This presentation covers Stretchable hybrid electronics.  Stretchable electronics have the most industry uses in wearable technology and for mobile sensing and response devices.  Thermosetting resins are used in the layers of the flexible electronics.  A new thermosetting resin is tested for stretchability, temperature, and washability.  The slides also discuss flexible encapsulants added for extra support over components.  

This presentation covers additive manufacturing and the direct deposit of multiple metals.  This additive capability is best utilized for the production of complicated circuits such as Radar and antennas.  There are a lot of potential uses for additive manufacturing including prototyping and low volume high complexity PCBs.

The defense industry has realized the importance of Additive Manufacturing (AM) and how this technology can be utilized where parts can be fabricated inexpensively with reduction in lead times.

The company investigated how AM could further reduce the cost and lead time of critical components such as cold plates. Traditionally, these parts were fabricated using a subtractive machining and brazing process incurring a twenty-six-week lead time after receipt of order to an external supplier.

With newly developed in-house AM capability, the lead time was reduced to four weeks and concurrently provided an overall material/manufacturing cost savings.

Cold plate thermal and structural performance was not compromised.

Thermally conductive adhesives are widely implemented in a variety of electronic assemblies. These adhesives combine the function of mechanical fasteners and thermal interface materials into one product. This combination of roles allows for the preparation of assemblies that are smaller, lighter, and easier to manufacture than traditional combinations of pads and greases or gels with mechanical fasteners. The use of thermally conductive adhesives requires an increased understanding of their mechanical properties, especially their fracture behavior so that the reliability of an assembly can be accurately determined. Since most thermally conductive adhesives are composed of a filler in conjunction with a polymeric resin this study examined the effects of the filler particle size distribution and morphology on the fracture behavior and mechanical properties of a silicone adhesive. It was seen that a greater proportion of small filler and an increased filler surface area for spherical fillers improved the fracture toughness of the adhesive.

The trend of incorporating more and more electronic devices into our daily life is bringing challenges for the industry. The need for smaller and more powerful devices is also facing one problem: heat dissipation. Processor chips, large capacitors, inverters, transformers and some ICs are usually the components in an electronic assembly generatingheat. Heat can reduce performance and usable life of the electronics and thus require thermal management to improve reliability and prevent premature failure.  More than 50% of power module failures are temperature related due to inadequate or improper thermal management.

Thermal Interface Materials (TIMs) play a key role in the thermal management of electronic systems by providing a path of low thermal resistance between the heat generating devices and the heat spreader/sink. Typical TIM solutions include adhesives, greases, gels, phase change materials, pads, and solder alloys. Among these different solutions, greases typically offer better thermal performance, reduce manufacturing cycle times and frequently are considered the lowest cost solution. In the area of thermal management, silicone thermally conductive greases are extensively used due to their proven thermal and environmental stability coupled with excellent wet-out performance. This paper presents reliability data to explore the thermal performance of a silicone thermally conductive grease formulation when exposed to different conditions such as: high temperature ageing, thermal cycling, damp heat, and power cycling. 

There is an increase in the number of optical sensors and cameras being integrated into electronics devices. These go beyond cell phone cameras into automotive sensors, wearables, and other smart devices. The applications can be lens bonding, waveguide imprinting, or other applications where the adhesive is in the optical pathway. To support these various optical applications, new materials with tailorable optical properties are required. There is often a mismatched refractive index between plastic lenses such as PC (Poly Carbonate), COP (Cyclo Olefin Polymer), COC (Cyclo Olefin Copolymer), PMMA (Poly Methyl Methacrylate), and UV curable liquid adhesive. A UV curable liquid adhesive is needed where you can alter the refractive index from 1.470 to 1.730, and maintain high optical performance as yellowness index, haze, and transmittance. This wide range of refractive index possibilities provides optimized optical design. Using particular plastic lens must consider how chemical attack is occurring during the process. Another consideration is that before the UV curable liquid adhesive is cured, chemical raw component can attack the plastic lens which then cracks and delaminates. We will also show engineering and reliability data which defined root cause and provided how optical performance is maintained under different reliability conditions.

The need to minimise thermal damage to components and laminates, to reduce warpage-induced defects to BGA packages, and to save energy, is driving the electronics industry towards lower process temperatures. For soldering processes the only way that temperatures can be substantially reduced is by using solders with lower melting points. Because of constraints of toxicity, cost and performance, the number of alloys that can be used for electronics assembly is limited and the best prospects appear to be those based around the eutectic in the Bi-Sn system, which has a melting point of about 139°C.

Experience so far indicates that such Bi-Sn alloys do not have the mechanical properties and microstructural stability necessary to deliver the reliability required for the mounting of BGA packages. Options for improving mechanical properties with alloying additions that do not also push the process temperature back over 200°C are limited. An alternative approach that maintains a low process temperature is to form a hybrid joint with a conventional solder ball reflowed with a Bi-Sn alloy paste. During reflow there is mixing of the ball and paste alloys but it has been found that to achieve the best reliability a proportion of the ball alloy has to be retained in the joint, particular in the part of the joint that is subjected to maximum shear stress in service, which is usually the area near the component side.

The challenge is then to find a reproducible method for controlling the fraction of the joint thickness that remains as the original solder ball alloy. Empirical evidence indicates that for a particular combination of ball and paste alloys and reflow temperature the extent to which the ball alloy is consumed by mixing with the paste alloy is dependent on the volume of paste deposited on the pad. If this promising method of achieving lower process temperatures is to be implemented in mass production without compromising reliability it would be necessary to have a method of ensuring the optimum proportion of ball alloy left in the joint after reflow can be consistently maintained.

In this paper the author explains how the volume of low melting point alloy paste that delivers the optimum proportion of retained ball alloy for a particular reflow temperature can be determined by reference to the phase diagrams of the ball and paste alloys. The example presented is based on the equilibrium phase diagram of the binary Bi-Sn system but the method could be applied to any combination of ball and paste alloys for which at least a partial phase diagram is available or could be easily determined.