Using a X5R capacitor above it's rated temperature? - Page 1
Forum section: electronics / projects

author: DutchGert
author_rank: Frequent Contributor
timestamp: March 12, 2015, 07:03:56 am
content: I am wondering what will happen if I use a X5R cap (=-55 to +85 deg C) above it's rated temperature rating. Will it be damaged or will the capacitance change beyond its rated value or will something else happen?I am asking this because X5R caps are available at higher capacitances (with DC bias taken into account) in the same packages than there X7R counterparts which are rated for -55 to +125 deg C.So (aside from the question if it is bad engineering or not in my particular case) I am thinking of using some X5R caps as bulk capacitors in my design instead of X7R which we normally use for our -40 to +85 rated products.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 12, 2015, 08:59:28 am
content: The value just keeps dropping off.If you need bulk energy storage, go with something more stable like aluminum polymer or tantalum.The energy storage of any type 2 ceramic (Y5P, X5R, Z5U, etc.) is typically 2-4 times worse than C0G* of the same size, so you're already taking a hit, straight off. It doesn't matter what grade you use, you're just getting shorted in a slightly different proportion all the same.*Assuming you can get the desired value in C0G dielectric, and most of all... assuming you can afford the expensive bastards!Tim

author: DutchGert
author_rank: Frequent Contributor
timestamp: March 12, 2015, 10:26:51 am
content: I cant use a elco or tantalum because I am quite size restrained and we have a policy against tantalums.I have a 0805 (2012) footprint populated with a 10uF 6V3 X7R cap. Unfortunately this is the bare minimum in terms of decoupling so I want to change it to a 22uF 6V3 or 47uF 4V X5R cap in 0805. In terms of DC bias this is still a big win (it decouples a 1.2V supply) and since the image sensor it powers gives a crappy image anyway above ~60 deg C ambient it is not a problem if above 85 degrees the X5R capacitor decreases in capacitance quickly since the product won't give a good enough quality output anyway.Question is if it physically harms the X5R cap to be occasionally powered at a higher then rated temperature spec over time? Because if it doesn't harm it I can (in this specific case) safely use it.(ps. we are talking about AEC-Q200 specced caps here so better than 10uF 6V3 X7R is not available in 0805 (2012))

author: SeanB
author_rank: Super Contributor
timestamp: March 12, 2015, 05:15:17 pm
content: They survive soldering, so you will have some stress, but you should have a good couple of cycles to 125C before it cracks in half. Place it with a minimum of solder paste, and preferably glue it down as well. Can you not split it into 2 or more smaller capacitors instead, you probably can place them on both sides of the board so it uses no extra space.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 12, 2015, 08:44:59 pm
content: 0805 is no problem for soldering or board flex stress.At 1.2V and those temperature ranges, that sounds perfectly fine in this case.High temperatures are arguably good, as annealing the dielectric above the curie point resets aging, increasing capacitance momentarily. Of course, after a few years, it'll age down by half anyway.Tim

author: Niklas
author_rank: Frequent Contributor
timestamp: March 15, 2015, 01:06:45 am
content: AEC-Q200 and camera sounds like something that can sit in the sun and perhaps also be sealed inside a small box. At my present job we have had some bad experience of X5R rated capacitors used outside of their spec, but it seems to be related to a combination both to applied voltage and temperature.Linear voltage regulation can dissipate a lot of heat. The ambient temperature might be specified to +85'C, but what is the temperature of the capacitors?The product I referred to above can be powered either by a 13.8 or 28 V supply (one or two 12V batteries) and has a linear supply in two stages. The first stage, the pre-regulator, is down to 12 V for the 28V supply or somewhere between 9 and 10 V for a 12 V supply due to the forward voltage drop. The power dissipation is higher for the 28 V application, about 1 W compared to 0.15W for the 13.8V application, resulting in a peak temp on the PCB of about 110'C at 85'C ambient.Failed X5R capacitors are found in the next stage around the 5V and 3.3V LDOs. 1uF, 16V, 0603 at the output of the pre-regulator and they fail more often in 28 V application, i.e. with 12V applied voltage instead of 8-9 V. Exactly the same capacitor is also found on the 5V rail, but there it never fails, even at higher temperatures.At the outputs of the 5V and 3.3V LDOs there are 10uF 0805 and 47uF 1206, both in parallel and with X5R and 6.3 V rating. The capacitors on the 3.3V rail have never failed, but the 47uF cap on the 5V rail is more common to fail as a short. It is also interesting to note that the 10uF cap on the 5V rail never fails, even if the temp and voltage ratings are the same as for the 47uF. There might be a connection between package size, capacitance, voltage rating and layer thickness.One more thing to consider during the prototyping and testing: Do you know the rating of the capacitors that are mounted on the board? Lets assume that a batch of X7R capacitors fail some test but they pass the tests for X5R, then you might have close to X7R specified components with X5R rating. You might be lucky with a small prototype series and receive boards with good specifications, but what about the normal distribution for a volume production? As long as you are with specifications and follow the recommended derating everything is safe, but when the first field claims occur and you must write 8D reports...