WO2020177436A1

WO2020177436A1 - Multilayer fpc

Info

Publication number: WO2020177436A1
Application number: PCT/CN2019/125269
Authority: WO
Inventors: 吴杨; 张玉安
Original assignee: 武汉光迅科技股份有限公司
Priority date: 2019-03-07
Filing date: 2019-12-13
Publication date: 2020-09-10
Also published as: CN109819584A; CN109819584B

Abstract

A multilayer FPC. The multilayer FPC is provided with an RF high-speed signal layer (1), a GND reference layer (2) and a DC control signal layer (3), the RF high-speed signal layer being used to transmit an RF high-speed signal, the DC control signal layer being used to transmit a DC control signal, the GND reference layer being used as a reference ground for the RF high-speed signal layer and isolating the interference on the RF high-speed signal from the DC control signal. The multilayer FPC can satisfy the transmission requirements of both the RF high-speed signal and the DC control signal, and can effectively reduce connection processing procedures of a module PCB and an optical device, facilitating the reduction of the size of the optical module. Moreover, the multilayer FPC performs impedance matching design on an RF high-speed signal metalized via hole, realizing impedance matching of the RF high-speed signal at a joint of bonding pads, and improving the transmission quality of the RF high-speed signal.

Description

A multi-layer FPC

【Technical Field】

The invention relates to the technical field of optical communication high-speed signal transmission, in particular to a multilayer FPC.

【Background technique】

Since its inception, FPC (Flexible Printed Circuit, abbreviated as FPC) has been widely used in electronics, electrical appliances, automobiles, and medical products due to its advantages of lightness, flexibility, small footprint, and high bending freedom. Especially in the field of optical communication, under the requirements of miniaturization, high integration and high speed of optoelectronic devices and optoelectronic modules, the application of FPC is increasing, and higher density and high reliability of FPC are also proposed. Claim.

At present, the integrated optical devices that conventionally use BOX hermetically sealed packaging use two FPCs to respectively transmit radio frequency (Radio Frequency, abbreviated as RF) high-speed signals and direct current DC control (Direct Current, abbreviated as DC) signals, on the module printed circuit board PCB (Printed Circuit Board, abbreviated as PCB) and both ends of the optical device need to design two pads to connect to RF_FPC and DC_FPC respectively, which are used to transmit RF high-speed signals and DC control signals, so that the module PCB and optical devices are not connected tightly. Long links are not conducive to improving work efficiency.

In view of this, overcoming the defects of the prior art is a problem to be solved in the technical field.

[Content of the invention]

The technical problem to be solved by the present invention is to solve the problem that the integrated optical device of the BOX hermetically sealed package in the prior art adopts two FPCs to transmit RF high-speed signals and DC control signals and respectively connect with the module PCB and the optical device, resulting in the failure of the module PCB and the optical device to connect. It is compact and has a long process link, which is not conducive to improving work efficiency.

The present invention adopts the following technical solutions:

In the first aspect, the present invention provides a multilayer FPC, including an RF high-speed signal layer 1, a GND reference layer 2 and a DC control signal layer 3;

The RF high-speed signal layer 1 is used to transmit RF high-speed signals;

The DC control signal layer 3 is used to transmit DC control signals;

The GND reference layer 2 is used as a reference ground for the RF high-speed signal, and to isolate the interference of the DC control signal to the RF high-speed signal, wherein the GND reference layer 2 is provided on the RF high-speed signal layer 1. And the DC control signal layer 3.

Preferably, the multilayer FPC further includes: a PCB substrate 4;

The RF high-speed signal layer 1 is provided on the first layer 41 of the PCB substrate 4, and the RF high-speed signal layer 1 includes at least one set of RF high-speed signal transmission lines 11;

The second layer 43 of the PCB substrate 4 is provided with the DC control signal layer 3, and the DC control signal layer 3 includes at least one set of DC control signal transmission lines 31;

The intermediate layer 42 of the PCB substrate 4 is provided with the GND reference layer 2;

Wherein, the intermediate layer 42 is arranged between the first layer 41 and the second layer 43.

