Printed wiring board and method for manufacturing printed wiring board

1. A printed wiring board, comprising:

an interlayer resin insulation layer;

a pad formed on the interlayer resin insulation layer and configured to mount an electronic component;

a solder-resist layer formed on the interlayer resin insulation layer and the pad and having an opening portion over the pad such that the opening portion of the solder-resist layer is exposing a portion of a surface of the pad;

an adhesive layer formed between the pad and the solder-resist layer; and

a coating layer formed in the opening portion of the solder-resist layer such that the coating layer is positioned on the portion of the pad exposed through the opening portion of the solder-resist layer,

wherein the solder-resist layer has a protruding portion protruding toward an inside of the opening portion in a bottom portion of the opening portion, and the protruding portion of the solder-resist layer has an end portion having a flat surface such that the flat surface is extending substantially along the surface of the pad.

2. The printed wiring board according to claim 1 , wherein the flat surface of the protruding portion is covered with the coating layer.

3. The printed wiring board according to claim 1 , wherein the flat surface of the protruding portion is embedded under the coating layer.

4. The printed wiring board according to claim 1 , wherein the solder-resist layer includes an inorganic filler in an amount of 5˜25 wt. %.

5. The printed wiring board according to claim 1 , wherein the solder-resist layer includes an inorganic filler having an average particle diameter of 1 μm or smaller.

6. The printed wiring board according to claim 1 , wherein the solder-resist layer does not contain an organic filler.

7. The printed wiring board according to claim 1 , wherein the solder-resist layer has a thickness which is set to be in a range of 10˜20 μm.

8. The printed wiring board according to claim 1 , wherein the opening portion of the solder-resist layer has a diameter which is set to be in a range of 45˜60 μm.

9. The printed wiring board according to claim 1 , wherein the pad has a surface roughness which is set to be in a range of 0.3 μm or less.

10. The printed wiring board according to claim 1 , wherein the adhesive layer has a first layer comprising Sn and a second layer formed on the first layer and comprising a coupling agent.

11. The printed wiring board according to claim 10 , wherein the first layer comprises Sn and Cu.

12. The printed wiring board according to claim 1 , wherein the pad comprises an electroless plated film on the interlayer resin insulation layer and an electrolytic plated film formed on the electroless plated film.

13. The printed wiring board according to claim 1 , wherein the coating layer has a surface having a recessed portion at a central portion of the surface of the coating layer.

14. A method for manufacturing a printed wiring board, comprising:

forming on an interlayer resin insulation layer a pad configured to mount an electronic component;

forming an adhesive layer on the pad;

forming a solder-resist layer on the interlayer resin insulation layer and the pad formed on the interlayer resin insulation layer such that the solder-resist layer covers the pad and the adhesive layer and the adhesive layer is formed between the pad and the solder-resist layer;

forming an opening portion in the solder-resist layer such that the opening portion of the solder-resist layer exposes at least a portion of the adhesive layer formed on the pad;

removing the portion of the adhesive layer exposed through the opening portion in the solder-resist layer such that the opening portion of the solder-resist layer exposes at least a portion of a surface of the pad; and

forming a coating layer in the opening portion of the solder-resist layer such that the coating layer is positioned on the portion of the pad exposed through the opening portion of the solder-resist layer,

wherein the forming of the opening portion of the solder-resist layer comprises forming in the solder-resist layer a protruding portion protruding toward an inside of the opening portion in a bottom portion of the opening portion such that the protruding portion of the solder-resist layer has an end portion having a flat surface extending substantially along the surface of the pad.

15. The method for manufacturing a printed wiring board according to claim 14 , wherein the forming of the protruding portion comprises forming the flat surface of the protruding portion such that the coating layer is covered by the flat surface of the protruding portion.

16. The method for manufacturing a printed wiring board according to claim 15 , wherein the solder-resist layer includes an inorganic filler in an amount in a range of 5˜25 wt. % and does not contain an organic filler.

17. The method for manufacturing a printed wiring board according to claim 14 , wherein the solder-resist layer includes an inorganic filler having an average particle diameter of 1 μm or smaller.

18. The method for manufacturing a printed wiring board according to claim 14 , wherein the adhesive layer has a first layer comprising Sn and a second layer formed on the first layer and comprising a coupling agent.

19. The method for manufacturing a printed wiring board according to claim 18 , wherein the first layer comprises Sn and Cu.

20. The method for manufacturing a printed wiring board according to claim 14 , wherein the forming of the pad comprises forming an electroless plated film on the interlayer resin insulation layer and forming an electrolytic plated film formed on the electroless plated film such that the pad comprising the electroless plated film and the electrolytic plated film is formed on the interlayer resin insulation layer.