Method for manufacturing flexible printed circuit board and flexible printed circuit board manufactured thereby
A method for manufacturing a flexible printed circuit board includes preliminarily thermally deforming s substrate through heating, forming a circuit pattern with a conductive paste on the preliminarily thermally deformed substrate, and firing the circuit pattern. A flexible printed circuit board includes a substrate, and a circuit pattern formed by firing a conductive paste on a first surface of the substrate. The substrate is preliminarily thermally deformed and, thus, a shrinkage variation thereof before and after firing the conductive paste is zero. Dimensional stability when firing the circuit pattern printed with the conductive paste can be ensured, deterioration of adhesion between the circuit pattern and the substrate attributable to film deformation upon firing can be prevented, and stable adhesion of the circuit pattern can be maintained even after firing.
1. A method for manufacturing a flexible printed circuit board, comprising:
preliminarily thermally deforming a substrate through heating;
forming a via hole in the substrate;
filling the via hole with a conductive paste;
laminating a carrier on a second surface of the substrate between forming the via hole and filling the via hole;
forming a first circuit pattern with a conductive paste on a first surface of the preliminarily thermally deformed substrate;
firing the first circuit pattern;
forming a protective coating layer for protecting the first circuit pattern by applying a coating solution on a the first surface of the substrate after firing the first circuit pattern;
removing the carrier from the second surface of the substrate after forming the first circuit pattern on the first surface of the substrate;
laminating the carrier on the first surface of the substrate before forming a second circuit pattern;
forming the second circuit pattern with a conductive paste on the second surface of the substrate;
then removing the carrier from the first surface of the substrate after forming the second circuit pattern;
forming an additional circuit pattern with a conductive paste on the protective coating layer; and firing the additional circuit pattern.
2. The method of claim 1 , wherein the substrate is a polyimide (PI) film or a PET film.
3. The method of claim 1 , wherein the conductive paste is a silver paste comprising a silver powder, a polymer resin, and a solvent.
4. The method of claim 1 , wherein firing the first circuit pattern is performed at 200 to 450 C.
5. The method of claim 1 , wherein preliminarily thermally deforming is performed by heating the substrate to a temperature higher than or equal to a temperature at which the first circuit pattern is fired.
6. The method of claim 1 , further comprising baking the preliminarily thermally deformed substrate through heating to remove water therefrom after preliminarily thermally deforming the substrate through heating and before forming the first circuit pattern.
7. The method of claim 1 , wherein forming the protective coating layer is performed by applying the coating solution on the first surface of the substrate to form a protective coating layer and drying the protective coating layer.
8. The method of claim 1 , wherein the protective coating layer is formed to a thickness of at least 9 μm on the first circuit pattern.
9. The method of claim 1 , wherein forming the protective coating layer is performed by applying the coating solution on the first surface of the substrate through screen printing, in which a thickness of the coating solution is adjusted by varying a mesh size of a screen.
10. The method of claim 1 , further comprising modifying a surface of the substrate before forming the first circuit pattern.
11. The method of claim 1 , wherein the first circuit pattern is an X-axis coordinate recognition pattern part including a plurality of X-axis electrodes spaced apart from each other, and the second circuit pattern is a Y-axis coordinate recognition pattern part including a plurality of Y-axis electrodes spaced apart from each other.
12. The method of claim 1 , wherein the carrier is a writing paper.
13. The method of claim 1 , wherein forming the protective coating layer comprises:
applying the coating solution on the first surface of the substrate, thus forming a first protective coating layer on the first surface of the substrate; and
applying the coating solution on the second surface of the substrate, thus forming a second protective coating layer on the second surface of the substrate.
14. The method of claim 13 , further comprising curing the first protective coating layer and the second protective coating layer through heating.
15. The method of claim 14 , wherein curing the first protective coating layer and the second protective coating layer is performed at 200 to 450 C.
16. The method of claim 1 , further comprising performing corona treatment for modifying the first surface and the second surface of the substrate before forming the first circuit pattern and the second circuit pattern, wherein performing the corona treatment comprises:
subjecting the first surface of the substrate to corona treatment before forming the first circuit pattern; and
subjecting the second surface of the substrate to corona treatment before forming the second circuit pattern.