Thyristor Semiconductor Products Page 45 Thyristor

2014 Littelfuse, Inc. Specifications are subject to change without notice. Revised: 12/14/14 Teccor brand Thyristors AN1005 Use vapor degrease with an azeotrope solvent or equivalent to remove flux. Allow to dry. After the drying procedure is complete, the assembly is ready for testing and/or further processing. Surface Mount Soldering R e c o m e n d a t i o n s Wave Soldering 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 C and 260 C, which affixes the component to the board. 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 soldering PCBs with surface mount devices only. Figure AN1005.7 shows the procedure for wave soldering PCBs with both surface mount and leaded components. Screen print glue Wave solder Apply glue Cure glue Place component or Devices Only PC board Insert leaded components Turn over the PC board Apply glue Place SMDs Cure glue Turn over the PC board Wave solder Mount and Leaded Components Immersion Soldering Maximum allowed temperature of the soldering bath is 235 C. Maximum duration of soldering cycle is five seconds, and forced cooling must be applied. Hand Soldering 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 to laboratory use and/or incidental repairs on production circuits. Recommended Metal-alloy (1) 63/37 Sn/Pb - non - RoHS (2) (SAC 305) 96.5/3/0.5 Sn/Ag/Cu - RoHS Pre-Heating 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 pre- heating temperature is 165 C 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 C. Surface Mount Soldering Recommendations (continued)

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