Method for repairing an electronic circuit board by laser ablation.

Abstract

A method for repairing an electronic circuit board (1) comprising a substrate (2) provided with conductive tracks (3) and a faulty electronic component (4, 6, 7) connected to the conductive tracks (3) by a joint (5), characterized in that the method comprises the steps of destroying the faulty electronic component (4, 6, 7) and performing at least partial laser ablation of the joint (5), then mounting a replacement electronic component (4', 6') in place of the faulty electronic component (4, 6, 7). Figure 5

Description

Title of the invention: Method for repairing an electronic circuit board by laser ablation.

[0001] The present invention relates to the field of electronic circuit board repair.

[0002] BACKGROUND OF THE INVENTION

[0003] Electronic boards comprising a substrate on which conductive tracks are extended (often referred to as PCB from the English printed circuit board) and electronic components soldered onto the conductive tracks are known.

[0004] When one of the electronic components fails, it may be advantageous to replace it, for example, for reasons of cost and ecology.

[0005] If the faulty electronic component is attached to the conductive tracks by brazed joints, it is known to heat the brazed joints until the brazing material melts, remove the faulty electronic component and then attach a replacement electronic component in its place by recreating brazed joints by melting a brazing material.

[0006] If the faulty electronic component is attached to the conductive tracks by adhesive, it is known that heating the adhesive to its glass transition temperature causes it to lose its adhesive power. The faulty electronic component can then be removed and the replacement electronic component glued in its place.

[0007] These operations are feasible because the heating temperature required to remove the electronic component does not require heating likely to impact the electronic components surrounding the faulty electronic component, provided that said surrounding electronic components are sufficiently far from the faulty electronic component.

[0008] It is also known to bond electronic components to conductive tracks using a sintered silver joint obtained by a sintering operation at a temperature of approximately 300°C. However, it is not possible to remove these electronic components by melting the sintered joint because the melting point of silver (962°C) is so high that the heating required to reach this temperature would necessarily damage the surrounding electronic components. Therefore, the failure of an electronic component bonded by silver sintering currently necessitates replacing the entire circuit board.

[0009] There is also a method for analyzing materials comprising a laser ablation step in which a pulsed laser is projected onto the surface of the material to be analyzed, from which particles are expelled perpendicularly to said surface, and a step of analyzing these particles in a mass spectrometer.

[0010] There is also a thin film deposition process comprising a laser ablation step in which a pulsed laser is projected onto the surface of a material to be deposited, particles of which are expelled perpendicularly to said surface and are deposited on a substrate positioned appropriately to expose a surface to said particles which will form a thin film on said surface.

[0011] SUBJECT OF THE INVENTION

[0012] The invention is intended in particular to provide a means for repairing electronic boards. Summary of the invention

[0013] To this end, the invention provides a method for repairing an electronic circuit board comprising a substrate with conductive tracks and a faulty electronic component connected to the conductive tracks by a joint. The method comprises the steps of destroying the faulty electronic component and performing at least partial laser ablation of the joint, then mounting a replacement electronic component in place of the faulty electronic component.

[0014] Thus, the aim is not simply to melt the seal and remove the faulty electronic component: the faulty electronic component is destroyed, and laser ablation is used to remove the seal. This technique is advantageous because the laser beam generates controlled and highly localized heating, which does not affect electronic components near the faulty component.

[0015] According to optional features, used individually or in whole or in combination: - the destruction of the faulty electronic component is carried out using a laser beam; - the destruction of the faulty electronic component is carried out by laser ablation; - Laser ablation is performed using a laser emitter and the process includes adapting the settings of the laser emitter according to the materials to be removed; - the laser emitter is arranged to emit infrared wavelength laser pulses, with a duration of approximately 750 fs at a frequency of approximately 600 kHz; - the laser emitter has a power of approximately 50 W; - the faulty electronic component is embedded in the substrate and the process includes the step of performing a laser ablation of the substrate area covering the faulty electronic component and, after replacing the faulty electronic component with the electronic component of replacement, to cover the replacement electronic component with a substrate material to bury the replacement electronic component; - the step of creating at least one replacement conductive trace on the external surface of the substrate material covering the replacement electronic component; - the seal is a sintered seal; - the replacement electronic component is fixed by means of a sintered gasket.

