Patent Publication Number: US-2003223131-A1

Title: Optical subassembly (OSA) having a multifunctional acrylate resin adhesive for optoelectronic modules, and method of making same

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
     [0001] This patent application is related to copending application Ser. No. 09/915,884 (docket no. ROC920010031 US 1), filed Jul. 26, 2001, entitled “OPTICAL SUBASSEMBLY (OSA) FOR OPTOELECTRONIC MODULES, AND METHOD OF MAKING SAME”, which is assigned to the assignee of the instant application. 
    
    
     
       FIELD OF THE INVENTION  
       [0002] The present invention relates in general to optoelectronic modules. More particularly, the present invention relates to an optical subassembly (OSA) having a multifunctional acrylate resin adhesive, and a method of making the same.  
       BACKGROUND  
       [0003] The development of the EDVAC computer system of 1948 is often cited as the beginning of the computer era. Since that time, computer systems have evolved into extremely sophisticated devices, and computer systems may be found in many different environments. Since the dawn of the computer age, cables have been used to transfer data between computers and input/output devices, and between computers. For example, cables are used in input/output (I/O) device attachment applications, such as disk drive, tape storage and printer attachment. Cables are also used in networking applications, such as local-area networks (LANs) and wide-area networks (WANs). An important trend in the past ten years has been the increasing use of fiber optic cables in such applications.  
       [0004] Fiber optic cables typically include a connector at each end that is plugged into a receptacle associated with the computer or I/O device. Typically the receptacle is part of an optoelectronic module that is electrically connected to the computer or I/O device. For example, the optoelectronic module may be connected to an electronic circuit board of the computer or I/O device using a fixed connection, e.g., a pin-through-hole arrangement, or a removable connection, e.g., a hot-pluggable contact pad mechanism. The optoelectronic module may receive optical signals from a fiber optic cable plugged into its receptacle and/or may transmit optical signals to a fiber optic cable plugged into the receptacle. An optoelectronic module that both transmits and receives optical signals is often referred to as an optoelectronic transceiver module.  
       [0005] An optoelectronic transceiver module typically receives optical signals from the fiber optic cable, converts the optical signals to electrical signals, and provides the electrical signals to the electronic circuit board of the computer or I/O device. Likewise, an optoelectronic transceiver module typically receives electrical signals from the electronic circuit board of the computer or I/O device, converts the electrical signals to optical signals, and provides the optical signals to the fiber optic cable. The optoelectronic transceiver module typically receives optical signals from the fiber optic cable using a receiver optical subassembly (ROSA) and provides the optical signals to the fiber optic cable using a transmitter optical subassembly (TOSA).  
       [0006] A ROSA typically includes a lens that receives the optical signals from the fiber optic cable and focuses the optical signals on an optoelectronic device provided with a receiver unit, e.g., a photoelectric receiver chip, that converts the fiber optic signals to electrical signals. Similarly, a TOSA typically includes an optoelectronic device provided with a transmitter unit, e.g., an edge-emitting laser (CD) or a surface-emitting laser (VCSEL), that converts electrical signals to optical signals that are directed onto a lens that directs the optical signals to the fiber optic cable.  
       [0007] Adhesives presently utilized for alignment of optical components (e.g., a lens, a laser and/or a photoelectric receiver chip) suffer from high coefficients of thermal expansion (CTE) and/or inadequate clarity. Alignment of optical components is typically accomplished at room temperature regardless of the continuous use temperature of the optical assembly. Because the CTE of optically clear adhesives often exceeds 100 ppm/° C., coupled with the fact that the optical assembly may operate at temperatures approaching 70° C., the adhesive will often expand significantly at operating temperature (as compared to its size when aligned at room temperature). This expansion can result in misalignment of the optical components (e.g., the lens relative to either the laser or the photoelectric receiver chip). In addition, this expansion can result in stress at the bond line (e.g., at an adhesive interface interposed between the lens and either the laser or the photoelectric receiver chip).  
       [0008] Unfilled adhesives, which provide the necessary clarity, typically possess CTE values well in excess of the maximum that can be tolerated to maintain alignment. For example, Norland NOA61 (available from Norland Products Inc., Cranbury, N.J.), possesses a CTE of 220 ppm/° C. at a typical operating temperature of an optical assembly. In addition to causing thermally-induced stress at the bond line, such a high CTE can result in approximately 2 microns of vertical offset at the operating temperature of 70° C., while often less than 0.5 micron of vertical offset can be tolerated. Clearly such high CTE adhesives are not acceptable.  
