Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1999-09-02
2001-09-04
Arbes, Carl J. (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S846000, C029S884000, C174S264000
Reexamination Certificate
active
06282782
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to circuit board layers, and more specifically to a method and apparatus for forming plugs in one or more vias defined by a circuit board layer, and the product obtained using this method.
BACKGROUND OF THE INVENTION
Circuit board through-holes are commonly plated or filled with conductive material in order to provide for the transfer of electrical signals from one surface of the circuit board layer to a second surface of the circuit board layer.
Filled through-holes are typically through-holes which receive contacts or pins of some element external to the circuit board. The through-holes typically are filled manually with a molten conductive material, to both physically and electrically connect the external element to the circuit board. It is also known to form a plug in the through-holes by a method which includes filling the through-holes with a first layer of conductive material, curing this layer, planarizing the circuit board layer to remove the conductive material cured to the surface of the circuit board layer, filling the through-holes with a second conductive material, and curing this second material. Both of these methods are time-consuming and expensive. Furthermore, not only does the latter method require several filling steps, but it also involves a substantial alteration of the surface of the circuit board layer in order to remove the conductive material that is cured onto the surface of the circuit board layer.
Plated through-holes generally involve electroless copper plating which is expensive and coats only the inside surface of the through-holes. It is known to form a thin meniscus of non-conductive or dielectric material within a via plated with conductive material using a screen without a stencil. This typically is done to allow vacuum hold down of circuit boards for testing, or to prevent assembly materials from propagating from one side of the circuit board to the other, but may be done for other reasons as well. However, the meniscus formed is susceptible to corrosion, thus decreasing the yield of acceptable circuit boards and increasing their cost.
Furthermore, methods of forming plugs in circuit board layers which result in significant alteration of the surfaces of circuit board layer is a disadvantage, particularly if it is desirable to print the circuit board prior to plug formation.
A problem encountered with sequential lamination, as well as lamination in general, is resin loss during lamination. Resin loss is problematic as lost resin present on the surface of the laminate will cure to the outer surfaces of the laminate. Further, resin loss may result in insufficient lamination of the layers. Also, loss of resin into vias may result in a dimpled laminate surface over the via, due to the loss of resin in that area.
In sequential lamination of printed circuit board subassemblies, resin loss typically is reduced by placing rubber pads against the outer layers of the subassemblies during lamination in order to stop resin flow to the outer surfaces of the subassemblies. One disadvantage to this approach is that resin still flows into the vias and, in some cases, results in unsatisfactory bonding between the subassemblies.
Therefore, there exists a need in the art for a method and apparatus to quickly and efficiently form plugs in circuit board through-holes at an acceptable yield and cost. There is a further need for a method of forming plugs in circuit board through-holes without significantly altering either surface of the circuit board layer. Finally, there exists a need in the art for a method to provide a plug with minimal voids formed therein.
SUMMARY OF THE INVENTION
This invention provides a novel method and apparatus for forming plugs in vias of a circuit board layer, and the novel product produced by this novel method.
In one aspect, the present invention provides a novel method of forming one or more plugs in a circuit board layer. First, a circuit board layer is provided, the circuit board layer having a first surface, a second surface, and defining a via containing a plug material in a volatile solvent. The volatile solvent is then evaporated. This may be accomplished at a controlled rate so that the presence of voids in the resulting plug is minimized. In one embodiment, plug material present on the first surface and the second surface of the circuit board layer is substantially removed without causing a significant alteration of either surface of the circuit board layer. Finally, the plug material is cured to form a plug contained within the via defined by the circuit board layer in the case of a conductive plug, or defined by the plated circuit board layer in the case of a nonconductive plug.
In another aspect, the circuit board layer including the plug formed therein is described in terms of the novel method described above.
In yet another aspect, the present invention provides a novel apparatus for filling the one or more of a plurality of vias formed in a circuit board layer. This apparatus is called a fixture and it includes a planar template and an air permeable layer. The template has a first surface, a second surface, and defines one or more through-holes corresponding in position to the one or more vias defined by the circuit board layer. The air permeable layer is disposed on the second surface of the template. In a preferred embodiment, this air permeable layer is substantially impermeable to the plug material so that the plug material is substantially contained within the fixture.
In yet another aspect, the present invention provides a novel method of forming a subassembly comprising a circuit board layer, the circuit board layer having one or more plugs formed therein. First, a circuit board layer is provided, the circuit board layer having a first surface and a second surface, and defining a via containing a plug material in a volatile solvent. The volatile solvent is then evaporated and the plug material cured. Finally, the circuit board layer is laminated to two sheets of conductive material with two intermediate layers of prepreg material.
In another aspect, the subasssembly and a printed circuit board including the subassembly is described in terms of the novel method described above.
In yet another aspect, the present invention provides a novel method of forming one or more plugs in a subassembly for use in a printed circuit board. First, a subassembly is provided. The subassembly includes a circuit board layer laminated to two sheets of conductive material with two intermediate sheets of prepreg material. A via is formed in the circuit board laminate, the via is plated, and then the via is filled with a plug material in a volatile solvent. The volatile solvent is evaporated and finally the plug material is cured.
In another aspect, a subassembly and a printed circuit board including the subassembly formed therein are described in terms of the novel method described above.
In yet another aspect, the present invention provides a novel method of forming a circuit board layer with a partially filled via. First a circuit board layer is provided that includes a first surface, a second surface, and defines a via. A portion of the via is filled with a plug material in a volatile solvent. The volatile solvent is evaporated and the plug material is then cured to form a partially filled via.
In another aspect, a printed circuit board and a circuit board including the partially filled via formed therein is described in terms of the novel method described above.
In yet another aspect, the present invention provides a novel method of forming a circuit board layer comprising a thermally conductive plug for transfer of thermal energy from a first surface of the circuit board layer to a second surface of the circuit board layer. First, a circuit board layer is provided that has a first surface, a second surface, and defines a via containing a thermally conductive plug material in a volatile solvent. The volatile solvent is evaporated and the thermally conductive plug mat
Biunno Nicholas
Bryan Scott
Hu Mason
Arbes Carl J.
Hadco Santa Clara, Inc.
Testa Hurwitz & Thibeault LLP
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