Method of making release coatings for composite materials

Abstract

A release film for soft composite materials is provided. The release film contains a film with a closely packed self-assembled monolayer. A method of applying soft composite materials to a substrate without loss of the soft composite material to the release film is also provided. The method is useful in applications such as applying thermal pastes to semiconductor packaging.

Description

TECHNICAL FIELD[0001]The disclosure relates to efficient release film coatings for soft composite materials. One embodiment of the disclosure relates to maximal release coatings for thermal paste preforms used in the microelectronics industry.BACKGROUND[0002]Highly filled granular pastes, comprising metal particles (0.1-100 microns) at a volume percent greater than 65% in an organic binder, are important in a variety of industries including the food, oral care, and microelectronics industries.[0003]In microelectronics these granular pastes often referred to as thermal pastes, play an important role in packaging technology by facilitating heat removal from the chip and accommodating mechanical stresses induced by thermal expansion mismatches between the silicon die and spreader / hat. The proper dispensing of thermal pastes, such that the entire chip area is adequately and homogeneously covered, is a major concern that has been addressed through the formulation of thermal paste preform...

AI Technical Summary

Benefits of technology

[0005]The disclosure involves a surface modification strategy for preform backing materials to reduce the retained deposit from soft composite materials, such as thermal pastes and other highly-filled pastes of this category, using closely packed self-assembled monolayers. Examples of molecules that can self-assemble to form closely packed layers include but are not limited to alkylphosphonates, alkyl phosphates, alkyl carboxylic acids, alkyl silanes, halogenated silanes, alkyl thiols, alkanethiolates and alkyl disulfides. Specific examples of molecule and substrate combinations include alkyl phosphonates and alkyl phosphates on metal oxides such as alumina and titania, carboxylic acids on metal oxides such as alumina and silver oxide, alkyl silanes and halogenated silanes on silicon and silicone polymer, alkyl methylenes on polymethacrylates and other polymers containing surface hydroxyl functional groups, and alkyl thiols and disulfides on metals such as gold, copper, and platinum. Molecules that form monolayers with a packing density of about 20 Angstroms squared per molecule provide good performance in surface-modified preform backing materials. Such closely packed self-assembled monolayers provide a water contact angle between about 100 to about 140 degrees. Such surfaces are non-wetting to liquids bearing low to moderate surface tension (greater than about 25 milli-Newtons / meter). This includes most organic binders used in thermal pastes, with the exception of low viscosity silicone oils. The mitigation of binder wetting on the surface also reduces particulate deposition because deposition is typically mediated through binder wetting.

Problems solved by technology

Retained material can result in minor changes in the composition of the preform applied to the die with potentially major changes in its properties such as viscosity and thermal conductivity which are highly sensitive to solids loading for these highly filled granular pastes.

The retained material can also introduce microscopic roughness in the preform that could serve as sites for air entrapment with subsequent negative impact on paste thermal conductivity and reliability.

Fluoropolymer films in general have better release properties than polyesters, have good thermal stability, but are more expensive and can have surface roughness on the order of 200 nanometers.

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