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A New Method Connecting Heavy Heat Sink to PCB and Packages

IP.com Disclosure Number: IPCOM000012803D
Original Publication Date: 2003-May-28
Included in the Prior Art Database: 2003-May-28
Document File: 4 page(s) / 223K

Publishing Venue

Motorola

Related People

Yuan Yuan: AUTHOR [+3]

Abstract

This article describes a novel method connecting heat sink to printed circuit board (PCB or PWB) and package. It has significant advantage over other methods when the heat sink is heavy and bulky. Different from the traditional method, the heat sink is firmly supported by a frame connected to the PCB. Additional control also provided to ensure adequate thermal contact between heat sink and the package. This method avoids excessive force on the package and prevents the heat sink from loosing contact with the package during shock and vibration.

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A New Method Connecting Heavy Heat Sink to

PCB and Packages

Yuan Yuan

Bennett Joiner

Tony Montes De Oca

Final Manufacture Technology Center, Motorola

Abstract

This article describes a novel method connecting heat sink to printed circuit board (PCB or PWB) and package.� It has significant advantage over other methods when the heat sink is heavy and bulky. Different from the traditional method, the heat sink is firmly supported by a frame connected to the PCB.� Additional control also provided to ensure adequate thermal contact between heat sink and the package.� This method avoids excessive force on the package and prevents the heat sink from loosing contact with the package during shock and vibration.

                                � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � The Full Contents of the Paper

1.� The traditional method

In the traditional method, the heat sink is pressed against the package by a clip fixed on the printed circuit board (PCB, also called printed wire board, PWB).� It is the vertical pressure and friction forces between Clip, heat sink, package and PCB that keep the heat sink contacting the package.� As integrated circuit (IC) package becomes smaller and consumes more power, the required heat sink becomes heavier and bulky.� It becomes more difficult for the traditional method to provide a stable connection for the heat sink.� It may require excessive pressure against the package to prevent the heat sink from rocking and destroying the thermal interface between the heat sink and the device.� For packages where the die is exposed, it is also necessary to prevent the chipping of the die.� The excessive pressure may also damage package interior structure.

2.� The proposed method

In the proposed method, the heat sink is primarily supported by a frame that is fixed to the PCB.� A typical frame for a rectangular shape package is shown in the Figure 1(a) and (b).� The frame has a step stage for the package to seat on and an “ear” for the spring clip to hook on.� Most of the bottom surface of the frame is cut out to leave only a few contacting legs to fix the frame to the PCB.� This leaves more space on the PCB for other components.� The frame can be attached to the PCB with bolts and nuts, glue, or clips.� The height of the stage should be lower than the thermal contact interface between the heat sink and the package top.� This allows a ring of soft material to be seated between heat sink and the frame stage.� The stage outline should basically follow the package outline and leave a small space for glue material to be put in between the side of the heat sink and the frame wall.� The advantage to apply glue to the side surface is to prevent the relatively high thermal expansion of the glue from disturbing the thermal interface.� Likewise, the glue can be applied in discrete manner rather than completely surrounding the heat sink.� While the frame is shown with a step and seal to connect the heat sink t...