DE102006039623B3 - Printed circuit board and LED connecting method, involves reproducing light beam by imaging lens, and dividing beam into number of partial light beams such that partial light beams form number of discrete light spots - Google Patents

Abstract

The method involves reproducing a light beam e.g. laser light beam, by an imaging lens (1), and dividing the beam into a number of partial light beams (12a-12c) such that the partial light beams form a number of discrete light spots for producing a number of discrete, material-conclusive connection points between a printed circuit board (13) and an LED. An independent claim is also included for a device for connecting a printed circuit board and an LED.

Description

Territory of invention

The The present invention relates generally to the connection of elements, especially by cohesive Compound, most preferably by soft soldering, and in particular relates to the contacting of electronic or microelectronic Components by soldering. Another aspect of the present invention relates generally the processing of a substrate with laser beams.

background the invention

In of electronics manufacturing Today, 40,000 components or more are soldered per hour. Therefore, takes place in the mass production of electronic devices, in particular in the mass production of printed circuit boards, mainly the so-called reflow soldering or reflow soldering Application. This is a soft soldering process for soldering SMD components. In a first step, the reflow soldering on the solder before placement the board applied. Then in a next step the components are equipped. Because the solder paste used is sticky, the components are held by the solder paste during assembly. You need to So not be glued on specially. During the subsequent melting of the solder, the assembled components center themselves through the surface tension on the landing pads and sit down.

Though let yourself by reflow soldering a high quantity realize, but requires the reflow soldering a high thermal load the one to be soldered Components. With increasing integration density and functionality is increasing however, the temperature sensitivity of microelectronic devices. This also applies to microelectromechanical systems (MEMS). To make matters worse, that on 1 July 2006 the European Waste Electrical and Electronic Equipment Regulation (WEEE) enters into force, causing the changeover on lead-free electronic products. The lead-free Soldering, as in the future prescribed by the WEEE, but normally requires higher soldering temperatures, easily by about 20 ° Celsius higher can, which further increases the thermal load during soldering. It exists therefore a need for soldering in electronics manufacturing, which has a low thermal load enable.

For increased tensile strength of solder joints Solders with a high antimony content are preferred. This is due to the higher one Melting temperature of antimony (Sb) higher soldering temperatures, which is the thermal Load of components also increased.

Other soldering, For example, the so-called wave soldering, create here as well no remedy.

Out other technical fields laser beam soldering is known. This will be the solder joints heated with a laser beam, which are focused precisely can and can enter so much energy in the solder joint. The soldered point becomes spatially heated very narrowly, what short soldering times of for example, less than 1 sec. This occurs to the Components almost no thermal load.

DE 20 2004 013 136 U1 discloses a modular lightwave optic for use in welding robots for automotive welding. The optical module is held by the hand of an industrial robot, which moves the light beam in appropriate geometry along the joint gap by means of process and pivoting to form a weld.

US 2005/0082265 A1 discloses a laser welding process for the production a controller for a hydraulic vehicle braking device. There are elements made of metal with plastic elements. To form the required closed welding line must while also the respective load beam are moved.

The Use of robots for beam deflection requires long welding or soldering times, which makes a use in electronics manufacturing impractical.

alternative can for beam deflection also galvanometer scanners are used, because of the almost inertia Beam deflection opposite the aforementioned motor beam deflections a clear Offer speed advantage. This basically allows the Use in electronics production.

US 2004/0190294 A1 discloses a method for laser soldering power LEDs. In this case, a plurality of solder joints along a line course, namely a circular line course, set. The beam deflection is accomplished by means of a scanner with two movable mirrors. However, the total production speed achieved is still not sufficient for high-volume electronics production, since such a soldering process continues to take place sequentially and takes at least about 0.5 sec. To about 2 sec. (Transport processes not yet included). Would you increase the number of scanners by this method hen this would require a very high control effort, which would require higher manufacturing costs.

comparable Problems also occur in the substrate processing, for example when selectively setting a plurality of through holes, blind holes and / or weakened areas in a predetermined geometric arrangement.

Summary the invention

task It is the object of the present invention to provide a method and an apparatus for providing at least two elements with light rays, bringing in a simple way a high production speed at the same time low thermal load to be connected Realize elements. A preferred application of the invention is the laser soldering of electronic, optoelectronic or microelectromechanical (MEMS) elements.