Preferably, the second layer 43 is further provided with at least one set of RF high-speed signal leads 12 corresponding to the at least one set of RF high-speed signal transmission lines 11;

The connection positions of the at least one set of RF high-speed signal transmission lines 11 and the at least one set of RF high-speed signal leads 12 are provided with RF high-speed signal metallized vias 13;

One end of the at least one set of RF high-speed signal transmission lines 11 is arranged on the first pad 5 of the multilayer FPC, and the other end is arranged on the second pad 6 of the multilayer FPC.

Preferably, the diameter of the RF high-speed signal metallization via 13 is set according to a preset rule to achieve impedance matching of the RF high-speed signal at the pad connection.

Preferably, the diameter of the RF high-speed signal metallization via 13 is set according to a preset rule, which specifically includes:

According to Formula 1, the diameter of the RF high-speed signal metallization via 13 is determined. Formula 1 is specifically as follows:

Wherein, h is the thickness of the PCB substrate 4, and the value range of h is 0.01mm≤h≤0.4mm; D is the pad width of the RF high-speed signal lead 12; ε is the dielectric constant of the PCB substrate 4 ; D is the diameter of the RF high-speed signal metallization via 13.

Preferably, the first pad 5 is used to connect to the module PCB, and the second pad 6 is used to connect to an optical device.

Preferably, the first pad 5 located on the first layer 41 is connected to the pad of the module PCB;

The second pad 6 on the second layer 43 is connected with the pad of the optical device by lap welding or connected with the metal pin 7 by plug welding.

Preferably, the first layer 41 is further provided with at least one set of DC control signal leads 32 corresponding to the at least one set of DC control signal transmission lines 31;

The connection positions of the at least one set of DC control signal leads 32 and the at least one set of DC control signal transmission lines 31 are provided with DC control signal metallized vias 33.

Preferably, the projection of the GND reference layer 2 on the first layer 41 or the second layer 43 overlaps with the first layer 41 or the second layer 43.

Preferably, the at least one set of RF high-speed signal transmission lines 11 are single-ended transmission lines or differential transmission lines.

The multilayer FPC provided by the present invention is respectively provided with an RF high-speed signal layer, a GND reference layer and a DC control signal layer. The RF high-speed signal layer is used to transmit RF high-speed signals, the DC control signal layer is used to transmit DC control signals, and the GND reference layer is used It serves as the reference ground for the RF high-speed signal layer and isolates the interference of the DC control signal to the RF high-speed signal. The multilayer FPC provided by the present invention can simultaneously meet the transmission requirements of RF high-speed signals and DC control signals, can effectively reduce the connection process links between the module PCB and the optical device, and is beneficial to reducing the size of the optical module.

Further, the multi-layer FPC provided by the present invention implements impedance matching design for the RF high-speed signal metallized via to achieve impedance matching of the RF high-speed signal at the pad connection, thereby improving the transmission quality of the RF high-speed signal.

Furthermore, the two ends of at least one RF high-speed signal transmission line of the RF high-speed signal layer in the present invention are respectively connected to the module PCB and the optical device. During the transmission of the RF high-speed signal from the module PCB to the optical device, the RF high-speed signal does not change layers. The transmission avoids the parasitic capacitive reactance and parasitic inductance effects of the RF high-speed signal passing through the RF high-speed signal metallized via-to-layer transmission, and improves the integrity of the RF high-speed signal.

【Explanation of drawings】

In order to explain the technical solutions of the embodiments of the present invention more clearly, the following will briefly introduce the drawings that need to be used in the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work.

FIG. 1 is a schematic diagram of a signal layer stack of a multilayer FPC provided by Embodiment 1 of the present invention;

FIG. 2 is a bottom view of a multilayer FPC provided by Embodiment 1 of the present invention;

Figure 3 is an A-A cross-sectional view of the multilayer FPC provided in Figure 2;

Figure 4 is a B-B cross-sectional view of the multilayer FPC provided in Figure 2;

FIG. 5 is a top view of a multilayer FPC provided by Embodiment 1 of the present invention;

6 is a schematic diagram of the positions of the first pad and the second pad of the multilayer FPC provided by the first embodiment of the present invention;

7 is a schematic diagram of a multilayer FPC and an optical device provided by the first embodiment of the present invention connected by plug-welding with metal pins;

FIG. 8 is a schematic diagram of an RF high-speed signal metallized via of a multilayer FPC provided by the first embodiment of the present invention;

9 is a schematic diagram of the structure of the GND reference layer of the multilayer FPC provided by the first embodiment of the present invention;

FIG. 10 is another top view of the multilayer FPC provided by the first embodiment of the present invention;

Fig. 11 is a C-C cross-sectional view of the multilayer FPC provided in Fig. 10.

