A resin film for mainly making a flexible printed circuit board and a method of making the film. When a copper foil (2) is etched in a specified pattern after heat-bonded to a resin film (1) in order to make a flexible printed circuit board, said board undergoes a dimensional variation. For the purpose of reducing such dimensional variation, a ration (a/b) of a linear expansion coefficient (a) of the resin film (1) in the mechanical feeding direction (MD direction) to that (b) in the direction (TD direction) perpendicular to said mechanical feeding one is set at 0.2 or more but less than 1.0, and the linear expansion coefficient in said mechanical feeding direction (MD direction) is set at 0.4 to 2.0 x 10⁻⁵°C⁻¹. As a resin film, a polyimide film including 90 % or more of identity period represented by a specified general formula is used. Further, for making said resin film, the film (1) is stretched 1.0 to 1.5 times in the mechanical feeding direction (MD direction) and 0.5 to 0.99 times in the direction (TD direction) perpendicular to the mechanical direction.
一种主要用于制作柔性印刷电路板的
树脂薄膜及其制作方法。当
铜箔(2)与
树脂薄膜(1)热粘合后按特定图案蚀刻,以制作柔性印刷电路板时,该电路板会发生尺寸变化。为了减少这种尺寸变化,将
树脂薄膜 (1) 在机械进给方向(MD 方向)上的线膨胀系数 (a) 与在垂直于所述机械进给方向(TD 方向)上的线膨胀系数 (b) 之比 (a/b) 设置为 0.2 或以上但小于 1.0,并且将所述机械进给方向(MD 方向)上的线膨胀系数设置为 0.4 至 2.0 x 10-⁵°C-¹。作为
树脂薄膜,使用聚
酰亚胺薄膜,其中包括 90% 或更多由指定通式表示的特性期。此外,在制造所述
树脂薄膜时,薄膜(1)在机械进料方向(MD 方向)上拉伸 1.0 至 1.5 倍,在垂直于机械方向的方向(TD 方向)上拉伸 0.5 至 0.99 倍。