Experimental Determination of Time-Independent Elastic-Plastic Behaviour of Solder Joints at High Strain Rates

Pb-Free BGA solder joints are more brittle and more susceptible to interfacial fails than the leaded versions. These brittle failures typically occur if the modules are subjected to high strain rates through module handling impacts or PCB flexural stress. The high speed ball shear technique is a useful method to submit solder joints to high strain rates in a controlled manner to emulate the levels of strain the BGAs may see in handling. This measurement technique was used to evaluate different laminate design and process variables on organic laminate substrates to create a more robust Pb-Free solder joint. Experiments were conducted to evaluate the effects and interactions of laminate, module assembly process, SAC alloy composition, and thermal treatments. Modulations of shear speed and shear angle made it possible to observe transitions from ductile to brittle solder fractures. The high speed ball shear method was successful to differentiate subtle effects resulting from different design points and process variables. The copper composition in the PbFree solder alloy, thermal history, and geometric factors such as solder volume, solder resist opening and solder resist thickness all had measurable impacts on the shear strength and transition point of ductile to brittle failure. Some BGA configurations have also been tested in reliability, namely in thermal cycling, and were shown to meet application requirements. Optimal design points can therefore be applied to enhance handling robustness without compromising on reliability.

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Determination of Tensile Properties of Polymers at High Strain Rates

EPJ Web of Conferences ◽

10.1051/epjconf/20100639008 ◽

2010 ◽

Vol 6 ◽

pp. 39008

Author(s):

M. Reiter ◽

Z. Major

Keyword(s):

Tensile Properties ◽

High Strain ◽

Strain Rates ◽

High Strain Rates

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Strain Rate Effects and Rate-Dependent Constitutive Models of Lead-Based and Lead-Free Solders

Journal of Applied Mechanics ◽

10.1115/1.3168600 ◽

2009 ◽

Vol 77 (1) ◽

Cited By ~ 18

Author(s):

Fei Qin ◽

Tong An ◽

Na Chen

Keyword(s):

Strain Rate ◽

Impact Analysis ◽

Solder Joints ◽

High Strain ◽

Drop Impact ◽

Lead Free ◽

Strain Rates ◽

High Strain Rates ◽

Rate Dependent ◽

Lead Free Solders

As traditional lead-based solders are banned and replaced by lead-free solders, the drop impact reliability is becoming increasingly crucial because there is little understanding of mechanical behaviors of these lead-free solders at high strain rates. In this paper, mechanical properties of one lead-based solder, Sn37Pb, and two lead-free solders, Sn3.5Ag and Sn3.0Ag0.5Cu, were investigated at strain rates that ranged from 600 s−1 to 2200 s−1 by the split Hopkinson pressure and tensile bar technique. At high strain rates, tensile strengths of lead-free solders are about 1.5 times greater than that of the Sn37Pb solder, and also their ductility are significantly greater than that of the Sn37Pb. Based on the experimental data, strain rate dependent Johnson–Cook models for the three solders were derived and employed to predict behaviors of solder joints in a board level electronic package subjected to standard drop impact load. Results indicate that for the drop impact analysis of lead-free solder joints, the strain rate effect must be considered and rate-dependent material models of lead-free solders are indispensable.

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