So, that leads us into temperature ranges. Depending on the market that your product is deployed or accepted, or specified thermal ranges for devices. In the US, a full military ranges from -55 C to +125. Automotive is a little more relaxed from -40 to +125. This is a variation on the automotive AEC-Q100. I hadn't heard that one until I went off and do a little research on this and came across this lists as a couple links to sites. One is Altera and this other one called maximumintegrated.com where this misinformation came from. There's an extended industrial range from -40 to +125 C. There's the industrial temperature range which operates from -40 to +85 C, and then there's a commercial ranges generally in the range of 0 C to +85 C. So, I'm going to talk about, now that you're aware that there's these ranges, when we talked about thermal stressing, the importance of thermal stressing, a product before you go into production because you want to find if failures that are susceptible to thermal stressing before your customers, so it's important to put your product into a thermal chamber and run the cycle on the temperature up and down some number of times and at a certain rate also. At C in our specifications where I work, I never saw this when I worked at Seagate, but there was how many degrees C per minute or per second, the ambient temperature could change. So, they're concerned about that, it could changes too quickly can cause excessive thermal stressing to a component or a device, whatever your testing in the thermal chamber. I want to introduce you to this notion of thermal gradients. So, here's a cartoon picture of product that I made and we're looking at it from the side. So, on the outside is a case, it could be plastic, it could be metal in case of drives are generally metal, aluminum, machined aluminum, or some kind of cast material, and here's our printed circuit board, and here's our package flip chip from the previous slide. Temperature starts out here at the ambient and this assumes there's an airflow that factors into this calculation as well. So, the more airflow you get, more heat you can pump away but I'm not going to focus on the airflow component, just imagine this is a still air environment. So, the ambient might be 85 degrees C, so that means the case is at 85 degrees C. So, working outward from the chip, the chip isn't capsulated in some package. Sometimes there's thermal or what we called heat spreaders, sometimes this chip will be moved up to the surface is the backside of the dye on the chip, is right at the surface level, it's actually exposed. We did this at Seagate all the time because it was the best way to get the heat out and get it to the case. But not all packages are like that, so here's our chip at the top of the chip, it's common to put what's called TIM stands for Thermal Interface Material because you want to conduct that heat away, you want to get it out to the case where the system may have, may or may not have fans, but when you want to get the heat out. So, there's a thermal gradient across the TIM, show here, and then there is a thermal gradient from the TIM material to the dye, and there's a number we use called the thermal resistance which is measured in degrees C per watt. So, you find out what your Theta-ja is for your package. So, that gets you from the junction temperature of the silicon to the ambient which is at the surface of the package and then there would be another Theta-ja to get from the top of the package across the TIM material to the case. So, in this cartoon example, I put together here the ambients at 85, and when the device is operating, you might see silicon junction temperatures at 115 degrees C. Let's be aware that there's this thermal gradient at play in products. I didn't learn any of this when I was in college. No one ever talked about this. I learned all about these thermal gradients and dealing with them on the job. Like "What? What is Theta-ja?" And someone had to tell me.
