Research
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
MORE RESEARCH
Latest Industry News
Smartphone Shipments to Plummet 11.9% in 2020
PC market to dip 7% this year
Alternate Roads to Flexible Electronics
Huawei hid business operation in Iran after Reuters reported links to CFO
Global Distributor Group Tackles Tariff Inefficiencies
How to Set Boundaries While Working Remotely
Apple must face U.S. shareholder lawsuit over CEO's iPhone, China comments
The AI-Based Competitive Revolution
MORE INDUSTRY NEWS

Crack Propagation Mechanism Study on Bismuth Contained Base Lead Free Solder



Crack Propagation Mechanism Study on Bismuth Contained Base Lead Free Solder
The thermal cycling reliability characteristics of solder containing a small amount of Bismuth which is below 4wt% in accordance with the new requirements were investigated.
Analysis Lab

DOWNLOAD

Authored By:


Imbok Lee and Young-Woo Lee
MK Electron Co., Ltd., Sejong University
Seoul, Korea

Aakash Valliappan and Tae-Kyu Lee, Ph.D.
Portland State University
OR, USA

Summary


The needs of the higher thermo-mechanical reliability performance in the Tin-based lead-free solder interconnections are drastically increased in wafer-level chip scale packages implemented in automotive field application. This study reveals that a few wt% Bismuth makes 64% improvement in thermo-mechanical reliability results compared with SAC405 solder. In this study, 12mm X 12mm X 1mm thickness 228LD CTBGA package assembled on 62mil thickness board with NSMD Cu-OSP pad using a SAC305 solder paste. This study is aimed to verify the key mechanism, which enabled the reliability improvements. The crack propagation path shifted with Bismuth contents variation in the lead-free solder interconnections under thermal cycling with -40 to 1250C temperature range and 10OC ramp rate.

Microstructure has been studied via polarized optical imaging and High-speed EBSD (electron backscattering diffraction) analysis. The associated grain structure evolution was observed, revealing identifiable signature grain structure development during thermal cycling. Along with the microstructure evolution during thermal cycling, detail resistance monitoring for each localized daisy chain enabled the comparison between various solder materials showing the crack initiation and propagation phenomenon. With this analysis, the decoupling of crack initiation and propagation was performed.


Conclusions


The thermal cycling test results identified that Bismuth added solder mitigates recrystallization and grain refinement, which plays a role as a strengthening mechanism and result in thermal cycling reliability performance improvement. It was observed that shift in the crack propagation path from the bulk region to the package side interface, without a subgrain structure development resulted in decreasing the crack propagation rate. Also, it has been observed that the resistance variation, from the initiation to final failure in Bismuth added solder is longer than normal SAC solder.

Initially Published in the SMTA Proceedings

Comments

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?
MORE BOARD TALK
Ask the Experts
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
What is the IPC Definition of Uncommonly Harsh?
MORE ASK THE EXPERTS