Die Attach using Pressure-Assisted Sintering for High-Temperature Applications

Transcription

1 Die Attach using Pressure-Assisted Sintering for High-Temperature Applications Erwin Peiner Institute of Semiconductor Technology, TU Braunschweig, University of Technology, Germany Opening Ceremony Elsold GmbH & Co KG, Ilsenburg, 27 Jun 2013

2 Outline Pressure-assisted sintering die-attach Low-Temperature Joining Technique (LTJT) Industrial applications Pick & place sintering die-attach Sintering paste Nano particles Porosity, thermal conductivity, shear strength, diamond filler, Cu paste Downhole electronics Pressure / vibration sensors, pulser driver module, TE cooler 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 2

4 Pressure-assisted sintering die-attach Power electronic multichip modules: large-area-chips attached on substrates today: bonding using lead-free or high-lead solder at 260 C to > 300 C operation temperature of 175 C or above -> fatigue damage under cyclic loading 1989 (Schwarzbauer & Kuhnert): Low-Temperature Joining Technique (LTJT) based on sintering of silver powder no liquid phase low process temperature no alloy very low homologous temperature (T op << T melt ) 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 4

5 Low-Temperature Joining Technique (LTJT) Chip Substrate Paste containing Ag micro-particles Cohesive connection by sintered Ag layer 5 µm T = 250 C p = 40 N/mm 2 t = 1 min 5 µm pores 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 5

6 features of LTJT Joining layer Ag-filled polymer adhesive PC3231 Lead-free solder Sn 96.5 Ag 3.5 High-lead solder Pb 92.5 Sn 5 Ag 2.5 Ag-Cubraze Incusil TM ABA* Ag sinter layer** Max. operation temp. T op ( C) > 380 Thermal conductivity (W/mK) Electrical conductivity (MS/m) CTE (ppmk -1 ) Young s modulus (kn/mm 2 ) Shear strength (N/mm 2 ) * Brazing alloy Ag59.0Cu27.25In12.50Ti1.25, recommended brazing atmosphere: vacuum or inert gas ** Standard LTJT: Ag micro paste, porosity = 15%, layer thickness = 25 µm 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 6

7 LTJT press setups automated setup for small series production 50 tons manual press for manufacturing of microstructured samples press for large-area interconnects high-precision press for small devices 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 7

8 LTJT at Volkswagen Modules for electrical power train of hydrid cars, fuel cell cars, increasing power density / device temperature range at high mechanical stress no lifetime loss LTJT for silver ribbon wires diode and IGBT die-attach Schulze et al. CIPS 2010, Nürnberg 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 8

9 LTJT at Semikron Semikron, Nürnberg (power IDM, e.g. for inverter in wind turbines): no bond wires -> flexible line carrier layer no thermal grease, base plate, and solder joint -> improved thermal contact resistance (-30 %) -> improved temperature cycling capability (10 ) 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 9

10 LTJT at BMW Thermoelectric generator (TEG) for energy harvesting from waste heat operated between 200 C and 500 C high temperature cycling capability LTJT for TE-leg attach to metal bridge low homologous temperature < 0.66 sinter layer TEG TEG exhaust gas Brück et al., 2012, German patent pending cooling water 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 10

12 Pick & place sintering die-attach Standard LTJT: large press ( 50 tons) required inconvenient assembly, misalignment can lead to damage of chip (silicon) and substrate (ceramic) Pick & place sintering die-attach replace press by pick & place bonder: can be combined with adhesive die-attach in hybrid technology replace powder by paste: one-to-one replacement to solder / epoxy paste can be processed by common SMT (screen / stencil printing) use nano-particle paste : pressure & temperature can be reduced 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 12

13 Pick & place sintering die-attach SCOPUS-search using sintering and die attach in title, abstract, keywords strongly increasing research activities since June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 13

14 Pick & place sintering die-attach screen printing of Ag paste on carrier sheet drying and expelling of solvents picking-up by stamp and placing onto substrate sintering (temperature, pressure, time) printing on chip using transfer method 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 14

