JP2007522664A - Circuit board and method for embedding optical components in a circuit board - Google Patents

Abstract

  The present invention relates to a circuit board in which an optically active component is at least partially embedded therein, and to a method of embedding an optically active component in a circuit board. A component that is at least partially embedded in the circuit board makes optically active contact with an optical signal in the circuit board such that the optically active area of the component is essentially perpendicular to the plane of the circuit board.

Description

  The invention relates to a method for embedding an optically active component in a circuit board according to the preamble of claim 1. The present invention also relates to a circuit board according to the preamble of claim 13.

  Prior art publications, such as US Patent Application Publication No. 2002/0141163, disclose a solution for embedding photoelectric components in a circuit board. In these solutions, mirrors are used to guide the optical signal along the optical bus to the component. The problem with these solutions is that the inversion of the optical signal is less efficient because it attenuates the light intensity. Typical losses can be around 50%.

In some prior art documents, the optical signal is guided along the optical bus without a mirror. For example, European Patent Publication No. 1376180 discloses embedding a light receiving / transmitting module in a circuit board so that the light receiving / transmitting module contacts an optical bus disposed between these modules. The light receiving / transmitting module is electrically connected to the wiring pattern. A corresponding solution is also disclosed in US Pat. No. 5,521,992. U.S. Pat. No. 6,477,286 discloses a solution in which components are embedded in a circuit board and attached to the base of the circuit board using solder balls. U.S. Pat. No. 4,732,446 discloses a solution for embedding a component carrier in a circuit board and connecting the circuit board between two other circuit boards.
US Patent Application Publication No. 2002/0141163 European Patent Publication No. 1376180 US Pat. No. 5,521,992 US Pat. No. 6,477,286 U.S. Pat. No. 4,732,446 US Patent Application Publication No. 2003/00000068 Finnish Patent Application No. 20031796

  The present invention seeks to create a new type of method for embedding optically active components in circuit boards.

  The present invention allows the optically active area of the component to be near the end of the optical bus, so that the surface of the optically active area is positioned essentially perpendicular to the plane of the circuit board and / or Based on the idea that components whose surface is optically active are partially or fully embedded in the circuit board.

  More particularly, the method according to the invention is characterized by what is presented in the characterizing part of claim 1.

  The structure according to the invention is then characterized by what is presented in the characterizing part of claim 13.

  In a structure according to a preferred embodiment of the present invention, there is an optically active region and a region or regions including a conductive material on the first side of the component. The optically active region is positioned near the end of the optical bus so that when the component is embedded, the optically active region of the component is essentially perpendicular to the plane of the circuit board. The optically active region can be, for example, a flat or curved surface that transmits or receives light. The active area can also be a surface composed of several subcomponents. The surface of the active region of the component that transmits or receives light and the surface of the subcomponent are preferably arranged at right angles to the plane of the circuit board. Thus, since the optical signal is directed straight at the surface of the active area of the component or from the surface of the optical bus, the signal need not be deflected. This avoids attenuation of the optical signal that occurs when the optical signal is reflected by the mirror.

  Electrical connection to the conductive layer of the circuit board can be made through the region of the component containing the conductive material. The conductive material can be, for example, on the same side of the component as the optically active region and on the opposite side or on an adjacent side.

  Significant advantages are obtained through the use of the present invention. In previous solutions, inversion of the optical signal away from the plane of the substrate results in a significant loss in signal strength. The loss due to inversion of the optical signal is generally about 50%. For example, if the optical path from the transmitter to the receiver includes two optical inversions, 75% of the signal strength will be lost only due to loss due to signal inversion.

  The present invention has many preferred embodiments. By using the present invention, it is possible to efficiently embed electro-optic components such as detectors and light emitting components. Active optical components, particularly those components that transmit or detect light from the top surface, are preferably embedded on the top and / or surface of the circuit board. Such components comprise both an optically active region and at least one conductive region on one side. Such components are considerably less expensive to manufacture than optical components that emit or detect light from the side, requiring special techniques for manufacturing.

  In the following, the invention will be examined in great detail using application examples and with reference to the accompanying drawings. The application is in no way intended to limit the scope of protection defined by the claims.

