Search

EP-4738729-A1 - OPTICAL TRANSCEIVER, AND METHOD AND APPARATUS FOR MANUFACTURING SAME

EP4738729A1EP 4738729 A1EP4738729 A1EP 4738729A1EP-4738729-A1

Abstract

Provided are a configuration for achieving an optical transceiver capable of operating at an ultra-high speed, and a manufacturing method and a manufacturing device for the same. An optical transceiver according to the present disclosure includes at least one optical module mounted on a PCB, a DSP, and an FPC that connects the DSP and the optical module, wherein the FPC further includes a first connection PAD on a first surface solder-connected to a PAD on a terrace surface of the optical module, a second connection PAD on a second surface solder-connected to a PAD on an upper surface of a DSP substrate, both side surfaces, and the first connection PAD, the FPC and the first connection PAD and the FPC and the second connection PAD are connected by one or more through-holes or buried VIAs, and the through-hole has a diameter of ϕ100 µm or more.

Inventors

  • OZAKI JOSUKE
  • OGISO YOSHIHIRO
  • NUNOYA NOBUHIRO

Assignees

  • NTT, Inc.

Dates

Publication Date
20260506
Application Date
20230628

Claims (8)

  1. An optical transceiver, comprising: at least one optical module that is mounted on a printed circuit board (PCB); a digital signal processor (DSP) that is mounted on the PCB; and a flexible printed circuit (FPC) that connects the DSP and the optical module, wherein the DSP includes a DSP chip mounted on a DSP substrate formed of a multilayer wiring substrate having a core layer for adjusting a thickness, the FPC includes a first connection PAD of a first surface solder-connected to a PAD of a terrace surface of the optical module and a second connection PAD of a second surface solder-connected to a PAD of an upper surface of the DSP substrate, the FPC and the first connection PAD, and the FPC and the second connection PAD are connected by one or more through-holes or buried VIAs, the FPC further includes a land connected to the through-hole or the buried VIA and formed on a front surface and a back surface of the FPC, and a notch having a diameter of ϕ300 µm or more capable of stably holding the FPC on both side surfaces of the FPC and at positions 500 µm or more away from an inner end of each of the first connection PAD and the second connection PAD, and the through-hole has a diameter of ϕ100 µm or more.
  2. The optical transceiver according to claim 1, wherein the DSP substrate has a thickness of 1 to 2 mm, and includes at least one second VIA in the core layer and at each position corresponding to a lower portion of the PAD on the DSP substrate.
  3. The optical transceiver according to claim 1, wherein the FPC further includes a heating PAD connected to the land and installed on a surface opposite to a position where the first connection PAD and the second connection PAD are disposed.
  4. The optical transceiver according to claim 1, wherein the PAD on the DSP substrate includes a heat separation portion that thermally separates a portion where solder is formed and a portion other than the portion where the solder is formed, and a high-frequency line for connecting the FPC and the DSP chip on the DSP substrate is formed in inner layer wiring of the DSP substrate.
  5. A manufacturing device for manufacturing the optical transceiver according to any one of claims 1 to 4, the manufacturing device comprising: a hot bar that contacts the FPC and applies heat and a load to solder formed between the first connection PAD and the PAD on the DSP substrate and between the second connection PAD and the PAD on a terrace; a mounting base that holds the PCB from below; and a holding mechanism that holds the FPC from a side surface and a lower surface by fitting with the notch.
  6. The manufacturing device according to claim 5, wherein the mounting base is configured to be hollow between the PCB and the mounting base, and the manufacturing device further comprising: a lower support structure that is disposed between the PCB and the mounting base at a position corresponding to a position where the hot bar comes into contact, and wherein the holding mechanism is formed of resin or metal when the notch is formed of only a dielectric, and is formed of resin when the notch is metallized.
  7. The manufacturing device according to claim 5, wherein the hot bar is configured to have a length of 20 to 30 mm and collectively solder-mount the FPCs connected to an optical transmission module including an optical modulator and a driver integrated circuit and an optical receiver module including a photodetector and a transimpedance amplifier, contact the FPC at a temperature higher by 50 degrees or more than a melting temperature of the solder, and apply a load of 10 N or more.
  8. A manufacturing method for manufacturing the optical transceiver according to any one of claims 1 to 4, the method comprising: mounting a DSP on the PCB; connecting the optical module and the FPC by soldering using a hot bar; installing the optical module to which the FPC is connected on the PCB, and connecting the FPC and the DSP by soldering using a hot bar; and connecting the PCB and a DC interface of the optical module, wherein the FPC and the first connection PAD, and the FPC and the second connection PAD are through-holes, the manufacturing method further comprising: performing pre-solder treatment of forming solder on at least the land or the heating PAD directly heated by the hot bar in soldering using the hot bar; and heating and pressurizing, with the hot bar, the solder formed by the pre-solder treatment, wherein the solder melted by the heating and pressurizing reaches between the first connection PAD and the terrace and between the second connection PAD and the DSP substrate through the through-hole, and the solder is formed between the first connection PAD and the terrace and between the second connection PAD and the DSP substrate, or the FPC and the first connection PAD, and the FPC and the second connection PAD are connected by the buried VIA, the manufacturing method further comprising: performing pre-solder treatment of forming solder between the first connection PAD and the terrace and between the second connection PAD and the DSP substrate in soldering using the hot bar; and heating and pressurizing the land or the heating PAD with the hot bar, wherein the solder formed by the pre-solder treatment is melted by heat transfer from the heated and pressurized land or heating PAD, and the solder is formed between the first connection PAD and the terrace and between the second connection PAD and the DSP substrate.

