Cold solder connections are the result of withdrawing the soldering iron too soon. The solder does not become liquid and leaves a connection that is dull gray in appearance.A fractured or disturbed connection is the result of movement of the component leads or wire before the solder sets. The fractured joint is evident by a granulated and frosty appearance with many cracks showing.Other types of defects include:• Rosin connection is caused by the flux and oxidation particles staying between thesolder pad and lead. It is the result of not enough heat.• Wicking is caused by the capillary action of stranded wire. It is the result of too much heat.• Voids are caused by impurities in the surface when soldering. • Bridging (inadvertently connecting two pads) is caused by not removing the solder soon enough.11/30/201724
Protective Coating of PCB•Conformal coatingsare nonconductive materials applied in a thin layer onprintedcircuitboards.Theyprovideenvironmentalandmechanicalprotection to significantly extend the life of the components and circuitry.Conformalcoatingsaretraditionallyappliedbydipping,spraying,orflow coating.•Conformal coatings protect electronic printed circuit boards from corrosion,dust, fungus, moisture, and environmental stresses.•Common conformal coatings include acrylic, epoxy, parylene, silicone, andurethane. Most conformal coatings consist of a synthetic resin developed ina volatile solvent. When they are properly applied to a clean surface, thesolvents evaporate, leaving a thin film of solid resins.11/30/201725
Safety Precautions during PCB FabricationAlways wear safety glasses when soldering.Never touch the soldering iron tip or heating element. Only pick up the iron by the handle. Never change the tip when the iron is hot.Beware of pressing the soldering iron too hard against the leads when heating. The soldering iron may slip.Beware of molten solder dripping from the connection. Cotton and wool clothing are the safest to wear when solderingUse care when handling printed circuit boards. Leads can cut or puncture the skin. Always have cuts or punctures cleaned and treated immediately.Avoid breathing in flux fumes when soldering.Wash hands before eating or drinking. The lead from the solder remaining on the hands can be ingested with food.Keep the work area neat and orderly.Be alert and attentive at all times.Know the correct operation and safety procedures of test equipment, tools, and machinery.If an accident occurs, know what action to take.11/30/201726
Hazards of current flow through the human body11/30/201727
Electrostatic Discharge•Static electricity is created when two substances are rubbed together orseparated. The substances can be solid or fluid. The rubbing or separatingcauses the transfer of electrons from one substance to the other. Thisresults in one substance being positively charged and the other substance
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- Summer '17
- Printed circuit board, Solder