Fraunhofer IZM Berlin

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1 Fraunhofer IZM Berlin Advanced Packaging for High Power LEDs Dr. Rafael Jordan SIIT

2 Agenda Gluing Soldering Sintering Transient Liquid Phase Bonding/Soldering Thermo Compression Junction Temperature Measurements

3 LED Packaging Taks Optics Filling Wire Bond 1st & 2nd Level Interconnect Chip Board Phosphor Submount Underfill Power Cooling

4 Agenda Gluing Soldering Sintering Transient Liquid Phase Bonding/Soldering Thermo Compression Junction Temperature Measurements

5 Glued Moduls ~ 1-2 Avago Excelitas

6 R th,eff [K/W] Characterization of Thermal Interface Materials R th,int1 R th,tim Rth, eff T Q R th, eff th,int1 th, TIM th,int2 R th, eff R R th,0 R 1 bulk R d A R th,int2 2,5 2,0 Linear function 1,5 1,0 TIM ~ 1/slop 0,5 R th0 0, BLT [µm]

Challenges for Glued Interfaces Nanotechnologies to improve heat transfer Multi modal particles Polymer fibres & metallic alloy Surface microstructuring Nano sponge interfaces Vertically aligned CNT

7 Challenges for Glued Interfaces Nanotechnologies to improve heat transfer Multi modal particles Polymer fibres & metallic alloy Surface microstructuring Nano sponge interfaces Vertically aligned CNT Nano-scale optimization TIM optimization Surface optimization Nano-scale optimization Increase thermal conductivity Increase thermal conductivity Reduce BLT Reduce interface resistance Increase thermal conductivity Improve phonon transfer

8 Failure Analyses Glued Die Bond overview focus diebond

I [ma] Failure Analyses by Diode Characteristic 20 F9

9 I [ma] Failure Analyses by Diode Characteristic 20 F A11 F1 F3 F7 F8 F9 F ,0 0,5 1,0 1,5 2,0 U [V]

10 Agenda Gluing Soldering Sintering Transient Liquid Phase Bonding/Soldering Thermo Compression Junction Temperature Measurements

11 Soldered Moduls OSRAM

12 wire for product compatibility, but not essentiell Wireless GaN - Chips Cree DA1000 OSRAM UX:3

13 Wetability of LED Dice Supplier B 40 mil (LM) Supplier B 24 mil (LM)

14 Wetability of LED Dice Supplier A old design Supplier A new design

15 Wetability of LED Dice Supplier A new design Supplier A new design

16 AuSn Phase Diagram Au-rich Sn-rich 278 C e C p: +L 1 L 1 +Au 217 C e 1 ~ 60

17 Copper Based LED on Silicon Substrate Reflow Soldering with AuSn no Activating Atmosphere x-ray x-ray LED-Module 1 x-ray LED-Module 2

18 Copper Based LED on Silicon Substrate Reflow Soldering with AuSn no Activating Atmosphere cross section Cross Section Chip on Silicon

19 Copper Based LED on Silicon Substrate Reflow Soldering with AuSn no Activating Atmosphere cross section close up look Cross Section Chip on Silicon

20 Copper Based LED on Silicon Substrate Thermode Soldering with AuSn no Activating Atmosphere x-ray x-ray LED-Module 1 x-ray LED-Module 2

21 Copper Based LED on Silicon Substrate Thermode Soldering with AuSn no Activating Atmosphere cross section Cross Section Chip on Silicon

22 Copper Based LED on Silicon Substrate Thermode Soldering with AuSn no Activating Atmosphere cross section close up look Cross Section Chip on Silicon

23 SnAgCu Phase Diagram ~ 30

24 Copper Based LED on Silicon Substrate Reflow Soldering with SnAg with Activating Atmosphere x-ray x-ray LED-Module 1 x-ray LED-Module 2

25 Copper Based LED on Silicon Substrate Reflow Soldering with SnAg with Activating Atmosphere cross section Cross Section Chip on Silicon

26 Copper Based LED on Silicon Substrate Reflow Soldering with SnAg with Activating Atmosphere cross section close up look Cross Section Chip on Silicon

Exsample (rigth): 8 SemiLeds LEDs soldered on AlN

27 COB assembly LEDs on AlN AlN/Si test board for optical, electrical, and thermal LED characterisation Exsample (rigth): 8 SemiLeds LEDs soldered on AlN with AuSn BMBF-Projekt Nanolux - White LEDs for General Lighting

