As the LED heat escalates, several key characteristics may become apparent, which demonstrate the importance of LED thermal management. The forward voltage will begin to decrease. The decreasing voltage can impose an increased load on related LED driver components causing their temperature to increase as well.

In resistor driven circuits, the forward current will increase. As the LED lights temperature continues to rise, the optical wavelength can shift. The increasing wavelength can cause orange LED lights to appear red or even white LED lights to appear bluish. This color shift typically intensifies with the AlInGaP technologies (red, orange, amber, and yellow). In addition, a thermally stressed LED lights will loose efficiency and light output will diminish. If the LED thermal management continues to race out of control, the LED junction may break down causing a state of complete thermal failure.

Thermal failure is the total loss of electronic function due to melting, partial vaporization of the component, thermal fracture of a support or separation between the leads. Thermal issues can also result in joint stresses and hot spots on your board.

Thermal management techniques must focus on effectively dissipating heat generated by high-power designs, providing high thermal conductivity, and on maintaining low coefficients of thermal expansion (CTE), while managing CTE mismatches between LED’s, components, their interconnects and the PCB.

Manufacturers of LED’s and IC components use a variety of packaging chips and often times the components may have a lower CTE than the standard PCB. This results in a thermal mismatch between the device and the PCB. The environment in which your PCB is to be operating can affect performance as well. For every 20°C rise in component temperature, the failure rate doubles.

All VCC proprietary products use UL rated (94-V0) material to protect against melting on the board during the reflow and/or wave soldering processes eliminating some of these concerns for the engineer.

While LED chipmakers are doing their part to improve thermal management for their devices, the design engineer must take heat dissipation into consideration as well, from using applicable board materials (like the UL rated (94-V0)) to paying special attention to mounting holes.  The use standoffs and different connection techniques will be integral in obtaining proper airflow to assist heat dissipation. Check out our selection here.

New patents are being issued as the industry continues to develop a variety of new LED thermal management materials and techniques. There are several prominent developments that are in the tool kit of seasoned PCB designers and engineers.

There are proven techniques such as copper thieving, increasing trace thickness, and using the mounting holes to dissipate heat.  Newer techniques and developments include using thermal modeling software, new heat sink material, high conductivity carbon composite board layers, special casing materials, and edge plating. Below I’d like to cover the latest developments in the area of heat sinks, which have historically served as the workhorse for thermal management in PCB design.

Heat Sink Developments

Heat sinks help keep LED components at temperatures below their specified maximum operating temperature. There are many different designs and various ways of optimizing heat sinks.

Over time, the technology has progressed with the use of new materials like carbon fiber and boron nitride. These materials are implemented into multi-layer PCBs to efficiently move heat from one fiber ply to the next. Due to their high cost, however, these materials will likely find limited use in future PCB fabrication and may not replace aluminum heat sinks in many LED applications.

Fin-based aluminum or copper heat sinks retain greater acceptance in many LED applications due to their low cost and ideal thermal dissipation characteristics. Aluminum has a highly acceptable thermal conductivity, while copper is about twice as high. Aluminum heat sinks are inexpensive; copper ones cost more and weigh more. Consequently, aluminum is chosen for most cost-effective applications, and copper is used in selected ones where performance reigns over cost.

Finally, while most heat sinks are finned to provide a simple way of increasing surface area for heat radiation and conduction. Newly developed special aluminum fin material is reported to be 15 percent more conductive than fin material used in previous heat sinks.  These current developments are sure to become as essential as the heat sink device itself.

1W High Power LED on Star Board

After enjoying initial success with our through-hole LED offering, VCC is moving forward with its surface-mount LED line. The introduction of the surface-mount line rounds out VCC’s ability to be a true single-source solution for LED needs. Whether its the LED, a light pipe, or any other of the many VCC mounting components, we are now a one-stop shop for our customers.

Standard package sizes will include 0402, 0603, 0805, 1206, and PLCC2. Additionally, VCC will be offering a line of high power SMD LED solutions. These include .5W, 1W, and 3W products. Custom design solutions are also available. LEDs will be available in early October.

All of the VCC LED specification sheets are currently available at the VCC website.