RELIABILITY AND PERFORMANCE OF THERMALLY CONDUCTIVE ADHESIVES Scott T. Allen Henkel Corporation Irvine, CA, USA scott.t.allen@us.henkel.com Slide page 1
Introduction Increasing Device Performance Drives Increasing Thermal Performance Materials needed to provide a thermal path from component to heat sink Various Methods of Providing a Thermal Solution Grease Tape Phase Change Adhesive Slide page 2
Thermal Materials Slide page 3
Adhesives Adhesives provide mechanical bonding as well as a thermal path Adhesives need to be cured Heat UV 2-part (catalyzed) Activator Slide page 4
Bead on Bead New Methodology The term Bead-on-Bead describes a unique chemistry for a two-part acrylic adhesive. Rather than premixing parts A & B, each part is applied to the component and the mixing occurs when the two items to be bonded are joined together. There are two methods for applying this material: Option 1 Apply Part A Apply Part B Mixing & curing occurs upon assembly Option 2 Slide page 5
Thermal Adhesives and Reliability Thermal Adhesives fail due to: Poor Adhesion Change in Thermal Performance This study looks at both adhesion and thermal performance under various stress conditions Adhesion Testing Lap Shear (Instron) Die Shear Thermal Performance Testing Thermal Resistance Different Substrates Different Stress Conditions Slide page 6
Adhesives in Test Slide page 7
Adhesion Testing Lap Shear Lap shear testing as per ASTMD 1002, Al Lap Shears Activated and BoB materials allowed to cure for 72 hours 200 air-to-air cycles of 25 C to 125 C, 15 mins at each temperature extreme Slide page 8
Adhesion Testing Die Shear Die Shear performed at Room Temp and 125 C (20 sec hold at 125 C) Die Size 0.250 x 0.250 x 0.030, 5 mil Spacers for bondline control Substrates Ceramic - Furnace clean at 425 C Silicon - Plasma clean 125 mtorr N 2 /O 2 mix, 200W, 120 seconds Ni plated Cu leadframe - Plasma clean 125 mtorr N 2 /O 2 mix, 200W, 120 seconds Mold Compound - IPA wipe Contaminated (Polydimethyl Siloxane - PDMS) Mold Compound Max Die Shear range is 100 kg-f Slide page 9
Adhesion Testing Die Shear RW Slide page 10
Adhesion Testing Die Shear Slide page 11
Thermal Performance Testing Environmental testing was performed on a variety of substrates, specifically chosen to represent the materials commonly found in electronics cooling applications. These materials are: Silicon Representative of bare die applications such as flip-chip packages Ceramic As found in ceramic lidded packages Mold compound Mold compound as used in molded packages such as power transistors Contaminated Mold Compound As above, coated with polydimethylsiloxane mold release agent Slide page 12
Thermal Performance Testing Environmental Test Conditions Thermal Shock -50 C to +150 C liquid to liquid One cycle = 5 mins @ high temp., 5 mins @ low temp. Total 15 cycles, No dwell between cycles Heat / Humidity 1000 hours at 85 C / 85% Relative Humidity Heat Aging 1000 hours @ 125 C Thermal Cycling JEDEC A104 condition J 1000 cycles from 25 C to 125 C at 10 minutes dwell Ramp rate 10 C / minute up and down Parts tested at room temperature for all environmental conditions Slide page 13
Testing Methodology Temperature T 1 Temperature T 2 Adhesive thermal resistance is determined by first establishing, then removing all other resistances Slide page 14
Parts/Equipment Illustrations Test Specimen TO-247 Power Semiconductor Test Equipment Analysis Tech Phase 10 Semiconductor Analyzer Slide page 15
Thermal Performance Thermal Shock Slide page 16
Thermal Performance Heat/Humidity Slide page 17
Thermal Performance Heat/Humidity (disregarding ceramic) Slide page 18
Thermal Performance Heat Aging Slide page 19
Thermal Performance RT Storage Slide page 20
Thermal Performance Thermal Cycling Delaminated Slide page 21
Performance by Material With Mold Compound BoB AC1 AC2 AC3 H1 MC - HH -7.1% 3.8% -1.6% 2.9% 4.9% MC - HA -0.7% 1.0% -4.7% 6.9% 3.1% MC - RT -0.3% 3.2% -2.9% 0.6% -0.8% MC - TC 0.3% 2.2% -6.5% 3.3% -4.6% CMC - HH 0.1% 4.5% 7.7% 1.4% -1.7% CMC - HA -4.1% -1.6% -1.2% 1.6% -0.5% CMC - RT 4.4% -1.3% 4.1% 0.9% 1.9% CMC - TC 5.5% 2.2% 3.2% Delam -6.2% Die Shear - CMC 22 kg 12 kg 22 kg 54 kg 26 kg Lap Shear - TC 2183 psi 1232 psi 1533 psi 1945 psi 1226 psi Slide page 22
Summary - Adhesion Poorest adhesion was observed on the PDMS contaminated surfaces Hot die shear strength is poor 70-90% reduction in strength for BoB, AC1, AC2, and AC3 40-60% reduction in strength for H1 Lap shear data shows that the adhesion strength is not affected by thermal cycling. Slide page 23
Summary - Thermal Thermal performance on ceramic with all materials under humid conditions was catastrophic Other than on Ceramic Substrates the thermal performance was under a 20% change under all the various stress conditions Second worst performer was the silicon substrate New Bead on Bead adhesive technology offers better thermal performance and smallest degree of change overall. Slide page 24
Thank you Questions? Acknowledgements: Van Chiem for his work on this project Brian Toleno and Jimmy Earle for their input Slide page 25