Optical module printed circuit board and preparation method thereof

Abstract

The invention discloses an optical module printed circuit board and a preparation method thereof. The invention aims to solve the problem of heat dissipation of the optical module under high-speed transmission. The method comprises the specific steps of firstly pressing a multilayer circuit board with a six-layer structure, then drilling a via hole in the circuit board, and then plating a layer of metal copper in the via hole; the via hole comprises a stratum heat dissipation hole and a device mounting hole, and finally, the stratum heat dissipation via hole in a heating device area is filled with copper paste; and forming a circuit pattern on the circuit board filled with the copper paste in the modes of dry film pasting, exposure, development and etching, and the like. According to the invention, a printed circuit board laminated structure is constructed, a heating device is embedded, and heat is conducted to a ground metal shell through an embedded copper block and copper column heat dissipation mode, so that the heat dissipation problem of the optical module under high-speed transmission is solved.

Description

Technical Field

[0001] The present invention relates to the field of circuit boards, and in particular to an optical module printed circuit board and a preparation method thereof. Background Art

[0002] As a core component of optical communication systems, optical modules perform the crucial function of converting optical and electrical signals. Their integrated lasers, photodetectors, fiber couplers, and high-density circuit boards work together to transmit information via the laser beam through optical fibers, where the photodetector converts the optical signal back into an electrical output. This energy conversion process is accompanied by significant thermal effects, particularly at high transmission rates. Device power consumption increases dramatically, leading to a rapid rise in operating temperature.

[0003] Ambient temperature and operating conditions have a dual impact on the thermal characteristics of optical modules. On the one hand, rising external temperatures directly exacerbate internal heat accumulation. On the other hand, to meet the demands of artificial intelligence and big data transmission, optical modules must operate continuously at ultra-high speeds (200Gbps and above per channel) such as QSFP-DD800. This creates a thermodynamic conflict between the quantum efficiency of photonic components and the signal integrity requirements of the circuit board. Existing heat dissipation solutions primarily manage heat through passive cooling structures (such as heat sinks and heat pipes) or active cooling systems (fans and TEC semiconductor cooling), while also employing strategies such as frequency reduction or low-power module substitution. However, these approaches have inherent limitations in balancing heat dissipation efficiency with transmission performance and power consumption, making them unable to meet the technological evolution requirements of future 800G and even 1.6T optical modules. Summary of the Invention

[0004] (1) Technical problems to be solved To address the shortcomings of the existing technology, the present invention provides an optical module printed circuit board and its preparation method. This invention utilizes a laminated printed circuit board structure, embeds the heat-generating device, and conducts heat to the underlying metal housing through embedded copper blocks and copper pillars, thereby solving the heat dissipation problem of optical modules at high transmission rates.

[0005] (2) Technical solution In order to overcome the above technical problems, the present invention provides such an optical module printed circuit board; A method for preparing an optical module printed circuit board comprises the following steps: S1: First, a 6-layer multi-layer circuit board is pressed together. Then, via holes are drilled on the circuit board and a layer of metal copper is plated in the via holes. The via holes include the ground heat dissipation holes and the device mounting holes. Finally, the ground heat dissipation via holes in the heat-generating device area are filled with copper paste. S2: Forming circuit patterns on the copper paste-filled circuit board by applying dry film, exposing, developing, and etching; S3: Afterwards, the non-optical module plug-in area is covered with selective ink, and the exposed plug-in gold fingers are electroplated with thick gold; S4: Afterwards, the selective ink on the circuit board is removed and washed, and the selective ink is printed again; S5: Apply solder mask ink on both sides of the circuit board, and expose the pads inside the board through exposure and development. Then, mark the device text on both sides of the circuit board through character printing. S6: Apply a selective dry film on the printed circuit board, and expose and develop the circuit pads corresponding to the ground heat dissipation holes in the heating device area on the bottom surface of the circuit board; S7: The exposed thermal via pads are plated with copper to a thickness of 150 μm by pattern electroplating. S8: Remove the dry film on both sides of the circuit board and install the components in the heating component area on the top surface of the circuit board; S9: The top and bottom FR-4 substrates with the heat-generating device areas hollowed out in advance are stacked and positioned through the peripheral positioning holes of the circuit board, and pressed together with pure epoxy resin to form a whole; S10: Fill the FR-4 hollow area on the bottom surface of the circuit board with a copper block, which will contact the ground heat dissipation hole pad of the heating device; use copper paste to fill it and pre-cure it; S11: Fill the device mounting area on the top layer of the circuit board with heat dissipation resin and cure it; S12: The copper surface of the circuit board with the top layer filled with thermal conductive resin and the bottom layer filled with copper paste is polished with ceramic to make the filling material level with the board surface; S13: Apply dry film on both sides of the circuit board and use the principles of exposure, development, and etching to create circuit patterns; S14: Laminating another FR-4 substrate on the circuit board with graphics on both sides; S15: Processing a blind hole in the buried copper block area by laser; then filling the laser blind hole by hole-filling electroplating; S16: Complete the solder mask, text and gold production of the circuit board; S17: Control the depth of the milling to expose the gold-plated gold fingers of the optical module on the inner layer; S18: The circuit board is formed, electrically tested, and FQC inspected.

