Printed circuit board (PCB) and PCB assembly having an encapsulating mold material on a bottom surface thereof and methods for molding an encapsulating mold material on a bottom surface of a PCB

Patent metadata

Field	Value
Publication number	US-9907169-B1
Application number	US-201615251230-A
Country	US
Kind code	B1
Filing date	Aug 30, 2016
Priority date	Aug 30, 2016
Publication date	Feb 27, 2018
Grant date	Feb 27, 2018

Abstract

A process for forming an encapsulating mold compound into a molded solder mask on a bottom surface of a PCB is provided that allows the molded solder mask to have a very precise, preselected thickness, or height, while also ensuring that no gaps between the solder mask and side walls of the electrical contact pads exist. A circuit board and circuit board assembly that incorporate the molded solder mask are also provided. The molded solder mask is fabricated in such a way that overlap between the molded solder mask and the electrical contact pads and gaps between the molded solder mask and the side walls of the electrical contact pads are avoided. In addition, the molded solder mask allows the pitch between adjacent electrical contact pads to be greatly reduced compared to the pitch that is possible using a traditional solder mask formed by the traditional photolithographic approach.

First claim

What is claimed is:

1. A circuit board comprising:
an array of metal electrical contact pads disposed on a bottom surface of the circuit board, the array of metal electrical contact pads having a height equal to a distance from the bottom surface of the circuit board to bottom surfaces of the metal electrical contact pads;
a cured first encapsulating mold compound formed on the bottom surface of the circuit board, bottom surfaces of the metal electrical contact pads being exposed through respective openings formed in the cured first encapsulating mold compound, the cured first encapsulating mold compound extending in between the array of metal electrical contact pads such that side walls of each of the array of metal electrical contact pads are surrounded by and in contact with the cured first encapsulating mold compound, the cured first encapsulating mold compound having a shape that is complementary to a shape of a cavity of a mold tool; and
a cured second encapsulating mold compound formed on a top surface of the circuit board, wherein the cured first encapsulating mold compound has a coefficient of thermal expansion (CTE) that is higher than a CTE of the cured second encapsulating mold compound, and wherein the higher CTE of the cured first encapsulating mold compound prevents or reduces warpage of the circuit board by the cured second encapsulating mold compound.

2. The circuit board of claim 1 , wherein the cured first encapsulating mold compound is cured epoxy resin.

3. The circuit board of claim 2 , wherein the cured epoxy resin is cured reinforced epoxy resin having reinforcing particles therein.

4. The circuit board of claim 2 , wherein the cured epoxy resin is cured non-reinforced epoxy resin devoid of reinforcing particles therein.

5. The circuit board of claim 1 , wherein the cured first encapsulating mold compound has a thickness that is less than or equal to the height of the array of metal electrical contact pads plus 3 micrometers.

6. The circuit board of claim 1 , wherein the cured first encapsulating mold compound has a thickness that is determined by the shape of the cavity of the mold tool.

7. The circuit board of claim 1 , wherein the cured first encapsulating mold compound has a thickness that is less than or equal to the height of the array of metal electrical contact pads minus 3 micrometers.

8. The circuit board of claim 1 , wherein a pitch between adjacent metal electrical contact pads is less than 400 micrometers.

9. The circuit board of claim 8 , wherein a pitch between adjacent metal electrical contact pads is less than or equal to 350 micrometers.

10. The circuit board of claim 1 , wherein the cured first encapsulating mold compound is in continuous contact with the side walls of the array of metal electrical contact pads such that no gap exists between the cured first encapsulating mold compound and any of the side walls of the array of metal electrical contact pads.

11. The circuit board of claim 1 , wherein the bottom surfaces of the metal electrical contact pads are devoid of dielectric residue.

12. The circuit board of claim 1 , wherein the bottom surface of the circuit board is devoid of the cured first encapsulating mold compound at an intersection of at least one side wall of the circuit board and the bottom surface of the circuit board.

