CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese patent application JP2020-140168 filed on Aug. 21, 2020, the contents of which are hereby incorporated by reference into this application.

BACKGROUND

1. Field

The disclosure relates to an optical module.

2. Description of the Related Art

To connect an FPC (Flexible Printed Circuit) and a PCB (Printed Circuit board), of an optical module, solder is often used. For example, a method is known where solder is applied to a terminal of the PCB and soldering is done by instantaneous heating using a hot bar (JP2016-127205A).

During the heating by the hot bar, the FPC and PCB are pressed with a jig, whereby the solder flows outward, resulting in difficulty of ensuring a sufficient amount of the solder. This necessitates adding the solder by hand to ensure mechanical strength and reliability.

SUMMARY

The disclosure aims at ensuring a sufficient amount of a filler metal.

(1) An optical module includes: an optical sub-assembly;

and a flexible substrate including an insulating film, an interconnection pattern, and a spacer layer, the flexible substrate being connected to the optical sub-assembly. The insulating film has some projections, the projections protruding from a basic area in a first direction, the projections being arranged in a second direction perpendicular to the first direction, the insulating film having a flat shape with a recess between an adjacent pair of the projections. The interconnection pattern includes some pads in the basic area on a first surface of the insulating film, the pads being arranged in the second direction. The pads include some first pads adjacent to the respective projections, the pads including at least one second pad adjacent to the recess. The spacer layer is on the first surface and at each of the protrusions.

The spacer layer can secure a space for bonding on the pads. This is beneficial for securing a sufficient amount of a filler metal.

(2) In the optical module according to (1), the at least one second pad may be one of the pads.

(3) In the optical module according to (1), the at least one second pad may be two of the pads.

(4) In the optical module according to any one of (1) to (3), the projections may be three or more projections.

(5) In the optical module according to any one of (1) to (4), the flexible substrate may include a cover layer on the first surface and in the basic area, the cover layer covering the interconnection pattern except for the pads, and the spacer layer may be equal in material and thickness to the cover layer.

(6) In the optical module according to (5), the interconnection pattern may include a ground plane on the first surface, and the ground plane may be between the insulating film and the cover layer.

(7) In the optical module according to (6), the ground plane may be continuous from the first pads.

(8) In the optical module according to any one of (1) to (7), the interconnection pattern may include some dummy terminals, the dummy terminals being between the insulating film and the spacer layer, the dummy terminals being at the projections, the dummy terminals being continuous from the first pads.

(9) In the optical module according to any one of (1) to (8), the interconnection pattern may include at least one signal line on a second surface opposite to the first surface, and the at least one signal line may penetrate the insulating film and may be connected to the at least one second pad.

(10) The optical module according to any one of (1) to (9) may include: a printed circuit board including a conductor pattern, the conductor pattern including some electrodes opposed to the respective pads, the printed circuit board being opposed to the projections and in contact with the spacer layer; and a filler metal between the pads and the electrodes.

(11) In the optical module according to (10), the conductor pattern may include a conductive plane continuous from at least one of the electrodes.

(12) In the optical module according to (11), the conductor pattern may include at least one transmission line continuous from another at least one of the electrodes, and the conductive plane may be on both sides of the at least one transmission line.

(13) In the optical module according to (12), the electrodes may include some first electrodes opposed to the respective first pads and at least one second electrode opposed to the at least one second pad.

(14) In the optical module according to any one of (11) to (13), the spacer layer may be in contact with the conductive plane.

(15) In the optical module according to any one of (10) to (13), the printed circuit board further may include a protective layer covering the conductor pattern except for the electrodes, and the spacer layer may be in contact with the protective layer.

(16) In the optical module according to any one of (1) to (15), the optical sub-assembly may be brazed or soldered to the interconnection pattern except at the pads.

