These novel SMT solutions pre-empt thermal issues in a unique way
Thermal management has always been an important part of design but is gaining prominence with the development of wide-band-gap semiconductors. The improved frequency and power capability of these devices are raising the average operating temperature of power conversion and amplifier circuits, thereby stressing surrounding components.
Copper-based heat pipes have great thermal conductivity but are also electrically conductive. Large ground planes and heat sinks work well but transferring heat to these devices from the source can be difficult to optimize. A novel thermal management solution is SMT heat pipes, like the Q-Bridge series from Kyocera-AVX. These are packaged in familiar EIA case sizes similar to MLCCs but are not electrically conductive and have extremely low capacitance loading. These SMT heat pipes fill a thermal management solution gap for applications needing to be smaller and lighter yet retain their performance and reliability at higher temperature operating conditions.
These SMT heat pipes are manufactured using Aluminum Nitride or Beryllium Oxide with thermal conductivities ranging from 40 to 380mW/°C and packaged in EIA case sizes from 3737 down to a miniature 0302. Capacitance values can get as low as 7 femtofarads (fF) and top out at 0.21pF, which makes them ideal for mounting directly on to transistor and IC signal pins.
Mounting follows traditional guidelines but three termination options exist for users to review different thermal conductivity and capacitance values. The varied amounts of metallization on the ceramic, cross-sectional area of the ceramic chip, and the amount of surface area contacting the heat source all contribute to these parameters. Voltage ratings are correlated to their size and range from 100 to 4000V. From reducing thermal noise in LNAs to cooling GaN transistors, their wide range of specifications make these viable for many applications encountering thermal and size design constraints.
Multiple tests were performed to quantify the improvements afforded by SMT heat pipes. The illustration shows two series resistors in parallel with a pair of Q-Bridges. The resistors were powered up until they reached 1W or until they heated up to 85°C, whichever came first. The heat pipes were mounted on the common resistor pad and the opposing terminations were connected to heat sinks. At 0.75W the uncooled resistors had already reached 85°C, while the cooled resistors only measured roughly 62°C. The cooled resistors could achieve 1W and were well below the maximum allowed component heating. A second test held the power constant at 841mW and instead compared the cooling performance of a metal heat sink against a singular SMT heat pipe. The heat sink attached to the resistor reduced heating by 17°C, while the Q-Bridge reduced heating by 45°C.
SMT heat pipes are one example of how the passive electronics industry is keeping up with active component trends. Designing high temperature capacitors, inductors, resistors, etc. to be able to withstand harsh environments is important, but it’s also relevant to know that there are devices like the Q-Bridge that are intended to pre-empt thermal issues in a unique way. Further, the availability of miniature pick-and-place-capable SMT heat pipes is a game changer. This device family can easily enable optimized end circuit performances ranging from lowered noise floors to lower operating temperature actives, thus increasing reliability.