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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.
An example is ball grid array (BGA) using tin-lead solder balls for connections losing their balls on bare copper traces or using lead-free solder paste. Other platings used are organic solderability preservative (OSP), immersion silver (IAg), immersion tin (ISn), electroless nickel immersion gold (ENIG) coating, electroless nickel electroless ...
Flexible placer, chip shooter, and other specialized machines. PWB with solder print. Components supplied by feeders. Computer files: computer program controls location of each component on the PWB (X, Y and angular theta), feeder inventory levels, placement machine vacuum holder capability, automatic component realignment, placement accuracy, vision systems, and transportation of PCBs through ...
Common solder alloys include tin-lead, tin-silver, and tin-copper, among others. Lead-free solder has also become more widely used in recent years due to health and environmental concerns associated with the use of lead. In addition to the type of solder used, the temperature and method of heating also play a crucial role in the soldering process.
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.
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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 ...