  In the context of the present invention, the term “circuit board” refers to a multilayer circuit board in which there are generally at least two conductor layers or conductive signal layers that are patterned. Patterning refers to the shape of a conductor pattern in which conductor layers are not uniform and are in the form of conductors that are electrically insulated from each other. The conductor consists of some conductive material, generally a metal, usually copper. The conductor layers are separated from each other by an insulating layer. At least one of the conductor layer or the insulating layer of the circuit board includes an optical bus.

  The term “optical bus” refers to a channel along which an optical signal can be directed to or derived from a component. The optical bus can be filled with a suitable material to form a path for light. Suitable materials for filling are, for example, various polymers or glass-like materials.

  The structure of the optical bus is disclosed in, for example, US Patent Application Publication No. 2003/006068.

  The circuit board structure in which the optoelectronic component is at least partially embedded is preferably such that only the insulating material is in the location where the component is embedded. Thus, the recesses can be made using laser drilling or other similar drilling methods to the desired embedding depth ending with the metal layer at the component embedding location. For example, it is possible to use several methods in which the initial recess is first made by machining and then finished by laser drilling.

  The recess for the component is made so that it traverses the optical bus in the circuit board. The term traversing means that a common interface is formed between the recess and the optical bus, and a signal traveling along the optical bus moves from the optical bus through the interface to the recess or correspondingly an optical signal. Means moving from the recess and proceeding along the optical bus. In this document, such an interface is referred to as a transverse surface. The transverse surface preferably completely interrupts the optical bus and is preferably essentially perpendicular to the direction of movement along the optical bus. Advantageously, the transverse surface essentially corresponds to the cross section of the optical bus at the end of the optical bus. The actual crossing surface can be manufactured using any suitable method, but with respect to the manufacturing technique, when creating the crossing surface, the material of the optical bus is removed at the end of the bus. It is easiest to produce a transverse surface. In some embodiments, the removal of material is performed in connection with the creation of the recess.

  When the component is embedded in the recess, the void remaining around the component is partially or completely filled using any suitable insulating material. The recess between the optically active area of the component and the end of the optical bus is filled with a transparent insulating material, preferably the same material that the optical bus contains. Other directional cavities around the component can be partially or fully filled with the same or some other insulating material. For circuit board manufacture, the manufacture is easier if the insulating material is the same transparent material as the optical bus. In some embodiments, at least a portion of the recess can be left unfilled.

  The component is placed in the recess so that the optically active area of the component is near the cross-surface of the optical bus. In this case, the concept “near” is intended to include the special case where the transverse surface of the optical bus contacts the optically active area of the component. In operation, the concept of “near” is sufficient for signals traveling along the optical bus, from the optical bus to the transverse surface, and through the possible medium to the active area of the component, and vice versa. Refers to the distance and position that allows to be moved. In practical embodiments, the distance between the surface of the optically active region and the transverse surface of the optical bus is generally in the range of 0-2 millimeters, preferably in the range of 100-500 micrometers.

  The component can include a conductive material on one or more sides of the component to form an electrical contact. The components can be electrically connected to conductor layers at different heights in the circuit board. For example, a connection can be made to the conductor layer on the first surface of the circuit board and the conductor layer on the second surface of the circuit board. In this case, the first surface of the circuit board refers to the component-embedded side, and the second surface refers to the opposite surface of the circuit board. The components can of course be connected to one or more conductor layers inside the circuit board in addition to or instead of the conductor layers on the surface of the circuit board.

  The connection to the conductor layer on the first surface of the circuit board is such that the recess between the component and the circuit board is not completely filled with an insulating material, but instead the upper part is filled with a conductive material and configured therethrough This can be done so that the conductive material of the component can be connected to the conductive layer on the surface of the circuit board. Alternatively, the insulating material can be removed from the recess between the component embedding location and the circuit board and replaced with a conductive material. The conductive material preferably does not extend to a point on the optical bus where it may interfere with the movement of the optical signal. If necessary, the conductive material can be fully extended to the bottom of the recess if the conductive material does not interfere with the progress of the optical signal.

