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ASSESSMENT OF WHISKER GROWTH FROM TIN COATED WIRE AND CABLE. Tom Lesniewski Northrop Grumman Corporation San Diego, CA. Objective. “What is the risk for whisker growth on tin-coated wire?”. Topics. Standards Historical data Analysis--variables Wire gauge Age
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Evaluation OF WHISKER GROWTH FROM TIN COATED WIRE AND CABLE Tom Lesniewski Northrop Grumman Corporation San Diego, CA

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Objective "What is the hazard for bristle development on tin-covered wire?"

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Topics Standards Historical information Analysis- - factors Wire gage Age Type of unadulterated tin covering/grain measure Results SEM review Cross area

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Wire & Cable Standards Pure tin is a typical complete for copper wire and link MIL-DTL-17 coaxial link AA-59551 (ss QQ-W-343) uninsulated "transport" wire NEMA-WC27500 (ss MIL-DTL-27500) link SAE-AS22759 (ss MIL-W-22759) and MIL-DTL-16878 protected Wire get back to outs follow to ASTM B33 No confinements or direction on immaculate tin

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Wire & Cable Standards ASTM B33 does not indicate a tin covering thickness "It is fundamental that the covering of tin on the wire be constant." Tin covering comprises of 2 sections Pure tin covering at surface Intermetallic mixes between tin & copper

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Wire & Cable Standards Most regular sort of uninsulated wire: QQ-W-343 (superseded by AA-59551) Two sorts: Type S wire –single stranded, uninsulated Tin covering is 40 uin (1 um) thick least. Sufficiently thick to ensure copper & forestall consumption yet restricted timeframe of realistic usability 1 um covering won\'t finish solderability test after steam maturing because of oxidation of IMCs Type H wire - "hookup wire" Additional solderability necessity (steam age) Thicker tin covering, commonly 300 uin (7.7 um) or more

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Literature/Historical Data Sparse references of hair development on tin plated wire Bell Labs examines in the 1950s and 60s On tin covered wire, " short bristles, moderately very few, were discovered" NASA Goddard tin stubble site: hairs on diode wire drives, Wire producers: modest bunch of client reports of hairs on tin covered wire over recent years, all on sort H wire. A few references propose that there is practically no hazard for significant hair development on tin covered wire and link. No hairs found on tin-covered wire on Titan rocket bridles MIL-STD-1547 ("Electronic Parts, Materials and Processes for Space and Launch Vehicles rev B") incorporates an exclusion for tin plated drawn wire items, for example, links, protecting and ground straps.

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Analysis 20 tests of tin-covered wire, link & interlace Manufactured somewhere around 1965 and 2008 10 unique providers Type S and H Two specimens temperature cycled for 1000 cycles between - 40 and 100°C Analysis Microscope examination Energy Dispersive Xray (EDX)- - material structure Scanning Electron Microscopy (SEM)- - size and thickness of hairs, grain estimate Cross area - intermetallic compound and tin layer thickness One electroplated mechanical part included for correlation

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Samples Analyzed

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Samples Analyzed

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EDX/SEM Inspection EDX affirmed immaculate tin covering over copper wire

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EDX/SEM Inspection None of the 20 wire and mesh tests indicated stubbles

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EDX/SEM Inspection Braid tests demonstrated some level strands, accepted to be "burrs" brought about from assembling process Electroplated terminal drag demonstrated lavish whiskering Tin plated copper terminal carry Tin plated copper plait

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Cross Sections Sample 2 7 year old transport wire IMC devours 30 to 100% of tin layer

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Cross Sections ← Sample 5 23 year old twist (sort S wire) IMC expends 100% of tin layer Sample 11 → 43 year old sort H wire IMC expends 20% of tin layer

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IMC Thickness General pattern of expanding IMC thickness with age. Anomalies (tests 17 and 23) have much thicker tin layer

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IMC Thickness Type S coatings are devoured by IMC in first years Type H coatings hold 50-75% of early immaculate tin

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Cross Sections

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Wire Manufacturing Processes Two procedures used to coat uncovered copper wire with tin: electroplating (otherwise known as electrodeposit) and hot plunging. Plating = electrochemical process Hot plunging = physical process Regardless of the covering procedure, the uncovered copper wire is prepared similar Copper poles or bars warmed and drawn through a progression of bites the dust to diminish breadth Drawing is like expulsion aside from that the wire is pulled through the bite the dust instead of pushed

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Copper drawn & moved Copper warm treat (500 to 850°C) Tin electroplate (35°C) Wire draw & toughen (200°C) Quench Spool Copper drawn & moved Copper warm treat (500 to 850°C) Tin electroplate (35°C) Spool Copper warm treat (500 to 850°C) Hot tin plunge (250° C) Wipe abundance tin Spool Copper drawn & moved Wire Manufacturing Processes Type S electroplated tin covered copper wire Type H electroplated tin covered copper wire Type S hot plunged tin covered copper wire

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Significant contrasts between hot plunging and electroplating: Hot plunging happens at much higher temperature, consequently bringing about thicker introductory IMC. Hot dunked wire is taken care of in the liquid state to evacuate abundance tin; procedures might be variable. Hot plunged wire produces littler, less particular grains Type S electroplated wire is drawn through a kick the bucket in the wake of plating

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Grain structure & measure test 23 (plated carry) Electroplated wire demonstrates bigger, more unmistakable grains with sharp edges. Grain size is 3.9 ± 1.8 μ m

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Grain Structure & Growth-Sample 4 (hot plunged mesh) Hot plunged wire indicates generally smooth, hints at reflow with less organized grains. Grain estimate 1.3 ± 0.6 μ m

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Pure tin on wire versus Segments

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Conclusions Three elements work to stifle hair development on wires Post-plating drawing steps chilly work the wire Annealing eases focuses in the plating Larger IMC layer in hot plunged wire brings about less immaculate tin material accessible for bristle development. Along these lines sort S wires (hot plunged or electroplated) would have a tendency to be at lower chance for bristle development than wires with thicker plating (sort H). As indicated by QQ-W-343 & AA-59551, Type H wire is favored as hookup wire on electrical gatherings in light of its solderability as far as stubble relief, nonetheless, sort S wire is liked to sort H.

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Conclusions No tin hairs were seen on any examples; 20 tests from 10 providers, matured somewhere around 1 and 44 years. No relationship between\'s stubble development and period of test, intermetallic compound thickness, provider or covering process (hot plunged versus electroplated). Critical contrasts between tin plated wire (no hairs) and tin plated part terminations (bristles) incorporate geometry, thickness of tin layer, and post plating toughening and chilly working procedures. None of these variables alone have all the earmarks of being totally fruitful in stifling hairs; rather it is likely a blend of components. Writing contains four reports of hair development on tin plated copper wire or wire drives (refs 8,9,10,11) Interviews with wire makers uncovered disconnected reports of tin bristles on wire in the course of recent years. A few information based references express that there is almost no hazard for considerable stubble development on tin-plated wire and link.

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