Electronics solder paste printing

Table 4.4 lists commercial cleaning solutions currently used in the electronics industry for cleaning printed-circuit boards, assemblies, ceramic printed circuits, thick-film interconnect substrates, electronic components, wiring harnesses, and stencils and screens (used in applying adhesives and solder pastes). 

Surface mounting. Surface mounting of components onto PWBs is commonly referred to in the industry as SMT or surface-mount technology. It consists of the attachment of electronic components by automated dispensing or screen printing of solder paste and adhesive onto a PWB, placement of the components, then curing the adhesive and reflowing the... 

Component Placement. The purpose of the component placement machine—also called the pick-and-place machine—is to select the proper component, orient it correctly, and then place it on the circuit board, all with degrees of accuracy and precision that minimize defects on the finished product. In addition, the component must be placed on the printed solder paste, the dispensed adhesive, or a combination of the two deposits with a controlled pressure or release distance that does not excessively spread out either material or damages the component package. Moreover, the placement machine must execute these tasks as quickly as possible in order to maximize the production volume. Lastly, the equipment must be sufficiently versatile to address continually changing electronic packages, specifically dimensions and I/O configurations. 

Study of the Rheological Behaviours of Sn-Ag-Cu Solder Pastes and their Correlation with Printing Performance. Proceedings of the 11 Electronics Packaging Technology Conference, Singapore, December 2009, pp. 869-874. 

The conventional method using screen printed solder pastes or isotropic conductive adhesives is drflicult to apply when the distance between adjacent connections is less than 0.5 mm. Thus, the main impetus for developing anisotropic conductive adhesives has been the fine pitch interconnection of electronic devices... 

A decade ago, PCAs comprised little more than a through-hole PCB with wave-soldered components. Today, modest electronics products can involve an array of surface mount, chip-scale, through-hole, and electromechanical technologies. Screen-printed solder paste and reflow/wave ovens no longer are sufficient to complete the build alone. This is where benchtop dispensing comes in. 

The processes generally employed to fix electronic components on three-dimensional circuit carriers are reflow soldering and electrically conductive-adhesive gluing. The first step in reflow soldering is to print solder paste on to the pads of the circuit trace (Fig. 4.1). The electronic components are subsequently placed in these solder depots. The module, complete with its electronic components, is then heated in a reflow oven, the solder particles of the paste melt, and the molten solder flows over... 

Reflow soldering involves the selective deposition of solder paste at termination pads or other features on printed wiring boards. Then, the electronic components and other devices are placed on the board, and the bond is completed by heating and melting the solder. The most common lead-free alternative alloys considered for solder paste are tin-silver (Sn-Ag), tin-silver-copper (Sn-Ag-Cu), and tin-silver-bismuth (Sn-Ag-Bi). Tin bismuth (SnBi), tin indium (Snin) and silver-fllled conductive epoxy are also considered for certain applications. 

Over the past decades, development and use of electrically conductive adhesives have expanded in the microelectronics industry. The major applications are die attachment, liquid crystal display and surface-mounted assembly of packaged components on printed wiring board. Recently, isotropic conductive adhesives (ICA s) have been widely used in electronics applications to replace lead-based soldering due to toxicity of the lead in Sn-Pb solders [1]. 

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