Apply Low Residue Flux to all the leads on the SMD you're removing
With a soldering iron, melt the low temperature alloy
Surface mount technology
SURFACE MOUNT TECHNOLOGY<br />A method of assembling printed wiring boards or hybrid circuits, where components are attached to pads on the board surface, as distinct from through-hole technology, where component leads are inserted into holes.<br />
There are 3 major types of Surface Mount Assemblies:<br />Type I<br /> (Full SMT board with parts on one or both sides of the board)<br />Type II<br />(Surface mount chip components are located on the secondary side of the Printed Board (PB). Active SMCs and DIPs are then found on the primary side)<br />Type III<br /> (They use passive chip SMCs on the secondary side, but on the primary side only DIPs are used)<br />TYPES OF SURFACE MOUNT TECHNOLOGY<br />
PROCESSES INVOLVED <br /><ul><li>SURFACE MOUNT DESIGN
As the packaging density increases, thermal problems are compounded, with a potential adverse impact on overall product reliability</li></li></ul><li>SOLDER PASTE APPLICATIONSolder paste, a sticky mixture of flux and tiny solder particles, is first applied to all the solder pads with a stainless steel or nickel stencil using a screen printingprocess<br />
COMPONENT PLACEMENTComponents to be placed on the boards are usually delivered to the production line in either paper/plastic tapes wound on reels or plastic tubes. Numeric Control pick-and-place machines remove the parts from the tapes, tubes or trays and place them on the PCB.<br />SMD pick-and-place machine (with simulated motion blurs)<br />Feed mechanism used to load components into a pick-and-place machine<br />
SOLDERING<br />Soldering is a process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a relatively low melting point.<br />
TYPES OF SOLDERING TECHNIQUES<br />INFRARED SOLDERING<br />CONVENTIONAL HOT GAS SOLDERING<br />
INFRARED SOLDERINGDuring infrared soldering, the energy for heating up the solder joint will be transmitted by long or short wave electromagnetic radiation<br />
CLEANING SMT ASSEMBLIES<br /><ul><li>A specially formulated alloy in wire form is designed to melt at the low temperature of around 136 degrees F, 58 degrees C. It eliminates the potential for damage to the circuit, adjacent components, and the device itself.
Liquid flux and a soldering iron are used to melt this low temperature alloy that is specially formulated to stay molten long enough to react with existing solder. The SMT device can then be easily removed with a vacuum pen.</li></li></ul><li>Apply Low Residue Flux to all the leads on the SMD you're removing<br />
With a soldering iron, melt the low temperature alloy<br />
Easily lift device off the board with a vacuum pen<br />
REPAIR / REWORK<br /><ul><li>Finally, the boards are visually inspected for missing or misaligned components and solder bridging.
If needed, they are sent to a rework station where a human operator corrects any errors.
They are then sent to the testing stations to verify that they operate correctly.</li></li></ul><li>Thoroughly clean site and solder new device to PBC<br />