(19)
(11)EP 2 178 354 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
22.06.2011 Bulletin 2011/25

(21)Application number: 08166750.3

(22)Date of filing:  16.10.2008
(51)International Patent Classification (IPC): 
H05K 3/36(2006.01)

(54)

A method of connecting printed circuit boards and corresponding arrangement

Verfahren zum Anschluss von Leiterplatten und entsprechende Anordnung

Procédé de connexion de cartes de circuits imprimés et agencement correspondant


(84)Designated Contracting States:
DE FR GB IT

(43)Date of publication of application:
21.04.2010 Bulletin 2010/16

(73)Proprietors:
  • OSRAM Gesellschaft mit beschränkter Haftung
    81543 München (DE)
  • OSRAM S.P.A. - SOCIETA' RIUNITE OSRAM EDISON CLERICI
    20144 Milano (IT)
    Designated Contracting States:
    IT 

(72)Inventors:
  • Capeleto, Simone
    35131, Padova (IT)
  • Hacker, Christian
    30880, Laatzen (DE)

(74)Representative: Bosotti, Luciano 
Buzzi, Notaro & Antonielli d'Oulx Via Maria Vittoria, 18
10123 Torino
10123 Torino (IT)


(56)References cited: : 
US-A- 3 579 206
US-A1- 2002 189 862
US-B1- 6 867 668
US-A- 5 742 484
US-A1- 2007 040 626
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    Field of the invention



    [0001] This disclosure relates to connecting Printed Circuit Boards (briefly, PCBs).

    [0002] This disclosure was devised with specific attention paid to its possibly use in PCB mounting arrangements for lighting sources such as LED lighting sources.

    Description of the related art



    [0003] Electrical connection between different PCBs is a critical point in production.

    [0004] For instance, in the case of LED modules, the LED or LEDs (i.e. the light sources) and the related driver electronics are frequently mounted on different PCBs (oftentimes referred to as the LED-PCB and the DRIVER-PCB). This may be the result of e.g. the LED or LEDs being already mounted on a PCB of their own and/or the requirement of thermally insulating the driver electronics from the heat-source represented by the LED or LEDS. Also, the driver electronics may be bulky and the mounting space available in the vicinity of the LED or LEDs may not be sufficient.

    [0005] With such a configuration, connection between the two (or more) PCBs involved may be critical. In fact, automatically soldering wires between the PCBs may be far from easy, while mechanical connectors are usually bulky and may represent an undue additional cost. More generally, connection may be labour- and time-consuming and lends itself poorly to up-scaling in the presence of higher production volumes. More specifically, the invention relates to a method according to the preamble of claim 1, which is known e.g. from US-A-5 742 484.

    Object and summary of the invention



    [0006] In designing LED modules, use of LEDs already mounted on respective PCBs may sometimes be avoided (for instance, plastic packages or ceramic submounts may be preferred).

    [0007] Also, if using LEDs already mounted on a PCB of their own cannot be avoided, efforts may be made at optimizing the connection process of the LED-PCB to the driver-PCB.

    [0008] While in that way the critical nature of connection between PCBs may be somehow palliated, the need is still felt for improved solutions which may radically dispense with the disadvantages discussed previously.

    [0009] The object of the invention is to provide such a solution.

    [0010] According to the invention, that object is achieved by means of a method as set forth in claim 1 that follows. The invention also relates to a corresponding arrangement as called for in claim 11.

    [0011] The claims are an integral part of the disclosure of the arrangement described herein.

    Brief description of the annexed representations



    [0012] The invention will now be described, by way of example only, with reference to the annexed representations, wherein:
    • Figure 1 is an exploded perspective view of the parts involved in an arrangement as described herein, and
    • Figure 2 represents the operation of connecting the various parts shown in figure 1.

    Detailed description of embodiments



    [0013] In the following description, numerous specific details are given to provide a thorough understanding of embodiments. The embodiments can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the embodiments.

    [0014] Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

    [0015] The headings provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.

    [0016] In figure 1, reference 10 denotes a LED light source (including one or more LEDs) mounted on a printed circuit board (PCB) 12. The PCB 12 is intended to be connected with another PCB 14 carrying thereon driver electronics for the LED light source 10. The two PCBs 12 and 14 are provided with connection pads 12a, 14a to enable electrical connection therebetween.