[0006] (3) Beneficial effects This invention breaks through the traditional thermal design paradigm and innovatively reconstructs the printed circuit board (PCB) stackup architecture from the perspective of system-level thermal-electrical synergy optimization. By constructing an anisotropic thermal conductive dielectric layer, embedded heat sinks, and embedded device structures, it establishes a highly efficient heat conduction path while maintaining signal integrity. This provides an innovative solution with excellent thermal and electrical performance for next-generation high-density optical interconnect systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 This is a schematic diagram of the structure of the printed circuit board of the optical module of the present invention. DETAILED DESCRIPTION

[0008] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the technical solutions in the specific implementation methods of the present invention are clearly and completely described below to further illustrate the present invention. Obviously, the specific implementation methods described are only part of the implementation methods of the present invention, rather than all styles.

[0009] A method for preparing an optical module printed circuit board comprises the following steps: S1: A six-layer multilayer PCB is first laminated. Vias are then drilled and plated with copper. These vias include ground-layer heat dissipation holes and component mounting holes. Finally, the ground-layer heat dissipation vias in the heat-generating component area are filled with copper paste.

[0010] S2: Forming circuit patterns on the copper paste-filled circuit board by applying dry film, exposing, developing, and etching.

[0011] S3: Thereafter, the non-optical module plug-in area is covered with selective ink, and the exposed plug-in gold fingers are electroplated with thick gold.

[0012] S4: Afterwards, the selective ink on the circuit board is removed and washed, and the selective ink is printed again. The function of this ink is to protect the position of the non-electro-gold lead in the circuit board, thereby facilitating the etching of the gold finger electro-gold lead.

[0013] S5: Solder mask ink is applied to both sides of the circuit board, and the pads are exposed through exposure and development. The device text is then marked on both sides of the circuit board through character printing.

[0014] S6: On the printed circuit board, apply a selective dry film, and expose and develop the circuit pads corresponding to the ground heat dissipation holes in the heating device area on the bottom surface of the circuit board.

[0015] S7: The exposed thermal via pads are plated with copper to a thickness of 150μm by graphic electroplating.

[0016] S8: Remove the dry film on both sides of the circuit board and install components in the heating component area on the top surface of the circuit board.

[0017] S9: The top and bottom surfaces of the FR-4 substrate with the heat-generating device area hollowed out in advance are stacked and positioned through the peripheral positioning holes of the circuit board, and pressed together with pure epoxy resin to form a whole.

[0018] S10: Fill the FR-4 hollow area on the bottom surface of the circuit board with copper blocks. This copper block will contact the ground layer heat dissipation hole pad of the heat generating device. Use copper paste to fill and pre-cure.

[0019] S11: Fill the device mounting area on the top layer of the circuit board with heat dissipation resin and cure it.

[0020] S12: For a circuit board with a top layer filled with thermal conductive resin and a bottom layer filled with copper paste, use ceramic to polish the copper surface so that the filling is level with the board surface.

[0021] S13: Further, dry films are applied to both sides of the circuit board, and circuit patterns are formed using the principles of exposure, development, and etching.

[0022] S14: Press another FR-4 substrate onto the circuit board with graphics on both sides.

[0023] S15: Laser blind hole processing is performed in the buried copper block area. The laser blind hole is then filled and leveled by hole-filling electroplating.

[0024] S16: Complete the solder mask, text and gold production of the circuit board.

[0025] S17: Control the depth of milling to expose the gold-plated gold fingers of the inner layer of the optical module.

[0026] S18: The circuit board is formed, electrically tested, and FQC inspected to complete the circuit board.

[0027] Below, the detailed steps of the invention are described.

[0028] First, two FR-4 substrates are prepared, with the thickness tailored to the customer's desired finished board thickness. The inner layer circuitry is then fabricated on these FR-4 substrates. A six-layer board is then stacked and pressed together. The stacking order is: copper foil - prepreg - first FR-4 substrate - prepreg - second FR-4 substrate - prepreg - copper foil.

[0029] After the six-layer substrate is laminated, through-holes are drilled and electroplated with copper. These through-holes include component mounting holes, substrate heat dissipation holes, and vias. Copper paste is then added to the substrate heat dissipation holes. After the copper paste is added, the copper surface is leveled by curing and polishing.

[0030] After polishing, the single-sided copper thickness is about 50μm.

