Solder joint reliability of plastic ball grid array packages

Abstract

Presents the results of a study of the effects of solder ball pad metallurgy, intermetallic compound (IMC) thickness and thermal cycling on the shear strengths of PBGA package solder balls. The study of the microstructures of solder balls revealed that only a very thin layer of intermetallic compound existed between solder balls and Ni or Ni alloy barrier layers immediately after ball placement and reflow. The protective Au layer was dissolved completely and a needle like AuSn4 intermetallic compound was then formed and dispersed evenly in the solder balls. The overall thickness of the IMC layers was thicker than 15 mm after storage at 150°C for 1,000 hours. During the shear tests failure occurred at the interface of the two IMC layers. The fracture surfaces of solder balls with electrolytic Ni and thick Au layers were smooth and brittle fracture was observed. The ball shear strength decreased dramatically with the formation of IMC layers. For the solder balls with electroless Ni and thin Au layers, only a single IMC layer was formed at the interface and its thickness was only 2.5 mm after storage at 150°C for 1,000 hours. Plate 8aFracture surface of solder balls with electroless Ni/Au layers after storage at 150˚C for 1,000 hours Plate 8bClose-up view of the fracture surface Plate 8cCross-section of the fracture surface of solder balls Plate 7cCross-section of packages after shear tests

The effect of isothermal aging on the thickness of intermetallic compound layer growth between low melting point solders and Ni-plated Cu substrate

“…However, most previous work reported that only the Ni 3 Sn 4 IMC was present in the Sn-based solder/Ni substrate. 10,13,14 According to Huang et al, 15 who investigated the interfacial reactions using In-Sn/Ni couples, the Ni 3 Sn 4 was also formed at the interface. In the as-soldered condition, as shown in Fig.…”

Multiphase Field Simulations of Intermetallic Compound Growth During Lead-Free Soldering

“…The nature of the interfacial reactions depends on the individual alloy systems and soldering temperatures under consideration. [1][2][3][4][5][6][7] In Cu-Sn/Cu systems, the intermetallic layers typically formed at the substrate/ solder interface at the early stages of the soldering process have been observed to consist mostly of Cu 6 Sn 5 , with Cu 3 Sn being a minor constituent of the IMC layer. It is important to note that, at later stages, Cu 3 Sn can become the dominant constituent of the IMC layer, depending on the particular soldering conditions and the relative amounts of the reactants (Cu and Sn).…”

ENIG Corrosion Induced by Second-Phase Precipitation

“…[1][2][3][4][5] In addition to having desirable solder wetting characteristics, ENIG provides a low-cost and longshelf-life surface finish that is easily adopted for use on fine-pitch BGA substrates without complicating the design layout. 6 Unfortunately, although ENIG solder joints are generally robust, brittle solder joint fractures are sometimes found in assembly and testing.…”