Help Point Basics

呜呼哀哉

Help Point Basics [Copy link]

 

邀请：@maychang   @chunyang   @qwqwqw2088   @gmchen   参与回复

Dear forum friends, could you please tell me the relationship between the temperature coefficients of resistors made of different materials and with different processes (carbon film, metal film, alloy, etc., welcome to list).

I checked Guangjie's chip resistors and found that the best temperature coefficient for low resistance (<100mΩ) is ±25ppm.

There is a leadless resistor similar to the LL40 package. The resistors above 10Ω have a 5ppm value, but those below 10Ω have a 25ppm value.

In addition, resistors only have rated power, but no thermal resistance. Is there any way to estimate the temperature rise of a 2512 packaged 1W rated chip resistor at a power of 100mW?

maychang

Let’s talk about the temperature coefficient of resistance first.

The temperature coefficients of pure metals such as copper and silver are all positive, and are close to 4 thousandths per degree Celsius change, which is relatively large.

Among the alloys, manganese copper has the smallest temperature coefficient, and the temperature coefficient of some grades of manganese copper is almost zero.

The carbon film resistance temperature coefficient is positive, but relatively small. The metal film resistance temperature coefficient depends on the alloy composition of the film.

The temperature coefficient of some precision metal film resistors is quite small. The process is to steam a double layer of film, one layer has a positive temperature coefficient and the other layer has a negative temperature coefficient. The two layers cancel each other out, so the temperature coefficient can be very small within a certain temperature range.

chunyang

Generally speaking, the temperature coefficient of resistors is better for metal film and metal oxide film than for carbon film. However, the SMD era is different from the past, so you can only check the manual to confirm. Generally speaking, the higher the precision level, the lower the temperature coefficient of resistors. If you need a special low temperature drift resistor, you may consider choosing a special resistor with pins, which is easier to find.

chunyang

Thermal resistance has nothing to do with the resistance value of the resistor, but only with the package and the specific application environment. To estimate, you can first check the thermal resistance corresponding to the package or estimate the thermal resistance based on packages of similar size.

呜呼哀哉

chunyang posted on 2023-7-17 16:36 Thermal resistance has nothing to do with the resistance value of the resistor, but only with the package and the specific application environment. To estimate, you can first check the thermal resistance corresponding to the package or based on the package of similar size...

Moderator, for resistors like 0805, 1206, and 2512, the data sheets only give the rated power and voltage related parameters, but there is no such thing as thermal resistance. I have searched many large passive component manufacturers but could not find it.

Do you have any ideas about the temperature coefficient of resistance?

The temperature coefficient of resistor is usually defined and calculated at 25℃-125℃. Is this temperature coefficient linear in this temperature range?

chunyang

Alas, published on 2023-7-17 16:57 Moderator, for resistors like 0805, 1206, 2512, the data sheet only gives the rated power and voltage related parameters, and there is no such thing as thermal resistance. Translate...

As mentioned in the previous post, thermal resistance is determined by the package size and the application environment. It is not a parameter of the resistor itself, so it is normal not to mark it.

The temperature coefficient of a resistor is determined by the material it is made of. As mentioned in the previous post, in the era of surface mount, you could only read the device manual because it was impossible to identify and distinguish the manufacturing material of the resistor by appearance.

The temperature variation curve of conventional resistors can be considered linear.

呜呼哀哉

chunyang posted on 2023-7-17 18:10 As mentioned in the previous post, thermal resistance is determined by the package size and the application environment, not the parameters of the resistor itself, so it is normal not to mark it. The temperature coefficient of the resistor...

OK, thank you. If the temperature coefficient is linear (only one value), I am considering whether to actually test the thermal resistance of a specific package resistor under specific layout, copper plating, and board size conditions.

qwqwqw2088

There is no thermal resistance for chip resistors

However, the temperature change under rated power is not uniform in the manuals or statements of different resistor manufacturers, so we can only make reference to it.

The following is the chip resistor related to the Hosei official website

Operating temperature range: -65℃~+170℃.
When the terminal temperature is higher than 70℃, the rated power must be derated according to the curve in the table below.

qwqwqw2088

Below is the specification of the 1W package 2512 of Housheng with ±100ppm/℃ accuracy of ±0.5%, ±1%, ±2%, ±5% and resistance of 10Ω＜R≤10MΩ. You can refer to it.

厚生贴片电阻手册1W.pdf (1000.18 KB, downloads: 1)

2023-7-17 21:08 上传

点击文件名下载附件

There is also the data sheet of the chip resistors on Shunhai's official website. It may not be the specifications mentioned by the OP. It is in Japanese, but the temperature characteristics can be referred to

贴片电阻数据手册.pdf (149.66 KB, downloads: 2)

2023-7-17 21:13 上传

点击文件名下载附件

吾妻思萌

It is best to get the material and ask the manufacturer's application engineer in detail. Each manufacturer will have such parameters.

呜呼哀哉

qwqwqw2088 posted on 2023-7-17 21:13 Below is the ±100ppm/℃ accuracy of Housheng 1W package 2512 ±0.5%,±1%,±2%,&pl ...

Thanks to the moderator, I will study it carefully, the moderator is really enthusiastic.

chunyang

Alas, posted on 2023-7-17 18:37 OK, thank you. If the temperature coefficient is linear (only one value), I am considering whether to actually test the specific layout, copper coating, and board size conditions...

As mentioned in the previous post, the thermal resistance here needs to be considered as a whole. It is not meaningful to pursue the thermal resistance of the package itself. In actual thermal design, the thermal resistance of the resistor package itself can be ignored, that is, it is considered to be zero. The heat generated by the resistor is ohmic heat, which can be directly calculated. Considering the thermal resistance of the system, the temperature rise of the resistor can be calculated.

呜呼哀哉

chunyang posted on 2023-7-19 18:56 As mentioned in the previous post, the thermal resistance here needs to be considered as a whole. It is not meaningful to pursue the thermal resistance of the package itself. In actual thermal design, the thermal resistance of the resistor package itself can be...

The moderator is right. After all, the resistor has pads at both ends, ceramic in the middle, a resistor on the ceramic, and a film on top. It is indeed unlike an IC package. The thermal resistance can be regarded as 0℃/W.

led2015

1. Carbon film resistor: The temperature coefficient is usually around ±100ppm/℃.
2. Metal film resistor: The temperature coefficient is usually around ±50ppm/℃.
3. Metal foil resistor: The temperature coefficient is usually around ±15ppm/℃.
4. Alloy resistors (such as Manganin, Constantan): The temperature coefficient is usually around ±20ppm/℃.
5. Thin film resistors (such as Vishay Foil Resistors): The temperature coefficient can be as low as ±0.5ppm/℃ or even lower.

史蒂芬

呜呼哀哉

Stephen posted on 2023-7-27 15:47

What is this? The temperature coefficient is even worse, and you didn't explain the question clearly, brother.