EP1594651A1

EP1594651A1 - Device and method for processing electric circuit substrates by laser

Info

Publication number: EP1594651A1
Application number: EP03785671A
Authority: EP
Inventors: Eddy Roelants; Stefan Lesjak; Sebastien Edme
Original assignee: Siemens AG; Hitachi Via Mechanics Ltd
Current assignee: Via Mechanics Ltd
Priority date: 2003-02-20
Filing date: 2003-11-26
Publication date: 2005-11-16
Also published as: DE10307309A1; US6849823B2; JP2006513862A; WO2004073917A1; CN100448594C; DE10307309B4; AU2003294733A1; CN1753755A; KR20050103951A; US20040164057A1

Abstract

According to the invention, a laser source (1) with a diode-pumped, goods-controlled, pulsed solid body laser is used to process electric circuit substrates. The laser radiation of said laser has a wave length of between 266 nm and 1064 nm, a pulse repetition rate of between 1 kHz and 1 MHz and a pulse length of 30 ns - 200 ns for an average laser power rate of between 0.1 W and approx. 5 W. Predetermined operational modes with correspondingly different combinations of laser power and repetition frequencies can be adjusted by controlling each application in order to selectively provide a hole operation mode, an ablation operation mode or an illumination operation mode using the same laser. The laser beam is deflected to the substrate corresponding to the respective operation mode by means of an adjustable galvo mirror deflection unit and by the control unit.

Description

description

Device and method for processing electrical circuit substrates using a laser

The invention relates to an apparatus and a method for processing electrical circuit substrates

a workpiece holder for holding and positioning the substrate, a laser source with a diode-pumped, quality-controlled, pulsed solid-state laser,

- a deflection unit,

- an imaging unit and

- A controller for setting the operating parameters of the laser.

It is known in principle to use the energy of a laser beam when processing printed circuit boards and comparable electrical circuit substrates. The use of a UV laser system with a continuously pumped, Q-switched Nd: YAG laser for drilling microholes in a multilayer substrate is known from US Pat. No. 5,593,606. Repetition frequencies of up to 5 kHz are typically used there.

EP 931 439 B1 discloses a method for forming at least two wiring levels on electrically insulating substrates, a laser, preferably an eined-YAG laser, being used both for drilling blind holes and for structuring conductor tracks. When forming conductor tracks, either the metal layer itself can be structured directly by the laser by partial ablation, or it is also possible to partially ablate an etching resist layer lying on the metal layer with the laser and then to etch away the area of the metal layer that is thereby exposed. Basically, it is also already known to use laser radiation to expose photoresist layers. For this purpose, EP 1 115 031 A2 proposes using, for example, a titanium sapphire laser with repetition rates of more than 80 MHz, which generates a quasi-continuous UV laser beam.

Depending on the application, different laser systems are used, which require considerable investment if different processing methods are to be used side by side in a printed circuit board production.

The aim of the present invention is to provide a laser system and a corresponding laser processing method, which enables substrates to be processed using a wide variety of laser methods without costly additional investments and expensive retrofitting.

According to the invention, this aim is achieved with a device for processing electrical circuit substrates with a workpiece holder for holding and positioning the substrate, a laser source with a diode-pumped, quality-controlled, pulsed solid-state laser with a wavelength between 266 and 1064 nm, which is able to emit laser radiation in the following value ranges : - a pulse repetition frequency between 1 kHz and 1 MHz, - a pulse length of 30 ns to 200 ns and

- an average laser power of approx. 0.1 W to approx. 5W, also with a deflection unit that enables deflection speeds of up to 600 mm / s,

- an imaging unit and - a controller that is able to use the laser with different combinations depending on the application operate from medium laser power and repetition frequencies.

The inventive selection of the laser with a hitherto unknown spectrum of characteristic values and a controller that is able to set a predetermined combination of characteristic data for the type of substrate processing provided in each case, makes it possible to carry out all laser processing steps occurring for printed circuit board processing, such as Boh - Removal of metal layers or of etch resist layers up to the mere exposure of photosensitive varnishes with a single laser source. The effort for the provision of production facilities and for the changeover between different production steps is correspondingly simplified.

