Method for embedding conductive glue and PCB board

Abstract

The application discloses a method for embedding conductive glue and a PCB, and comprises the following steps: cutting - inner layer circuit - locally pasting conductive glue - glue pressing - PP slotting - pre-laminating - pressing - drilling - PTH slotting - PTH plating - outer layer circuit - solder mask - character - depth control slotting - surface treatment - plate slotting - electrical measurement - FQC - FQA. The application pastes the conductive glue with a required thickness at a corresponding specified position, then fixes the PP and the substrate through rivets, and then performs pressing, so that the conductive glue can be embedded in the substrate. Then, a metalized slot or a metalized hole is realized through conventional mechanical slotting or mechanical drilling, and then the metal slot hole is slotted along the conductive glue position by a certain length through mechanical depth control slotting, so that a T-shaped half metalized half non-metalized slot hole is formed, the non-metalized half can accommodate components, high thermal conductivity is realized, the lower layer of the electric layer is fully wrapped around the components, and the shielding effect is realized.

Description

Technical Field

[0001] This invention relates to a method for manufacturing special printed circuit boards with high thermal conductivity, and more particularly to a method for embedding conductive adhesive and a printed circuit board. Background Technology

[0002] With the development of 5G high-speed products, especially millimeter-wave transmission and reception circuits, TRX (radio frequency board of the base station, which plays a role in signal modulation, mixing and transmission) and PA (power amplifier) ​​are often integrated into a single PCB board. These products have several distinct characteristics: they combine high-frequency signals and ordinary transmission, requiring a mixture of high-frequency board material and FR4 material, while also possessing high power and high-frequency characteristics. Both of these factors are prone to generating electromagnetic radiation and interference noise. If the design is not scientifically sound, it can easily lead to low circuit efficiency, and in severe cases, may cause signal interference and distortion, or even burn out the PCB board and the entire device. To address these shortcomings, the industry commonly embeds high thermal conductivity components within the circuit board, such as T-shaped (or boss) devices. These T-shaped devices need to achieve high thermal conductivity with the PA module side of the PCB board while avoiding interference with the TRX side. Therefore, one side of the PCB is designed with a conductive PTH slot (or hole), and the other side with a non-conductive NPTH slot (or hole). A reliable connection between the inner copper layer of the circuit board and the T-type device achieves grounding shielding and heat conduction functions. When there are multiple inner ground layers, in order to maximize the use of the shielding and grounding effects of the ground layers, one approach is to locally embed conductive adhesive to achieve the required functions of the product.

[0003] There is a lot of information about external conductive adhesives as auxiliary processing materials in the industry, but there is less research on internal conductive adhesives. For example, the paper "A Processing Method and Testing Method of Internal Conductive Adhesive for PCB" (CN 113660784 A) records a method of first creating a PCB by cutting slots and embedding pre-existing copper bosses, then applying conductive adhesive to the copper bosses for positioning. This method is not very practical for local embedding where stepped slots need to be cut on the board surface, because this method is for installing T-shaped components after the PCB is finished. The process is as follows: material cutting - inner layer circuit - core board routing - PP routing - copper base mounting (with conductive adhesive) - pre-stack - lamination - drilling - PTH electroplating - outer layer circuit - solder mask - characters - surface treatment - routing - electrical testing - FQC - FQA. This method has problems such as poor viscosity of conductive adhesive and the need to rely on copper base for positioning. The installation of copper base itself consumes materials, and due to the poor viscosity of conductive adhesive, the copper base is also prone to falling off. Summary of the Invention

[0004] This invention discloses a method for embedding conductive adhesive. This invention can produce shielding layer structures that offer high thermal conductivity, heat dissipation, and complete component placement. Through a prefabrication method, it can be manufactured rapidly, exhibiting high efficiency and high reliability.

[0005] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0006] A method for embedding conductive adhesive includes the following steps:

[0007] Step 1: Etch marking lines at predetermined locations on the first core board 112 containing conductor lines, where conductive adhesive will be applied.

[0008] Step 2: Apply conductive adhesive 200 along the etched marking line to the pre-defined position for applying conductive adhesive;

[0009] Step 3: Creating windows on the prepreg: Create windows on the prepreg 120 according to the pre-defined positions for applying conductive adhesive.

[0010] Step 4: Press the second core board 111 containing conductor lines and the first core board 112 containing conductor lines together using the prepreg 120, with the conductive adhesive inside the window, to form a preliminary PCB board.

[0011] Step 5: Run the slots that need to be metallized, namely PTH slots, on the preliminary PCB board. The PTH slots run through the middle of the conductive adhesive 200 on the entire preliminary PCB board.

[0012] Step 6: Perform copper plating to achieve conductivity between the PTH tank and the inner copper layer;

[0013] Step 7: After completing the outer layer pattern and solder mask, perform mechanical depth control routing. The depth control routing groove forms a non-metallized groove, i.e., an NPTH groove. The diameter of the mechanical depth control router is larger than the diameter of the PTH groove and is coaxial with the PTH groove. The depth control reaches the conductive adhesive but does not exceed the bottom of the conductive adhesive, forming a T-shaped hole structure. The PCB board with the conductive adhesive embedded is obtained.

