Thermal cycling of leadfree Sn3.8Ag0.7Cu 388PBGA packages

• Published in: Soldering & surface mount technology 2009-04, Vol.21 (2), p.28-38
• Main Authors: Andersson, C., Vandevelde, B., Noritake, C., Sun, P., Tegehall, P.E., Andersson, D.R., Wetter, G., Liu, J.
• Format: Article
• Language: English
• Subjects: Finite element analysis; Lead; Modelling; Solders; Stress materials; Thermal testing
• ISSN: 0954-0911
• DOI: 10.1108/09540910910947453

Purpose The purpose of this paper is to assess the effect of different temperature cycling profiles on the reliability of leadfree 388 plastic ball grid array PBGA packages and to deeply understand crack initiation and propagation. Designmethodologyapproach Temperature cycling of Sn3.8Ag0.7Cu PBGA packages was carried out at two temperature profiles, the first ranging between 55C and 100C TC1 and the second between 0C and 100C TC2. Crack initiation and propagation was analyzed periodically and totally 7,000 cycles were run for TC1 and 14,500 for TC2. Finite element modeling FEM, for the analysis of strain and stress, was used to corroborate the experimental results. Findings The paper finds that TC1 had a characteristic life of 5,415 cycles and TC2 of 14,094 cycles, resulting in an acceleration factor of 2.6 between both profiles. Cracks were first visible for TC1, after 2,500 cycles, and only after 4,000 cycles for TC2. The crack propagation rate was faster for TC1 compared to TC2, and faster at the package side compared to the substrate side. The difference in crack propagation rate between the package side and substrate side was much larger for TC1 compared to TC2. Cracks developed first at the package side, and were also larger compared to the substrate side. The Cu tracks on the substrate side affected the crack propagation sites and behaved as SMD. All cracks propagated through the solder and crack propagation was mainly intergranular. Crack propagation was very random and did not follow the distance to neutral point DNP theory. FEM corroborated the experimental results, showing both the same critical location of highest creep strain and the independence of DNP. Originalityvalue Such extensive work on the reliability assessment of Pbfree 388 PBGA packages has never been performed. This work also corroborates the results from other studies showing the difference in behavior between Pbfree and Pbcontaining alloys.