WO2004060602A1

WO2004060602A1 - Method and device for treating with a laser beam a carrier for at least one electrical component

Info

Publication number: WO2004060602A1
Application number: PCT/NL2003/000862
Authority: WO
Inventors: Willem Antonie Hennekes; Henri Joseph Van Egmond; Joannes Leonardus Jurrian Zijl
Original assignee: Fico B.V.
Priority date: 2002-12-20
Filing date: 2003-12-04
Publication date: 2004-07-22
Also published as: TW200418245A; NL1022231C2; AU2003285832A1

Abstract

The invention relates to a method for treating a carrier (4) for at least one electrical component with a laser beam by directing the laser beam at the carrier. The invention also relates to a device for treating a carrier (4) for at least one electrical component with a laser beam (3), comprising: a laser source having directing means which connect to the laser source for directing a laser beam (3) at an object for treating, and a housing (1) with a gas feed arranged at least partially around the laser source.

Description

Method and device for treating with a laser beam a carrier for at least one electrical component

The invention relates to a method for treating a carrier for at least one electrical component with a laser beam by directing the laser beam at the carrier. The invention also relates to a device for treating a carrier for at least one electrical component with a laser beam, comprising: a laser source having directing means which connect to the laser source for directing a laser beam at an object for treating, and a housing with a gas feed arranged at least partially around the laser source.

The use of laser light in the form of a laser beam for engraving or cutting through materials is already generally known. For this purpose a laser beam is directed at the object for treating, often in combination with a gas flow. The purpose of this gas flow is to cool the object and to prevent undesired chemical reactions occurring, such as for instance excessive oxidation. Laser cutting is particularly applied for rougher mechanical work. A significant drawback of the existing techniques is that metal deposition (deposition of sublimating material in particular) occurs on both sides of a cut produced by means of laser cutting. This can be explained by the evaporation of material at the position where the laser beam strikes the object for treating. As a result of cooling, the thus evaporated material will be deposited a short distance (in the order of magnitude of millimetres in usual process conditions) from the cut. This does not have to be a drawback for less precise constructions or for material which undergoes a finishing after the laser cutting, but for more high-precision application of the laser cutting the phenomenon of material deposition occurring on both sides of the cut is undesirable or unacceptable.

The object of the present invention is, while retaining the advantages of the prior art, to also make laser cutting possible for application in high-precision conditions, and more in particular in the production of semiconductors.

The invention provides for this purpose a method of the type stated in the preamble, characterized in that at the position where the laser beam comes into contact with the carrier a gas flow is present which has at least one movement component in a direction perpendicular to the direction of the laser beam. Owing to the gas flow at the location where the laser beam strikes the object for treating, the material released from the object will be entrained to at least a significant extent with the gas flow. The consequence hereof is that the material deposition on the object for treating will occur (at least substantially) downstream of the location where the laser beam contacts the object for treating. The object for treating will therefore only be partly contaminated around the location where the laser beam contacts the object for treating. An important advantage here is that, when cutting through a carrier with electronic components, such as more particularly semiconductor products, the components can be separated such that, without further treatment (thus without further cleaning or mechanical processing), the severed contact parts thereof remain clean such that they are immediately suitable for further use, despite the high standards set for the quality of the contact parts for this purpose. Use of the components is usually understood to mean the incorporation of the electronic component in an electrical installation.

The gas flow is preferably supplied substantially parallel to the laser beam through a housing arranged around the laser beam, in order to change this gas flow closer to the carrier into the gas flow with at least one movement component in a direction perpendicular to the direction of the laser beam. Since there is little space for the supply of the gas flow, a much-applied solution is to combine the supply of gas with a shielded passage for the laser beam. Only where the laser beam carries out its function (when it strikes the object) is it necessary according to the invention to have available a gas flow which discharges the residue in a preferred direction. Using for instance a form of the housing which is not rotation-symmetrical relative to the laser beam, the direction of the gas flow supplied parallel to the laser beam can be changed into a gas flow with at least one movement component in a direction perpendicular to the direction of the laser beam. Owing to the form differing from rotationrsymmetrical relative to the laser beam, the housing provides a direction (or directions) of the gas flow which encloses (enclose) an angle with the laser beam. The gas flow is preferably formed herein by at least substantially inert gas, such as Ar (or another inert gas) and N₂. A combination of different gases is also possible. Alternatively, it is also possible to envisage the gas being enriched with for instance O₂, although this is less obvious since this can enhance separation of objects but also results in a less controllable end result, which is precisely what is sought in high-precision applications. Nevertheless, specific applications can be envisaged (material which is difficult to separate, separation of material parts with a form which is less critical and so on) wherein an enriched gas is recommended.