【detailed description】

In order to make the objectives, technical solutions, and advantages of the present invention clearer, the following further describes the present invention in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, but not to limit the present invention.

In the description of the present invention, the terms "inner", "outer", "longitudinal", "horizontal", "upper", "lower", "top", "bottom", etc. indicate the orientation or positional relationship based on the accompanying drawings. The orientation or positional relationship shown is only for the convenience of describing the present invention and does not require that the present invention must be constructed and operated in a specific orientation, so it should not be understood as a limitation to the present invention.

In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

Example one:

The first embodiment of the present invention provides a multilayer FPC, referring to FIG. 1, including an RF high-speed signal layer 1, a GND reference layer 2 and a DC control signal layer 3;

The RF high-speed signal layer 1 is used to transmit RF high-speed signals;

The DC control signal layer 3 is used to transmit DC control signals;

The GND reference layer 2 is used as the reference ground of the RF high-speed signal layer 1, and to isolate the interference of the DC control signal on the RF high-speed signal, wherein the GND reference layer 2 is set on the RF high-speed signal Between layer 1 and the DC control signal layer 3.

The multilayer FPC provided in the first embodiment of the present invention is respectively provided with an RF high-speed signal layer, a GND reference layer, and a DC control signal layer. The RF high-speed signal layer is used to transmit RF high-speed signals, and the DC control signal layer is used to transmit DC control signals. The reference layer is used as the reference ground of the RF high-speed signal layer and isolates the interference of the DC control signal to the RF high-speed signal. The multilayer FPC provided by the present invention can simultaneously meet the transmission requirements of RF high-speed signals and DC control signals, can effectively reduce the connection process links between the module PCB and the optical device, and is beneficial to reducing the size of the optical module.

With reference to the first embodiment of the present invention, referring to FIGS. 2 to 5, in order to fully disclose the multilayer FPC provided in the first embodiment of the present invention, the structure of the multilayer FPC is now described. The multi-layer FPC also includes a PCB substrate 4. The board of the PCB substrate 4 has a first layer 41 and a second layer 43. There is an intermediate layer 42 between the first layer 41 and the second layer 43, wherein the RF high-speed signal layer 1 is provided On the first layer 41, the DC control signal layer 3 is provided on the second layer 43, and the GND reference layer 2 is provided on the intermediate layer 42.

When the multi-layer FPC is placed parallel to the horizontal plane, the PCB substrate 4 can be the first layer 41, the middle layer 42, and the second layer 43 from bottom to top, or the PCB substrate 4 can be the second layer 43 from bottom to top. , The intermediate layer 42 and the first layer 41, those skilled in the art may know that the first layer 41 and the second layer 43 are only used to distinguish each other, and are not used to limit the first layer 41 and the second layer 43 to be in a specific position.

An RF high-speed signal layer 1 is provided on the first layer 41 of the PCB substrate 4. The RF high-speed signal layer 1 includes at least one set of RF high-speed signal transmission lines 11, and the second layer 43 is also provided with at least one set of RF high-speed signal transmission lines 11 Correspondingly, at least one set of RF high-speed signal leads 12, at least one set of RF high-speed signal transmission lines 11 and at least one set of RF high-speed signal leads 12 are provided with RF high-speed signal metallized vias 13 at the connection positions. In an optional technical solution, at one end of a set of RF high-speed signal transmission lines 11, two RF high-speed signal metallized vias 13 are provided at the connection position between the RF high-speed signal transmission line 11 and the RF high-speed signal lead 12, wherein RF The high-speed signal metallization via 13 penetrates the PCB substrate 4.

