Thin multi-chip flex module

Abstract

A flexible circuit comprises a folded dielectric sheet having conductive patterns on its surface(s) to which microelectronic device(s) are attached. The dielectric sheet is folded 180° about a selected axis and a bond layer joins the two halves over a portion of their respective surface areas so that a remaining portion of their areas remain unbonded and a bifurcated structure is thereby formed. Electrical contacts are provided on the unbonded or bifurcated portions of the flexible sheets. The flex may be attached to a rigid frame and provided with protective heat spreading covers. The folded flex design is particularly suitable for reel-to-reel manufacturing.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application claims the benefit of Provisional Patent Application No. 61 / 009,781 by the present inventors, filed on Jan. 2, 2008, the entire disclosure of which is incorporated herein by reference.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention relates generally to means for packaging microelectronic devices and multichip modules. More particularly, the invention relates to improved flex-circuit solutions for SIMM and DIMM type memory modules and other modular electronic circuits.[0004]2. Description of Related Art[0005]High density computing is continually evolving to offer high performance devices with higher densities and smaller form factors. Servers are designed with these goals in mind and are key enablers for various computing applications. Servers contain, among other electronic components, microprocessors and memory modules, which generate considerable heat during operation. Currently high...

AI Technical Summary

Problems solved by technology

Servers contain, among other electronic components, microprocessors and memory modules, which generate considerable heat during operation.

When multiple memory modules are tightly spaced together inside the tightly packed server chassis, the circulation of air as a cooling fluid becomes ineffective.

Air can be restricted, leading to overheating of memory modules which in turn leads to premature failures including device failures and corrupt data streams.

These characteristics are inter-related and the optimization of one may adversely impact the other; so, a balance must be found among these various characteristics to determine the most effective solution.

However, stacking of chips is accompanied by an increase in cost of the stacked chips.

Also, stacking of chips is accompanied by greater heat that is concentrated between the stacked chips and is more difficult to dissipate which leads to an overall hotter module.

However, the addition of larger heat sinks and heat spreaders is accompanied by an increase in thickness.

In turn, increasing thickness leads to a pressure drop between adjacent modules which impedes the flow of air and adversely affects cooling.

However, flexible circuits can be more expensive than standard PCB based on FR4 materials.

Furthermore, thickness reduction causes a mismatch between the thin laminate or the flexible substrate and the standard connector.

However, when the chips are in an optimal heat path configuration, they may not be in an optimal electrical path configuration.

Usually this results in an increase in the layer count of rigid PWB circuit boards.

This may increase the cost of these special PCBs.

Although the use of flexible circuits in packaging semiconductors and consumer electronics is well known and offers the capability of high density interconnect signal stability at high frequencies, and flexible form factor (connecting sites that are not aligned), the technology based on flexile circuits is not without disadvantages.

Flexible circuits present an overall cost disadvantage, they are inherently a non-rigid form factor and need structural members to be incorporated.

One of the challenges caused by the use of flexible circuits is that it reduces the thickness of the substrate to the point that it becomes incompatible with current standard connectors.

However, solving the thickness issues create other issues.

These thin laminates can reduce thickness of the PCB but may not be good for high density modules and high frequency operations due to the limited number of layers they utilize and their dielectric properties.

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