| 摘要 |
PROBLEM TO BE SOLVED: To improve quality, to simplify stages and to improve productivity by forming a single layer of a thermally fusible polyimide resin as a polyimide resin layer which is the second layer of circuit layers constituted by forming a first layer of a stainless steel layer, the second layer of the polyimide resin and a third layer of copper foil. SOLUTION: The first layer of the circuit layers is formed of the stainless steel layer 2 having a thickness of 10 to 50 μm, the second layer of the polyimide resin layer 3 having a thickness of 0.5 to 20 μm and the third layer of the circuit layer 4 made of the copper foil having a thickness of 5 to 35 μm. The polyimide layer 3 is formed of the single layer of the thermally fusible polyimide resin. If the thickness of the stainless steel layer 2 is below 10 μm, the rigidity of the stainless steel base material is small and such material is undesirable as the base material. If the thickness exceeds 50 μm, the base material is too rigid and is unsuitable as a spring. More preferably the thickness of the stainless steel layer 2 is specified to 20 to 40 μm. If the thickness of the polyimide resin 3 is below 0.5 μm the reliability at the time of long-term use is not obtainable and if the thickness exceeds 20 μm, the production is low. The thickness is preferably specified to 1 to 10 μm. |
