Shearing tests of solder joints on tape ball grid array substrates
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Shearing behavior of Sn-37Pb, Sn-3Ag-0.5Cu, and Sn-3Ag-0.5Cu-8 in solder joints on tape ball grid array (TBGA) substrates were investigated with different shearing speeds from 7 m/s to 700 m/s and over a wide temperature range from −25 °C to 150 °C. Both shearing speed and testing temperature were found to have strong effects on the shearing strength and fracture mechanisms of the solder joints. At certain temperature, the shearing force increases sharply with the increase of shearing speed due to a small amount of grain boundary deformation and incomplete dislocation movement as well as more work hardening at a high strain rate. With a fixed speed, the shearing force decreases dramatically with the increase of shearing temperature as a result of a small amount of work hardening and more dynamic recovery, as well as a reduction in Young’s modulus at elevated temperatures. Two lead-free solder joints were much stronger than the tin-lead solder joints under any given shearing condition. At a low temperature of −25 °C, the tin-lead solder joints failed with a combination of intermetallic compounds (IMC) fracture and solder/IMC interface detachment, whereas both lead-free solder joints failed by IMC/Ni interfacial separation. From 25 °C to 150 °C, the fracture mode of all solder joints was complete ball cut through the bulk solder with a ductile rupture. The underlying mechanisms for different shearing performance are interpreted in relation to the properties of the interconnecting materials.
I. INTRODUCTION
Tape ball grid array (TBGA) packages are a large family of BGA components designed for high performance at competitive cost. Instead of using bismaleimide triazine strips as substrate in common BGA, an integral copper heat spreader is used for high power dissipation, mechanical support, and as an active ground plate in a TBGA package. A thin layer of polyimide tape with built-in copper traces is laminated with adhesive onto the heat spreader to provide high density routing and interconnection. Owing to the inherent benefits of low electrical parasitics, less noise, and high thermal conduction, the TBGA package has received widespread applications in high-speed and high-power devices.1 As the modern component packaging technology develops further towards higher density with finer pitch and
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0296 2224 J. Mater. Res., Vol. 21, No. 9, Sep 2006 http://journals.cambridge.org Downloaded: 13 Mar 2015
smaller feature size, the importance of mechanical integrity of the interconnection structure is essentially emphasized to be a serious reliability concern. When the solder joints of a TBGA component decrease down to a few hundred micrometers in diameter, they become fragile and sensitive to damage under external thermal or mechanical loadings. Components frequently experience loadings during fabrication, storage, shipment, assembly, and field operation. Hence, fracture of the solder joints may occur due to lower mechanical st
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