Lead Free Sinterable Pastes for Die and Component Attach Applications Michael Matthews Ormet Circuits, Inc. April 8, 2015
Transient Liquid Phase Sintering [TLPS] [1] Tin-based Solder Particle [2] Copper Particles TEMPERATURE Room Temp Cu Copper and Solder particles Cu suspended in polymer resin Sn system [epoxy] [3] Polymer Matrix Cu [Epoxy-based] Liquid Phase Sn Alloy Cu Temperature 180-220C Cu Alloy begins to melt Sn (liquid phase) Cu Sintered metal network Sn Cu Temperature >225C Sn-Cu Sn Cu Sn Sn-Cu sintering Alloy reaction occurs Melt Point > 400C SINTERED Cu Sn MICROSTRUCTURE
Benefits of Transient Liquid Phase Sintering Technology • Low temperature metallic joining – Can be processed in box oven or tunnel reflow • Thermally stable at elevated temperatures – Will not remelt after sintering is complete • Superior mechanical properties at elevated temperatures – Metallic bonds have higher strength compared to adhesives • Pb-free & Halogen-free composition – Copper and Tin alloys • Excellent Electrical and Thermal Conductivity – <100 uohm-cm volume resistivity – 25-60 W/mK Thermal Conductivity 3 Transient liquid phase sintering materials offer a unique combination of properties.
The Convergence of Wafer Fab, Semiconductor Packaging and Electronics Assembly is Creating Requirements for New Materials Substrate innovation for higher density, performance & lower cost Assembly materials and Materials that substrates that leverage are Green , both fab and enable mobile packaging devices and are infrastructure temperature resistant The rapidly blurring lines between wafer fab, packaging and assembly are creating opportunities for new material technologies
TLPS Technology is Aligned to the Future Roadmap of Electronics Packaging & Substrates • Near Term Trends – Green conductive materials • Industry is looking to replace Lead in consumer and industrial electronics – Form factor reduction and component integration • System-in-package and wafer level packaging require new interconnect materials – Higher operating temperature electronics • Components in hot, harsh environments for Automotive, lighting, high power applications & solar • Longer Term Trends – Yield improvements • Incumbent materials at the end of their cost/ performance curve for the leading edge
Product Platforms developed using TLPS Technology Pb-free Circuit Board Solder Semiconductor LED Substrate Replacement Interconnect Packaging Circuit Materials Materials Materials Materials Applications using Liquid Phase Sintering-based Materials
TLPS Value Proposition by Platform • Pb-free Semiconductor Die Attach – Pb-free alternative to soft solder – Alternative technologies either fail to meet reliability or price/performance requirements. • Solder Replacement Materials – TLPS materials provide electrical and thermal performance of solder, but will not remelt. – Solder remelt causes yield problems for system-in-package and high temperature applications. • PCB Interconnects – Paste interconnects enable high-signal-speed circuit boards for semiconductor test and RF applications. • LED Substrates – TLPS additive circuitry instead of conventional subtractive etching process enables green manufacturing at low cost.
Pb-free Die Attach
Power Semiconductors Utilize a Diversity of Packaging Technologies Power ¡SO ¡ Power ¡QFN ¡Packages ¡ IGBT ¡ TO/Dpak ¡Packages ¡ 9
Package Reliability Requirements • Pb-free die attach solutions should meet or exceed the reliability performance of existing PbSn materials • Electrical and thermal performance of the device must demonstrate stability through stress testing – JEDEC moisture sensitivity – Temperature cycling – Pressure pot – High temperature storage • Electrical resistance (Rdson) is a primary output measure – Within 5% of solder initially – Less than 10% change after reliability testing
TLPS vs. PbSn Solder: Wirebond QFN Packages TLPS vs. Solder RDson >10% shift 11.7 Rdson (m-ohm) 11.2 5-10% shift 10.7 0-5% shift 10.2 Source: Prismark 9.7 Initial MSL 1 1000 T-cycle C PbSn TLPS TLPS materials have equivalent electrical and thermal performance to soft solder.
Clip-Based Power Packages • Clip-based power packaging is growing in popularity for medium power packages. Clip technology offers improved electrical and thermal performance in a low-cost package. – Dpack – Power SO – QFN Source: NXP Source: Prismark Source: Prismark TLPS technology has ability to have high reliability performance to a wide range of surfaces found in clip-base power packages: - Ag plated die and leadframe - PPF plated leadframe - Bare copper leadframe and clip - Nickel plated bondpads
TLPS die attach vs. PbSn Solder: Clip Packages: Customer Feedback Package Rdson T0 % Delta Package #2 Rdson % Delta #1 (mohm) Rdson (mohm) Rdson (mohm) (mohm) AVG Delta vs AVG Delta vs Solder Solder PbSn 4.3 0 PbSn Control 1.8 0 Control TLPS 4.3 +1.5% TLPS Split #1 1.9 +2.0% Split #1 TLPS 4.4 +1.1% TLPS Split #2 1.8 +0.2% Split #2 TLPS technology is equivalent to solder’s electrical performance and has a broad process window to meet customer factory process requirements.
