Teccor® brand Thyristors Surface Mount Soldering Recommendations Introduction The most important consideration in reliability is achieving a good solder bond between surface mount device (SMD) and substrate since the solder provides the thermal path from the chip. A good bond is less subject to thermal fatiguing and will result in improved device reliability. The most economic method of soldering is a process in which all different components are soldered simultaneously, such as DO-214, Compak, TO-252 devices, capacitors, and resistors. With the components in position, the substrate is heated to a point where the solder begins to flow. This can be done on a heating plate, on a conveyor belt running through an infrared tunnel, or by using vapor phase soldering. In the vapor phase soldering process, the entire PC board is uniformly heated within a vapor phase zone at a temperature of approximately 215 ºC. The saturated vapor phase zone is obtained by heating an inert (inactive) fluid to the boiling point. The vapor phase is locked in place by a secondary vapor. (Figure AN1005.1) Vapor phase soldering provides uniform heating and prevents overheating. Reflow Of Soldering Transport The preferred technique for mounting microminiature components on hybrid thick- and thin-film is reflow soldering. Vapor lock (secondary medium) The DO-214 is designed to be mounted directly to or on thick-film metallization which has been screened and fired on a substrate. The recommended substrates are Alumina or P.C. Board material. After the substrate is prepared, devices are put in place with vacuum pencils. The device may be laid in place without special alignment procedures since it is selfaligning during the solder reflow process and will be held in place by surface tension. PC board Vapor phase zone Recommended metallization is silver palladium or molymanganese (plated with nickel or other elements to enhance solderability). For more information, consult Du Pont’s Thick-Film handbook or the factory. It is best to prepare the substrate by either dipping it in a solder bath or by screen printing a solder paste. Cooling pipes Heating elements Boiling liquid (primary medium) Figure AN1005.1 Principle of Vapor Phase Soldering No matter which method of heating is used, the maximum allowed temperature of the plastic body must not exceed 250 ºC during the soldering process. For additional information on temperature behavior during the soldering process, see Figure AN1005.2 and Figure AN1005.3. For reliable connections, keep the following in mind: (2) Flux must affect neither components nor connectors. (3) Residue of the flux must be easy to remove. Good flux or solder paste with these properties is available on the market. A recommended flux is Alpha 5003 diluted with benzyl alcohol. Dilution used will vary with application and must be determined empirically. tP TP Temperature (1) Maximum temperature of the leads or tab during the soldering cycle does not exceed 280 ºC. Ramp-up TL tL TS(max) Preheat TS(min) Ramp-do Ramp-down tS 25 Having first been fluxed, all components are positioned on the substrate. The slight adhesive force of the flux is sufficient to keep the components in place. time to peak temperature Figure AN1005.2 Time Reflow Soldering Profile Because solder paste contains a flux, it has good inherent adhesive properties which eases positioning of the components. Allow flux to dry at room temperature or in a 70 ºC oven. Flux should be dry to the touch. Time required will depend on flux used. ©2008 Littelfuse, Inc. Specifications are subject to change without notice. Please refer to http://www.littelfuse.com for current information. Surface Mount Soldering Recommendations AN1005 AN1005 Teccor® brand Thyristors AN1005 Reflow Condition Pre Heat - Temperature Min (Ts(min)) 150°C - Temperature Max (Ts(max)) 200°C - Time (min to max) (ts) Average ramp up rate (Liquidus Temp (TL) to peak TS(max) to TL - Ramp-up Rate Reflow 0.079 (2.0) Pb – Free assembly 0.110 (2.8) 60 – 190 secs ¡$TFDPOENBY 0.079 (2.0) ¡$TFDPOENBY - Temperature (TL) (Liquidus) 217°C - Time (min to max) (ts) 60 – 150 seconds Peak Temperature (TP) Time within 5°C of actual peak Temperature (tp) Ramp-down Rate 20 – 40 seconds Time 25°C to peak Temperature (TP) 8 minutes Max. Do