Film and flexible metal-clad laminate

Abstract

A film and a flexible metal-clad laminate obtained with the film. The laminate is improved in post-moisture absorption solderability. The film comprises a heat-resistant polyimide film and, disposed on at least one side thereof, an adhesive layer containing a thermoplastic polyimide. It is characterized in that the thermoplastic polyimide contained in the adhesive layer has crystallinity and that the film, when analyzed with a differential scanning calorimeter, has an endothermic peak attributable to the melting of the crystalline thermoplastic polyimide, the absolute value of the area of the peak being 4.0 mJ/mg or larger. The flexible metal-clad laminate is characterized by comprising the film and a metal layer disposed thereon.

1 . A film comprising an adhesive layer on at least one side surface of a heat-resistant polyimide film, the adhesive layer containing a thermoplastic polyimide, the thermoplastic polyimide being a crystalline thermoplastic polyimide, the film being such that an absolute value of an endothermic peak area attributed to melting of the crystalline thermoplastic polyimide is 4.0 mJ/mg or higher, the endothermic peak area being measured by performing a differential scanning calorimetry on the film. 
     
     
         2 . The film according to  claim 1 , wherein an absolute value of an exothermic peak area attributed to recrystallization of the crystalline thermoplastic polyimide is 4.0 mJ/mg or lower, the exothermic peak area being measured by performing the differential scanning calorimetry on the film. 
     
     
         3 . The film according to  claim 1 , wherein the thermoplastic polyimide has a melting point within a range of 340° C. to 450° C. 
     
     
         4 . The film according to  claim 1 , wherein a water absorption coefficient of the heat-resistant polyimide film is 1.5% or lower. 
     
     
         5 . The film according to  claim 1 , wherein the crystalline thermoplastic polyimide is obtainable by imidizing a polyamic acid composed from a combination of a diamine component and a dianhydride component, the diamine component being selected from the group consisting of 1,4-bis(4-aminophenoxy)benzene; 1,3-bis(4-aminophenoxy)benzene; 4,4′-bis(3-aminophenoxy)biphenyl; 4,4′-bis(4-aminophenoxy)biphenyl; 1,4-diaminobenzene; and 3,4′-diaminodiphenyl ether, the dianhydride component being selected from the group consisting of pyromellitic dianhydride; 3,3′,4,4′-biphenyl tetra carboxylic dianhydride; and 3,3′,4,4′-benzophenone tetra carboxylic dianhydride. 
     
     
         6 . The film according to  claim 1 , wherein the crystalline thermoplastic polyimide is contained in an amount of 85 wt % to 100 wt % with respect to the thermoplastic polyimide contained in the adhesive layer. 
     
     
         7 . The film according to  claim 1 , wherein the crystalline thermoplastic polyimide is obtainable by imidizing a polyamic acid obtained through the following steps (a) to (c):
 (a) a step for obtaining a prepolymer having an amino group or an acid anhydride group at both ends by reacting an aromatic diamine with an aromatic dianhydride in an organic polar solvent under a condition where the aromatic diamine or the aromatic dianhydride is contained in excess;   (b) a step for further adding (i) an aromatic diamine having a different structure from the aromatic diamine used in (a) or (ii) an aromatic dianhydride having a different structure from the aromatic dianhydride used in (a); and   (c) a step for further adding (i) the aromatic diamine having the different structure from the aromatic diamine used in (a) or (ii) the aromatic dianhydride having the different structure from the aromatic dianhydride used in (a) so that the aromatic diamine and the aromatic dianhydride are contained in a substantially equimolar amount throughout all steps and then performing polymerization.   
     
     
         8 . The film according to  claim 7 , wherein the crystalline thermoplastic polyimide is obtainable by imidizing a polyamic acid obtained through the following steps (a) to (c):
 (a) a step for obtaining a prepolymer having amino groups at both ends by reacting the aromatic diamine with the aromatic dianhydride in the organic polar solvent under a condition where the aromatic diamine is contained in excess;   (b) a step for further adding the aromatic diamine having a different structure from the aromatic diamine used in (a); and   (c) a step for further adding the aromatic dianhydride having a different structure from the aromatic dianhydride used in (a) so that the aromatic diamine and the aromatic dianhydride are contained in a substantially equimolar amount throughout all steps and then performing polymerization.   
     
     
         9 . The film according to  claim 7 , wherein the crystalline thermoplastic polyimide is obtainable by imidizing a polyamic acid obtained through the following steps (a) to (c):
 (a) a step for obtaining a prepolymer having acid anhydride groups at both ends by reacting the aromatic diamine with the aromatic dianhydride in the organic polar solvent under a condition where the aromatic dianhydride is contained in excess;   (b) a step for further adding an aromatic dianhydride having a different structure from the aromatic dianhydride used in (a); and   (c) a step for further adding the aromatic diamine having a different structure from the aromatic diamine used in (a) so that the aromatic diamine and the aromatic dianhydride are contained in a substantially equimolar amount throughout all steps and then performing polymerization.   
     
     
         10 . The film according to  claim 7 , wherein the crystalline thermoplastic polyimide contained in the adhesive layer has a melting point at least 5° C. lower than a crystalline thermoplastic polyimide obtainable by imidizing (i) a polyamic acid obtained through a polymerization performed so that the aromatic diamine used in the step (a) and the aromatic dianhydride used in the step (a) are contained in a substantially equimolar amount or (ii) a polyamic acid obtained through a polymerization performed so that the aromatic diamine used in the steps (b) and (c) and the aromatic dianhydride used in the steps (b) and (c) are contained in a substantially equimolar amount. 
     
     
         11 . The film according to  claim 7 , wherein the crystalline thermoplastic polyimide has a melting point within a range of 340° C. to 380° C. 
     
     
         12 . A flexible metal-clad laminate comprising a film as set forth in  claim 1  and a metal layer formed on at least one side surface of the film. 
     
     
         13 . The flexible metal-clad laminate according to  claim 12 , which meets both of the following conditions (i) and (ii):
 (i) a peeling strength for the metal layer is 10 N/cm or greater, where a force to peel the metal layer is applied in a 180 degrees direction; and   (ii) defective appearance such as swelling and whitening does not occur even if being exposed under a moisture condition of 40° C. of temperature and 90% R.H. for 96 hours and thereafter immersed in solder dip of 300° C. for 10 seconds.   
     
     
         14 . The flexible metal-clad laminates according to  claim 12 , wherein the film resulting from removal of the metal layer provided on the film by etching etc. is such that (i) an absolute value of an endothermic peak area attributed to melting of the crystalline thermoplastic polyimide is 4.0 mJ/mg or higher, the endothermic peak area being measured by performing a differential scanning calorimetry on the film, and (ii) an absolute value of an exothermic peak area attributed to recrystallization of the crystalline thermoplastic polyimide is 0.5 mJ/mg or lower, the exothermic peak area being measured by performing the differential scanning calorimetry on the film.