       [0009] One common method of providing adequate CTE control is to load adhesives with an inorganic filler. The most commonly employed fillers are fused silica and quartz. Commercially available adhesives rely on an inorganic filler to achieve low CTE. An illustrative commercially available mineral filled adhesive is Optocast 3408 (available from Electronic Materials Inc., Breckenridge, Colo.) which has a CTE of 40.6 ppm/° C. at a typical operating temperature of an optical assembly. Unfortunately, the use of inorganic fillers results in opaque adhesives. For numerous precision alignment applications (e.g., when aligning a ball lens relative to an optical bench), the adhesive must be transparent in order to ensure proper dispense volume. Also, for applications where the adhesive serves as an interface between the lens and either the laser or the photoelectric receiver chip, the adhesive must be transparent to ensure proper light transmission. In such applications, inorganic fillers render the adhesive unacceptable. In addition, the use of inorganic fillers can adversely result in high viscosity and reduced photospeed (i.e., a measure of the rate at which a photocurable adhesive cures).  
       [0010] Therefore, there exists a need to provide an enhanced optical subassembly (OSA), and a method of making the same.  
       SUMMARY OF THE INVENTION  
       [0011] An object of the present invention is to provide an enhanced optical subassembly (OSA), and method of making the same, that addresses these and other problems associated with the prior art.  
       [0012] These and other objects of the present invention are achieved by providing an enhanced optical subassembly, and a method of making the same, that includes a multifunctional acrylate resin adhesive to adhere a lens and/or an optoelectronic device, e.g., having a laser or a photoelectric receiver chip. An adhesive composition including a multifunctional acrylate resin cures to form an adhesive having a tightly cross-linked network of low CTE (coefficient of thermal expansion). The adhesive&#39;s low CTE can improve (as compared to conventional, optically clear adhesives) the vertical offset, for example, of the lens relative to the optoelectronic device at the operating temperature of the subassembly. For example, an adhesive composition including a multifunctional acrylate resin (e.g., a di-, tri-, tetra-, pentafunctional acrylate resin, or a mixture thereof) may be applied to a ball lens and/or a recess of a silicon optical bench, which are then joined and the adhesive composition cured. The adhesive composition may be cured by exposure to UV radiation and/or heat, for example.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0013] The present invention together with the above and other objects and advantages can best be understood from the following detailed description of the embodiments of the invention illustrated in the drawings, wherein like reference numerals denote like elements.  
     [0014]FIG. 1 is a block diagram of a networked computer system consistent with the present invention.  
     [0015]FIG. 2 is an exploded perspective view of an optoelectronic transceiver module having a pair of optical subassemblies (OSAs) consistent with the present invention.  
     [0016]FIG. 3 is an exploded perspective enlarged view of one of the optical subassemblies (OSAs) of the optoelectronic transceiver module shown in FIG. 2. The OSA is shown in FIG. 3 prior to application of a multifunctional acrylate resin adhesive interface according to an embodiment of the present invention shown in FIG. 4.  
     [0017]FIG. 4 is a cross-sectional view of an optical subassembly (OSA) that includes a multifunctional acrylate resin adhesive interface according to an embodiment of the present invention.  
     [0018]FIG. 5 is a side elevational view of an optical subassembly (OSA) that includes multifunctional acrylate resin adhesive contact points according to another embodiment of the present invention.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     Hardware Environment  
     [0019]FIG. 1 illustrates a computer system  10  that is consistent with the invention. Computer system  10  is illustrated as a networked computer system. Computer system  10  includes one or more client computers  12 ,  14  and  16  (e.g., desktop or PC-based computers, workstations, etc.) coupled to server computer  18  (e.g., a PC-based server, a minicomputer, a midrange computer, a mainframe computer, etc.) through a network  20 . The server computer  18  may comprise a plurality of enclosures as an alternative to the single enclosure illustrated in FIG. 1. Network  20  may represent practically any type of networked interconnection. For example, network  20  may be a local-area network (LAN), a wide-area network (WAN), a wireless network, and a public network (e.g., the Internet). Moreover, any number of computers and other devices may be networked through the network  20 , e.g., multiple servers. In one application of the present invention, server computer  18  and one or more of client computers  12 ,  14  and  16  may each include an optoelectronic module (shown in FIG. 2) having an optical subassembly provided with a multifunctional acrylate resin adhesive according to the present invention and a receptacle into which may be plugged an optic fiber cable to form network  20  or a portion thereof. For example, the optoelectronic module may be connected to an electronic circuit board of a networking adapter of the computer using a conventional fixed connection, e.g., a pin-through-hole arrangement, or a conventional removable connection, e.g., a hot-pluggable contact pad mechanism.  
