p lessey | tamerton road | roborough | plymouth | devon | pl 6 7bq phone: +44 1752 693000 fax: +44 1752 693200 web: www.plesseysemi.com datasheet no 292552 issue 1 page 1 of 3 magic led PLW114050 series application note thermal management solid-state light emitting diodes (led) are highly efficient and reliable when compared with traditional light source technologies . their long-term reliability performance depends highly on maintaining the opera ting conditions within the datasheet recommendations. although today leds are very efficient, a considerable amount of the electrical input power is still not c onverted into light but simply lost and transformed into heat. unfortunately, the heat gen erated inside the led impacts negatively on its performance and in extreme cases can even cause catastrophic failure. the leds are designed to dissipate heat e fficiently but users need to make sure the leds are operating within specification. the performance of plessey led is characterized versus its junction temperature tj . the junction temperature can not be measured directly and therefore it is calculated using equation (1) below; t j = t a + (r ? j-sp + r ? sp-hs + r ? hs-a ) * (v f * i f ? w op ) (1) where, t j is the junction temperature in degrees celsius (c ) t a is the ambient temperature (c) r ? j-sp is the thermal resistance between junction and sol der point (c/w) r ? sp-hs is the thermal resistance of the pcb heat sink (c/ w) r ? hs-a is the thermal resistance between pcb heat sink an d ambient (c/w) i f is the forward current and v f is forward voltage. w op is the optical radiant power (w). therefore, a good thermal dissipation design consis ts of minimizing both thermal resistances r ? sp-hs and r ? hs-a achieved by optimising the heat conduction path.
p lessey | tamerton road | roborough | plymouth | devon | pl 6 7bq phone: +44 1752 693000 fax: +44 1752 693200 web: www.plesseysemi.com datasheet no 292552 issue 1 page 2 of 3 handling precautions compared to epoxy encapsulate that is hard and brit tle, silicone is softer and flexible. although its characteristic significantly reduces t hermal stress, it is more susceptible to damage by external mechanical force. as a resul t, special handling precautions need to be observed during assembly using silicon e ncapsulated led products, failure to comply might lead to damage and prematur e failure of the led. 1. handle the component along the side surface by u sing forceps or appropriate tools; do not directly touch or handle the silicone lens surface; it may damage the internal bond wire. 2. the outer diameter of the smd pickup nozzle shou ld not exceed the size of the led to prevent air leaks. the inner diameter of th e nozzle should be as large as possible. the nozzle should preferably be made of soft and elastic material to prevent scratching or damaging the led surface duri ng pickup. the dimensions of the component must be accurately programmed in the pick-and-place machine to insure precise pickup and avoid damage during produ ction. electrostatic discharge and electrical overstress plessey leds are not designed to operate with rever se bias. precautions are required to prevent reverse bias in applications an d during handling. electrostatic discharge (esd) or electrical overstress (eos) may damage leds. precautions such as esd wrist straps, esd shoe straps or antist atic gloves must be worn whenever handling the leds. all devices, equipment and machinery must be properly grounded. it is recommended to perform el ectrical tests to screen out esd failures at final inspection. it is important to e liminate the possibility of electrical overstress during circuitry design.
p lessey | tamerton road | roborough | plymouth | devon | pl 6 7bq phone: +44 1752 693000 fax: +44 1752 693200 web: www.plesseysemi.com datasheet no 292552 issue 1 page 3 of 3 evaluation board fr4 evaluation boards are available on request. pl ease contact plessey sales team for further information. recommended solder-pad design for heat dissipation: note: metal (copper) area at 1 should not be less t han 50mm 2 for sufficient heat dissipation while area 2 and 3 should not be less t han 5mm 2 .
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