SAC Aging IIISAC Aging IIIIdea Stage ProjectIdea Stage Project

Richard J. Coyle

HDP User Group Member MeetingHost: Engent

Atlanta Ga, USA

Sept 9, 2015

© HDP User Group International, Inc.

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Project BackgroundProject Background

• A follow-on to the HDPUG SAC Aging2 project applying lessons learned

– SAC Aging2 thermal cycling test results were flawed due to warpage of the test boards. Although flawed, these data indicated that the aging conditions used in the experiment were insufficient to induce decreased reliability

– Results from iNEMI Aging study corroborate SAC Aging2, indicating that longer aging times are required to demonstrate aging effects

– No acceleration factor exits to allow correlation of aging at the relatively high temperature of 125 C used in the experiment to aging at the lower temperatures such as 30 C typical of storage conditions or 75 C typical of some operating conditions. It is debatable whether high temperature,125 C aging effects are relevant to “real world” applications.

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Project BackgroundProject Background• Previously: ATC performance of SAC solder joints is

known to be affected by thermal pre-conditioning often simply called aging.– Lower reliability measured by characteristic lifetime and lower

Weibull slope of ATC failures sometimes with earlier failures

– The effect is not the same or apparent in all cases and likely is dependent on component and strain

Microstructural Focus

• Baseline microstructure without cycling:– ambient aged and elevated temperature isothermally aged

– long term isothermal aging.

• Characterization of cycled joints – microstructural evolution and failure mode.

Warpage Discussion

PCB warpage corrupted the thermal cycling data from SAC Aging2. What caused the PCB warpage?

We suspect that there was incomplete curing in some regions of some panels. Subsequent thermal exposure in either reflow, pre-aging, or thermal cycling completed the curing and this unbalance caused the warpage.

How does warpage affect reliability?

We speculate that out-of-plane tensile stress from warpage interacts with the in-plane shear stress due to CTE mismatch to alter the number of cycles to failure. Tensile stress may reduce the number of cycles to failure and compressive stress may increase the number of cycles to failure.

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The Effect of AgingThe Effect of Aging

•Aging, thermal preconditioning, or pre-aging initiates the microstructural evolution process of IMC particle coarsening in advance of the temperature cycling.

• IMC particle coarsening is the precursor to recrystallization and crack initiation in the bulk solder.

• If aging “jumpstarts” the particle coarsening process, crack initiation should occur in fewer thermal cycles than in un-aged samples. Thus, we expect aging to reduce the reliability or number of cycles to failure.

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The Test VehicleThe Test Vehicle

Components

192 CABGA

84 CTGA

PCB

Developed for iNEMIAlloy project and used in SAC Aging2 project

Project OverviewProject Overview

• Use the existing test board design and components to facilitate the launch of a new SAC Aging Project. – The test board design already exists and the components can

be procured easily. – The exact test board is completely compatible with the ALU

ATC chamber and rack system. – This testing can address some of the existing gaps in the

current SAC Aging project• Perform baseline microstructural characterization on ambient (no

age) and aged samples. Perform failure mode analysis and characterization on ATC samples to determine extent of microstructural evolution and impact on final failure.

• Build additional samples for microstructural analysis at different aging times/temperatures – complete plan to be worked out (tentative based on resource availability).

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Design of ExperimentDesign of Experiment• Evaluates SAC305 solder alloy• Characterizes PCB board warpage prior to building assemblies

or initiating thermal cycling to avoid issues that corrupted the SAC Aging2 data

• Single precondition aging temperature: 125ºC with three different aging times: 0 days (baseline), 20 days, and 40 days

• Optional extended low temperature aging at 75 C depending on available resources

• Evaluates one component type: 192 CABGA. Optional second component (84CTBGA) depending on available resources

• Cycling temperature range using two different ATC profiles: 0/100 C and -40/125 C

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Design of ExperimentDesign of ExperimentSAC Aging Project

Basic Single Component Single ATC Profile Test CellSAC305

ATC - 0 days (RT aging) 32ATC - 20 days@125 °C 32ATC - 40 days@125 °C 32ATC – xxx days@75 °C 32 Baseline (no ATC) 0 days 16 Baseline – (ATC) 20 days @125 °C 16 Baseline – (ATC) 40 days @125 °C 16 Baseline – (ATC) xxx days @75 °C 16Total components 192

• Evaluates SAC305 solder alloy with single precondition aging temperature of 125ºC with three different aging times: 0 days (baseline), 20 days, and 40 days

• Optional extended low temperature aging at 75 C depending on available resources

• Evaluates one component type: 192 CABGA. Optional second component (84CTBGA) depending on available resources

• Cycling temperature range 0-100ºC. Number of components required roughly doubles with two ATC profiles (0/100 C and -40/125 C )

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SummarySummary

This SAC Aging3 proposal uses lessons learned from previous industry aging projects to design a more focused evaluation plan.

• Single solder alloy: SAC305 solder alloy• Single component type: 192 CABGA. Optional second component

(84CTBGA) depending on available resources. The inherent characteristic lifetime of the 192CABGA is much lower than the 84CTBGA, providing shorter test time (fewer cycles to failure).

• Single precondition aging temperature of 125ºC with three different aging times: 0 days (baseline), 20 days, and 40 days. Longer aging times will emphasize aging effects.

• Optional extended lower temperature aging at 75 C depending on available resources.

• Cycling temperature range 0-100ºC. Number of components required roughly doubles with two ATC profiles (0/100 C and -40/125 C ). The - 40/125 C test can be executed in roughly half the number of cycles as the 0/100 C test.

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Project ScheduleProject Schedule

Planned Actual _Design TV Complete CompleteReceive Components 11/2015Receive Boards 11/2015Assembly Complete 02/2016Wire Boards 03/2016Precondition Boards 05/2016Begin Long Term aging 05/2016ATC start (short term aging) 05/2016Begin Microstructure Analysis 05/2016Complete Microstructure Evaluation 08/2016ATC start (long term aging) 11/2016ATC complete short term aging 12/2016 Interim Report 12/2016ATC complete long term aging 07/2017ATC Weibull Analysis Ongoing with ATCFinal Report 2017

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Project Team Project Team (So Far)(So Far)

• Alcatel-Lucent*

• Keysight

• Nihon-Superior

• Sanmina (PCB and assembly)

• Akrometrix

• Panasonic

* project leader