Adhesive bonding of printed circuit boards to heat sinks

• US 20030019562A1
• Filed: 09/19/2002
• Published: 01/30/2003
• Est. Priority Date: 08/03/2000
• Status: Abandoned Application

• Current Assignee: Kunno John Warn
• Original Assignee: Kunno John Warn
• Inventors: Warn, Kunno John
• Application Number:
  US10/247,385
• Publication Number:
  US 20030019562A1
• Time in Patent Office: Days
• US Class Current: 156/87
• CPC Class Codes: C09J 2301/124 the adhesive layer being present on both sides of the carrier, e.g. double-sided adhesive tape
• CPC Class Codes: C09J 2301/1242 the opposite adhesive layers being different
• CPC Class Codes: C09J 2301/208 the adhesive layer being constituted by at least two or more adjacent or superposed adhesive layers, e.g. multilayer adhesive
• CPC Class Codes: C09J 2301/302 the adhesive being pressure-sensitive, i.e. tacky at temperatures inferior to 30°C
• CPC Class Codes: C09J 2301/304 the adhesive being heat-activatable, i.e. not tacky at temperatures inferior to 30°C
• CPC Class Codes: C09J 5/06 involving heating of the applied adhesive
• CPC Class Codes: C09J 7/22 Plastics; Metallised plastics
• CPC Class Codes: C09J 7/35 Heat-activated
• CPC Class Codes: C09J 7/38 Pressure-sensitive adhesives [PSA]
• CPC Class Codes: H05K 2201/0195 Dielectric or adhesive layers comprising a plurality of layers, e.g. in a multilayer structure
• CPC Class Codes: H05K 2201/0209 Inorganic, non-metallic particles
• CPC Class Codes: H05K 2203/0278 Flat pressure, e.g. for connecting terminals with anisotropic conductive adhesive
• CPC Class Codes: H05K 3/0061 onto a metallic substrate, e.g. a heat sink heat sinks for electric apparatus H05K7/20
• CPC Class Codes: H05K 3/386 by the use of an organic polymeric bonding layer, e.g. adhesive

Abstract

Voids (26) at the interface of a printed circuit board (10) bonded to a heat sink (24) which impede heat transfer from a heat generating electronic component (12) mounted on the printed circuit board (10) to the heat sink (24), and thus limit the density of electronic components (12) that may be mounted to a given printed circuit board (10) are avoided by a method wherein the adhesive securing the printed circuit board (10) to the heat sink (24) is formed of a pressure sensitive adhesive layer (22) and a thermosetting adhesive layer (28). The latter fills the voids and thus provides for greater thermal conductivity from a heat generating component (12) to the heat sink (24) with the result in increase in heat rejection (30).

Claims

1. A method of bonding a printed circuit board to a heat sink comprising the steps of:

a) providing an adhesive composite having at least one exposed layer of pressure sensitive adhesive and at least one exposed layer of thermosetting adhesive;

b) sandwiching the composite between a printed circuit board and a board receiving surface on a heat sink with the exposed layer of pressure sensitive adhesive facing said board receiving surface and the exposed layer of thermosetting adhesive facing the printed circuit board;

c) subjecting the assembly resulting from step b) to both a vacuum and heat to remove gas between the heat sink and the printed circuit board and to cure the thermosetting adhesive.

2. The method of claim 1 where step a) is succeeded by and step b) is preceded by the step of compacting the adhesive composite to remove gas bubbles.

3. The method of claim 2 wherein the step of compacting includes compacting the adhesive composite against the heat sink.

4. The method of claim 3 wherein step c) also includes compressing the assembly resulting from step b).

5. The method of claim 1 wherein step c) also includes compressing the assembly resulting from step b).

6. A printed circuit board and heat sink assembly made according to the method of claim 1.

9. The method of claim 1 wherein step c) is effective to additionally liquify the thermosetting adhesive to cause it to flow into void spaced on the printed circuit board caused by the vacuum.

7. A method of bonding a printed circuit board having at least one heat generating component mounted thereon to a heat sink comprising the steps of:

a) sandwiching at least one layer of pressure sensitive adhesive and at least one layer of thermosetting adhesive between the heat sink and the printed circuit board with a pressure sensitive adhesive layer contacting the heat sink and a layer of thermosetting adhesive contacting the printed circuit board;

b) compacting the assembly resulting from step a) under vacuum to remove gas at or between the layers of adhesive; and

c) applying heat to the assembly resulting from step a) during or after the performance of step b) to cure the thermosetting adhesive.

8. The method of claim 7 wherein step a) is performed by locating an adhesive composite containing said layers between said printed circuit board and said heat sink.

10. A printed circuit board and heat sink assembly made according to the method of claim 7.

11. A printed circuit board and heat sink assembly comprising:

a) a printed circuit board;

b) a heat sink having a printed circuit board receiving surface spaced from said printed circuit board;

c) at least one layer of pressure sensitive adhesive and bonded to said heat sink;

d) at least one layer of thermosetting adhesive and bonded to said printed circuit board;

e) said adhesive layers being adhered to each other and filling the space between said heat sink and said printed circuit board;

f) said filled space being characterized by the substantial absence of gas pockets or voids.