The present invention provides a non-halogen polyamide-imide resin soluble in an amide solvent at a concentration of 10%, the resulting varnish, when stored at 5°C for 1 month, exhibiting a solution viscosity change ((solution viscosity after 1 month - initial solution viscosity) / initial solution viscosity), expressed as an absolute value, of not greater than 3.0, and the resin having a moisture absorption (25°C, 90% RH, 24 hours) of not greater than 2.0%; a flexible metal-clad laminates using such a resin; and a flexible printed wiring board prepared from such a flexible metal-clad laminate by circuit formation. The flexible metal-clad laminate of the invention does not curl under any conditions, including humid conditions, and exhibits excellent dimensional stability since the heat resistant resin used as an insulation material has low moisture absorption and low thermal expansion coefficient and there is less internal stress in the flexible metal-clad laminate. Moreover, since the solder heat resistance and the insulation properties are not impaired even after humidification and since the heat resistant resin is soluble in organic solvents with high solution stability, the flexible metal-clad laminate of the invention can be inexpensively produced.
                            本发明提供了一种非卤素聚酰胺-
酰亚胺树脂,可溶于浓度为10%的酰胺溶剂中,所得清漆在5℃下存放1个月后,溶液粘度变化((1个月后的溶液粘度-初始溶液粘度)/初始溶液粘度)(以绝对值表示)不大于3.0,且该
树脂的吸湿性(25°C,90% RH,24 小时)不大于 2.0%;使用这种
树脂的柔性
金属覆层板;以及由这种柔性
金属覆层板通过电路形成制备的柔性印刷线路板。由于用作绝缘材料的耐热
树脂具有低吸湿性和低热膨胀系数,而且柔性
金属覆层板的内应力较小,因此本发明的柔性
金属覆层板在任何条件下(包括
潮湿条件)都不会卷曲,并具有出色的尺寸稳定性。此外,由于即使在加湿后焊料的耐热性和绝缘性能也不会受到影响,而且耐热
树脂可溶于有机溶剂,溶液稳定性高,因此本发明的柔性
金属覆层板的生产成本低廉。