CN113064238B

CN113064238B - Soft board for realizing connection with optical device, connection method and optical module

Info

Publication number: CN113064238B
Application number: CN202110303308.3A
Authority: CN
Inventors: 金卫; 薄生伟; 鲁振华
Original assignee: Yangtze Optical Fibre and Cable Co Ltd
Current assignee: Yangtze Optical Fibre and Cable Co Ltd
Priority date: 2021-03-22
Filing date: 2021-03-22
Publication date: 2022-05-06
Anticipated expiration: 2041-03-22
Also published as: CN113064238A

Abstract

The invention discloses a flexible board for realizing connection with an optical device, a connection method and an optical module, and belongs TO the technical field of optical communication.

Description

Soft board for realizing connection with optical device, connection method and optical module

Technical Field

The invention belongs to the technical field of optical communication, and particularly relates to a flexible board for realizing connection with an optical device, a connection method and an optical module.

Background

With the increasing data flow, the single channel rate of the optical module is higher and higher in the coming 5G era, the rate of the previous generation 10Gbps is increased TO the current 25Gbps, and the rate of the next generation coming 50Gbps or 100Gbps, however, the connection mode of a soft board FPC and an optical device TO-can is still adopted for the optical device of the optical module in the industrial grade, and with the increase of the rate, the requirement of the whole link on the signal integrity is higher and higher, and the FPC and the TO-can are required TO be grounded well, so that the backflow path is shortest.

The FPC + TO-can currently used in 25G industrial optical modules is mainly formed by connecting two separate components together by solder TO conduct signals. The FPC mainly comprises a high-speed through hole, a grounding through hole, a front high-speed signal line, a back reference ground and a copper exposed area, and the TO-can mainly comprises a TO base, a high-speed pin and a grounding pin, wherein the grounding pin is connected with the TO base. As shown in fig. 1, (a) in fig. 1 shows a schematic diagram of a TO-can, fig. 1 (b) shows a front view of an FPC, and fig. 1 (c) shows a rear view of an FPC.

A high-speed pin of a TO-can is welded with a high-speed pad on the front surface of an FPC, a TO-can grounding pin is welded with a grounding through hole of the FPC, tin is poured between the FPC and the TO-can through the grounding through hole of the FPC by heating, and a copper-exposed area on the back surface of the FPC and a TO-can base are welded together by the welding tin, as shown in figure 2, wherein (a) in figure 2 shows a schematic diagram of the FPC + TO-can, and (b) in figure 2 shows a schematic diagram of the back surface of the FPC after welding.

During welding, the oxide on the metal surface is removed by the soldering flux, the soldering flux flows along with the soldering tin and is filled between the FPC and the TO-can, the nearby temperature is relatively reduced along with the increase of the distance between the soldering flux and the grounding via hole, the viscosity of the mixture of the solder resist and the oxide is increased, the wetting effect of the soldering tin is poor, the liquid soldering tin is prevented from flowing around, the soldering tin cannot be spread out in a large area, and therefore the FPC and the TO-can are connected well nearby without the soldering tin near the high-speed via hole.

In the traditional FPC design, only tin is poured into the vicinity of the ground via hole, tin is not basically arranged in the vicinity of the high-speed via hole, and the ground in the vicinity of the high-speed via hole and the TO base do not form direct grounding, so that the high-speed signal backflow path is not shortest, the signal reference is incomplete, and the high-speed signal quality is directly deteriorated under the condition of the speed of 25G or higher. The final performance is that some 25G optical modules can not meet the industrial specification, the product yield is not high, and the overall cost is higher.

Disclosure of Invention

Aiming at the defects or the improvement requirements of the prior art, the invention provides a soft board for realizing the connection with an optical device, a connection method and an optical module, which solve the problem that the return flow path of a high-speed through hole is shortest, thereby realizing the low cost and high quality of a 25G optical module.

To achieve the above object, according to one aspect of the present invention, there is provided a flexible board for realizing connection with an optical device, comprising:

and a plurality of slots are formed in the soft board, wherein each slot is a through hole which is not directly corresponding to the pin of the optical device.

In some alternative embodiments, the walls of each slot are metallized.

In some alternative embodiments, the distance between each slot and the high-speed via hole or the high-speed signal line on the flexible board is greater than or equal to several times of the line width of the high-speed signal line.

In some alternative embodiments, the high speed via of the flexible board has a metal pad on the front side and no metal pad on the back side.