For a controlled deposition of material residues, the gas flow can be carried at least some distance along the carrier from the position where the laser beam comes into contact with the carrier. The deposition will then take place where the gas flow is carried along the carrier at a short distance from the operative location of the laser beam. It is however also possible for the gas flow to be extracted a short distance from the position where the laser beam comes into contact with the carrier. The advantage of direct extraction of the gas flow after it leaves the operative location of the laser beam is that deposition on the carrier can be (at least partially) prevented. The residue of the carrier entrained with the gas flow will then (in optimal conditions) already have been carried a distance from the carrier before it can deposit on the carrier.

Advantageous results can be realized when the gas flow is heated such that it has a higher temperature (for instance higher than the ambient temperature) at the position where the laser beam comes into contact with the carrier. An advantage of using a heated gas is that the dynamic viscosity of the gas increases at higher gas temperature; the active effect of the gas is thus increased. Another advantage of a raised gas temperature is that deposition of residue entrained in the gas flow can hereby be reduced or even prevented. If acceptable results are already achieved without heating the gas, the same result can be obtained with a smaller gas volume by heating the gas flow. Operation can hereby take place with a reduced gas consumption, which will evidently reduce costs.

In another preferred variant, the gas flow is at least partially ionized. Charged particles in the residue entrained in the gas flow can thus be neutralized, which can have an advantageous effect on preventing deposition at undesired locations of residue entrained in the gas flow. This measure also provides the possibility of reducing gas consumption.

The invention also provides a device of the type stated in the preamble, characterized in that the housing has a form differing from rotation-symmetrical relative to the laser beam such that a gas flow supplied by means of the gas feed has, after leaving the housing, at least one movement component in a direction perpendicular to the direction of the laser beam. Using such a device the advantages can be realized as already described in the foregoing with reference to the method according to the invention. It is also noted that such a device need entail no extra costs at all compared to the prior art. For good operation it is desirable that the gas feed connects to a gas source of an at least partially inert gas. The particular aim is a gas flow, after leaving the housing, at a distance of 0.5 to 1.0 mm from the housing. This is after all the usual distance at which a carrier for processing is situated from the housing.

In an advantageous embodiment variant the laser beam and the housing are displaceable relative to each other such that the movement component of the gas flow after leaving the housing can be changed in a direction perpendicular to the direction of the laser beam. The important advantage hereof is that the direction in which the material deposition (the contamination of the object for treating) takes place can hereby be controlled. By guiding the gas flow (at least the component thereof perpendicular to the laser beam) in a determined direction, the deposition will also be oriented accordingly. When separating for instance encapsulated semiconductors from a collective carrier, during the making of each separate cut the deposition will be guided in a direction such that the released contacts of the encapsulated semiconductors remain free of deposition.

The directing of the gas flow can for instance be realized in relatively inexpensive manner by a housing which is rotatable relative to the laser beam. Alternatively (or in combination with the rotatable housing), the housing can be given a translatable form relative to the laser beam. As described above, it is additionally advantageous to extract the gas flow shortly after it has passed the operative location of the laser beam, so that the degree of deposition is reduced, and this becomes possible when the housing is provided with a gas discharge for discharging gas which has had at least one movement component in a direction perpendicular to the direction of the laser beam. It is desirable here that the gas discharge is opened on a side of the housing remote from the laser beam. The gas from the housing can then come into contact with the object for treating and then be extracted. The undesired mixing of gas which has not yet been carried along the operative location with gas which has already passed this location can thus he_ prevented. In order to increase the rate of flow of the gas (up to preferably a maximum of sonic speed) and to reduce the gas consumption, it is advantageous to provide the housing with an internal constriction, which constriction allows passage of both the laser beam and the gas flow. Another possibility is for the housing to be provided with a separate, eccentrically placed second feed channel for gas. With a second feed channel for gas it becomes even better possible to control the direction of gas flow outside the housing (particularly at the position where the laser beam strikes the carrier for treating).

