Photocopying – Projection printing and copying cameras – Photographing on both sides of photo-sensitive paper
Reexamination Certificate
2000-03-10
2001-04-03
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Photographing on both sides of photo-sensitive paper
C355S053000, C355S072000, C355S075000
Reexamination Certificate
active
06211942
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a double-sided exposure system. More specifically, the present invention relates to a double-sided exposure system capable of sequentially exposing the first and second surfaces of a plate, such as a substrate for a printed wiring board or a sheet for lead frames, through an exposure mask provided with a predetermined exposure pattern to light, and, particularly, provided with a single exposure light source.
2. Description of the Related Art
Generally, an exposure system employed in, for example, a process for fabricating a high-density printed wiring board is provided with an extra-high pressure mercury lamp as an exposure light source for high resolution. The mercury lamp of such a type is a very expensive lamp costing as much as about ¥500,000. The process requires the mercury lamp to be kept continuously lighted and the life of the mercury lamp is only about 500 hr. Therefore, the exposure system of this type must be provided, if possible, with a single light source and the light source must be used at the highest possible economic efficiency; that is, it is desired to reduce the exposure cost of each substrate for a printed wiring board (the running cost of the light source) to the lowest possible extent by using the light source for as many exposure cycles as possible in its life.
To enhance the economic efficiency of the light source, it is important to enhance the operating speeds of mechanical units including a carrying mechanism for carrying substrates and alignment adjusting mechanism for aligning the substrates with an exposure mask and to reduce waiting time, such as exposure waiting time, near to naught.
Referring to
FIG. 13
showing a double-sided exposure system
100
disclosed in Japanese Patent Application No. 343971/1997 (JP-A No. 333337/1998), a work holding base
101
for detachably holding a substrate P has opposite surfaces respectively provided with vacuum pads
103
, and the work holding base
101
is moved repeatedly between a home position, i.e., a position indicated by chain lines, between a work receiving unit
105
and a work delivering unit
107
, and an exposure position, i.e., a position indicated by solid lines, between two mask holding mechanisms
109
L and
109
R respectively holding exposure masks
113
.
Light emitted by a mercury-short-arc lamp
111
, i.e., a light source, is transmitted through a left optical path and falls on the back surface of the exposure mask
113
held by the left mask holding mechanism
109
L, or the light is transmitted through a right optical path and falls on the back surface of the exposure mask
113
held by the right mask holding mechanism
109
R. An optical path selecting unit, not shown, connects the mercury-short-arc lamp selectively to the left optical path or the right optical path. The work receiving unit
105
adjusts the position of an unexposed substrate P fed thereto for preparatory positioning and transfers the substrate P to the vacuum pad
103
on the left surface, as viewed in
FIG. 13
, of the work holding base
101
located at the home position. Upon the arrival of the work holding base
101
holding the unexposed substrate P on its left surface at the exposure position, the left mask holding mechanism
109
L advances to bring the exposure mask
113
into contact with the substrate P so that the exposure mask
113
is aligned with the substrate P. After the exposure mask
113
has been exactly aligned with the substrate P, the exposure mask
113
is contacted fixedly to the substrate P. Then an exposure cycle is executed to expose a first surface, i.e., one of the surfaces, of the substrate P through the exposure mask
113
to light.
After the exposure cycle has been completed, the left mask holding mechanism
109
L is removed from the substrate P, the left mask holding mechanism
109
L is retracted, a left transfer hand
115
L holds the substrate P and transfers the same to a right transfer hand
115
R. Meanwhile, the work holding base
101
is returned to the home position, and then moved again to the exposure position. Subsequently, the right transfer hand
115
R transfers the substrate P to the right vacuum pad
103
, the right mask holding mechanism
109
R is advanced into contact with the substrate P so that the exposure mask
113
is aligned with the substrate P. After the exposure mask
113
has been exactly aligned with the substrate P, the exposure mask
113
is contacted fixedly to the substrate P. Then an exposure cycle is executed to expose a second surface, i.e., the other surface, of the substrate P through the exposure mask
113
to light. Thus, the exposure of both the surfaces of the substrate P is completed.
After the completion of the exposure cycle, the right mask holding mechanism
109
R is removed from the substrate P, the right mask holding mechanism
109
R is retracted and the work holding base
101
is returned to the home position. Then, the left vacuum pad
103
receives an unexposed substrate P from the work receiving unit
105
, and the work delivering unit
107
receives the two-side exposed substrate from the right vacuum pad
103
and delivers the same.
FIG. 14A
is a time chart representing sequential operations of the prior art double-sided exposure system
100
. In
FIG. 14A
, time is measured in seconds on the horizontal axis. Generally, exposure time is about 3 s or below. In this time chart, the exposure time is 3 s, and cycle time, i.e., time need to carry out a sequence of operations from the start of reception of an unexposed substrate P to the start of reception of the next unexposed substrate P, is 22 s. As obvious from
FIG. 14A
, there is a scarce waiting time between the completion of the exposure of the first surface of the substrate P and the start of the exposure of the second surface of the substrate P when the exposure time of the double-sided exposure system
100
is on the order of 3 s.
Some resist that is applied to the substrate P requires a longer exposure time. When a long exposure time is necessary, an exposure operation for exposing the second surface of the substrate P to light cannot be started before the completion of an exposure operation for exposing the first surface of the substrate P to light even if preparatory operations of the mechanical units for exposure are completed, which produces a time loss.
FIG. 14B
is a time chart representing sequential operations of the prior art double-sided exposure system
100
, in which exposure time is 8 s for both the surfaces of the substrate P. In this case, there is a waiting time of 5.5 s between the completion of preparations for the exposure of the second surface of the substrate P to light and the start of the exposure operation for exposing the second surface to light, and there is a waiting time of 5.5 s between the completion of transfer of the substrate P from the left side to the right side of the work holding base
101
and the start of shifting the work holding base
101
to the home position, i.e., during operations for exposing the second surface of the substrate P to light and post-operations. Consequently, the cycle time is as long as 32 s, which is about 1.5 times the cycle time needed by the operations shown in FIG.
14
A and hence the running cost of the lamp
111
increases sharply near to 1.5 times the running cost needed by the operations shown in FIG.
14
A.
SUMMARY OF THE INVENTION
The present invention has been made in view of the foregoing problems and it is therefore an object of the present invention to provide a double-sided exposure system capable of suppressing significant increase in time loss even if exposure time increases.
With the foregoing object in view, the present invention provides a double-sided exposure system for exposing opposite side surfaces of a plate to light through a pair of exposure masks respectively provided with necessary exposure patterns, comprising a first mask holding mechanism holding a first exposure mask to be used in exposing a first
Adams Russell
Howa Machinery Ltd.
Ladas and Parry
Nguyen Hung Henry
LandOfFree
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