Lead Free Sinterable Pastes for Die and Component Attach - - PowerPoint PPT Presentation

Lead Free Sinterable Pastes for Die and Component Attach Applications

Michael Matthews Ormet Circuits, Inc. April 8, 2015

Transient Liquid Phase Sintering [TLPS]

Sn

Room Temp Copper and Solder particles suspended in polymer resin system [epoxy] Temperature >225C Sn-Cu sintering reaction occurs

Cu Cu Cu Cu Cu Cu

Sn Sn

Cu

Cu Sn

Cu

Sn

[1] Tin-based Solder Particle

Sn

[3] Polymer Matrix [Epoxy-based] [2] Copper Particles TEMPERATURE

Sn-Cu Alloy Melt Point > 400C

Liquid Phase Sn Alloy

Temperature 180-220C Alloy begins to melt (liquid phase)

Sintered metal network

SINTERED 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.

Materials that leverage both fab and packaging infrastructure

Assembly materials and substrates that are Green, enable mobile devices and are temperature resistant

Substrate innovation for higher density, performance & lower cost

The rapidly blurring lines between wafer fab, packaging and assembly are creating opportunities for new material technologies

The Convergence of Wafer Fab, Semiconductor Packaging and Electronics Assembly is Creating Requirements for New Materials

TLPS Technology is Aligned to the Future Roadmap

• f 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 Semiconductor Packaging Materials Solder Replacement Materials Circuit Board Interconnect Materials LED Substrate Circuit 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

IGBT ¡ 9

TO/Dpak ¡Packages ¡

Power ¡SO ¡ Power ¡QFN ¡Packages ¡

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 materials have equivalent electrical and thermal performance to soft solder.

Source: Prismark

9.7 10.2 10.7 11.2 11.7 Initial MSL 1 1000 T-cycle C

Rdson (m-ohm)

TLPS vs. Solder RDson

PbSn TLPS

0-5% shift 5-10% shift >10% shift

• 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

Clip-Based Power Packages

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

Source: NXP Source: Prismark Source: Prismark

Package #1 Rdson (mohm) T0 % Delta Rdson (mohm) AVG Delta vs Solder PbSn Control 4.3 TLPS Split #1 4.3 +1.5% TLPS Split #2 4.4 +1.1% Package #2 Rdson (mohm) % Delta Rdson (mohm) AVG Delta vs Solder PbSn Control 1.8 TLPS Split #1 1.9 +2.0% TLPS Split #2 1.8 +0.2%

TLPS die attach vs. PbSn Solder: Clip Packages: Customer Feedback

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 Max: 81.3°C Ormet 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 at interfaces Black Regions are Epoxy Resin

Sn-Cu

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

• 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 SIP modules utilizing copper leadframes or BT substrate can have a range of issues:

TLPS for SiP

Pb-free TLPS materials can be used to attach die and/or components in leadframe and substrate-based modules

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

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

Cap Size: 0402 and 0603 Fillets are similar to conductive adhesive rather than solder

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 storage 150°C, 1000 hour <10% change in ER Hot/wet storage 85°C/85% RH, 1000 hour <10% change in ER Thermal shock

• 78°C (liquid) to 150°C

(air) (5min:30sec:5min), 100 cycle No failures Thermal cycle

• 65°C to 150°C, 3000

cycles No failures Power cycle 20 amp load, 59 min. on 1 min. off >5000 cycles No failures

Property Test Method Unit Ormet 406 Ormet SPC 073

Application System-in-package Component Attach Pb-free Die Attach Process Stencil Print Dispense or Print Sintering (Cure) Box Oven or Reflow Oven Box Oven or Reflow Oven Viscosity (Paste) Brookfield CP-51 @5.0 rpm cPs 38,000 20,000 TI(0.5/5.0) N/A 6.5 4.5 Worklife RT 25% Viscosity Increase hrs 24 24 Thermal Conductivity W/mK 40 40 CTE TMA (Post cure) ppm/C 21 20

• Max. particle size

Microns 40 25

Properties of TLPS Materials for Die Attach and Component Attach

Note: Sintering process requires O2 < 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

Contact Information

• Colleen Ewanich

– colleen.ewanich@ormetcircuits.net – (925) 785-0327

• Michael Matthews

– michael.matthews@ormetcircuits.net – (858) 831-0010