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Accelerated Stress Testing and Reliability Conference

Reliability of Staked Surface Mount Packages

Deng Y. Chen and Dr. Michael Osterman

Center for Advanced Life Cycle Engineering (CALCE)

University of Maryland, College Park, MD 20742

Email: [email protected]

ASTR 2016, Sep 28-30, Pensacola, FL January-4-17 1


CALCE Facilities and Capabilities

www.ieee-astr.org September 28- 30 2016, Pensacola Beach, Florida 2

Non-Destructive Evaluation 3D X-ray Imaging System Scanning Acoustic Microscope (SAM) Fourier Transform Infrared Spectroscopy (FTIR) Automated Contact Resistance Probe (ACRP) X-Ray Fluorescence Spectroscopy (XRF)

Electronic Testing and Analysis Semiconductor Parameter Analyzer Impedance Analyzer (1.86GHz) Microcircuit Probe High Power Curve Tracer LCR meter Dynamic Signal Analyzer Event Detectors Electrometer LCZ Meter Thermal Inducing System (-80oC to 225oC) Time Domain Reflectometer Analog Oscilloscopes Power Supplies High Speed Digital Oscilloscope up to 20 GS/sec Digital Communication Analyzer Arbitrary Wave Form Generator Function Generator Contact Resistance Tester Noise Figure Analyzer Vector Network Analyzer High Resistance Meter Digital Multimeters Automated Data Acquisition Systems Cascade Probe Station with RF probing capability Automatic Battery Testers (Four and Sixteen Channel Systems) Ripple Current Tester

Thermal Assessment and Management Liquid Crystal Thermography Hot Wire Anemometer Flow Visualization System High Speed Video Camera Thermal Conductivity Testing System Flow/Velocity Measurement Facilities Pressure Measurement Facilities

Materials Characterization Differential Scanning Calorimeter (DSC) Micro-Mechanical Materials Tester Dynamic Mechanical Analyzer (DMA) Nanoindentation Creep Testing Equipment MTS servo-hydraulic mechanical test system (5 grams to 200 kg)

• High-strain rate characterization (100/sec) • Tests can be conducted in vacuum, inert or

reactive atmospheres (-125oC to 300oC) Micro-Hardness Tester Micro-Fatigue Tester Adhesion Tester 1D Electrodynamic Shaker 6D Electrodynamic Shaker Drop Towers Torsion Tester

Opto-Mechanics Experimentation Geometric Moire Microscopic and Shadow Moire Interferometry Infrared Fizeau Interferometry Twyman-Green Interferometry Luminous Flux Measurement System

• 40” Integrating Sphere • Spectroradiometer

Sample Preparation Diamond Saw Polishing and Grinding Station Plasma Etching Ultrasonic Cleaning Wire Bonder Die Bonder

Buehler MPC 2000 Cross-sectioning System

Failure Analysis Environmental Scanning Electron Microscope (ESEM)

• (25x-2500000x) • Energy Dispersive Spectroscopy (EDS) • In-situ Heating/Mechanical Testing

Focused Ion Beam (FIB) Stereoscopes (10x-63x) Optical Microscopes (25x-1000x, Inverted and Upright) Image Analysis Software Transmission Electron Microscope (TEM) Wire Pull, Bond Shear, Cold Bump Pull and Die Strength Automatic Chemical Decapsulator Ion Chromatograph

Virtual Qualification Lab

calcePWA CADMP-II calceFAST Defects Webbook PEMs Webbook

Accelerated Test Webbook PWA Assembly Webbook Integral Passives Webbook PWA Failure Mechanism Webbook Sensor Technology Webbook

Environmental/Accelerated Testing Temperature-Humidity Chambers HALT Temperature-Vibration Chamber Thermal Shock Chambers

• Liquid to Liquid • Air to Air

HAST Temperature-Humidity Chambers High Altitude Simulation Chamber • Pressure, Humidity, and Temp. Cycling High Temperature Aging Chambers Mixed Flowing Gas (MFG) Chamber Electrodynamic Vibration Chamber Impact and Drop Test Apparatus SIR Testing Hollow Fiber Assessment Acoustic Anechoic Chamber

www.calce.umd.edu


Lead Free Solder Reliability

• The European legislation, the Restriction of Hazardous Substances (RoHS), limited the use of lead containing solders commercial electronics in 2006.

