Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Post imaging radiant energy exposure
Utility Patent
1999-06-17
2001-01-02
Duda, Kathleen (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Post imaging radiant energy exposure
C430S329000, C430S945000, C134S001300, C438S940000
Utility Patent
active
06168910
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for producing a printed board. More particularly, the present invention relates to a high-precision, low cost technique for forming a through-hole or dead-end hole in a printed resin board, and to a technique for reducing the amount of resin residue remaining inside or around the hole.
BACKGROUND OF THE INVENTION
Along with the recent miniatuarization and high functionalization of electronics, a printed board used for mounting a semiconductor or testing has been increasingly required to permit fine and high density wiring. As a result, a hole formed for providing a protruding contact point and the like as a probe on a printed board needs to be fine and formed at high densities.
In particular, fine holes having a diameter of not more than 100 &mgr;m are advantageously formed by laser ablation. As the light source for such hole-forming, an excimer laser is particularly preferable. The excimer laser has an oscillation wavelength of not more than 400 nm, and laser ablation using said laser for resin decomposition enables formation of fine holes having a diameter of not more than 100 &mgr;m with high precision.
On the other hand, laser ablation is uneconomical due to its high processing cost caused by the long processing time necessary for forming holes and low energy utilization efficiency, as explained in the following.
FIG. 5
shows an embodiment of conventional processing, wherein a laser beam
2
is output from a light source
1
(excimer laser), passes through a scanning mirror
14
, a mask
4
and an imaging lens
6
, and hits a printed board
7
to form a through-hole. Such a method for forming a hole (inclusive of through-hole and dead-end hole) which comprises shooting a laser beam through the mask
4
, the mask
4
having light path holes
5
for the passage of the light, which correspond to the holes to be formed in the printed board
7
, wherein the laser beam
2
which passed the light path holes
5
ablates the printed board
7
and forms holes, is a mask imaging method.
As shown in
FIG. 6
wherein conventional laser ablation is used, when the entire pattern
13
of the arrangement of the light path holes
5
formed in a mask
4
is greater in size than the sectional area
12
(the size of the section perpendicular to the advance direction of said beam, namely, the size of irradiation area) of the laser beam, the laser beam needs to be moved for scanning.
For example, the laser beam irradiation area should be moved to sequentially follow the pattern
13
of the light path holes
5
(e.g., route
15
shown by arrows in the embodiment of FIG.
6
), so that the laser beam successively passes the light path holes
5
. In the embodiment of
FIG. 5
, for example, the scanning mirror
14
is moved to change the irradiation area of the laser beam
2
on the mask. Consequently, some time is necessary for completing entire holes, thus increasing the processing cost.
As shown in
FIG. 7
, moreover, when the entire pattern
13
of the arrangement of the light path holes
5
is smaller in size than the sectional area
12
of the laser beam, the total sectional area (area of the section perpendicular to the axis of the hole) of the light path holes
5
becomes much smaller than the sectional area of the beam, so that only a part of the energy of the laser beam output from the light source passes the holes, wasting the light prevented by the mask. Consequently, this method is uneconomical with low energy utilization efficiency.
For forming a probe, Japanese Patent Unexamined Publication No. 2-129938 proposes a method for producing a circuit board, which comprises forming, by laser processing, fine through-holes in an insulating resin film having a conductive circuit in the thickness direction of said insulating resin film, filling the through-holes with a metallic material to be a contact material by a method such as plating, and forming a bump electrode by allowing further protrusion.
When the hole in which a bump electrode is to be formed is provided by various laser beams having a relatively high output power, such as CO
2
laser, YAG laser and excimer laser, the residue produced thereby imposes a different problem.
For example, when a through-hole is formed in a resin layer by CO
2
laser, YAC laser and the like and a conductive circuit is exposed on the inner bottom of said hole, a slight amount of a processing residue is produced on the exposed conductive circuit, as shown in FIG.
8
(
b
), due to which a bump electrode cannot be formed.
In the ablation processing using excimer laser beam, the material of the resin layer which absorbed the laser beam is decomposed and diffused, and, as shown in FIG.
8
(
b
), adheres not only to the inside of the through-hole but to the circumference of said hole as a decomposition residue. When the decomposition residue is present around the hole during the growth of a bump electrode, the main component, carbon, causes unintended growth of the bump electrode extending from the hole in the planar direction of the resin layer to result in short circuit between neighboring bump electrodes and variation in height and outer diameters of the bump electrodes, thus resulting in possible occurrence of defective products.
The processing residue and decomposition residue produced by the above-mentioned laser processing cannot be removed sufficiently by a mechanical removing means using a brush and the like, immersion in water or organic solvent, ultrasonic vibration and the like. In particular, when the center pitch or diameter of the through-hole is not more than several dozen gm, this problem becomes prominent.
It is therefore an object of the present invention to provide a method for forming a hole by laser ablation capable of forming a hole in the resin layer of a printed board at a higher speed with an improved energy utility efficiency, while producing less amount of residue.
It is another object of the present invention to provide a method for removing a residue remaining inside and in the circumference of the hole provided in the resin layer of a printed board, by adapting the above-mentioned processing method of the present invention.
SUMMARY OF THE INVENTION
According to the present invention, when the resin layer of a printed board is exposed to a laser beam having a wavelength permitting laser ablation processing, by a mask imaging method to form a hole, the sectional shape of the laser beam (section perpendicular to the advance direction of said beam) is so reshaped by beam reshaping optics as to individually cover all light path holes corresponding to the holes to be formed, such that the reshaped beam individually shoots the light path holes in the mask at once. The sectional areas of the beams covering individual light path holes upon irradiation of the mask may or may not be connected with the areas of adjacent path holes. The total area thereof is 100%-2000% of the total sectional area (sectional area perpendicular to the axis of the hole) of the light path holes formed in the mask. The laser beam is shot to simultaneously cover said light path holes to form the holes at once.
According to the present invention, moreover, the decomposition residue and/or processing residue of a resin layer material which are/is attached to the periphery or inside of the holes formed by laser processing the resin layer of a printed board are removed by exposure to a laser beam having a wavelength permitting laser ablation processing.
REFERENCES:
patent: 5114834 (1992-05-01), Nachshon
patent: 5294567 (1994-03-01), Dorfman et al.
patent: 5674414 (1997-10-01), Schweizer
patent: 5676866 (1997-10-01), In Den Baumen et al.
patent: 0 679 469 A1 (1995-11-01), None
patent: 5-198496 (1993-08-01), None
patent: 07290264 (1995-11-01), None
patent: 8-323488 (1996-12-01), None
patent: 09029473 (1997-02-01), None
patent: 10-173318 (1998-06-01), None
patent: 10-341069 (1998-12-01), None
Hino Atsushi
Ishizaka Hitoshi
Duda Kathleen
Nitto Denko Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
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