Mats Lindgren

CFD Aided Reflow Oven Profiling for PCB Preheating in a Soldering Process

A CFD-aided reflow oven profile prediction algorithm has been developed and applied to modelling of preheating of a PCB with non-uniform distribution of component thermal mass in a forced air convection solder reflow oven. The iterative algorithm combines an analytic approach with CFD modelling. It requires an experimentally validated CFD model of the solder reflow oven and a CFD model of the PCB as main inputs. Results of computational experiments have been presented to reveal good agreement between predicted PCB profiles and corresponding CFD calculations. Application guidelines contained in the description of the algorithm will assist potential users both during the virtual prototyping phase of a PCB including designing for assembly and in the phase of reflow oven profiling.

Multi-disciplinary approach to design of a power electronics module for harsh environments

A set of experimental and computer simulation methods has been applied to reliability analysis of a newly designed resin transfer molded power electronics module for automotive applications, comprising the glass-fiber epoxy multi-layer PCB, populated with various electronic packages. Evaluation of thermo-mechanical stability, determination of moisture ingress, and testing the adhesion quality between the molding compound and the module PCB have been performed along with investigation of heat transfer paths in the module. The experiments in harsh environments have revealed thermo-mechanical stability and acceptable moisture ingress for the module test samples with relatively large BGA components on the glass-fiber epoxy PCBs of different thickness and different solder mask types. Thermal images of the module have been obtained and the CFD model was created and validated with temperature measurements in power-on tests. Extreme heat dissipation modes have been studied by modeling.

Application of simulation-based decision making in product development of an RF module

This paper presents results of simulation-based design evaluation for thermal and thermo-mechanical performance and cost of packaging technology of an RF module for automotive applications. A combination of thermal, thermo-mechanical and cost analysis within the multi-attribute decision making framework enabled design ranking and revealed two MCM-L/D (multi-chip module-laminate/deposition) and MCM-D (deposition) designs with the wire bonding assembly preferred for use in automotive applications for different temperature environments. Simulation-based design guidelines were developed for designing electronic modules exhibiting good thermal and thermo-mechanical performance. By application-based partitioning of the importance weights assigned to the reliability and cost criteria, the guidelines were extended to cover other application areas.

Experimental Evaluation of Glob-top Materials for use in Harsh Environments

This article presents results of experimental evaluation of glob-top materials for multi-chip-modules (MCM) in harsh environments. Material and process tests have been performed with the purpose to find a material which would fulfill the reliability requirements for use e.g. in military or automotive applications. Seven polymer materials, i.e. four epoxies, two silicones and one polyurethane material have been selected and evaluated in the experiments. The most critical material and process parameters for glob-top have been identified and measured. Based on the experimental results, application-based scoring of studied epoxy materials has been performed. Material evaluation results have been summarized in conclusions about the most suitable glob-top material for use in harsh environments.

Methods for predicting corrosion on electronic products

Abstract Surface insulation resistance (SIR) measurements have become necessary to perform, especially due to the introduction of lead free solders. It has been reported that SIR and other test methods have to be used for evaluating the reliability of printed wiring boards. This paper presents an investigation on how the SIR test environment influences the test results. The factors varied were temperature and humidity. The temperature was varied between 40 and 85°C, and the relative humidity was varied between 60 and 85%. Furthermore, the influence of different types of process chemicals on SIR was evaluated. Seven lead free solder pastes, of which five were no-clean and two were water soluble, were compared. The influence of using conformal coating was also studied. These solder pastes were used to verify the developed method. A proper test method for SIR measurements is suggested in the paper, as well as a recommendation for use of conformal coating.

CFD assisted design evaluation and experimental verification of a logic controlled local PCB heater for humidity management in electronics enclosure

Humidity management of commercial-of-the-shelf electronic components in non-controlled climatic environments can be realized e.g. by introducing a local printed circuit board heater. By choosing appropriate size and location of the heater plate in the vicinity of the critical electronic packages, and utilizing logic control function, it is possible to improve the quality of local humidity management and reduce power consumption of the heater, which is important especially in case of battery driven portable or vehicle mounted devices. A computational fluid dynamics assisted methodology has been developed to determine the best feasible design of the heater, followed by experimental verification of the constructed logic controlled heater. The experiment has been performed in a harsh climatic environment including temperature variation from +33°C to +40°C, and relative humidity variation from 54% to 80%. Analysis of the experimental %RH and temperature curves as well as power profile of the heater has confirmed the feasibility of the chosen approach to maintain greater than 9°C difference between the electronics package surface temperature and the local dew point temperature, by applying discrete power pulses with the amplitude less than 6 W.

Simulation assisted investigation and improvement of the performance of an electronics assembly subjected to temperature cycling

Numerical simulation techniques are used increasingly in the (re-)design of micro-electronics because of their time and cost saving potentials. The current paper describes the application of such techniques for analysing and improving the thermo-mechanical performance of an electronics assembly. An initial finite element model is implemented and its predictions are compared to measurements. Based on this comparison, the model is further refined by an improved assessment of the input to the model in the form of materials properties: the properties of the moulding compound, failure behaviour of the lead-compound interface and failure behaviour of the lead material itself. Finally an updated model is used to determine directions for improvement of the behaviour of the assembly design.

Application of simulation-based decision making in product development of an RF module [automotive MCM]

This paper presents results of simulation-based design evaluation for thermal and thermo-mechanical performance and cost of packaging technology of an RF module for automotive applications. A combination of thermal, thermo-mechanical and cost analysis within the multi-attribute decision making framework enabled design ranking and revealed two MCM-L/D (multi-chip module-laminate/deposition) and MCM-D (deposition) designs with the wire bonding assembly preferred for use in automotive applications for different temperature environments. Simulation-based design guidelines were developed for designing electronic modules exhibiting good thermal and thermo-mechanical performance. By application-based partitioning of the importance weights assigned to the reliability and cost criteria, the guidelines were extended to cover other application areas.