Electronics Assembly Knowledge, Vision & Wisdom
Backward Compatible Solder Joint Reliability Under Accelerated Conditions
Backward Compatible Solder Joint Reliability Under Accelerated Conditions
Accelerated temperature cycling was used to assess the thermal fatigue reliability of a Pb free grid array package assembled.
Production Floor

Production Floor programs cover topics including:
CAD/CAM/CIM/EDA, Circuit Board Handling, Clean Room, Cleaning Operations, Component Insertion, Component Prep, Dispensing, Feeders, Fume Extraction, Hand Tools, Labeling/Marking, Lasers, Material Handling, Odd Form, Ovens/Curing, Packaging, Stencil Printing, Repair/Rework, Soldering and more.
Submit A Comment
Comments are reviewed prior to posting. You must include your full name to have your comments posted. We will not post your email address.

Your Name

Your Company

Your E-mail

Your Country

Your Comment

Authored By:
Richard Coyle, Peter Read, Richard Popowich, Debra Fleming
Alcatel Lucent, Murray Hill, NJ

Vasu Vasudevan, Raiyo Aspandiar
Intel Corporation, Hillsboro, OR

Iulia Muntele
Sanmina Corporation, Huntsville, AL

Steve Tisdale
Intel Corporation, Chandler, AZ

Accelerated temperature cycling (ATC) was used to assess the thermal fatigue reliability of a Pb free, 37.5 mm fully populated, 1284 I/O ball grid array (BGA) package assembled with backward compatible, mixed alloy (Pb free BGA/SnPb paste) assembly processes. Two different temperature cycling profiles were used in the evaluation. The baseline profile was the standard accelerated temperature test cycle of 0 to 100 C as prescribed by the IPC-9701 attachment reliability guideline (TC1).

The second profile was a mildly accelerated cycle using a less aggressive temperature extremes and a smaller T with a resultant range of 20 to 80 C. The limited temperature extremes provided by the latter cycle result in lower strains more typical of service conditions. The surface mount assembly was done using custom SnPb eutectic soldering profiles designed to optimize the complete (full) mixing of the Pb and to create two additional test cells with levels of Pb mixing in the Pb-free BGA balls defined as low and medium. To complete the reliability comparisons and provide experimental controls, SAC405-SAC405 and SnPb- SnPb assemblies were included.

The results indicate that backward compatible, mixed alloy assemblies should have acceptable reliability under service conditions. Complete or full Pb mixing is preferred in order to achieve consistent and acceptable solder joint reliability.

The results from this experimental study show that the thermal fatigue performance measured by characteristic lifetime of the large-body 1284 I/O full array BGA with Full Pb Mixed solder joints, is comparable to that of the 1284 I/O BGA with Pb-free SAC405 solder joints. The Full Pb Mixed and the SAC405 Pb free assemblies perform equally well when tested with the standard 0/100 C thermal cycle as with the mildly accelerated 20/80 C cycle.

Additionally, the mixed and Pb-free assemblies outperform the SnPb eutectic assemblies by a factor of 2.5 to 3 in 0/100 C testing and by a factor of almost 5 in 20/80 C testing. The latter result indicates that the acceleration factor for mixed alloy assemblies is comparable to or greater than Pb-free or SnPb.

There is no indication from the thermal cycling data or the metallurgical failure analysis that the Pb introduced by the mixed alloy assembly has a significant impact on thermal fatigue performance. The fracture features and failure modes of thermally fatigued mixed microstructures are the same as the fracture features of Pb-free SAC failures and the common fracture characteristics are consistent with their virtually identical fatigue performance.

Although these experimental results are consistent with some previous studies it is important to recognize that in practice, mixed alloy assembly is a custom process and its level of risk always should be assessed with respect to specific package construction, product design, and assembly parameters.

Initially Published in the SMTA Proceedings

No comments have been submitted to date.
Free Newsletter Subscription
Every issue of the Circuit Insight email newsletter will bring you the latest information on the issues affecting you and your company.

Insert Your Email Address

Directory Search

Program Search
Related Programs
bullet Determining the Effect of Fine Mesh Solder Powder on Flux Residue Removal
bullet Jetting Solder Paste Opens Up New Possibilities
bullet Bending Strength of Solder Joints as a Function of Joint Length
bullet Assembly Process Feasibility of Low Silver Solder Paste
bullet Electrochemical Methods to Measure Corrosion Potential of Flux Residue
bullet Screening of Lower Melting Point Pb-Free Alloys
bullet Jetting Solder Paste Opens Up New Possibilities
bullet Ultra-Low Voiding No-Clean Lead-Free Paste for Large Pads
bullet Reliability of Doped Lead-Free Solder Joints Under Isothermal Aging
bullet Pressure-Less Silver Sintering Pastes for Low Porosity Joint and Large Die
More Related Programs