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Moteur de recherche de fiches techniques de composants électroniques |
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Moteur de recherche de fiches techniques de composants électroniques |
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74HC258DB Fiches technique(PDF) 11 Page - NXP Semiconductors |
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74HC258DB Fiches technique(HTML) 11 Page - NXP Semiconductors |
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11 / 16 page  1999 Sep 02 11 Philips Semiconductors Product specification Quad 2-input multiplexer; 3-state; inverting 74HC/HCT258 SOLDERING Introduction This text gives a very brief insight to a complex technology. A more in-depth account of soldering ICs can be found in our “Data Handbook IC26; Integrated Circuit Packages” (document order number 9398 652 90011). There is no soldering method that is ideal for all IC packages. Wave soldering is often preferred when through-hole and surface mount components are mixed on one printed-circuit board. However, wave soldering is not always suitable for surface mount ICs, or for printed-circuit boards with high population densities. In these situations reflow soldering is often used. Through-hole mount packages SOLDERING BY DIPPING OR BY SOLDER WAVE The maximum permissible temperature of the solder is 260 °C; solder at this temperature must not be in contact with the joints for more than 5 seconds. The total contact time of successive solder waves must not exceed 5 seconds. The device may be mounted up to the seating plane, but the temperature of the plastic body must not exceed the specified maximum storage temperature (Tstg(max)). If the printed-circuit board has been pre-heated, forced cooling may be necessary immediately after soldering to keep the temperature within the permissible limit. MANUAL SOLDERING Apply the soldering iron (24 V or less) to the lead(s) of the package, either below the seating plane or not more than 2 mm above it. If the temperature of the soldering iron bit is less than 300 °C it may remain in contact for up to 10 seconds. If the bit temperature is between 300 and 400 °C, contact may be up to 5 seconds. Surface mount packages REFLOW SOLDERING Reflow soldering requires solder paste (a suspension of fine solder particles, flux and binding agent) to be applied to the printed-circuit board by screen printing, stencilling or pressure-syringe dispensing before package placement. Several methods exist for reflowing; for example, infrared/convection heating in a conveyor type oven. Throughput times (preheating, soldering and cooling) vary between 100 and 200 seconds depending on heating method. Typical reflow peak temperatures range from 215 to 250 °C. The top-surface temperature of the packages should preferable be kept below 230 °C. WAVE SOLDERING Conventional single wave soldering is not recommended for surface mount devices (SMDs) or printed-circuit boards with a high component density, as solder bridging and non-wetting can present major problems. To overcome these problems the double-wave soldering method was specifically developed. If wave soldering is used the following conditions must be observed for optimal results: • Use a double-wave soldering method comprising a turbulent wave with high upward pressure followed by a smooth laminar wave. • For packages with leads on two sides and a pitch (e): – larger than or equal to 1.27 mm, the footprint longitudinal axis is preferred to be parallel to the transport direction of the printed-circuit board; – smaller than 1.27 mm, the footprint longitudinal axis must be parallel to the transport direction of the printed-circuit board. The footprint must incorporate solder thieves at the downstream end. • For packages with leads on four sides, the footprint must be placed at a 45 ° angle to the transport direction of the printed-circuit board. The footprint must incorporate solder thieves downstream and at the side corners. During placement and before soldering, the package must be fixed with a droplet of adhesive. The adhesive can be applied by screen printing, pin transfer or syringe dispensing. The package can be soldered after the adhesive is cured. Typical dwell time is 4 seconds at 250 °C. A mildly-activated flux will eliminate the need for removal of corrosive residues in most applications. MANUAL SOLDERING Fix the component by first soldering two diagonally-opposite end leads. Use a low voltage (24 V or less) soldering iron applied to the flat part of the lead. Contact time must be limited to 10 seconds at up to 300 °C. When using a dedicated tool, all other leads can be soldered in one operation within 2 to 5 seconds between 270 and 320 °C. |
Numéro de pièce similaire - 74HC258DB |
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Description similaire - 74HC258DB |
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