Thermal Fatigue Damage in the Solder Joints of Leadless Chip Resistors

Abstract

Leadless chip resistors (LCR) made by two different manufacturers and surface mounted on glass/epoxy printed circuit board (PCB) were subjected to thermal cycling between −55°C to 125°C in order to induce thermal fatigue failure/damage. The test units were subjected to a maximum of 250 thermal cycles. Solder joints in both types of LCRs were examined in scanning electron microscope and a relative comparison of the extent of fatigue damage is presented. The failure mechanism is associated with cracking in the eutectic compostion Sn/Pb solder initiated at the stress concentration sites. A nonlinear, time-dependent finite element modeling analysis has been performed to determine critical stress concentration sites in the solder joint. Key parameters leading to the initiation of solder damage are identified, and recommendations are made to improve the design in terms of solder configuration such as the radius of corner of the alumina substrate and the standoff height.

Thermomechanical fatigue behavior of Sn-Ag solder joints

“…1. 4,23 These solder joints were also reexamined using ESEM without any further treatments after about 10 months. The cross section in A and B direction is used to examine as-soldered and thermally cycled joints, respectively.…”

“…3c. 4 Since the Ni protective layer was breached, a ternary intermetallic layer consisting of Sn, Ni, and Cu replaced Sn or Sn-Pb layer tinning adjacent to the Ni layer. 3a.…”

Creep deformation behavior in eutectic Sn-Ag solder joints using a novel mapping technique

“…Solder materials exposed to higher temperatures, mechanical loads, and creep conditions undergo extensive microstructural evolution involving grain growth, phase changes, composition redistribution, and precipitate coarsening. [5][6][7] Coarsening of interface intermetallic layers and microconstituent phases in solder joints promotes premature fracture 8 and excessive creep deformation. Efforts have been made to mitigate the detrimental effects of microstructural evolution and aging in solder joint materials.…”

Material issues in electronic interconnects and packaging

“…In addition, metallization of the electrical components and the electrically non-conducting substrates, based on the processing methods and parameters used can pose problems. [6][7][8] Although issues related to other properties like dielectric constants of the polymeric materials become important due to the ever increasing speed of the electronic devices such as Electronic packages consist of metallic, polymeric, and sometimes ceramic materials as integral entities. Individual physical and mechanical properties of these constituents, and their influence on each other's behavior, affect the overall reliability of the electronic packages.…”