Optical module printed circuit board and method of manufacturing the same

Abstract

The application discloses an optical module printed circuit board and a preparation method thereof. The method is used for solving the heat dissipation of the optical module under high-speed transmission. The specific steps of the method are as follows: firstly, a 6-layer structure multilayer circuit board is pressed; then, a through hole is drilled on the circuit board; subsequently, a layer of metal copper is plated in the through hole; the through hole comprises a ground layer heat dissipation hole and a device mounting hole; finally, copper paste is filled in the ground layer heat dissipation through hole of the heating device area; and the circuit board with the filled copper paste is subjected to the steps of dry film pasting, exposure, development and etching to form a circuit pattern. The heating device is embedded by constructing a printed circuit board laminated structure, and the heat is conducted to the ground layer metal shell through the 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 application relates to the field of circuit board, and particularly to a kind of optical module printed circuit board and preparation method thereof. BACKGROUND

[0002] As the core component of optical communication system, optical module undertakes the key function of converting optical signal and electrical signal. Laser, photodetector, fiber coupler and high-density circuit board integrated in the optical module work together to transmit information through laser beam via optical fiber, and then restore optical signal to electrical signal output by photodetector. The energy conversion process is accompanied by significant thermal effect, especially in high transmission rate scenarios, the device power density rises sharply, resulting in rapid increase of operating temperature.

[0003] Ambient temperature and operating conditions have a dual influence mechanism on the thermal characteristics of optical module: on the one hand, the increase of external temperature directly aggravates the heat accumulation inside the device; on the other hand, in response to the demand of artificial intelligence and big data transmission, optical module needs to work continuously at ultra-high speed (single channel 200Gbps and above) such as QSFP-DD800, and the quantum efficiency of photonic device and the signal integrity requirement of circuit board form a thermodynamic contradiction. The existing heat dissipation scheme mainly manages heat through passive heat dissipation structure (such as heat sink, heat pipe) or active heat dissipation system (fan, TEC semiconductor refrigeration), and adopts strategies such as frequency reduction operation or low-power module replacement. However, these methods have inherent limitations in balancing heat dissipation efficiency and transmission performance, power consumption control, and are difficult to meet the technical evolution needs of future 800G or even 1.6T optical modules. SUMMARY

[0004] (1) Technical problem to be solved

[0005] In view of the deficiencies in the prior art, the present application provides an optical module printed circuit board and a preparation method thereof. The present application solves the problem of heat dissipation of optical module at high transmission rate by constructing a printed circuit board laminated structure, embedding the heat generating device, and conducting heat to the ground layer metal shell through embedded copper block and copper column heat dissipation method.

[0006] (2) Technical scheme

[0007] In order to overcome the above technical problems, the present application provides an optical module printed circuit board;

[0008] A preparation method of an optical module printed circuit board, comprising the following steps:

[0009] S1: first, press a 6-layer structure of multilayer circuit board, then drill a through hole on the circuit board, and then coat a layer of metal copper in the through hole; the through hole includes a ground layer heat dissipation hole and a device mounting hole, and finally, the ground layer heat dissipation through hole in the heat generating device area is filled with copper paste;

[0010] S2: Forming a circuit pattern on the circuit board with the copper paste by pasting dry film, exposing, developing and etching;

[0011] S3: Then, covering the selected ink on the non-optical module plug area, and electroplating thick gold on the exposed plug gold fingers;

[0012] S4: Then, stripping the selected ink on the circuit board, and printing the selected ink again;

[0013] S5: Coating the anti-soldering ink on both sides of the circuit board, and exposing the board inner pads by exposing and developing; then, marking the device characters on both sides of the circuit board by character jet printing;

[0014] S6: Pasting the selected dry film on the circuit board with the printed characters, and exposing the circuit board bottom surface heat device area ground layer heat dissipation hole corresponding pad by exposing and developing;

[0015] S7: Thick plating the exposed heat dissipation hole pad copper to 150 μm by pattern electroplating;

[0016] S8: Stripping the dry film on both sides of the circuit board, and installing the device on the circuit board top surface heat device area;

[0017] S9: Positioning the top and bottom surface FR-4 substrate with the hollow heat device area by the circuit board peripheral positioning hole, and pressing with epoxy resin pure glue, so as to form a whole;

[0018] S10: Filling the copper block in the circuit board bottom surface FR-4 hollow area, which will contact with the heat device ground layer heat dissipation hole pad; and filling with copper paste, and pre-solidifying;

[0019] S11: Filling the heat dissipation resin in the circuit board top layer installation device area, and solidifying;

[0020] S12: Polishing the copper surface of the circuit board with the top layer filled heat dissipation resin and the bottom layer filled copper paste with ceramic, so as to make the filling and the board surface flat;

[0021] S13: Pasting the dry film on both sides of the circuit board, and making the circuit pattern by exposing, developing and etching principle;

[0022] S14: Pressing another FR-4 substrate on the circuit board with the two sides patterned;

[0023] S15: Processing the blind hole in the buried copper block area by laser; then, filling the laser blind hole by hole filling electroplating;

[0024] S16: complete the anti-soldering, text, and gold making of the circuit board;

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

[0026] S18: perform the molding, electrical testing, and FQC inspection processes on the circuit board.