    [0017] Unless otherwise detailed in the following, these parts and elements are conventional in the art, which makes it unnecessary to provide a more detailed description herein.

    [0018] Reference 16 denotes as whole a so-called "flex" PCB (namely, a flexible PCB o FCB) carrying respective connection lines as well as pads 16a to be soldered to the pads 12a, 14a of the PCBs 10 and 14 to ensure electrical connection therebetween.

    [0019] In the embodiment shown, the pads 12a, 14a of the PCBs 12 and 14 face "upwardly" while the connection pads 16b of the flex 16 face downwardly. The flex 16 can thus be arranged in a bridge-like arrangement above and across the PCBs 10 and 14 while bonding (e.g. soldering) of the pads 12a, respectively 14a with the pads 16a of the flex 16. This result can be achieved - in a known manner - by means of a hot bar HB which is temporally superposed to the flex 16 (or at least the ends thereof) to produce soldering of the pads 12a, 14a and 16a.

    [0020] For facilitating the soldering process, the pads 12a and 14a can be partially left uncovered by the flex allowing the direct contact between the hot bar HB and the metal pads.

    [0021] The bonding process can be also carried out by means of laser soldering techniques. In that case the pads 12a and 14a may be left partially uncovered in order to allow the laser beam to reach the soldering area.

    [0022] A "flex" is a well known component adapted for connecting electrical/electronic components expected to move mutually during operation (e.g. in hard disk drives) and/or components of apparatus whose mutual positions are changed during assembly of the apparatus.

    [0023] In the embodiment shown, connecting the PCBs 12, 14 via the flex involves a base plate 20.

    [0024] In the embodiment shown, the metal plate 20 includes three recessed areas 120, 140 and 160.

    [0025] These recesses can be easily produced when manufacturing the plate 20 and are intended to house:
    • the PCB 12 (recess 120),
    • the PCB 14 (recess 140); and
    • the "flex" 16 (recess 160).


    [0026] In the embodiment shown, the recesses 120, 140 and 160 are generally "shallow" recesses having thicknesses substantially equal to the "height" or "depth" of the element intended to be received therein.

    [0027] As a result of this (and as better appreciated in figure 2) the PCBs 12 and 14 may be arranged in the recesses 100, 140 and the flex 16 arranged in a bridge-like arrangement therebetween in such a way that the upper surface of the flex 16 lies at least approximately "flush" with the upper surface of the plate 20.

    [0028] In that way, when the hot bar HB or the soldering laser is applied, the flex 16 (or at least the ends of the flex 16) are very precisely positioned, with the pads 16a exactly facing and abutting against the pads 12a, 14a. The desired bonding action may be achieved in a rapid and reliable manner by minimising the amount of the heat energy applied.

    [0029] The arrangement described herein completely dispenses with the need of using wires and/or mechanical connectors and is ideally adapted for an automated soldering process. The fixed shape of the flex 16 derives from the layout design, related cut and mechanical properties while the flat bonding pads (12a, 14a, 16a) provide a wide contact surface thus facilitating an automated bonding process. The bonding process may be automated by resorting to simple machinery (essentially a metal base properly shaped and a movable hot bar or laser soldering head).

    [0030] The layout of the flex PCB 16 can be selected to match the relative expected positions of the two PCBs 12 and 14 in the final application. Exact positioning on the three components involved in the connection process (12, 14 and 16, in the drawings herein) permits the hot bar HB (or the laser soldering beam) to move in correspondence with the pads to be soldered and apply the thermal profile required for the bonding process. Manual work is completely dispensed with in the production of lighting modules since no manual soldering is being resorted to thus giving rise to a completely automated process. No additional components are introduced by rendering the production process a very fast one. Also, the arrangement described herein lends itself to a semi-automatic implementation in the case of small volumes to be produced.

    [0031] Of course, without prejudice to the underlying principles of the invention, the details and embodiments may vary, even significantly, with respect to what has been described and illustrated by way of example only, without departing from the scope of the invention as defined by the annexed claims. For instance, the method described in the foregoing can be extended to connecting more than two PCBs. Also, at least one of the PCBs involved may already include a flexible part providing the bridge-like function (i.e. the flex PCB).