The device according to the invention is preferably operated with a laser with a wavelength between 350 and 550 nm, in particular with a UV laser with a 355 nm wavelength.

As mentioned, predetermined combinations of the laser characteristic values can be provided for certain processing steps that are to be considered. The laser can thus have a first operating mode for removing layers, in which it is operated with an average laser power of approximately 1 to 2 W and a repetition frequency of approximately 60 to 80 kHz. It should be noted that the somewhat higher laser power and the somewhat lower repetition frequency for structuring metallic layers, for example, and the somewhat lower laser power of approximately 1 W with the somewhat higher repetition frequency of 80 kHz for the removal of non-metallic layers, such as solder resist. is combined. In a second operating mode for drilling holes in metallic and dielectric layers of the circuit substrate, the laser can, for example, be set to an average laser power of 3 to 4 W and a repetition frequency of 10 to 30 kHz. In a third mode for exposing Photosensitive layers, the laser is set to a significantly lower laser power in the order of about 100 mW at a repetition frequency of 200 kHz to 1 MHz.

A galvanometer mirror unit expediently serves as the deflection unit, which enables the high deflection speeds of typically 300 to 600 mm / s. With a suitable combination of laser power and spot diameter, a significantly higher deflection speed can also be used. At these speeds, the laser beam is moved essentially linearly when structuring layers, while circular movements are carried out in a known manner during drilling.

A method according to the invention for processing an electrical circuit substrate, wherein a laser with a wavelength between approximately 266 and approximately 1064 nm, a pulse repetition rate between 1 kHz and 1 MHz, a pulse length between 30 ns and 200 ns and an average laser power between approximately 0.1 W and approx. 5 W is used, has the following steps:

- The substrate is fixed and positioned on a workpiece holder - The laser beam is set to one of the following operating modes via a control unit: a) Drilling holes with an average laser power of 3 to 5 W, a repetition frequency of about 10 to 30 kHz. and a pulse length of approximately 30 to 50 ns, b) structuring of metallic or dielectric

Layers with an average laser power of 1 to 2 W, a repetition frequency of about 50 to 90 kHz, preferably 60 to 80 kHz, and a pulse length of about 50 to 60 ns, c) exposure of a photosensitive layer with an average laser power of approximately 0, 1 W, a repeat frequency frequency of 200 kHz to 1 MHz and a pulse length of 100 to 200 ns, preferably 120 ns, - the substrate is processed with the laser beam in the set operating mode, the laser beam using a galvo mirror deflection unit at a speed of 300 to 600 mm / s is moved.

In a preferred embodiment, the photosensitive layer exposed in operating mode c) is developed in a further step, and then the unexposed areas of the layer are removed.

The invention is explained in more detail below using exemplary embodiments with reference to the drawing: It shows

1 shows the schematic structure of a laser processing device designed according to the invention with a substrate provided for drilling holes, FIG. 2 shows a schematically illustrated substrate in which an etching resist layer is structured with the laser beam and the exposed pattern is subsequently etched,

FIG. 3 shows a schematically shown substrate, in which a metallic surface layer is structured directly with the laser beam, FIG. 4 shows a schematically illustrated substrate, in which a photosensitive layer applied to a metal layer is exposed with the laser, and

5 shows a substrate in plan view, in which, according to FIG. 4, a track is exposed with a laser and then washed out.

In Figure 1, the structure of a laser processing device is shown schematically. The centerpiece is a laser 1, which is designed as a diode-pumped, quality-controlled, pulsed solid-state laser for the purposes of the invention. The laser beam 2 emanating from this laser source is preferably emitted via a deflection unit 3 with two galvo mirrors 31 and 32 and one Imaging unit 4 formed by a lens is fed to a substrate 10 which is arranged on a receiving device 5, primarily a positioning table which can be adjusted in all directions. A control unit 6 is used to control the device, which controls both the laser 1 and the “deflection unit 3 and the receiving device 5 in accordance with the desired processing.