     [0020] Client computer  16 , which may be similar to client computers  12  and  14 , may include a central processing unit (CPU)  22 ; a number of peripheral components such as a computer display  24 ; a storage device  26 ; and various input devices (e.g., a mouse  28  and a keyboard  30 ), among others. Server computer  18  may be similarly configured, albeit typically with greater processing performance and storage capacity, as is well known in the art. In another application of the present invention, input/output devices (e.g., disk drives, tape drives and printers) and client computer  16  (or server computer  18 ) may each include an optoelectronic module (shown in FIG. 2) having an optical subassembly provided with a multifunctional acrylate resin adhesive according to the present invention and a receptacle into which may be plugged an optic fiber cable that forms an interconnection (or a portion thereof) between the input/output devices and client computer  16  (or server computer  18 ). For example, the optoelectronic module may be connected to an electronic circuit board of an I/O adapter of the computer using a conventional fixed connection, e.g., a pin-through-hole arrangement, or a conventional removable connection, e.g., a hot-pluggable contact pad mechanism.  
     [0021] In yet another application of the present invention, various other electronic components of client computer  16  (or server computer  18 ) may each include an optoelectronic module (shown in FIG. 2) having an optical subassembly provided with a multifunctional acrylate resin adhesive according to the present invention and a receptacle into which may be plugged an optic fiber cable that forms an interconnection (or a portion thereof) between the electronic components within a single computer enclosure and/or between a plurality of enclosures of the computer. For example, the optoelectronic module may be connected to an electronic circuit board of each of such electronic components of the computer using a conventional fixed connection, e.g., a pin-through-hole arrangement, or a conventional removable connection, e.g., a hot-pluggable contact pad mechanism.  
     [0022] Although shown and described above in the environment of a computer, the present invention is not limited thereto. In general, the optical subassembly of the present invention may be used in any electrical devices or components that utilize a fiber optic cable interconnection, for example.  
     [0023]FIG. 2 is an exploded perspective view of an optoelectronic transceiver module  200  having a pair of optical subassemblies (OSAs)  202  consistent with the present invention. The pair of OSAs includes a receiver optical subassembly (ROSA)  202 R and a transmitter optical subassembly (TOSA)  202 T. It should be appreciated, however, that the present invention is not limited to the use of a pair of OSAs. Any number of OSAs may be used. Moreover, the present invention is not limited to use in the context of an optical transceiver module. For example, the present invention may be employed with respect to an optoelectronic receiver module or a optoelectronic transmitter module.  
     [0024] Optoelectronic transceiver module  200  includes a pair of receptacles  204 , each of which is associated with one of OSAs  202  and into which may be plugged a connector (not shown) of a fiber optic cable (not shown). The OSAs  202  and receptacles  204  shown in FIG. 2 are based on the LC optical connector. The OSAs  202  each include a projection  206  that extends into one receptacle  204  and has an optical fiber bore  208  for receiving a ferrule of a fiber optic cable connector that is to be mated therewith. Although OSAs  202  and receptacles  204  shown in FIG. 2 are based on the LC optical connector, the OSAs and receptacles may be based on other types of connectors, such as the MTP optical connector (also known as the type MPO connector), the SC optical connector, or the like.  
     [0025] The OSAs  202  are electrically connected to an electronic circuit board  210  that incorporates circuitry of the type conventionally included in optoelectronic transceiver modules, such as a laser driver, laser control, receiver post-amplifier, signal-detect circuits, and power-on reset circuits. Typically, receptacles  204  are integrally formed as a portion of a plastic retainer  212  that retains OSAs  202  and electronic circuit board  210  in position. Alternatively, receptacles  204  and a retainer member may be formed separately as two or more pieces. A bottom cover  214 , a top front cover  216 , and a top rear cover  218  form the housing of optoelectronic transceiver module  200 . Typically, these cover members are made of metal to provide electromagnetic shielding.  
