xcerpt irect Bonded Copper Presented by ouglas C. Hopkins, Ph.. 312 Bonner Hall University at Buffalo Buffalo, Y 14620-1900 607-729-9949, fax: 607-729-7129
Authors thank Curamik lectronics A member of for providing information and photos
CB Process Oxygen reduces the melting point of Cu from 1083 C to 1065 C (utectic melting temperature). Oxidation of copper foils or injection of oxygen during high temperature annealing (1065 C and 1080 C) forms thin layer of eutectic melt. Melt reacts with the Alumina by forming a very thin Copper-Aluminum-Spinel layer. Copper to copper is fused the same way. Copper-Aluminum-itride (Al) BC is possible. The Al-Surface must be transformed to Alumina by high temperature oxidation.
BC Process Copper Copper Ceramic Copper O 2 Copper Ceramic Copper Oxide Copper Copper 1080-1070 - Heating O 2 iffusion and Cooling Copper Ceramic Copper Ceramic utectic Melt Copper Copper Copper Copper 1060-1050 - utectic 0 0.4 0.8 1.2 1.6 O 2 -Concentration in Atom-%
BC - Interfaces Copper Al 2 O 3 Al 2 O 3 Al Copper Copper
Flow Chart of BC Processing BC Process Masking tching Laser Scribing Final Cleaning lectroless ickel lectroless Gold Substrate blank copper surface Substrate i plated Substrate i + Au surface Control Separating mastercards by breaking Shipping to customer as single parts Shipping to customer as mastercards
Masking High precision screen printers for high volume Semiautomatic and fully automatic with pattern recognition Redundant equipment Photomasking for high density circuits Air conditioned clean rooms
tching Specially designed precision etchers for thick copper layers Automatic chemistry control Mask stripping integrated 3 separate high volume lines in operation Controlled by SPC
Plating / Final Cleaning Fully automatic high volume plating line for electroless i + Au Controlled by SPC Final cleaning for Cu integrated Parallel backup lines Solderability and wire bond testing
Laser Machining Fully automatic high precision CO 2 lasers with pattern recognition esigned for high volume throughput Scribing and drilling Multiple equipment Controlled by SPC
Features of BC Substrates Low thermal coefficient of expansion despite relatively thick copper layers (TC = 7.2-7.4-10-6 at 0.3mm / 12mil copper) High current carrying capability with thick copper (Copper width 1mm / 40mil, height 0.3mm / 12mil, continuous flow 100amps = temp rise of 14-17 C) High peel strength of copper to Al2O3 60/cm; Al 45/cm at 50mm/min peel speed High thermal conductivity (Al2O3 = 24W/mK; Al =170 W/mK) Low capacitance between front- and backside copper (Appr. 18pF/cm2 for 0.63mm ceramic thickness)
Relative Heat Flux (W/sqm) 100.000.000 Chips need Cooling Surface of Sun 10.000.000 Power Semiconductor Chip 1.000.000 Saturn V ngine (Case) 100.000 Hot-Plate Logic Chips 10.000 Light Bulb (100 W) 1.000 Heat Loss from Human Body 100 10 100 1000 10000 Absolute temperature [K] Source: Semikron
Principal esign of IGBT Power Module Current contact Plastic casing Hard encapsulation Al thick wire bond Soft encapsulation IGBT / iode BC substrate Cu baseplate Heat sink Solder joint Thermal grease
Single Switch Module 4 Substrates, 4 IGBT s and 4 iodes BC substrate iode IGBT
Power Module Thermal Resistance Thermal Resistance as a function of Substrate Thermal Conductivity 0,7 Thermal resistance [K/W] 0,65 0,6 0,55 0,5 0,45 Al2O3 Al 0,4 iamond 10 100 1000 10000 Thermal conductivity[w/mk] Chip area = 100mm 2 ; ceramic thickness; 0,635mm; copper baseplate 3mm; power dissipation 100W; solder 0,070mm
Thermal Mass Junction Temperature [ C] 160 140 120 100 80 60 40 20 0 Influence of copper thickness Cu-thickness (3) Influence of Rth static 1-2 1-1 10 11 12 13 ln time [sec] 0,15 mm 0,3 mm 0,6 mm Junction temperature as function of the dynamic thermal resistance