[0014] In a further improvement, in step one, a marking line is etched at the preset position for applying conductive adhesive on the core board 112 of the conductor circuit. The marking line is ≥500um larger than the single side of the slot hole than the single side of the NPTH slot.

[0015] In a further improvement, in step one, the edge of the marking line is 25µm-50µm larger than the size outline of the conductive adhesive on one side.

[0016] As a further improvement, in step two, after applying the conductive adhesive, air bubbles are removed by pressing the film to prevent subsequent PP leakage.

[0017] In a further improvement, in step two, the thickness of the prepreg is less than or equal to that of the conductive adhesive, and the thickness difference between the prepreg and the conductive adhesive does not exceed 5 μm.

[0018] As a further improvement, in step three, the single side of the PP window opening is 50-200µm larger than the single side of the conductive adhesive.

[0019] A further improvement is that the prepreg is a PP prepreg.

[0020] In a further improvement, the thickness of the conductive adhesive 200 is 100-200 μm.

[0021] A printed circuit board manufactured by the above-described method of embedding conductive adhesive is characterized in that it includes a first core board 112 containing conductor lines and a second core board 111 containing conductor lines, which are fixed together by a prepreg 120; conductive adhesive 200 is adhered to the first core board 112 containing conductor lines, and the prepreg 120 has a window that mates with the conductive adhesive 200; the first core board 112 containing conductor lines, the second core board 111 containing conductor lines, and the prepreg 120 form a press-fit structure, and a T-shaped hole structure is formed on the press-fit structure that extends to the location of the conductive adhesive; wherein the inner sidewall of the conductive adhesive 200 and the inner sidewall of the first core board 112 containing conductor lines are plated with a PTH metallized copper layer 311, the PTH metallized copper layer 311 contains a PTH metallized slot 310, and the PTH metallized slot 310 is above an NPTH non-metallized slot 320.

[0022] Advantages of this invention:

[0023] This invention involves applying conductive adhesive of the required thickness to designated locations, removing air bubbles through film pressing, and then pre-positioning pre-cut PP sheets with openings to the substrate via alignment holes and securing them with rivets. The sheets are then pressed and cured under high temperature and pressure to ensure the conductive adhesive is embedded within the substrate. Metallized slots or holes are then created using conventional mechanical milling or drilling. Further depth milling removes a section of the metal slot or hole, forming a T-shaped semi-metallic, semi-non-metallic slot. This allows the non-metallic section to accommodate components, achieving high thermal conductivity and providing full shielding by completely enclosing the components. Attached Figure Description

[0024] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0025] Figure 1 A schematic diagram of the structure for applying conductive adhesive;

[0026] Figure 2 A schematic diagram of a windowed structure for a prepreg;

[0027] Figure 3This is a schematic diagram of a prepreg sheet fitted over conductive adhesive.

[0028] Figure 4 A schematic diagram of the pre-stacked core board containing conductor lines;

[0029] Figure 5 This is a schematic diagram of the borehole structure;

[0030] Figure 6 A schematic diagram of the hole metallization structure;

[0031] Figure 7 This is a schematic diagram of the structure after mechanical control of the deep mill.

[0032] Among them, 111-second core board containing conductor lines, 112-core board with slot containing conductor lines, 120-prepreg; 200-conductive adhesive; 310-PTH metallized slot; 311-PTH metallized copper layer; 320-NPTH non-metallized slot. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the present invention clearer, the invention will be described clearly and completely below in conjunction with specific embodiments. It should be understood that the terms "center," "vertical," "horizontal," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0034] Example

[0035] The method of the present invention is:

[0036] Material cutting - Inner layer circuitry - Partial application of conductive adhesive - Adhesive pressing - PP router groove - Pre-stack - Pressing - Drilling - Routing PTH grooves - PTH electroplating - Outer layer circuitry - Solder resist - Characters - Controlled depth router - Surface treatment - Routing board - Electrical testing - FQC - FQA.

[0037] To elaborate further:

[0038] 1. Product Design Features: The product is manufactured on a four-layer PCB using a core-plus-core stack. Core 1 (L1 / L2 layers) is 0.5mm thick, and Core 2 (L3 / L4 layers) is 0.5mm thick, with a 200µm thick prepreg sandwiched between them, ensuring a finished board thickness of 1.2±0.12mm. A conductive adhesive is pre-placed in the graphic unit, and the adhesive must be tightly bonded to the copper traces of L2 and L3 layers to ensure circuit continuity between L2 and L3 layers at that location. NPTH (non-metallized) slots with dimensions of 50mm x 30mm are designed at the L1 / L2 positions on the substrate, with a slot depth of 0.58±0.01µm. Conductive adhesive with dimensions of 51*31mm needs to be embedded in the middle of the stack.