15 Pick & place sintering die-attach high-temperature-stable chip metallization including noble-metal finish mean-time-to-failure: t MTF ( T ) = t ( T ) MTF 0 E exp k a 1 1 T T0 Metallization Layer thickness (nm) E a (ev) t MTF (h) T = 250 C T = 300 C Ti/Pt/Au 80/80/ ± Ti/Pd/Au 80/100/ ± Ti/TiN/Au 60/100/ ± June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 15

16 Pick & place sintering die-attach covering of a polymerfoil with silver paste: by screen printing by stencil printing transferring of paste from foil to dies by cold pressing: transferred layer-thickness: 10 µm 150 µm (typical: 25 µm ± 2.5 µm) GaP-PD inherent safe nano particle handling (no use of loose powders) 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 16

17 Pick & place sintering die-attach modified Flip-Chip bonder: high positioning accuracy easy handling of small devices (chip area > µm 2 ) variation of process parameters possible (temperature, pressure, time) immediate process control Fineplacer, Finetech GmbH & Co. KG 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 17

19 Sintering paste target specifications low porosity high electrical & thermal conductivity strong adhesion to chip and substrate low CTE compliant with adhesive die-attach (low process temperature) no chip damage (soft stamp, low process pressure) 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 19

20 porosity densification rate: viscosity: decreases with T, i.e. T 1 dρ 1 ρ dt η [ p+ Σ( r )] ( T ) process pressure: p sintering stress: decreases with particle radius, i.e. r Ferro Corporation (2009) using nanoparticles process temperature & pressure can be reduced 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 20

21 porosity RT 200 C 250 C micro (< 3 µm), flakes micro & nano t = 2 min p = 0 nano (< 100 nm), spheres densification of nano paste occurs already at 200 C pure nano paste poorly processable -> mixture of micro and nano paste 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 21

22 porosity nano paste high-nano content paste T= 230 C p =13 N/mm 2 t = 2 min micro paste porosity decreases with decreasing layer thickness slope increases with increasing nano content porosities down to 10 % using high-nano content paste 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 22

23 thermal conductivity thermal conductivity increase with decreasing porosity 230 W/m/K using high-nano content paste of 10 % porosity 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 23

24 adhesion high-nano content paste T= 230 C P=13 N/mm 2 t = 2 min adhesion increase with decreasing particle size / layer thickness 20 N/mm 2 using high-nano content paste at µm thickness 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 24

25 effect of nano nano particles in paste + densification rate higher than for micro pastes + low porosity of thin layers -> high electrical & thermal conductivity, high shear strength + lower process temperature and pressure - nanoparticles tend to the formation of agglomerates before die-attach - pure nano paste is highly viscous -> poor processability agglomerates (250 C for 5 min) tradeoff: use mixture of micro and nano powder (high-nano content) 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 25

26 diamond filler diamond has low CTE and large thermal conductivity sinter layer with 10 wt.% diamond filler 250 C, 6 N/mm 2, 2 min) Material Diamond content (wt.%) T max ( C) CTE (ppm/k) Thermal conductivity (W/m/K) Porosity (%) Electrical conduct. (MS/m) P-1011* micro** ± N/mm 2 ** ± N/mm 2 ** ± * electrically conductive modified polyimide; ** sinter layer: T = 230 C, t = 2 min; reduced CTE and increased thermal conductivity however increased porosity and electrical conductivity 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 26

27 Cu paste Cu much less expensive than Ag: < 1/1000 electrical & thermal conductivity, CTE, melting point, Young s modulus nearly the same diffusion barrier necessary oxide has to be removed, pre-annealing under oxygen-free conditions successful sintering at 350 C, 40 N/mm 2, 2 min in ambient air properties of sintered layers: layer thickness: 100 µm porosity: 39 % electrical conductivity: 12.9 MS/m thermal conductivity: 94 W/m/K shear strength: 9 N/mm 2 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 27

