BCP56T1 Series NPN Silicon Epitaxial Transistor - Datasheet Catalog

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BCP56T1 SeriesINFORMATION FOR USING THE SOT–223 SURFACE MOUNT PACKAGEMINIMUM RECOMMENDED FOOTPRINT FOR SURFACE MOUNTED APPLICATIONSSurface mount board layout is a critical portion of the totaldesign. The footprint for the semiconductor packages mustbe the correct size to insure proper solder connectioninterface between the board and the package. With thecorrect pad geometry, the packages will self align whensubjected to a solder reflow process.SOT–223mminchesSOT–223 POWER DISSIPATIONThe power dissipation of the SOT–223 is a function ofthe pad size. This can vary from the minimum pad size forsoldering to the pad size given for maximum power dissipation.Power dissipation for a surface mount device is determinedby TJ(max), the maximum rated junction temperatureof the die, RθJA, the thermal resistance from the devicejunction to ambient; and the operating temperature, TA. Usingthe values provided on the data sheet for the SOT–223package, PD can be calculated as follows.PD =PD =150°C – 25°C83.3°C/WTJ(max) – TARθJAThe values for the equation are found in the maximumratings table on the data sheet. Substituting these values intothe equation for an ambient temperature TA of 25°C, onecan calculate the power dissipation of the device which inthis case is 1.5 watts.= 1.50 wattsThe 83.3°C/W for the SOT-223 package assumes theuse of the recommended footprint on a glass epoxyprinted circuit board to achieve a power dissipation of 1.5watts. There are other alternatives to achieving higherpower dissipation from the SOT-223 package. One is toincrease the area of the collector pad. By increasing thearea of the collector pad, the power dissipation can beincreased. Although the power dissipation can almost beθdoubled with this method, area is taken up on the printedcircuit board which can defeat the purpose of usingsurface mount technology. A graph of RθJA versus collectorpad area is shown in Figure 6.° ″° Figure 6. Thermal Resistance versus CollectorPad Area for the SOT-223 Package (Typical)Another alternative would be to use a ceramic substrateor an aluminum core board such as Thermal Clad. Usinga board material such as Thermal Clad, an aluminum coreboard, the power dissipation can be doubled using the samefootprint.http://onsemi.com4
BCP56T1 SeriesSOLDER STENCIL GUIDELINESPrior to placing surface mount components onto a printedcircuit board, solder paste must be applied to the pads. Asolder stencil is required to screen the optimum amount ofsolder paste onto the footprint. The stencil is made of brassor stainless steel with a typical thickness of 0.008 inches.The stencil opening size for the surface mounted packageshould be the same as the pad size on the printed circuitboard, i.e., a 1:1 registration.SOLDERING PRECAUTIONSThe melting temperature of solder is higher than the ratedtemperature of the device. When the entire device is heatedto a high temperature, failure to complete soldering withina short time could result in device failure. Therefore, thefollowing items should always be observed in order tominimize the thermal stress to which the devices aresubjected.• Always preheat the device.• The delta temperature between the preheat andsoldering should be 100°C or less.*• When preheating and soldering, the temperature of theleads and the case must not exceed the maximumtemperature ratings as shown on the data sheet. Whenusing infrared heating with the reflow solderingmethod, the difference should be a maximum of 10°C.• The soldering temperature and time should not exceed260°C for more than 10 seconds.• When shifting from preheating to soldering, themaximum temperature gradient should be 5°C or less.• After soldering has been completed, the device shouldbe allowed to cool naturally for at least three minutes.Gradual cooling should be used as the use of forcedcooling will increase the temperature gradient andresult in latent failure due to mechanical stress.• Mechanical stress or shock should not be applied duringcooling* Soldering a device without preheating can cause excessivethermal shock and stress which can result in damageto the device.For any given circuit board, there will be a group ofcontrol settings that will give the desired heat pattern. Theoperator must set temperatures for several heating zones,and a figure for belt speed. Taken together, these controlsettings make up a heating “profile” for that particularcircuit board. On machines controlled by a computer, thecomputer remembers these profiles from one operatingsession to the next. Figure 7 shows a typical heating profilefor use when soldering a surface mount device to a printedcircuit board. This profile will vary among solderingsystems but it is a good starting point. Factors that canaffect the profile include the type of soldering system inuse, density and types of components on the board, type ofsolder used, and the type of board or substrate materialbeing used. This profile shows temperature versus time.TYPICAL SOLDER HEATING PROFILEThe line on the graph shows the actual temperature thatmight be experienced on the surface of a test board at ornear a central solder joint. The two profiles are based on ahigh density and a low density board. The VitronicsSMD310 convection/infrared reflow soldering system wasused to generate this profile. The type of solder used was62/36/2 Tin Lead Silver with a melting point between177–189°C. When this type of furnace is used for solderreflow work, the circuit boards and solder joints tend toheat first. The components on the board are then heated byconduction. The circuit board, because it has a large surfacearea, absorbs the thermal energy more efficiently, thendistributes this energy to the components. Because of thiseffect, the main body of a component may be up to 30degrees cooler than the adjacent solder joints.http://onsemi.com5
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BCP56T1 Series NPN Silicon Epitaxial Transistor - Datasheet Catalog

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