallization. In conditions where there were few recrystallized grains, recovery led to formation of subgrains that strengthened the solder, and the higher strength led to a larger driving force for crack growth through the solder, leading to failure after less than half of the cycles in the continuous accelerated thermal cycling condition. This work shows that there is a critical point where sufficient strain energy accumulation will trigger recrystallization, but this point depends on the rate of strain accumulation in each cycle and various recovery processes, which further depends on local crystal orientations, stress state evolution, and specific activated slip and twinning systems.

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