A DC control signal layer 3 is provided on the second layer 43 of the PCB substrate 4. The DC control signal layer 3 includes at least one set of DC control signal transmission lines 31, and the first layer 41 is also provided with at least one set of DC control signal transmission lines At least one set of DC control signal leads 32 corresponding to 31, and the connection positions between the at least one set of DC control signal leads 32 and the at least one set of DC control signal transmission lines 31 are provided with DC control signal metal vias 33. In an optional technical solution, at one end of a set of DC control signal transmission lines 31, two DC control signal metallized vias 33 are provided at the connection position between the DC control signal transmission line 31 and the DC control signal lead 32, wherein the DC control signal The signal metallization via 33 penetrates the PCB substrate 4.

In conjunction with Embodiment 1 of the present invention, referring to Figures 2 and 5, the RF high-speed signal layer 1 and the DC control signal layer 3 are respectively arranged on the first layer 41 and the second layer 43 on the PCB substrate 4, and the RF high-speed signal transmission line 11 and the DC control signal lead 32 are sequentially arranged on the first layer 41 at intervals, and the RF high-speed signal lead 12 and the DC control signal transmission line 31 are sequentially arranged on the second layer 43 at intervals.

With reference to the first embodiment of the present invention, in an optional technical solution, the RF high-speed signal layer 1 includes n groups of RF high-speed signal transmission lines 11, and n has a value of 1≤n≤16, where n is a positive integer. In the first embodiment of the present invention, Here, the description is made by taking four sets of RF high-speed signal transmission lines 11 as an example. In an optional technical solution, the RF high-speed signal transmission line 11 is a single-ended transmission line or a differential transmission line.

With reference to the first embodiment of the present invention, refer to Figures 6 to 7, in order to illustrate that the multilayer FPC provided in the first embodiment of the present invention can reduce the connection process between the module PCB and the optical device, and is beneficial to reduce the size of the optical module. The connection method with the module PCB and the multilayer FPC and the optical device will be explained. Since the multilayer FPC provided in the first embodiment of the present invention can transmit RF high-speed signals and DC control signals at the same time, the connection process links between the multilayer FPC and the module PCB and the optical device can be reduced, and the size of the optical module can be reduced. Still taking the four sets of RF high-speed signal transmission lines 11 arranged on the first layer 41 as an example, one end of the four sets of high-speed signal transmission lines 11 is set on the first pad 5 of the multilayer FPC, and the other end is set on the first pad 5 of the multilayer FPC. On the two bonding pads 6, the first bonding pad 5 is used for connecting the module PCB, and the second bonding pad 6 is used for connecting the optical device.

With reference to Embodiment 1 of the present invention, in an optional technical solution, the first pad 5 is a module PCB connection pad, and the second pad 6 is a transmitting/receiving pad. The multi-layer FPC is connected to the module PCB by lap welding through the module PCB connection pad, and is connected to the electrical interface pad of the ceramic shell of the optical device through the transmitting/receiving pad or the metal pin 7 by plug welding. The four sets of RF high-speed signal transmission lines 11 are connected to the RF high-speed signal pins of the optical device through the transmitting/receiving pads, and the DC control signal lead 32 is connected to the DC control signal pins of the optical device through the transmitting/receiving pads.

With reference to the first embodiment of the present invention, in a preferred technical solution, the first pad 5 located on the first layer 41 is connected to the pad of the module PCB, and the second pad 6 located on the first layer 41 is connected to the optical device. , RF high-speed signal layer 1 transmits RF high-speed signals through the first layer 41. RF high-speed signals do not pass through RF high-speed signal metallization vias 13 in the transmission link between the module PCB and the optical device. The influence of parasitic capacitive reactance and parasitic inductance generated by signal via-to-layer exchange transmission improves the integrity of RF high-speed signals. In a specific implementation, when the module PCB and the optical device are located above the multilayer FPC, the multilayer FPC from top to bottom is the RF high-speed signal layer 1, the GND reference layer 2, and the DC control signal layer 3, and the RF high-speed signal layer 1 It is directly connected to the module PCB and the optical device to avoid the influence of parasitic capacitive reactance and parasitic inductance caused by the transmission of RF high-speed signal via vias. In another specific embodiment, when the module PCB and optical device are located in a multilayer FPC Below is the multi-layer FPC, from top to bottom, the DC control signal layer 3, the GND reference layer 2 and the RF high-speed signal layer 1. The RF high-speed signal layer 1 is directly connected to the module PCB and optical components to avoid RF high-speed signal vias. The influence of parasitic capacitive reactance and parasitic inductance generated by layer-changing transmission