13. The circuit board of claim 1 , wherein the circuit board has side walls and a top surface, the circuit board further comprising:
at least one of an electrical, electronic and optoelectronic component mounted on the top surface of the circuit board and electrically interconnected with the circuit board,
the cured second encapsulating mold compound encapsulating the top surface of the circuit board and said at least one of an electrical, electronic and optoelectronic component; and
an electromagnetic interference (EMI) shield comprising a metallic material covering outer surfaces of the cured second encapsulating mold compound and the side walls of the circuit board, wherein the cured first encapsulating mold compound disposed on the bottom surface of the circuit board ensures that the bottom surface of the circuit board is devoid of the metallic material of the EMI shield.

14. A circuit board assembly comprising:
a circuit board comprising:
an array of metal electrical contact pads disposed on a bottom surface of the circuit board, the array of metal electrical contact pads having a height equal to a distance from the bottom surface of the circuit board to bottom surfaces of the array of metal electrical contact pads; and
a cured first encapsulating mold compound formed on the bottom surface of the circuit board and extending in between the array of metal electrical contact pads such that side walls of each of the array of metal electrical contact pads are surrounded by and in contact with the cured first encapsulating mold compound; and

at least one of an electrical, electronic and optoelectronic component mounted on a top surface of the circuit board and electrically interconnected with the circuit board; and
a cured second encapsulating mold compound encapsulating the top surface of the circuit board and said at least one of an electrical, electronic and optoelectronic component, the cured first encapsulating mold compound having a coefficient of thermal expansion (CTE) that is higher than a CTE of the cured second encapsulating mold compound, and wherein the higher CTE of the cured first encapsulating mold compound prevents or reduces warpage of the circuit board by the cured second encapsulating mold compound.

15. The circuit board assembly of claim 14 , wherein the cured first encapsulating mold compound is cured epoxy resin.

16. The circuit board assembly of claim 15 , wherein the cured epoxy resin is cured reinforced epoxy resin having reinforcing particles therein.

17. The circuit board assembly of claim 15 , wherein the cured epoxy resin is cured non-reinforced epoxy resin devoid of reinforcing fibers therein.

18. The circuit board assembly of claim 14 , wherein the cured first encapsulating mold compound has a thickness equal to a distance from the bottom surface of the circuit board to a bottom surface of the cured first encapsulating mold compound, and wherein the height of the array of metal electrical contact pads is substantially the same as the thickness of the cured first encapsulating mold compound.

19. The circuit board assembly of claim 14 , wherein a bottom surface of the cured first encapsulating mold compound and the bottom surfaces of the electrical contact pads are substantially co-planar with one another.

20. The circuit board assembly of claim 14 , wherein no overlap exists between a bottom surface of the cured first encapsulating mold compound and the bottom surfaces of the metal electrical contact pads.

21. The circuit board assembly of claim 14 , wherein the bottom surface of the circuit board is exposed between an outer peripheral edge of the cured first encapsulating mold compound and a sidewall of the circuit board.

22. The circuit board assembly of claim 14 , wherein the cured first encapsulating mold compound is in continuous contact with the side walls of the array of metal electrical contact pads such that no gap exists between the cured first encapsulating mold compound and any of the side walls of the array of metal electrical contact pads.

Assignees

• Avago Technologies General Ip

Inventors

• Kumbhat Nitesh
• Sun Li
• Lee Aaron
• Choi Deog Soon
• Ku Hyun Mo
• Ajoian Jack

Classifications

• H10W90/724

  between a chip and a stacked insulating package substrate, interposer or RDL · CPC title

• H10W74/114

  by a substrate and the encapsulations · CPC title

• H05K9/0081

  Electromagnetic shielding materials, e.g. EMI, RFI shielding (H05K9/0003 takes precedence) · CPC title

• H05K1/185

  associated with components encapsulated in the insulating substrate of the PCBs; associated with components incorporated in internal layers of multilayer circuit boards · CPC title

• H05K3/0014

  Shaping of the substrate, e.g. by moulding · CPC title