Hermetic chip on board

Abstract

A low permeability laminate film includes one or more low moisture permeability homogeneous polymer films with a total thickness between 0.5 and ten mils without glass or ceramic fillers and with a moisture permeability measured at 37° C. and 100% RH of less than 2.6 E-05 atm·cc·mm / in2·sec of air. The polymer film includes one of polychlorotrifluoroethylene, polytetrafluorethylene, fluorinated ethylene propylene, and perfluoro alkoxy alkane. The low permeability laminate film further includes a nanolaminate including alternate combinations of nanolaminate material that is selected from the group consisting of alumina, titanium dioxide, zirconium oxide, beryllium oxide, hafnium oxide, titanium oxide, silicon nitride, tantalum nitride, silica, parylene F, parylene AF-4, parylene HT® and PTFE (polytetrafluoroethylene). A resulting coated nanolaminate film has a moisture permeability less than an equivalent standard leak rate per square inch of 3.0 E-08 atm·cc / in2·sec of air.

Description

BACKGROUND OF THE DISCLOSURE[0001]This disclosure relates generally to mounting electronic components onto a substrate or circuit board, and more particularly, to a circuit board construction and an associated environmental protection system and method of manufacturing the same.[0002]Present day microelectronic assemblies utilize printed circuit boards with active and passive components attached to the circuit board in hermetically sealed and / or plastic encapsulated packages. The hermetic or plastic encapsulated packages are required to environmentally protect the active components from moisture and other adverse materials. Such packages are inherently expensive, and require significantly more size, weight and cost than would be required by directly mounting the active components to the circuit board. Additionally, the prepackaged devices increase the electrical loss and thermal impedance of the assembled devices. Plastic encapsulated devices are also inherently more moisture sensit...

AI Technical Summary

Benefits of technology

[0004]Embodiments of the low permeability, nanolaminate coated film comprise inclusion of a copper layer for use in multilayer printed circuit boards and other applications. The nanolaminate layer can be applied before or after the nanolaminate coated, low permeability polymer film is attached to a conventional high permeability multilayer printed circuit board assembly constructed of inorganic fillers and high permeability resins such as epoxy-based resins. Inclusion of the nanolaminate layer within a free standing, metallized low permeability homogeneous polymer film eliminates the need for application of the nanolaminate coating and selective patterning of the nanolaminate film at the board fabricator or circuit board assembly facility. The low permeability free standing nanolaminate film can then be fabricated cost effectively in batch coating systems and in higher class clean room conditions.

[0005]Further embodiments employ hermetic electronic, optical or electro-mechanical architectures utilizing the metallized, nanolaminate coated, low permeability homogeneous polymer film laminated to conventional multilayer printed circuit board layers. The thin, low permeability film is mechanically constrained by the relatively thick conventional circuit board composed of epoxy-based, polyimide-based or other laminates filled with glass, ceramic or other filler materials designed to lower the coefficient of expansion of the multilayer circuit board. A hermetic lid assembly is fluxlessly sealed to metallized regions on the circuit board to enclose open faced or lip chip semiconductor or other components. The standard leak rate allowed by Military and Industry Standards for packages greater than 0.4 cc in volume is 1.0 E-6 atm·cc / sec. For packages less than or equal to 0.4 cc in volume and greater than 0.01 cc in volume, the standard allowed leak rate is 1 E-07 atm·cc / sec. Thus, organic or polymer based hermetic packages can be realized over a wide range of sizes using embodiments of this disclosure. Embodiments of this architecture further provide hermetic construction features allowing for the efficient removal of heat from components which dissipate a high amount of power.

Problems solved by technology

Such packages are inherently expensive, and require significantly more size, weight and cost than would be required by directly mounting the active components to the circuit board.

Additionally, the prepackaged devices increase the electrical loss and thermal impedance of the assembled devices.

Plastic encapsulated devices are also inherently more moisture sensitive and can subject the semiconductor devices to dielectric loading effects that degrade device performance and reliability.

For flip chip devices, dielectric loading from flip chip underfill or aerogel can be a major source of degraded output power due to increased internode capacitance.

Prior attempts to achieve a hermetic board assembly using polymeric based materials do not recognize or embody the design features, construction and material properties of the board laminate and coating required to achieve a hermetic level of environmental protection to military and industrial leak rate standards.

While low permeability coatings on conventional circuit boards have been envisioned to offer the potential to seal high moisture permeability boards, the board and laminate construction and circuit board fabrication process and the associated coating construction and coating process to realize requisite hermeticity has not been envisioned.

The difficulty in achieving a coated, low permeability circuit board arises from multiples causes including the use of conventional board material construction and properties, the three-dimensional nature of the board's metallized surface and inherent defects in the board's surface and inherent defects in the coating limiting the ability of the coating to achieve the requisite low moisture permeability.

Further, the requisite materials and associated property characteristics have not been defined.

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