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Updates in silicon and electronics technology.

Ed.: This is a special feature courtesy of Binghamton University.

Breakthrough quantum-dot transistors create a flexible alternative to conventional electronics. Researchers at Los Alamos National Laboratory have created fundamental electronic building blocks out of tiny structures known as quantum dots and used them to assemble functional logic circuits. This development provides a low-cost and manufacturing-friendly approach to complex electronic devices. The building blocks can be fabricated in a laboratory with simple, solution-based techniques, and provide these components for a host of innovative devices. Potential applications of the new approach to electronic devices based on non-toxic quantum dots include printable circuits, flexible displays, lab-on-a-chip, wearable devices, medical testing, smart implants, and biometrics. (IEEC file #11971, Science Daily, 10/29/20)

This flexible and rechargeable battery is 10 times more powerful than state-of-the-art. University of California researchers working with ZPower have developed a flexible, rechargeable silver oxide-zinc battery that provides five to 10 times greater energy density than current state-of-the-art. The battery also is easier to manufacture, as it can be screen-printed in normal lab conditions. The areal capacity for this innovative battery is 50ma/cm2 at room temperature, which is 10 to 20 times greater than the areal capacity of a typical lithium-ion battery. The device can be used in flexible, stretchable electronics for wearables as well as soft robotics. (IEEC file #12027, Science Daily, 12/7/20)

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One year in, Covid-19 has shifted priorities in the industry – or has it?

One year in, has Covid-19 shifted priorities in the industry? To find out, CIRCUITS ASSEMBLY reached out in January to experts for insights on how the pandemic has impacted everything from inside the factory to the business decisions we make. Then, for good measure, we asked how the semiconductor industry might change in the wake of Intel’s proposed sale of some manufacturing assets, a move that could have lasting impacts on the IC. We spoke with a range of leaders covering various segments of the electronics manufacturing supply chain. Their responses, lightly edited for clarity and length, follow. After reading their thoughts, share your own on our LinkedIn page (https://www.linkedin.com/groups/2847418).

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How a new trade group is aiding the DoD’s desire for a trusted supply chain.

For decades the printed circuit industry has asserted the lack of government support has a deleterious effect on the supply chain’s ability to properly supply the US military. Attempts to correct this over the years have been numerous but largely unsuccessful.

Led by IPC, industry has lobbied the US Congress since the early 1990s to reduce barriers to winning military contracts, and, as margins were slashed beginning in the early 2000s, to fund research and development that could be shared among Defense Department suppliers to help their competitiveness.

IPC, for its part, has threaded the needle in terms of trying to support its domestic constituents and meet the needs of the DoD while not alienating other members that are foreign-based. It has provided support and advocacy to the Executive Agent for Printed Circuit Boards and Interconnect Technology, a position funded by Congress in the annual National Defense Authorization Act and assigned to the Navy. The EA’s role is to help the DoD access reliable, trusted and affordable PCB fabrication and assembly products, and facilitate R&D collaboration. In practice, it’s a politically intense position that comes with unwritten but very real limits on how hard the EA can push for funding and priorities. The results are clear: The US industry remains behind several geographical competitors in terms of capabilities and capacity. Moreover, as new edicts were handed down to promote greater security of IP, smaller companies, especially fabricators, have found it financially treacherous to remain on the DoD’s acquisition list.

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A case study characterizes solder joint integrity of different BTC constructions in an accelerated lifetime test.

The electronics industry has extensively documented the influence of component construction on solder joint integrity. Materials used in the construction of a component package body result in a composite coefficient of thermal expansion (CTE) for the package that may result in the degradation of the package solder joint integrity. The industry discovered in the 2000s the construction design of ball grid array (BGA) packages had a significant influence on solder joint integrity. BGA solder balls located directly beneath and sometimes adjacent to the package internal die-to-package transition region (i.e., the die shadow region) failed first due to the CTE mismatch forces.1-3 Extensive finite element modeling, combined with use environment experiences and test data4-5 resulted in package redesign protocols that for the most part eliminated die shadow solder ball failure in BGA packages.

This paper documents an investigation of the impact of bottom-terminated component (BTC) package construction on solder joint integrity using thermal cycle testing (-55° to +125°C) in accordance with IPC-9701.

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Can a change of solvent in the printer improve SMT printing?

Any engineer will testify lab testing may not correlate with field results. Laboratory data are developed under ideal conditions to generate accurate and repeatable data, whereas a production setting introduces variables not reproducible in the lab environment.

In this report, AIM’s application lab approximated a production environment in a multi-hour printing test to quantify the effect of under-stencil wipe solvent on solder paste performance. This experiment compared isopropyl alcohol (IPA) and a novel stencil cleaner. IPA is not recommended as an in-process stencil cleaner, but is often used because it is inexpensive, effective and readily available. However, IPA is not a constituent of solder pastes and can therefore cause changes to paste that will negatively impact performance.

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Because electrochemical failure risk is site-specific, different components need different plans.

Highly dense electronic assemblies incorporate bottom-terminated components. Miniaturized components create numerous challenges, resulting in a shorter distance between conductors of opposite polarity, solder sphere size reduction, low-standoff gaps, flux entrapment under the bottom termination, blocked outgassing channels, and more significant potential for leakage currents.1

In the presence of humidity, moisture (mono-layers of water) hydrogen bonds with ionic contaminants to create an electrolytic solution. Ions such as flux activators can dissolve metal oxides present in the flux residue at the soldered connection.2 When the system is in operation, the electrical field attraction of the positively charged metal ions migrate to the negative conductor. These metal ions can plate small dendrites, resulting in leakage currents and/or parasitic leakage. As such, ionic residue testing is used to test for problematic residues that could hinder reliable circuit function.3

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