  The conductive material of the component can be connected to the conductor layer on the first surface of the circuit board through several connections, or some of the connections are made to the conductor layers on the first surface of the circuit board, Such a connection can be made to the conductor layer on the second surface of the circuit board. In the manufacturing stage of the circuit board, a continuous or discontinuous metal layer can be left at the embedded depth under the component, and the metal layer is preferably made of the same material as the conductor layer at the same height. The component can be attached to this metal layer using a conductive adhesive, solder, or conductive polymer when other connections are made by the lower surface of the component. The metal layer under the component can then be connected to a conductor layer disposed on the lower surface of the circuit board using any suitable feed-through method, such as a micro via method. Alternatively, if all of the connections are made on the top side of the component, the component can be attached to the metal layer using an insulating adhesive. According to a preferred embodiment, an optical component with an active top surface, disposed on the side of the circuit board, is connected to the underlying metal layer using a conductive adhesive.

  Some of the connections or connections are made to a conductor layer placed on or in the surface of the circuit board using, for example, bonding (eg, wire bonding using gold or aluminum wires or conductive adhesive) You can also.

  A “component” is generally an optoelectronic component, such as a detector or a light emitting component. Thus, the components can be equally suitable for transmission as well as reception. The component is preferably an optical component that is active on the top and / or surface, particularly a component that emits or detects light from the top surface. The component that emits or detects light from the top surface is preferably a component that has a conductive material on the same side, ie, an electrical contact such as an anode contact, as well as an optically active region. An electrical contact, such as a second region containing a conductive material, ie a cathode contact, can be located on the same side of the component as the optically active region, or on the opposite side of the component. When the component is set in place on the side of the circuit board, the surface of the optically active area and also the electrical anode and cathode contacts (pads) are placed perpendicular to the surface of the circuit board. Examples of active optical components are photodiodes, photo lasers, and LEDs.

  The components can be partially or fully embedded in the circuit board and can be attached to either side of the circuit board.

  The term “active region” of an optical component refers to the surface of the optical component that transmits and / or receives light to achieve a desired function. The active region of a semiconductor component can, for example, convert electrical energy into light energy and vice versa. Also, the received light emits charge carriers, for example, into the active region, which can change the conductivity of the component. The term active region also refers to the surface of a component made up of several subcomponents that transmit or receive light. Optical transmitting or receiving semiconductors such as semiconductor lasers, LEDs or photodiodes have, for example, the function of the active region.

  The number of conductor layers that can be used depends on the application. At least one of the semiconductor layers corresponds to 0, ie, a ground reference plane, which can be grounded or connected to some other zero potential, eg, a circuit zero potential.

  If necessary, the component can be protected from the top of the component, i.e. from the embedded side of the component, for example using a conductive sticker.

  There can also be a layer around the embedded component that protects against electromagnetic radiation coming from the direction of the circuit board, ie a so-called EMI shield. A preferred structure is disclosed, for example, in the unpublished Finnish patent application 20031796. To construct the EMI shield, a recess is made around the embedding location of a circuit board component, the recess is flattened or filled with a conductive material, and the flattened or filled recess is a component. The bezel protects the component from electromagnetic radiation coming from at least the lateral direction of the circuit board. The insulating layer that insulates the component and the bezel from each other is preferably left between the formed bezel and the embedded opening for the component. In the present case, the shielding bezel must not be continuous. That is, an opening should instead be left at the location of the optical bus. Further, the material in the opening should be transparent so that optical signals can travel from the optical bus through the material to the component or from the component to the optical bus. The term “transparent” is relative to the wavelength used, that is, a transparent material should be understood to easily pass the wavelength used but is opaque to other wavelengths. Thus, for application, a transparent material can, for example, pass light of infrared wavelengths but not visible wavelengths to the human eye.

  Possible materials for the optical bus are, for example, siloxane polymers, acrylates, polyimides, olefins, SU-8, sol-gels, ORMOCER (Organically Modified Ceramics), PMGITM, and Ultem.

  The insulating material between the conductive layers of the circuit board can be plastic, epoxy, or some similar material. An insulating material is a material that does not act as an electrical transmission path. The insulating material can be selected, for example, from the following groups: various resins, epoxy glass, polyimide (eg, Dupont KAPTON ™), polyimide-quartz, polyester, acrylic, bismaleimide, triatosine, Glass fiber, cyanate ester glass, XPC (paper phenol), FR-1 (paper material containing phenol resin binder), FR-2 (paper material containing phenol resin binder UL94-V0), FR-3 (epoxy resin) Paper material), FR-4 (glass fiber epoxy laminate), CEM (composite epoxy material), CEM-1 (paper laminate, in which there is one layer of glass fiber fabric (7628)), CEM- 3 (glass epoxy), aromatic polyamide (aramid fiber, eg Du ont's Kevlar (TM) (Kevlar), epoxy - Kevlar or Nobel's Twaron (registered trademark) (Twaron), PTFE (Teflon)), benzocyclobutene, microfiber laminates, Bakelite.

