Authors: A. Guédon-Gracia, H. Frémont, J.-Y. and K. Weide-Zaage Company: Delétage Laboratoire IMS, Université de Bordeaux and RESRI Group, Institute of Microelectronic Systems (IMS-AS), Leibniz Universität Hannover Date Published: 1/25/2016
Pan Pacific Symposium
Abstract: For some applications like ship, aircraft and car, electronic systems are submitted to salt environment. In this case, the main reliability issue is the corrosion of the metals from the pads and the solder alloys. More than 20% of failures in microelectronic devices can be attributed to corrosion. Nevertheless this phenomenon is little studied on microelectronic assemblies. This paper presents ageing tests in salt spray chamber performed on BGA (Ball Grid Array) assemblies. The test vehicle is composed of BGA components with SnAgCu ball mounted on FR4 board. This BGA is a daisy chained component. So the electrical continuity of the assembly can be tested thanks to the electrical resistance measurement of the solder joint chain. The assemblies are put in a salt spray chamber at 35°C with 5% sodium chloride (NaCl) aqua according to the ASTM B117-09 standard, which is an accelerated test to stimulate the effects of a severe marine atmosphere on exposed surfaces. The assemblies are removed at 24, 48, 72 and 96 hours. The electrical resistance and the weight are measured during the test. The solder joints and the copper pads are observed and analysed with optical microscope. Then samples are cross-sectioned and polished to reveal the solder microstructure, in order to be examined by a scanning electron microscope (SEM) equipped with an energy-dispersive x-ray (EDX) system. The corrosion of some Cu pads is observed, in particular for the pads without solder alloy. The solder joint deterioration is visible but no electrical failure is detected. The microstructure is observed in order to determine the corroded residues found on the surface solder balls after the salt spray test. The Ag3Sn contained in SnAgCu solder joints seems to accelerate the corrosion of tin because of the galvanic corrosion mechanism.
Corrosion, Salt spray test, BGA assembly, Lead-free solder