28 Test Assembly with OSRAM LEDs OSRAM LEDs on AlN MC-PCB Subassembly mit Drahtbonds

29 OSRAM LED Dice on metallized AlN Watercooler, 600 W

30 OSRAM LED Dice on metallized AlN Watercooler, 600 W

31 OSRAM LED Dice on metallized AlN Watercooler, x-ray

32 Agenda Gluing Soldering Sintering Transient Liquid Phase Bonding/Soldering Thermo Compression Junction Temperature Measurements

33 Assembly with Ag Sintering Chip to Chip Chip to copper

34 Ag Sintering SEM Pictures Ag-Powder after drying Ag-Powder heat without force Ag-powder heat and force

35 Ag Sintered Interconnects comparing of two suppliers Cross Section with SEM preparation effect AlN Ag Plated Layer Ag Plated Layer Ag Bond Ag Bond Cu

36 Ag Sintered Interconnection, FIB Analysis Ag plated well defined interface Ag sintered

37 Ag Sintered Interconnection, FIB Analysis small pores almost disoluted ~ 370

38 OSRAM LED Dice on metallized AlN Watercooler, 1200 W

39 Shear Forces for Pressure Less Sintered LEDs Temperature Chip A on Ceramic Chip B on Ceramic Chip A on IMS Chip B on IMS 225 C (8,4 ± 2,1) N (8,8 ± 3,0) N (7,6 ± 3,1) N (7,5 ± 1,5) N 275 C < 0,5 N (8,3 ± 1,9) N < 2,0 N (12,7 ± 2,9) N

40 Pressure Less Sintering pro/contra Standard Equipment (Screen printer + P&P + Reflow) No mechanical fixing of parts during sintering No special atmosphere during sintering Lower Shear forces than sintered/soldered dice Metallization of die bond pad must be suitable Smaller process windows (especially regarding drying)

41 Agenda Gluing Soldering Sintering Transient Liquid Phase Bonding/Soldering Thermo Compression Junction Temperature Measurements

42 TLPB using electroplated Cu/Sn soldering annealing Si Cu 3 Sn Cu 6 Sn 5 Cu 3 Sn Cu

43 TLPS SAC-paste plus Cu spheres Cu Cu 6 Sn 5 Sn Cu 3 Sn 40 wt.-% Cu ( Cu 6 Sn 5 ) 20 wt.-% Cu Pore 40 wt.-% Cu (Cu 6 Sn 5 ) After soldering 40 wt.-% Cu

44 TLPS SAC-paste plus 40 wt.-% Cu spheres Proprietary Process and Paste Si-Chip DAB

45 Agenda Gluing Soldering Sintering Transient Liquid Phase Bonding/Soldering Thermo Compression Junction Temperature Measurements

46 Modules Assembled by Themocompression LumiLEDs

47 Thermocompression Bonding with Stud Bumps

48 Thermocompression Bonding with electroplated Bumps

Nano - Sponge Potential Application: - low pressure, low temperature

containment for medical applications - large surface area (sensors,

neuronal interface) 13 nm pore size - optical devices (plasmonics, SERS)

49 Nano - Sponge Potential Application: - low pressure, low temperature bonding (MEMS, laser) - compressible bonding (acommodate topography) - containment for medical applications - large surface area (sensors, catalytics) - bio compatible (e.g. neuronal interface) 13 nm pore size - optical devices (plasmonics, SERS) Flip Chip Sintering bonding zone densified zone 80% pore volume H. Oppermann, M. Hutter, R. Jordan, et al. (Fraunhofer IZM)

50 Agenda Gluing Soldering Sintering Transient Liquid Phase Bonding/Soldering Thermo Compression Junction Temperature Measurements

51 Critical Value is the Junction Temperature T J?

52 Junction Temperature Measurement Principles 1) Wavelength shift The recombination of the electron from the conducting band (n-type semiconductor) with the holes of the valence band (p-type) is a light emitting process. As the wavelength is directly correlated to the recombination energy and therefore depending on the forward voltage, the wavelength is increasing with decreasing forward voltage and increasing temperature. 2) Forward Voltage The Forward voltage is depending on the electron band gap and the Boltzmann distribution. The Boltzmann distribution is temperature depending and therefore the voltage is decreasing with increasing temperature.

