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A majority of the defects in circuit-board assembly are caused due to issues in the solder-paste printing process or due to defects in the solder paste. There are many different types of defects possible, e.g. too much solder, or the solder melts and connects too many wires (bridging), resulting in a short circuit.
Stencil printing is the process of depositing solder paste on the printed wiring boards (PWBs) to establish electrical connections. It is immediately followed by the component placement stage. The equipment and materials used in this stage are a stencil , solder paste, and a printer.
High volume production is usually done with a pick-and-place machine and bulk wave soldering for through-hole parts or reflow ovens for SMT components or through-hole parts, but skilled technicians are able to hand-solder very tiny parts (for instance 0201 packages which are 0.02 in. by 0.01 in.) [29] under a microscope, using tweezers and a ...
Screen-printing is the process of transferring an ink through a patterned woven mesh screen or stencil using a squeegee. [8] For improving accuracy, increasing integration density and improving line and space accuracy of traditional screen-printing photoimageable thick-film technology has been developed. Use of these materials however changes ...
If the circuit board is double-sided then this printing, placement, reflow process may be repeated using either solder paste or glue to hold the components in place. If a wave soldering process is used, then the parts must be glued to the board before processing to prevent them from floating off when the solder paste holding them in place is ...
Reflow soldering is a process in which a solder paste (a mixture of prealloyed solder powder and a flux-vehicle that has a peanut butter-like consistency [8]) is used to stick the components to their attachment pads, after which the assembly is heated by an infrared lamp, a hot air pencil, or, more commonly, by passing it through a carefully ...
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Lead-free reflow soldering temperatures are higher, which results in more graping. Graping is also caused by increased surface oxidation. The increased surface oxidation is the result of smaller printed paste deposit volumes that cause a diminished surface area to flux ratio of the solder particle, resulting in flux exhaustion.