Flexural Strength of BC as a function of copper thickness 99 Probability of Failure F [%] 90 75 63,3 25 10 1 Alumina Standard BC d Cu =0,20mm BC d Cu =0,25mm BC d Cu =0,30mm 300 400 500 600 700 800 900 1000 Flexural Strength [MPa]
Flexural Strength of HPS BC Compared with Blank HPS (optimized Alumina) Ceramic 99 90 75 63,3 25 10 1 BC Optimized Alumina 500 550 600 650 700 750 800 850 900 950 1000 1500 2000 Probability of Failure F [%] Flexural Strength [MPa]
imple esign Top view Cross section
Thermal Cycling Reliability Standard Alumina BC with and w/o imples Probability of Chonchoidal Fracture F [%] 99 90 75 63,3 25 10 1 Standard BC imples BC 20 40 60 80 100 200 300 400 umber of Temperature Cycles 500 600 700 800 900 1000 2000
Average Life 0 (Weibull) 2200 2000 1800 1600 1400 1200 1000 800 350 300 250 200 150 100 50 0 umber of thermal cycles >2000 >2000 without imples with imples (Copper pattern design for thermal stress relief) CurStd CurHPI CurHP* CurMil Al *d (ceramic) = 25 mil, d (Cu) = 12 mil -55 C / 150 C / 15 min. d (ceramic) = 15 mil, d (Cu) = 8 mil -55 C / 150 C / 15 min.
Special Substrates Active Metal Brazed (AMB) Refractory Metallization Substrates with vias Substrates with lead offs 3-imensional substrates BC Packages Water cooled substrates
Via Technology Both sides flat surface. Ceramic hole diameter min. 1.0mm R<100µΩ One side flat surface. Ceramic hole diameter min. 1.0mm R<100µΩ One side flat surface low cost. Ceramic hole diameter 2.5mm (0.3mm copper layer) R<100µΩ
Vias in BC Substrates High current front to back feed-through 100 A current 100 µohm For backside groundplane or shield Both hermetic Version 1 can be used as thermal path also
Integral Terminals Terminals made of same copper sheet as circuit High electrical conductivity due to solid metal without interface resistance Very high reliability
3-imensional BC For very high density circuits xtremely reliable due to integral connectors Base for power Sidewalls for non-power components Assembled flat and bend up
Package Types Kovar Lid Side Lead Kovar Frame Wirebond Chip 1 Kovar Lid Top Lead Kovar Frame Wirebond Chip 2 Ceramic Copper 1 Via 2 irect Bonded Pin
Package Types Kovar Lid own Lead Kovar Frame Wirebond Chip Kovar Lid Glass to Metal Seals Wirebond Chip Kovar Frame Glass Kovar Pin 1 Kovar Lid Surface Mount Kovar Frame Wirebond Chip 1 Ceramic Copper 1 Via 2 irect Bonded Pin
Kovar Frame Brazed on BC Substrate Glass Sealed Feed-Through
Fluid Cooled BC Lowest thermal resistance of all available solutions for COB Rth ranging from 0.08 to 0.02 K/W using Al2O3 or Al Power dissipation up to 3 kw on 2 x 2 xtremely compact design Modular system assembly
Liquid flow-through micro channels Liquid Ceramic Isolation Layer Basis lement Chip Mounting Layer
Micro Channels Cut A Cut B
Micro Channel Water Cooled Module Half bridge 6 IGBT 12 iodes 62 mm Standard module size 450 A Cooling water temperature up to 80 C possible
R thja as a Function of Water Flow 70 65 RtHja [ mk/w ] 60 55 50 45 40 35 Al integ. Al2O3 integ. Al2O3 substrate Al substrate 30 25 0 1 2 3 4 5 6 7 Water Flow [ l/min. ]
Module comparison Conventional v. Integrated water cooling R th [K/kW] 100 80 60 40 20 0 Heat Sink Ambient Case-Heat Sink Junction - Case Junction Ambient 1 2 About 60% reduction of R thja (flowrate 2.5l/min.) 2 1 About 60% reduction of R thja (flowrate 2.5l/min.) 3 1 Junction Ambient 3 1 Standard module on closed cooling system (calculation) 2 Module with integrated cooling system (measurement: soldered Al 2 O 3 ceramics) 3 Module with integrated Al substrate