The effect of Cu-Sn intermetallic compounds (IMC) on the fatigue failure of solder joint during thermal cycling has been studied. The samples consist of components [leadless ceramic chip carrier (LCCC)] soldered onto FR-4 printed circuit board (PCB), and are prepared by conventional reflow soldering using a 63Sn-37Pb solder paste. The specimens are subjected to thermal cycling between 035 C and 125 C with a frequency of two cycles per hour until failure. The results indicate that the fatigue lifetime of the solder joints depends on the thickness of IMC's layer between Cu-pad and bulk solder, and the relation of the lifetime to the thickness can be described as a monotonically decreasing curve. The lifetime is very sensitive to the thickness of the IMC when the thickness is less than 1.4 m. During thermal cycling, the thickness of the IMC layer increases and then the interface between IMC and solder becomes gradually flatter. The results of X-ray diffraction and scanning electron microscope (SEM) analysis show that cracks propagate along the interface between the IMC layer and the solder joint. The Cu3Sn ("-phase) is also found to form between the Cu-pad and-phase during thermal cycling. On the basis of the above results, the thick and flattened IMC layer is shown to responsible for the fatigue failure of solder joint during thermal cycling. The results of this paper can be used to optimize the reflow soldering process for the fabrication of robust solder joints.

No abstract

No abstract

The effect of Cu-Sn intermetallic compounds (IMC) on the fatigue failure of solder joints has been studied by means of shear cycling. The samples consist of leadless ceramic chip carriers (LCCC) soldered onto FR-4 printed circuit boards (PCB), and are prepared by conventional reflow soldering using a 63Sn-37Pb solder paste and then aged at 150 C for 1, 4, 9, 16, 25, 36, and 49 days. The specimens are subjected to low cycle fatigue shear tests controlled by the displacement. The results indicate that the fatigue lifetime of the solder joints depends on the thickness of the IMC layer between the Cu-pad and bulk solder, and the quantitative relationship between the lifetime and thickness can be described as a monotonically decreasing curve. The greatest decrease is over the thickness range up to 2.8 m, when the IMC/bulk solder interface becomes flat, corresponding to a lifetime decrease to 62% of the as assembled value. For further increase in IMC thickness the lifetime decreases more slowly. Evidently, the effect of the Cu-Sn intermetallic compounds on the joint fatigue lifetime is not only concerned with the IMC thickness but also the interface morphology. A thick and flat IMC layer has a deleterious effect. The results of X-ray diffraction and metallographic analysis show that cracks initiate underneath the component metallization, and propagate along the IMC/solder interface, then toward the fillet. The Cu 3 Sn ("-phase) is formed between the Cu-pad and -phase, and grows more quickly than thephase during storage and long term operation or aging tests. However, the Cu 3 Sn makes only a small direct contribution toward fatigue failure.

No abstract

No abstract

To investigate the effect of stencil thickness and reflow ambient atmosphere on the reliability of ceramic ball grid array (CBGA) assemblies, three levels of stencil thickness, 0.10, 0.15, and 0.20 mm, were used to print solder paste on printed circuit board (PCB). After the CBGA modules were placed on PCBs, the specimens were divided into two groups, and reflowed in nitrogen and compressed air separately. Properties of the six groups of assemblies, such as shear strength, bending fatigue life, thermal shock cycles, and vibration fatigue life, were tested to find out the optimum assembling process. The results show that assemblies prepared with a stencil 0.15 mm thick yield maximized performance. And the nitrogen ambient atmosphere demonstrates a remarkable effect on improving the fatigue life. Theoretical models are given to qualitatively explain the relationship between the solder joint volume and performance. This work provides a guideline on how to determine the soldering process parameters of CBGA assemblies.

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...