Vibration fatigue of μBGA solder joint

Abstract

This paper studies the vibration fatigue failure of pBGA solder-joints reflowed with different temperature profiles, and ageing at 120°C for 1,4,9, 16,25, 36 days. The effect of the thickness of the Ni3Sn4 and Cu-Sn intermetallic compound (IMC) on the fatigue lifetime is also reported. During the vibration fatigue test, in order to identify the failure of pBGA solder joint, electrical interruption was monitored continuously through the daisy-chain network. Our results show that the fatigue lifetime of the solder joint firstly increases and then decreases with increasing heating factor (Q,,), which is defined as the integral of the measured temperature over the dwell time above liquidus (1 83°C) in the reflow profile. The greatest lifetime occurs when Q, is near 500 SOC. Moreover, the lifetime of the solder joint decreases linearly with the increasing fourth root of the ageing time. The SEMEDX inspection shows that only Ni3Sn4 IMC and Cu6Sn5/Cu3Sn IMCs are formed between the solder and the nickel-plated PCB pad, and the solder/componentmetallization interface respectively. For non-aged samples reflowed with different profiles, the fatigue crack generally initiates at valleys in the rough surface of the interface of the Ni3Sn4 IMC with the bulk solder. Then it propagates mostly near the Nilsolder, and occasionally in the IMC layer or along the Nilsolder interface. For aged samples, the fatigue crack mostly initiates and propagates in the Cu6Sn5-phase/bulksolder interface or the Cu3Sn/Cu6Sn5 interface on componentmetallization.Evidently, the intermetallic compounds contribute mainly to the fatigue failure of pBGA solder joints. The thicker the IMC layer, the shorter the fatigue lifetime of solder joint. The initial formation of the IMCs at the interface during soldering ensures a good metallurgical bond between the solder and the substrate. However, a thick IMC layer influences the solder joint strength, which results in mechanical failure due to volume shrinkage during the transformation from solid phase to the intermetallic compound. IntroductionThe micro ball grid array (pBGA) package has been successfully applied in many electronic products, i.e. computer processor, flash memory and mobile phone. Current issues include availability, cost, testability, assemblyinspection, rework methods, etc. Solder joint reliability is one of the most critical issues in the development of these technologies [l]. The pBGA structure includes a low stress die-attach elastomer between the silicon die and the solder bump array, which dissipates thermally induced stress caused by mismatches between the silicon and the substrate, allowing good solder joint reliability under thermal shock and temperature cycling [2]. However, in normal use, locomotor and portable products are always faced with various kinds of mechanical and environmental stresses, such as vibration and bending of a PCB with pBGAs soldered to its surface [l]. Moreover, vibration load due to the operation of vehicle may also cause fatigue failure of solder joints too [3...

Effect of Isothermal Aging on Ball Shear Strength in BGA Joints with Sn-3.5Ag-0.75Cu Solder

“…5) Thick intermetallic compound layer poses potential reliability issues due to an 8.5% and 5% volume shrinkage during the transformation from solid phase to the Cu 3 Sn and Cu 6 Sn 5 intermetallics.…”

“…[1][2][3] The BGA package has been successfully applied in many electronic products. [4][5][6] There are an increasing number of higher density BGA substrates that use immersion Au/electroless Ni for the surface finish. The principal advantage of electroless plating is the ability to meet the requirements of increasing in the terminal density.…”

Effect of cooling rate on the isothermal fatigue behavior of CBGA solder joints in shear

“…1, the 183 C melting temperature of the eutectic solder is defined as the reference temperature line-the liquidus. In our previous work [10], it was found that the integral of the measured temperature above the liquidus line with respect to time, defined as "heating factor," can characterize the reflow profile in the melting section.…”

Thermal profiling: a reflow process based on the heating factor

“…The IMC layer thickness increases almost linearly with the heating factor (Tao, 2006). Hence, heating factors of all the solder joints in a PCBA should be controlled within a certain range (such as 200-700 s 8C) to obtain high reliability and soldering quality (Tu and Chan, 2000b; Figure 2). Since the IMC formation mechanism for Sn-Ag-Cu solder paste is fundamentally the same as that for Sn-Pb solder paste (Harris, 1998), the heating factor based optimization of a reflow profile can also be applied to Sn-Ag-Cu solder paste.…”