The The above and other objects are achieved by a method Claim 1 and solved by a device according to claim 10. Further advantageous embodiments are the subject of the referenced Dependent claims.

at a method according to the present invention Invention shares an imaging optics the light beam, preferably Laser light beam, simultaneously into a plurality of partial light beams, which are mapped to the elements to be connected, where these form a plurality of discrete spots of light. This effect by the energy input according to the invention the formation of a plurality of discrete, cohesive Connecting points between the elements to be connected. Prefers the elements are at the joints by melting a Soft solder interconnected. The present invention is suitable but in principle also for brazing, welding or to the initiated by the light spots photocuring of an adhesive.

Consequently can according to the invention several at cohesive Connecting points, in particular solder joints are formed. A time-consuming and expensive beam deflection is not according to the invention required. As is known, light rays divided in a simple manner into a plurality of partial light beams become. As for cohesive Connection of elements, in particular for soldering, each connection point certain minimum power is required, subject to the inventive method practically only of restriction, that the respective partial light beams still have sufficient intensity or power must have. This leaves by suitable design of the beam splitter and by suitable choice of the light output of the input light beam in almost any desired Realize way.

According to the invention the partial light beams are suitable directly from the imaging optics imaged and deflected to simultaneously a plurality of connection points train. As particularly useful for suitable beam splitting has become the use of one of the imaging optics associated diffractive optical element (DOE) proved, as this high light intensities almost lossless and with a suitable beam profile of the partial light rays can be shared. In particular, lets With diffractive optical elements also a further beam shaping easy to realize, especially with respect to the beam cross section, the intensity, Shape or beam profile and / or divergence of the respective partial light beams.

According to one another embodiment the connection points are predetermined in a predetermined arrangement. This can be achieved for example by the design of the Elements and / or by their geometric arrangement, for example on a holding device for positioning the to be connected Elements during of the process, be conditional. According to the invention, the diffractive optical Element designed and designed so that the partial light rays in correspondence with this predetermined arrangement of joints generated and directed in corresponding directions and mapped become. It is advantageous that a more elaborate distraction the partial light rays is not required. To convert the Procedure for a different geometric arrangement of the joints the diffractive optical element can be exchangeable, for example in a revolver unit or other turning or changing device being held.

In principle it can be provided that the imaging optics are associated with a plurality of diffractive optical elements, for example, are held directly in this, to divide the input light beam suitable in a plurality of partial light beams. Preferably, however, according to a further embodiment, a single diffractive optical element is used, which is penetrated overall by the input partial light beam and has a plurality of diffractive optical zones or active zones whose arrangement and design are matched to the aforementioned predetermined arrangement of joints. Thus, the diffractive optical element has one or more diffractive optical zones or active zones, for example in the form of alternating raised and recessed line, circle or elliptical zones or of alternating regions with different refractive indices or in others Way, are designed as suitable light-diffractive structures. These active zones are preferably provided on a single, transparent to the input light beam substrate, which may be held for this purpose also changeable in the beam path of the input light beam.

According to one preferred aspect of the present invention is each of designed diffractive optical zones of the diffractive optical element, around the associated partial light beam a suitable intensity, a suitable beam cross-section, a suitable beam shape and / or Impose beam divergence. Thus, you can the individual diffractive optical zones differ in any way be designed.

Especially Thus, partial light beams with different intensities can also be made easier Realize manner, so that material connection points, such as for example, solder joints, at the same time be generated with a different energy input from a single input light beam can.

According to one Another aspect of the present invention includes the imaging optics at least an input lens and a spaced apart in the beam direction Output lens, so that by varying the distance a larger or smaller diameter of the laser beam can be adjusted. When using an optical waveguide, in particular a glass fiber, for coupling the input light beam into the imaging optics Furthermore, the distance of the input lens to the output side of Fiber optic can be varied, which opens up more degrees of freedom.

According to one Another aspect of the present invention is the diffractive optical element between the aforementioned input lens and output lens arranged, which facilitates adjustment and adjustment tolerances decreases. At the same time, the diffractive optical element together with the input and output lens in a modular optical unit sealed housed be. The housing The imaging optics can be designed to be a change of the diffractive optical element for forming another Arrangement of joints to allow, for example by means a revolver unit or another rotary or exchange unit, wherein several differently formed diffractive optical Elements are kept.

