JPS62293248A - Method for exposing both-face of flexible substrate - Google Patents

Abstract

PURPOSE:To highly accurately match wired pattern projection images formed on the both-face of a flexible substrate by carrying the substrate in the vertical direction and projecting light beams to reticles forming wired patterns from both the sides by projection optical systems having telecentric images sides. CONSTITUTION:The flexible substrate 3 obtained by forming conductive layers and photosenstive resist layers covering the conductive layers on the both-face of an insulating band-like substrate is laid between a feeding shaft 4 and a winding shaft 5, carried in the vertical direction by rollers 4a, 5a and led into the image formation side of the projection optical systems 1a, 1b arranged on symmetrical positions about a vertical line and having telecentric image sides. The reticles 2a, 2b forming wiring patterns are arranged on the opposite sides of respective projection optical systems 1a, 1b to the substrate 3. The reticles 2a, 2b are projected by uniform light radiated from light sources 6a, 6b consisting of a pair of mercury lamps arranged vertically and upward, converted their direction into the horizontal direction by reflectors 7a, 7b and made incident in parallel with an optical axis C by condenser lenses 9a, 9b through integrators 8a, 8b.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a double-sided exposure method for a flexible substrate in which a reticle having a wiring pattern formed on both sides of the flexible substrate is projected and exposed.

[Conventional technology]

With the recent trend toward high-density packaging of electronic devices, the wiring density of flexible substrates is also increasing significantly. In particular, in extremely complex circuits such as digital circuits, double-sided printed circuit boards with wiring patterns on both the front and back sides are increasingly used, and the matching of the wiring patterns on both sides requires, for example, 0.1 mm.
High precision is required.

Generally, printed circuit boards are made by uniformly bonding extremely thin copper foil to the surface of an insulating plate-like base material such as phenol paper, epoxy paper, or epoxy glass, and then forming a photosensitive resist layer on top of it, and then forming the desired wiring pattern. exposed and printed,
It is made by removing the unexposed portions of the copper foil by etching to form printed wiring, and then peeling off the remaining resist with a solvent or alkaline solution.

For exposing wiring patterns, there are two methods: a contact exposure method in which a reticle with a wiring pattern formed thereon is brought into direct contact with the surface of the printed circuit board, and a projection exposure method in which the reticle is projected onto the surface of the printed circuit board for exposure. There is.

[Problem that the invention seeks to solve]

However, in this type of printed circuit board method, the former uses a simple exposure device and can maintain good adhesion of the reticle, so it is especially suitable for cases where flatness is difficult to maintain, such as with flexible circuit boards. However, there is a serious problem in that the substrate slides on the reticle and is prone to scratches.

On the other hand, with the latter, there is no risk of scratches because the reticle is located far away from the substrate, but the exposure equipment becomes more complex, and when it is difficult to maintain flatness such as with a flexible substrate, the reticle and substrate may There is a problem in that it is difficult to maintain the distance at a predetermined value, and the size of the image projected onto the substrate varies due to variations in this distance.

For this reason, it is not used for anything other than very small devices for which maintaining flatness is not so difficult, especially in double-sided printed circuit boards, where even a slight deviation in the position of the board doubles the error in the size of the images on both the front and back sides. It could not be applied in such cases.

In addition, in the case of double-sided exposure by projection, the flexible substrate is fed horizontally as in the case of single-sided fog light, and if you try to project the reticle from above and below, the mercury lamp, which is the light source for projection, is placed horizontally and the light is reflected. The optical path can be changed vertically using a mirror, or the beam can be placed upside down and emitted directly.

However, mercury lamps originally have directional light distribution characteristics, and their installation conditions are limited to vertical upward orientation.
There is a problem in that none of the methods of vertical arrangement is preferable.

An object of the present invention is to provide a double-sided exposure method for a flexible substrate that can solve these conventional problems.

[Means for solving problems]

Therefore, in the double-sided exposure method for a flexible substrate according to the present invention, the flexible substrate is fed in the vertical direction, and a reticle on which a wiring pattern is formed is projected from both sides of the flexible substrate using a projection optical system that is telecentric on the image plane side for exposure.

[For production]

With this method, the mercury lamps, which are the light sources for the flexible substrate, can be placed in the vertical direction.
By simply changing the optical path using a reflector, both sides of the board can be exposed equally.

=3- Furthermore, by providing an optical system that is telecentric on the image plane side, even if the position of the flexible substrate shifts slightly,
It becomes possible to always maintain the projected images on both sides at a predetermined position and size.

〔Example〕

The present invention will be described in detail below with reference to the accompanying drawings, but first the principle of the invention will be explained with reference to FIGS. 2 and 3.

FIG. 2 is an optical path diagram using a conventional projection optical system.
In this case, El is an entrance pupil that limits the luminous flux of the incident light ray, and A1 is an exit pupil that limits the luminous flux of the exiting ray.

