Method of fabricating circuitized structures

Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device

Reexamination Certificate

Rate now

  [ 0.00 ] – not rated yet Voters 0   Comments 0

Details

C430S272100

Reexamination Certificate

active

06706464

ABSTRACT:

BACKGROUND OF THE INVENTION
Photoimageable dielectrics in film form, rather than paste or liquid form, are desirable for a number of reasons. For example, liquid photoimageable dielectrics and paste photoimageable dielectrics run into and partially plug holes, such as via holes; upon development they typically leave a residue in the hole. This leads to defective circuitized substrates and reduces yields. The film photoimageable dielectrics are also employed to cover or “tent” holes thereby eliminating hole filling operations which are expensive and inconvenient. However, for photoimageable dielectric films to remain flexible and not crack during fabrication of the film, application and processing, about a 12% solvent content is typically employed. The presence of the solvent however, leads to additional problems. Often, such photoimageable dielectric films have a low Tg which in turn impairs dielectric properties of the photoimageable dielectric layer in the circuitized substrate. Also, such photoimageable dielectric films tend to stick to the photo-tool used in photoimaging. In an attempt to overcome such problems, such photoimageable dielectric films are baked prior to photoimaging, to drive off a portion of the solvent. However, the bake often causes the photoimageable dielectric film to become quite tacky while the photoimageable dielectric film is being heated. As a result, dust and debris from the bake oven and the ambient surroundings adheres to the surface of the photoimageable dielectric film. During subsequent photoimaging of the photoimageable dielectric film, the dust and debris block the transmission of the ultraviolet light during the photoimaging step. As a result, during the subsequent development of the photoimageable dielectric film, the photoimageable dielectric film which was shielded from the UV by the dust and debris, is unintentionally removed. The unintended removal of the photoimageable dielectric film produces an undesired void in the photoimaged dielectric film. When the workpiece is metallized, the void is often metallized, which may produce a short between circuitry lines.
It is desirable to have methods of fabricating circuitized structures which reduce the formation of unintentional voids or shorts, and which does not plug holes or leave residue in holes.
SUMMARY OF THE INVENTION
The present invention provides a new method for fabricating circuitized substrates which reduces the formation of shorts, and which does not require a bake step to drive off solvent before photoimaging. The method employs an essentially solventless photoimageable dielectric film, having a solvent content typically less than about 5%, preferably less than about 2% and a glass transition temperature, when cured, which is greater than about 110° C. The method for fabricating circuitized structures comprises the following steps: providing a photoimagable dielectric film, which film comprises: from about 95% to about 100% solids, comprising: from 0% to about 30% by weight of the solids, of a particulate rheology modifier; from about 70% to about 100% by weight of the solids of an epoxy resin system comprising: from about 85% to about 99.9% epoxy resins; and from about 0.1 to 15 parts by weight of the total resin weight, a cationic photoinitiator; from 0 to about 5% solvent; applying the photoimagable dielectric film to a circuitized substrate; then exposing the photoimagable dielectric film to actinic radiation.
The epoxy resin system comprises: from about 5% to about 80% of phenoxy polyol resin which is the condensation product of epichlorohydrin and bisphenol A, having a molecular weight of from about 40,000 to about 130,000; from about 0% to about 90% of an epoxidized multifunctional bisphenol A formaldehyde novolac resin having a molecular weight of from about 4,000 to about 10,000; from 20% to 80% of a diglycidyl ether of bisphenol A having a molecular weight of from about 600 to 2,500; from about 10% to about 35% liquid epoxy resin, having a molecular weight of from about 200 to about 600 preferably from about 250 to about 450. The “liquid epoxy resins” are liquid at 20° C. Preferably, the liquid epoxy resins are selected from the group consisting of: a cycloaliphatic epoxy resin, a bisphenol A epoxy resin, and mixtures thereof.
The solvent-less photoimageable dielectrics film eliminates the need for a bake step before photoimaging; thus the circuitized substrate with the non-crosslinked photoimagable dielectric film disposed thereon, is not exposed to, and does not accumulate dust and or debris from the bake oven.
The invention also relates to photoimagable dielectric films employed herein.


REFERENCES:
patent: 3469982 (1969-09-01), Celeste
patent: 3794576 (1974-02-01), Watt
patent: 3984244 (1976-10-01), Collier et al.
patent: 4075051 (1978-02-01), Brzozowski
patent: 4193799 (1980-03-01), Crivello
patent: 4451550 (1984-05-01), Bennett et al.
patent: 4544623 (1985-10-01), Audykowski et al.
patent: 4624912 (1986-11-01), Zweifel et al.
patent: 4948700 (1990-08-01), Maeda et al.
patent: 4985340 (1991-01-01), Palazzotto et al.
patent: 4994346 (1991-02-01), Meier et al.
patent: 5008175 (1991-04-01), Hsieh et al.
patent: 5026624 (1991-06-01), Day et al.
patent: 5079129 (1992-01-01), Roth et al.
patent: 5397685 (1995-03-01), Daniels et al.
patent: 5439766 (1995-08-01), Day et al.
patent: 5665650 (1997-09-01), Lauffer et al.
patent: 5830374 (1998-11-01), Boyko et al.
patent: 6027858 (2000-02-01), Jones et al.
patent: 6204456 (2001-03-01), Lauffer et al.
patent: 2001/0006759 (2001-07-01), Shipley et al.
“Photoimagable Laminates for Thin Applications”, IBM Technical Disclosure Bulletin, Apr. 1995, vol. 38, Issue No. 4, pp. 359-360. (TDB-ACC-No. NN9504359).*
“plate”, “plated, plating, plates” The American Heritage Dictionary, Second College Edition, Houghton Mifflin Company, Bostaon, MA, 1982, p. 949.*
IBM Technical Disclosure Bulletin, Improved Composition for a Dry Film Soldermask, vol. 33, No. 7, Dec., 1990, pp. 162-163.

LandOfFree

Say what you really think

Search LandOfFree.com for the USA inventors and patents. Rate them and share your experience with other people.

Rating

Method of fabricating circuitized structures does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Method of fabricating circuitized structures, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of fabricating circuitized structures will most certainly appreciate the feedback.

Rate now

     

Profile ID: LFUS-PAI-O-3191005

  Search
All data on this website is collected from public sources. Our data reflects the most accurate information available at the time of publication.