     [0026] Typically, optoelectronic transceiver module  200  is electrically connected to an electronic circuit board  220  of a computer or I/O device. For example, optoelectronic transceiver module  200  may be connected to electronic circuit board  220  of the computer or I/O device using a fixed connection as shown in FIG. 2, e.g., a pin-through-hole arrangement that connects electronic circuit board  210  of optoelectronic transceiver module  200  to electronic circuit board  220  of the computer or I/O device. Alternatively, optoelectronic transceiver module  200  may be connected to electronic circuit board  220  of the computer or I/O device using a removable connection, e.g., a hot-pluggable contact pad mechanism that connects electronic circuit board  210  of optoelectronic transceiver module  200  to electronic circuit board  220  of the computer or I/O device.  
     [0027] Optoelectronic transceiver module  200  receives optical signals from the fiber optic cable, converts the optical signals to electrical signals, and provides the electrical signals to the electronic circuit board  220  of the computer or I/O device. Likewise, optoelectronic transceiver module  200  receives electrical signals from the electronic circuit board  220  of the computer or I/O device, converts the electrical signals to optical signals, and provides the optical signals to the fiber optic cable. Optoelectronic transceiver module  200  receives optical signals from the fiber optic cable using receiver optical subassembly (ROSA)  202 R and provides the optical signals to the fiber optic cable using transmitter optical subassembly (TOSA)  202 T.  
     [0028] A ROSA typically includes a lens that receives the optical signals from the fiber optic cable and focuses the optical signals on an optoelectronic device provided with a receiver unit, e.g., a photoelectric receiver chip, that converts the fiber optic signals to electrical signals. Similarly, a TOSA typically includes an optoelectronic device provided with a transmitter unit, e.g., an edge-emitting laser (CD) or a surface-emitting laser (VCSEL), that converts electrical signals to optical signals that are directed onto a lens that directs the optical signals to the fiber optic cable.  
     [0029]FIG. 3 is an exploded perspective enlarged view of one of the optical subassemblies (OSAs)  202  of the optoelectronic transceiver module shown in FIG. 2. The OSA is shown in FIG. 3 prior to application of a multifunctional acrylate resin adhesive interface according to an embodiment of the present invention shown in FIG. 4. Although only transmitter optical subassembly (TOSA)  202 T is shown in FIG. 3, the present invention may also be employed in receiver optical subassembly (ROSA)  202 R, which has a similar structure.  
     [0030] The present invention is not limited to use in the OSA structure shown in FIGS. 3 and 4, and may be used in other types of optical subassemblies. For example, the present invention may be used in an optical subassembly having optical components mounted on an optical bench as discussed in detail below with reference to FIG. 5.  
     [0031] Referring back to FIG. 3, TOSA  202 T includes an optoelectronic device  300  provided with a transmitter unit  302 , e.g., an edge-emitting laser (CD) or a surface-emitting laser (VCSEL), that converts electrical signals to optical signals that are directed onto a lens  322  that directs the optical signals to the fiber optic cable. Although not shown, ROSA  202 R includes a similar optoelectronic device with a receiver unit, e.g., a photoelectric receiver chip, that converts the fiber optic signals to electrical signals. Typically, optoelectronic device  300  is in the form of a transistor-outline (TO) can as shown in FIG. 3, both for TOSAs and ROSAs. TO-cans are advantageous in that they offer a hermetic, high-reliability package. The electrical signals are provided to TOSA  202 T through electrodes  304  that exit a deck portion  306  at the rear of the TO-can. The optical signals exit TOSA  202 T through a window  308  in a cup-shaped portion  310  at the front of the TO-can.  
