Lithographic exposure system and method for exposure and curing a solder resist

Abstract

A lithographic exposure system and method for exposing and structuring a substrate coated with a solder resist is provided. The lithographic exposure system having at least one light beam, formed preferably by two or more laser beams of different UV wavelengths, which is deflected relative to the substrate by a variable deflection device, in order to generate structures on the substrate. In particular, the light beam is superimposed, spatially in the image plane and temporally in the exposure, by a spatially limited, high-energy, preferably externally mounted heat source, wherein preferably infrared laser diodes having linear optics are used.

Claims

1. A lithographic exposure system for direct maskless exposure and curing of a desired structure in a solder resist, the direct exposure system comprising: at least one exposure device which comprises at least one ultraviolet (UV) laser light source for generating a UV laser light beam, and a laser deflection device which is configured to deflect the UV laser light beam to an exposure plane in order to expose the desired structure in the solder resist which is arranged in the exposure plane, wherein the lithographic exposure system further comprises a heat source device includes homogenization optical element for generating a homogeneous heat irradiation (IR) area on the solder resist, wherein the heat source device is configured such that an area in the exposure plane is exposed, in a way overlapping in terms of homogeneous space and time, to the deflected UV laser light beam and to the IR emitted by the heat source device, and the deflection device deflects the UV laser light beam in the two dimensions, wherein deflection operation variable in terms of time is carried out with two identical oscillation frequencies.

2. The lithographic exposure system according to claim 1, further comprising an accommodation device for accommodating a substrate coated with the solder resist, and at least one movement device for generating a relative movement between the at least one exposure device and the substrate.

3. The lithographic exposure system according to claim 1, wherein the at least one exposure device comprises at least two UV laser light sources, including at least two UV laser diodes, which emit UV laser light in at least two different wavelengths in a range of 350 nm-450 nm.

4. The lithographic exposure system according to claim 3, wherein the at least two UV laser diodes are configured to emit UV laser light in at least two different wavelengths in the range of 350 nm-450 nm.

5. The lithographic exposure system according to claim 1, wherein the heat source device comprises at least one IR laser which is coupled to the direct exposure device such that a substantially fixed exposure area is generated in the exposure plane and the UV laser light beam deflected by the deflection device is deflected within the exposure plane.

6. The lithographic exposure system according to claim 1, wherein the homogenization optical element is a microlens arrangement, configured to generate the homogeneous IR area irradiation on the solder resist.

7. The lithographic exposure system according to claim 1, further comprising an adjustment device configured to position of the IR exposure area on the solder resist can be adjusted.

8. The lithographic exposure system according to claim 1, wherein the exposure plane is further configured to provide an inert gas directly above the area of the exposure plane.

9. The lithographic exposure system according to claim 1, further comprising coupling optics which are adapted to combine light of a plurality of UV laser light sources to direct UV laser light via the deflection device onto the solder resist.

10. A method operatively associated with a lithographic exposure system for maskless exposure and curing of a desired structure in a solder resist, the method comprising the steps: providing an exposure device includes a heater source, a laser deflecting device, generating an ultraviolet (UV) laser light beam with the exposure device, deflecting the UV laser light beam by the laser deflecting device onto an exposure plane in which the solder resist is located in order to expose the desired structure in the solder resist, wherein the deflecting the UV laser light beam further comprises: emitting heat radiation of the heat source device onto the solder resist, wherein the heat source device comprises at least one homogenization optical element in order to generate a homogeneous IR area irradiation on the solder resist, wherein the emitted heat radiation overlaps in terms of homogeneous space and time with the UV laser light beam deflected onto the exposure plane, whereby the deflected UV laser light beam hits an area of the solder resist that has been heated by the emitted heat radiation, and the deflection device deflects the UV laser light beam in two dimensions, wherein the deflection operation variable in terms of time is carried out with two identical oscillation frequencies.

11. The method according to claim 10, wherein the generating the UV laser light beam comprises at least two or three different wavelengths in the UV range, in the range of 350-450 nm.

12. The method according to claim 10, wherein the emitting heat radiation is IR light which is emitted by an IR laser which generates a substantially geometrically fixed exposure area in the exposure plane, and the deflected UV laser light beam is deflected within this exposure area.

13. The method according to claim 10, wherein in the generating UV laser further comprising providing of an inert gas directly above the exposure plane during the UV exposure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, preferred embodiments of the present invention are described in detail with reference to the Figures, in which:

(2) FIG. 1 shows a perspective view of a direct exposure device according to the present invention comprising an external heat source arrangement;

(3) FIG. 2 shows a perspective view of a direct exposure device according to the present invention comprising an external heat source arrangement in the form of a two-axis portal arrangement comprising a four-level projection unit in the exposure device; and

(4) FIG. 3 shows a schematic illustration of the overlapping of the UV laser line of the exposure device comprising the line area of an external heat source arrangement.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(5) FIG. 1 shows a perspective view of a direct exposure device 1 (in the following also referred to as lithographic exposure device) comprising an exposure device 20 and an external heat source device 10. The heat source device 10 can be mounted to the exposure device 20, for example, via an adjustment device 60.

