Aerospace and defense applications present unique challenges for material suppliers. As increasingly adoption of wide bandgap semiconductor materials and advanced diverse accessible heterogeneous integration technologies, power density of defense and aerospace devices increases rapidly. Traditional die attaching materials is becoming an increasingly limiting factor in microelectronics packaging for the next generation aerospace and defense systems.

This paper introduces an advanced die attaching material based on pressure-less silver sintering technology and epoxy-based adhesive technology. This die attach paste can be sintered at temperatures that are normal in typical die attach processes while delivering outstanding mechanical, electrical, and thermal performances. This paper presents the results of an application study aimed at developing this unique technology in the field of high-power density devices for aerospace and defense applications.

The rapid change to and steep rise of electric vehicles (EV) results in many challenges for the design, manufacturing, testing, and the understanding of reliability and robustness for printed circuit board (PCB) in automotive powertrain applications. The greatest change is that high voltage—up to 1000 Volt operating voltage—and several hundred Amps operating current is required. The high voltage is creating a very high electrical field in the PCB. In combination with the tight designs and the environmental conditions, there is a possibility of effects which can cause ionic migration and/or partial discharges, which lead to failures over time. CAF (Conductive Anodic Filament) failures can be observed already at low voltage where ionic migration appears along glass fibers or laminate borderlines. At high-voltage conditions with a respectively high electrical field, vertical failure can grow through the bulk resin material of a PCB, creating over time a short from layer to layer. This article shows the failure characteristic of such vertical high-voltage failures in PCB. Which conditions can lead to such failures in a PCB— considering design, stackup, manufacturing, and testing aspects—will be discussed. Solutions to reduce the risk in generating such failures are shown and discussed. For solutions to allow higher currents, it is essential to have good thermal pathways in order to get the heat out of the system. Combinations of such thermal solutions with the high-voltage robust PCBs are shown as system solutions.

“Light weighting” has become an important trend in numerous manufacturing divisions. Lightweight materials are particularly valuable in any portable device including mass transit systems, automotive systems, and portable tools. They provide a wide range of benefits including reduced fuel consumption required for transport, lighter materials minimize waste through material saving, reduce consumption of finite resources, reduce environmental footprint, and achieve cost saving. The ability to do more with less could be game-changing to electronics ruggedization. More and more organizations are committing to working towards a more sustainable future. Traditionally, conformal coatings and encapsulation resins are used as part of circuit board assembly to meet the performance challenges in a variety of electronic applications, such protective polymer materials are often essential to ruggedize a system and give much needed protection from harsh external environments and reduce negative impacts from long term wear-and-tear such as shock and vibration. Encapsulation resins are typically derived from crude oil and are heavily filled with mineral rock powders, and thus have a high density and contribute significantly to the weight of the overall encapsulated device. This paper presents a novel, bio-based, expandable, thermoset solution, a low density, light weight method to effectively encapsulate and protect electronic components.

The performance of low density, bio-based polymers, synthetic conformal coatings, and encapsulation resins is assessed using numerous accelerated life tests. Bare and reflowed TB33A test coupons were coated, and the Surface Insulation Resistance recorded at 85°C (+185°F), 85% Relative Humidity, to understand the impact high temperature high humidity has on electrical resistivity. Test assemblies with a variety of surface mount components were subject to short term Condensation Testing, the Insulation Resistance was recorded. The electrical performance of a novel Foam Topcoat ruggedization solution was evaluated by monitoring the Insulation Resistance of B-24 test coupons when completely immersed in water. This comparative study concludes that the proposed bio-based, expandable polymer acts as a lightweight solution to effectively protect an electronic device subject to harsh operating conditions, including high temperature high humidity and condensing environments. For underwater applications a novel Foam Topcoat ruggedization solution can be used to achieve a perfect scoring solution and achieve a significant weight reduction, greater than 80% weight saving is obtained when compared to traditional encapsulation resins.

Selective soldering utilizes wettable metal nozzles for controlled application of solder to components. The wetting of solder to the nozzles is part of a complex mechanism that causes wear of the nozzle due to chemical interaction between the solder and the nozzle. This study explores the fundamental interactions between flowing solder and the nozzle.

Nozzles can last for hundreds of hours with the correct maintenance, however dewetting and eventual wear results in a loss of productivity and therefore revenue. Performance improvements to selective soldering nozzles allows for operation in more demanding process environments, producing higher quality and more reliable products, whilst also reducing process downtime and producing fewer defects. Thus far, limited work has been produced analyzing the efficacy of alternative alloys to improve the lifespan and wettability of selective solder nozzles.

A joint research project between industry and academia1 has been established to investigate the fundamental wear mechanisms of selective soldering nozzles and develop improved nozzles with increased wettability and lifetime. Alternative alloys are investigated for their operational viability.

Details of the methodologies employed will be given. Wear was quantified by proportional mass loss measured at regular time intervals measured throughout the nozzle's operational life. Wettability was quantified by measurement of the contact angle with solder in an inert atmosphere to mimic in-situ conditions.

Insights into field performance of these new nozzles will be presented with reports from key testing partners.

Surface mount technology was developed in the 1960s and implemented on printed circuit boards in the 1980s. High-density electronic assemblies are dominated nowadays by surface mount devices. The number of through-hole components left on the assembly continuously declines. Although many through-hole devices are soldered with pin-in-paste solder technology in a reflow oven, for some, this is no option. The reason for this can be the higher process temperatures of a reflow process or the lack of space for more solder-paste deposits on the board. Liquid soldering of through-hole leads remains a robust method of making reliable component-to-board solder joints. A point-to-point soldering process takes too much time for a high-volume product and dip soldering comes with additional tooling that makes the production line less flexible. To meet short cycle times and still be flexible, a dip technology was introduced on an inline machine. This method of soldering is possible due to new advanced nozzle designs made possible with new 3D printing technology. Soldering methods are compared using Design of Experiments (DOE) to determine throughput, as well as energy and material consumption. Several experiments contain methods to eliminate bridges and optimize heat transfer by improving the design of nozzles and solder flow dynamics and reducing cycle times.

Advanced implementation of wearables and IOT applications require attachment of components on lightweight, mechanically flexible, and low-cost substrates. Candidate materials that meet these substrate requirements are typically made from temperature-sensitive polymers, such as polyethylene terephthalate (PET), and are thus challenging to use alongside standard high-temperature solder alloys. Reliable attachment of chip components to PET substrates with high-temperature solder has been demonstrated previously using a photonic soldering approach. This report expands the application of photonic soldering to components without line-of-sight, where direct exposure of solder junctions is not possible, using off-the-shelf lead-free solder alloys.

In this work, we show that wafer-level chip-scale packages (WLCSP) of various sizes can be photonically soldered to metallized PET substrates, using commercially available solder paste. The attached components feature ball grid array (BGA) footprints of three sizes to show the scaling of the process with I/O complexity. The quality of the solder junctions are characterized using continuity testing, optical, x-ray, and electron microscopy. The experimental results show that photonic soldering is an effective and capable processing technique for producing high quality and high reliability joints. Advances with this technique extend the range of design options, materials, and applications accessible for flexible electronic devices.