Method of manufacturing circuit board

1. A method of manufacturing a circuit board comprising the steps of:

preparing a fiber piece housing paste including a conductive paste having conductive powder and a resin and a fiber piece taken away from a first prepreg;

filtering the fiber piece housing paste in a paste state by using a filter to remove the fiber piece from the fiber piece housing paste for fabricating a filtered recovery paste;

adding at least one of a solvent, a resin, and a paste having a different composition from the filtered recovery paste to the filtered recovery paste for fabricating a reuse paste;

sticking a first protective film to a surface of a second prepreg;

forming a first hole on the second prepreg through the first protective film;

filling the first hole with the reuse paste;

peeling the first protective film to form a protruded portion constituted of the reuse paste on the surface of the second prepreg;

disposing a metallic foil on both sides of the second prepreg to pressurize the second prepreg from an outside of the metallic foil;

heating the second prepreg to cure the second prepreg and the reuse paste; and

processing the metallic foil into a wiring pattern.

2. The method of manufacturing a circuit board according to claim 1 , wherein the fiber piece housing paste is prepared in such a manner that a fiber having a length of ten times as great as an average particle diameter of the conductive powder or more is contained in the fiber piece housing paste is 50 wt % or more of all of the fiber pieces in the fiber piece housing paste.

3. The method of manufacturing a circuit board according to claim 1 , wherein the fiber piece housing paste is prepared in such a manner that a fiber having a length of ten times as great as an average particle diameter of the conductive powder or more is contained in the fiber piece housing paste is equal to or more than 0.01 wt % and is equal to or less than 10 wt % of the fiber piece housing paste.

4. The method of manufacturing a circuit board according to claim 1 , wherein the reuse paste is fabricated in such a manner that a fiber having a length of ten times as great as an average particle diameter of the conductive powder or more is contained in the reuse paste is equal to or less than 10 wt % of all fiber pieces in the reuse paste.

5. The method of manufacturing a circuit board according to claim 1 , wherein a viscosity of the reuse paste is equal to or more than 5 Pa·s and is equal to or less than 50 Pa·s.

6. The method of manufacturing a circuit board according to claim 1 , wherein the fiber piece housing paste is held at a temperature ranging from 0° C. to 80° C. inclusive in the step of fabricating a filtered recovery paste.

7. The method of manufacturing a circuit board according to claim 1 , wherein an opening diameter of the filter is three times as great as an average particle diameter of the metal particle or more and is 20 times as great as an average diameter of the fiber piece or less.

8. The method of manufacturing a circuit board according to claim 1 , wherein the fiber piece contained in the fiber piece housing paste is a glass fiber or an aramid fiber.

9. The method of manufacturing a circuit board according to claim 1 , wherein the filter is net-like stainless or polyester.

10. The method of manufacturing a circuit board according to claim 1 , wherein the resin in the conductive paste is a thermosetting resin.

11. The method of manufacturing a circuit board according to claim 1 , wherein a latent curing agent is used as a curing agent of the resin in the conductive paste, and

an opening diameter of the filter is three times as great as an average particle diameter of the metal particle or more, is 20 times as great as an average diameter of the fiber piece or less, and is a double of a diameter of the latent curing agent or more.

12. The method of manufacturing a circuit board according to claim 1 , wherein the solvent is the same as that contained in the conductive paste.

13. The method of manufacturing a circuit board according to claim 1 , wherein the solvent is diethylene glycol monobutyl ether.

14. The method of manufacturing a circuit board according to claim 1 , wherein the resin to be added to the filtered recovery paste is the same as that contained in the conductive paste.

15. The method of manufacturing a circuit board according to claim 1 , wherein the resin to be added to the filtered recovery paste is an epoxy resin.

16. The method of manufacturing a circuit board according to claim 1 , further comprising the step of measuring a viscosity of the fiber piece housing paste between the preparation of the fiber piece housing paste and the fabrication of the filtered recovery paste, and when the measurement finds the viscosity not smaller than a predetermined value, the step moves on to the fabrication of the filtered recovery paste.

17. The method of manufacturing a circuit board according to claim 1 , further comprising the step of measuring a viscosity of the fiber piece housing paste between the preparation of the fiber piece housing paste and the fabrication of the filtered recovery paste, when the measurement finds the viscosity not smaller than a value predetermined times as great as that of the conductive paste, the step moves on to the fabrication of the filtered recovery paste.

18. The method of manufacturing a circuit board according to claim 1 , wherein the fiber piece housing paste is obtained by recovering the conductive paste or the reuse paste which is not filled in a second hole after

the step of sticking a second protective film to a surface of the first prepreg;

the step of forming a second hole on the first prepreg through the second protective film; and

the step of filling the second hole with the conductive paste or the reuse paste.