Analytical Thermal Stress Modeling in Physical Design for Reliability of Micro- and Opto-Electronic Systems: Role, Attributes, Challenges, Results

Abstract

"Mathematical formulas have their own life, they are smarter than we, even smarter than their authors, and provide more than what has been put into them"Heinrich Hertz, German Physicist "If my theory is in conflict with the experiment, I pity the experiment", Friedrich Hegel, German Philisopher"A formula longer than three inches is most likely wrong" Unknown Reliability Engineer ABSTRACTSome basic thermal stress and thermal stress related reliability problems in microelectronics (ME) and optoelectronics (OE) are addressed. The emphasis is on analytical ("mathematical") stress modeling and design for reliability. The review is based primarily on the author's research conducted during his eighteen-year tenure with Bell Laboratories, Basic Research, Physical Sciences and Engineering Research Division, as well as on his recent research, based on government contracts. THERMAL LOADING AND THERMAL STRESS FAILURESVarious areas of engineering differ, from the Structural Analysis and Structural Reliability point of view, by the employed materials, typical structures used, and the nature of the applied loads. The most typical ME and OE structures are bodies made of a large variety of dissimilar materials. The most typical loads are thermal loads. These are caused by CTE mismatch and/or by temperature gradients [1][2][3][4][5][6][7][8].Thermal loading takes place during the normal operation of the system, as well as during its fabrication, testing, or storage. Thermal stresses, strains and displacements are the major contributor to the finite service life and elevated failure rate of ME and OE equipment. Examples are ductile rupture, brittle fracture, thermal fatigue, creep, excessive deformation or displacement, stress relaxation (that might lead to excessive displacements), thermal shock, stress corrosion.Elevated thermal stresses and strains can lead not only to structural ("physical") failure, but also to functional (electrical or optical) failure. If the heat, produced by the chip, cannot readily escape, then the high thermal stress in the IC can result in failure of the p-n junction [9]. Low temperature microbending (buckling of the glass fiber within the low modulus primary coating) in dual-coated optical fibers, although might be too small to lead to appreciable bending stresses and delayed fracture ("static fatigue"), can result in appreciable added transmission losses. Loss in optical coupling efficiency can occur, when the displacement in the lateral (often less than 0.2 micrometers) or angular (often less than a split of one percent of a degree) misalignment in the gap between two light-guides or between a light source and a light-guide becomes too large, because of thermally induced deformations or because of thermal stress relaxation in a laser weld. Small lateral or angular displacements in MEMS-based photonic systems (such as, say, some types of tunable lasers) can lead to a complete optical failure of the device. Tiny temperature-change-induced changes in the distance between Bragg gratings "written" on an ...

On a paradoxical situation related to lap shear joints: could transverse grooves in the adherends reduce the interfacial stresses?

“…Analytical modelling has been applied by one of the authors of this paper (Suhir) to many practical problems in microand opto-electronic packaging and structural analysis (see, for instance, [1][2][3][4][5][6][7][8][9]). One important merit of such modelling is that it is often able to explain the physics of a particular paradoxical phenomenon (see, for instance, [10,11]), which might be difficult to obtain using finite element analysis (FEA) or even an experimental technique.…”

Thermal failure of carbon nanostructures

“…We note that such mechanisms can occur at every level of packaging, from transistors to solder joints [57]. Often, thermal stress-induced failure goes hand in hand with other failure mechanisms [58]. For example, delamination may prevent heat extraction resulting in significant temperature increases that can accelerate electro-migration or electro-burning (see section 1.3.2 and 1.3.3).…”

“…However, due to the recent trend in IC packaging density, this would generally result in lower performances. Second, the Young moduli of the components could also be lowered, this reduces the thermal stresses and increases the reliability [58]. For instance, this can be done by making stretchable integrated circuits with flexible polymer-based substrates [59].…”