[0027] (3) Beneficial effects

[0028] The present application breaks through the traditional heat dissipation design paradigm and innovatively restructures the laminated architecture of a printed circuit board (PCB) from the perspective of system-level thermal-electric collaborative optimization. By constructing an anisotropic thermal conductive medium layer, embedded heat dissipation, and an embedded device structure, an efficient heat conduction path is established under the premise of ensuring signal integrity. This provides an innovative solution with optimized thermal-electric performance for the next generation of high-density optical interconnection systems. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The figure is a structural diagram of the optical module printed circuit board of the present application. DETAILED DESCRIPTION

[0030] To make the technical means, creative features, and purposes and effects achieved by the present application easy to understand, the technical solutions in the specific embodiments of the present application are described below in a clear and complete manner to further illustrate the present application. Obviously, the described specific embodiments are only a part of the embodiments of the present application, not all.

[0031] A method for preparing an optical module printed circuit board, comprising the following steps:

[0032] S1: first, press a 6-layer structure of a multilayer circuit board, then drill through holes on the circuit board, and then coat a layer of metal copper in the through holes. The through holes include ground layer heat dissipation holes and device mounting holes, and finally, plug copper paste in the ground layer heat dissipation through holes in the heating device area.

[0033] S2: on the circuit board with plugged copper paste, form a circuit pattern by means of dry film pasting, exposure, development, and etching.

[0034] S3: then, cover the selected color ink on the non-optical module plug area, and electroplate thick gold on the exposed plug gold fingers.

[0035] S4: then, wash off the selected color ink on the circuit board, and print the selected color ink again. The function of this ink is to protect the non-electric gold lead position in the circuit board, thereby facilitating the etching of the gold finger electric lead.

[0036] S5: Apply anti-soldering ink on both sides of the circuit board, and expose the inner soldering pad by means of exposure and development. Then, mark the device characters on both sides of the circuit board by means of character jet printing.

[0037] S6: Paste the selected dry film on the circuit board with marked characters, and expose the circuit board bottom surface heat generating device area ground layer heat dissipation hole corresponding circuit soldering pad by means of exposure and development.

[0038] S7: Add plating to 150 μm by means of pattern plating to the exposed heat dissipation hole soldering pad copper thickness.

[0039] S8: Remove the dry film on both sides of the circuit board, and install the device in the heat generating device area on the top surface of the circuit board.

[0040] S9: Position the FR-4 substrate with the top and bottom surfaces of the heat generating device area hollowed out by means of the peripheral positioning holes of the circuit board, and press together using pure epoxy resin glue, thereby forming a whole.

[0041] S10: Fill the copper block in the FR-4 hollowed-out area on the bottom surface of the circuit board, which will be in contact with the ground layer heat dissipation hole soldering pad of the heat generating device. Use copper paste for filling and pre-solidification.

[0042] S11: Fill the heat dissipation resin in the device installation area on the top layer of the circuit board, and solidify.

[0043] S12: Use ceramic to polish the copper surface of the circuit board with the top layer filled with heat conductive resin and the bottom layer filled with copper paste, so that the fillers are flat with the surface.

[0044] S13: Further, paste the dry film on both sides of the circuit board, and make the circuit pattern by means of exposure, development and etching principle.

[0045] S14: Press another FR-4 substrate on the circuit board with the pattern made on both sides.

[0046] S15: Process the blind hole in the copper block buried area by means of laser radiation. Then, fill the hole by means of hole filling plating to make the laser blind hole flat inside the hole.

[0047] S16: Complete the anti-soldering, character and gold plating of the circuit board.

[0048] S17: Control the depth of the milling to expose the gold fingers of the inner layer with gold plating.

[0049] S18: Complete the circuit board by means of molding, electrical testing, FQC inspection and other processes.

[0050] Next, the detailed steps of the invention scheme are described.

[0051] First, two FR-4 substrates are prepared, the substrate thickness is matched according to the thickness of the finished product plate required by the customer, and the FR-4 substrate is prepared to complete the production of the inner layer circuit. Then stack a six-layer board and press and form, the stacking order is: copper foil - prepreg - first FR-4 substrate - prepreg - second FR-4 substrate - prepreg - copper foil.

[0052] Further, through-hole drilling is performed on the six-layer substrate after pressing, and electroplated copper is plated in the drilled holes through electroplating. The through holes include device mounting holes, ground layer heat dissipation holes, and overcurrent holes, and then copper paste is inserted into the ground layer heat dissipation holes. After the copper paste is inserted, the copper surface is flattened by solidification and polishing.