not exceed 280°C Dimensions are in inches (and millimeters). Figure AN1005.3 260 °C Zone 1: Initial Pre-heating Stage (25 ºC to 150 ºC) t &YDFTTTPMWFOUJTESJWFOPGG Minimum Required Dimensions of Metal Connection of Typical DO-214 Pads on Hybrid Thick- and Thin-film Substrates 0.079 (2.0) ¡$TFDPOENBY Surface Mount Soldering Soldering Zones o m R co e n sm iReflow tn d a e Pad Outline 0.079 (2.0) 0.079 (2.0) 0.040 (1.0) 0.030 (0.76) 0.110 (2.8) Pad Outline Dimensions are in inches (and millimeters). Figure AN1005.4 t 1$#BOE$PNQPOFOUTBSFHSBEVBMMZIFBUFEVQ Modified DO-214 Compak — Three-leaded Surface Mount Package t 5FNQFSBUVSFHSBEJFOUTIBMMCF$4FD Zone 2: Soak Stage (150 ºC to 180 ºC) t 'MVYDPNQPOFOUTTUBSUBDUJWBUJPOBOECFHJOUPSFEVDF the oxides on component leads and PCB pads. t 1$#DPNQPOFOUTBSFCSPVHIUOFBSFSUPUIF temperature at which solder bonding can occur. 1. Screen print solder paste (or flux) t 4PBLBMMPXTEJGGFSFOUNBTTDPNQPOFOUTUPSFBDIUIF same temperature. t "DUJWBUFEnVYLFFQTNFUBMTVSGBDFTGSPNSFPYJEJ[JOH Zone 3: Reflow Stage (180 ºC to 235 ºC) t 1BTUFJTCSPVHIUUPUIFBMMPZTNFMUJOHQPJOU t "DUJWBUFEnVYSFEVDFTTVSGBDFUFOTJPOBUUIFNFUBM interface so metallurgical bonding occurs. 2. Place component (allow flux to dry) Zone 4: Cool-down Stage (180 ºC to 25 ºC) Assembly is cooled evenly so thermal shock to the components or PCB is reduced. The surface tension of the liquid solder tends to draw the leads of the device towards the center of the soldering area and so has a correcting effect on slight mispositionings. However, if the layout is not optimized, the same effect can result in undesirable shifts, particularly if the soldering areas on the substrate and the components are not concentrically arranged. This problem can be solved by using a standard contact pattern which leaves sufficient scope for the self-positioning effect (Figure AN1005.3 and Figure AN1005.4) Figure AN1005.5 shows the reflow soldering procedure. Surface Mount Soldering Recommendations 3. Reflow solder Figure AN1005.5 Reflow Soldering Procedure After the solder is set and cooled, visually inspect the connections and, where necessary, correct with a soldering iron. Finally, the remnants of the flux must be removed carefully. ©2008 Littelfuse, Inc. Specifications are subject to change without notice. Please refer to http://www.littelfuse.com for current information. Teccor® brand Thyristors Use vapor degrease with an azeotrope solvent or equivalent to remove flux. Allow to dry. PC board After the drying procedure is complete, the assembly is SFBEZGPSUFTUJOHBOEPSGVSUIFSQSPDFTTJOH Insert leaded components Surface Mount Soldering o m R co e n sm iWave tn d a e Soldering Turn over the PC board Wave soldering is the most commonly used method for soldering components in PCB assemblies. As with other soldering processes, a flux is applied before soldering. After the flux is applied, the surface mount devices are glued into place on a PC board. The board is then placed in contact with a molten wave of solder at a temperature between 240 ºC and 260 ºC, which affixes the component to the board. Apply glue Place SMDs Cure glue Dual wave solder baths are also in use. This procedure is the same as mentioned above except a second wave of solder removes excess solder. Although wave soldering is the most popular method of PCB assembly, drawbacks exist. The negative features include solder bridging and shadows (pads and leads not completely wetted) as board density increases. Also, this method has the sharpest thermal gradient. To prevent thermal shock, some sort of pre-heating device must be used. Figure AN1005.6 shows the procedure for wave soldering PCBs with surface mount devices only. Figure AN1005.7 shows the procedure for wave soldering PCBs with both surface mount and leaded components. Turn over the PC board Wave solder Figure AN1005.7 Wave Soldering PCBs With Both Surface Mount and Leaded Components Immersion Soldering Maximum allowed temperature of the soldering bath is 235 ºC. Maximum duration of soldering cycle is five seconds, and forced cooling must be applied. or Apply glue Screen print glue Hand Soldering Place component It is possible to solder the DO-214, Compak, and TO-252 devices with a miniature hand-held soldering iron, but this method has particular drawbacks and