Optical module with fluxless laser reflow soldered joints

#This invention relates to optical data transmission and particularly to optical modules which are connected to optical fibers for providing such data transmissions. Even more particularly, this invention relates to interconnection of components within optical modules and to flexible circuit boards.

#This application is related to the following concurrently filed application:

#U.S. Ser. No. 07/976,632 filed Nov. 16, 1992 now U.S. Pat. No. 5,295,214 issued Mar. 15, 1994 to Mukund K. Saraiya, Duane F. Card and Eberhard Dittmann, entitled: Optical Module With Tolerant Wave Soldered Joints (IBM Docket EN9-92-141), incorporated herein by reference.

#FIG. 1 is a exploded perspective view of an optical module in accordance with this invention and showing a duel optical plug connector for connection thereto;

#FIG. 2 is a side elevation partial section of the optical module of FIG. 1, showing the connection of the invention between one of the optical sub-assemblies and the ceramic electrical interconnect structure within the housing;

#FIG. 3 is a schematic elevation view of the optical module in a machine of the invention for fluxless laser soldering;

#FIG. 1 shows a specific embodiment of the optical module 100 of this invention. Longate optical sub-assembly 102 receives a first, optical signal in a port (not shown) in one longitudinal end of module 102. The module converts the first, optical signal into a first, electrical signal which is output through conductive pins 104 at the distal longitudinal end of the module. Pins 104 are soldered to flat, donut-shaped conductive, solder-wettable lands 105 encircling through holes at 106. The lands are on the surface of flexible ribbon cable 110 and are integrally connected to conductors 108 extending within dielectric layers of flexible ribbon cable 110. The connection between pins 104 and cable 110 may be made by introducing solder preforms or solder paste and reflowing or preferably by mass soldering such as immersion or most preferably by wave soldering. The flexible ribbon cable is bent 90 degrees as shown so that exposed leads 112 of conductors 108 are positioned on interconnection pads 120 of thin film screen printed electrical circuit 122 which is on the top surface of interconnect structure 124 which is preferably of rigid construction and more preferably of ceramic construction. The connection of cable 110 with pads 120 is provided by laser soldering as later described in this specification. Electronic circuit 126 processes the first, electrical signal and transmits a first processed electrical signal. Electronic circuit 126 is connected through output conduits of electrical circuit 122 which are connected to pins 128. The first, processed, electrical signal is transmitted from electronic circuit 126, through electrical circuit 122, to pins 128. When the optical sub-assembly is positioned on electrical interconnect structure 130 such as a flexible circuit board or a printed circuit board, pins 128 couple with connectors 132 of an electrical circuit 134 which extends on the exterior and/or the interior of interconnect structure 130. The first, processed, electrical signal is transmitted from the pins into interconnect structure 130.

#A second, electrical signal is transmitted from external interconnect structure 130, through pins 128, through electrical circuit 122, and to electronic circuit 138 which processes the second electrical signal. In a manner similar to the connection of optical sub-assembly 102, optical sub-assembly 140 is connected through flexible ribbon cable 142 to interconnection pads 144 of electrical circuit 122 which is connected to electronic circuit 138. Thus, the second electrical signal is processed and transmitted to optical sub-assembly 140 which converts the second, processed, electrical signal into a second optical signal which is transmitted through a port (not shown) in one end of the module.

#Optical modules 102 and 140 and rigid interconnect structure 124 are mounted within a housing of two part construction preferably of cast aluminum which may be machined as required. The bottom of lower part 150 of the housing includes a matrix of apertures 152 through which pins 128 of interconnect structure 124 extend to communicate with interconnect structure 130. Alternately a window (not shown) could be provided in the bottom of lower part 150 for the pins. Preferably structure 124 is held in a fixed position in lower part 150 by adhesive, preferably epoxy. The optical sub-assemblies may also be fixed in position by an adhesive such as epoxy or may be positioned by keys to allow limited movement for adjustment to tolerances in the dimensions of plug in module 160. The top of upper part 154 of the housing includes fins 156 for cooling the optical module.