SECOND LEVEL SOLDER JOINT RELIABILITY OF QUAD FLAT NO-LEAD (QFN) PACKAGES FOR USE IN IPC CLASS-2 ASSEMBLIESAuthors: Alex Chan, Aman Khan, Ph.D., and Robert Kinyanjui, Ph.D.
Company: Alcatel-Lucent Canada Inc., International Rectifier, and Sanmina-SCI Corporation
Date Published: 10/11/2007 Conference: SMTA International
This study was conducted to examine the impact of die and package size as well as solder alloy type (two solder paste types: the lead-free Sn-3.0wt.Ag-0.5wt.%Cu or SAC305 and the eutectic SnPb) on the solder joint reliability of QFN devices. Three different package size schemes were selected for study. These included 5 x 5mm2, 7 x 7mm2 and 9 x 9mm2 with the corresponding number of package input/output pins being 32, 48 and 64, respectively. Five different die size schemes were used: two each for the 5 x 5mm2, 7 x 7mm2 package sizes and one for the 9 x 9mm2 package size, with the smallest die size measuring 2.44 x 2.90mm2 while the largest die measured 7.14 x 7.14mm2.
Total of 48 devices per die size were assembled on test vehicles for each solder paste. After the build 10 devices per die size were reworked and then inspected. All the assemblies were then subjected to accelerated thermal cycling (ATC) test in the temperature range 0 to 100oC with a 10oC per minute ramp rate and 10 minutes dwell time. The samples were cycled to a maximum of 3600 cycles. After the ATC testing, Weibull plot were created to analyze the failure characteristics observed. To examine the solder joint failure modes, devices were cut, cross-sectioned and analyzed using both the optical and scanning electron microscopy. The data from the Weibull plots revealed the die-to-package size ratio to be critical to the solder joint reliability. Further the solder joint reliability of SnPb joints was found to be significantly different from that of the leadfree joints. Discussion of these results is presented in the paper.
Key words: QFN, Lead-free, QFN Die Size, solder Joint Reliability.
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