     [0032] In the embodiment shown in FIG. 3, TOSA  202 T (ROSA  202 R) has a housing member  320  that is used to enclose optoelectronic device  300  and a lens  322  and to align lens  322  with respect to the transmitter unit (receiver unit) of optoelectronic device  300 . Housing member  320  is preferably injection molded using an optically clear plastic, e.g., Ultem® polyetherimide available from GE Plastics, so that lens  322  and projection  206  may be integrally formed with housing member  320 . As discussed above, projection  206  is provided with an optical fiber bore  208  for receiving a ferrule of a fiber optic cable connector that is to be mated therewith. Alternatively, housing member  320 , lens  322  and projection  206  may be formed separately as two or more pieces.  
     [0033] Optoelectronic Subassembly with Multifunctional Acrylate Resin Adhesive Interface  
     [0034]FIG. 4 is a cross-sectional view of an optical subassembly (OSA) that includes a multifunctional acrylate resin adhesive interface  400  according to an embodiment of the present invention. Although a transmitter optical subassembly (TOSA) is shown in FIG. 4 for the purpose of illustration, the present invention is also applicable in a receiver optical subassembly (ROSA).  
     [0035] Multifunctional acrylate resin adhesive interface  400  is included between lens  322  and optoelectronic device  300 , e.g., having a laser  302  or a photoelectric receiver chip. Multifunctional acrylate resin adhesive interface  400  is formed by curing an adhesive material including a multifunctional acrylate resin and, preferably, a photoinitiator and/or a thermal initiator. Suitable multifunctional acrylate resins include, for example, di-, tri-, tetra-, pentafunctional acrylate resins, or a mixture thereof. Illustrative suitable commercially-available multifunctional acrylate resins include, for example, Sartomer 351 (trimethylolpropane triacrylate), Sartomer 350 (trimethylolpropane trimethaacrylate), Sartomer 444 (pentaerythritol di-, tri-, tetraacrylates), and Sartomer 399 (dipentaerythritol pentaacrylate), each available from the Sartomer Company, Exton, Pa. Additionally, the adhesive material preferably includes a conventional thermal initiator (e.g., organic peroxide) and/or a photoinitiator (e.g., an aromatic ketone) such as Irgacure 184 (1-Hydoxycyclohexyl phenyl ketone) available from Ciba Specialty Chemicals, Inc. As shown in the TABLE below, an adhesive material including a multifunctional acrylate resin cures to form an adhesive having a tightly cross-linked network of low CTE (coefficient of thermal expansion). The low CTE of multifunctional acrylate resin adhesive interface  400  can reduce (as compared to conventional, optically clear adhesives) thermally-induced stress at the bond line at the operating temperature of the subassembly.  
     [0036] In preparing the TABLE below, various multifunctional acrylate resins with 1 wt % Irgacure 184 as photoinitiator were cast into right cylinders (i.e., disks) and UV cured (90 J/cm 2  dose from a Novacure® UV spot curing source available from EFOS USA Inc., Williamsville, N.Y.). CTE measurements were conducted over a temperature range of 0-100° C. at a scan rate of 5° C./min using a 1 mm quartz probe. For comparison, a conventional unfilled adhesive (Norland NOA61 available from Norland Products Inc., Cranbury, N.J.), a conventional filled adhesive (Optocast 3408 available from Electronics Materials Inc., Breckenridge, Colo.), and a monofunctional acrylate resin (Sartomer 440 available from the Sartomer Company, Exton, Pa.) were prepared and processed in an identical manner.  
                       TABLE                               CTE               (ppm/° C.),       Resin   Functionality   T &lt; T g                                              Norland NOA61   Difunctional   220.0           (unfilled)       Optocast 3408   Difunctional   40.6           (mineral filled)       Sartomer 351   Trifunctional   53.1       (trimethylolpropane triacrylate)   (unfilled)       Sartomer 350   Trifunctional   46.1       (trimethylolpropane trimethacrylate)   (unfilled)       Sartomer 444   Mixed di, tri,   43.0       (pentaerythritol di-, tri-, tetraacrylates)   tetrafunctional           (unfilled)       Sartomer 399   Pentafunctional   28.4       (dipentaerythritol pentaacrylate)   (unfilled)       Sartomer 440   Monofunctional   NA       (isooctyl acrylate)   (unfilled)                  
 
     [0037] Within the multifunctional acrylate resin series, it can be seen that increasing the functionality results in markedly lower CTE. The pentafunctional acrylate resin exhibits a very low CTE of 28.4 ppm/° C. up to 100° C. This is much lower than the unacceptable CTE of Norland NOA61 (which is unfilled and provides the necessary clarity) and is even lower than the acceptable CTE of Optocast 3408 (which is filled to control CTE, but is unacceptably opaque). The isooctyl acrylate resin, being monofunctional, polymerized into a linear polymer with little or no cohesive integrity rendering CTE determination impossible.  
