Plasma reflow bumping of Sn-3.5 Ag solder for flux-free flip chip package application

Soon Min Hong; Choon Sik Kang; Jae Pil Jung

doi:10.1109/TADVP.2003.821079

Plasma reflow bumping of Sn-3.5 Ag solder for flux-free flip chip package application

Soon Min Hong, Choon Sik Kang, Jae Pil Jung

Department of Materials Science and Engineering

Research output: Contribution to journal › Article › peer-review

19 Scopus citations

Abstract

A new flux-free reflow process using Ar + 10%H₂ plasma was investigated for application to solder bump flip chip packaging. The 100-μm diameter Sn-3.5wt% Ag solder balls were bonded to 250-μm pitch Cu/Ni under bump metallurgy (UBM) pattern by laser solder ball bonding method. Then, the Sn-Ag solder balls were reflowed in Ar + H₂ plasma. Without flux, the wetting between solder and UBM occurred in Ar + H₂ plasma. During plasma reflow, the solder bump reshaped and the crater on the top of bump disappeared. The bump shear strength increased as the Ni₃Sn₄ intermetallic compounds formed in the initial reflow stage but began to decrease as coarse (Cu, Ni)₆Sn₅ grew at the solder/UBM interface. As the plasma reflow time increased, the fracture mode changed from ductile fracture within the solder to brittle fracture at the solder/UBM interface. The off-centered bumps self-aligned to patterned UBM pad during plasma reflow. The micro-solder ball defects occurred at high power prolonged plasma reflow.

Original language	English
Pages (from-to)	90-96
Number of pages	7
Journal	IEEE Transactions on Advanced Packaging
Volume	27
Issue number	1
DOIs	https://doi.org/10.1109/TADVP.2003.821079
State	Published - Feb 2004

Keywords

Bump
Flip chip
Flux-free
Intermetallic compound
Joint strength
Microstructure
Pb-free solder
Plasma
Reflow

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10.1109/TADVP.2003.821079

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title = "Plasma reflow bumping of Sn-3.5 Ag solder for flux-free flip chip package application",

abstract = "A new flux-free reflow process using Ar + 10%H2 plasma was investigated for application to solder bump flip chip packaging. The 100-μm diameter Sn-3.5wt% Ag solder balls were bonded to 250-μm pitch Cu/Ni under bump metallurgy (UBM) pattern by laser solder ball bonding method. Then, the Sn-Ag solder balls were reflowed in Ar + H2 plasma. Without flux, the wetting between solder and UBM occurred in Ar + H2 plasma. During plasma reflow, the solder bump reshaped and the crater on the top of bump disappeared. The bump shear strength increased as the Ni3Sn4 intermetallic compounds formed in the initial reflow stage but began to decrease as coarse (Cu, Ni)6Sn5 grew at the solder/UBM interface. As the plasma reflow time increased, the fracture mode changed from ductile fracture within the solder to brittle fracture at the solder/UBM interface. The off-centered bumps self-aligned to patterned UBM pad during plasma reflow. The micro-solder ball defects occurred at high power prolonged plasma reflow.",

keywords = "Bump, Flip chip, Flux-free, Intermetallic compound, Joint strength, Microstructure, Pb-free solder, Plasma, Reflow",

author = "Hong, {Soon Min} and Kang, {Choon Sik} and Jung, {Jae Pil}",

year = "2004",

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doi = "10.1109/TADVP.2003.821079",

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N2 - A new flux-free reflow process using Ar + 10%H2 plasma was investigated for application to solder bump flip chip packaging. The 100-μm diameter Sn-3.5wt% Ag solder balls were bonded to 250-μm pitch Cu/Ni under bump metallurgy (UBM) pattern by laser solder ball bonding method. Then, the Sn-Ag solder balls were reflowed in Ar + H2 plasma. Without flux, the wetting between solder and UBM occurred in Ar + H2 plasma. During plasma reflow, the solder bump reshaped and the crater on the top of bump disappeared. The bump shear strength increased as the Ni3Sn4 intermetallic compounds formed in the initial reflow stage but began to decrease as coarse (Cu, Ni)6Sn5 grew at the solder/UBM interface. As the plasma reflow time increased, the fracture mode changed from ductile fracture within the solder to brittle fracture at the solder/UBM interface. The off-centered bumps self-aligned to patterned UBM pad during plasma reflow. The micro-solder ball defects occurred at high power prolonged plasma reflow.

AB - A new flux-free reflow process using Ar + 10%H2 plasma was investigated for application to solder bump flip chip packaging. The 100-μm diameter Sn-3.5wt% Ag solder balls were bonded to 250-μm pitch Cu/Ni under bump metallurgy (UBM) pattern by laser solder ball bonding method. Then, the Sn-Ag solder balls were reflowed in Ar + H2 plasma. Without flux, the wetting between solder and UBM occurred in Ar + H2 plasma. During plasma reflow, the solder bump reshaped and the crater on the top of bump disappeared. The bump shear strength increased as the Ni3Sn4 intermetallic compounds formed in the initial reflow stage but began to decrease as coarse (Cu, Ni)6Sn5 grew at the solder/UBM interface. As the plasma reflow time increased, the fracture mode changed from ductile fracture within the solder to brittle fracture at the solder/UBM interface. The off-centered bumps self-aligned to patterned UBM pad during plasma reflow. The micro-solder ball defects occurred at high power prolonged plasma reflow.

KW - Bump

KW - Flip chip

KW - Flux-free

KW - Intermetallic compound

KW - Joint strength

KW - Microstructure

KW - Pb-free solder

KW - Plasma

KW - Reflow

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Plasma reflow bumping of Sn-3.5 Ag solder for flux-free flip chip package application

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