[0053] After polishing, the single-sided copper thickness is about 50μm.

[0054] Further, circuit patterns are made on the front and back of the circuit board with inserted copper paste, including SMD patch pads, bonding gold wire pads, and optical module gold finger plug-in pads, and the process is as follows:

[0055] Pre-treatment - dry film - exposure - development - etching.

[0056] The process is the conventional process of circuit board production, which will not be described again here.

[0057] Further, dry film is selected and pasted in the optical module pattern area, and through exposure and development, the optical module gold finger plug-in pad is exposed, and then thick gold plating is performed on the exposed area through electroplated gold.

[0058] The thickness of the electroplated thick gold is specified by the customer, but the maximum is not more than 30u"

[0059] Further, after electroplating, the selected dry film on the circuit board is washed and printed again with selected ink, which protects the non-electric gold lead position in the circuit board, thereby facilitating etching of the gold finger electric lead.

[0060] The electric lead is a connecting line added between the patterns in the board, which makes the pattern circuit the same electrical network. When electroplating thick gold, the current can be conducted through the connecting line of different electrical networks, so that the exposed optical module gold finger plug-in pad is electroplated with thick gold. Therefore, after electroplating thick gold, the connecting line needs to be removed again to prevent short circuit of electrical performance.

[0061] Further, solder resist ink is applied on both sides of the pattern, and through exposure and development, the board pads are exposed, and then the device characters are marked on both sides of the circuit board through text jet printing.

[0062] The solder resist ink and the text are only printed in the gold finger plug-in area of the optical module.

[0063] Further, on the circuit board with printed characters, paste the selected dry film, and through the exposure, development, expose the circuit board bottom surface heat device area of the ground layer heat dissipation hole corresponding to the circuit pad.

[0064] The ground layer heat dissipation hole refers to the ground copper paste hole.

[0065] Further, through the pattern copper plating method, the exposed circuit pad is copper-plated, and the copper thickness reaches 150μm.

[0066] The main role of this step is to make the exposed copper pad contact with the copper block, and after filling the copper paste, the side contact area is increased.

[0067] Further, the dry film on both sides of the circuit board is removed, and the device installation is performed in the top surface heat device area of the circuit board.

[0068] The device installation includes but is not limited to gold wire bonding and chip packaging.

[0069] At this time, the effect of the circuit board is that the top layer device packaging area has a heat device, and the bottom layer heat area copper pad is higher than the board surface by about 100μm; except for the device area with ink, the exposed area is copper surface and wire.

[0070] Further, two 1.5mm FR-4 core boards are prepared, and the core board is first drilled through the positioning hole on the board edge, and the positioning hole is consistent with the coordinates of the packaging device positioning hole, which is convenient for positioning.

[0071] Secondly, through the board edge positioning hole, through the dry film, exposure, development, etching method, one side circuit pattern is made.

[0072] One side circuit pattern refers to making a circuit pattern on one side close to the middle layer substrate when superimposed, and the other side is reserved as a large copper surface.

[0073] Further, the two 1.5mm FR-4 substrates are hollowed out in the device packaging area.

[0074] Synchronously, 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 area, and the positioning points of the hollowed out areas are consistent with the circuit board substrate.

[0075] Further, the two 1.5mm substrates are respectively placed on the upper and lower of the middle layer circuit board, and the AD pure glue is placed in the middle.

[0076] Through fast pressing, the circuit board is pressed for 2 minutes.

[0077] Further, the circuit board after fast pressing is baked at 75℃*1H.

[0078] Further, the circuit board after baking 1H is pressed again, and the pressing time is 3 minutes.

[0079] Further, the circuit board after pressing is baked again at 75°C for 3H.

[0080] Further, resin is filled in the device packaging area of the circuit board, then low-temperature 75°C*2H baking is performed, and the resin is polished flat by a ceramic polishing machine.

[0081] Further, a copper block with a thickness of 1.3mm is filled in the reverse side of the packaging area of the circuit board, and after filling, the thickness of the copper block is about 0.05mm.

[0082] Further, copper paste is filled in the area of the filled copper block, so that the copper paste is connected with the copper block and the ground layer heat dissipation pad, thereby forming a whole buried copper heat dissipation area.

[0083] Further, after low-temperature 75°C*2H baking, the copper surface is polished by a ceramic polishing device to ensure the flatness and smoothness of the copper surface.

[0084] Further, by means of dry film pasting, exposure, development and etching, line patterns are made on both sides of the circuit board.

[0085] Further, two 0.05mm FR-4 substrates are prepared, and one side copper is etched away by single-sided etching, and the other side copper is reserved.

