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MMBD717LT1D Datasheet(PDF) 4 Page - ON Semiconductor |
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MMBD717LT1D Datasheet(HTML) 4 Page - ON Semiconductor |
4 / 8 page MMBD717LT1 http://onsemi.com 4 STEP 1 PREHEAT ZONE 1 RAMP" STEP 2 VENT SOAK" STEP 3 HEATING ZONES 2 & 5 RAMP" STEP 4 HEATING ZONES 3 & 6 SOAK" STEP 5 HEATING ZONES 4 & 7 SPIKE" STEP 6 VENT STEP 7 COOLING 200°C 150°C 100°C 50°C TIME (3 TO 7 MINUTES TOTAL) TMAX SOLDER IS LIQUID FOR 40 TO 80 SECONDS (DEPENDING ON MASS OF ASSEMBLY) 205° TO 219°C PEAK AT SOLDER JOINT DESIRED CURVE FOR LOW MASS ASSEMBLIES 100°C 150°C 160°C 140°C Figure 5. Typical Solder Heating Profile DESIRED CURVE FOR HIGH MASS ASSEMBLIES 170°C For any given circuit board, there will be a group of control settings that will give the desired heat pattern. The operator must set temperatures for several heating zones, and a figure for belt speed. Taken together, these control settings make up a heating “profile” for that particular circuit board. On machines controlled by a computer, the computer remembers these profiles from one operating session to the next. Figure 7 shows a typical heating profile for use when soldering a surface mount device to a printed circuit board. This profile will vary among soldering systems but it is a good starting point. Factors that can affect the profile include the type of soldering system in use, density and types of components on the board, type of solder used, and the type of board or substrate material being used. This profile shows temperature versus time. SOLDER STENCIL GUIDELINES Prior to placing surface mount components onto a printed circuit board, solder paste must be applied to the pads. A solder stencil is required to screen the optimum amount of solder paste onto the footprint. The stencil is made of brass or stainless steel with a typical thickness of 0.008 inches. The stencil opening size for the surface mounted package should be the same as the pad size on the printed circuit board, i.e., a 1:1 registration. TYPICAL SOLDER HEATING PROFILE The line on the graph shows the actual temperature that might be experienced on the surface of a test board at or near a central solder joint. The two profiles are based on a high density and a low density board. The Vitronics SMD310 convection/infrared reflow soldering system was used to generate this profile. The type of solder used was 62/36/2 Tin Lead Silver with a melting point between 177–189 °C. When this type of furnace is used for solder reflow work, the circuit boards and solder joints tend to heat first. The components on the board are then heated by conduction. The circuit board, because it has a large surface area, absorbs the thermal energy more efficiently, then distributes this energy to the components. Because of this effect, the main body of a component may be up to 30 degrees cooler than the adjacent solder joints. |
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