FCCSP IMC growth under reliability stress follows automotive criteria

Abstract

Purpose -The Kirkendall void had been a well-known issue for long-term reliability of semiconductor interconnects; while even the KVs exist at the interfaces of Cu and Sn, it may still be able to pass the condition of unbias long-term reliability testing, especially for 2,000 cycles of temperature cycling test and 2,000 h of high temperature storage. A large number of KVs were observed after 200 cycles of temperature cycling test at the intermetallic Cu 3 Sn layer which locate between the intermetallic Cu 6 Sn 5 and Cu layers. These kinds of voids will grow proportional with the aging time at the initial stage. This paper aims to compare various IMC thickness as a function of stress test, the Cu 3 Sn and Cu 6 Sn 5 do affected seriously by heat, but Ni 3 Sn 4 is not affected by heat or moisture.Design/methodology/approach -The package is the design in the flip chip-chip scale package with bumping process and assembly. The package was put in reliability stress test that followed AEC-Q100 automotive criteria and recorded the IMC growing morphology.Findings -The Cu 6 Sn 5 intermetallic compound is the most sensitive to continuous heat which grows from 3 to 10 mm at high temperature storage 2,000 h testing, and the second is Cu 3 Sn IMC. Cu 6 Sn 5 IMC will convert to Cu 3 Sn IMC at initial stage, and then Kirkendall void will be found at the interface of Cu and Cu 3 Sn IMC, which has quality concerning issue if the void's density grows up. The first phase to form and grow into observable thickness for Ni and lead-free interface is Ni 3 Sn 4 IMC, and the thickness has little relationship to the environmental stress, as no IMC thickness variation between TCT, uHAST and HTSL stress test. The more the Sn exists, the thicker Ni 3 Sn 4 IMC will be derived from this experimental finding compare the Cu/Ni/SnAg cell and Ni/SnAg cell.Research limitations/implications -The research found that FCCSP can pass automotive criteria that follow AEC-Q100, which give the confidence for upgrading the package type with higher efficiency and complexities of the pin design.Practical implications -This result will impact to the future automotive package, how to choose the best package methodology and what is the way to do the package. The authors can understand the tolerance for the kind of flip chip package, and the bump structure is then applied for high-end technology.Originality/value -The overall three kinds of bump structures, Cu/Ni/SnAg, Cu/SnAg and Ni/SnAg, were taken into consideration, and the IMC growing morphology had been recorded. Also, the IMC had changed during the environmental stress, and KV formation was reserved.