[0086] Further, positioning holes are drilled on the single-sided copper foil substrate, and the positioning holes are consistent with the previous positioning holes.

[0087] Further, the single-sided copper foil FR-4 substrate is stacked on the copper-free surface of the board, and 50μm thick epoxy resin AD pure glue is used for fast pressing and bonding in the middle.

[0088] Further, laser drilling is performed on the buried copper block surface of the circuit board, and the drilling diameter is 0.15mm, and the drilling contacts the inner copper block, thereby forming a ground layer heat dissipation hole.

[0089] Further, through-hole drilling, inner copper plating, outer pattern making, solder mask printing, character printing and gold making are performed on the circuit board.

[0090] Further, the gold finger area of the optical module is controlled in depth by depth control milling, and since the AD pure glue in this area is hollowed out in advance during fast pressing, the gold finger is exposed after depth control.

[0091] Further, the circuit board is processed after forming, electrical testing, appearance inspection and other post-processing.

[0092] The above describes the main technical features and basic principles of the present application and related advantages, for those skilled in the art, it is obvious that the present application is not limited to the details of the above exemplary embodiments, and the present application can be implemented in other specific forms without departing from the concept or basic features of the present application. Therefore, no matter from which point of view, the above-mentioned specific embodiments should be regarded as exemplary and non-limiting, the scope of the present application is defined by the appended claims rather than the above description, therefore all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application.

[0093] In addition, it should be understood that although the present specification is described in terms of various embodiments, not every embodiment contains only one independent technical solution, and the description manner of the specification is only for the sake of clarity, those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that those skilled in the art can understand.

Claims

1. A method for fabricating a printed circuit board for an optical module, characterized in that, Includes the following steps: S1: First, a 6-layer multilayer circuit board is laminated. Then, through holes are drilled on the circuit board, and a layer of copper is plated inside the through holes. The through holes include ground heat dissipation holes and device mounting holes. Finally, copper paste is filled into the ground heat dissipation through holes in the area of ​​heat-generating devices. S2: On a circuit board filled with copper paste, a circuit pattern is formed by applying dry film, exposing, developing, and etching. S3: Subsequently, apply selective ink to the non-optical module plug-in area and electroplate the exposed plug-in gold fingers with thick gold. S4: Subsequently, the selective ink on the circuit board is washed off and the selective ink is printed again; S5: Apply solder resist ink to both sides of the circuit board and expose the pads inside the board through exposure and development; then mark the component text on both sides of the circuit board by character inkjet printing. S6: On the printed circuit board, apply a selective dry film and expose the circuit pads corresponding to the ground heat dissipation holes in the heat-generating device area on the bottom of the circuit board through exposure and development. S7: The exposed heat dissipation hole pads are plated with copper to a thickness of 150μm using pattern electroplating. S8: Remove the dry film from both sides of the circuit board and install the components in the area of ​​the heat-generating components on the top surface of the circuit board; S9: The top and bottom surfaces of the FR-4 substrate with the pre-cut heating element area are stacked and positioned through the positioning holes on the outer side of the circuit board, and then pressed together with epoxy resin to form a whole. S10: Fill the FR-4 cutout area on the bottom of the circuit board with a copper block that will contact the ground plane heat dissipation hole pads of the heat-generating devices; fill with copper paste and pre-cur it. S11: Fill the area on the top layer of the circuit board where the components are mounted with heat-dissipating resin and then cure it.

2. The method for fabricating an optical module printed circuit board according to claim 1, characterized in that, It also includes: S12: The copper surface of the circuit board with the top layer filled with thermally conductive resin and the bottom layer filled with copper paste is polished with ceramic to make the filler flat with the board surface.

3. The method for preparing an optical module printed circuit board according to claim 2, characterized in that, It also includes: S13: Apply dry film to both sides of the circuit board and use the principles of exposure, development, and etching to create the circuit pattern.

4. The method for preparing an optical module printed circuit board according to claim 3, characterized in that, It also includes: S14: On the circuit board with the patterns on both sides, another FR-4 substrate is laminated.

5. The method for preparing an optical module printed circuit board according to claim 4, characterized in that, It also includes: S15: Blind holes are machined in the copper block area using laser engraving; then, the blind holes are filled by electroplating.

6. The method for fabricating an optical module printed circuit board according to claim 5, characterized in that, It also includes: S16: Complete the solder mask, text, and electroless gold plating on the circuit board.

7. The method for preparing an optical module printed circuit board according to claim 6, characterized in that, It also includes: S17: controlled depth milling, which exposes the gold fingers of the inner layer of the optical module that have been electroplated with gold.

8. The method for preparing an optical module printed circuit board according to claim 7, characterized in that, It also includes: S18: the production of circuit boards through molding, electrical testing, and FQC inspection processes.

9. An optical module printed circuit board, manufactured by the method for preparing an optical module printed circuit board as described in claim 8.

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