What are heat sink ?

 

What are heat sink?

Welcome and today we are going to be talking about heat sinks. In short, heat sinks provide an efficient path for heat to be transferred from an electronic device to ambient air.

They do this by increasing the surface area in contact with the air, providing more area for the hot device to transfer energy to the cooler air around it.

Some of the most commonly recognized heat sinks are board level and BGA versions like the examples I have here. The concepts behind heat sinks are incredibly straight forward, and their usage is not too much more complicated.

How to select heat sink?

Let’s jump right into it and talk about what to consider when deciding whether you even need a heat sink, and how to size your heat sink if you do.

There will be some math required to do this but only basic addition and multiplication, so nothing to worry about.

Let’s work through the process using an example and assume we use a T0-220. These through-hole packages are often used in power electronics for 3 terminal devices such as transistors.

What is T0-220?

The T0-220 has the silicon device encapsulated but with a metal baseplate, here, that is sometimes used for ground connections and also provides an excellent point on which to mount a heat sink.

It should say in the data sheet exactly how the metal plate is connected electrically, which I highly recommend you look into.

A critical portion of these calculations is thermal impedance. Thermal impedance is just the measure of how easily heat can transfer from one point to another. The lower the number, the easier heat is transferred.

How many degrees warmer?

This is typically measured in degrees Celsius per watt, which tells us how many degrees warmer, in Celsius, a junction will get, per watt of power dissipated.

With each device, you should have access to a data sheet that will provide you the value of the different thermal impedance between junctions. Without a heat sink, the junction between a T0-220 device and ambient air can be upwards of 70 degrees Celsius per watt.

For Example:

For our example, we’ll assume that our package has a junction-to-ambient thermal impedance of 55. Again, this means that the junction temperature will increase 55 degrees above ambient temperature. For every watt of power dissipated. Let’s establish the rest of the assumptions and then do the math.

We’ll arbitrarily say we need to dissipate 2.42 watts, our ambient temperature will be no greater than 60 degrees Celsius, and we need to keep the silicon below 125 degrees Celsius.

Now, those numbers are all we need to find out if our T0-220 device will get too hot without a heat sink.

We simply multiply the watts dissipated by our thermal impedance, or 2.42 watts by 55, which gives us 133.1 degrees. Add that to our ambient temperature of 60 degrees, and we get 193.1 degrees Celsius, well above the required 125 degrees. So, that isn’t going to work.

Now, using that same math in a different direction, we can figure out how much we need to drop. The thermal impedance path to keep us in safer temperatures. So, let’s go backwards.

We can have no greater than a 65-degree rise, and, in this sample, we can’t drop the power requirements.

So, a 65-degree rise divided by 2.42 gives us 26.9 degrees Celsius per watt. Now, we will round that down to 26 to give us a little cushion and give us less decimal. Points to worry about.

The addition of a heat sink:

Unfortunately, the addition of a heat sink complicates things because there are now more junctions to worry about.

Fortunately, it only requires some addition to add the impedance together.

Instead of just worrying about the device-to-air junction, we need to know the silicon-to-case. Junction impedance, case-to-heatsink junction, and finally the heatsink-to-ambient air. The silicon-to-case junction impedance will be provided by your device data sheet.

It’s typically between 0.5 degrees per watt up to 4 degrees per watt. Let’s say 0.5 degrees Celsius per watt for our example.

The case-to-heatsink impedance will be based on the thermal interface material or TIM, which is the typically gray paste that smooths the very small imperfections in a surface.

So that the tab on the package and the heat sink have optimal surface area contact. This is dependent on both the thickness of the TIM and the surface area of the contact. On this, we’ll just skip the details and assume the TIM thermal impedance is 0.5 degrees per watt.

Finally, the heatsink-to-air thermal impedance will also be found in the data sheet, which for this sample, we find that this heat sink with no fan blowing air over it, is 14.36.

Now we have the thermal impedance of all three junctions, which we can now add together. The sum of these items is 0.5 + 0.5 + 14.36 which gives us 15.36 and is well under our maximum value of 26 required.

Looking at these results, we could either choose a smaller heat sink or leave it alone. It is good practice to leave some headroom, so you don’t approach your temperature limit, if at all possible.

Just a quick calculation of the performance we should expect with 15.36 degrees Celsius per watt, you would get 2.42 times 15.36 degrees per watt to see a temperature increase of 37.2 degrees over ambient, which as a reminder is 60 degrees.

So, if our assumptions all hold up, we should never go over 97.2 degrees Celsius. You can see how the addition of the heat sink significantly drops the thermal impedance. And keeps the device much cooler, well below the 125-degree threshold mentioned earlier.

Heat sinks can be the difference between failure and success and if you don’t need a heat sink, don’t just make that assumption.

Running the numbers on whether you need a heat sink is a straight forward process whose most time-consuming step is finding those values from data sheets, and you will. Greatly increase your peace of mind if you do the calculations.

Why do led fittings require heat dissipation?

Which are a really quality product that we had the privilege of seeing being made over in Italy soothe light fittings all seem to have this kind of fin shaped structures on the back of them and in fact for most large LED light fittings you'll see some kind of similar molding on the back now these are not simply are designed to make the fitting look as futuristic as possible.

Important functional purpose:

They actually serve an important functional purpose and that is that they act as cooling fins for heat dissipation the fin-like structures give the fitting a larger surface area which allows for the heat generated by the LEDs to dissipate more quickly.

Why is it so essential to do?

So well for one thing while LEDs are way more efficient than any other form of artificial lighting they still generate heat as part of their natural operation and this heat isn't in the form of infrared like incandescent sources.

but rather the heat builds up inside the LED itself, and it's this internal heat that needs to be managed because if the heat inside the LED gets too high it won't necessarily make the LED fail completely but rather it will significantly change the output characteristics of the fitting lowering the lumens that it delivers very quickly and drastically reducing the lifespan of the fitting as a whole the key to minimizing this effect is removing the heat from inside the LED and dissipating it as effectively as possible.

The best way to extract that heat is by using conduction so mounting the LEDs onto a material that's thermally conductive and then making the surface area of that material as large as possible this is normally achieved by creating the thin lite structures that we mentioned earlier that then allows air moving across the surface to pick up.

The heat and remove it from the vetting via. Convection so there we go that's the reason why led fittings require heat dissipation but as always we want to hear from you would do you think of led lighting do you look back wistfully on the days of incandescent lighting or are you a certified lead head.

Way to dissipate high heat loads in a sealed environment:

This is our best-selling option as the sleek side mounted design can be coupled to any outside surface creating a NEA tight seal that keeps your electronics not only cool but safe from the external environment.

The efficient heat transfer is achieved by having air circulate throughout the cabinet to collect waste heat at an internal heat sink conducting that heat through the mounting plate and rejecting that heat with a mirrored external heat sink fan assembly the seal plus efficient heat transfer provides a reliable solution that keeps your electronics cool and your cabinet clean.

The HSC includes three power capacity:

Ratings and multiple NEA ratings including the 4x option with corrosion resistant e-coated fins and aircraft quality aluminum with fans rated for over a hundred thousand hours of operation this product offers the best in class combination of price maintenance-free operation and performance need a quick solution this product can be ordered online and deliver within two weeks.

The distance between the heat gun and the heat sink is kept at one centimeter after heating it for 10 seconds remove the heat sink after heating the back side for 10 seconds remove it with force heat the chip and remove it after about 10 seconds.