In another preferred variant, the device is provided with heating means connecting to the gas feed, and in yet another variant the device is provided with ionizing means connecting to the gas feed. With these means the gas flow can be respectively heated and ionized. A heated and/or ionized gas flow has advantages as already described above on the basis of the method according to the present invention.

The present invention will be further elucidated on the basis of the non-limitative embodiments shown in the following figures. Herein: figure 1 shows a schematic view of a cross-section through a part of a laser device according to the invention, figure 2 is a schematic view of a cross-section through a part of an embodiment variant of a laser device according to the invention, figure 3 is a schematic view of a cross-section through a part of a second embodiment variant of a laser device according to the invention, figure 4 shows a schematic view of a cross-section through a part of a third embodiment variant of a laser device according to the invention, figure 5 shows a schematic view of a cross-section through a part of a fourth embodiment variant of a laser device according to the invention, figure 6 is a schematic view of a cross-section through a part of a fifth embodiment variant of a laser device according to the invention, figure 7A shows a schematically represented top view of a laser beam and housing which form part of a device according to the invention, figure 7B shows a schematically represented top view of a laser beam and housing according to figure 7A in a second relative orientation, figure 7C shows a schematically represented top view of a laser beam and housing according to figures 7A and 7B in a third relative orientation, and figure 7D shows a schematically represented top view of a laser beam and housing according to figures 7A-7C in a fourth relative orientation.

Figure 1 shows a part of a head of a housing 1 with a passage 2 through which a laser beam 3, shown by means of broken lines, is projected onto a material layer 4 for treating. Laser beam 3 is so powerful (for instance 1064 nm, 24 Watt effective at a diameter of 15 um) that it arranges a cut 5 in the carrier (for instance manufactured from copper, epoxy, plastic or a composite product such as a "BGA-board"), whereby the carrier 4 can be separated completely. Through passage 2 is carried a gas (for instance at an overpressure of 2.5 to 4 Bar), the flow of which is shown by means of arrows. At the position where laser beam 3 contacts the cut 5 in carrier 4, the gas is flowing at least partially parallel to carrier 4 (see herefor arrow PI). Owing to the direction of this gas flow PI close to cut 5, the carrier material released and evaporated by the laser beam will be precipitated as deposit 6 at least substantially on one side of cut 5. In order to now achieve this effect, laser beam 3 is placed out of centre in passage 2 so that housing 1 is no longer placed rotation-symmetrically relative to laser beam 3. It is also noted that the constriction in passage 2 is provided in order to accelerate the gas flow (to a speed of more than 100 metres per second, or more preferably to sonic speed) and to limit the gas consumption.

Figure 2 once again shows the carrier 4 in which a cut 5 is being made. The housing 7 shown in this figure has a passage 8 through which a laser beam 9 now passes centrally. The housing is now however chamfered at the outer end such that after leaving the housing the gas flow will be urged substantially in a preferred direction. See also herefor the direction of the gas flow indicated symbolically by means of the arrows. The gas flow close to cut 5 (see arrow P2) ensures that material deposition 10 occurs at least substantially on one side.

Figure 3 shows another embodiment variant of a housing 11 with which the gas flow can be urged in a preferred direction from a passage 12. The laser beam 13 placed centrally in passage 12 makes a cut 5 in carrier 4, whereby, as a result of the local direction of the gas flow close to cut 5(see arrow P3), material deposition 10 will again occur substantially on only one side of cut 5. Figure 4 shows a variant 14 of a head of housing 1 in figure 1 in which now however a discharge opening 15 for gas is arranged. Because a part of the material released from carrier 4 by laser beam 3 will now be extracted before it is deposited, the deposition 16 occurring substantially on one side of cut 5 will be less than the deposition 6 as shown in figure 1.

Figure 5 shows a housing 30 which displays a great resemblance to housing 14 as shown in figure 5, although housing 30 is also provided with an extra feed channel 31 for gas. Laser beam 3 can be carried centrally through this housing 30, whereby housing 30 can be centrally rotated in simple manner to displace the direction in which deposition 16 occurs. Attention is also drawn to the form of central passage 32 which, similarly to the form of the passage shown in figure 4, has a converging shape. A thus formed central passage 32 is particularly suitable for creating a gas flow with a maximal sonic (sub-sonic) speed.