Description

Technical Field The present disclosure relates to an optical transceiver used in optical communication, and a manufacturing method and a manufacturing device for the same. Background Art In order to cope with increasing communication traffic demand, a high-speed optical modulator and an optical receiver compatible with an advanced optical modulation system are required. In optical modulators and optical receivers in early 100G digital coherent communications systems, each of the components is packaged and these parts are mounted on a printed circuit board (PCB). For example, in the case of an optical modulator, a driver IC and an optical modulator chip are individually packaged, and the packaged IC and chip are mounted on the PCB. In the case of an optical receiver, a transimpedance amplifier (TIA) and an optical light-receiving chip are individually packaged and mounted as separate parts on the PCB. In a digital coherent communications system exceeding 400G with further advanced speed, an optical modulator and an optical receiver are also required to have a wide band so as to be able to handle a signal of 40 GHz or more, and it is necessary to reduce high-frequency loss and reduce a size. In the case of the optical modulator, the driver IC and the optical modulator chip are integrally mounted in one package as an optical module. Also in the case of the optical receiver, the TIA and the optical light-receiving chip are integrally mounted as a single optical module. Also for a signal format for inputting and outputting a baseband signal, design from a single-ended format to a differential format has been generalized as one of means for achieving high speed, small size, and low power consumption. At present, device development for achieving 800 Gbps and 1 Tbps (128 GBd operation) is in progress. The optical internetworking forum (OIF) has standardized under the name of a high-bandwidth coherent driver modulator (HB-CDM) as an optical transmitter in which a driver IC and an optical modulator are mounted in an integrated package. In Non Patent Literature 1, physical configurations, interface specifications, and the like are defined as various types of modules. Also on the reception side, the TIA and the optical light receiver are mounted in an integrated package, which is also called high-bandwidth intradyne coherent receiver (HB-ICR). An optical transceiver (optical transmission/reception device) includes a transmission-side (Tx) optical module and a reception-side (Rx) optical module. Initially, in the above-described optical module, a surface mount (SMT) type package having excellent mountability has been used. In the optical module of the SMT type package, since the optical module is mounted on the PCB of the optical transceiver, a via (VIA) structure for passing a high-frequency electric signal into the package is essential. In the VIA, deterioration of high frequency characteristics and the like are inevitable, and thus the VIA structure is a structure not suitable for further achieving a wide band. In addition, in the SMT type package, in a connection portion between a lead pin and a ceramic package, the high-frequency transmission characteristics of an electric signal are also deteriorated due to electromagnetic field mode mismatching or impedance mismatching (Non Patent Literature 2). Therefore, a package configuration using a flexible printed circuit (FPC) is newly standardized (Non Patent Literature 1). Optimization design including a digital signal processor (DSP) is important in achieving an increase in speed of the entire optical transceiver in addition to an increase in speed of an individual optical module. In early optical transceivers, a DSP, a transmission module, and a reception module are mounted in separate packages and mounted at separate locations on a PCB. For this reason, there is a limit to speed up of the optical transceiver due to propagation loss generated in the individual packages or on the PCB. As one of the solutions, a "co-package structure" in which an optical modulator chip, an optical receiver chip, and a DSP are mounted close to each other in a single package has also been studied. This structure is ideal that can greatly reduce the loss of a high-frequency electric signal, but the DSP, which is the largest heat generation source, is disposed close to the periphery of the optical modulator or the optical receiver. When an optical modulator that requires temperature control, such as an InP modulator that is excellent in speed, is used, the optical modulator chip needs to be mounted on a Peltier element. The Peltier element has a risk of an increase in power consumption and thermal runaway, and it is difficult to mount the Peltier element in a single package in proximity to the DSP that causes heat inflow. The co-package structure has various problems in terms of mounting processes. Therefore, another configuration of the optical transceiver has been proposed (Patent Literat