Characterising Solder Materials from Random Vibration Response of their Interconnects in BGA Packaging

Solder interconnection in electronic packaging is the weakest link, thus driving the reliability of electronic modules and systems. Improving interconnection integrity in safety-critical applications is vital in enhancing application reliability. This investigation qualifies the random vibration response of five essential solder compositions in ball grid array (BGA) solder joints used in safety-critical applications. The solder compositions are eutectic Sn63Pb37 and SnAgCu (SAC) 305, 387, 396, and 405. Computer-aided engineering (CAE) employing ANSYS FEA and SolidWorks software is implemented in this investigation. The solder Sn63Pb37 deformed least at 0.43 µm, followed by SAC396 at 0.58 µm, while SAC405 deformed highest at 0.88 µm. Further analysis demonstrates that possession of higher elastic modulus and mass density culminates in lower solder joint deformation. Stress is concentrated at the periphery of the solder joints in contact with the printed circuit board (PCB). The SAC396 solder accumulates the lowest stress of 14.1 MPa, followed by SAC405 at 17.9 MPa, while eutectic Sn63Pb37 accrues the highest at 34.6 MPa. Similarly, strain concentration is found at the interface between the solder joint and copper pad on PCB. SAC405 acquires the lowest elastic strain magnitude of 0.0011 mm/mm, while SAC305 records the highest strain of 0.002 mm/mm. These results demonstrate that SAC405 solder has maximum and SAC387 solder has minimum fatigue lives

Effects of reflow profile and miniaturisation on integrity of solder joints in surface mount chip resistor

Integrity of solder joints of components in an electronic device is critical to the device reliability. Miniaturisation manufacturing trend in electronic products development has continued to challenge the shear strength of the solder joints in these devices and necessitates implementation of optimal reflow profile to achieve maximum strength of the joints. This research proposes optimal parameter combination of reflow profile factors which demonstrate potential of delivering maximum shear strength of solder joint. The Taguchi design of experiment (DoE) is employed to generate eight orthogonal array designs of L24 of reflow profiles. The factors/parameters investigated are preheat gradient, time above liquidus (TAL), peak temperature and cooling rate. Three test vehicles of varying solder joint sizes are made from R1206, R0805 and R0603 resistors. Reflow profile number 3 constituting 1.2 °C/s preheat, 45 s TAL, 245 °C peak temperature and 60% cooling rate is optimal because it yielded joints with highest strength and circa 4 µm thickness of intermetallic compound (IMC). Solder joint shear strength decreases with decrease in size of lead-free joint irrespective of reflow profile implemented. These results will be useful to electronic packaging and reliability engineers faced with challenges of improving device operational mechanical performance in the continuing product miniaturisation trend

Stencil Printing Behavior of Lead-Free Sn-3Ag-0.5Cu Solder Paste for Wafer Level Bumping for Sub-100 μm Size Solder Bumps

Stencil printing for flip chip packaging using fine particle solder pastes is a low cost assembly solution with high throughput for fine pitch solder joint interconnects. The manufacturing challenges associated with both solder paste printing increases as electronic device size decreases due to trend of miniaturization in electronic components. Among multiple parameters, the two most important stencil printing parameters are squeegee pressure and printing speed. In this paper, the printing behavior of Pb free Sn-3Ag-0.5Cu solder paste with a particle size distribution of 2-12 μm for wafer level bumping using a stencil printing method (stencil opening dimension -30 μm) was evaluated by varying the printing speed and squeegee pressure to fabricate solder bumps with a sub 100 μm size. The optimal squeegee pressure and print speed for the defect free printing behavior and fairly uniform size distribution of reflowed paste were found to be 7 kgf and 20 mm/s, respectively. The average size of the reflowed printed paste decreased with the increasing squeegee pressure