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Research Papers

Influence of Intermetallic Characteristics on the Solder Joint Strength of Halogen-Free Printed Circuit Board Assembly

[+] Author and Article Information
Hung-Jen Chang, Jung-Hua Chou

Department of Engineering Science,  National Cheng Kung University, Tainan 70101, Taiwan

Tao-Chih Chang1

Assembly and Reliability Technology Department,  Industrial Technology Research Institute, Hsinchu 31040, TaiwanTaoChih@itri.org.tw

Chau-Jie Zhan

Assembly and Reliability Technology Department,  Industrial Technology Research Institute, Hsinchu 31040, Taiwan

Min-Hsiung Hon

Department of Materials Science and Engineering,  National Cheng Kung University, Tainan 70101, Taiwan

Chi-Shiung Hsi

Department of Materials Science and Engineering,  National United University, Maoli 36003, Taiwan

1

Corresponding author.

J. Electron. Packag 133(2), 021004 (Jun 23, 2011) (8 pages) doi:10.1115/1.4003989 History: Received May 14, 2010; Revised February 23, 2011; Published June 23, 2011; Online June 23, 2011

Five halogen-free (HF) dummy plastic ball grid array (PBGA) components with daisy-chains and Sn4.0Ag0.5Cu (SAC405) Pb-free solder balls were assembled on a HF high density interconnection (HDI) printed circuit board (PCB) using Sn1.0Ag0.5Cu (SAC105) and Sn3.0Ag0.5Cu (SAC305) Pb-free solder pastes, respectively. The above compositions were in weight percent. The assemblies were then experienced to moisture sensitive level testing with three times reflow at a peak temperature of 260 °C; no delamination was found present in both the component and PCB laminates. The microstructure showed that the utilization of SAC105 solder paste was beneficial in refining the Ag3Sn intermetallic compound (IMC) within the solder joint and the intermetallic layers formed at various interfaces with different Ni contents and thicknesses due to different metal finishes. The IMC spalling was found at the BGA-side interface within the solder joints formed with SAC105 solder paste but not discovered within the ones made of SAC305 solder paste. The pull strength of the solder joint formed with SAC305 solder paste was always higher than that made from SAC105 no matter on Cu or electroless Ni. Moreover, the fracture was found at the interface between the Cu foil and epoxy in the halogen-free test device. Numerical analysis showed that the thickness of IMC layer dominated the pull strength of the solder joint because the Z-axial normal stress applied to the solder joints formed with Cu and electroless Ni were 752.0 and 816.6 MPa, respectively, and a thicker IMC layer was beneficial to provide a higher pull strength of solder joint.

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Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Top view of the assembled PCBA test vehicle and schematic cross-section of PCB

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Figure 2

Schematic outline and the finite element model of the vehicle structure

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Figure 3

Interfacial microstructures of PCB-side when the SAC405 solder balls were soldered on PCB with OSP finish by (a) SAC105 solder paste, (b) SAC305 solder paste, and (c) the Ag3 Sn formed within the solder bulk

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Figure 4

Interfacial microstructures of chip-side when the SAC405 solder balls were soldered on PCB with OSP finish by (a) SAC105 and (b) SAC305 solder pastes

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Figure 5

Interfacial microstructures of chip-side when the SAC405 solder balls were soldered on PCB with ENIG finish by (a) SAC105 and (b) SAC305 solder pastes

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Figure 6

Interfacial microstructures of (a) PCB-side and (b) chip-side when the SAC405 solder balls were soldered on PCB with ENIG finish by SAC105 and then passed MSL test

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Figure 7

Interfacial microstructures of the PCB-side when the SAC405 solder balls were soldered on PCB with OSP finish by SAC105 and then passed MSL test

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Figure 8

Interfacial microstructures of (a) PCB-side and (b) chip-side when the SAC405 solder balls were soldered on PCB with ENIG finish by SAC305 and then passed MSL test

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Figure 9

Comparison of pull strengths for various solder joints

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Figure 10

Failure mode of the HF PCBA after pull test

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