Solder joint reliability Materials properties

Solder Joint Technology Materials, Properties, and Reliability By K.-N. Tu... 

We have developed new high TCE ceramic material of 13ppm/°C. This material and 11.5 ppm/° C material have almost same properties with the exception of TCE. By using the 13 ppm/°C material, the TCE mismatch between the substrate and the potting compound decreases, and the improvement of solder joint reliability is obtained as shown in Figure 1.1.11. 

Numerical computation inevitably requires that trade-offs be made between the level and degree of detail modeled and the cost, time, or computational resources required to perform the solution. Despite the rigorous formalism associated with the development of finite element tools, the analyst must judiciously make selections regarding the element type and number, the material properties, boundary conditions, and solution parameters. A skillfully executed analysis will have compromises and approximations that are obvious to those versed in mechanics, yet produce accurate results for the quantities of interest. The ability to make these trade-offs requires an understanding of the approximations and inaccuracies in the numerical tools (Ref 41, 42) and an anticipation of the expected results based on either experimental evidence or first principles. A number of issues pertaining to the absolute accuracy of any solder joint reliability... 

In this section, the structural response of a 256 PBGA package subject to part-on-board temperature cycling will be examined. A recent experimental program (Ref 49-52) studied the solder joint reliability of this package with both Sn-Pb and Sn-Ag-Cu solder balls. The elastic and creep properties of both solders will be incorporated in the analysis in order to demonstrate the influence of the new Sn-Ag-Cu material in the context of the structural responses of the familiar Sn-Pb solder. 

It is well known that the microstructure of a solder alloy, like any material, has a very significant effect on its mechanical properties. The higher the application temperature in proportion to a material s melting point, the more rapid is the microstructural change, and hence the impact on solder joint reliability. Successfully migrating onto and implementing lead-free solders requires better understanding of how these solder alloys interact with the termination and lead materials... 

The accepted method of nondestructive testing used to control the underfill process is SAM. The thin layer allows this technique to detect voids in the underfill material, which when located near the solder interconnections can be responsible for a significant loss of thermal mechanical fatigue reliability. X-ray techniques can be used to monitor the density of the underfill material, specifically, the distribution of filler material within the layer under the die. Density variations can indicate a larger distribution of underfill mechanical and physical properties, which may affect long-term reliability performance of the solder joints. Quantitative image analysis can be coupled into SAM and x-ray analysis data to provide valuable process control tools for the factory floor. 

Soldering is a technology that has been used extensively for utilitarian and decorative purposes for thousands of years. In the last 100 years, soldering has been raised from art to science for joining electrical assemblies. By the late twentieth century, the tin-lead solder joint and properties of its constituent materials had been studied well enough that it could be modeled for purposes of predicting reliability. 

This chapter has focused on the numerical tools used in the design for reliability of lead-free solder joints. These tools include the finite element method, in general, and, in particular, the use of 3D strip models, specific material properties, and the use of a creep strain energy... 

THE ROLE OF A SOLDER JOINT IN THE QUALITY AND RELIABILITY OF ELECTRONICS CIRCUITS HAS EVOLVED. HOWEVER, LITTLE ATTENTION IS GIVEN TO SPECIFIC MATERIAL PROPERTIES REQUIRED TO CREATE A VIABLE SOLDER JOINT. WHEN CONSIDERING MATERIALS IN LEAD-FREE TECHNOLOGY, COMPONENT COMPATIBILITY IS KEY. 

The doctrine of the solder joint as key to quality and reliability of electronics circuits has evolved over the last four decades. Still, little attention is given to specific properties of materials that are necessary to form a good lead-free solder joint. 

There are two main drivers motivating the migration to lead-free solders legislative-based issues and health concerns related to lead (Pb)-containing materials including solder. Also, there is pressure to support the growing worldwide movement to remove lead from processes and products to demonstrate environmental consciousness and maintain a competitive posture in the market place. However, assuring the reliability of solder joints made with lead-free materials is difficult due to the lack of field experience and lack of fundamental property data upon which to construct reliable service life models [2]. 

Choi, S.L. Gibson, A.W. McDougall, J.L. Bieler, T.R. Subramanian, K.N. Mechanical properties of Sn-Ag composite solder joints containing copper-based intermetallics. Design Reliability of Solders and Solder Interconnections—Proceedings of Minerals, Metals Materials Society (TMS) Symposium Orlando, FL, 1997 241-245. 

The effects of small Ge additions on physical and mechanical properties were also studied. It was concluded that small additions of Ge contribute to enhance both surface and interface characteristics to improve bonding and bulk materials properties. It was reported that Ge-containing solders have similar or better performance and higher reliability than eutectic Sn-Pb solders. Although these results are very promising, this solder family must be appropriately tested and exercised under actual assembly conditions in manufacturing. The interfacial microstructures and joint rehability require further investigation. 

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