New Pb-Free Solder Alloy for Demanding Applications Presented by Karl Seelig, VP Technology, AIM
Why REL? The evolution and expansion of electronics into more harsh operating environments performing more critical functions Drawbacks of SAC305: Poor drop/shock performance High melting temperature (217-220 C) Increased concern of tin whisker growth Weakened strength due to thermal cycling/aging Cosmetic appearance
Large IMC Plates in SAC Alloys with >3% Ag F. Mutuku et al, Journal of ELECTRONIC MATERIALS, Vol. 46, No. 4, 2017 Optical micrograph of free-standing Sn3.8-Ag0.7-Cu solder alloy showing a large Ag 3 Sn primary precipitate.
Large IMC Plates in SAC Alloys with >3% Ag Fracture boundaries created by platelets in high silver alloys reduce drop shock performance. K. Zeng et al, 2012
Tin Whiskers Test Method Humidity 85%, T=60 C, t=3100hr The coated wire was stressed by making a U-shaped bend to 90 degrees. SAC305 REL22
Microstructure Comparison After High Temperature Aging 24h @150 C SAC305 As Cast REL22 As Cast SAC305 Aged REL22 Aged Microstructure of REL61 & REL22 remains stable vs. SAC305
How to Improve SAC305 Bismuth (Bi) offers some benefits improvements but has limitations. Antimony (Sb) can increase durability. There is a long list of grain refiners. A variety of micro-alloy elements can be incorporated to stabilize alloys.
Melting Behavior Differential scanning calorimetry (DSC): heating rate of 10 C/min
Thermal Behavior Parallel Solidus and liquidus lines deviate at 3% Bi
Mechanical Behavior Samples annealed 96hr at 125 C SAC305 is shown for comparison
AIM s REL22 TM Alloy REL22 is a new, patent pending, high-reliability alloy for use in extremely harsh environments. High reliability / high strength Mitigates tin whisker formation Exceptional thermal cycling performance Melting point 210 C Drop-in to SAC305 assembly processes Sn/Ag/Cu/Bi/Sb/Ni/X
REL22 Kinetics of Intermetallic Growth (IMC) 740hrs at 150 C SAC305 / 480hr@150C REL22 / 480hr@150C Cu 3 Sn Cu 3 Sn Cu 3 Sn introduces brittleness.
Tensile Creep (Aged 24hrs @ 150 ⁰C) In aged condition, RT creep performance of REL22 is superior to SAC305. In fact, SAC305 shows very poor creep performance after aging.
Compression Creep (@ 150 C 10MPa and 175 C 20MPa) High temperature creep resistance of REL22 is superior to SAC305 and REL61.
Tension Test Tension test performed per (ASTM E8/E8M-11) Samples aged 24hrs at 150 C Cross head speed: 2 mm/min REL22 shows much higher strength as compared with SAC305. Elongation of REL22 is higher than REL61 and slightly lower than SAC305.
Thermal Cycle Testing Scope DfR Solutions performed thermal cycling experiments on test coupons assembled with three different solder alloys SAC305 and two alternative Pb-free solders (REL61 & REL22) Sufficient time to failure data was obtained from three different package styles LED, MLF and Resistor Other packages tested had insufficient failure data or failure data that was suspect Both alternative Pb-free solders demonstrated improvement in thermal cycle lifetime over SAC305 Data provided by:
Thermal Cycle Testing Samples Eight boards were assembled for each solder alloy. Data derived from highlighted components. Data provided by:
Thermal Cycle Testing Setup Thermal cycle profile (per IPC-SM-785) -40 C to 125 C / 15 minute dwells / 20 C per min ramp Test suspended after 3950 thermal cycles. In-situ resistance monitoring tracked changes of resistance with time for each component through out the duration of the test. Failure was taken at a number of thermal cycles corresponding to resistance change per IPC- 9701A standard. Data provided by:
Thermal Cycle Testing Setup Data provided by: Test boards were hanged vertically with sufficient spacing to allow adequate airflow.
Package Thermal Cycling Comparison of Solders SAC305 REL61 REL 22 Cycles to Failure (η) Cycles to Failure (η) Ratio to SAC305 Cycles to Failure (η) Ratio to SAC305 LED 918 1165 1.3 2128 2.3 MLF156-12mm 900 1360 1.5 1884 2.1 MLF48-7mm 1623 2045 1.3 2900 1.8 MLF32-7mm 1405 2126 1.5 2815 2.0 2512 1975** 1925** 1.0 5194 2.6 Average Ratio to SAC305 (=1) 1.4 2.2 Data provided by: **Characteristic lifetime based on first population set (indications of mixed mode behavior)
Thermal Cycle Test Results Data provided by: REL22 is twice as durable as SAC305.
Thermal Cycle Test Results Data provided by: REL61 is equal to or better than SAC305 at a lower cost.
Thermal Cycle Test Results LED Data provided by:
Thermal Cycle Test Results MLF48-7MM Data provided by:
Thermal Cycle Test Results 2512 Resistor Data provided by:
Thermal Cycle Testing REL61 and REL22 Relative to SAC305 REL61 provides ~40% improvement in thermal cycle fatigue lifetime Measured range is 0 to 50% REL22 provides ~120% improvement in thermal cycle fatigue lifetime Measured range is 80 to 160% Data provided by:
REL22 Wetting Balance Behavior Wetting Force Wetting Time REL22 = faster stronger wetting than SAC305 or Sn/Ag/Bi/Sb/Ni/Cu.
REL61 Wetting Comparison REL61 SAC305 Sn/Cu/Ni Sn/Cu/Ni Sessile Drop Test measures surface energy via contact angle. Lower contact angles = better wetting.
REL22 No Clean Solder Paste Test Data
REL22 vs. SAC305 No Clean Paste BGA and QFN Voiding NC REL22 NC SAC305 Improved BGA Voiding with REL22 NC REL22 NC SAC305 QFN Voiding Lower with REL22
REL22 vs. SAC305 vs. Sn/Ag/Bi/Sb/Ni/Cu No Clean Paste 0603 Voiding REL22 is more consistent than SAC305 and Sn/Ag/Bi/Sb/Ni/Cu alloys.
REL22 Drop-in for SAC305
RSS-L-HS- LTAL RSS-HS-L RTS-1 Wetting QFP144 / Paste vs. Profile NC SAC305 T4 NC REL22
REL22 No Clean Solder Paste Field Data
M8 REL22 Solder Paste vs. Competitor SAC305 Immersion Silver Surface Finish - 1.6mm thick FR4 6 layer
M8 REL22 Solder Paste Competitor SAC305 M8 REL22 M8 REL22 results in better wetting and smoother solder joint appearance.
M8 REL22 Solder Paste Competitor SAC305 M8 REL22 M8 REL22 results in better wetting and smoother solder joint appearance.
M8 REL22 Solder Paste Competitor SAC305 M8 REL22 M8 REL22 results in better wetting and smoother solder joint appearance.
REL22 Alloy Summary
REL22 Summary Enhanced durability for use in extremely harsh environments Mitigates tin whisker formation High reliability / high strength Exceptional thermal cycling performance Reduces voiding Melting point 210 C Drop-in to SAC305 assembly processes
REL61 Summary Superior barrel fill Lower solder pot maintenance Reduces voiding Lower cost than SAC305 alloy Enhanced reliability versus SAC alloys Higher strength and hardness compared to SAC alloys Improved thermal cycling performance Mitigates tin whisker formation Melting point 208-216 C Sn/Cu/Ag/Bi
Thank You