should be restricted UPMBCPSBUPSZVTFBOEPSJODJEFOUBMSFQBJSTPOQSPEVDUJPO circuits. Recommended Metal-alloy 4O1COPO3P)4 Cure glue 4"$ 4O"H$V3P)4 Pre-Heating Wave solder Figure AN1005.6 Wave Soldering PCBs With Surface Mount Devices Only ©2008 Littelfuse, Inc. Specifications are subject to change without notice. Please refer to http://www.littelfuse.com for current information. Pre-heating is recommended for good soldering and to avoid damage to the DO-214, Compak, TO-252 devices, other components, and the substrate. Maximum preheating temperature is 165 ºC while the maximum pre-heating duration may be 10 seconds. However, atmospheric pre-heating is permissible for several minutes provided temperature does not exceed 125 ºC. Surface Mount Soldering Recommendations AN1005 AN1005 Teccor® brand Thyristors AN1005 (3) Cut small pieces of the alloy solder and flow each piece onto each of the other legs of the component. o m R co e n sm iGluing tn d a e Recommendations Prior to wave soldering, surface mount devices (SMDs) must be fixed to the PCB or substrate by means of an appropriate adhesive. The adhesive (in most cases a multicomponent adhesive) has to fulfill the following demands: Indium-tin solder is available from ACI Alloys, San Jose, CA and Indium Corporation of America, Utica, NY. Multi-use Footprint Package soldering footprints can be designed to accommodate more than one package. Figure AN1005.8 shows a footprint design for using both the Compak and an SOT-223. Using the dual pad outline makes it possible to use more than one supplier source. t 6OJGPSNWJTDPTJUZUPFOTVSFFBTZDPBUJOH t /PDIFNJDBMSFBDUJPOTVQPOIBSEFOJOHJOPSEFSOPUUP deteriorate component and PC board t 4USBJHIUGPSXBSEFYDIBOHFPGDPNQPOFOUTJODBTFPG repair Cleaning Recommendations Low-temperature Solder for Reducing PC Board Damage In testing and troubleshooting surface-mounted components, changing parts can be time consuming. Moreover, desoldering and soldering cycles can loosen and damage circuit-board pads. Use low-temperature solder to minimize damage to the PC board and to quickly remove a component. One low-temperature alloy is indium-tin, in a NJYUVSF*UNFMUTCFUXFFO$BOE$BOEUJO lead melts at 183 ºC. If a component needs replacement, holding the board upside down and heating the area with a heat gun will cause the component to fall off. Performing the operation quickly minimizes damage to the board and component. Proper surface preparation is necessary for the In-Sn alloy to wet the surface of the copper. The copper must be clean, and you must add flux to allow the alloy to flow freely.You can use rosin dissolved in alcohol. Perform the following steps: (1) Cut a small piece of solder and flow it onto one of the pads. (2) Place the surface-mount component on the pad and melt the soldered pad to its pin while aligning the part. (This operation places all the pins flat onto their pads.) Using solvents for PC board or substrate cleaning is permitted from approximately 70 ºC to 80 ºC. The soldered parts should be cleaned with azeotrope solvent followed by a solvent such as methol, ethyl, or isopropyl alcohol. Ultrasonic cleaning of surface mount components on PCBs or substrates is possible. The following guidelines are recommended when using ultrasonic cleaning: t $MFBOJOHBHFOU*TPQSPQBOPM t #BUIUFNQFSBUVSFBQQSPYJNBUFMZ$ t %VSBUJPOPGDMFBOJOH."9TFDPOET t 6MUSBTPOJDGSFRVFODZL)[ t 6MUSBTPOJDDIBOHJOHQSFTTVSFBQQSPYJNBUFMZCBS Cleaning of the parts is best accomplished using an ultrasonic cleaner which has approximately 20 W of output per one liter of solvent. Replace the solvent on a regular basis. Gate 0.079 (2.0) MT2 / Anode MT1 / Cathode Gate M T 2 Not used Compak Footprint MT1 / Cathode 0.040 (1.0) 0.030 (.76) Pad Outline Footprint for either Compak or SOT-223 0.328 (8.33) 0.019 (.48) 0.040 (1.0) 0.079 (2.0) 0.059 (1.5) TYP 0.091 TYP (2.31) 0.150 (3.8) Gate MT2 / Anode 0.079 (2.0) 0.110 (2.8) MT1 MT2 / Anode 0.079 (2.0) 0.030 (.76) SOT-223 Footprint 0.079 (2.0) 0.079 (2.0) .055 (1.4) Dual Pad Outline Dimensions are in inches (and millimeters). Figure AN10058 Dual Footprint for Compak Package Surface Mount Soldering Recommendations ©2008 Littelfuse, Inc. Specifications are subject to change without notice. Please refer to http://www.littelfuse.com for current information.