As a rule, the workpiece, namely the substrate, is brought into a position in the horizontal direction with the holding device 5, that is to say the positioning table, in such a way that a certain field of the substrate intended for processing reaches the effective range of the laser beam 2 (X - Y positioning). In addition, it is possible, by means of a vertical adjustment of the positioning table 5, to bring the substrate into the focus of the imaging unit 4 or at a predetermined distance from the focus, depending on the desired focusing of the laser beam. The substrate is held in the set position during laser processing, since the movements on the field to be processed are carried out by deflecting the laser beam via the deflection unit 3. The deflection via galvo mirrors enables much higher speeds to be achieved than by adjusting the positioning table 5, which has a relatively large mass. The deflection of the laser beam 2 on the field of the substrate 10 to be processed is therefore carried out by the control unit 6 via the galvo mirrors 31 and 32. Furthermore, programs are stored in the control device with which the laser 1 is set to specific combinations of performance data for the respective application purposes.

In the example of FIG. 1, it is assumed that 10 holes, so-called vias, are to be drilled in the substrate in the form of through holes or blind holes. The substrate has a central dielectric layer 11 and a metallic layer 12 and 13 on the top and bottom, respectively. Assuming that a blind hole 14 is drilled through the metallic layer 12 and the dielectric layer 11 If so, the laser is set so that it emits an average laser power of, for example, 3.5 to 4 W at a repetition frequency of 10 to 30 kHz and a pulse length of 30 to 50 ns. In this case, the laser itself is preferably a UV laser with a wavelength of 355 nm. However, a laser with a wavelength of 532 nm could also be used. If the laser is now set to the specified power for the drilling mode, the required holes 14 are drilled in the substrate 10, the laser beam, for example, having to perform a certain number of circular movements in order to on the one hand the metallic layer 12 and on the other hand the dielectric layer 11 in the desired borehole.

If structuring by etching conductor tracks is to be carried out on the substrate 10 in a different working step, then according to FIG. 2 an etching resist layer 15 can first be applied to the metal layer 12, which is removed with the laser in a predetermined pattern in regions 15a, so that in these areas, the metal layer 12 is exposed and can then be etched off. The laser beam, which is referred to in this figure as 2-2, is adjusted via the control unit so that it has, for example, an average laser power of approximately 1 W at a repetition frequency of 80 kHz and a pulse length of 60 ns for removing the etching resist , These values are only examples, since the exact setting depends on the layer to be removed, its nature, its thickness and the like.

FIG. 3 shows, for example, how a metal layer 12 is structured, ie partially removed, using a laser beam 2-3 directly according to a predetermined conductor pattern. The metallic layer 12 therefore only remains where conductor tracks are desired, while the dielectric layer 11 is exposed in the regions 12a. For this purpose, the laser beam 2-3 is tion set so that it has, for example, an average power of 1.5 W at a repetition frequency of 60 kHz and a pulse length of about 50 ns. In this case too, the exact setting depends on the nature and the thickness of the metal layer 12 to be removed.

Finally, FIG. 4 shows how structuring can be carried out on the substrate by means of photolithography. Here, a photosensitive layer 16 is first applied to the metal layer 12, which is exposed to a laser beam 2-4 in predetermined areas 16a. The exposed layer is then developed and washed out, so that the underlying metal layer regions 12a are exposed and can be etched away.

FIG. 5 shows a photo in plan view of a substrate 10 with a photosensitive layer 16, which was exposed in the region 16a with a laser beam and then washed out. In this example, a photoresist known under the trade name Probelec with a sensitivity of 1200 mJ / cm ² at a laser wavelength of 355 nm was used. It was exposed with a frequency-tripled, diode-pumped semiconductor laser with a wavelength of 355 nm, a repetition frequency of 200 kHz and a pulse duration of approximately 100-200 ns with an average laser power of approximately 100 mW. A line width of about 30 μ was exposed with a deflection speed of about 100 to 600 nm / s. It can be seen in FIG. 5 that, despite the pulsed exposure to the laser light, an essentially straight edge profile of the exposed strip 16a is achieved. One recognizes an inner stripe with the width bl, in which the copper layer 12 (FIG. 4) emerges particularly cleanly after washing out, and the overall stripe of the illumination with the width b2, the edge regions of which were exposed to the light distribution somewhat less, but always exposed to a sufficient degree and then removed the so that the metal layer can be etched off in full width b2.

