Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
1999-06-07
2001-05-08
Lam, Cathy F. (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C174S255000, C174S258000, C174S261000
Reexamination Certificate
active
06228466
ABSTRACT:
This application is the national phase of international application PCT/JP98/00956 filed Mar. 9, 1998 which designated the U.S.
BACKGROUND OF THE INVENTION
The present invention relates to a printed wiring board having bumps, ball pads or the like to which solder balls are applied, and a method of manufacturing the same.
There is a conventional printed wiring board which has a conductor circuit on an insulating substrate and a surface insulating layer provided on the surfaces of the insulating substrate and the conductor circuit and formed of a solder resist layer or a glass cloth resin layer.
In general, bumps or ball pads are provided on the surface of the printed wiring board which is connected to an electronic part, another printed wiring board or the like via solder balls applied on those bumps or ball pads.
The bumps or ball pads are formed by exposing the conductor circuit underlying the surface insulating layer by local removal of the surface insulating layer.
This conventional printed wiring board has the following drawbacks.
At the time of forming bumps or ball pads on the printed wiring board, the surface insulating layer is locally removed, thereby exposing the sides of the conductor circuit. This may reduce the strength of adhesion between the conductor circuit and the insulating substrate.
In providing solder balls on the bumps or ball pads with the above structure, the solder balls on the bumps or ball pads may be flattened due to the exposed sides of the conductor circuit and high adhesion strength of the solder balls to those sides.
When the solder balls are flattened, it is not possible to maintain the proper distance between the insulating substrate and an electronic part, another printed wiring board or the like which is connected to this printed wiring board via the solder balls. This may result in a reduced reliability of connection between them.
As the amount of heat generated by electronic parts tends to increase, printed wiring boards are provided with heat discharging means such as connection of solder balls or formation of thermal via holes for discharging heat. The heat discharging performance of the conventional printed wiring boards, however, has not yet been improved to a satisfactory level.
Accordingly, it is an object of the present invention to provide a printed wiring board with excellent heat discharging performance, which has an enhanced adhesion strength between a conductor circuit and an insulating substrate and ensures a high reliability of connection between this printed wiring board and a mounted part, such as another electronic part or another printed wiring board at the time of connecting such a part to this printed wiring board via solder balls applied to bumps, ball pads or the like provided on the conductor circuit and the insulating substrate, and a method of manufacturing the same.
SUMMARY OF THE INVENTION
According to a first aspect of this invention, a printed wiring board comprises an insulating substrate having a conductor circuit thereon; and a surface insulating layer provided on surfaces of the insulating substrate and the conductor circuit and formed of a solder resist layer or a glass cloth resin layer, part of the conductor circuit having an exposed conductor section with an exposed surface, the surface insulating layer around the exposed conductor section forming a recessed section level the same height as or lower than the surface of that exposed conductor section and higher than the surface of the insulating substrate, the surface insulating layer of the recessed section being in contact with sides of the exposed conductor section.
The recessed section and the exposed conductor section can be used as a so-called bump or a ball pad. Specifically, a solder ball or the like is put on the exposed conductor section, and a to-be-mounted part such as another electronic part or another printed wiring board can be connected to this printed wiring board via such solder balls while securing electric connection to the conductor circuit.
The to-be-mounted part may be a pad of an electronic part such as a flip chip, BGA (Ball Grid Array), chip scale package, chip size package, TCP (Tape Carrier Package) or lead-less chip carrier, or a printed wiring board on which such an electronic part is to be mounted.
The advantages of the first aspect of this invention will be described below.
In a printed wiring board according to the first aspect of this invention, part of the conductor circuit has an exposed conductor section with an exposed surface.
The surface insulating layer around the exposed conductor section forms a recessed section level the same height as or lower than the surface of that exposed conductor section and higher than the surface of the insulating substrate, and the surface insulating layer of the recessed section is in contact with sides of the exposed conductor section.
This structure allows the surface insulating layer to cover the sides of the conductor circuit, thereby reducing the amount of exposure of the sides. This enhances the adhesion strength between the conductor circuit and the insulating substrate. The increased adhesion strength can prevent the conductor circuit from being separated from the insulating substrate.
When a solder ball is put on the exposed conductor section, it is repelled by the surface insulating layer and is less likely become flattened.
That is, a solder ball adheres well to the sides of the conductor circuit. Therefore, solder forming the solder ball easily moves to cover the sides of the conductor circuit so that the amount of solder remaining on the surface of the exposed conductor section is reduced by the amount of the movement.
As the amount of exposure of the sides of the conductor circuit of the printed wiring board according to the first aspect of the invention is small, a large amount of solder can remain on the exposed conductor section.
This permits the proper distance to be maintained between the exposed conductor section and a to-be-mounted part, such as another electronic part or another printed wiring board, at the time of connecting the to-be-mounted part to this printed wiring board using solder balls. It is thus possible to increase the reliability of connection between the to-be-mounted part and the exposed conductor section (conductor circuit).
As apparent from the above, the first aspect of this invention can provide a printed wiring board, which has an enhanced adhesion strength between a conductor circuit and an insulating substrate and can ensure a high reliability of connection between this printed wiring board and a to-be-mounted part such as another electronic part or another printed wiring board at the time of connecting such a part to this printed wiring board via solder balls applied to bumps, ball pads or the like provided on the conductor circuit and the insulating substrate.
The printed wiring board acquired by the first aspect of this invention can be used for a memory module, multi-chip module, mother board, daughter board, plastic package or the like which demands a high connection reliability.
It is preferable that the surface insulating layer is formed of a glass cloth resin layer. This provides a structure which can endure stress caused by a thermal expansion difference between a chip or package and the substrate. Further, this structure reduces the thermal expansion difference, resulting in a better performance.
It is preferable that the surface insulating layer should have a double-layer structure comprising a solder resist layer and a glass cloth resin layer formed on the surface thereof.
As the solder resist effectively repels solder, it suppresses sideward spreading of solder and has an effect of setting a chip or package apart from the printed wiring board so that thermal stress can be avoided more.
It is preferable that the surface insulating layer of the recessed section is positioned lower than the surface of the exposed conductor section by 0 to 15 &mgr;m. This ensures high strength of solder balls and high positioning precision. Furt
Kobayashi Hiroyuki
Kondo Mitsuhiro
Takada Masaru
Tsukada Kiyotaka
Ibiden Co. Ltd.
Lam Cathy F.
Pillsbury & Winthrop LLP
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