Figure 6 also shows a housing 17 for a laser beam 18 with a discharge channel 19 for gas. In the embodiment shown in this figure 6 the discharge channel 19 is however provided with a separate jacket 24 arranged against the outside of housing 17. Illustrated once again is that the material deposition 20 occurring on carrier 4 is less than the deposition 6, 10 as shown in figures 1-3.

Figures 7A-7D show an inner wall 21 of housing 1 of figure 1 through which a laser beam 22 passes eccentrically. Owing to the eccentric disposition of laser beam 22 in housing 1, the material deposition will not occur evenly around the centre of inner wall 21 but will occur mainly in a hatched region 23. By changing the relative orientation of laser beam 22 and inner wall 21 it is thus possible to determine where the hatched region 23 is situated. The mutual displacement of inner wall 21 and laser beam 22 can take place by means of translation and/or eccentric rotation of one of the two. In respect of the embodiment variants of housing 7, 11 shown in figures 2 and 3, it is noted that the direction of deposition 10 can herein be controlled most simply by central rotation (relative to laser beam 9, 13) of housing 7,11.

Claims

1. Method for treating a carrier for at least one electrical component with a laser beam by directing the laser beam at the carrier, characterized in that at the position where the laser beam comes into contact with the carrier a gas flow is present which has at least one movement component in a direction perpendicular to the direction of the laser beam.

2. Method as claimed in claim 1, characterized in that the gas flow is supplied substantially parallel to the laser beam through a housing arranged around the laser beam, in order to change this gas flow closer to the carrier into the gas flow with at least one movement component in a direction perpendicular to the direction of the laser beam.

3. Method as claimed in claim 2, characterized in that the direction of the gas flow supplied parallel to the laser beam is changed by a form of the housing not rotation-symmetrical relative to the laser beam into a gas flow with at least one movement component in a direction perpendicular to the direction of the laser beam.

4. Method as claimed in any of the foregoing claims, characterized in that the gas flow is formed by at least substantially inert gas, such as Ar and N₂.

5. Method as claimed in any of the foregoing claims, characterized in that the gas flow with at least one movement component in a direction perpendicular to the direction of the laser beam is carried at least some distance along the carrier from the position where the laser beam comes into contact with the carrier.

6. Method as claimed in any of the foregoing claims, characterized in that the gas flow with at least one movement component in a direction perpendicular to the direction of the laser beam is extracted from the position where the laser beam comes into contact with the carrier.

7. Method as claimed in any of the foregoing claims, characterized in that the gas flow is heated.

8. Method as claimed in any of the foregoing claims, characterized in that the gas flow is at least partially ionized.

9. Device for treating a carrier for at least one electrical component with a laser beam, comprising:

- a laser source having directing means which connect to the laser source for directing a laser beam at an object for treating, and

- a housing with a gas feed arranged at least partially around the laser source, characterized in that the housing has a form differing from rotation-symmetrical relative to the laser beam such that a gas flow supplied by means of the gas feed has, after leaving the housing, at least one movement component in a direction perpendicular to the direction of the laser beam.

10. Device as claimed in claim 9, characterized in that the gas feed connects to a gas source of an at least partially inert gas.

11. Device as claimed in claim 9 or 10, characterized in that the laser beam and the housing are displaceable relative to each other such that the movement component of the gas flow after leaving the housing can be changed in a direction perpendicular to the direction of the laser beam.

12. Device as claimed in claim 11, characterized in that the housing is rotatable relative to the laser beam.

13. Device as claimed in claim 11 or 12, characterized in that the housing is translatable relative to the laser beam.

14. Device as claimed in any of the claims 9-13, characterized in that the housing is provided with a gas discharge for discharging gas which has had at least one movement component in a direction perpendicular to the direction of the laser beam.

15. Device as claimed in claim 14, characterized in that the gas discharge is opened on a side of the housing remote from the laser beam.

16. Device as claimed in any of the claims 9-15, characterized in that the housing is provided with an internal constriction, which constriction allows passage of both the laser beam and the gas flow.

17. Device as claimed in any of the claims 9-16, characterized in that the housing is provided with a separate, eccentrically placed second feed channel for gas.

18. Device as claimed in any of the claims 9-17, characterized in that the device is provided with heating means connecting to the gas feed.

19. Device as claimed in any of the claims 9-18, characterized in that the device is provided with ionizing means connecting to the gas feed.