A preferred application of the method relates to the soft soldering of electronic or optoelectronic devices, of microelectromechanical Elements or connectors on a carrier, such as a printed circuit board. at these applications can according to the invention simultaneously several solder joints be set, by appropriate division of a light beam, preferably Laser beam, in several partial light beams under simultaneous suitable deflection and imaging of the same on the solder joints, by the design of the elements and / or by their geometric Arrangement are conditional. A complex sequential distraction of a Laser beam by means of a scanner optics is not according to the invention required. Thus, high processing speeds can be achieve. At the same time, the thermal load of the elements to be soldered negligible. The The diffractive optical element to be used can be designed in this way be that at the same time a variety of elements are soldered can. The inventive method is also suitable for the electronics production in high quantity. The partial light rays can in particular with different intensities or Services are generated, so that at the same time solder joints can be set with different interpretation, for example, the electrical Contacting the elements themselves, for contacting connectors or also of strain reliefs for Elements or connectors.

LIST OF FIGURES

following the invention will be described by way of example and with reference on the attached Drawings are described, resulting in more features, benefits and to be solved Tasks will result. Show it:

1 in a schematic representation of a system for laser soldering electronic components according to the present invention;

2 in an enlarged sectional view of an imaging optics of the system according to the 1 ;

3 in a schematic partial section, a method for laser soldering an LED according to the present invention;

4a in a schematic plan view of the distribution of solder joints for electrically contacting a connector on a carrier, such as a printed circuit board; and

4b in a schematic plan view and in a section of a substrate which has been processed by the method according to the invention.

In the figures denote identical reference numerals identical or Substantially equal elements or groups of elements.

Full Description of exemplary embodiments the invention

According to the 1 becomes the laser beam of a diode laser 8th in a fiberglass 9 coupled and forwarded to the plant, where a processing head an imaging optics 1 with an associated diffractive optical element (DOE) 5 wearing. Through the imaging optics 1 becomes the input light beam 10 in a plurality of partial light rays 12a - 12c divided. At the same time they are properly focused. The distance between the machining head and the printed circuit board 13 is therefore in accordance with the achieved focal length of the imaging optics 1 and the desired diameter of the beam spots on the printed circuit board 13 selected. By way of example, a distance between the machining head and the workpiece to be machined of the order of magnitude of about 10 cm to about 50 cm has been realized. According to the 1 are on the circuit board 13 several components (not shown) positioned in a regular array, of which only three contact pins 14a . 14b . 14c are shown for electrical contact. The contact pins are, for example, on solder pads, pads or the like of the printed circuit board 13 in a suitable geometric arrangement, as predetermined by a circuit layout, positioned. In the plane of the printed circuit board 13 the geometric arrangement of the contact pins or solder joints can be almost arbitrary. For suitable imaging and deflection of the partial light rays 12a - 12c only needs the imaging optics 1 and the diffractive optical element 5 be designed suitably, as described in more detail below.

For adjusting the imaging optics 1 is an adjusting device 4 provided, in particular, as in the 2 shown, the distance z1 of the input lens 2 the imaging optics 1 to the exit side of the fiber 9 and / or the distance z2 between the input lens 2 and the associated output lens 3 the imaging optics 1 may vary suitably to the diameter of the input light beam 10 and the partial light rays 12a - 12c as well as the light spots suitable to specify.

According to the 1 can the DOE 5 in a manually or motor driven driveable device 7 be stored, for example, a revolver unit or a comparable rotating device. By pressing the changer 7 For example, the DOE can be changed to set another suitable geometric arrangement of solder joints.

According to the 1 is the printed circuit board 13 on a translation device 15 , For example, a conveyor belt or a x- / y-displacement table, stored by a drive 16 is driven.

In the process, those are on the printed circuit board 13 components to be soldered preferably positioned in a regular, recurring arrangement. During a first process step, in a first area of the printed circuit board 13 simultaneously set a plurality of solder joints, for example on the illustrated contact pins 14a - 14c , These solder joints can be located on a component, but can also be set to different components that in the first process step due to the beam splitting into the multiple partial light beams 12a - 12c can be trained simultaneously. Subsequently, the adjustment 15 operated and becomes an adjacent set of elements in the same geometric arrangement in the working area of the imaging optics 1 and the DOE 5 driven, in such a way that the partial light rays 12a - 12c in the same way as in the first process step, are mapped to the corresponding solder joints, for example, on the marked with the apostrophe contact pins 14a ' . 14b ' and 14c ' , This forms the second process step, which can be repeated as often as desired. Between the process steps, the substrate is thereby moved by an always identical travel path, which is predetermined by the distance between the individual regular arrangement of the components on the substrate.

To control the laser soldering according to the 1 a control device is provided, for example a CPU (not shown), which in particular the adjusting device 4 , the changing device 7 , the translation device 15 with the assigned drive 16 as well as the laser diode 8th controlled appropriately.