(6) This assembly preferably comprises a laser diode module comprising coupling optics 50 with transmitting laser light beams in the ultraviolet spectral range of 350 nm-450 nm.

(7) Preferably the coupling takes place within the laser module and is performed by optical elements from the prior art. To this end, for example, pole cubes and semipermeable mirrors as well as other combination optics are used. Preferably, lasers having discrete single-mode wavelengths with different main maxima are coupled or combined in the coupling optics 50. For example, the light beams of three laser sources with main maxima at about 375 nm, 390 nm and 405 nm can be coupled.

(8) The individual beams and/or the coupled beams of the UV laser light sources, which preferably are laser diode sources, are imaged onto the exposure plane 40 by means of a deflection device (in the following also referred to as laser deflection device 30). Preferably, the area to be exposed is in the exposure plane 40 or substantially parallel to the exposure plane 40. Preferably, the solder stop coated area of a substrate or a printed circuit board 100 is to be exposed according to the present invention.

(9) The laser deflection device 30 can be, for example, a galvano scanner comprising a mirror coating that reflects UV wavelengths and imaging preferably via an achromatic telecentric F-theta lens 70 onto the exposure plane 40 or the focal plane. The cuboid below the lens 70 illustrated in FIG. 1 represents the work area of the lens 70. According to a further preferred embodiment, the work area can also be smaller or larger and/or wider.

(10) FIG. 2 shows a perspective view of a further direct exposure device 1 according to the present invention comprising four exposure devices 20.sub.1, 20.sub.2, 20.sub.3 and 20.sub.4. Each of these four exposure devices 20.sub.X is additionally coupled to an external heat source device 10.sub.X, which in turn are mounted via respective adjustment devices 60.sub.X to the exposure devices 20.sub.X.

(11) Moreover, FIG. 2 illustrates the assembly of the exposure devices 20 to a movement device 90. By means of the movement device 90, a relative movement between the exposure device 20 and the substrate 100 to be exposed is generated, whereby it is possible to expose larger areas of a substrate 100.

(12) The direct exposure device according to the present invention can alternatively or additionally comprise a second movement device 110. The second movement device 110 can preferably be configured as a vacuum table onto which the substrate 100 is attachable by means of an underpressure. The movement of the second movement device 110 can provide, for example, a movement in the XY-plane, preferably parallel to the exposure plane. The movement can be performed by means of an electric motor or electric motors, preferably by means of linear motors comprising corresponding guiding mechanisms. By means of the movement device or movement devices, the exposure devices 20 can move along the exposure plane in a cascading way, preferably in a cascading way in column form. In other words, a parallelization with a plurality of exposure devices is possible.

(13) The focal plane or the exposure plane 40 can be readjusted by integrated servomotors 80 which permit a movement of the exposure devices 20 along the Z-axis. Preferably, an adjustment of the exposure plane 20 is performed prior to the exposure process.

(14) FIG. 3 illustrates a schematic side view of an exposure device 20 comprising an external heat source arrangement 10 according to the present invention, wherein in this embodiment said heat source arrangement 10 is mounted to the exposure device 20 via an adjustment device 60.

(15) In FIG. 3, the beam path 51 of the emitted UV laser beam on the exposure plane is purely schematically depicted in a way not true to scale. For example, the UV laser beam is deflected by means of the deflection device 30, which is preferably a galvano scanner system 30, along a line or column. According to the present invention, the beam path 51 is superimposed with the IR laser beam on the exposure plane. In particular, it is preferred that the light emitted by the heat source device 10 substantially represents a rectangular exposure area 11 on the exposure plane 40, and exhibits a Gaussian light intensity distribution along one direction.

(16) The modulated and thus structuring UV laser beam line 51, preferably 1-6 beams having a typical laser line dimension of 80 mm in width and preferably 5-25 μm in height (FWHM, Gaussian intensity profile), is positioned directly centrically above the heat field 11 of the IR laser beam by means of the adjustment device 60.

(17) The intensity profile of the heat field 11 thus formed is preferably rectangular, strongly sloping and preferably adapted by means of lens adjustments in two dimensions. Preferably, there is a top hat intensity profile distribution in the width as well as a Gaussian intensity profile distribution in the height. The heat field dimensions should be preferably configured larger than the UV laser beam line 51 both in the width and in the height. Preferably, a width of about 85 mm and a height of about 2 mm should be observed so that the temperature variation in the area of the UV laser beam line 51 is two-dimensionally homogeneously distributed.

REFERENCE SIGNS AND TERMS

(18) 1 Direct exposure device, lithographic exposure device (the entire system)

(19) 5. Solder resist

(20) 6 Substrate

(21) 7 Heat source device, heat source

(22) 11 Exposure area, heat field

(23) 20 Exposure device (the “laser system” comprising the UV lasers)

(24) 30 Deflection device, laser deflection device

(25) 40 Exposure plane, exposure plane (XY-plane)

(26) 50 Coupling optics

(27) 51 Beam path

(28) 60 Adjustment device

(29) 70 Lens

(30) 80 Servomotors

(31) 90 First movement device

(32) 100 Printed circuit board, substrate

(33) 110 Second movement device