     [0038] Multifunctional acrylate resin adhesive interface  400  preferably contacts substantially the entire interior surface of housing member  320  and substantially the entire exterior surface of the cup-shaped portion  310  of optoelectronic device  300 . This increases the surface area available for bonding. The surface shape of lens  322  is selected based on the refractive index of multifunctional acrylate resin adhesive interface  400 .  
     [0039] Preferably, the adhesive material is optically clear at the operating wavelength of the optoelectronic device, curable via UV and/or thermal initiation, rapid curing, has excellent adhesion to high surface energy plastics and metals, and has adequate viscosity. With regard to the adhesive material preferably being optically clear at the operating wavelength (e.g., 850 nm) of the optoelectronic device, a transmittance of at least 90% is preferred for an unattenuated OSA. However, transmittance can be tailored via incorporation of an appropriate conventional dye such that the laser power is reduced to acceptable levels. Highly filled adhesive materials will be opaque at the operating wavelength of the optoelectronic device.  
     [0040] With regard to the adhesive material preferably being curable via UV and/or thermal initiation, the adhesive material may have a sluggish cure speed due to absorption of UV radiation by the housing member. In this case, a conventional thermal initiator may be added to the adhesive material to drive the conversion toward completion. With regard to the adhesive material preferably being rapid curing, the OSAs are typically individually aligned (i.e., the laser (or receiver chip) of optoelectronic device is aligned with respect to the lens) and thus throughput is gated by the alignment/cure process. Rapid curing ensures that cycle time will be kept to a minimum.  
     [0041] With regard to the adhesive material preferably having excellent adhesion to high surface energy plastics and metals, the adhesive material will preferably function to better adhere the optoelectronic device to the housing member (as well as being an index-matching material). Thus, the adhesive material will preferably exhibit excellent adhesion to surfaces of the housing member (e.g., Ultem) and surfaces of the optoelectronic device (e.g., gold and/or nickel).  
     [0042] With respect to the adhesive material preferably having adequate viscosity, the adhesive material is preferably dispensed on both the laser (or receiver chip) and the lens surfaces prior to mating the optoelectronic device to the housing member in order to prevent air entrapment at either the laser or the lens surfaces. The viscosity must be high enough to prevent excessive slumping or dripping yet low enough to enable adequate wetting of both surfaces. A suitable range is between 500-100,000 cP.  
     [0043] The adhesive material is applied both to lens  322  (preferably, to substantially the entire interior surface of housing member  320 ) and window  308  of optoelectronic device  310  (preferably, to substantially the entire exterior surface of the cup-shaped portion  310  of optoelectronic device  300 ). Next, housing member  320  and optoelectronic device  300  are joined and aligned. Finally, the adhesive material is cured to form multifunctional acrylate resin adhesive interface  400 . The adhesive material may be cured by exposure to UV radiation and/or heat, for example. In addition, a conventional structural adhesive  402  may be dispensed in an area between deck portion  306  of the TO-can and a lip portion  324  of housing member  320  and cured to provide additional rigidity and durability to OSA  202 .  
     [0044] Optoelectronic Subassembly with Multifunctional Acrylate Resin Adhesive Contact Points  
     [0045] The present invention is not limited to use in the OSA structure shown in FIGS. 3 and 4, and may be used in other types of optical subassemblies. For example, as shown in FIG. 5, the present invention may be used in an optical subassembly having optical components (e.g., a lens, a laser and/or a photoelectric receiver chip) mounted on an optical bench.  