Further details of the imaging optics 1 are the 2 removable. Between the along the optical axis 11 spaced apart lenses 2 . 3 is a DOE 5 arranged, which the input light beam 10 by light diffraction in the partial light rays shown 12a - 12c Splits. By the imaging properties of the lenses 2 . 3 and / or the DOE 5 become the partial light rays 12a - 12c appropriately focused or imaged. By different diffraction in partial areas 6a - 6c of the DOE 5 become the partial light rays 12a - 12c deflected in suitable directions. According to the 2 can on the DOE 5 several differently designed diffractive optical zones 6a - 6c be provided, which the partial light rays 12a - 12c imprint different intensities, beam cross sections, beam profiles or beam shapes and / or divergences. Those skilled in the art will appreciate a suitable embodiment of the DOE 5 and the diffractive optical zones 6a - 6c be possible without further ado. As the skilled person readily apparent Lich can be, by suitable expansion of the input light beam 10 and suitable provision of diffractive optical zones 6a - 6c very many partial light rays 12 - 12c be designed to be suitable at the same time.

The 3 schematically shows a method according to the invention for laser soldering an LED 20 , This includes a pedestal 21 on which a light emitter 23 is positioned over a bonding wire 24 is contacted. On the pedestal 21 is also an optical lens element 22 for beam shaping of the emitted light beam. The light emitter 23 sits on a heat sink 25 of high thermal conductivity to the thermal load of the light emitter 23 to minimize. According to the 3 are through the pedestal 21 contact pins 14a . 14b guided, the electrical contacting of the p- and n-side of the light emitter 23 serve. The LED 20 is on a printed circuit board 13 positioned. Like in the 3 is represented by means of an imaging optics, as described above with reference to 1 and 2 described a laser beam divided into two partial light beams L1, L2 and on the contact pins 14a . 14b imaged so that a soft solder melted in these areas and so the solder joints shown 17a . 17b in correspondence with the geometry of the contact pins 14a and 14b be formed. Of course, several LEDs can be soldered in this way in one process step at the same time.

The inventive method is also suitable for contacting of connectors, microelectromechanical components or the like, as exemplified by the 4a described. According to the 4a has the connector 30 in plan view a total of three contact pins 14a - 14c and two tongues serving a strain relief 18a . 18b on, by means of the solder joints shown 17a - 17e contacted or connected. For connecting the strain relief tongues 18a . 18b may require a higher laser power. This is accomplished by appropriate beam splitting by means of the DOE of the imaging optics. When splitting the input light beam, basically any desired beam splitting ratios can be realized. Also in the embodiment according to the 3 can for contacting or fixing the heat reduction 25 a higher laser power or laser intensity may be required.

The inventive method is basically also suitable for substrate processing by simultaneous processing of a substrate at a plurality of sites. For this purpose, an input light beam is divided into a plurality of partial light beams in the manner described above, which according to the 4b on the workpiece 40 a plurality of discrete processing stations 41 form, for example, through holes, blind holes and / or weakening areas. The method is suitable for processing any substrates, for example paper or cardboard sheets, plastic materials or metal sheets. The majority of processing points 41 can according to the 4b along any line course 42 be arranged.

In summary Thus, according to another Another aspect of the present invention is a method for Substrate processing provided, in which method a light beam, In particular, a laser light beam is provided and a Imaging optics images the light beam in such a way and in a plurality Partial light rays say that these are a plurality of discrete ones Forming light spots that cause a processing of the respective substrate.

there can the light spots through holes, blind holes and / or weakening areas in one by the design of the diffractive optical element form predetermined geometric arrangement.

As the expert in studying the present application readily can be seen the discrete connection or processing points certainly also partially overlap. The Partial light rays can in any way from a front and / or a back a carrier be directed to the connection or processing points. For this purpose can also in the carrier Through holes be provided or this at least partially transparent be designed to provide optical access to the connection or machining points to allow. For further details regarding the laser soldering of optoelectronic Devices, such as power LEDs or power diode lasers, Reference is made to US 2004/0190294 A1, the content of which is hereby incorporated by reference expressly by reference, in particular as regards the As regards the design of the printed circuit board for electrical contacting.

