AB136 datasheet(13/22 Pages) LUMILEDS

13 / 22 page

Figure 12. Top diagram shows spillover of thermal adhesive to the top of the package.

Bottom diagram shows good amount of thermal adhesive coverage to secure the TC wire.

4.3 Effect of Placing T

s point Further Away from LED Package

As described in 4.2, one of the factors that can affect the T

s measurement is its location. Ideally the most accurate method

to determine T

j is by placing the TC wire directly underneath the center of the thermal pad and then using the typical LED

package thermal resistance, which is widely quoted published in any an LED datasheet, to calculate the T

Such measurements are difficult to make in real life situation, so the next best step is to place the TC wire as close as

possible to the thermal pad.

Figure 13 shows a representative thermal simulation of a LED emitter package. This simulation highlights the impact

of the calculated Rq

j-s if the Ts points are located at two different locations (Ts1 and Ts2). To characterize Rqj-s , Lumileds

selected T

s1 location since this is the closest to the LED package thermal pad when it comes to actual placement of TC wire.

Once the Rq

j-s value is known at location Ts1, if the actual TC wire is then misplaced at location Ts2, the calculated junction

temperature, T

j will be under-estimated.

Figure 13. Representative of thermal simulation of a typical LED package mounted on MCPCB,

showing the contour temperature on one cross section through the LED package.

AB136 Datasheet(PDF) 13 Page - Lumileds Lighting Company