[0016] Other features and advantages of the invention will become apparent from the following description of particular and non-limiting embodiments of the invention. Brief description of the drawings

[0017] Reference will be made to the attached drawings, among which:

[0018] [Fig.la] is a partial schematic cross-sectional view of a first electronic board comprising a faulty electronic component before repair according to a first implementation of the process according to the invention;

[0019] [Fig.lb] is a view, analogous to [Fig.la], of the first electronic board with the faulty electronic component being ablated;

[0020] [Fig.le] is a view, analogous to [Fig.la], of the first electronic board after removal of the faulty electronic component and the seal;

[0021] [Fig.2a] is a view, analogous to [Fig.la], of the first electronic board during the installation of a replacement electronic component;

[0022] [Fig.2b] is a view, analogous to [Fig.la], of the first electronic board after the replacement electronic component has been installed;

[0023] [Fig.3a] is a partial schematic cross-sectional view of a second electronic board comprising a faulty electronic component before repair according to the first embodiment of the method according to the invention;

[0024] [Fig.3b] is a view, analogous to [Fig.3a], of the second electronic board with the faulty electronic component being ablated;

[0025] [Fig.3c] is a view, analogous to [Fig.3a], of the second electronic board after removal of the faulty electronic component and the seal;

[0026] [Fig.3d] is a view, analogous to [Fig.3a], of the second electronic board after the replacement electronic component has been installed;

[0027] [Fig.4a] is a partial schematic cross-sectional view of the second electronic board comprising a faulty electronic component before repair according to a second embodiment of the method according to the invention;

[0028] [Fig.4b] is a view, analogous to [Fig.4a], of the second electronic board with the faulty electronic component in the process of being destroyed;

[0029] [Fig.4c] is a view, analogous to [Fig.4a], of the second electronic board after partial destruction of the faulty electronic component;

[0030] [Fig.4d] is a view, analogous to [Fig.4a], of the second electronic board with remnants of the faulty electronic component and the seal being removed;

[0031] [Fig.4e] is a view, analogous to [Fig.4a], of the second electronic board after removal;

[0032] [Fig.4f] is a view, analogous to [Fig.4a], of the second electronic board after the replacement electronic component has been installed;

[0033] [Fig. 5] is a partial schematic cross-sectional view of a third electronic board comprising a faulty electronic component prior to repair according to a third embodiment of the method according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0034] With reference to Figures 1a, 2a, 5, the invention is a method for repairing an electronic circuit board 1 comprising a substrate 2, provided with conductive tracks 3, and a faulty electronic component 4, 6, 7 connected to the conductive tracks 3 by a metallic joint 5. The joint 5 is here made of silver and produced by sintering silver particles. These sintered joints and their fabrication are known per se and will not be described further here.

[0035] The process includes the steps of destroying the faulty electronic component 4, 6, 7 and performing at least partial laser ablation of the seal 5 and then mounting a replacement electronic component 4', 6' in place of the faulty electronic component 4, 6, 7.

[0036] In the first embodiment illustrated in Figures 1b and 1a, the faulty electronic component 4, the joint 5 and the upper part of the conductive tracks 3 are destroyed by laser ablation.

[0037] Laser ablation is performed using a laser emitter 10 with a power of approximately 50 W, configured to emit laser pulses 11 with a wavelength in the infrared range, specifically 1030 nm. The process includes adjusting the settings of the laser emitter 10 according to the materials to be removed. The laser emitter 10 is set to emit a laser beam 11 in the form of laser pulses with a duration of approximately 750 fs at a frequency of approximately 600 kHz. It should be noted that laser ablation is an operation, known in itself in other applications, aimed at locally decomposing a material by subjecting it to a high-energy laser beam.

[0038] The laser beam 11 causes sublimation of the materials it encounters. The laser emitter 10 is here attached to a motorized carriage mounted on a frame to extend in relation to the surface of the elements to be destroyed and to be movable, at least horizontally, in a programmable manner so that the laser beam 11 sweeps across said surface.

