V. Szekely

Measuring partial thermal resistances in a heat-flow path

The paper presents techniques of measuring partial steady state thermal resistance values in a heat flow path with the help of thermal transient measurements and the subsequent numerical evaluation. The method is based on the further evaluation of the structure functions of the heat flow path. After presenting the theoretical background of the evaluation two different practical examples are presented to demonstrate the use of the method. The first example presents a series of experiments on how to use the method to detect die attach and/or soldering failures in packaged devices. The second example demonstrates that the method can be applied to measure the very small R/sub th/ values of thin conducting layers. Various practical solutions are discussed and demonstrated by simulations. The chances and the limits of the methodology are discussed in detail in the conclusion section.

CMOS sensors for on-line thermal monitoring of VLSI circuits

The paper presents appropriate sensors for the realization of the design principle of design for thermal testability (DfTT). After a short overview of the available CMOS temperature sensors, a new family of temperature sensors will be presented, developed by the authors especially for the purpose of thermal monitoring of VLSI chips. These sensors are characterized by the very low silicon area of about 0.003-0.02 mm/sup 2/ and the low power consumption (200 /spl mu/W). The accuracy is in the order of 1/spl deg/C. Using the frequency-output versions an easy interfacing of digital test circuitry is assured. They can be very easily incorporated into the usual test circuitry, via the boundary-scan architecture. The paper presents measured results obtained by the experimental circuits. The facilities provided by the sensor connected to the boundary-scan test circuitry are also demonstrated experimentally.

Thermal dynamics and the time constant domain

The time-constant spectrum representation is a useful description of the dynamic thermal behavior of packages, assemblies and microsystems. After presenting the idea of the time constant spectrum representation of microelectronic structures, the paper provides an algorithm that can be used for time constant spectrum calculation in thermal simulator programs. The obtained time-constant spectrum can be the basis of calculating the transient behavior pulse thermal resistance diagrams, and structure reconstruction. All these applications are presented in the paper with examples.

Structure function evaluation of stacked dies

In this paper simulation experiments demonstrate, that the structure function evaluation of the thermal transient testing is capable to locate die attach failure(s) of stacked die packages. The strength and the location of the die attach failure may be determined with the methodology of a fast thermal transient measurement and the subsequent computer evaluation. The special advantage of the methodology is that normally it does not require any additional circuit elements on any of the dies of the stacked die structure. The paper demonstrates the feasibility of the method both for stacked die structures of the same die size, and for pyramidal stacked die packages.

Studies on the nonlinearity effects in dynamic compact model generation of packages

In this paper, we present a series of measurement and simulation experiments that were accomplished to check the order of magnitude of the error caused by neglecting the temperature dependence of the dynamic compact models of packages. We present a methodology to create nonlinear, temperature dependent compact models. With this methodology we created temperature dependent compact models of packages based both on measured and simulated results and compared the behavior of the temperature dependent model to the temperature independent (linear) model. We have found that neglecting the nonlinearity is acceptable in a moderate temperature range. If the temperature excursion remains below 60-80/spl deg/C the error is expected to be less than 2-3%. For higher temperature rise the use of nonlinear compact models is recommended.

Determining partial thermal resistances with transient measurements, and using the method to detect die attach discontinuities

The evaluation of the thermal transient measurements may result in the time constant density function and the structure function of the measured structure. In this paper we show how these results can be used to detect die attach or soldering problems of packages. Another application of the method in detecting partial thermal resistances in the heat flow path is also presented and evaluated.

Thermal Measurement and Modeling of Multi-Die Packages

Thermal measurement and modeling of multi-die packages with vertical (stacked) and lateral arrangement became a hot topic recently in different fields like RAM chip packaging or LEDs and LED assemblies. In our present study, we present results for a more complex structure: an opto-coupler device with four chips in a combined lateral and vertical arrangement. The paper gives an overview of measurement and modeling techniques and results for stacked and multichip module (MCM) structures. It describes actual measurement results along with our structure function-based methodology which helps validating the detailed model of the package being studied. For stack-die packages, we suggest an extension of the DELPHI model topology. Also, we show how one can derive junction-to-pin thermal resistances with a technique using structure functions.

Dynamic thermal multiport modeling of IC packages

The dynamic thermal behavior of electronic subsystems is characterized by their dynamic compact models. These models have to be similar to the steady state models in describing the fact that the heat is usually leaving at different locations (ports), necessitating multiport description of the thermal behavior. In our paper we present a method suitable for direct generation of multiport dynamic compact thermal models from a series of thermal transient simulations or measurements. The generated RC electrical equivalent circuit model, exercised with a network simulator program provided the same transient functions as the measured ones for various boundary conditions, proving the accuracy of the method.

Enhancing reliability with thermal transient testing

Abstract Thermal transient measurement, the method for the characterisation of IC packages is gaining increasing importance. The measurement of these transients requires dedicated equipment. The paper discusses the methodology of thermal transient measurements in details, including the compensation of second order effects as non-linearity, non-constant powering etc. In the following part the evaluation methods and algorithmic solutions are discussed. A typical example is presented. Reliability issues are discussed in the last section of the paper, including the problem of die attach testing. The contribution of the thermal transient measurements to the analysis of thermo-mechanical strain is demonstrated.

Thermal monitoring of microelectronic structures

Abstract This paper presents possible solutions for the lifetime thermal monitoring of microelectronic structures. To capture the detailed thermal state of an encapsulated device, insertion of a number of temperature sensors is proposed. A new temperature sensor element is introduced: the thermal-feedback oscillator (TFO). This temperature sensor has a digital output signal, and is therefore suitable for integration with other built-in test circuits such as the boundary scan. The paper investigates the feasibility of the TFO temperature sensor.