With reference to the first embodiment of the present invention, it can be known that the RF high-speed signal layer 1 located on the first layer 41 is connected to the module PCB and the optical device through the first pad 5 and the second pad 6 respectively, and directly transmits the RF high-speed signal without passing through RF high-speed signal metallized vias change layer to transmit RF high-speed signals. It can also be known that the DC control signal of the DC control signal layer 3 in the second layer 43 is transferred from the first layer 41 to the second layer 43 for transmission.

With reference to the first embodiment of the present invention, referring to Figures 3 and 8, in order to achieve impedance matching of RF high-speed signals at the pad connection, the impedance matching design of the diameter size of the RF high-speed signal metallized via 13 of the multilayer FPC is now explained . Still taking the four sets of RF high-speed signal transmission lines 11 arranged on the first layer 41 as an example, four sets of RF high-speed signal leads 12, RF high-speed signal transmission lines 11 and RF high-speed signal are correspondingly arranged on the second layer 43 of the PCB substrate 4. An RF high-speed signal metallization via 13 is provided at the connection position between the leads 12. By setting the diameter of the RF high-speed signal metallization via 13 according to preset rules, the capacitive reactance and inductance of the RF high-speed signal metallization via 13 The resistance to generate a resonance in the RF high-speed signal transmission frequency band is equivalent to the band-pass transmission of RF high-speed signals in this frequency band. RF high-speed signals are transmitted almost losslessly, which can effectively improve the transmission quality of RF high-speed signals.

In conjunction with the first embodiment of the present invention, in a specific implementation, the RF high-speed signal transmission frequency band is: input return loss S11<-40dB, gain S21<-0.1dB, and 4 sets of RF high-speed signal transmission lines 11 transmit RF high-speed signals The rate is 25Gbit/s; the PCB substrate 4 uses Dupont Pyralux AP8525R, the dielectric constant ε of the PCB substrate 4 is 3.4, the loss tangent of the PCB substrate 4 is 0.002, and the thickness of the first layer 41 to the middle layer 42 is 0.05 mm, the thickness of the plate from the middle layer 42 to the second layer 43 is 0.05 mm, so the thickness h of the PCB substrate 4 is 0.10 mm, and the pad width D of the RF high-speed signal lead 12 is 0.25 mm.

Determine the diameter of the RF high-speed signal metallization via 13 according to formula 1. The specific formula of formula 1 is as follows:

Wherein, h is the thickness of the PCB substrate 4, and the value range of h is 0.01mm≤h≤0.4mm; D is the pad width of the RF high-speed signal lead 12; ε is the dielectric constant of the PCB substrate 4 D is the diameter of the RF high-speed signal metallization via 4.

According to the dielectric constant ε of the PCB substrate 4, the thickness h of the PCB substrate 4, and the pad width D of the RF high-speed signal lead 12 provided above, the diameter d of the RF high-speed signal metallization via 13 is 0.125mm. The diameter size and accuracy of the RF high-speed signal metallized via 13 are within the production process range of the FPC plate maker.

With reference to the first embodiment of the present invention, referring to FIG. 9, the implementation of the GND reference layer will be described. The GND reference layer 2 is used as the reference ground of the RF high-speed signal, and at the same time plays a role in isolating the interference of the DC control signal from the RF high-speed signal. The GND reference layer 2 is arranged on the RF high-speed signal layer 1 and the DC control signal. Between signal layer 3.

The projection of the GND reference layer 2 on the first layer 41 or the second layer 43 shown in FIG. 9 overlaps the first layer 41 or the second layer 43, wherein the GND reference layer 2 is Flake structure. The GND reference layer 2 shown in FIG. 9 can effectively isolate the interference of the DC control signal on the RF high-speed signal, and the GND reference layer 2 of the chip structure is less difficult to manufacture.