[0039] Ablation is preferably carried out in successive layers, one layer being destroyed with each pass of the laser beam 11, in order to limit heating of the electronic board 1. The heating must in fact remain very localized so as not to run the risk of damaging one of the electronic components surrounding the faulty electronic component (by "deterioration", we mean an alteration of the surrounding electronic component itself, of the joint linking it to the conductive tracks, or of the conductive tracks themselves).

[0040] At the end of the ablation operation, a layer of silver particles is deposited on the conductive tracks 3 and a replacement electronic component 4' is placed on said layer ([Fig. 2a]) before a sintering operation transforms the layer of silver particles into a joint 5' linking the replacement electronic component 4' to the conductive tracks 3 ([Fig. 2b]). The sintering process is known per se and will not be described in further detail here.

[0041] The electronic board of figures 3a to 4f differs from that of figures 1a to 2b in that the faulty electronic component 6 is an SMD component having a lower surface which is partly free of any attachment.

[0042] The replacement of the faulty electronic component 6 is illustrated using the first embodiment (already described above - figures 1b and 1e) which will be shown in relation to figures 3a to 3d, or a second embodiment which will be shown in relation to figures 4a to 4f.

[0043] According to the first embodiment (figures 3a to 3d), the faulty electronic component 6, the seal 5 and the upper part of the conductive tracks 3 are destroyed by laser ablation.

[0044] Laser ablation is performed using a laser emitter 10 as previously indicated.

[0045] The laser beam 11 causes sublimation of the materials it encounters and is displaced, at least horizontally, in such a way that the laser beam 11 scans the surface of the elements to be destroyed ([Fig. 3b]). The ablation is preferably carried out in successive layers, one layer being destroyed with each pass of the laser beam 11, in order to limit heating of the electronic board 1 as indicated above.

[0046] At the end of the ablation operation ([Fig. 3c]), a layer of silver particles is deposited on the conductive tracks 3 and a replacement electronic component 6' is placed on said layer before a sintering operation transforms the layer of silver particles in a joint 5' linking the replacement electronic component 6' to the conductive tracks 3 ([Fig.3d]).

[0047] According to the second embodiment (figures 4a to 4f), the repair is carried out in two operations: - a first operation during which the faulty electronic component 6 is destroyed by means of a cutting laser (figures 4b, 4c); - a second operation during which the remains of the faulty electronic component 6, the seal 5 and the upper part of the conductive tracks 3 are destroyed by laser ablation ([Fig.4d]).

[0048] The first operation consists of heating the faulty electronic component 6 to cut it and free it as much as possible from the seal 5. A laser emitter 12 is used for this purpose, emitting a continuous laser beam 13 having a wavelength in the infrared range ([Fig. 4b]). Alternatively, the laser beam 13 can be emitted in the form of pulses with sufficiently long durations (in the millisecond or microsecond range) to heat the faulty electronic component 6 sufficiently to cut it.

[0049] At the end of this first operation, only pieces 6* of the faulty electronic component 6 remain attached to the joint 5 ([Fig.4c]).

[0050] Laser ablation is performed using a laser emitter 10 as previously indicated for the first embodiment.

[0051] The laser beam 11 causes sublimation of the materials it encounters and is displaced, at least horizontally, in such a way that the laser beam 11 scans the surface of the elements to be destroyed, namely here the pieces 6* and the joint 5 and possibly the upper part of the conductive tracks 3 ([Fig. 4d]). The ablation is preferably carried out in successive layers, one layer being destroyed with each pass of the laser beam 11, in order to limit heating of the electronic board 1.

[0052] At the end of the ablation operation ([Fig.4e]), a layer of silver particles is deposited on the conductive tracks 3 and a replacement electronic component 6' is placed on said layer before a sintering operation transforms the layer of silver particles into a joint 5' linking the replacement electronic component 6' to the conductive tracks 3 ([Fig.4f]).

[0053] A third embodiment of the method of the invention will now be described with reference to [Fig.5], in the case where the faulty electronic component 7 is embedded in the substrate 2.

