Circuit soldering

Ease of maintenance Poor—large number of contacts Poor if integrated circuits soldered Poor—several custom boards Good—few standard cards... 

In fabrication of printed circuit boards (Goh 1994), a resin formula is prepared and impregnated with fibreglass and other particles. This is baked to form a panel or a board. Lamination involves metallic copper being bonded to the board in (sandwiched) layers. Each side of the laminate is cleaned, photoprinted and etched to form the electrical circuits. Solder plating is done, and the boards are drilled and cut to the required sizes. Finally, the boards are marked and tested. 

If no socket is available for connecting the initiator to the firing circuit, solder the connecting wires to the bulb base. 

Outer layer graphics (for circuit, solder mask, and legend images)... 

Electro- and electroless plating of tin, nickel, gold, and solder are common surface treatments for flexible circuits. Solder plating by a hot-air leveler could be a low-cost solution. However, it entails severe high-temperature process conditions, and the poor uniformity of the solder is not acceptable for several applications. 

Sugunama, K. Microstructural features of lift off phenomena in through hole circuit soldered by Sn-Bi Alloy. Scripta Metallurgica. 1998, 38 (9), 1333-1340. 

Plating Processes, Tin-Tead Solder Mlloy Fluoborate Plating Process for Printed Circuit Applications, HTPP3N 0272, Harshaw Chemical Co., Solon, Ohio. 

Conformal coatings are protective coatings appHed to circuit board assembHes. They protect the interconnect conductors, solder joints, components, and the board itself they reduce permeabiHty to moisture, hostile chemical vapors, and solvents in the coating. Use of conformal coatings eliminates dendritic growth between conductors, conductor bridging from moisture condensation, and reduction in insulation resistance by water absorption. 

Diallyl terephthalate [1026-92-2] is utilized less, but lenses made of copolymers with triaHyl cyanurate and methacrylates have been suggested (62). Diallyl tetrabromophthalate and tetrachlorophthalate polymers have been proposed for electronic circuit boards of low flammabiUty (63). They are uv-curable and solder-resistant. Copolymers with unsaturated polyester, vinyl acetate and DAP have been studied (64). 

Because of the ease with which they can be soldered, electroplated tin—lead coatings of near eutectic composition (62 wt % tin) are extensively used in the electronics industry for coating printed circuit boards and electrical coimectors, lead wires, capacitor and condenser cases, and chassis. 

Surface mount refers to a method of securing connectors to the conductors of a printed circuit board by soldering appropriately shaped contacts to the board surface. Higher contact densities can be achieved and the need to drill holes in the board is avoided. Contact spacings may vary from about 0.5 cm for large current-carrying appHcations to 0.18 cm or less when miniaturization and high density is a requirement. 

Tin—Nickel. AHoy deposits having 65% fin have been commercially plated siace about 1951 (135). The 65% fin alloy exhibits good resistance to chemical attack, staining, and atmospheric corrosion, especially when plated copper or bron2e undercoats are used. This alloy has a low coefficient of friction. Deposits are solderable, hard (650—710 HV ), act as etch resists, and find use ia pfinted circuit boards, watch parts, and as a substitute for chromium ia some apphcafions. The rose-pink color of 65% fin is attractive. In marine exposure, tin—nickel is about equal to nickel—chromium deposits, but has been found to be superior ia some iadustfial exposure sites. Chromium topcoats iacrease the protection further. Tia-nickel deposits are bfitde and difficult to strip from steel. Temperature of deposits should be kept below 300°C. 

Printed circuit board component such as laminates, conformal coatings, solder masks, masking tapes, component attachment adhesives, vibration dampers and photoresists. 

The generally very good electrical insulation properties coupled with heat resistance and non-burning behaviour indicate usage in coil bobbins, printed circuit boards (which resist heat of soldering), lamp bulb bases and TV... 

Films have been used for insulating electric motors, in capacitors requiring a heat resistance not met by conventional polyester and polycarbonate dielectrics and as a soldering-resistant base for flexible printed circuits. 

PCT may be used for the production of electronic and automotive components such as circuit board components, connectors, switches and relays, and alternator armatures and pressure sensors. The main application has been in the fabrication of surface-mount connectors that can withstand infrared reflow soldering operations. 

The secondary production of lead begins with the recovery of old scrap from worn-out, damaged, or obsolete products and with new scrap. The chief source of old scrap is lead-acid batteries other sources include cable coverings, pipe, sheet, and other lead-bearing metals. Solder, a tin-based alloy, may be recovered from the processing of circuit boards for use as lead charge. 

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