As a result of this possibility given by the invention, the exposure can also be carried out with the same laser device as the structuring or drilling. The achievable lines and spaces between the desired structures are determined by the diameter of the focused laser spot, the sensitivity of the photoresist and the repetition rate of the laser pulses. From a mathematical point of view, the line width that can be achieved is a folding of the spatial beam distribution in focus with the spectral sensitivity of the photoresist. Although it is a pulsed laser beam, a straight, continuous line is achieved by superimposing the successive pulses. The corresponding setting of the laser repetition frequency and the deflection speed of the galvo mirror ensures that the photoresist is not removed but is exposed, so that the same effect as with the frequently used cw-Ar ⁺ laser is achieved. With the values given above, for example, line widths of about 30 µm can be generated.

Claims

claims

1.Device for processing electrical circuit substrates with a workpiece holder (5) for holding and positioning the substrate (10), a laser source (1) with a diode-pumped, quality-controlled, pulsed solid-state laser with a wavelength between 266 nm and 1064 nm, which emits a laser radiation ( 2) can deliver in the following value ranges: a pulse repetition frequency between 1 kHz and 1 MHz, a pulse length of 30 ns to 200 ns and an average laser power of approx. 0.1 W to approx. 5 W, furthermore with one arranged in the beam path of the laser Deflection unit (3), which enables deflection speeds of up to 600 mm / s, an imaging unit (4) and a controller that is able to operate the laser with different combinations of average laser power and repetition frequencies depending on the application.

2. Device according to claim 1, d a d u r c h g e k e n z e i c h n e t that a laser with a wavelength between 350 and 550 nm, preferably a UV laser with 355 nm wavelength, is used.

3. Apparatus according to claim 1 or 2, so that the laser has a first operating mode for removing layers in which it is operated with an average laser power of approximately 1 to 2 W and a repetition frequency of approximately 60 to 80 kHz.

4. Device according to one of claims 1 to 3, characterized in that the laser a second mode of operation for drilling holes (14) in metallic see (12) and dielectric layers (11) of the circuit substrate (10), in which it is operated with an average laser power of 3 to 4 W and a repetition frequency of 10 to 30 kHz.

5. Device according to one of claims 1 to 4, characterized in that the laser has a third operating mode for exposing photosensitive layers (16), in which it has an average laser power in the order of 100 mW and a repetition frequency of 200 kHz is operated up to 1 MHz.

6. Device according to one of claims 1 to 5, d a d u r c h g e k e n n z e i c h n e t that a galvanometer mirror unit (3) with a deflection speed of 100 to 600 mm / s is used as the deflection unit.

7. Method for processing an electrical circuit substrate, wherein a laser (1) with a wavelength between approximately 266 nm and approximately 1064 nm, a pulse repetition rate between 1 kHz and 1 MHz, a pulse length between 30 ns and 200 ns and an average laser power between approx 0.1 W to about 5 W is used, with the following steps:

- The substrate (10) is fixed and positioned on a workpiece holder (5),

- The laser beam (2) is set via a control unit (6) to one of the following operating modes: a) drilling holes (14) with an average laser power of 3 to 5 W, a repetition frequency of about 10 to 30 kHz and a pulse length of about 30 to 50 ns, b) structuring or ablation of metallic or dielectric layers (15, 12) with an average laser power of 1 to 2 W, a repetition frequency of about 50 to 90, preferably 60 to 80 kHz, and a pulse length of about 50 to 60 ns, c) exposing a photosensitive layer (16) with an average laser power of approximately 0.1 W, a renewed frequency from 200 kHz to 1 MHz and a pulse length of approx. 100 to 200 ns, preferably approx. 120 ns, and - the substrate is processed with the laser beam (2) in the set operating mode, the laser beam using a galvo mirror deflection unit (3 ) is moved at a speed of 300 to 600 mm / s.

8. The method according to claim 7, that the photosensitive layer (16) exposed in operating mode c) is developed in a further step and that the unexposed areas of the layer (16) are then removed.