Effect of Interfacial Reactions on the Reliability of Lead-Free Assemblies after Board Level Drop Tests

Abstract

The reliability of lead-free electronic assemblies after board level drop tests was investigated. Thin small outline package (TSOP) components with 42 FeNi alloy leads were reflow soldered on FR4 printed circuit boards (PCBs) with Sn3.0Ag0.5Cu (wt%) solder. The effects of different PCB finishes [organic solderability preservative (OSP) and electroless nickel immersion gold (ENIG)], multiple reflow (once and three times), and isothermal aging (500 h at 125°C after one time reflow) were studied. The ENIG finish showed better performance than its OSP counterparts. With the OSP finish, solder joints reflowed three times showed obvious improvement compared to those of the sample reflowed once, while aging led to apparent degradation. The results showed that intermetallic compound (IMC) types, IMC microstructure and solder microstructure compete with each other, all playing very important roles in the solder joint lifetime. The results also showed that it is important to specify adequate conditions for a given reliability assessment program, to allow meaningful comparison between results of different investigators.

Strain Rate Dependence on Nanoindentation Responses of Interfacial Intermetallic Compounds in Electronic Solder Joints with Cu and Ag Substrates

“…The solders were placed in a quartz tube and then soaked in an oil bath at 250 C. Cu and Ag wires with diameter of 1 mm were used. The metallic wires were sequentially degreased in NaOH solution, deoixed in HNO 3 and dipped in a dimethylammonium chloride (DMAHCl) solution before soldering. The fluxed specimen was soaked in the isothermal solder liquid for a desired duration (20$60 min) to obtain IMC layers with enough thickness for nanoindentation tesing.…”

“…1) Instead of solder bulk, fracturing of solder joints subjected to drop impact generally occurs at brittle IMCs at the interface. 2,3) In order to increase the reliability of solder interconnections, this study aims to study the mechanical behavior of IMCs at the interfaces between Pb-free solders (Sn-Ag-Cu and Sn-Zn) and common electronic substrates, Cu and Ag using nanoindentation. The effect of strain rate on the mechanical properties is the main concern.…”

Mechanical Property Evaluation of Sn-3.0A-0.5Cu BGA Solder Joints Using High-Speed Ball Shear Test

“…This fracture mode, in particular, was observed only in the samples deformed under high loading speeds (3 m/s) after aging for 1000 h. These traits suggest that this mode corresponded to the fracture typically observed in drop events. [25][26][27][28] The schematic diagrams shown in Fig. 8 summarize the three fracture modes: a ductile fracture through the solder (mode I), an abrupt fracture after some plastic deformation (mode II), and a brittle fracture through the IMC (mode III).…”

Effects of Different Kinds of Underfills and Temperature–Humidity Treatments on Drop Reliability of Board-Level Packages

“…On the other hand, the board-level drop test is convenient to characterize solder joint performance, because it is more controllable than product-level drop testing. [3][4][5][6][7][8][9] Generally, board-level reliability of fine-pitch packages has been investigated by bending testing, thermal cycle testing, tensile testing, and metallurgical characterization. 1,2 Routine use of portable electronic devices applies low-frequency, random vibration to the electronic packages within.…”

“…17,18 Many studies have been performed to investigate the drop reliability of board-level packages, varying parameters such as drop test conditions, under bump metallurgy, solder, PCB finishes, and pad structure. [1][2][3][4][5][6][7][8][9][10][11][12][13] Nevertheless, insufficient studies have investigated the drop reliability of board-level packages with different kinds of underfill under hygrothermal and mechanical stresses. Therefore, we investigated the hygrothermal and mechanical reliability of board-level packages with various underfills using the temperature and humidity (TH) test and drop test.…”