[0031] Furthermore, circuit patterns are made on the front and back of the circuit substrate filled with copper paste. The patterns include SMD patch pads, bonding gold wire pads, optical module gold finger plug-in pads, etc. The process is as follows: Pretreatment - dry film application - exposure - development - etching.

[0032] The process is the conventional process for circuit board production and will not be repeated here.

[0033] Furthermore, a selective dry film is applied to the pattern area of ​​the optical module, and the gold finger plug pads of the optical module are exposed through exposure and development, and then thick gold is electroplated on the exposed area through gold electroplating.

[0034] The thickness of the gold plating is specified by the customer, but the maximum does not exceed 30u" Furthermore, after the gold plating is completed, the selective dry film on the circuit board is stripped and washed, and the selective ink is printed again. The function of the ink is to protect the non-gold lead position in the circuit board, thereby facilitating the etching of the gold finger gold lead.

[0035] Electroplated gold leads are connecting wires added between graphics on the board, making the graphic circuits a single electrical network. When thick gold plating is applied, current can flow through the connecting wires of different electrical networks, causing the exposed optical module gold finger plug-in pads to be plated with thick gold. Therefore, after thick gold plating, these connecting wires need to be removed again to prevent electrical shorts.

[0036] Furthermore, solder mask ink is applied on both sides of the pattern, and the pads inside the board are exposed through exposure and development. Then, the device characters are marked on both sides of the circuit board through text printing.

[0037] Solder mask ink and text are only printed on the gold finger plug-in area of ​​the optical module.

[0038] Furthermore, a selective dry film is applied to the printed circuit board, and the circuit pads corresponding to the ground heat dissipation holes in the heating device area on the bottom surface of the circuit board are exposed through exposure and development.

[0039] Ground heat dissipation holes refer to holes plugged with ground copper paste.

[0040] Furthermore, the exposed circuit pads are copper plated by pattern copper electroplating, and the copper thickness reaches 150μm.

[0041] The main function of this step is to enable the exposed copper pad to contact with its copper block, and to increase the side contact area after the copper paste is subsequently filled.

[0042] Furthermore, the dry films on both sides of the circuit board are removed and components are installed in the heating component area on the top surface of the circuit board.

[0043] The device installation includes but is not limited to gold wire bonding and chip packaging.

[0044] At this point, the effect presented by the circuit board is that there are heating devices in the top device packaging area, and the copper pads in the bottom heating area are about 100μm higher than the board surface; except for the ink in the device area, the other exposed areas are copper surfaces and wires.

[0045] Furthermore, two 1.5mm FR-4 core boards are prepared. Positioning holes are first drilled on the edges of the core boards. The coordinates of the positioning holes are consistent with the positioning holes of the packaged components, which is convenient for positioning.

[0046] Secondly, through the positioning holes on the edge of the board, the circuit pattern on one side is made by applying dry film, exposing, developing and etching.

[0047] One-sided circuit pattern means that when stacking, the circuit pattern is made on the side close to the middle layer substrate, and the other side retains the large copper surface.

[0048] Furthermore, two 1.5 mm FR-4 substrates are hollowed out in the device packaging area.

[0049] At the same time, prepare 50μm thick epoxy resin AD pure glue, and use a laser cutting machine to hollow out the device packaging area and the optical module gold finger plug-in area. The positioning points of the hollowed areas are consistent with the circuit board substrate.

[0050] Furthermore, two 1.5mm substrates were placed on the upper and lower sides of the middle layer circuit board, with AD pure glue placed in the middle.

[0051] The circuit board is pressed together by fast pressing, and the fast pressing time is 2 minutes.

[0052] Furthermore, the printed circuit board is baked at 75°C for 1 hour.

[0053] Furthermore, the circuit board after being baked for 1 hour was fast pressed again for 3 minutes.

[0054] Furthermore, the printed circuit board is baked again at 75°C for 3 hours.

[0055] Furthermore, the device packaging area of ​​the circuit board is filled with resin, and then baked at a low temperature of 75°C*2H, and the resin is polished and smoothed using a ceramic polisher.

[0056] Furthermore, a copper block is filled on the reverse side of the packaging area of ​​the circuit board. The thickness of the copper block is 1.3 mm. After filling, the bottom of the copper block is about 0.05 mm below the board surface.

[0057] Furthermore, copper paste is filled in the copper block filling area to conduct the copper paste with the copper block and the ground heat dissipation pad, thereby forming an integrated buried copper heat dissipation area.

[0058] Furthermore, after baking at a low temperature of 75℃*2H, the copper surface is polished with ceramic polishing equipment to ensure the flatness and smoothness of the copper surface.

[0059] Furthermore, circuit patterns are made on both sides of the circuit board by applying dry film, exposing, developing and etching.

[0060] Furthermore, two 0.05 mm thick FR-4 substrates were prepared, and copper on one side was etched away by single-sided etching, while the copper on the other side was retained.