In some optional embodiments, a plurality of slots are formed on the connection area of the flexible board and the optical device.

In some alternative embodiments, each slot is oval, circular, or square.

According to another aspect of the present invention, there is provided a method for connecting a flexible board to an optical device according to any one of the above aspects, comprising:

setting the welding temperature of the electric soldering iron;

welding the middle grounding via hole on the soft board, heating the pin and the bonding pad at the grounding via hole through an electric soldering iron, and then melting enough soldering tin at the grounding via hole through a tin wire;

after the electric soldering iron is heated for a preset time, keeping the position of the soft board, moving away the electric soldering iron, and waiting for soldering tin to solidify;

and welding a high-speed signal pin on the soft board, heating the pin at the high-speed through hole and the bonding pad through an electric soldering iron, wrapping the whole pin by the tin to be soldered, and sequentially removing the tin wire and the electric soldering iron.

In some alternative embodiments, the soldering temperature of the electric soldering iron is 350 ℃.

According to another aspect of the present invention, an optical module obtained by the method for connecting a flexible board to an optical device is provided.

In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:

according TO the invention, the copper-exposed area on the back surface of the FPC can be completely tinned by grooving the holes on the FPC, so that the copper-exposed area can be completely and directly connected with the TO base, the FPC and the TO-can are well grounded, the problem that the backflow path of the high-speed via hole is shortest is solved, and the low-cost and high-quality targets of the 25G optical module are realized.

Drawings

FIG. 1 is a schematic diagram of an FPC and a TO-can provided by an embodiment of the present invention, wherein (a) shows a schematic diagram of the TO-can, (b) shows a front view of the FPC, and (c) shows a back view of the FPC;

FIG. 2 is a schematic diagram of a printed circuit board (FPC) with copper-exposed areas on the back surface and a TO-can base bonded together by soldering, wherein (a) shows a schematic diagram of FPC + TO-can, and (b) shows a view of the back surface of the FPC after soldering;

fig. 3 is a schematic diagram of an improved FPC according to an embodiment of the present invention, in which (a) shows a front view of the improved FPC, and (b) shows a back view of the improved FPC;

FIG. 4 is a schematic diagram illustrating a flux and an oxide drain removed by the flux according to an embodiment of the present invention;

FIG. 5 is a schematic diagram illustrating air venting provided by an embodiment of the present invention;

FIG. 6 is a schematic diagram illustrating an increased solder spreading capability according to an embodiment of the present invention;

FIG. 7 is a schematic view of a soldered FPC and a TO-can using the present invention, wherein (a) shows a schematic view of FPC + TO-can, (b) shows a schematic view of the soldered TO-can, and (c) shows a schematic view of the soldered back of the FPC.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

In order TO enable the copper-exposed area on the back surface of the FPC TO be completely tinned and enable the copper-exposed area TO be completely directly connected with the TO base, the technical scheme of the invention is as follows:

firstly, the solder wire is mainly composed of tin alloy and soldering flux. During welding, intermolecular bonds are formed between the soldering tin and the metal, and the two metal surfaces are connected together; the soldering flux is a substance with chemical and physical activity, can remove oxides on the surface of metal, can protect the surface of metal from being oxidized at high temperature, reduces the surface tension of molten tin, and promotes the dispersion and flowing energy functions of soldering tin.

Solder tin is required to flow around as much as possible, and the problem can be solved from two aspects, namely, a node is added at a position far away from a welding point and can play a role of pulling force to enlarge the dispersion range of the solder tin; secondly, oxides and air between the FPC and the TO-can removed by the soldering flux are removed from the middle part, and the resistance of soldering tin dispersion is reduced; therefore, the 25G optical module is specially processed on the FPC, as shown in fig. 3, wherein (a) in fig. 3 shows a front view of the FPC of the present invention, and (b) in fig. 3 shows a rear view of the FPC of the present invention.

As shown in fig. 3, the FPC of the present invention mainly includes the following contents:

1. four slotted holes are formed near the high-speed through holes of the FPC, and the hole walls of the slotted holes are metallized;

2. the distance between each slot hole and the high-speed through hole or the high-speed line is more than or equal to three times of the line width of the high-speed signal line;

3. the numbering holes 1 and 2 are horizontally arranged, and the numbering holes 3 and 4 are vertically arranged;

4. the slotted hole is an ellipse;

and 5, the back of the FPC high-speed signal via hole can not be provided with a metal bonding pad, and only the front is provided with the bonding pad.

