IMAPS/SMTA hold spring technical symposium

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The IMAPS Chesapeake Chapter combined with the University of Maryland student chapter of IMAPS and SMTA, held its Spring Technical Symposium on March 6th, 2019, at the Applied Physics Laboratory (APL) of Johns Hopkins University.

The symposium focused on emerging trends in electronics packaging and their reliability concerns and was the first collaborative meeting between IMAPS and SMTA student chapters. Selected topics were presented as posters University of Maryland students Lingxi Kong, Lovlesh Kaushik, and Saurabh Saxena. Their abstracts are listed below.

The event included presentations from, Subramani Manoharan, CALCE, Maxim Serebreni, DfR Solutions, and Michael Fish, Army Research Laboratory.

Interfacial Degradation of Copper Wire Bond in Combined (Thermal Aging + Cycling) Loading Condition by Subramani Manoharan.

Abstract: Copper (Cu) wire bonds have become the dominant wire material used in microelectronic packages, which has replaced gold (Au) in majority of applications. Cost savings has been the key factor to drive this transition in wire bond material, although there are other advantages to Cu such as better electrical and thermal conductivity, slower intermetallic compound (IMC) formation and reduced wire sweep during transfer molding. However, two critical reliability concerns exist with Cu wire bonds, namely, growth of electrically resistive and brittle IMCs and fatigue of bond wire, which makes them not suitable for harsh environments such as in industrial, military and automotive electronics.

A review of literature shows fracture at wire neck as the most commonly reported failure mode. However, with the growth of IMC at interface, the location of failure shifts to interfacial separation. This is studied in detail through performing thermal cycling experiments with long dwell times at high temperature that promotes interfacial IMC growth, to replicate actual use condition. Additionally, most of the work presented in literature use lab made wire-bonded specimen in their study on test packages, which may not replicate actual commercial off-the-shelf (COTS) parts which have several different geometrical and material parameters. A unique test approach is adopted to study this two-part failure and model its failure time by including the myriad of factors that exists in COTS packages. Additionally, critical factors contributing to failure are identified and studied in detail to establish a physics-based model to predict failure.

The Impact of Glass Style and Orientation on Reliability of SMT Components by Maxim Serebreni.

Abstract: Printed circuit board (PCB) glass style and orientation can have a significant influence on thermal cycling reliability of surface mounted components.  DfR has conducted thermal cycling (-40°C to 125°C) tests on two PCB glass styles (1080 and 7628). The in-plane and out of plane Coefficients of Thermal Expansion (CTE) were measured and found to be about 3-4ppm/°C different in the X-Y directions of the boards.  To facilitate the reliability assessment of SMT component reliability four 0-ohm resistor sizes (2512, 1206, 0602 and 0402) were mounted on each board. Each board had 20 resistors with multiple orientations. The overall sample size consisted of 32 resistors of each size per glass style.  In addition, the PCBs have two pad sizes. The purpose of these experiments is to develop a model for validating fatigue life predictions for different laminate materials. This paper will present the experimental structure, results of the stress tests and variables on the reliability of the chip components and insight into the development of appropriate models.

Design Challenges and Opportunities in Package-Integrated Transient Thermal Mitigation by Michael Fish.

Abstract: Phase change materials (PCMs) have attracted the attention of researchers for their promise to buffer or mitigate the effects of transient thermal pulses within electronic systems. While widespread adoption has historically been held back by the by the low thermal conductivity of otherwise attractive materials with relevant transition temperatures, advancements in PCM enhanced composite materials, additive manufacturing, and more recent interest in low melting point metals has tipped the balance towards feasibility in highly transient systems. One impediment to deploying PCM enhanced packaging is a lack of package-level design tools that can illustrate the tradeoffs between performance, size/weight, and cost that results from integrating phase-change materials and/or their composites. This work exhibits the extensions made to the Army Research Laboratory’s thermal-mechanical co-design tool, ARL ParaPower, to enable both phase change transient modeling and integration into system-level design tools. By providing rapid surveying capability within any particular design space, detailed simulation burden is reduced and the most promising demonstrators are prioritized.

The University of Maryland IMAPS student chapter is currently planning a fall semester technical symposium. More information to follow.

For information regarding membership, contact Subramani Manoharan, University of Maryland IMAPS Student Chapter President.

Published March 7, 2019