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Method for a low CTE core for organic substrates

IP.com Disclosure Number: IPCOM000022334D
Publication Date: 2004-Mar-08
Document File: 4 page(s) / 48K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for a low coefficient of thermal expansion (CTE) core for organic substrates. Benefits include improved functionality and improved performance.

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Method for a low CTE core for organic substrates

Disclosed is a method for a low coefficient of thermal expansion (CTE) core for organic substrates. Benefits include improved functionality and improved performance.

Background

Conventionally, substrates can warp (see Figure 1). Package assembly and post assembly exposure to temperature cycles and moisture can increase package warpage. It can cause increased stress in several areas, including:

•         First level interconnection

•         Second level interconnection

•         Die

Warpage and stress can reduce the performance of the thermal interface material (TIM).

Conventionally, this problem is solved by using a woven or non-woven glass material in the production of the organic substrate to enhance the modulus (~20 GPa). The material also lowers the CTE of the core but only to the 16 to 25 ppm range (see Figure 2). To achieve even lower CTE cores, inorganic fillers are typically added by one of two ways (see Figures 3 and 4):

•         Impregnating the glass core with calcium carbonate and talc or silica, which have a very low positive CTE of 9-15x10-6

•         Mixing calcium carbonate, talc, or silica into the organic resin before impregnating the glass material

The thermal expansion of the core is reduced by adding calcium carbonate and silica talc and the bulk CTE of the core.

Requirements for a low CTE substrate are expected to be critical for future thin die, thin TIM package designs.

General description

The disclosed method is the utilization of CTE-lowering fillers in a glass-reinforced substrate core to reduce the CTE of the substrate, reduce thermomechanical stress on the die, and reduce warpage.

         The key elements of the method include:

•         Organic-based substrate core

•         Fiber reinforcement, woven material, or fiber preforms

•         Negative thermal expansion filler material, such as zinc cyanide

•         Adhering low CTE filler electrostatically or using a tackifier

•         Blending the low CTE filler into an organic thermoset resin before the impregnation of the glass material

Advantages

         The disclosed method provides advantages, including:

•         Improved performance due to reduced first-level interconnection not-wet areas and solder joint cracking

•         Improved performance due to improved CTE values because of the use of fillers in the substrate core materials

•         Improved performance due to reduced IHS warpage

•         Improved reliability due to reduced warpage

•         Improved reliability due to reduced TIM...