Reliability Testing: Clip Packages – Baseline (Time 0) Rdson: • Within 2% of High-Pb Control – HTS (150C) 168 Hour: • Complete w/ no Rdson degradation – MSL2: No Failures – Autoclave 144 Hours: No failures – Thermal Characterization: • Comparable to High-Pb Control – Post 1500 Temperature Cycles • (-65/150C): No Failures • (-55/125C): No Failures • (-40/125C): No Failures
System Level Performance Assessment Solder Control Ormet Max: 81.3°C Max: 79.7°C No observed difference in device electrical response, power loss or thermal performance
Cross Section • The metal network is thermally stable to over 400C • The liquid Sn bonds to the metalized die backside and leadframe • The strong metallurgical bonds at the leadframe and die interfaces enable stable RDson performance post MSL and TCT Metallurgical bonds Black Regions are Sn-Cu at interfaces Epoxy Resin TLPS’s sintered metal network will not re-melt below 400C 3 ¡
System-in-Package Solder Replacement
Challenges with SIP Modules Source: Linear Technologies website SIP modules utilizing copper leadframes or BT substrate can have a range of issues: 1. Yield: Solders often have significant voiding underneath QFN packages 2. Reliability: Solders inside the SIP remelt during surface mount reflow and may extrude from the package 3. Cost: • Solder hierarchy drives narrow process windows • Variable component height drives thick (expensive) mold cap 4. Rework: Package rework difficult unless mold compound is used 5. Green: High temperature solder compositions can contain hazardous materials
TLPS for SiP Benefits for SIP: 1. Paste will not flow or splash during assembly, enabling higher component density 2. TLPS Materials will not re-melt during subsequent reflows, reducing potential for solder extrusion during surface mount assembly 3. Pastes can be used for both die attach and passive attach, simplifying assembly processes System-in-Package Component Solder - Inside SIP - Joins SIP to PCB PCB Pb-free TLPS materials can be used to attach die and/or components in leadframe and substrate-based modules
TLPS Paste Before and After Reflow TLPS materials do not slump/flow like solder during reflow. Cu-Sn TLPS materials change from copper to gray color during sintering process.
TLPS Solder Replacement Materials can be used without Solder Mask for Small Components Fillets are similar to conductive adhesive rather than solder Cap Size: 0402 and 0603
Shear Strength Comparison TLPS shear strength comparable to SAC305 after 1000 cycles -65C to 150C
Reliability Data for Ormet 406 Test Conditions Result MSL3 24 hour soak, 3X reflow Pass, No shorts High temperature 150 ° C, 1000 hour <10% change in ER storage Hot/wet storage 85 ° C/85% RH, 1000 <10% change in ER hour Thermal shock -78 ° C (liquid) to 150 ° C No failures (air) (5min:30sec:5min), 100 cycle Thermal cycle -65 ° C to 150 ° C, 3000 No failures cycles Power cycle 20 amp load, No failures 59 min. on 1 min. off >5000 cycles
Properties of TLPS Materials for Die Attach and Component Attach Property Test Method Unit Ormet 406 Ormet SPC 073 System-in-package Pb-free Application Component Attach Die Attach Process Stencil Print Dispense or Print Box Oven or Box Oven or Sintering (Cure) Reflow Oven Reflow Oven Brookfield CP-51 @5.0 38,000 20,000 cPs rpm Viscosity (Paste) 6.5 4.5 TI(0.5/5.0) N/A RT 25% Viscosity 24 24 Worklife hrs Increase 40 40 Thermal Conductivity W/mK 21 20 CTE TMA (Post cure) ppm/C 40 25 Max. particle size Microns Note: Sintering process requires O 2 < 500ppm in the oven
Summary • TLPS-based Pb free die attach pastes are suitable for Power QFN and Power SO packages – RDSon within 2% of solder • Excellent manufacturability and reliability – Compatible with Au and Ag die back and Ag/Cu, bare Cu, and PPF Lead Frames • TLPS materials can address issues in System-in- package components having issues with solders – Sintered paste does not remelt, improving reliability and component reworkability at the system level
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