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Method for cooling small form factor devices

IP.com Disclosure Number: IPCOM000021725D
Publication Date: 2004-Feb-04
Document File: 7 page(s) / 391K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for cooling small form factor devices. Benefits include improved functionality, improved performance, improved reliability, and improved power performance.

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Method for cooling small form factor devices

Disclosed is a method for cooling small form factor devices. Benefits include improved functionality, improved performance, improved reliability, and improved power performance.

Background

         Thermal management is required for hand held, portable, and mobile environments where forced convection is not practical and natural convection/radiation is very limited. The increasing power requirement is expected to exceed the levels bare die can handle, resulting in high operation temperatures and increased risk to product reliability.

         A conventional solution is to implement a 1.5-mm thick integrated heat spreader (IHS) to spread the heat from the die and reduce the overall power density on the package top surface (see Figure 1). However, the IHS significantly increases the overall package profile, which may not be acceptable for small form factor applications, such as hand-held, portable, and mobile devices.

Additionally, a separate sealant material is required to retain the IHS to the package body. The alignment of IHS to the package body becomes more critical and difficult especially for flip-chip ball grid array (FCBGA) packages with a smaller body size (less than 10 mm).

         Another solution is to rely on the PCB to dissipate heat without the assistance of a thermal pad (see Figure 2).

         For ultra-thin stacked chip scale packages (UTSCSPs), the PCB dissipates heat inside the hand-held device. Junction-to-board thermal resistance (θjb) becomes very critical for managing thermal performance. Because conventional mold compound materials with low thermal conductivity are typically used for molded packages, heat conduction through the package top case is usually not efficient (see Figure 3).

         The typical power profile for a digital media player indicates surged power can be much higher during MPEG4 movie decompression than during other operation modes. However, the duration of the surged power is very short when compared to low-power operation modes, such as sleep and idle (see Figure 4).

General description

The disclosed method is cooling for small form factor devices. The method includes the following designs:

•         Thermal cap heat-spreader design for FCBGA packages with a small body size (less than 10 mm)

•         Heat-absorbing pads that can be attached to the printed circuit board (PCB) near the hot components or to the PCB backside in a hand-held or portable device

•         Heat-absorbing molding compound that can be used on any molded packages for hand-held and mobile applications

The key elements of the disclosed method include the following:

•         Low-profile thermal cap made of Cu or thermal conductive materials, such as metal, ceramic, and composite materials

•         Addition of solder balls and vias to connect the thermal cap to the ground plane inside the PCB

•         Elastomer heat-absorbing pads that absorb heat generated by components and gradually release the heat to the PCB and ambient environment during device low-pow...