Browse Prior Art Database

Method for restricting the spread of electrically conductive TIM

IP.com Disclosure Number: IPCOM000101729D
Publication Date: 2005-Mar-16
Document File: 6 page(s) / 148K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for restricting the spread of electrically conductive thermal interface material (TIM). Benefits include improved functionality, improved performance, and improved reliability.

This text was extracted from a Microsoft Word document.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 52% of the total text.

Method for restricting the spread of electrically conductive TIM

 

Disclosed is a method for restricting the spread of electrically conductive thermal interface material (TIM). Benefits include improved functionality, improved performance, and improved reliability.

Background

      The spread of TIM into and around die-side component areas can cause the shorting of components. To prevent this problem, keep-out zones (KOZs) are designed into packages. Areas are left without components to provide room for TIM flow without causing damage. This technique has required an increase in package sizes and package cost. An alternative solution is required.

      Ball-grid array (BGA) packages cannot use the conventional solder TIM material/process due to the reflow of solder under integrated heat spreaders (IHSs). Conventionally, IHSs remove heat from the die. IHS shorting results in die failure from overheating.

      To resolve the problems of TIM flow and component/IHS shorting, a polymer TIM is used instead of solder TIM on BGA packages. Alternatively, a smaller IHS is used and die-side components are located farther from the IHS to keep solder TIM from reflowing into the die-side component layout region. Another solution is to create breaks in the solder mask (solder trenches) to prevent the flow of epoxy material into the die-side component area (see Figure 1).

      Other problems that occur with IHSs on printed circuit boards include controlled collapse chip connect (C4) solder joint fatigue and interlayer dielectric (ILD) material stress. They are caused by the coupling effects of larger IHS lids to the substrate. To solve these problems, multiple lots with different size IHS lids are built to determine which sized lid performs best in the application. Typically, smaller lids perform better. However, smaller lids limit the area of good thermal performance for the device (see Figure 2).

General description

              The disclosed method provides two IHS lid shapes to prevent TIM from spreading, the dual-cavity design and the dual-lip design.

      The key elements of the method include:

•             TIM placed on top of the die

•             For the dual-cavity design, the inner cavity contains the TIM for cooling the IHS and the outer cavity adheres the IHS to the package

•             For the dual-cavity design, two sealant applications, one to restrict the TIM flow and one to adhere the IHS to the package, use nonconductive silicon material

•             For the dual-lip design, the inner lip becomes secured to the substrate surface with sealant and the outer lip floats freely during temperature cycling

Advantages

              The disclosed method provides advantages, including:

•             Improved functionality due to enabling BGA packages to meet lower thermal targets, using the dual-cavity design

•             Improved functionality due to enabling solder TIM material to be used on BGA products with die-side componen...