芯片热阻影响因素
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Factors in Thermal Resistance | Renesas --- 热阻因素 | Renesas
The most important way to achieve better heat dissipation is to decrease the thermal resistance of the semiconductor device. The factors that determine thermal resistance are described in detail below.
实现更好散热的最重要方法是降低半导体器件的热阻。下面详细描述决定热阻的因素。
Thermal Resistance that can be Calculated in the Same Manner as Ohm's Law
热阻的计算方法与欧姆定律相同
Thermal design that considers heat dissipated from semiconductor devices uses the concept of "thermal resistance," based on the fact that heat transfer can be compared with the way electricity is transmitted.
考虑从半导体器件散发的热量的热设计使用 “热阻” 的概念，基于热传递可以与电的传输方式进行比较的事实。
In the case of electricity, the relationship among voltage (electric potential difference), current, and resistance is expressed by Ohm's law, as shown below. Heat resistance can be calculated using a law similar to Ohm's law by replacing voltage with temperature difference, current with heat flow, and resistance with thermal resistance.
在电的情况下，电压 (电势差) 、电流和电阻之间的关系由欧姆定律表示，如下所示。可以使用类似于欧姆定律的定律，通过将电压替换为温度差，将电流替换为热流，将电阻替换为热阻来计算热阻。
As can be seen from the above expression, thermal resistance indicates how readily heat is dissipated.
从上述表达式可以看出，热阻表示散热的容易程度。
The Four Factors that Determine the Thermal Resistance of a Package
决定封装热阻的四个因素
The overall thermal resistance of a package is almost entirely determined by:
封装的整体热阻几乎完全由以下因素决定:
Package structure 封装结构
Chip dimensions 芯片尺寸
Air flow rate 空气流量
Package size 封装尺寸
Each of these elements influences the thermal resistance as follows.
这些元素中的每一个对热阻的影响如下。
Thermal Resistance Differences According to Package Structure
根据封装结构的热阻差异
Package structure 封装结构
Packages come in various types, each with different thermal resistance characteristics (refer to the diagram above). Packages such as FCBGA, which features a copper lid to which the chip is directly attached, offer excellent thermal resistance characteristics. In the case of PBGAs, thermal resistance can be lowered by using a 4-layer substrate instead of a 2-layer substrate, and it can be further lowered by placing solder balls directly underneath the thermal via holes.
封装有各种类型，每种类型具有不同的热阻特性 (请参阅上图)。诸如FCBGA之类的封装具有直接连接芯片的铜盖，具有出色的热阻特性。在pbga的情况下，可以通过使用4层衬底代替2层衬底来降低热阻，并且可以通过将焊球直接放置在热通孔下面来进一步降低热阻。
Chip dimensions 芯片尺寸
The thermal conductivity of silicon chip is about 100 times higher than that of mold resin and about 10 times higher than that of package substrates; therefore, the chip size is a major contribution factor to the heat conductivity.
硅芯片的热导率比模制树脂高约100倍，比封装基板高约10倍; 因此，芯片尺寸是热导率的主要贡献因素。
Air flow rate 空气流量
Forced air cooling, including fan cooling, does not affect the thermal conductivity of the package but efficiently removes heat from the package surface or PWB to the atmosphere, and thus lowers overall thermal resistance.
包括风扇冷却在内的强制空气冷却不会影响封装的导热性，但会有效地将热量从封装表面或PWB转移到大气中，从而降低整体热阻。
Package size 封装尺寸
Generally, larger package is said to have a better thermal conductivity. It is true for FCBGA, which has a large copper lid offering excellent thermal conductivity over a package. But for the packages with lower thermal conductivity such as FBGAs, package sizes do not much help enhancing thermal conductivity; therefore, there is little variation in thermal resistance among different size packages if the chip dimensions are the same.
通常，较大的封装被认为具有较好的导热性。这对于FCBGA来说是正确的，其具有在封装上提供优良导热性的大铜盖。但是对于诸如fbga的具有较低热导率的封装，封装尺寸对增强热导率没有太大帮助; 因此，如果芯片尺寸相同，则在不同尺寸的封装之间热阻几乎没有变化。