29 Downhole electronics Drilling rig Drill string BHA Drilling Bottom Hole Assembly (BHA) equipped with electronic modules for sensors for MWD (azimuth, inclination, toolface, vibration pressure, rock porosity, ) communication (mud pulse) power supply (alternator) MWD tools Drill bit Oil reserves locked in deep depths high well temperatures: ( C) long-term data logging: ( h) 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 29

30 geothermal power generation Enhanced Geothermal Systems (EGS) in Germany R. Schellschmidt, database of GGA-institute (2005) According to Al Gore (2009) efficient geothermal power generation: T > 150 C (better 250 C, η = 14 %) (Reinecke et al., coll. project gebo (2010)) 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 30

31 chip transistor Fairchild, BC817 2 T = 250 C; t = 2 min Pressure (N/mm 2 ) Process capability stainless steel PEEK CA silicone PEEK stainless steel silicone low. specific. limit Silicone stamp: highly reproducible (process capability C pk = 1.8 / 4.1 low p = 3 N/mm 2 at T = 250 C PEEK stamp: low T = 200 C at p = N/mm 2 ; N/mm 2 ; C pk = June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 31

32 optomechanical pressure sensor input/output module no degradation of dark current after 400 temperature cycles between 100 C and 250 C 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 32

33 MEMS-vibration sensor delicate spring-mass element 6.2-µm-thin spring -> prone to fracture bonding only to frame low bonding pressure 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 33

34 MEMS-vibration sensor stencil printing of paste onto foil transfer of past to substrate picking-up of sensor using silicone stamp and placing onto substrate die-attach at low pressure (4 N/mm 2 ) silicone stamp with recess for sensor 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 34

35 MEMS-vibration sensor diffused DL SOI Shear strength at RT (N/mm 2 ) Shear strength at 250 C (N/mm 2 ) Offset at 250 C, t = 0 (mv) Offset at 250 C, t = 120 h (mv) TCO (µv/v/k) 13.0 ± ± offset drift < 1 % after 400 temperature cycles between 110 C and 250 C 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 35

36 MEMS-vibration sensor vibration test using constant voltage supply of Wheatstone bridge TCS given by temperature dependence of gauge factor can be eliminated using constant current supply 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 36

37 Peltier cooler Long-term data logging active cooling of downhole electronics necessary TE coolers: compact, no moving parts sintered TE cooler tested at ambient temperatures up to 300 C T = K at zero power dissipation and ambient temperatures of RT to 300 C R i /R i < 1.3 % after 850 cycles between 100 C and 250 C low contact resistance (1.4 ± 0.1) 10-5 Ωcm 2 ; < typical values of lead-free solder (SnAgCu) commercial modules (Marlow, TEC) limited to < 200 C 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 37

38 Summary: Pick & place sintering die-attach Die Fairchild, BC817 Nat. Semic., LM139A Infineon, SIGC15T60 Cree, InGaN-LED Epigap, GaP-PD MEMS vib. sensor Peltron, p-,n-te-legs Area (mm 2 ) Temperature ( C) Pressure (N/mm 2 ) Time (min) Stamp PEEK PEEK silicone steel steel silicone silicone 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 38

39 Conclusions Pressure sintering for vs. soldering & adhesive bonding at > 175 C better thermal contact better cycling capability of die-attach Nano particles improve the densification rate of sinter paste for lower process temperature and pressure damage-free attach of small dies compliance with adhesive bonding Pick-and-place sintering die-attach demonstrated for transistors, ICs, and bumped devices in hybrid modules LEDs, PDs, and MEMS for MWD TE devices for active cooling of downhole electronics 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 39

40 Acknowledgements Collaborative project "gebo" (Geothermal Energy and High Performance Drilling) funded by the Ministry of Science and Culture, Lower Saxony (MWK) and Baker Hughes, Celle, Germany Dr. J. Kähler, Dr. A. Stranz, J. Arens, F. Brunke, S. Lüttig, M. Nothdurft C. Schnöing, (Baker Hughes, Celle) 27 June 2013 Erwin Peiner Die Attach using Pressure-Assisted Sintering Slide 40