[0054] The process then comprises the step of performing a laser ablation of the substrate area 2' covering the faulty electronic component 7. The faulty electronic component 7 and the seal 5 are then destroyed as in the first or second implementation method. After replacing the faulty electronic component 7 with the replacement electronic component, the method includes the step of covering the replacement electronic component with a substrate material to bury the replacement electronic component.

[0055] If the substrate area 2' contained a conductive track that was destroyed by laser ablation, the method includes the additional step of creating at least one replacement conductive track on the external surface of the substrate material covering the replacement electronic component. The conductive track is, for example, created using an aerosol jet printing or material projection technique, or any other related process.

[0056] Of course, the invention is not limited to the embodiments described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0057] In particular, the electronic board may have a different structure from that described.

[0058] By “substrate”, we mean any support suitable for carrying at least one electronic component, of any shape (e.g. PCB type plate, case, etc.) and of any material, flexible or rigid, and in particular of organic material, ceramic or metal.

[0059] The term "joint" means any assembly of material that secures an electronic component to a conductive track and ensures an electrical connection of the electronic component to said conductive track. The joint may be a brazed joint or a sintered joint, regardless of the material used (for example, silver or copper for sintering).

[0060] By "electronic component" is meant any type of electrically conductive or semiconductive device providing an active or passive function, in an analog or digital manner, in an electronic circuit.

[0061] By "defective electronic component" is meant an electronic component which no longer performs its function or performs it imperfectly or suboptimally or which is no longer up to date.

[0062] The electronic board may include one or more electronic components, and the same electronic board may include several faulty electronic components.

[0063] It is possible to mount one or more laser emitters on a motorized trolley that moves on a fixed frame, or to mount one or more laser emitters on a robot programmed to move the laser emitter(s). Alternatively, each laser emitter is fixed and the electronic board is mounted on a motorized table that moves in relation to the emitter(s).

[0064] The replacement electronic component can be fixed by means of a brazed or sintered joint or by gluing.

[0065] Advantageously, the settings of the laser emitter 10 are modified, during the ablation operation, according to the materials encountered, the nature of which is known according to the height relative to the upper surface of the substrate 2 (and therefore also according to the thickness of material already removed).

[0066] Laser ablation may be used to remove all or part of a conductive track and / or via.

Claims

Demands

1. A method for repairing an electronic board (1) comprising a substrate (2) provided with conductive tracks (3) and a faulty electronic component (4, 6, 7) linked to the conductive tracks (3) by a joint (5), characterized in that the method comprises the steps of destroying the faulty electronic component (4, 6, 7) and performing at least partial laser ablation of the joint (5) and then mounting a replacement electronic component (4', 6') in place of the faulty electronic component (4, 6, 7).

2. A method according to claim 1, wherein the destruction of the faulty electronic component (4, 6, 7) is carried out by means of a laser beam (11, 13).

3. A method according to claim 2, wherein the destruction of the faulty electronic component (4, 6, 7) is carried out by laser ablation.

4. A method according to any one of the preceding claims, wherein the laser ablation is carried out using a laser emitter (10) and the method includes adapting the settings of the laser emitter (10) according to the materials to be removed.

5. A method according to claim 4, wherein the laser emitter (10) is arranged to emit laser pulses (11) of infrared wavelength, with a duration of about 750 fs at a frequency of about 600 kHz.

6. Method according to claim 4 or 5, wherein the laser emitter (10) has a power of approximately 50 W.

7. A method according to any one of the preceding claims, wherein the faulty electronic component (7) is embedded in the substrate (2) and the method comprises the step of performing a laser ablation of the substrate area (2') covering the faulty electronic component (7) and, after replacing the faulty electronic component (7) with the replacement electronic component, covering the replacement electronic component with a substrate material to embed the replacement electronic component.

8. Method according to claim 7, comprising the step of making at least one replacement conductive track on the external surface of the substrate material (2) covering the replacement electronic component.

9. 10 Method according to any one of the preceding claims, wherein the seal (5) is a sintered seal.

10. Method according to claim 9, wherein the replacement electronic component is fixed by means of a sintered seal (5').

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