Thyristor Semiconductor Products Page 40 Thyristor

2014 Littelfuse, Inc. Specifications are subject to change without notice. Revised: 12/14/14 Teccor brand Thyristors AN1004 should be removed. Iridite or chromate acid dip finish offers low electrical and thermal resistance. Either TO-218, Fastpak or TO-220 devices may be mounted directly to this surface, regardless of application. Both finishes should be cleaned prior to use to remove manufacturing oils and films. Some of the more economical heat sinks are painted black. Due to the high thermal resistance of paint, the paint should be removed in the area where the semiconductor is attached. Bare aluminum should be buffed with #000 steel wool and followed with an acetone or alcohol rinse. Immediately, thermal grease should be applied to the surface and the device mounted down to prevent dust or metal particles from lodging in the critical interface area. For good thermal contact, the use of thermal grease is essential to fill the air pockets between the semiconductor and the mounting surface. This decreases the thermal resistance by 20%. For example, a typical TO-220 with R JC of 1.2 C/W may be lowered to 1 C/W by using thermal grease. Littelfuse recommends Dow-Corning 340 as a proven effective thermal grease. Fibrous applicators are not recommended as they may tend to leave lint or dust in the interface area. Ensure that the grease is spread adequately across the device mounting surface, and torque down the device to specification. Contact Littelfuse Applications Engineering for assistance in choosing and using the proper heat sink for specific application. Hardware And Methods TO-220 The mounting hole for the Teccor TO-220 devices should No insulating bushings are needed for the L Package (isolated) devices as the tab is electrically isolated from the semiconductor chip. 6/32 mounting hardware, especially round head or Fillister machine screws, is recommended and should be torqued to a value of 6 inch-lbs. Lockwasher 6-32 Nut Heatsink * Mounting screw 6-32 * Screw head must not touch the epoxy body of the device Avoid axial stress Boundary of exposed metal tab On heavy aluminum heatsinks High potential appication using Isolated TO-220 Figure AN1004.7 TO-220 Mounting Punched holes are not acceptable due to cratering around the hole which can cause the device to be pulled into the crater by the fastener or can leave a significant portion of the device out of contact with the heat sink. The first effect may cause immediate damage to the package and early failure, while the second can create higher operating temperatures which will shorten operating life. Punched holes are quite acceptable in thin metal plates where fine- edge blanking or sheared-through holes are employed. Drilled holes must have a properly prepared surface. Excessive chamfering is not acceptable as it may create a crater effect. Edges must be deburred to promote good contact and avoid puncturing isolation materials. For high-voltage applications, it is recommended that only the metal portion of the TO-220 package (as viewed from the bottom of the package) be in contact with the heat sink. This will provide maximum oversurface distance and prevent a high voltage path over the plastic case to a grounded heat sink. TO-218 The mounting hole for the TO-218 device should not do not require any insulating material since mounting tab is electrically isolated from the semiconductor chip. Round lead or Fillister machine screws are recommended. Maximum torque to be applied to mounting tab should not exceed 8 inch-lbs. The same precautions given for the TO-220 package concerning punched holes, drilled holes, and proper prepared heat sink mounting surface apply to the TO-218 package. Also for high-voltage applications, it is recommended that only the metal portion of the mounting surface of the TO-218 package be in contact with heat sink. This achieves maximum oversurface distance to prevent a high-voltage path over the device body to grounded heat sink. General Mounting Notes Care must be taken on TO-220 & TO-218 packages at all times to avoid strain to the mounting tab or leads. For easy insertion of the part onto the board or heat sink, avoid axial strain on the leads. Carefully measure holes for the mounting tab and the leads, and do any forming of the form operations. Rivets may be used for less demanding and more can be used on both TO-220 and TO-218 packages. Use rivet from the top side, as shown in Figure AN1004.9. An recommended. A wide selection of grip ranges Mounting and Handling of Semiconductor Devices (continued)

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