In the embodiment of the present invention, the slot hole schematic diagram in fig. 3 is only one implementation manner of the present invention, and the method for designing a slot hole on an FPC of the present invention includes: the slots can be oval or round or square, the number of the slots can be 1/2/3/4/5 or more, the placement direction of the slots comprises any angle, the slots refer TO through holes which do not directly correspond TO pins of the TO-can, and the slots can be opened TO the whole area of the TO-can.

In the embodiment of the invention, the principle that the slotted holes can increase the solder dispersing capacity has three aspects:

1. the flux and the oxides removed by the flux flow in the direction of the arrows and can be discharged from the slots and collected in the central areas of the slots, thereby reducing the resistance to solder spreading, as shown in fig. 4;

air between the FPC and the TO-can base is exhausted from the slotted holes, so that the surface tension of the soldering tin is reduced, the wetting effect is increased, and the soldering tin can be diffused TO a farther place, as shown in FIG. 5;

3. when the soldering tin reaches the hole wall of the slot hole, the soldering tin can climb upwards along the hole wall, which is equivalent to that the soldering tin inside is pulled outwards by the action of external force, so that the capability of soldering tin diffusion is increased, as shown in fig. 6.

In the production process of 25G optical modules, special attention needs TO be paid TO the FPC design during welding, and the manufacturing process of welding the FPC and the TO-can is as follows:

1. the welding temperature of the electric iron is set to 350 ℃;

2. firstly, welding a grounding through hole in the middle of the FPC, heating a pin and a bonding pad at the grounding through hole by an electric soldering iron, enabling a tin wire to be close to the grounding pin, melting enough soldering tin at the pin, and removing the tin wire;

3. because the metal areas of the FPC and the TO-can are large, the heat dissipation is fast, the electric soldering iron needs TO be heated for about 10s in the whole process, and soldering tin can be seen from the diffusion positions of the walls of the four slotted holes;

4. slightly pressing the FPC by using tweezers, removing the electric soldering iron, and removing the tweezers after the tin to be soldered is solidified;

5. and then welding the high-speed signal pins, heating the pins and the bonding pad by using an electric iron, wrapping the whole pins by the tin to be welded, and removing the tin wire and the electric iron in sequence, wherein the time for welding each high-speed pin is only about 2 s.

The effect of soldering the FPC and the TO-can of the 25G optical module is shown in FIG. 7, wherein (a) in FIG. 7 shows a schematic diagram of FPC + TO-can, (b) in FIG. 7 shows a schematic diagram of the TO-can after soldering, and (c) in FIG. 7 shows a schematic diagram of the back side after soldering.

It should be noted that, according to the implementation requirement, each step/component described in the present application can be divided into more steps/components, and two or more steps/components or partial operations of the steps/components can be combined into new steps/components to achieve the purpose of the present invention.

It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims

1. A method for connecting a flexible board with an optical device is characterized in that the flexible board for connecting with the optical device comprises the following steps: the method comprises the following steps of forming a plurality of slots on a soft board, wherein each slot is a via hole which is not directly corresponding TO a pin of an optical device, the slots are formed in the TO-can whole surface area, and a plurality of slots are formed in a connecting area of the soft board and the optical device, so that the copper-exposed area on the back surface of the FPC can be completely coated with tin; the method comprises the following steps:

setting the welding temperature of the electric soldering iron;

welding the middle grounding via hole on the soft board, heating the pin and the bonding pad at the grounding via hole through an electric soldering iron, and then melting enough soldering tin at the grounding via hole through a tin wire so that the copper-exposed area on the back surface of the FPC can be completely soldered;

after the electric soldering iron is heated for a preset time, after soldering tin diffuses from the hole wall of each slotted hole, keeping the position of the soft board, moving away the electric soldering iron, and waiting for the soldering tin to solidify;

2. The connection method as claimed in claim 1, wherein the soldering temperature of the electric soldering iron is 350 ℃.

3. The method of claim 1, wherein the walls of each slot are metallized.

4. The connection method according to claim 1 or 3, wherein the distance from each slot to the high-speed via hole or the high-speed signal line on the flexible printed circuit board is equal to or greater than several times the line width of the high-speed signal line.

5. The method of claim 4, wherein the high speed vias of the flexible board have metal pads on the front side and no metal pads on the back side.

6. The method of joining according to claim 5 wherein each slot is oval, circular or square.