smic工艺算AC情况下的过电流能力中，公式里的∆T怎么求？

西瓜慧子

设计规则描述如下：
Current density rule (AC) for Cu metal layers

The below table lists the maximum Irms allowed for each of the metal lines of 1P8M (2TM)at 110℃. If designer
would like to use M7 and M8, please refer to M6 layer.
W (in µm) : the width of the metal line
∆T (℃ ): the temperature rise due to Joule heating


其中∆T 具体数值要怎么计算呢？