1

imaging optics

2

Input lens / optics

3

Output lens / optics

4

adjustment

5

diffractive optical element

6a. 6c

diffractive optical element / diffractive optical zones

7

changer

8th

light source (Laser diode, LED)

9

Light source conductor

10

Input light beam

11

optical axis

12a-12c

Wedge light beams

13

printed circuit board

14a-14c

 contact pins

15

translation device

16

drive

17a-17e

solder joints

 18a-18d

Zugentlastungszungen

20

LED

21

base

22

lens

23

Halt state device / light emitters

24

bonding wire

25

heat sink

30

connector

31

base

40

workpiece

41

Perforation / weakening region

42

line

Claims (16)

Method for connecting at least two elements ( 13 . 20 ), in which method a light beam ( 10 ), in particular a laser light beam, is provided and an imaging optics ( 1 . 5 ) images the light beam in such a way and into a plurality of partial light beams ( 12a - 12c ) discloses that it has a plurality of discrete spots of light to produce a plurality of discrete, integral joints ( 17a - 17e ) between the at least two elements ( 13 . 20 ) train. Method according to Claim 1, in which the imaging optics comprise a diffractive optical element ( 5 ) comprising the light beam ( 10 ) is divided by light diffraction into the plurality of partial light rays. Method according to Claim 2, in which the connection points ( 17a - 17e ) are formed in a predetermined arrangement, which by the design of the elements to be connected ( 13 . 20 ) and / or by its geometric arrangement is given, and in which the diffractive optical element ( 5 ) corresponding to the predetermined arrangement of connection points in the partial light beams ( 12a - 12c ) and directed in different directions. Method according to Claim 3, in which the diffractive optical element ( 5 ) a plurality of diffractive optical zones ( 6a - 6c ) in correspondence with the predetermined arrangement of joints. Method according to Claim 4, in which the diffractive optical zones ( 6a - 6c ) a different intensity, beam cross-section, shape and / or divergence of the partial light beams ( 12a - 12c ) cause. Method according to one of Claims 2 to 5, in which the light beam ( 10 ) of an optical waveguide ( 9 ) and the imaging optics is an input lens ( 2 ) and an exit lens ( 3 ), wherein by varying the distance (Z1) of the input lens to the optical waveguide and / or the distance (Z2) of the lenses to each other a beam diameter of the light beam ( 10 ) or partial light rays ( 12a - 12c ) is adjusted. Method according to Claim 6, in which the diffractive optical element ( 5 ) between the input lens ( 2 ) and the exit lens ( 3 ) is arranged. Method according to one of the preceding claims, in the cohesive one Joints by soldering, welding or by photohardening an adhesive can be formed. Method according to one of the preceding claims, in which the connection points on contact pins ( 14a - 14c ) of at least one electronic or optoelectronic component ( 20 ) or at least one connector ( 30 ) are formed by melting a solder, in order to connect these with a carrier, in particular a printed circuit board ( 13 ), connect to. Device for connecting at least two elements ( 13 . 20 ), comprising: a holding device ( 15 ) for positioning the elements or the substrate; a light source ( 8th ), which has a light beam ( 10 ), in particular providing a laser light beam; and an imaging optics ( 1 . 5 ), which images the light beam in such a way and into a plurality of partial light beams ( 12a - 12c ) that they form a plurality of discrete spots of light which are a compound of the at least two elements ( 13 . 20 ) at a plurality of discrete, cohesive connection points ( 17a - 17e ) cause. Device according to Claim 10, in which the imaging optics comprise a diffractive optical element ( 5 ) comprising the light beam ( 10 ) is divided by light diffraction into the plurality of partial light rays. Apparatus according to claim 11, wherein the holding device ( 15 ) the Elements ( 13 . 20 ) is positioned in a predetermined arrangement and the diffractive optical element ( 5 ) the partial light beams ( 17a - 17c ) in correspondence with the predetermined arrangement and directed in different directions. Device according to Claim 12, in which the diffractive optical element ( 5 ) a plurality of diffractive optical zones ( 6a - 6c ) in correspondence with the predetermined arrangement of joints. Device according to Claim 13, in which the diffractive optical zones ( 6a - 6c ) a different intensity, beam cross-section, shape and / or divergence of the partial light beams ( 12a - 12c ) cause. Device according to one of claims 11 to 14, further comprising an optical waveguide ( 9 ), wherein the imaging optics an input lens ( 2 ) and an exit lens ( 3 ), such that by varying the distance (Z1) of the input lens to the optical waveguide and / or the distance (Z2) of the lenses ( 2 . 3 ) to each other a beam diameter of the light beam ( 10 ) or partial light rays ( 12a - 12c ) is adjusted. Device according to Claim 15, in which the diffractive optical element ( 5 ) between the input lens ( 2 ) and the exit lens ( 3 ) is arranged.