    Claims

    1. A method of connecting a first (12) and a second (14) printed circuit board, the method including:

    - providing board connection pads (12a, 14a) on at least one of said first (12) and second (14) printed circuit boards,

    - arranging a flexible printed circuit board (16) in a bridge-like fashion between said first (12) and second (14) printed circuit boards, said flexible printed circuit board (16) having connection pads (16a) for bonding with said board connection pads (12a, 14a), and bonding (HB) the connection pads (16a) in said flexible printed circuit board (16) arranged in a bridge-like fashion between said first (12) and second (14) printed circuit board with said board connection pads(12a, 14a), whereby said first (12) and second (14) printed circuit board are connected,

    characterized in that the method includes the steps of providing a support structure (20) having recesses (120, 140) for arranging therein said first (10) and second (14) printed circuit boards at least during said step of bonding (HB).
     
    2. The method of Claim 1, wherein said first (12) and second (14) PCBs carry a LED lighting source (10) and the drive circuitry for said LED lighting source (10), respectively.
     
    3. The method of Claim 1, wherein said recesses (120, 140) have a depth such that said flex PCB (16) arranged in a bridge-like fashion between said first (12) and second (14) printed circuit board is flush to the outer surface of said support structure (20).
     
    4. The method of either of Claims 1 or 3, wherein said support structure is a support plate (20).
     
    5. The method of any of Claims 1, 3 or 4, wherein said support structure is a heat conductive structure (20).
     
    6. The method of any of the previous claims, including the step of arranging said first (10) and second (14) printed circuit boards with said board connection pads (12a, 14a) facing upwardly and arranging said flexible printed circuit board (16) with the respective connection pads (16a) facing downwardly against said board connection pads(12a, 14a).
     
    7. The method of any of the previous claims, wherein said bonding includes soldering said board connection pads (12a, 14a) with the connection pads(16) in said flexible printed circuit board (16).
     
    8. The method of any of the previous claims, wherein said bonding includes controlled application of heat (HB) and/or laser radiation to said boar connection pads (12a, 14a) and said connection pads(16) in said flexible printed circuit board (16).
     
    9. The method of any of the previous claims, including providing said board connection pads (12a, 14a) on each of said first (12) and second (14) printed circuit boards.
     
    10. The method of any of the previous claims, applied to connecting more than two printed circuit boards.
     
    11. An arrangement including:

    - a first (12) and a second (14) printed circuit board with board connection pads (12a, 14a) provided on at least one of said first (12) and second (14) printed circuit boards,

    - a flexible printed circuit board (16) arranged in a bridge-like fashion between said first (12) and second (14) printed circuit boards, said flexible printed circuit board (16) having connection pads (16a) bonded with said board connection pads (12a, 14a) to provide connection of said first (12) and second (14) printed circuit boards,

    the arrangement characterized in that it includes a support structure (20) having recesses (120, 140) with said first (10) and second (14) printed circuit boards arranged therein.
     
    12. The arrangement of Claim 11, wherein said support structure (20) is a heat conductive structure.
     
    13. The arrangement of any of Claims 11 to 12, wherein at least one of said first (12) and a second (14) printed circuit boards includes a flexible part providing said bridge-like function.
     


    Ansprüche

    1. Verfahren zum Verbinden einer ersten (12) und einer zweiten (14) Leiterplatte, wobei das Verfahren aufweist:

    Bereitstellen von Plattenverbindungsflächen (12a, 14a) auf mindestens einer der ersten (12) und der zweiten (14) Leiterplatte,

    Anordnen einer flexiblen Leiterplatte (16) in einer brückenartigen Weise zwischen der ersten (12) und der zweiten (14) Leiterplatte, wobei die flexible Leiterplatte (16) Verbindungsflächen (16a) aufweist zum Bonden mit den Plattenverbindungsflächen (12a, 14a), und

    Bonden (HB) der Verbindungsflächen (16a) auf der flexiblen Leiterplatte (16), die in einer brückenartigen Weise zwischen der ersten (12) und der zweiten (14) Leiterplatte mit den Verbindungsflächen (12a, 14a) angeordnet ist, wobei die erste (12) und die zweite (14) Leiterplatte verbunden werden,

    dadurch gekennzeichnet, dass das Verfahren die Schritte aufweist von Bereitstellen einer Stützstruktur (20), die Aussparungen (120, 140) aufweist zum darin Anordnen der ersten (10) und der zweiten (14) Leiterplatte zumindest während des Schritts des Bondens (HB).
     
