Method for drilling thru-holes on a lamination substrate and a sheet used therein

A multilayer sheet for forming thru-holes obtained by layering a water soluble high molecular compound layer whose principal component is at least one selected from the group consisting of the following component (a) and component (b):

• (a) a water soluble high molecular compound comprising an organic compound residue having two active hydrogen groups, ##STR32## wherein the above ##STR33## is contained at not less than 70% by weight, and (b) a water soluble high molecular compound comprising a repetitive unit represented as the following general formula (1):
• ##STR34## wherein in the above formula (1), A is a unit composed of a repetition of ##STR35## provided that the above ##STR36## exists at not less than 70% by weight in A, a repetitive number of ##STR37## is a positive number, and a repetitive number of R1 ? ##STR38## is zero or a positive number;
• R.sub.1 is a hydrocarbon group, X is an organic compound residue with two active hydrogen groups, and R.sub.2 is a polycarboxylate compound residue or a diisocyanate compound residue.

A method for forming thru-holes in a lamination substrate made of insulating material and metal foil comprising placing a sheet on the entry surface of the lamination substrate and forming thru-holes on the lamination substrate through the sheet, said sheet comprising a high molecular sheet comprising a water soluble high molecular compound wherein one component at least selected from the group of component (a) and component (b) below is a principal component, wherein:

• (a) is a water soluble high molecular compound comprising an organic compound residue having two active hydrogen groups, ##STR39## wherein the above ##STR40## is contained at not less than 70% by weight, and (b) is a water soluble high molecular compound comprising a repetitive unit represented as the following general formuala (1):
• ##STR41## wherein, in the above formula (1), A is a unit composed of a repetition of ##STR42## provided that the above ##STR43## exists at not less than 70% by weight in A, a repetitive number of ##STR44## is a positive number, and a repetitive number of ##STR45## is zero or a positive number;
• R.sub.1 is a hydro carbon group, X is an organic compound residue with two active hydrogen groups, and R.sub.2 is a polycarboxylate compound residue or a diisocyanate compound residue.