• Although military and aerospace electronics are exempted, obtaining lead containing components are becoming more difficult [1].

• The exemption of power electronics ends in 2016 [2].

• Tin silver copper (SAC) alloys have been the most promising lead free replacement for microelectronics.

• SAC solders have higher modulus and lower ductility and are prone to shock impact failures.


[1] Army works to decrease lead-free electronic components, http://www.army.mil/article/40712/army-works-to-decrease-lead-free-electronic-components/, accessed

May 1, 2016

[2] RoHS Substances and Exemptions List, http://www.ipc.org/3.0_Industry/3.4_EHS/2011/March-2011-Update-to-IPC-1752A-Appendices-B-C-D.pdf , accessed May 1,

2016

http://www.ipc.org/3.0_Industry/3.4_EHS/2011/March-2011-Update-to-IPC-1752A-Appendices-B-C-D.pdf































































Possible Failure Mitigation Strategies

• Change mechanical design of the electronic system to reduce the stress transmitted to the solder joints.

• Board level underfill can be used for ball grid arrays (BGAs) to reduce the failure of BGAs under drop impact loadings.

• The thermal mechanical reliability of BGAs with underfill can be reduced [3].

• Staking provides an alternative to underfill.


[3] Shi, Hongbin, Cuihua Tian, Michael Pecht, and Toshitsugu Ueda. "Board-level shear, bend, drop and thermal cycling reliability of lead-free chip scale packages with

partial underfill: a low-cost alternative to full underfill." In Electronics Packaging Technology Conference (EPTC), 2012 IEEE 14th, pp. 1-12. IEEE, 2012.


Literature Review • Study has shown that corner staking improves drop impact reliability of

BGAs with corner staking [4].

• Shi’s study showed corner staking can improve the thermomechanical reliability of the BGAs [5]. • Shi Investigated the reliability of BGAs with edge bond and corner staking under -40◦C

to 125◦C temperature cycling.

• BGAs with corner staking had the highest mean time to failure.

• While one of the studies claimed that corner staking may reduce the reliability of BGAs under temperature cycling [6]. • Lee et al., compared the thermomechanical reliability of BGAs with and without

underfill and corner staking and found that BGAs with corner staking and underfill have reduced life.


[4] Guoyun Tian et al., "Corner bonding of CSPs: processing and reliability," in IEEE Transactions on Electronics Packaging Manufacturing, vol. 28, no. 3, pp. 231-240,

July 2005.

[5] H. Shi, D. Yu and T. Ueda, "Systematic studies of second level interconnection reliability of edge and corner bonded lead-free array-based packages under mechanical

and thermal loading," 2012 IEEE 62nd Electronic Components and Technology Conference, San Diego, CA, 2012, pp. 965-976

[6] J. Y. Lee et al., "Study on the Board Level Reliability Test of Package on Package (PoP) with 2nd Level Underfill," 2007 Proceedings 57th Electronic Components and

Technology Conference, Reno, NV, 2007, pp. 1905-1910.


Motivation

• Literature presents discrepancy on the effects of staking on the thermomechanical reliability of BGAs

• No study has been done on the vibrational reliability of staked packages.

• Majority of the studies in the literature focused on the reliability of BGAs with corner staking.



Research Objective

To examine the reliability of staked surface mount components under temperature cycling, vibration, and drop impact.