    2. Verfahren nach Anspruch 1, wobei die erste (12) und die zweite (14) Leiterplatte eine LED-Lichtquelle (10) bzw. die Treiberschaltung für die LED-Lichtquelle (10) trägt.
     
    3. Verfahren nach Anspruch 1, wobei die Aussparungen (120, 140) eine Tiefe aufweisen, so dass die flexible Leiterplatte (16), die in einer brückenartigen Weise zwischen der ersten (12) und der zweiten (14) Leiterplatte angeordnet ist, bündig mit der äußeren Oberfläche der Stützstruktur (20) abschließt.
     
    4. Verfahren nach einem der Ansprüche 1 oder 3, wobei die Stützstruktur eine Trägerplatte (20) ist.
     
    5. Verfahren nach einem der Ansprüche 1, 3 oder 4, wobei die Stützstruktur eine wärmeleitende Struktur (20) ist.
     
    6. Verfahren nach einem der vorhergehenden Ansprüche, aufweisend den Schritt eines Anordnens der ersten (10) und der zweiten (14) Leiterplatte, so dass die Plattenverbindungsflächen (12a, 14a) nach oben zeigen, und eines Anordnens der flexiblen Leiterplatte (16), wobei die jeweiligen Kontaktflächen (16a) nach unten den Plattenverbindungsflächen (12a, 14a) zugewandt sind.
     
    7. Verfahren nach einem der vorhergehenden Ansprüche, wobei das Bonden ein Verlöten mit der Plattenverbindungsflächen (12a, 14a) mit den Verbindungsflächen (16) auf der flexiblen Leiterplatte (16) umfasst.
     
    8. Verfahren nach einem der vorhergehenden Ansprüche, wobei das Bonden eine gesteuerte Anwendung von Hitze (HB) und/oder Laserbestrahlung auf die Plattenverbindungsflächen (12a, 14a) und die Kontaktflächen (16) auf der flexiblen Leiterplatte (16) umfasst.
     
    9. Verfahren nach einem der vorhergehenden Ansprüche, aufweisend ein Bereitstellen der Plattenverbindungsflächen (12a, 14a) sowohl auf der ersten (12) und der zweiten (14) Leiterplatte.
     
    10. Verfahren nach einem der vorhergehenden Ansprüche, das angewandt wird um mehr als zwei Leiterplatten zu verbinden.
     
    11. Anordnung, aufweisend:

    eine erste (12) und eine zweite (14) Leiterplatte mit Plattenverbindungsflächen (12a, 14a), die auf mindestens einer der ersten (12) und der zweiten (14) Leiterplatte bereitgestellt werden,

    eine flexible Leiterplatte (16), die in einer brückenartigen Weise zwischen der ersten (12) und der zweiten (14) Leiterplatte angeordnet ist, wobei die flexible Leiterplatte (16) mit den Plattenverbindungsflächen (12a, 14a) gebondeten Kontaktflächen (16a) aufweist, um eine Verbindung der ersten (12) und der zweiten (14) Leiterplatte bereitzustellen,

    wobei die Anordnung dadurch gekennzeichnet ist, dass sie eine Stützstruktur (20) aufweist mit Aussparungen (120, 140), in denen die erste (10) und die zweite (14) Leiterplatte angeordnet sind.
     
    12. Anordnung nach Anspruch 11, wobei diese Stützstruktur (20) eine wärmeleitende Struktur ist.
     
    13. Anordnung nach einem der Ansprüche 11 bis 12, wobei mindestens eine der ersten (12) und einer zweiten (14) Leiterplatte einen flexiblen Teil aufweist, der diese brückenartige Funktion bereitstellt.
     


