Innovative Panel Plating for Heterogeneous Integration
A Method to Investigate PCB Supplier Rework Processes and Best Practices
The Effects of PCB Fabrication on High-Frequency Electrical Performance
Aerosol Jet Printing of Conductive Epoxy for 3D
EOS Exposure of Components in the Soldering Process
High Thermo-Mechanical Fatigue and Drop Shock Resistant Alloys
Filling of Microvias and Through Holes by Electrolytic Copper Plating
NASA DOD Phase 2: Copper Dissolution Testing
Latest Industry News
How Telecom is Rolling Out 5G During a Pandemic
Can Software Performance Engineering Save Us From the End of Moore's Law?
Tech stocks have been a winning bet, but investors worry it will fade
All This Chaos Might Be Giving You 'Crisis Fatigue'
Notebook PCB makers to see tight capacity through 3Q20
How Effective Is Nano Coating On Stencils?
U.S. Critical Infrastructure Full of Security Holes
Auto Interior Is the New Exterior

Microstructure and Reliability of Low Ag, Bi-Containing Solder Alloys

Microstructure and Reliability of Low Ag, Bi-Containing Solder Alloys
This paper investigates a number of low (or no) Silver (Ag), Bi-containing Pb-free alloys for performance in accelerated thermal cycling (ATC).
Analysis Lab


Authored By:

Eva Kosiba, Simin Bagheri, Polina Snugovsky, Ph.D.
Celestica Inc. Toronto, ON, Canada

Doug Perovic, Ph.D.
University of Toronto
Toronto, ON, Canada


Accelerated thermal cycling (ATC) was performed on a test vehicle which included various components, built with three low (or no) Ag, Bi-containing solders and compared to a baseline of SAC305 (Sn/Ag3%Cu 0.5%). Lead free SAC305 has become the default lead-free alloy for consumer electronic application use since the implementation of the RoHS legislation banning the use of Pb in solder.

SAC305 however does not perform as well as SnPb in some key areas which are of importance to consumer electronic applications; specifically drop/shock performance and survival under accelerate thermal cycling conditions. Efforts have been made in the consumer sector to improve upon these properties of SAC305 by, for example reducing the amount of Ag in order to improve drop/shock performance, however an alternate alloy is still required to meet all of the existing concerns.

It has been shown in the previous paper presented at last year's ICSR conference "Assembly Feasibility and Property Evaluation of Low Ag, Bi-Containing Solder Alloys" that these alloys show promise in drop/shock performance. This work shows that these same Bi-containing ternary and quaternary alloys also show promise in ATC. ATC of 3000 cycles was performed from 0 C to 100C. The results of the three Bi containing alloys were compared to SAC305. Additionally microstructural evaluation was performed at time zero and after ATC. Bi containing solders may prove to be adequate replacement for SAC305 in consumer electronic applications.


This screening experiment for selecting a Pb-free solder with a lower melting temperature then conventional SAC305 for consumer electronics is on going.

Observations and conclusions that can be made at this time are as follows:
  • All for Pb-free solders survived 0C-to-100C ATC in excess of 3000 cycles.
  • Even though there were no electrical failures at 3000 cycles ATC (i.e. all solder joints were electrically sound), cracks had initiated and were propagating through the solder joint.
  • These fatigue cracks form along the high strain region where recrystalization is occurring rapidly, induced by the stress that thermal cycling induces in materials with mismatched CTE

Initially Published in the SMTA Proceedings


No comments have been submitted to date.

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 Comments

Board Talk
How Effective Is Nano Coating On Stencils?
What Causes Board Delamination?
01005 Component Challenges and Bugs
Sticky Residue Under Low Clearance Parts
Soldering Relays Intrusively in Lead Free Process
Printing vs. Dispensing
Maximum Board Temperature During Tin-Lead
Is There a Spacing Spec for SMD Components?
Ask the Experts
Recommended Fiducial Shape
HASL vs. Immersion Gold
Very Low Temp PCBs
Looking for Long-term Component Storage Options
Baking After Cleaning Hand Placed Parts
Conformal Coating Recommendation
Burned Chip Repair
BGA Component Grounding Problem