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90 SMT Magazine • August 2016 um" space systems. Although the mass reduc- tion was deemed a significant success, the lower than expected thermal performance (92C com- pared with a predicted 85C) during thermal balance testing was thought to be due to the difficulty in mixing the nano-particles into the components of the Huntsman resin. Materials and molding/manufacturing times were costed. It was calculated that if more than seven hous- ings were to be procured, CRFP housings would become cheaper than if manufactured from aluminum alloy. David Pinsky described the results of an in- dustry round-robin (including Raytheon-Boe- ing-Rockwell Collins and Raytheon Space) that investigated the risk of tin whisker growths on surface-mount components solder-assembled to PCBs. These components had been electro- plated (leads and terminations) with pure tin containing less than 3% lead. Various well-de- fined soldering processes were selected by the participating companies in order to assemble a large variety of component types onto PCBs. Some soldering processes could achieve full dis- solution of the pure tin into the resulting sol- der joints. These are termed "self-mitigation" processes as they prevent the risk of whisker growths and electrical shorting. The study in- cluded various PCB finishes and a very wide range of component package styles. The as- sembled sample boards were then inspected by XRF in several lead locations. It was found that the PCB finish and the PCB pad size had minor effects on whisker mitigation, but the actual soldering process applied was extremely signifi- cant. Pinsky's presentation highlights the com- ponent types nearly certain to self-mitigate un- der all process conditions (e.g., the smaller chip components). Usually it was the process which caused some components to self-mitigate, but one component (0612 chip) stood out as ex- hibiting a very low probability to self-mitigate. This round-robin study is continuing and will incorporate many new families of components/ packages. Tin whisker mitigation for lead-free surfaces was also described by Marko Pudas (Picosun Oy, Finland). Here, atomic layer deposition (ALD) conformal coatings were applied to finishes having a propensity to whisker. Scanning elec- tron microscopy revealed that ALD coatings markedly reduce the occurrence and length of tin whiskers on so-treated PCBs. Mark Ashworth (Loughborough University) also characterized whisker mitigation processes that utilized the electrochemical oxidation of electroplated tin and tin-copper samples. The oxidation of paral- lel sets of samples was achieved either naturally in air, or by using both borate buffer solutions, and potassium carbonate/bicarbonate solu- tions. After almost 4 years of ambient storage the tin whisker density on samples naturally oxidized in air remained high (6000 whiskers cm-2), whereas the artificially oxidized coat- ings demonstrated far lower whisker densities (about two orders of magnitude below the un- treated samples). Another coating was finally described; it was based on a molybdate conver- sion coating. Although this produced the thick- est of all measured oxides on tin, remarkably, it was less able to mitigate whisker growth. The session covering Space Design and Components commenced with Johan Leijtens (LENS R&D, Netherlands), and an overview of his designed and built BiSon series of sun sen- sors (Figure 6). These sun sensors have been used in commercial applications, in particular for the management of continually rotating/ moving of solar arrays in the Sahara Desert in order to achieve optimal orientation to the Sun's rays. His latest design of sun sensor in- corporates an integrated connector and PEEK inserts to a ceramic molded part. All build ma- terials are selected so have low-outgassing-un- der-vacuum and matched coefficients of expan- 7TH ELECTRONIC MATERIALS AND PROCESSES FOR SPACE WORKSHOP Figure 6: BiSon 64 type miniature sun sensor from LENS R&D.