[0061] Furthermore, a positioning hole is drilled on the single-sided copper foil substrate, and the zero point of the positioning hole is consistent with the previous positioning hole.

[0062] Furthermore, a single-sided copper foil FR-4 substrate and a copper-free stacked layer midplane were bonded by quick press bonding using 50 μm thick epoxy resin AD pure glue in the middle.

[0063] Furthermore, a laser is used to drill holes with a diameter of 0.15 mm on the buried copper block surface of the circuit board. The holes touch the inner copper block, thereby forming heat dissipation holes in the ground layer.

[0064] Furthermore, through holes are drilled on the circuit board, copper is electroplated in the holes, outer layer graphics are produced, solder mask ink is printed, characters are printed, and gold is produced.

[0065] Furthermore, the depth of the gold finger area of ​​the optical module is controlled by depth-controlled milling. Since the AD pure glue in this area is hollowed out in advance during fast pressing, the gold finger can be exposed after depth control.

[0066] Furthermore, the circuit board is subjected to post-processing such as molding, electrical testing, and appearance inspection.

[0067] The above describes the main technical features and basic principles of the present invention and the related advantages. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments and that the present invention can be implemented in other specific forms without departing from the concept or essential characteristics of the present invention. Therefore, from all perspectives, the above-mentioned specific embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the appended claims rather than the foregoing description, and it is intended that all changes that come within the meaning and range of equivalents of the claims be included within the present invention.

[0068] In addition, it should be understood that although this specification is described according to various implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each implementation method can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for preparing an optical module printed circuit board, characterized in that: The following steps are involved: S1: First, a 6-layer multi-layer circuit board is pressed together. Then, via holes are drilled on the circuit board and a layer of metal copper is plated in the via holes. The via holes include the ground heat dissipation holes and the device mounting holes. Finally, the ground heat dissipation via holes in the heat-generating device area are filled with copper paste. S2: Forming circuit patterns on the copper paste-filled circuit board by applying dry film, exposing, developing, and etching; S3: Afterwards, the non-optical module plug-in area is covered with selective ink, and the exposed plug-in gold fingers are electroplated with thick gold; S4: Afterwards, the selective ink on the circuit board is removed and washed, and the selective ink is printed again; S5: Apply solder mask ink on both sides of the circuit board, and expose the pads inside the board through exposure and development. Then, mark the device text on both sides of the circuit board through character printing. S6: Apply a selective dry film on the printed circuit board, and expose and develop the circuit pads corresponding to the ground heat dissipation holes in the heating device area on the bottom surface of the circuit board; S7: The exposed thermal via pads are plated with copper to a thickness of 150 μm by pattern electroplating. S8: Remove the dry film on both sides of the circuit board and install the components in the heating component area on the top surface of the circuit board; S9: The top and bottom surfaces of the FR-4 substrate with the heat-generating device area hollowed out in advance are stacked and positioned through the peripheral positioning holes of the circuit board, and pressed together with pure epoxy resin to form a whole.

2. The method for preparing an optical module printed circuit board according to claim 1, wherein: Also included are: S10: Fill the FR-4 hollow area on the bottom surface of the circuit board with a copper block, which will contact the ground heat dissipation hole pad of the heating device; use copper paste to fill it and pre-cure it; S11: Fill the device mounting area on the top layer of the circuit board with heat dissipation resin and cure it.

3. The method for preparing an optical module printed circuit board according to claim 2, wherein: Also included are: S12: For a circuit board with a top layer filled with thermal conductive resin and a bottom layer filled with copper paste, use ceramic to polish the copper surface so that the filling is level with the board surface.

4. The method for preparing an optical module printed circuit board according to claim 3, wherein: Also included are: S13: Apply dry film on both sides of the circuit board and use the principles of exposure, development, and etching to create circuit patterns.

5. The method for preparing an optical module printed circuit board according to claim 4, wherein: Also included are: S14: Press another FR-4 substrate onto the circuit board with graphics on both sides.

6. The method for preparing an optical module printed circuit board according to claim 5, wherein: Also included are: S15: Processing a blind hole in the buried copper block area by laser; then filling the laser blind hole by hole-filling electroplating.

7. The method for preparing an optical module printed circuit board according to claim 6, wherein: Also included are: S16: Complete the solder mask, text and gold production of the circuit board.

8. The method for preparing an optical module printed circuit board according to claim 7, wherein: The process also includes: S17: controlling the depth of the milling to expose the gold fingers of the optical module that have been electroplated with gold on the inner layer.

9. The method for preparing an optical module printed circuit board according to claim 8, wherein: It also includes: S18: forming, electrical testing and FQC inspection of the circuit board.

10. An optical module printed circuit board, manufactured by the method for manufacturing an optical module printed circuit board according to claim 9.

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