  Special substrates can generally be aluminum, LTCC (low temperature cofired ceramics), HTCC (high temperature cofired ceramics), glass, quartz / silicon dioxide, AlN, SiC, silicon, BeO, and BN.

  Plastics used as insulating materials in circuit boards include, but are not limited to: polyethene, polypropene, polybutene, polymethylpentene, polyamide, polyimide, polysulfone, polyetheretherketone (eg, Denso and Mitsubishi Plastics) PALAP ™, developed by the company, polyvinyl chloride, styrene plastic, cellulose plastic, polymethyl methacrylate (PMMA), polyacrylonitrile, polycarbonate, polyethene terephthalate, and fluoroplastics.

  Conductive polymers and adhesives can be classified into thermosetting polymers and thermoplastic polymers. In order to increase the conductivity, fillers such as silver, gold, or nickel can be used.

  The conductive polymer is, for example, polyacetylene, polythiophene, polypyrrole, poly (p-phenylene vinylene, polyaniline, poly / 2,3-ethyldioxytophene).

  Conductive adhesives usually consist of three main components: a conductive filler, a polymer such as epoxy, modified epoxy, or silicone, and an additive / agent that provides, for example, antistatic properties. Curing / drying is done using UV light or heat depending on the adhesive used. Some adhesives may already be dry at room temperature.

Commercial (one-component or two-component) isotropic conductive adhesives include the following (trade names, trademarks).
Emerson & Cumming Ablebond 976-1, flexible, conductive adhesive, filler silver
Ablebond 84-ILMI NB, conductive epoxy adhesive, filler silver Eccobond 57 C, conductive epoxy adhesive, filler silver Eccobond 50298, two components, conductive epoxy adhesive, filler silver AMICON C 850-6, epoxy adhesive, Filler silver AMICON CE 8500, conductive, modified epoxy adhesive, filler silver

Northrop Grumman SE-SECURE 9502, conductive adhesive, filler silver

Loctite Product 3880, conductive epoxy adhesive, filler silver (especially for EMI component mounting)
Product 3888, epoxy adhesive, filler silver Product 5420, conductive silicone Product 5421 RTV, silicone (with EMI / RFI shielding)

Dow Corning DA 6524, Conductive Silicone Adhesive DA 6533, Conductive and Thermal Conductive Silicone Adhesives Pancol-Elosol Elecolit 312 LV, Solventless Epoxy Adhesive, Filler Silver Elecolit 323, Conductive Epoxy Adhesive, Filler Silver Elecolit 342, conductive acrylate adhesive, filler silver Elecolit X-160378, conductive epoxy adhesive, filler silver

Commercial (one-component or two-component) anisotropic conductive adhesives include the following (trade names and trademarks).
Loctite Product 3441, epoxy adhesive, gold-surfaced polymer
Product 3446, epoxy adhesive, fusible filler Product 3440, gold polymer filler Product 3445, fusible solder filler

Telehus AcpMat series, epoxy adhesive resin paste containing conductive filler and other special fillers

  FIG. 1 shows a cross section of one basic structure of a circuit board. For the production of circuit boards, alternating conductive layers 1 and insulating layers 2 are constructed on the circuit board. In addition, the optical bus extends through the circuit board, along which optical signals can be transmitted to or from the component. In the circuit board of this example, there are at least two conductor layers: one conductor layer above the bus and one conductor layer below the bus. Generally, there are two to four conductor layers above or below the light layer. The optical layer can be disposed not only at the conductor layer but also at the insulating layer. Furthermore, one of the conductive layers can correspond to a ground reference level, ie, zero level.

  In order to make it easier to embed components in the circuit board during the circuit board manufacturing stage, at least one side, i.e. the side facing the component embedding location, is separated from the conductive layer and thus only the insulating material A region to be included is configured at a component embedding location. In the embodiment shown in FIG. 1, the opening is left in the conductor layer 1 at the embedding depth of the component embedding location. In the manufacturing stage of the circuit board, a continuous or discontinuous metal layer 5 made of a material of the conductor layer 1 at the same height, for example copper, can be left in this opening. The insulating material 2 is left in the opening.

