ME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 1 Joining – Part 2 ver. 1ME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 2 Overview • Mechanical fastening not covered • Joining technique issues • Welding using interfacial shear • Adhesive bonding • Diffusion bonding • Soldering and brazing • Fusion weldingME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 3 Diffusion bonding • High pressure and temperature for extended periods of time can lead to bonding. • Heat permits deformation of asperities.ME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 4 Initial asperity contactME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 5 First stage - deformation, interfacial boundary formationME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 6 Second stage - grain boundary migration and pore eliminationME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 7 Third stage - volume diffusion pore eliminationME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 8 Diffusion bonding • If oxide layer is soluble in base material, it can diffuse into bulk, leading to inter-atomic bonding.ME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 9 Diffusion bonding - examples • Silver oxide is not stable at high temperatures, easy to diffusion bond. • Iron, titanium and copper also can be diffusion bonded, because the oxide, which is stable, diffuses into the base metal. • Aluminum and magnesium are hard to diffusion bond, as their oxides are stable and insoluble.ME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 10 Processing - contact conditions • 500 to 5,000 psi • T > 0.6 Tmelting (absolute) • Minutes to hours to 10s of hoursME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 11 Diffusion bonding • Complex inaccessible joints can be bonded. • Removes cold working. • Dissimilar materials can be bonded. – residual stresses due to thermal coefficient mismatch.ME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 12 Interface Material A Material BME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 13 Soldering and brazing • Typically, a liquid metal joins two solid surfaces. • Solder T < 425oC • Braze T > 425oCME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 14 Pipe solder jointME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 15 Circuit boardsME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 16 Intel Mini-cartridgeBumps and Alignment ME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 17 Misaligned AlignedME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 18 Solder tapeME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 19 Soldering uses • Join dissimilar materials • Electronics • Microelectronics • Pipes • Repairing jewelryME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 20 Brazing uses • Join dissimilar materials – repairing metal parts – ceramics and glasses to other materialsME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 21 • A - flux over oxidized metal • B - boiling flux removes oxide • C - base metal in contact with molten flux • D - molten solder displaces molten flux • E - solder alloys with base metal • F - solder solidifiesME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 22 Wave soldering schematic direction of travel chip leads circuit board solder wave solder jointME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 23 Wave soldering machineME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 24 Flux applicationME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 25 Solder wave WaveME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 26 Solder and braze materials • Tin • Lead • Antimony • Silver • Copper • Phosphorous • Cadmium • Gold • Iron • Chrome • Nickel • Silicon • Zinc • ManganeseME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 27 Brazing materials • Aluminum-silicon for aluminum alloys – 570 – 620oC • Gold for iron, nickel alloysME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 28 Flux • To prevent oxidation. • Used to clean off surface contaminants. • Proper flux needed to decompose surface oxides. • Clean surfaces are needed for good wetting and bonding. • High temperatures increase cleaning and speed of process.ME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 29 Flux • Molten metals have very high surface tensions. • Fluxes must have lower surface tensions, so they can be displaced by solder. • Solders are usually metals. • Fluxes can be organic or inorganic. – e.g. boric acid, fluorides/chloridesME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 30 Joint strength • Solder: – Controlled by creep of solder • Solder rule of thumb: – Don’t exceed 1,000 psi above 0.75 Tmelting (absolute) • Brazing – strengths up to 5,000 to 10,000 psiME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 31 Joint strength • Typically, thinner is better. – “contact strengthening” – tri-axial stress state • Thicker joints can relieve differential thermal stress concentrations.ME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 32 Joint DesignME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011 33 Summary • Joining technique issues • Welding using interfacial shear • Adhesive bonding • Diffusion bonding • Soldering and brazingME 6222: Manufacturing Processes and Systems Prof. J.S. Colton © GIT 2011