Surface mount technology soldering

The standard is a collection of visual quality acceptability requirements for electronic assemblies. It covers criteria for both pin through-hole and surface-mount technology solder connections. It also reflects requirements for three different classes of end prodncts ... 

PCX withstands SMT (surface mount technology) reflow soldering. 

Multilayer boards, which use multiple interior laminates of plastic and copper, now comprise over half of the value of production, though much less on a surface area basis. Surface mount technologies demand extreme flatness and reproducibility from surfaces. Greater packing density has led to commercial production of finer lines and holes, often less than 50 Jim and 500 Jim, respectively. Electroless gold over electroless nickel—phosphorus, or electroless nickel—boron alone, is often used as a topcoating for wire bonding or improved solderability. 

Morris JR, WojcikT (1990). Soldering Surface Mount Technology, No. 5. 

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. 

In order to miniaturize products and to improve productivity in the electronics industry, a method of soldering resinous electronic parts has been developed for affixing parts, such as connectors, switches, relays and coil bobbins to printed circuit board (PCB). This method is addressed as surface-mount technology. 

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... 

In surface mount technology, the components are soldered directly to the surface of a PWB, as opposed to thro ugh-hole mounting. This allows efficient use of board real estate, resulting in smaller boards and simpler assembly. Significant improvement in electrical performance is possible with the reduced package parasitics and the short interconnections. However, the reliability of the solder joint is a concern if there are CTE mismatches (Seraphim et al, 1989). 

Hollomon, J.K., Jr. 1995. Surface Mount Technology for PC Board Design. Prompt, Indianapolis, IN. Holmes, J.G. 1993. Surface mount solution for power devices. Surface Mount Technology 7(9) 18-20. Hwang, J.S. 1989. Solder Paste in Electronics Packaging. Van Nostrand Reinhold, New York. 

Bono, D., The Assessment of the Corrosivity of Soldering Flux Residues Using Printed Copper Circuit Board Tracks, Solder Surface Mount Technology, No. 2, June 1989, pp. 22-29. 

Coleman W.E., Jean, D., and Bradbury-Bennett, J.R., Stencil design for mixed technology through-hole/SMT placement and reflow. Soldering and Surface Mount Technology, Vol. 12, No. 3, 8-12, 2000. 

Surface mount technology is being used increasingly in assemblies such as in-car telephones and audio equipment. PBT and PET, more stable dimensionally than PA 66, are widely used. Distributorless ignition systems (DIS), for example, use a tray in PBT, with surface mounted conductors, filled with epoxy and encapsulated with PET. Vapour phase soldering can involve temperatures of up to 260°C for several seconds. This is encouraging the use of fully aromatic polymers like PPS and PEI, which not only have a high HDT but are also inherently non-flammable. 

The need to use lead-free solder in surface mount technology applications where soldering temperatures of between 220 °C and 240 °C are likely to be encountered has necessitated the use of such high temperamre polyamides as DuPont s Zytel HTN LX resins for board assembly. It is interesting to note that some Japanese companies have been using lead-free solders in their flow soldering processes since 1997. 

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