Additive manufacturing (AM), commonly known as 3D printing, is a recent development in manufacturing processes whereby parts are built incrementally, layer by layer adding material where needed based on slices extracted from a CAD model [1]. The new approach offers significant advantages over conventional manufacturing, including unlimited complexity, higher performance parts, improved sustainability, reduction of assembly and mass customization. Nevertheless, parts made by AM suffer from high anisotropy and inherent weakness in mechanical properties especially in the plane of the layers compared to parts manufactured by conventional methods [2,3,4].In this work, we study the effect of build orientation on the fracture behavior of polymers made by filament-based extrusion (better known as fused deposition modeling), which is the most versatile and wide spread AM process for polymers. Build orientation is one of the most important process parameters which affect the mechanical behavior of parts built by this process and has been studied under tensile, flexure, compression and impact loading, but not using notched tensile test [2,3,4]. Three different build orientations were studied: flat, upright and at 45 o -inclined, Figure 1. In all cases, ABS samples with rectangular cross section were built using Stratasys uPrint SE plus FDM printer. The samples had a length of 4", thickness of 0.16" and width of 0.5". After printing, the samples were notched as shown, and tested under uniaxial tension. The different orientations result is different relationships between the loading axis and the plane of the layers. The flat build orientation divides the crack, the 45 o inclined build orientation deflects the crack, while the upright build orientation allows easy interlayer crack propagation. The tensile loading was performed on MTS Sintech 5/D materials testing system equipped with a 5000 lb. load cell with cross head speed of 0.5mm/min. The fracture surface was also examined to correlate the mechanical testing results and the fractorgraphy results, which were performed using Hitachi S-3400 N Scanning Electron Microscope operated in variable pressure vacuum mode (40 Pa) with an accelerating voltage of 10kV at 500m level. Figure 1 compares the nominal stress-strain curves for the three build orientations, while Figure 2 shows the corresponding fracture morphology. The upright case has the least strength and toughness while the 45 o -inclined sample has the highest. The interlayer crack propagation in the upright case has only to cut through the interface between the fused beads which offers the least resistance to crack propagation compared to cutting through the beads (deposited filaments). In the case of the 45 o -inclined sample, the crack path is diverted to follow a longer path explaining the higher toughness and ductility as well as the higher strength, Figure 2.c3. The flat build orientation leads to strength and toughness in between the two previous cases. Instead of traveling interlayer or along the longer 45 o pat...

Tin whiskers are microscopic growths made of single crystals of pure tin that are formed on the surface of tin plated copper substrates or electronic circuit boards. Their growths are a current challenge in the aerospace, defense and high performance electronics industry as the reliability of electronics is in question due to the formation of bridging short circuits between two whiskers in high impedance electrical equipment.[1] They can grow spontaneously at room temperature with a diameter of a few microns and an elongation of up to few millimeters. The growth mechanisms have been discussed by many researchers resulting in a number of hypotheses. Tin (Sn) Whisker formation is promoted in regions where stress is applied which indicates their initiation is associated with dislocation behavior [2]. Stress accelerated growth of whiskers is caused by the diffusion of Cu into Sn to form grain boundary precipitates that cause compressive stresses [3]. Other growth mechanisms include residual stresses, externally applied stresses, stored energy, surface energy effects, thermal expansion mismatch, corrosion, electroplating, etc. [1-3].The current study identifies tin whisker growth on a lead frame exposed to different environmental conditions. The tracking of the growth of these whiskers over periods of time was examined using SEM. The tin plated copper leads were supplied by The Boeing Company and were subjected to a) hygrothermal environment with 90% relative humidity at 90˚C and b) 5 wt% salt bath solution (suspended above liquid).The identification and analysis of hillock formation and whisker growth was carried out using a Hitachi SN-3400 Scanning Electron Microscope (SEM). Figure 1a shows the early stage of whisker growth by hillocks formation, as well as isolated growth of whiskers. Figure 1b is a high magnification of one of the hillocks showing an early formation (indicated by an arrow). Figure 1c shows a hillock, with salt scale deposits, that was captured on a lead frame in the salt environment. Figure 2a shows a whisker in the corner of the lead that was captured July 20, 2016. After 4 months the same whisker was observed at the same magnification. The effect of time on the growth of Sn whiskers can be examined from Figures 2a &2b. The whiskers have grown in length and reduced in diameter by 42µm and 8 µm, respectively. This gives an elongation rate of 10.5 µm/month in length and reduction rate of 2 µm/month in diameter. Figure 3 shows a fully developed whisker from the surface of the lead frame. The facets can be vividly seen on the surface of the whisker and shows a change in direction of the growth. Energy Dispersive X-ray Spectroscopy (EDS) was conducted on the whisker in figure 3a to determine and confirm its composition. It was found that the composition was 98.39 % Sn.In summary, SEM analysis has provided practical means to study the initiation and growth of tin whiskers on the surface of a lead frame. The composition of the whisker was determined to be almost pure tin. Based on this limited experim...