     [0046]FIG. 5 is a side elevational view of an optical subassembly (OSA)  500  that includes multifunctional acrylate resin adhesive contact points  502  according to another embodiment of the present invention. The multifunctional acrylate resin adhesive contact points  502  adhere a ball lens  504  to a recess  506  of an optical bench  508 . Preferably, optical bench  508  is silicon and recess  506  is precision machined or etched onto a surface thereof. The optical bench  508  also has an optoelectronic device  510 , e.g., a device having a laser or a photoelectric receiver chip, mounted thereon. The optoelectronic device  510  may be adhered to optical bench  508  using conventional techniques or, alternatively, using multifunctional acrylate resin adhesive contact points consistent with the present invention. In addition, optoelectronic device  510  may be soldered or otherwise electrically connected to electrical pads or traces on optical bench  508 , if desired, using methods and materials generally known to those skilled in the art. Precision alignment of ball lens  504  to optical bench, and thus to optoelectronic device  510 , is essential for proper functioning of subassembly  500 , i.e., ball lens  504  is precisely aligned to focus light from a fiber optic cable to a photoelectric receiver chip, or from a laser to a fiber optic cable.  
     [0047] Multifunctional acrylate resin adhesive contact points  502  are formed by curing an adhesive material including a multifunctional acrylate resin and, preferably, a photoinitiator and/or a thermal initiator. Suitable multifunctional acrylate resins include, for example, di-, tri-, tetra-, pentafunctional acrylate resins, or a mixture thereof. Illustrative suitable commercially-available multifunctional acrylate resins include, for example, Sartomer 351 (trimethylolpropane triacrylate), Sartomer 350 (trimethylolpropane trimethaacrylate), Sartomer 444 (pentaerythritol di-, tri-, tetraacrylates), and Sartomer 399 (dipentaerythritol pentaacrylate), each available from the Sartomer Company, Exton, Pa. Additionally, the adhesive material preferably includes a conventional thermal initiator (e.g., organic peroxide) and/or a photoinitiator (e.g., an aromatic ketone) such as Irgacure 184 (1-Hydoxycyclohexyl phenyl ketone) available from Ciba Specialty Chemicals, Inc. As shown in the TABLE set forth above in the discussion of the previous embodiment, an adhesive material including a multifunctional acrylate resin cures to form an adhesive having a tightly cross-linked network of low CTE (coefficient of thermal expansion). The low CTE of multifunctional acrylate resin adhesive contact points  502  can reduce (as compared to conventional, optically clear adhesives) thermally-induced vertical offset (in the direction denoted as arrow  512  in FIG. 5), for example, of ball lens  504  relative to optical bench  508  and optoelectronic device  510  at the operating temperature of subassembly  500 .  
     [0048] Alignment of ball lens  504  relative to optical bench  508  and optoelectronic device  510  is typically accomplished at room temperature regardless of the continuous use temperature of subassembly  500 . Because the CTE of conventional optically clear adhesives often exceeds 100 ppm/° C., coupled with the fact that subassembly  500  may operate at temperatures approaching 70° C., the conventional adhesive will often expand significantly at operating temperature (as compared to its size when aligned at room temperature). This expansion can result in misalignment of ball lens  504  relative to optoelectronic device  510 . The low CTE of multifunctional acrylate resin adhesive contact points  502  solves this problem. Ball lenses bonded to optical benches with multifunctional acrylate resin adhesive contact points (preferably di-, tri-, tetra-, pentafunctional acrylate resins, or a mixture thereof; and more preferably pentafunctional acrylate resins) exhibit essentially no vertical movement thereby ensuring precision alignment of ball lens  504  to the optical bench  508  and optoelectronic device  510 .  
     [0049] As mentioned in the discussion of the previous embodiment, the pentafunctional acrylate resin in the TABLE above exhibits a very low CTE of 28.4 ppm/° C. up to 100° C. This is much lower than the unacceptable CTE of Norland NOA61 (which is unfilled and provides the necessary clarity) and is even lower than the acceptable CTE of Optocast 3408 (which is filled to control CTE, but is unacceptably opaque). For precision alignment of ball lens  504  relative to optical bench  508 , the adhesive material must be transparent in order to ensure proper dispense volume.  
     [0050] An adhesive material including a multifunctional acrylate resin is applied to ball lens  504  and/or recess  506  of silicon optical bench  508 , which are then joined and the adhesive material cured. The adhesive material is preferably cured by exposure to UV radiation and/or heat.  
     [0051] While this invention has been described with respect to the preferred and alternative embodiments, it will be understood by those skilled in the art that various changes in detail may be made therein without departing from the spirit, scope, and teaching of the invention. Accordingly, the herein disclosed invention is to be limited only as specified in the following claims.