Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
1998-04-03
2001-07-03
Duda, Kathleen (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S313000, C430S316000, C428S096000
Reexamination Certificate
active
06255039
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention pertains to the production of printed circuit boards. More particularly, the invention concerns the production of high density built-up multilayer circuit boards by constructing microvias with photoimageable dielectric materials.
2. Description of the Prior Art
As the need for faster, smaller, less expensive integrated circuit products continues grow, the ability to wire-bond reaches the limits of the available technology and chips must be mounted using a flip-chip approach and solder bumps. This leads to a direct chip attachment package. The requirement to fan-out the high number of I/O's from the underside of the chip places increasing demands on utilization of the printed circuit board area. Plated-through-holes use too much space and block routing channels. This drives the need for a high density package with a significant number of interconnections on the outer surface of the board as well as for increasing use of blind microvias.
Resin coated copper (RCC) has been used in the past to economically fabricate high density built-up multilayer circuit boards. Currently microvias in such circuit boards fabricated with RCC are produced by two methods, including plasma etching and laser drilling. As such, only printed circuit fabricators with access to plasma etching or laser drilling equipment can provide these advanced, blind-via boards. The high cost of the plasma and laser equipment hinders widespread adoption of RCC technology. Furthermore, the technical disadvantages associated with the plasma etching and laser drilling techniques, such as undercutting due to isotropic etching of plasma, and low throughput due to sequential drilling by laser, also limit large scale commercialization of RCC based high density multilayer circuit boards.
Alternatively, photovia processes, which use photoimageable dielectric materials to fabricate builtup multilayer printed circuit boards have been developed. In theses processes, photodielectrics are coated on a patterned core and photoimaged to define via holes. The via holes along with the surface of the dielectric layer are then plated with copper. U.S. Pat. No. 5,354,593 sequentially laminates and photoimages two photodielectrics onto a conductive core to define via holes and then copper plates the via holes. U.S. Pat. No. 5,451,721 produces a multilayer printed circuit board by applying a photosensitive resin layer onto a core having a metal line on its surface. After imaging to form via holes, the resin layer is deposited with a copper layer by electroless plating techniques. U.S. Pat. No. 5,334,487 produces a pattered layer on a substrate by applying and exposing different photosensitive compositions on opposite sides of a copper foil. One side is developed and the copper etched, followed by developing the other side and metallization of through holes.
The foregoing photovia technologies allow for fabrication of high density interconnection printed circuit boards with conventional equipment but they suffer from similar drawbacks such as difficult copper plating processes and poor resin-to-copper adhesion. These problems usually lead to poor reliability of the circuit boards. These problems are solved by the present invention whereby a photosensitive dielectric composition on a conductive foil is laminated to conductive lines on a substrate. After imaging the foil, and imaging and curing the photosensitive dielectric composition, vias are formed to the conductive lines. Thereafter the conductive lines are connected through the vias to the conductive foil, and then the conductive foil is patterned.
SUMMARY OF THE INVENTION
The invention provides a process for producing a printed circuit board which comprises:
(a) attaching a photosensitive element onto a pattern of conductive lines on the surface of a substrate; which photosensitive element comprises a negative working photosensitive dielectric composition on a surface of a conductive foil, such that the photosensitive dielectric composition is positioned on the conductive lines;
(b) applying a layer of a photoresist onto an opposite surface of said foil;
(c) imagewise exposing the photoresist to actinic radiation and developing the photoresist to thereby form imagewise removed and imagewise nonremoved portions of the photoresist such that the imagewise removed portions are above at least some conductive lines;
(d) removing the portions of the conductive foil underlying the imagewise removed portions of the photoresist without removing the underlying photosensitive dielectric composition;
(e) imagewise exposing a portion of the photosensitive dielectric composition to actinic radiation through the removed portions of the conductive foil; developing the photosensitive dielectric composition to thereby form imagewise removed and imagewise nonremoved portions of the photosensitive dielectric composition such that the imagewise removed portions form vias to the conductive lines;
(f) curing the nonremoved portions of the photosensitive dielectric composition;
(g) electrically connecting the conductive lines through the vias to a part of the conductive foil; and
(h) patterning the conductive foil to thereby produce a pattern of conductive foil lines.
The invention also provides a process for producing a printed circuit board which comprises applying a layer of a negative working photosensitive dielectric composition onto a surface of a conductive foil thereby forming a photosensitive element and then following steps (a) through (h) above.
The invention further provides process for producing a printed circuit board which comprises:
(a) attaching a photosensitive element onto a pattern of conductive lines on the surface of a substrate; which photosensitive element comprises a negative working photosensitive dielectric composition on a surface of a conductive foil, such that the photosensitive dielectric composition is positioned on the conductive lines;
(b) removing the conductive foil;
(c) imagewise exposing a portion of the photosensitive dielectric composition to actinic radiation and developing the dielectric composition to thereby form imagewise removed and imagewise nonremoved portions of the dielectric composition such that the imagewise removed portions are above at least some conductive lines thus forming vias to the conductive lines;
(d) curing the nonremoved portions of the photosensitive dielectric composition;
(e) simultaneously forming an electrically conductive layer on the nonremoved portions of the dielectric composition and electrically connecting the conductive lines through the vias to the electrically conductive layer; and
(f) patterning the electrically conductive layer to thereby produce a pattern of conductive lines.
The invention still further provides a process for producing a printed circuit board which comprises applying a layer of a negative working photosensitive dielectric composition onto a surface of a conductive foil thereby forming a photosensitive element and then following steps (a) through (f) in the preceding paragraph.
By the process of the invention microvias are produced by using negative acting photosensitive resin coated metals such as copper. This product and process allows a substantial reduction in the cost of printed circuit board fabrication process as compared to plasma or laser drilling techniques. The photo microvia technology also avoids the technical barriers associated with the plasma and laser drilling methods such as undercutting due to isotropic etching of plasma and low throughput due to sequential drilling by laser. As compared with the existing photovia technologies, this invention permits easy copper plating and better copper-to-resin adhesion.
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patent: 5334487 (1994-08-01), Kindle et al.
patent: 5354
Gotro Jeffrey T.
Haas David
Petti Michael A.
Vallance Michael
Xu Chengzeng
Duda Kathleen
Isola Laminate Systems Corp.
McDonnell Boehnen Hulbert & Berhgoff
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