Chip-on-Board (CoB) technology for low temperature environments. Part I: Wire profile modeling in unencapsulated chips

Chip-on board technology for low temperature environment. Part II: Thermomechanical stresses in encapsulated ball–wedge bond wires

“…The initial wire profile is obtained by minimizing the strain energy of the wire [4]. Plastic deformations are ignored in this study.…”

“…A ball-wedge wire profile is modeled using a piece-wise continuous polynomial function (cubic spline) with appropriate boundary conditions at the two bond sites. The development of the cubic spline model follows similar earlier work for wedge-wedge bonds in the literature [3] and was also discussed in Part I of this series [4]. Subsequently, in this paper, a simple variational Raleigh-Ritz (RR) model is developed to estimate the thermomechanical stresses in the encapsulated bond wire due to temperature cycling.…”

“…The initial geometry of the bond wire before encapsulation was determined by simple RR analysis in an earlier paper by the authors [4]. This geometry was expressed in parametric notation as: yðuÞ ¼ uh À uhð1 À uÞ 2 À ðd  H c À hÞu 2 ð1 À uÞ; xðuÞ ¼ ud In order to guide the model development, an FEA model is first developed for a single wire-bond interconnection embedded in the encapsulated CoB package and subjected to unit temperature change.…”

A motor drive electronics assembly for Mars Curiosity Rover: An example of assembly qualification for extreme environments

“…The monitoring and data recording for electrical continuity was a continuous scan during the temperature cycling. Details of the selection process and assembly testing and analysis, including the design of the test vehicles, test set-up and continuous monitoring, detailed test results, wire bond modeling, failure analysis with SEM cross-section images, and some materials combination suggestions can be found in the references [3][4][12][13][14][15]. This paper is focused on the qualification process for the technology development with the summary of the results.…”

“…Aluminum bond wire with 217 µm in diameter survived with 6000.2 die attach and either Q1-4939 or Paralene C on both substrates. The failures of the heavy Al wire with 508 µm in diameter were due to thermal stress induced by the difference in coefficient of thermal expansion and change of temperature and manufacturing conditions [13][14]. For comparison of the two wires, the bonded region was small compared to the footprint of the wire bond foot on the pad, which yielded a lower strength bond under the wide temperature range.…”