SAC Aging 3 84

The aim of the SAC Aging 3 project is to use the Alloy Common Test Vehicle and to perform baseline microstructural characterization on ambient aged and elevated temperature isothermally aged samples.  In addition, it will perform failure mode analysis and characterization of ATC samples to determine extent of microstructural evolution and impact on final failure. At the same time the project will thermal cycle additional non-monitored samples for microstructural analysis at different thermal aging times and temperatures.

Project stage: 
Lead company: 
Nokia

If you are interested in participating in this project:

Members - Go to the "Subscribe Here" section to the right and select the "Subscribe to space" key.

Non Members - Go to the "Contact" section to the right and select the "Contact project facilitator" key.

Idea Information

Background: 

 

  • When the SAC Aging3 project was proposed, it was designed to have two sets of build, test and analysis done.  One for the 192 CABGA and one for the 84CTBGA . At the time of Implementation approval we did not have the resources to do both so we chose to do the 192 only. 
  • When the project had an unexplainable outcome the team decided to now do the 84 leg in hopes of understanding the surprising results that occurred on the 192 leg.
  • The test data indicate that the characteristic lifetime of the SAC305 192CABGA increases as the aging time increases. This is exactly opposite to the expected effect for thermal fatigue of the solder.
  • Failure analysis shows that the crack propagation is not purely thermal fatigue and is not located at the package side of the joint as expected. This is a mixed failure mode, which is a random combination of interfacial cracking and bulk solder cracking.
  • The test results cannot be correlated directly to aging-induced microstructural degradation in the bulk solder because the failure path is not through the bulk solder exclusively. While there is no explanation for the mixed mode cracking, it has been reported recently in other studies using this 192CABGA package. 
Problem: 

 

  • Solder joints are degraded by both isothermal aging and thermal cycling in service.
  • We use pre-aging before temperature cycling to initiate the microstructural evolution that results in degradation.  Aging “jumpstarts” the degradation process, allowing crack initiation to occur in fewer thermal cycles than in non-aged samples. This is meant to simulate the effect of  isothermal aging in service
  • Pre-aging causes intermetallic networks to degrade or coarsen during aging.

       NO AGING (as assembled)           

      AGED

Definition Information

Goals / Benefits: 

 

 

  • SAC Aging 3 thermal cycling test results were compromised. Because we could not quantify the effect of warpage, all attempts to correlate ATC results and aging parameters were suspect.
  • The objective of SAC Aging 3-84 is to generate meaningful data using good test boards to test the aging hypothesis.

Approach: 

 TEST PARAMETERS

  • SAC305 solder alloy
  • Characterize PCB board warpage prior to building assemblies or initiating thermal cycling
  • Single precondition aging temperature: 125ºC with three different aging times: 0 days (baseline),  20 days, and 40 days
  • Evaluate one component type: 84CTBGA
  • The two candidate thermal cycling temperature ranges are: 0/100 °C and -40/125 °C. 

 

 TEST MATRIX

SAC Aging Project

Basic Single Component Single ATC Profile Test Cell

0-100oC

-40 to125oC

 

SAC305

SAC305

ATC - 0 days (RT aging)

32

32

ATC  - 20 days@125 °C

32

32

ATC - 40 days@125 °C

32

32

 Baseline (no ATC) 0 days

16

16

 Baseline – (ATC) 20 days @125 °C

16

16

 Baseline – (ATC) 40 days @125 °C

16

16

Total components

144

144

 

  • Evaluate SAC305 solder alloy with single precondition aging temperature of  125ºC with three different aging times: 0 days (baseline),  20 days, and 40 days
  • Evaluates one component type: 84 CTBGA
  • Accelerated thermal cycling (ATC) profile of 0-100ºC or -40/125 °C. The number of components required roughly doubles if both ATC profiles are used.

 

TEST VEHICLE


PCB - iNEMI ALLOY TEST VEHICLE

COMPONENT - 84 CTBGA

 

PROJECT FLOW CHART

 

 

 

Public