Avionics box design is not quite as difficult for designers as trying to fit a square peg into a round hole. It does, however, often seem impossible, with the amount of electronics, connectors, etc. being forced into small volumes. This is especially true on military aircraft, where space and weight are at a premium, while functionality and output capability requirements are continuously increasing.
By the end of the design process, avionics boxes are packed so tightly that there is virtually no room inside the sealed chassis for thermal solutions. For designers to accomplish integrating the required number of components, high cost electronics are strategically placed on boards, so that when each board is stacked in the chassis, there are minimal gaps. This allows more boards to be stacked into the same volume. Unfortunately, this optimized packaging is counter-intuitive to overall thermal management, as with the amount of waste heat the designers packed into their avionics box design, there is almost no room for heat spreaders. In many cases, this leads to the heat spreaders being thinned down to less than 1 mm in most areas, to accommodate the tight packaging demands.
Watch the arguments begin! Thermal engineers will run simulations and let the team know that they are going to fry all the high cost electronics in the box. They’ll provide options such as increasing the board thickness, changing the material to copper, adding enhanced conduction features such as heat pipes, or de-rate the electronics. After (what I’m sure is significant) consideration, the mechanical team will come back with; no- not enough space, no- too heavy, no- not enough height and no- the customer needs continuous function. Often times this debate ends in compromise where nobody, including the end user, is fully pleased, all while adding months to the design cycle.
We’ve run into this situation many times when working with customers designing compact avionics boxes. Analyzing the entire thermal resistance network in these embedded designs is key. In certain cases, you can stick with the thin frame heat spreader and gain thermal efficiency downstream. Now, if the thermal simulations show that you need to gain 50 degrees, you’ll likely need to compromise. However, if you need to pick up a couple degrees to assure all power can be safely dissipated, the ICE-Lok™ has come to the rescue time and time again. This thermal enhancement is a drop-in replacement for what most avionics boxes are already using to mechanically join the board to the chassis. The ICE-Lok™, compared to the traditional wedgelocks, provides additional surface contact and heat paths, which can reduce the temperature rise across this interface by over 5 degrees C (for 100 W of power). It requires very few modifications to the board or chassis design, which is always an important factor when you’re in a crunch and your design time is about to run out. Next time you’re attempting to fit too much, into too little space, consider the ICE-Lok™.