Surface-mount technology wave soldering

Surface-mount technology replaces previous methods of inserting component leads into plated through-holes of PWBs, wave soldering from the back side to flow solder into the holes, and simultaneously forming both mechanical and electrical connections. SMT is highly automated and currently the most widely used production process for the assembly of single-layer, double-sided, and multilayer circuit boards. 

Before the widespread use of solder mask, a primary method for protecting copper circuitry was to electroplate a coating of tin or tin-lead on the copper. After component insertion, the tin plating could be liquefied with oven or vapor-phase reflow to form solderjoints.The use of solder mask over bare copper to take advantage of surface mount, wave soldering, and mixed assembly restricted the use of tin plate finishing. For simple technology product, tin or tin-lead plate and reflow remains a viable fabrication and assembly method. 

An advantage of through-hole technology is reduced cost in some appUcations. That cost benefit may be realized by lower labor costs in some parts of the world that support hand assembly, which is relatively easy with the larger components and products, and lower board densities. Even when fully automated—either by wave soldering, selective soldering, or paste-in-hole/reflow—the capital equipment and manufacturing costs can stiU be lower than those required for surface-mount assembly. 

Besides die attachment, ICAs are utilized in surface mount and flip-chip packages as alternatives to traditional solders. Due to their low surface tensions, ICAs are not suitable for wave soldering (Ref 6). Despite the advantages of ICA interconnection, the wide use of this technology has not been adopted by the electronics industry. The main concern is long-term reliability. 

In addition to wire harness connectors, printed circuit board-attached connectors, for automotive or electronic applications, also benefit from many of SPS s performance characteristics, including low viscosity, which helps to fill thin walls and heat resistance to maintain dimensional stability through lead-free reflow soldering operations (see Table 15.2). The trend toward miniaturization in automotive electronic control modules has increased the need for compact surface mount connector technology, as opposed to bulkier through-hole and wave-soldered alternatives. 

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. 

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