Polyamic acid varnish composition and a flexible printed board

A flexible printed board comprising a polyimide insulating layer furnished on a metal foil, the polyimide insulating layer being formed by forming a film of a polyamic acid varnish composition on the metal foil, and subsequently imidizing the polyamic acid varnish composition;

• wherein:
• the polyamic acid varnish composition comprises a polyamic acid obtained by addition polymerization of an aromatic diamine and an aromatic acid dianhydride, a solvent, and an imidazolyl-diaminoazine;
• the imidazolyl-diaminoazine is present at a ratio of 0.1 to 10 wt parts per 100 wt parts polyamic acid;
• and
• the imidazolyl-diaminoazine is selected from the group consisting of:
• 2,4-diamino-6-(2-(2-ethyl-1-imidazolyl)ethyl)-s-triazine;
• 2,4-diamino-6-(2-(2-imidazolyl)ethyl)-s-triazine;
• 2,4-diamino-6-(2-(1-imidazolyl)ethyl)-s-triazine;
• 2,4-diamino-6-(2-ethyl-4-imidazolyl)-s-triazine;
• 2,4-diamino-6-(2-(4-methyl-1-imidazolyl)ethyl)-s-triazine;
• 2,4-diamino-6-(2-ethyl-5-methyl-4-imidazolyl)-s-triazine;
• 2,4 -diamino-6-(4-ethyl-2-methyl-1-imidazolyl)-s-triazine;
• 2,4-diamino-6-(3-(2-methyl-1-imidazolyl)propyl)-s-triazine;
• 2,4-diamino-6-(4-(2-imidazolyl)butyl)-s-triazine;
• 2,4-diamino-6-(2-(2-methyl-1-imidazolyl)propyl)-s-triazine;
• 2,4-diamino-6-(1-methyl-2-(2-methyl-1-imidazolyl)ethyl)-s-triazine;
• 2,4-diamino-6-(2-(2,5-dimethyl-1-imidazolyl)ethyl)-s-triazine;
• and
• 2,4-diamino-6-(2-(2,4-dimethyl-1-imidazolyl)ethyl)-s-triazine.