[0039] 1. In the inner layer circuitry, at the location where conductive adhesive is embedded in layer L3, etch out a marker line with dimensions corresponding to the area where conductive adhesive needs to be applied. The marker line is 100µm wide, with a rectangular outline, and the dimensions within the outline are 51.5*31.5mm. The marker line does not affect the open / short circuit of the pattern. The marker line is 500µm larger on one side than the NPTH slot. The conductive adhesive application area is 25µm smaller on one side than the marker line outline.

[0040] 2. Apply conductive adhesive locally. The conductive adhesive should be 51mm long x 31mm wide. It needs to be applied to the area where the conductive adhesive is needed. After application, press the film to remove air bubbles to prevent the PP from leaking out later.

[0041] 3. PP window opening, the window size is larger than that of conductive adhesive, with dimensions of 53*33mm; PP thickness is 200um.

[0042] 4. Drill PTH slots, with a size of 20mm*16mm, running through the entire board. The size is smaller than that of NPTH slots.

[0043] 5. Then perform copper plating to achieve conductivity between the PTH tank and the inner copper layer.

[0044] 6. After completing the outer layer pattern and solder mask, perform mechanical depth-controlled milling at the PTH slot locations, setting the depth to 0.55mm. The dimensions are 50mm x 30mm (length x width). This ensures that the L1 / L2 core board is milled through, guaranteeing that the conductive adhesive is completely exposed at the milling location. This results in the upper part (L1 / L2 section) having NPTH slots, and the lower part (L3 / L4 core board layers) having...

[0045] This method of quickly embedding conductive adhesive in slots allows the conductive adhesive to interconnect with the components after installation, ensuring high thermal conductivity and rapidly dissipating heat from the power amplifier. The conductive adhesive also provides connectivity with the inner copper layer and the PTH section, isolating the components from other components below the shielding layer and achieving a shielding effect.

[0046] By first applying conductive adhesive to the positions marked with scale lines on the pre-designed inner layer pattern, the alignment accuracy of the conductive adhesive is improved, and the pattern accuracy is reduced due to material expansion and contraction and PP alignment misalignment. This method is suitable for the production of high-precision conductive adhesives.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for embedding conductive adhesive, characterized in that, Includes the following steps: Step 1: Etch marking lines at the predetermined positions for applying conductive adhesive on the first core board (112) containing conductor lines; Step 2: Apply conductive adhesive (200) along the etched marking line to the preset position for applying conductive adhesive. Step 3: Creating windows on the prepreg: Create windows on the prepreg (120) according to the preset positions for applying conductive adhesive. Step 4: Press the second core board (111) containing conductor lines with the first core board (112) containing conductor lines using a prepreg (120), with the conductive adhesive inside the window, to form a preliminary PCB board; Step 5: Run the slots that need to be metallized, namely PTH slots, on the preliminary PCB board. The PTH slots run through the middle of the conductive adhesive (200) of the entire preliminary PCB board. Step 6: Perform copper plating to achieve conductivity between the PTH tank and the inner copper layer; Step 7: After completing the outer layer pattern and solder mask, perform mechanical depth control router (MDR) to form a non-metallized groove, i.e., an NPTH groove. The diameter of the mechanical MMR is larger than the diameter of the PTH groove and is coaxial with the PTH groove. The depth control reaches the conductive adhesive but does not exceed the bottom of the conductive adhesive, forming a T-shaped hole structure. A PCB board with the conductive adhesive embedded is obtained. In Step 1, the preset conductive adhesive placement position on the core board (112) of the conductor circuit is etched with a marking line. The marking line is ≥500um longer than the NPTH groove on one side than the groove on one side. In Step 1, The edge of the marking line is 25-50µm larger than the size outline of the conductive adhesive on one side; in step two, after applying the conductive adhesive, air bubbles are removed by pressing to prevent subsequent PP leakage; in step two, the thickness of the prepreg is less than or equal to the thickness of the conductive adhesive, and the thickness difference between the two does not exceed 5µm; in step three, the single side of the PP window is 50-200µm larger than the single side of the conductive adhesive; the prepreg is a resin mixture that is solid at room temperature and liquid at high temperature; the thickness of the conductive adhesive (200) is 100-200µm. The PCB board includes a first core board (112) containing conductor lines and a second core board (111) containing conductor lines. The first core board (112) and the second core board (111) containing conductor lines are fixed together by a prepreg (120). Conductive adhesive (200) is adhered to the first core board (112), and the prepreg (120) has a window that mates with the conductive adhesive (200). The first core board (112) and the second core board (111) containing conductor lines are fixed together by a prepreg (120). The core board (111) and the prepreg (120) of the circuit form a press-fit structure. A T-shaped hole structure is formed on the press-fit structure, which extends to the location of the conductive adhesive. The inner wall of the conductive adhesive (200) and the inner wall of the first core board (112) containing the conductor circuit are plated with a PTH metallized copper layer (311). The PTH metallized copper layer (311) contains a PTH metallized slot (310), and the PTH metallized slot (310) is above the NPTH non-metallized slot (320).

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