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12 SMT Magazine • June 2016 Las Marias: What other indus- try trends are affecting the sol- der paste printing process? Holtzer: The desire to elimi- nate wave soldering and less expensive components and laminate material has forced many end users to use lower melting lead-free solder al- loys, using pin-in-paste pro- cessing. Las Marias: What factors do users need to con- sider when it comes to solder paste printing? Holtzer: Best practices would include good board support, a reasonably well-controlled en- vironment (especially temperature), high-quali- ty stencils, and using a wipe frequency suitable for the process set up. Las Marias: What about equipment? Holtzer: Jetting is good for high-mix, low-vol- ume applications. It is slower, but changeover is much quicker, and you don't need a sten- cil. Screen printing is much faster in terms of assemblies per hour, making it well-suited for longer production runs. Las Marias: What do you think is the future for solder paste printing? Holtzer: The trend from type 3 pastes to type 4 will continue as components and spacing con- tinue to decline. Las Marias: Is there anything we haven't talked about when it comes to the solder paste printing process that you think we should be talking about? Holtzer: Although printing is a very important part of the SMT process, most common de- fects occur during reflow, after all of the cost of components and time has been spent on the boards. Reflow associated costs are much more expensive. Las Marias: Thank you very much, Mitch. Holtzer: Thank you. SMT Researchers at Singapore's Nanyang Technological Univer- sity have developed an adhesive that they believe may be a game- changer in manufacturing fields as diverse as biological implants and automobiles. The new adhesive is a liquid gel that "cures" to form a polymer bond when a voltage of less than 2V is passed through it. The glue stops curing as soon as the current is turned off. Users can fine-tune the bond's strength and flexibility by varying the current's voltage and duration. The bonding agent is a light, low-viscosity flowing liquid that allows users to coat and ex - actly position the materials to be joined. Applying voltage to the gel cures it to a strong bond with high elasticity and shear strength. Currently available quick-curing adhesives used in industry are activated by light, heat or chemical catalysts, each of which limits uses to particular materials and appropriate environments. Such quick-curing adhesives are used widely in the manufacture of medical devices, automobiles and other consumer goods, where they are favored over more labor- intensive, heavier mechanical fas - teners such as rivets, screws or bolts, which weaken the materials to be fixed. However, there has been little innovation in the field for decades. Potential uses for electro-cured adhesives in- clude biological devices for which photo- or ther- mo-setting glues are problematic, such as bioelec- tronics or polymer electronics designed for attach- ment to living tissue. The new adhesive could also make automotive assembly lines more efficient, as photo- and thermo-setting glues require costly, high-maintenance hardware. New Glue Instantly Hardens with Electric Current THE SOLDER PASTE FACTOR IN PRINTING Mitch Holtzer

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