Study on the Board Level Reliability Test of Package on Package (PoP) with 2nd Level Underfill

Board-level reliability of conventional Sn-37Pb and Pb-free Sn-3.0Ag-0.5Cu solder joints was evaluated using thermal shock testing. In the microstructural investigation of the solder joints, the formation of Cu6Sn5 intermetallic compound (IMC) layer was observed between both solders and Cu lead frame, but any crack or newly introduced defect cannot be found even after 2000 cycles of thermal shocks. Shear test of the multi layer ceramic capacitor (MLCC) joints were also conducted to investigate the effect of microstructural variations on the bonding strength of the solder joints. Shear forces of the both solder joints decreased with increasing thermal shock cycles. The reason to the decrease in shear force was discussed with fracture surfaces of the shear tested solder joints.

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Use-Conditions-Based Board Level Shock Test Development for Handheld Components

Electronic and Photonic Packaging, Electrical Systems Design and Photonics, and Nanotechnology ◽

10.1115/imece2004-60121 ◽

2004 ◽

Author(s):

Shubhada Sahasrabudhe ◽

Vinayak Pandey ◽

Betty Phillips ◽

Kang Joon Lee ◽

Lei Mercado

Keyword(s):

Solder Joint ◽

Cell Phone ◽

Standardized Test ◽

Test Development ◽

Failure Mechanisms ◽

Reliability Test ◽

Shock Test ◽

Board Level ◽

Test Repeatability

For handheld electronic applications such as cell phones and Personal Digital Assistants (PDAs), drop/impact could result in considerable flexure of the printed circuit board (PCB) mounted inside the cell phone housing. The mechanical stresses may cause electrical failure of the components, with typical failure mechanisms of board trace cracking, solder joint fatigue, and solder pad cracking. A standardized test needs to be developed to assess reliability of handheld components subjected to impacts. The test should facilitate high volume testing, maximize margin for safety factors, and capture the failure mechanisms in the field environment. To develop the reliability test using use conditions based reliability methodology, comprehensive characterization of the mechanical field stresses during end use conditions is particularly essential. This paper discusses complete cell phone drop characterization along with the shock test developed to test the components subjected to such drops. Novel fixtures have been designed to simulate free fall of the cell phone in specific orientations. After the complete characterization of cell phone use conditions, board level shock test has been selected to assess component reliability. Test repeatability, number of components on the test board, and layout of the components are some of the factors considered during the board level shock test development. Several parameters like screw and washer designs, torque have been studied to yield excellent test repeatability. Nonlinear Dynamic Finite Element Simulation has been performed to provide more insight into the interaction of the bending modes and its impact on the solder joint failures. This paper demonstrates the process of understanding use conditions, developing reliability tests, validating test results and driving industry standards.

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