PPN0500B ABL Heatsinks

INDEX PRINT INTRODUCTION 2 The function of a heatsink is to increase the surface EQUATION 1 area available for the transfer of heat from a component or device thereby increasing the amount of Thus PD = Tj - Ta heat that can be dissipated. jc + cs + sa The following products/services are available: Where PD = Power dissipation (W) 1 A range of Standard heatsinks and accessories Tj = Max allowable junction temp (C) (specified by device manufacturer) which permit optimum flexibility in the design of Ta = Ambient temperature (C) Electrical and Electronic equipment requiring jc = Thermal resistance junction to heatsink applications. case (C/W) 2 Custom designed heatsinks. We have facilities (specified by device manufacturer) available which enable us to provide design and cs = Thermal resistance, case to manufacturing of custom and specialised heatsinks heatsink (C/W) to your requirements. sa = Thermal resistance, heatsinks to ambient air (C/W) HEATSINK SELECTION The maximum value for thermal resistance heatsink to air (sa) is usually determined by rearranging The main factors to consider when selecting a equation 1 to the following: heatsink are:- 1 Geometry EQUATION 2 2 Thermal Resistance sa = Tj - Ta 3 Cost - (jc + cs) PD Defining the necessary heatsink performance. The result of the above equation provides a thermal In order to calculate the maximum acceptable thermal resistance value which must be equalled or bettered resistance for the heatsink so that the device being by the heatsink selected. cooled does not overheat it is first necessary to define the thermal parameters under which it is to operate. EXAMPLE The basic equation for thermal equilibrium is:- Temperature difference A semi-conductor device is to be operated with its across the system junction temperature not exceeding 80C whilst dissi- Power dissipated = pating 16 watts to ambient air at a temperature of40C. Sum of all the thermal The thermal resistance, junction to case, is specified resistance in the heat by the manufacturer as 1.25C/W and the thermal flow path. resistance, case to sink (using an insulating washer and thermally conductive compound) is taken as 0.50C/W. Thermal Performance of any heatsink is influenced by sa = 80 - 40 - (1.25 + 0.50) many factors and for this reason all performance fig- 16 ures quoted should be treated as indicative only. It is recommended that the effectiveness of any heatsink is = 0.75C/W tested in the specific operating environment in which The heatsink therefore must have a thermal resistance it will be subjected. which does not exceed 0.75C/W.INDEX PRINT GENERAL INFORMATION 3 MATERIAL INSTALLATION NOTCHES For heatsink lengths up to 87.5mm one single notch in Aluminium Alloy to BS1474 6063, T6. each flange centrally along its length. DIMENSIONS Profile Tolerances: All profile dimensions are toleranced within BS1474 and this should be taken into consideration when designing our profiles into your equipment. Further details of specific tolerances can be supplied if required. C L Length Tolerances: +/- 0.4mm For heatsink lengths from 88mm to 150mm three Tighter Tolerances can be offered if required. notches in each flange 38mm apart. SURFACE FINISH 38 38 Plain Wet spray painted Matt black anodised Clear anodised Alocromed Coloured anodised Powder Coated C L HOLE PATTERNS Standard hole patterns for popular devices STANDARD NOTCH DIMENSIONS TO3/TO66/TO220 etc. Non standard hole patterns to customers own requirements. 6.4 PERFORMANCE 6.4 Performance figures given are for natural convection operating conditions and are for a 60C temperature rise with a centrally mounted heat source and vertically FULL RADIUS mounted fins. Under general operating conditions the thermal mounting arrangement of devices is not known and therefore the figures should be used only as a STUDS AND SOLDERABLE PINS guide to heatsink selection. Some heatsinks have standard solderable pins for flow It is recommended that the effectiveness of any soldering to circuit boards. Non standard pins and heatsink is confirmed in the specific operating studs can also be fitted. environment in which it will be subjected SAFETY CLIPS In some circumstances exposed heatsink surfaces A full range of standard clips are available from stock. may become very hot. Contact with these surfaces may cause burns damage to skin.