![]() ![]() Therefore, an understanding of thermal fatigue performance for new alloys is necessary for OEMs to make design and procurement decisions, and for component suppliers to ensure the reliability of their products over a range of field use conditions. As such devices begin use in the next generation Pb-free servers thermal fatigue resistance is likely to be a concern due to their relatively large die and the demanding thermal environment. One example is in memory devices, where low-Ag alloys are being introduced by some suppliers. In situations where thermal fatigue resistance is critical to product life, this knowledge gap creates a significant risk. However, iNEMI has identified the thermal fatigue resistance of the new Pb-free ball alloys to be a major knowledge gap. Process Window RTS (Ramp to Spike) Now we consider the ramp to spike/peak. to increase the process window soak temperature to 155-200C. To maintain a soak profile this would be changed as indicated in Figure 1. A number of BGA/CSP component suppliers are now shipping devices that use these new solder alloys. Below (Figure 2.) is a view of a reflow soak profile commonly used for lead-free solder manufacturing. Introduction Several publications have demonstrated improved mechanical shock fracture resistance for a variety of " second generation " Pb-free solder ball alloys. The implications of these findings and areas for further study are discussed. The impact of failure criterion on the Weibull curves is also presented. The data indicate that SAC105 has the lowest thermal fatigue resistance among the alloys tested, with Sn-3.5Ag and SAC 305 having similar and superior performance. ATC testing was performed using the IPC-9701A TC1 condition of 0/100☌ with 10-minute dwells (nominal) 3 different failure criteria were used in constructing the Weibull failure curves. These components were assembled to high-temperature rated Cu-OSP coated printed circuit boards using SAC 305 solder paste, which represents one of the most common assembly practices in industry today. Accelerated thermal cycle (ATC) testing was performed using 676 PBGA components with 1.0 mm pitch and electrolytic Ni/Au finished component pads. In this study, the thermal fatigue performance under accelerated test conditions is compared for three common BGA ball alloys: SAC105, Sn-3.5Ag, and SAC305 as a control. Therefore, an understanding of thermal fatigue performance for new alloys is necessary for OEM/ EMS/ ODM companies to make design and procurement decisions, and for component suppliers to ensure the reliability of their products under a range of field use conditions. As these components and alloys become mainstream, their use in situations where thermal fatigue resistance is critical to product life will become an important consideration. Several publications have established the improved performance of such 2 nd level BGA/CSP sphere alloys however, much less has been published regarding the thermal fatigue resistance of components with these new Pb-free ball alloys. Much of the motivation for the alloy changes has been to improve mechanical shock resistance. 21-38.Many BGA and CSP component suppliers have begun shipment of components with a variety of " second generation " Pb-free solder ball alloys. ![]() (2001), "Lead‐free reflow soldering for electronics assembly", Soldering & Surface Mount Technology, Vol. ![]() No justification was found for minor additions of Sb, but 2‐5 per cent Bi was found to allow a reduction of the peak reflow temperature, though at the cost of reduced reliability if any Pb was present. ![]() The effects of Sb and Bi were also evaluated. Overall the SnAg3.8Cu0.7 gave results approximately equivalent to conventional solders, and different board finishes had no significant effect. The Bi-Sn solder system is one low melting metallurgical system of interest, but the inherent brittleness of bismuth is its major drawback. Reliability was tested on soldered test boards using thermal shock cycling, power cycling, and vibration. Lowering peak reflow temperature from the current 240☌+ level for SnAgCu (SAC) solder paste during the assembly of electronic board products has economic, environmental and technical benefits. Reflow process window studies showed that sound reliable joints could be obtained with a peak temperature as low as 225☌. Differences in alloy density, melting point, and surface tension relative to conventional solders were found to give higher levels of internal voids, reduced spread on copper, and rougher, duller joints. Implications for solder paste medium development are discussed. On the basis of fundamental data from the literature, a shortlist of candidate lead‐free solders was selected, and results from tests on physical and soldering characteristics, and wetting balance testing, led to the choice of SnAg3.8Cu0.7, melting at 217☌. Results for reflow soldering are presented from a three‐year EC funded project “IDEALS” to develop lead‐free soldering solutions. ![]()
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