A Multiphysics Based Finite Element Approach to Evaluate the Reliability of IC Packages

A Multiphysics Based Finite Element Approach to Evaluate the Reliability of IC Packages

Padmanabhan Krishnan (VIT University, India)
DOI: 10.4018/978-1-4666-9479-8.ch002
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Abstract

The aim of this book chapter is to generate 3D models of different Thin Dual or Quad Leadless Moulded IC packages and conduct multiphysics based finite element analyses to evaluate the static reliability of IC packages. The performance analyses using die shear, thermal experiments and finite element analysis were conceived and conducted to evaluate the reliability of these packages. Reliability plays a major role at every stage in the manufacturing, testing and use of integrated circuit packages. The coupled influence of operating voltages and joule heating on the mechanical reliability of ICs is discussed here. Die shear tests were conducted on the ICs and the shear strength compared with the values obtained from the finite element results. Thermal tests were carried out on the ICs that were later inspected under a Scanning Acoustic Microscope (SAM) for delaminations arising from hygrothermal stresses. Finally the results of the electro-hygrothermo-mechanical analyses were analyzed and presented at the maximum operating temperature (MOT) that highlight the overall static reliability of the ICs with acceptable factors of safety. The main objective of this investigation is the construction of the failure envelopes through determination of the maximum operating temperatures and test temperatures of the ICs that aid in the evaluation of the overall static reliability of the ICs.
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Introduction

Electronic packaging is relatively a new subject compared to superplasticity, composite materials or solid state devices. With the advent of miniaturization and the demonstration of Moore’s law (every 18 months the chipmakers double the number of transistors that can be packed on to a silicon wafer), there was a need to package the newer working principles and concepts efficiently and reduce size for a superior performance and manage thermal aspects of the ICs as well. Thus the concept of microsystems and nanosystems packaging came in to being (Rao Tummala, 2001). The role of a package is to shut out environmental influences, enable electrical connectivity, dissipate heat and improve handling and assembly. Some of the popular types of electronic packages are the dual packages, shrink small outline packages, pin grid arrays and plastic leaded chip carriers (Harper, 2004). The micro Dual Leadless Moulded Packages (μDLMP) and the Thin Quad Leadless Moulded Packages (TQLMP) come with superior function at a small size and are increasingly being used in mobile phones, digital cameras, PDAs and automobile control systems (www.spel.com) . There is enormous customer curiosity on the reliability of the miniaturized products manufactured with these ICs. Hence there is an imperative need to address the reliability issues, demonstrate the evaluation techniques and conformance of these packages to user requirements. Figure 1 shows the architecture of a simplified plastic IC package. Plastic packages are non-hermetic meaning permeable to heat and moisture, but flexible and cost effective at operating temperatures below 200 ° C.

Figure 1.

2D cross section model of an example IC package; dimensions in mm

(www.spel.com).

Plastic based non-hermetic packages are more popular with the manufacturers of electronic packaging. However, at their maximum operating temperature they may face a hoard of problems that may lead to premature failure. The causes of such failures are mostly by joule heating due to the resistance offered by the material to current flow (I2 R losses), Seebeck effect, Peltier effect, Thomson effect, Electro Static Discharge (ESD), hygrothermal fracture, electro-thermo-mechanical fatigue, manufacturing defects like delaminations, soldering defects and material defects (Rao Tummala, 2001).

Key Terms in this Chapter

Scanning Acoustic Microscopy: The principle involved in the function of the SAM (Scanning Acoustic Microscopy) lies in imaging the sound attenuation and the differing ultra sound velocities in various solids and their impedance mismatches. The impedance mismatch can be reduced through coupling fluids or media. IC delaminations can easily be detected.

Fatigue: The response of a material or a structure to repeated loading and the ensuing loss of integrity resulting in failure. Loading can be electrical, thermal or structural. Coupled physics problems can also lead to fatigue.

TQLMP: The abbreviation for a class of miniature IC chips called the thin quad leadless moulded packages. Their quad pins do not have leads.

Finite Element Analysis: The simulation of a physical problem or an event through mathematical approximation and numerical methods by discretizing the continuum in to finite elements that are interconnected.

Die Shear Test: The test conducted to demonstrate the shear strength of the silicon die attached to the copper lead frame in an Integrated Circuit. The interfacial bond must withstand continuous hygrothermo-mechanical stresses with a factor of safety.

Reliability: Reliability is a statistical term in production engineering. It is defined as 1- probability of failure. Alternatively, 1- probability of survival is the probability of failure.

µ DLMP: The micro dual leadless moulded package IC consists of pins in a dual in line manner. They are also leadless.

Multi-Physics Problems: Sequentially or directly coupled physical problems like the piezo electric, thermo-mechanical or solid-fluid interaction problems.

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