Metal treatment – Process of modifying or maintaining internal physical... – Producing or treating layered – bonded – welded – or...
Reexamination Certificate
1999-04-21
2001-04-10
Wyszomierski, George (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Producing or treating layered, bonded, welded, or...
C228S115000, C228S117000
Reexamination Certificate
active
06214135
ABSTRACT:
FIELD OF THE INVENTION.
The present invention relates to an entry board for drilling small holes, e.g. having a diameter of 0.1 mm-2.0 mm, through an article requiring high accuracy such as a printed circuit board, and also relates to a method of making the entry board and further relates to a method for drilling small holes through a printed circuit board by using the entry board.
BACKGROUND OF THE INVENTION
Electronic techniques have been widely applied in various kinds of fields including not only the electric or communication fields of telephones, televisions, computers (including personal computers), lights and controlling devices utilized in various kinds of manufacturing industries, but also other fields including automobiles, office electronic supplies, cameras, toys, and the like. At the same time, the techniques have required high performance and high accuracy. Thus, in the fields of printed circuit boards, circuit patterns formed on the board have rapidly become more minute, as well as high density and multi-layered. As a result, the width of each circuit pattern and the distance therebetween have become narrower. Especially, in printed circuit boards of a through hole type, the holes have become smaller in diameter, and the number of holes has been increased. Further, the positions of holes have required high accuracy.
In drilling holes through a multilayered board, drilling small holes each having a diameter of 0.3-0.4 mm has been conventionally conducted. Recently, drilling much smaller holes each having a diameter of 0.1-0.3 mm has been practically conducted, and such demands as drilling smaller holes and increasing the number of holes with higher accuracy of drilling to position will be further required.
In drilling such small holes, as shown in
FIG. 4
, it has been known that placing an entry board
1
on a printed circuit board
5
enables easy introduction of a drill
8
which in turn improves accuracy of the drilling positions of a hole
9
drilled on the printed circuit board
5
and also enables drilling holes without causing burrs, or the like, around the holes. There have been several proposals concerning such entry boards.
Japanese Patent Publication 61-61921 (hereinafter referred to as JP 61-61921) discloses a method for drilling through a printed circuit board by using an entry board. The entry board comprises a base plate made of wood pulp and glass fiber and aluminum foils or the like covering both surfaces of the base plate. Japanese Patent Unexamined Publication SHO 62-214000 (hereinafter referred to as JP 62-214000) discloses a method for drilling a printed is circuit board by using an entry board which comprises a base plate made of aluminum foils and papers covering both surfaces of the base plate. Japanese Patent Unexamined Publication SHO 63-11207 (hereinafter referred to as JP 63-11207) discloses a method for drilling through a printed circuit board by placing an entry board made of metallic foil on the printed circuit board and by way of an adhesive layer formed on one surface of the metallic foil.
However, in the method disclosed in JP 61-61921, because hard materials such as JIS (Japanese Industrial Standard) 3003-H19 homogenized aluminum alloy as the aluminum foils are used as a surface layer of an entry board, a drill tends to slip on the aluminum foil, resulting in decreased drill positioning accuracy. Further, in such a case that adhesive layers are used to connect the aluminum foils to the base plate, the entry board becomes a five-layered structure, resulting in an increased manufacturing cost. In the disclosure of JP 62-214000, the paper thereof lacks heat-resistance ability and paper dust is generated during drilling, resulting in problems in the following procedures such as a plating procedure. Further, in the method disclosed in JP 63-11207, it is unavoidable to have the sticking of chips produced when drilling to the adhesive layers.
As mentioned above, in the conventional methods, there have still been problems in drilling small holes. Further, as the pattern formed on the printed circuit board reduces in size, the size of each hole to be drilled becomes smaller and the number of the holes increases, the rotation speed of the drill becomes higher and the diameter of the drill becomes smaller which results in rotational deflection of the drill. Furthermore, there have been more strict demands for improving accuracy of the drilling position and decreasing the allowable height of burrs. In spite of such demands, as the above mentioned conventional entry boards are still being used, accuracy of the drilling position has not been improved and drill breakages occur when it is attempted to improve the accuracy of the drilling position and to decrease the generation of burrs.
SUMMARY OF THE INVENTION
In view of the foregoing disadvantages that are inherent in conventional entry boards, the present invention aims to provide an improved entry board for drilling small holes through a printed circuit board, or the like, which enables easy introducing of a drill, improving accuracy of drilling position by restraining slipping of a drill on the surface of the entry board, increasing the number of work items (“works”) to be drilled such as a printed circuits board at one time, decreasing the number of drill breakages and further decreasing the generation of burrs.
It is also an object of the invention to provide a method for making the entry board mentioned above.
It is another object of the invention to provide a method of drilling small holes by using the entry board mentioned above.
The above and other objects are accomplished by an entry board including a front surface layer made of aluminum or aluminum alloy disposed on a drilling inlet side, a back surface layer made of aluminum or aluminum alloy disposed on a drilling outlet side, wherein both the layers are bonded together or are joined by clad rolling, and wherein hardness of the front surface layer is smaller than that of the back surface layer.
Because of the front surface layer having smaller hardness, a drill can easily be introduced, accuracy of drilling position can be improved and slipping of a drill on the entry board can be restrained, vibration of a rotating drill caused by a thin drill can be effectively restrained and drill breakages can be decreased. On the other hand, because of the back surface layer having higher hardness, generation of burrs can be decreased.
Thickness of the front surface layer may preferably fall within the range of from 5 to 100 &mgr;m and micro vickers hardness (Hv) of the front surface layer may fall within the range of from 20-50. Thickness of the back surface layer may preferably fall within the range of from 30-200 &mgr;m and micro vickers hardness (Hv) of the back surface layer may exceed 50, but does not exceed 140.
Roughening treatment may preferably be conducted on the surface of the front layer to obtain a central average roughness (Ra) of 0.15-0.30 &mgr;m. This treatment is effective to prevent a drill from slipping when drilling and improves accuracy of drilling position. However, hardness of the front surface layer most effectively contributes to improvement of the accuracy of the drilling position. The next important contributions to such improvement include thickness and surface roughness.
The above objects are also accomplished by a method for making an entry board. The method includes the steps of clad rolling a pure aluminum alloy sheet to be composed of a surface layer and an Al—Mn aluminum alloy to be composed of a back surface layer, and then annealing them at the temperature of 200-260° C. This method easily enables one to differentiate hardness of both of the layers by utilizing softening characteristics thereof.
Furthermore, the above objects are accomplished by a method for drilling small holes through a printed circuit board. The method includes the steps of preparing an entry board. The entry board includes a front surface layer made of aluminum or an aluminum alloy to be disposed on a drilling inlet side and a back
Fukuda Akio
Miyano Koji
Washio Yasushi
Showa Aluminum Corporation
Wyszomierski George
LandOfFree
Entry board for drilling small holes, a method of making the... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Entry board for drilling small holes, a method of making the..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Entry board for drilling small holes, a method of making the... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2546455