ICSR (Soldering and Reliability) Conference Proceedings


SOLDER JOINT MICROSTRUCTURE AND RELIABILITY STUDY OF PLASTIC BALL GRID ARRAY (PBGA196) AND MICRO LEAD FRAME (MLF) COMPONENTS IN LEAD FREE PROCESSES

Authors: Simin Bagheri, et al.
Company: Celestica Inc.
Date Published: 5/22/2009   Conference: ICSR (Soldering and Reliability)


Abstract: PBGA196 (Plastic Ball Grid Array) and MLF20 (Micro Lead Frame) packages were assembled on several Printed Circuit Board (PCB) test vehicle designs using no clean, lead free SAC (Sn-Ag-Cu) 305 and SAC 385 as well as tin/lead (Sn/Pb) solder pastes.

The packages studied were (Restriction of Hazardous Substances) RoHS compliant. PBGA196s used had SAC 305 and SAC 385 balls. The purpose of this investigation was to evaluate thermal fatigue reliability performance of the solder joints formed in pure lead free systems and compare it to the mixed assembly alloy systems.

This evaluation included different surface finishes on assembly test vehicles such as High Temperature OSP (HT OSP), Immersion Silver (ImmAg), Immersion Tin (ImmSn), Electroless Nickel Immersion Gold (ENIG) as well as Electrolytic Nickel Gold (Ni/Au). Assembly was performed in both Air and N2 environment.

Accelerated thermal cycling (ATC) was performed for PBGA196 and MLF components as per IPC-9701 specification to 3000 and 6000 cycles at -55°C-125°C and 0°C-100°C respectively[1].

Thermal fatigue reliability of reworked PBGA196 components assembled on the top side of the test boards as well as the influence of their SAC rework on the mirror imaged PBGA196 components on the board bottom side was also evaluated. Solder joints were examined after assembly and ATC using optical and scanning Electron microscopy, EDX and X-ray methods.



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