53 Concept of measuring Tj with the forward voltage I [ma] I [ma] 50 Ideal 50 II R p Real R i 0 U v U [V] 0 I U v U [V] An ideal light emitting diode is closed up to a certain voltage, the forward voltage, and afterwards open without any influence of the current. The real LED has a different behavior and can be described in an easy equivalent circuit diagram as shown above. It is influenced by resistors parallel and in serious to the junction.

54 Strom [A] Spannung [V] Measuring Tj with the forward voltage, calibration 0,005 0,004 0,003 0,002 testing range 0,001 0,000 2,4 2,6 2,8 Spannung [V] 2,64 2,63 2,62 2,61 2,60 2,59 2,58 T = -t1 * ln (U/A1) 03B 2,637: T = -1152,913 ln(u/2,66220) 16B 2,620: T = -1398,438 ln(u/2,64008) 19B 2,640: T = -1220,828 ln(u/2,67310) 08B 2,642: T = -1179,331 ln(u/2,66607) 11B 2,634: T = -1423,025 ln(u/2,65662) 2,57 2,56 2,55 2,54 2,53 2,52 2,51 2,50 2,49 2,48 2, Temperatur [ C] The measurement current must be kept small, not to heat the die up, but out of the horizontal area of the UI characteristic, as otherwise the recalculation of the temperature will be imprecise. As Rp and Ri are different for every die, even within one lot, each LED must be calibrated.

55 Measurement Setup The internal resistance of the LED is strongly current depending and due to further distortions of higher order it is not possible to recalculate the pure forward voltage under running conditions. The running current must be lowered immediately to the measuring current, to measure the calibrated forward voltage without cooling down the LED. A possible circuit can look like the following.

56 Spannung [V] Spannung [V] Measurement Interpretation 3,2 2, mA = 2,58783 V = 25,1 C 3,0 2,56 2,8 2,55 2, T [µs] Meßpunkt [Einheit] Even within the realized switching time below 10 µs, a cooling of the LED is visible. Therefore the record transient is fitted with a biexponential curve with offset. The first half-value period is related to the thermal equilibration of the junction with the LED die, the second for the equilibration of the die with the substrate. The offset is simplified sum for the equilibration with the ambient and the final forward voltage at ambient temperature.

57 Voltage [V] Example of a Flat Panel Light Source 2,535 2,530 2,525 2,520 2,515 2,510 2,505 LED@010mA at secundary current = 010mA = 2, V = 24,16 C LED@050mA at secundary current = 050mA = 2, V = 26,44 C LED@080mA at secundary current = 080mA = 2, V = 28,51 C LED@120mA at secundary current = 120mA = 2, V = 31,72 C LED@120mA at secundary current = 080mA = 2, V = 30,08 C LED@150mA at secundary current = 150mA = 2, V = 34,28 C LED@175mA at secundary current = 175mA = 2, V = 36,11 C LED@200mA at secundary current = 200mA = 2, V = 38,66 C LED@225mA at secundary current = 225mA = 2, V = 40,91 C LED@250mA at secundary current = 250mA = 2, V = 43,52 C Time [µs]

58 Thermal comparative study gluing/soldering/sintering Test Szenario: LED auf MC-PCB, MC-PCB auf Kühlkörper, T = 25,0 C I 1 = 100 ma, I 2 = 350 ma, I 3 = 700 ma

59 U [V] Thermal comparative study gluing/soldering/sintering e.g. blue LED glued 2,44 2,42 I 1 = 100 ma 2,40 I 2 = 350 ma 2,38 I 3 = 700 ma 2,36 2,34 0,000 0,002 0,004 t [s] sample 1 sample 2 sample 3

60 T [ C] Thermal comparative study: blue LED blue glued blue soldered blue sintered thermal load (optical emission corrected) [mw]

61 T [ C] Thermal comparative study: white LED 'white' glued 'white' soldered 'white' sintered thermal load (optical emission corrected) [mw]

62 T [ C] Thermal comparative study: red LED red glued red soldered thermal load (optical emission corrected) [mw] red sintered

63 LED Bulb Simulation Heat sink Silicon-oil Air Helium

64 LED Bulb Simulation

Test stand for the Characterisation of Thermal Interface Materials from the macro level up to the nano level

13th LEIBNIZ CONFERENCE OF ADVANCED SCIENCE 26. - 27. April 2012 NANOSCIENCE 2012 Test stand for the Characterisation of Thermal Interface Materials from the macro level up to the nano level Mohamad Abo