Pb free solder is fast becoming a reality in electronic manufacturing due to marketing and legislative pressures. The industry has pretty much concluded that various version of SnAgCu solder alloy offer the best alternative for eutectic SnPb solder currently in use. With the current trend of cheaper, faster, and better electronic equipment, it has become increasingly important to evaluate the package and system performance very early in the design cycle using simulation tools. This requires life prediction models for new solder alloy systems so that the package-to-board interconnect reliability can be predicted for various environmental and field conditions. This paper describes in detail the life prediction models foi SnAgCu solder joints. The models are based on published coiistitutive equations for this alloy and thermal cycle fatigue dai a on actual components. The approach uses advance finite element modeling and analysis techniques and is based on mechanics of deformation. Both accumulated creep strain and creep strain energy density based models are developed. The model has been correlated with a number of data points and predicts life within 25% in most cases. The framework of modeling and prediction methodology described here is fully coinpatible with the framework used for SnPb solder previously. In1 roductionThe reliability of solder joints is one of the most important factors when selecting a package for a particular application. Thle CTE and stiffness mismatch between the package and the board results in thermal stresses in solder joints during temperature and power cycling. The damage caused by these stresses accumulates as the electronic assembly is subjected to multiple cycles, ultimately causing failures of solder joints. This is a very well documented failure mode for electronic assemblies and a wealth of data is available in the literature for SnPb solder. Due to this reason, the reliability of Pb free sobier joints is an important factor for selecting the proper replacement of SnPb solder. Based on various studied conducted, the industry as a whole has converged towards SnAgCu solder alloy (with different compositions) to replace SnPb solder from electronic assemblies.The reliability of SnAgCu solder joints has been a subject of major research in electronic industry and a number of researchers have published data [l, 2, 31 showing SnAgCu performs better or worse than SnPb solder, depending on the conaponents tested and test conditions employed. While more test data is being gathered under accelerated test conditions, it is also becoming apparent that this will not be enough due to rapid implementation of this soldering system. Today, electronic industry uses electronic components using lead frame or laminate technology with countless number of packages in various lead counts, leadhall pitches, and die sizes. Since every component has a different interconnect reliability behavior, it is unrealistic and cost prohibitive to generate test data for every case. The interconnect reliability also dep...

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There are two sources of errors in any finite element based life prediction model: the finite element mesh and assumptions, and the material properties usedspecifically the constitutive model used to describe the behavior of solder joints during temperature cycling. The use of these assumptions may prohibit the application of life prediction model to conditions beyond the ones used to develop the model.The author has previously proposed life prediction models for SnPb and SnAgCu solder joints using advanced finite element modeling techniques such as substructuring and multi-point constraints. The assumptions were necessary to increase the efficiency of solution with available computing power. With the advances in computing technology, these assumptions are no longer necessary, and more accurate life prediction can be achieved by eliminating most of the modeling assumptions.In this paper, the updated life prediction model parameters for SnAgCu solder joints are presented without the use of sub-structuring and multi-point constraints. All joints for a particular package-board interconnection are modeled as having non-linear properties. In addition, a detailed mesh refinement study is done to determine the minimum mesh density required to yield near mesh-independent results.In addition to modeling assumptions, the constitutive equation used for solder joints may also influence the life prediction model parameters. To investigate this further, the creep behavior of SnAgCu solder joints is represented by using published constitutive equations (double power law creep and hyperbolic sine equation). The results show a significant influence of constitutive equation on creep strain based life prediction model but minimum impact when energy density based approach is used.

As handheld electronic products are more prone to being dropped during useful life, package to board interconnect reliability has become a major concern for these products. This has prompted the industry to evaluate the drop performance of CSP packages while mounted on printed wiring boards using board level drop testing.Although a new board level test method has been standardized through JEDEC (JESD22-B111), characterization tests take quite a long time to complete, extending the design cycle. This paper proposes a method to compare and evaluate the drop performance through simulations at the design stage. A global-local approach is used to first determine the dynamic response of the board during drop and then to translate it into stresses and strain energy density in solder joints and intermetallic layers. The dynamic response of the board is validated by using data from actual board level testing as per JEDEC standard. The solder joint and intermetallic stresses are then related to drop to failure test data to derive a prediction model.The method is then applied to quantify the effect of package design parameters on the drop performance. Factors considered include material set, thickness of various material layers, pad size, and ball size. The same factors were tested in board level drop to further validate the prediction model. Experiments were also conducted to quantify the effects of package ball pad finish on the drop performance through board level testing according to JESD22-B111.The results indicate that the drop performance can be increased by a factor of 4 or more by changing package design and material variables.

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A11 A1 A14 A21 Alloy Codes -1st Fail -2P 0.1% -2P Mean -3P Gamma A32 A62 A66 0.00 0.50 1.00 1.50 2.00 2.50 Relative LifeThis paper reports results of a four-year industrial consortium effort to develop leadfree solders for high-temperature applications (up to 160∞C). Work included preliminary evaluations of 32 tin-based alloys, a screening of the thermomechanical fatigue performance of 13 promising alloys, and a full manufacturability and fatigue testing of the seven most promising of those alloys, namely . Eight different components were used on the reliability test vehicle, and the alloys were compared through Weibull analysis. In addition, the same seven experimental alloys were tested with ball grid array packages cycled up to 100∞C or 125∞C. All the leadfree alloys performed well, but those containing bismuth showed especially outstanding performance. In general, the ternary and higher alloys performed as well or better than the industry standard tin-silver eutectic, suggesting that solders other than the tin-silver eutectic should be considered for high-reliability, high-temperature applications.

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This paper presents a collection of test data showing how the choice of package design and material can have a different effect on performance depending on the loading conditions. Board level temperature cycling, drop (JESD22-B111), and cyclic bend (JESD22-B113) tests were performed on 0.4mm ball pitch packages. Factors investigated for this evaluation include mold compound material, mold cap thickness (0.45 vs. 0.7mm), ball pad finish (NiAu vs. Cu OSP), solder ball composition (SAC305, SAC105, SAC125Ni, Sn3.5Ag), solder volume (ball vs. bump), package material (RoHS vs Green), and board material (RoHS vs Green). The data presented in this paper indicates that lower silver content solder balls perform better under drop conditions, while temperature cycling reliability suffers as silver content decreases.In addition, mold compound material and thickness, die size, and solder volume have the opposite effect depending on the loading condition. The Green material for test board also showed lower performance than RoHS compliant board material. IntroductionThe reliability of an electronic package is ultimately determined by the environment and application in which it is used. Traditionally, only temperature and power cycling were of concern for board level reliability, and CTE mismatch between the package and the board was considered as the primary failure mechanism. However, due to the proliferation of electronic devices across market segments ranging from automotive to small, hand-held devices, electronic packages experience mechanical loading conditions other than just temperature cycling. Handheld products are prone to being dropped and their keys are pressed millions of times during the useful life to send text messages. Similarly electronic assemblies for telecom and automotive applications experience mechanical bending and shock conditions during installation and actual use conditions. This mechanical drop and cyclic bending due to key press have introduced failure modes where flexibility of the package is more important than the CTE mismatch. These additional failure mechanisms have their implications on package design and material selection. The one-size-fits-all model is no longer suitable for package design and material selection and customization is necessary