  If it is desired to make the component in electrical contact with the conductor layer 1 below the component embedding location, prior to the production of the metal layer 5, using any suitable feed-through method, for example a micro via method It is optimal to fabricate the feed-through 6 through the insulating layer 2 at the component embedding location to the underlying conductor layer. The feed-through 6 is made of some conductive material such as metal.

  FIG. 2 shows a cross section of a recess 4 drilled in the circuit board of FIG. A recess 4 extending to a conductor layer located at the embedding depth below the component embedding location is drilled into the circuit board at the component embedding location by selective laser drilling or similar methods. The conductor layer is preferably under the entire area where drilling is performed to facilitate control of the depth of drilling. It is preferred that the conductor layer 1 is not in the excavation area, so that depth control can be performed using a metal conductor layer. For example, selective laser drilling does not erode the metal, but erodes only the insulating layer, so that the excavation stops when the conductor layer 1 is reached.

  FIG. 3 shows a cross section of the component 8 embedded in a predetermined location on the side of the circuit board of FIGS. In the embodiment of FIG. 3, there are conductive materials 10 and 12 on two separate sides of the component so that the component is a conductive layer located at different heights within the circuit board, eg, the first of the circuit board. The conductor layer 1 located on the surface and the conductor layer 1 located on the second surface can be connected. One side of the component includes an optically active region 11. The component is embedded in place so that the surface of the optically active region is essentially perpendicular to the direction of movement of the optical signal and thus also to the plane of the circuit board. In the embodiment of FIG. 3, the optically active region 11 and the region 12 containing the conductive material are on the same side of the component, and the second region containing the conductive material 10 is on the opposite side. One of the regions of conductive material may be on a side surface adjacent to the optically active region.

  The component 8 is attached to the contact base using, for example, an isotropic or anisotropic conductive adhesive 7, or by soldering or using a conductive polymer with a sufficiently high conductivity. It is done. In the embodiment of FIG. 3, the component is attached to the metal layer 5 using a conductive adhesive 7. Electrical connection to the conductive conductor layer 1 located below the component 8 can be made using any feed-through method through the insulating layer 2, for example the micro-via method (micro-via 5). The conductor layer 1 under the component 8 can only be constructed after an electrical connection has been made through the insulating layer 2 under the embedding location of the component 8. Alternatively, the conductor layer 1 below the location where the component 8 is embedded can be prepared and connected accordingly.

  If all connections are made from above the component using conductive adhesive, wire bonding, or some other suitable method, the component can also be attached to the base using non-conductive adhesive it can.

  FIG. 4 shows a cross section of the component 8 embedded in place on the circuit board of FIGS. 1 and 2. After embedding of the component 8, the recess 4 remaining around the component is partially or completely filled with any suitable insulating material 9. An essential factor is that the insulating material fills at least the region between the optically active region 11 of the component and the optical bus, and at least in this respect the insulating material is transparent. The insulating material 9 is preferably the same material as the material of the optical bus 3. The insulating material 9 on the other side surface of the component 8 is also the same material and is preferably the insulating material of the optical bus 3.

  FIG. 5 is embedded in place on the circuit board of FIGS. 1 and 2 and is applied to conductor layers at different heights of the circuit board, for example to the conductor layer 1 on the first surface of the circuit board, or to the second A cross section of the component 8 connected to the conductor layer on the side or to both is shown. Conductive material on the first surface of the component such that a pit filled with a conductive material 13 such as a conductive adhesive or polymer is formed in the upper part of the recess 4 between the component 8 and the circuit board Layer 12 can be connected to conductor layer 1 on the first surface of the circuit board. If the recess 4 between the component 8 and the circuit board is completely filled with an insulating material, the insulating material should be removed and replaced with a conductive material 13. Alternatively, the recess 4 is filled to a little above the optical bus 3, and the upper part of the recess is filled with a conductive material. The electrical contact is made by the region of the conductive material 13 in the upper part of the recess 3 between the component and the circuit board, and the conductive material layer 12 on the first side of the component and the first surface of the circuit board. Between the conductive layer 1 and the conductive layer 1.

