Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
2002-01-08
2004-10-19
Hamilton, Cynthia (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S280100, C430S330000, C430S325000, C522S146000, C427S496000, C427S504000, C427S510000, C427S511000
Reexamination Certificate
active
06806033
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of photoimagable dielectric materials and their manufacture. It also relates to the use of such materials in the production of printed circuit boards and printed wiring boards.
BACKGROUND OF THE INVENTION
Current photoimagable dielectric (PID) materials, such as Probimer and Probelec from Vantico, and Dynavia 2000 from Shipley Ronal, have been used in Surface Laminar Circuit™ (SLC) technology as a build-up material. The material is applied to the subcomposite circuit board, and is dried. The vias are then imaged into the dielectric layer, and then the material is cured. Subsequent processing includes a surface treatment, copper plating, and circuitization. This process can be repeated for additional build-up layers, or the substrate can be finished by applying solder mask and the appropriate surface finish.
A common use of SLC technology is in chip carrier substrates. In some applications, specifically those relating to original equipment manufacture, it is desirable to conform to JEDEC standards. One of the JEDEC tests, deep thermal cycling (DTC), subjects the assembled modules to thermal cycling between −55° C. and 125° C. and, in some cases, from −65° C. to 150° C. With certain designs, the PID material may crack during thermal cycling and the crack often propagates through the material causing a break in the underlying electrical circuit line, creating a short or open circuit. This cracking is due to the strain placed on the material by bending of the substrate and by mismatches in the coefficient of thermal expansion (CTE), for example between the copper and the epoxy. Typically, if the localized strain exceeds the ductility of the material, the material will fail. A material may also break by repeated bending at a lower strain, such as during thermal cycling, due to material fatigue. Another factor here is the glass transition temperature (Tg) of the material. This is the temperature at which an amorphous material, such as most polymers, changes from a brittle vitreous state to a plastic state. Since the CTE of polymers typically increases significantly above the Tg, it is desirable to use a material with a Tg higher than the maximum temperature at which the material is stressed.
Typical approaches to solving these problems include adding a thermoplastic component to increase the ductility of the polymer, or adding a filler material to lower the CTE. However, adding a filler can significantly reduce the ductility. In addition, both of these approaches can degrade the photo resolution of the PID.
The resins that are combined to create a polymer formulation will be hereinafter referred to as a “resin blend” This resin blend needs to meet various material and processing objectives for easy manufacture. Also, it is desirable to have a polymer formulation that has high ductility and high flex fatigue life. Furthermore, it is necessary that this polymer system be photoimagable. One approach to formulating a PID material is to use epoxy resins and cationic photoinitiators. There are many epoxy resins available with a range of properties. Cationic photoinitiators suitable for polymerizing epoxies include sulfonium and onium salts and ferrocene derivative salts.
Epoxy starting materials available in the industry may be mono, di, or poly functional. Most epoxy pre polymers are low molecular weight. It is typical for resins synthesized from polymers of low molecular weight epoxy starting materials to be brittle. Some epoxies have a high Tg, but the general trend is for materials with a high Tg to be brittle below the transition temperature. Flexible polymers typically do not have a high Tg. This makes the formulating of such a material with a high Tg, a high ductility, and a low CTE, a challenge.
U.S. Pat. No. 5,061,779 describes the production of a resin capable of filling plated through holes. This resin contains brominated materials and is thermally cured resulting a material having a Tg>75° C. This patent does not teach the production of high Tg and high flex materials for photoimagable applications.
U.S. Pat. Nos. 4,686,250 and 4,593,056 relate to a resin capable of yielding high tensile strength fibers via a wet winding process. The resin in −250 contains cycloaliphatic epoxy and Epon-type resins and aromatic diamine components. The resin in −056 utilizes difunctional epoxy and Epon-like epoxy resins along with an aromatic diamine hardener component. The resin is thermally cured by use of an aromatic trihydroxy cure accelerator. The patents do not teach the production of high Tg and high flex materials for PID applications. Furthermore, these diamines are basic and would tend to neutralize the effect of acidic compounds that are used as cationic photoinitiators.
U.S. Pat. No. 6,184,263 relates to the production of a photoimagable material. This objective is achieved by incorporating a photocationic initiator into a polymeric backbone. Crosslinking is achieved by attaching reactive pendant groups, such as epoxies, acrylates or allyl ethers, to an unrelated polymer backbone.
U.S. Pat. No. 5,278,259 relates to a polymeric resin with good heat resistance and good adhesion to copper, along with good flexibility and high bend strength. The resins can include a blend of difunctional and trifunctional epoxies that are thermally cured using imidazoles.
U.S. Pat. No. 5,584,121 relates to difunctional and trifunctional epoxies that are catalyzed by a photocationic initiator for use as an adhesive. It also includes tin and a polybutadiene toughener. The reported Tg is in the range of 100° to 130° C.
U.S. Pat. No. 5,726,216 describes formulations containing difunctional and trifunctional epoxies along with a thermoplastic toughener, with an object of producing high Tg materials. The formulations are cured utilizing high energy radiation. The use of UV light is not described. The use of the formulations for photoimagable dielectrics is not discussed.
German Pat. No. DE 4217509 discloses a low viscosity mixture of a trifunctional epoxy with a diclycidyl ether based on bisphenol F and a highly functionalized amine-based resin component. The mixture may include silica. It is cured using a thermal catalyst. The mixture is used for prepreg/laminate applications, but is not mentioned as being useful for the photoimagable dielectrics.
BRIEF DESCRIPTION OF THE INVENTION
It is an objective of the present invention to provide a photoimagable polymer having a high glass transition temperature along with good flexibility.
Another objective is the use of a photoimagable polymer as a surface layer on an electronic substrate wherein the polymer has a high Tg and high flexibility.
These and other objectives that will become apparent are achieved in accordance with the following discussion.
The present invention relates to a polymer consisting of a mixture of a polyfunctional epoxy resin and the condensation product of a bisphenol and an epihalohydrin. The polymer is cured by a photocationic initiator, such as a sulfonium compound. The polymer is characterized by a glass transition temperature of at least about 140° C., preferably about 150° C. or above and a flex fatigue life of at least about 10,000 cycles measured at a 3% strain. The polyfunctional epoxy resin typically comprises the triglycidyl ether of tris (hydroxy phenyl) while the condensation product of the bisphenol and epihalohydrin comprises a diglycidyl ether of bisphenol A (abbreviated as DGEBPA). Up to about 10% of a third selected resin may be added to further improve the flexibility of the polymer without lowering the glass transition temperature. The process of making the polymer comprises the steps of: a) preparing a resin mixture of a polyfunctional epoxy resin and the condensation product of a bisphenol and an epihalohydrin; b) incorporating an effective amount of a cationic photoinitiator into the resin mixture, c) exposing the resin mixture to a source of actinic radiation, and d) further processing the resin mixture using heat or other means to cr
Appelt Heike
Jakubek Vladimir
Russell David John
Ruud Cory J.
Driggs Lucas Brubaker & Hogg Co. LPA
Hamilton Cynthia
International Business Machines - Corporation
Lucas James A.
LandOfFree
Photoimaged dielectric, its manufacture and use in electronics does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Photoimaged dielectric, its manufacture and use in electronics, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Photoimaged dielectric, its manufacture and use in electronics will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3263494