    Revendications

    1. Un procédé pour connecter une première (12) et une seconde (14) carte de circuit imprimé, le procédé comprenant :

    - l'obtention de plages de connexion de carte (12a, 14a) sur au moins l'une des première (12) et seconde (14) cartes de circuit imprimé,

    - la configuration d'une carte de circuit imprimé flexible (16) à la manière d'un pont entre lesdites première (12) et seconde (14) cartes de circuit imprimé, ladite carte de circuit imprimé flexible (16) possédant des plages de connexion (16a) pour une liaison avec lesdites plages de connexion de carte (12a, 14a),

    - la liaison (HB) des plages de connexion (16a) de ladite carte de circuit imprimé flexible (16) configurée à la manière d'un pont entre lesdites première (12) et seconde (14) cartes de circuit imprimé avec lesdites plages de connexion de carte (12a, 14a) de façon à connecter lesdites première (12) et seconde (14) cartes de circuit imprimé,

    caractérisé en ce que le procédé comprend les étapes d'obtention d'une structure support (20) possédant des évidements (120, 140) pour y configurer lesdites première (10) et seconde (14) cartes de circuit imprimé au moins durant ladite étape de liaison (HB).
     
    2. Le procédé de la revendication 1, dans lequel lesdites première (12) et seconde (14) cartes de circuit imprimé portent une source d'éclairage LED (10) et les circuits de pilotage pour ladite source d'éclairage LED (10), respectivement.
     
    3. Le procédé de la revendication 1, dans lequel lesdits évidements (120, 140) possèdent une profondeur telle que ladite carte de circuit imprimé flexible (16) configurée à la manière d'un pont entre lesdites première (12) et seconde (14) cartes de circuit imprimé arrive au ras de la surface extérieure de ladite structure support (20).
     
    4. Le procédé de l'une ou l'autre des revendications 1 ou 3, dans lequel ladite structure support est une plaque support (20).
     
    5. Le procédé de l'une des revendications 1, 3 ou 4, dans lequel ladite structure support est une structure conductrice de la chaleur (20).
     
    6. Le procédé de l'une des revendications précédentes, comprenant l'étape de configuration desdites première (10) et seconde (14) cartes de circuit imprimé avec les plages de connexion de carte (12a, 14a) tournées vers le haut, et de configuration de ladite carte de circuit imprimé flexible (16) avec les plages de connexion respectives (16a) tournées vers le bas contre lesdites plages de connexion de carte (12a, 14a).
     
    7. Le procédé de l'une des revendications précédentes, dans lequel ladite liaison comprend le soudage desdites plages de connexion de carte (12a, 14a) avec les plages de connexion (16) dans ladite carte de circuit imprimé flexible (16).
     
    8. Le procédé de l'une des revendications précédentes, dans lequel ledit collage comprend l'application contrôlée de chaleur (HB) et/ou de rayonnement laser sur lesdites plages de connexion de carte (12a, 14a) et lesdites plages de connexion (16) de ladite carte de circuit imprimé flexible (16).
     
    9. Le procédé de l'une des revendications précédentes, comprenant l'obtention desdites plages de connexion de carte (12a, 14a) sur chacune desdites première (12) et seconde (14) cartes de circuit imprimé.
     
    10. Le procédé de l'une des revendications précédentes, appliqué à la connexion de plus de deux cartes de circuit imprimé.
     
    11. Une configuration comprenant :

    - une première (12) et une seconde (14) carte de circuit imprimé avec des plages de connexion de carte (12a, 14a) formées sur au moins l'une desdites première (12) et une seconde (14) cartes de circuit imprimé,

    - une carte de circuit imprimé flexible (16) configurée à la manière d'un pont entre lesdites première (12) et seconde (14) cartes de circuit imprimé, ladite carte de circuit imprimé flexible (16) ayant des plages de connexion (16a) reliées auxdites plages de connexion de carte (12a, 14a) pour obtenir la connexion desdites première (12) et seconde (14) cartes de circuit imprimé,

    la configuration étant caractérisée en ce qu'elle comprend une structure support (20) possédant des évidements (120, 140) dans lesquels sont disposées lesdites première (10) et seconde (14) cartes de circuit imprimé.
     
    12. La configuration de la revendication 11, dans laquelle ladite structure support (20) est une structure conductrice de la chaleur.
     
    13. La configuration de l'une des revendications 11 à 12, dans laquelle au moins l'une desdites première (12) et seconde (14) cartes de circuit imprimé comprend une partie flexible formant ladite fonction à la manière d'un pont.
     




    Drawing








    Cited references

    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description