Now, when the substrate 3 is on the imaging plane of the projection optical system 1, the size of the image of the reticle 2 is Qo, but when the substrate 3 approaches the reticle 1 by a distance d and reaches the position of the substrate 3a, the image size becomes Qo. is Ql, and when it is at the position of the substrate 3b separated by a distance d, it becomes Q2, and the focal point 4 is shifted and the size of the image is different.

Applying this to the case where the projection optical systems are located symmetrically on both sides of the substrate 3, the substrate 3 that approaches one projection optical system by a distance d will be separated from the other projection optical system by a distance d. Therefore, when the substrate surface moves by a distance d in the optical axis direction, the difference in size between the images of the reticle 2 of the same size projected on both sides of the substrate B becomes Q2-u.

On the other hand, in the projection optical system in which the image plane side is telecentric as shown in FIG. It becomes a state of parallel perspective.

To move the entrance pupil position to infinity, a common method is to provide a lens in front of the projection lens group so that the focus is at the pupil position, but various other methods can be considered.

According to such a projection optical system in which the image plane side is telecentric, even if the position of the substrate 3 moves back and forth by a distance d from the focal position to the position of the substrates 3a,')b, the image will be slightly out of focus. The size of is the size Q of the image at the focal position. is kept equal to.

In other words, if projection optical systems with telecentric image plane sides are provided on both sides of the substrate 3, even if the position of the substrate 3 moves by a distance d in the optical axis direction, the reticle 2 of the same size will be projected.
The size of the image remains unchanged.

Next, an embodiment of the present invention utilizing this principle is shown in FIG. In the figure, a flexible substrate 3 having a conductive layer and a photosensitive resist layer covering it formed on both sides of an insulating strip base material is stretched between a supply shaft 4 and a take-up shaft 5, and a roller 4a,
5a, and a projection optical system 1 whose image plane side is telecentric, which is placed in a symmetrical position sandwiching the projection optical system 1.
a.

1b to the imaging plane.

On the side opposite to the substrate 6 of each projection optical system la, lb, reticles 2a, 2b on which a wiring pattern is formed are arranged, and a light source f3a consisting of a pair of mercury lamps with the reticles 2a, 2b oriented vertically -h. , (Emitted from 3h and reflecting mirror 7a
, 7b, the entire surface is irradiated with an even beam of light that passes through integrators 8a, 8b and enters the optical axis C through condenser lenses 9a, 9h.

Thereby, the wiring patterns of each reticle 2a, 2b are projected and exposed onto the photosensitive resist layers on both sides of the substrate B by the projection optical systems la and lh whose image plane side is telecentric.

According to this embodiment, since the projection optical systems 1a and lb are both optical systems that are telecentric on the image plane side, even if the surface of the substrate B moves in the direction of the optical axis C, the size of the images of the reticles 2a and 2b remains unchanged. remains unchanged.

Furthermore, the resolution of the projected image should be slightly degraded due to the movement of the substrate 3, but since the aperture ratio of the telecenter 1-link optical system is originally small and the amount of plane movement of the substrate 6 is not large, the projected image The reduction in resolution remains to a completely negligible extent.

In addition, the consistency of the relative positions of the projected images projected on both sides of the substrate B is corrected by finely adjusting the positions of the reticles 2a and 2b, but since the size of the projected images does not change due to slight movement of the reticles, Adjustment is extremely easy.

Note that the projection optical system that is telecentric on the image plane side used in the present invention does not necessarily have to be completely telecentric because the amount of movement of the substrate B is small, and may be anything close to this.

〔Effect of the invention〕

As described above, in the double-sided exposure method for a flexible substrate according to the present invention, the flexible substrate is fed in the vertical direction, so that the mercury lamp, which is the light source, is placed at symmetrical positions on both sides of the substrate with equal directionality under normal usage conditions. This makes it possible to maximize the performance of the mercury lamp and equalize the intensity of the projected light beam on both sides of the substrate, which eliminates the difference in the size of the projected image on both sides due to the difference in exposure amount. There will be no problems at all.

In addition, since the reticle image is projected onto the substrate from both sides by a projection optical system that is telecentric on the image plane side, even if the position of the flexible substrate moves slightly in the optical axis direction, the position and size of the projected image will not change. This makes it possible to align the wiring pattern projection images on both sides of the board with high precision without causing any errors.

4. Description of the drawings Figure 1 is an optical path diagram showing an embodiment of the present invention, Figure 2 is an optical path diagram showing the principle of the conventional printed circuit board projection exposure method, and Figure 3 is a printed circuit board according to the present invention. FIG. 2 is an optical path diagram showing the principle of projection exposure method.

la, 1b...projection optical system telecentric on the image plane side

Claims (1)

[Claims] 1. A flexible substrate in which a conductive layer and a photosensitive resist layer covering it are formed on both sides of an insulating strip base material is fed in the vertical direction, and the flexible substrate is sandwiched and projected from both sides using projection optics whose image plane side is telecentric. A double-sided exposure method for a flexible substrate, characterized in that a reticle on which a wiring pattern is formed by a system is projected and exposed.