Approach


Design and Manufacturing of Test Vehicle

Stake the Assembly

Temperature Cycling -55 to 125oC, 15 mins dwell

Harmonic Vibration 3G and 4G acceleration

Drop Testing 3000G

Failure Data Comparison


Test Vehicle Specifications


Board Details Components Count

− 4 Layers

− 9"x4.5"x0.063"

− ImAg Surface Finish

− SAC305

− CTEx :13.8 ppm/°C

− CTEy 15.1ppm/°C

BGA 4

QFP 4

QFN 4

Resistor (50% Pad Width) 4

Resistor (50% Pad Length) 4

Y

X


Staking on Test Vehicle



Temperature Cycling Test


• Resistance monitoring is carried out for all components on the board to determine failure. Failure is defined based on the IPC-9701 standard, 20% increase in initial resistance value for five consecutive scans.

(-55 to 125oC, 15 min dwell)

[7] JEDEC Solid State Technology Association. “Temperature Cycling,” JESD22-A104D. JEDEC Solid State Technology Association, 2009.


Failure Distribution of BGAs


• It is observed that staking enhances the reliability of BGA under thermal cycling loadings.

• The characteristic life of staked BGAs is about twice the characteristic life of nonstaked BGAs

.

Temperature Cycling Test (-55 to 125oC, 15min dwell)


Failure Distribution of QFNs


• Results indicates that the QFN with corner staking has a higher characteristic life than without.

• Distribution is wider for the staked QFNs indicating there may be multiple failure modes

Temperature Cycling Test (-55 to 125oC, 15 min dwell)


Harmonic Vibration Test Setup


• 3G and 4G base excitation vibration were exerted on the fixture

• The resonant frequencies of the boards are about 190Hz

• At the resonant frequency, a transmissibility of ~ 28 was observed on the test vehicle.

Schematic of test setup

Direction of vibration

Clamped Ends

6.0''

[8] JEDEC Solid State Technology Association. “Vibration, Variable Frequency,” JESD22- B103B, 2002


Failure Distributions of BGA


Staked

Nonstaked

• With the fixture vibrating at 3G, it is observed that the BGA components with corner stakings have about 300x higher characteristic life than the BGAs without corner staking.

• The reason for the improved vibrational fatigue life is that the staking material mitigated the stresses on the solder joints.

Harmonic Unidirectional Vibration (3G at fixture)


Failure Distributions of QFPs


• Under 3G vibration, QFPs with corner staking had lower characteristic life than the ones without corrnerstaking.

• Corner staked QFPs have much higher shape parameters


Failure Distributions of QFNs


• Staked QFNs and nonstaked QFNs have similar characteristic lives.

• Corner staked QFNs have higher shape parameters compare to nonstaked QFNs.


Failure Distributions of BGA


With the fixture vibrating at 4G, the characteristic life of staked BGAs is about 400x the nonstaked BGAs

Harmonic Unidirectional Vibration (4G at fixture)


Drop Test


• Drop test was performed on Lansmont drop tower.

• The boards were mounted with the components facing downward.

• 3000G drop impact test with 0.35 millisecond pulse width.

[9] JEDEC Solid State Technology Association. "Mechanical Shock." JESD22-B104C, Arlington, VA 3 2004


Failure Distributions (BGA)


Shock Impact Testing (3000G at fixture)

• The result shows that the BGA components with corner stakings have almost 10x the characteristic life of the BGAs without the corner staking under 3000G drop testing.

• The first time to failure is also much higher for staked BGAs



Failure Distributions (QFP) Shock Impact Testing (3000G at fixture)

• QFPs with corner staking have reduced drops to failure life compared to nonstaked QFPs.

• Staking may have created stress concentration on the PCB, and thus increased the likelihood of pad cratering.


QFN Reliability

• Drop tests were terminated at 1200 drops.

• Three out of four nonstaked QFNs have failed by 900 drops.

• No failure of staked QFNs was observed by the end of 1200 drops.

• Comparatively, staked QFNs have improved time to first failure.



Summary

• BGAs with corner staking exhibited superior reliability compared to non staked BGAs under temperature cycling, harmonic vibration and drop tests.

• QFNs with staking have shown improved reliability under temperature cycling and drop tests compared to nonstaked QFNs.

• QFPs with staking showed equivalent or reduced life under vibration and drop tests.


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