In combination with the first embodiment of the present invention, there is no electrical connection between the GND reference layer 2 and the RF high-speed signal layer 1 and the DC control signal layer 3. In order to make the GND reference layer 2 electrically connect with the external circuit, refer to Figures 10 and 11, In an optional technical solution, part of the pads of the DC control signal transmission line 31 of the DC control signal layer 3 are defined as the connection pads 21 of the GND reference layer 2. The GND reference layer 2 is welded through the line where the part of the DC control signal transmission line 31 is located. The disk is connected to an external circuit.

The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modification, equivalent replacement and improvement made within the spirit and principle of the present invention shall be included in the protection of the present invention. Within range.

Claims

A multilayer FPC, which is characterized by comprising: an RF high-speed signal layer (1), a GND reference layer (2) and a DC control signal layer (3);

The RF high-speed signal layer (1) is used to transmit RF high-speed signals;

The DC control signal layer (3) is used to transmit DC control signals;

The GND reference layer (2) is used as a reference ground for the RF high-speed signal, and to isolate the interference of the DC control signal on the RF high-speed signal, wherein the GND reference layer (2) is set on the RF Between the high-speed signal layer (1) and the DC control signal layer (3).
The multi-layer FPC according to claim 1, wherein the multi-layer FPC further comprises: a PCB substrate (4);

The RF high-speed signal layer (1) is provided on the first layer (41) of the PCB substrate (4), and the RF high-speed signal layer (1) includes at least one set of RF high-speed signal transmission lines (11);

The second layer (43) of the PCB substrate (4) is provided with the DC control signal layer (3), and the DC control signal layer (3) includes at least one set of DC control signal transmission lines (31);

The intermediate layer (42) of the PCB substrate (4) is provided with the GND reference layer (2);

Wherein, the intermediate layer (42) is arranged between the first layer (41) and the second layer (43).
The multilayer FPC according to claim 2, wherein the second layer (43) is further provided with at least one set of RF high-speed signal leads (12) corresponding to the at least one set of RF high-speed signal transmission lines (11). );

The connection positions of the at least one set of RF high-speed signal transmission lines (11) and the at least one set of RF high-speed signal leads (12) are provided with RF high-speed signal metallized vias (13);

One end of the at least one set of RF high-speed signal transmission lines (11) is arranged on the first pad (5) of the multilayer FPC, and the other end is arranged on the second pad (6) of the multilayer FPC.
The multilayer FPC according to claim 3, wherein the diameter of the RF high-speed signal metallization via (13) is set according to a preset rule to achieve impedance matching of the RF high-speed signal at the pad connection.
The multilayer FPC according to claim 4, wherein the diameter of the RF high-speed signal metallization via (13) is set according to a preset rule, which specifically includes:

According to Formula 1, the diameter of the RF high-speed signal metallization via (13) is determined. Formula 1 is specifically as follows:

Wherein, h is the thickness of the PCB substrate (4), and the value range of h is 0.01mm≤h≤0.4mm; D is the pad width of the RF high-speed signal lead 12; ε is the PCB substrate (4) The dielectric constant; d is the diameter of the RF high-speed signal metallization via (13).
The multilayer FPC according to claim 3, characterized in that the first pad (5) is used to connect the module PCB, and the second pad (6) is used to connect an optical device.
The multilayer FPC according to claim 6, wherein the first pad (5) located on the first layer (41) is connected to the pad of the module PCB;

The second pad (6) located on the second layer (43) is connected with the pad of the optical device by lap welding or connected with the metal pin (7) by plug welding.
The multilayer FPC according to claim 7, wherein the first layer (41) is also provided with at least one set of DC control signal leads (32) corresponding to the at least one set of DC control signal transmission lines (31). );

The connection positions of the at least one set of DC control signal leads (32) and the at least one set of DC control signal transmission lines (31) are provided with DC control signal metallization vias (33).
The multilayer FPC according to claim 3, characterized in that the projection of the GND reference layer (2) on the first layer (41) or the second layer (43) is the same as the projection of the first layer ( 41) or the second layer (43) overlaps.
The multilayer FPC according to claim 2, wherein the at least one set of RF high-speed signal transmission lines (11) are single-ended transmission lines or differential transmission lines.