  Electrical connection can also be made to the conductor layer 1 disposed on the second surface of the circuit board through the conductive material 10 disposed on the second side of the component. Electrical contact is made from the conductive adhesive 7, solder, or polymer at the mounting point of the component, through the metal layer 5 placed below the component embedding location, and below the component by the micro via 6 Up to the disposed conductor layer 1 can be formed.

  Alternatively, the connection, or part of the connection, is made using bonding (for example, wire bonding using gold wire or aluminum wire) to the conductor layer disposed on the first or second surface of the circuit board.

  If necessary, the component can be protected from above the component, i.e. from the opposite side of the mounting point of the component, for example using a conductive sticker.

1 is a cross-sectional view of one circuit board according to the present invention with feed throughs for components. FIG. It is sectional drawing of the recessed part drilled in the circuit board. It is sectional drawing of the component attached to the predetermined place of a recessed part. It is sectional drawing of what filled the recessed part which remains around a component. It is sectional drawing of what connected the component to the conductor layer of a circuit board.

Claims (17)

A method of at least partially embedding a component (8) in a circuit board, said component comprising an optically active region (11), said circuit board comprising alternating conductor layers (1) and insulating layers (2) As well as at least one optical bus (3),
A recess (4) is formed at a location where the component (8) is embedded so that the recess crosses the optical bus (3);
The component comprising both the optically active region (11) and at least one conductive region (10, 12) on one side is such that the optically active region (11) of the component is a transverse surface of the optical bus. Approaching and being set in place so that the surface of the optically active region is essentially perpendicular to the plane of the circuit board.   The method according to claim 1, wherein when forming the recess (4), only one substance or a plurality of substances that do not function as an electrical transmission path (1) are removed from the circuit board.   A transparent insulating material (9) remains around the component after embedding so that the insulating material fills the space between the optically active region and the transverse surface of the optical bus. 3. A method according to claim 1 or 2, characterized in that   Method according to claim 3, characterized in that the recess (4) remaining around the component after embedding is completely filled with insulating material (9).   The method according to claim 3 or 4, characterized in that pits are left or formed in the upper part of the recess (4) and are filled with a conductive material (13).   6. The method according to claim 5, wherein the conductive material (13) filling the recess is a conductive polymer, a conductive adhesive, or a metal.   The side surface of the component facing the optical bus comprises an optically active region (11) and one region or a plurality of regions (10, 12) of conductive material. The method according to item.   The one or more regions (10, 12) of conductive material are electrically connected to the conductor layer (1) disposed on the surface of the circuit board on the embedded side of the component The method according to claim 5, wherein the method is connected.   9. A method according to any one of the preceding claims, wherein the side surface of the component facing away from the optical bus or an adjacent side surface comprises a region of conductive material (10).   The region (10) of the component of conductive material is electrically connected to the conductor layer (1) disposed on the surface of the circuit board under the component embedding location. Item 10. The method according to Item 9.   11. A method according to any one of the preceding claims, wherein the component is attached to a metal layer (5) under the component using a conductive adhesive.   12. A method according to any one of the preceding claims, characterized in that the top surface of the component (8) is a light emitting or receiving optical component. An optical component (8);
A circuit board comprising an optical bus (3) capable of guiding an optical signal to or from the component;
The component (8) is at least partially embedded in the circuit board so that the component is in optical contact with the optical bus, the optically active region (11) and at least one conductive region on one side The component (8) including both (10, 12) is set in place so that the optically active region (11) of the component is essentially perpendicular to the plane of the circuit board. A circuit board characterized by being made.   The component (8) is embedded in the circuit board such that the component is completely disposed between the first surface and the second surface of the circuit board. The circuit board according to claim 13.   14. The space between the optically active region (11) of the component (8) and the optical bus (3) is filled with the same material as the optical bus (3). Or the circuit board according to 14.   The component (8) includes a first conductor material region (12) and a second conductor material region (10), from the first conductor material region (12) to the first conductor layer of the circuit board. (1) together with the second conductor layer (1) of the circuit board, wherein an electrical contact is formed and is at a different height from the second conductor material region (10) in the thickness direction of the circuit board. The circuit board according to claim 15, wherein an electrical contact portion is formed.   The circuit board according to claim 1, wherein the upper surface of the component is a light emitting or receiving optical component.

Images