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Self-Centering Lid for IC Packaging and Method of Assembly

IP.com Disclosure Number: IPCOM000241125D
Publication Date: 2015-Mar-27
Document File: 4 page(s) / 88K

Publishing Venue

The IP.com Prior Art Database

Abstract

High power devices require efficient thermal management. Attaching a lid or heat spreader is a common method to achieve the objective. The size and type of lid chosen varies. The current trend is to have an almost 1:1 ratio of lid to package size in order to have a wider flat area to ease heat sink attachment process and increase thermal interface coverage. This poses a challenge to assembly. Lid misalignment is a typical reject especially if external force is required to achieve a very thin Thermal Interface Material (TIM) bond line thickness during the lid attach process.

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Self-Centering Lid for IC Packaging and Method of Assembly

High power devices require efficient thermal management.  Attaching a lid or heat spreader is a common method to achieve the objective.  The size and type of lid chosen varies.  The current trend is to have an almost 1:1 ratio of lid to package size in order to have a wider flat area to ease heat sink attachment process and increase thermal interface coverage.  This poses a challenge to assembly.  Lid misalignment is a typical reject especially if external force is required to achieve a very thin Thermal Interface Material (TIM) bond line thickness during the lid attach process. 

Figure 1 shows an IC package with a lid misalignment defect.  Silicon based adhesive has been used widely in the industry to attach the lid to the IC substrate as shown in Figure 2.  Rework is almost impossible since the lid adhesive (LA) is a thermo-set material upon curing.    

Figure 1.  Lid misalignment defect   

Figure 2.  Typical cross section of flip chip package with lid adhesive

Flip chip packages use a self-alignment mechanism of solder balls/bumps to define pads on substrates to form a connection.  This self-centering ability can be applied to the lid or heat spreader by introducing a wet-able material such as solder balls on lid and/or substrate during the lid attachment process. 

The lid has rows of individual dimples with wet-able pads around its periphary.  Figure 3 illustrates a flip chip package that uses...