Overmolded electronic module with underfilled surface-mount components

• US 6,307,749 B1
• Filed: 10/23/2000
• Issued: 10/23/2001
• Est. Priority Date: 10/23/2000
• Status: Expired due to Term

• Current Assignee: Delphi Technologies Ip Limited (BorgWarner Incorporated)
• Original Assignee: Delphi Technologies, Inc. (BorgWarner Incorporated)
• Inventors: Brandenburg, Scott David, Daanen, Jeffery Ralph
• Primary Examiner(s): Picard, Leo P.
• Assistant Examiner(s): CHERVINSKY, BORIS LEO
• Application Number:
  US09/692,866
• Time in Patent Office: 365 Days
• Field of Search: 361/704, 361/707, 361/709, 361/712, 361/713, 361/714, 361/715, 361/718-720, 361/728, 174/16.3, 174/50, 174/50.5, 174/50.51, 174/50.52, 174/50.53, 174/50.54, 174/50.56, 165/80.2, 257/687, 257/796
• US Class Current: 361/704
• CPC Class Codes: H05K 3/284 for encapsulating mounted components H05K1/185 takes precedence
• CPC Class Codes: H05K 5/0034 having an overmolded housing covering the PCB
• CPC Class Codes: H05K 7/20854 Heat transfer by conduction from internal heat source to heat radiating structure H05K7/20863 takes precedence

Abstract

An overmolded electronic module and a method for forming the module. The method entails both overmolding a circuit board and underfilling one or more surface-mount circuit devices physically and electrically connected to the board with solder bump connections. The circuit board is supported on a heatsink that thermally contacts a surface of the device opposite the circuit board. The board is optionally then encased on the heatsink with a retainer that includes means for biasing the circuit device against the heatsink. Finally, the circuit board is overmolded with a polymeric material to form an overmolded body that encases the circuit board and the circuit device with the heatsink. The overmold process is carried out so that a portion of the overmolded body completely underfills the circuit device and encapsulates its solder bump connections.

Claims

1. An overmolded electronic module comprising:

a circuit board having a first surface and an oppositely-disposed second surface;

a surface-mount circuit device attached to the second surface of the circuit board with solder bump connections, the circuit device being spaced above the second surface of the circuit board by the solder bump connections so as to define a gap therebetween;

a heatsink thermally contacting a surface of the circuit device oppositely-disposed from the circuit board; and

an overmolded body formed of an overmold material that encases the circuit board and the circuit device with the heatsink to provide a moisture-impermeable seal around the circuit board and the circuit device, the overmolded body having an underfill portion that completely underfills the circuit device and encapsulates the solder bump connections.

2. An overmolded electronic module according to claim 1, wherein the heatsink comprises pedestals that contact the circuit device.

3. An overmolded electronic module according to claim 1, further comprising supports spacing the circuit board from the heatsink.

4. An overmolded electronic module according to claim 1, further comprising:

a connector housing integrally formed in an external surface of the overmolded body; and

input/output pins that extend through the overmolded body and into the connector housing of the overmolded body, the input/output pins providing for electrical connection to the circuit device.

5. An overmolded electronic module according to claim 4, further comprising dielectric supports that surround the input/output pins and space the circuit board from the heatsink.

6. An overmolded electronic module according to claim 5, wherein the overmolded body contacts and covers the first and second surfaces of the circuit board and encases the circuit board, the dielectric supports and the circuit device.

7. An overmolded electronic module according to claim 1, further comprising a retainer enclosing the circuit board with the heatsink, the retainer comprising means for biasing the circuit device against the heatsink.

8. An overmolded electronic module according to claim 1, wherein the overmold material is an epoxy having a CTE of about 12 to 17 ppm/°

C. and containing about 80 to about 90 volume percent of a fill material having an average particle size of less than 25 micrometers.

9. An overmolded electronic module according to claim 1, wherein the circuit device is under a compressive load from the overmold material.

10. An overmolded electronic module comprising:

a heatsink having at least one pedestal;

a circuit board supported on the heatsink so that a first surface of the circuit board faces away from the heatsink and a second surface of the circuit board faces the heatsink;

a surface-mount circuit device attached to the second surface of the circuit board with solder bump connections at a first surface thereof, the circuit device being spaced above the second surface of the circuit board by the solder bump connections so as to define a gap therebetween;

a metal snap-fit retainer mechanically locked to the heatsink so as to enclose the circuit board with the heatsink, the retainer contacting the circuit board so as to bias the circuit device against the heatsink;

an overmolded body encasing the circuit board and the circuit device with the heatsink to provide a moisture-impermeable seal around the circuit board and the circuit device, the overmolded body having an underfill portion that completely fills the gap between the circuit device and the circuit board so as to underfill the circuit device and encapsulate the solder bump connections, the overmolded body applying a compressive load to the circuit device; and

a connector housing integrally formed in an external surface of the overmolded body, the connector housing comprising input/output pins that extend through the overmolded body and provide electrical connection to the circuit device.

11. An overmolded electronic module according to claim 10, wherein the overmold material is an epoxy having a CTE of about 12 to 17 ppm/°

C. and containing about 80 to about 90 volume percent of a fill material having an average particle size of less than 25 micrometers.

12. A method of assembling an overmolded electronic module, the method comprising the steps of:

providing a circuit board having a first surface, an oppositely-disposed second surface, and a surface-mount circuit device attached to the second surface of the circuit board with solder bump connections, the circuit device being spaced above the second surface of the circuit board by the solder bump connections so as to define a gap therebetween;

supporting the circuit board on a heatsink that thermally contacting a surface of the circuit device oppositely-disposed from the circuit board; and

overmolding the circuit board with an overmold material so as to form an overmolded body that encases the circuit board and the circuit device with the heatsink to provide a moisture-impermeable seal around the circuit board and the circuit device, the overmolded body having an underfill portion that completely underfills the circuit device and encapsulates the solder bump connections.

13. A method according to claim 12, further comprising the step of forming the heatsink to have pedestals that contact the circuit device as a result of the supporting step.

14. A method according to claim 12, further comprising the step of placing first supports between the circuit board and the heatsink to space the circuit board from the heatsink following the supporting step.

15. A method according to claim 12, further comprising the steps of:

equipping the circuit board with input/output pins that provide electrical connection to the circuit device; and

integrally forming a connector housing in an external surface of the overmolded body during the overmolding step, the input-output pins extending through the overmolded body and into the connector housing of the overmolded body as a result of the overmolding step.

16. A method according to claim 15, further comprising the step of surrounding the input/output pins with dielectric supports between the circuit board and the heatsink, the dielectric supports spacing the circuit board from the heatsink following the supporting step.

17. A method according to claim 12, further comprising the steps of:

enclosing the circuit board with the heatsink and a retainer comprising means for biasing the circuit device against the heatsink; and

mechanically locking the retainer to the heatsink with an integrally-formed resilient appendage of the retainer.

18. A method according to claim 17, further comprising the step of forming the biasing means as an integrally-formed resilient appendage of the retainer.

19. A method according to claim 12, wherein the overmold material is an epoxy having a CTE of about 12 to 17 ppm/°

C. and containing about 80 to about 90 volume percent of a fill material having an average particle size of less than 25 micrometers.

20. A method according to claim 12, wherein the circuit device is under a compressive load from the overmold material.