Rivet-free fixing and pressing method of electric press

Abstract

The invention discloses a rivet-free fixing and pressing method for a voltage machine. The rivet-free fixing and pressing method comprises the following steps of 1, cutting, wherein a large copper-clad plate is cut into a PNL-specification core plate according to the engineering design size; the required inner layer graph is completed through the sub-processes of inner layer pretreatment, coating, exposure, development, etching and film removal according to the graph requirement of a client, circular targeting targets are arranged in the hot melting block range of the four corners of the core plate, the targets are symmetrically distributed at the four corners of the core plate, and the distance between the circle center and the edge of the core plate is 1.2-1.5 times of the plate thickness. Compared with the prior art, the four-corner target hole filling and curing structure has the advantages that physical interlocking is achieved, the diameter tolerance of the target hole is controlled to be + / -0.02 mm, accordingly, the interlayer displacement amount is reduced, three interlocking nodes arranged in the curing and connecting structure can disperse shear stress, the shear strength is improved, and the stability of the structure is improved. Therefore, the interlayer fixing stability is ensured on the premise that rivet fixing is not needed, and the manufacturing requirement of the multi-layer PCB is met.

Description

Technical Field

[0001] The present invention relates to the technical field of PCB pressing, and in particular to a rivet-free fixing and pressing method of an electric press. Background Art

[0002] In the manufacturing of multilayer printed circuit boards (PCBs), interlayer offset (or layer deviation) is a core issue limiting the yield of high-density interconnect boards (HDIs). As electronic devices evolve toward higher frequencies, higher speeds, and greater miniaturization, high-end PCBs with six or more layers require even higher interlayer alignment accuracy. However, traditional processes have significant drawbacks in material compatibility, processing accuracy, and cost control.

[0003] For example, the rivet fixing method requires setting metal rivets on the edge of the core board to lock the interlayer position, which not only takes up wiring space but also blocks the high-frequency signal transmission path. At the same time, the rivet processing cost will increase the overall manufacturing cost and cannot be adapted to ultra-thin core boards.

[0004] The local pre-curing technology achieves temporary fixation through hot melting of semi-cured sheet (PP), but the shear strength of the cured area is low, and sliding is prone to occur during high-pressure pressing, especially for PCBs with more than 6 layers, the possibility of layer deviation will increase significantly.

[0005] In summary, both traditional rivet fixing and local pre-curing technologies have drawbacks such as poor material compatibility, insufficient process stability, and high costs. Therefore, a rivet-free, high-precision pressing method that is suitable for ultra-thin high-frequency materials is urgently needed to break through the yield bottleneck of high-density PCB manufacturing. Summary of the Invention

[0006] The main purpose of the present invention is to provide a rivet-free fixing and pressing method using an electric machine, which achieves physical interlocking by filling the solidification structure with target holes at the four corners. The target hole diameter tolerance is controlled within ±0.02mm, thereby reducing the interlayer displacement. The three interlocking nodes set in the solidification connection structure can disperse the shear stress and increase the shear strength.

[0007] To achieve the above object, the technical solution adopted by the present invention is: A rivet-free fixing and pressing method using an electric press comprises the following steps: Step 1: Cutting: Cut the large copper clad laminate into PNL specification core boards according to the engineering design size; Step 2: Inner layer pattern production: According to the customer's pattern requirements, the required inner layer pattern is completed through the inner layer pre-treatment, coating, exposure, development, etching, and film stripping sub-processes, and circular shooting targets are set within the range of the hot melt blocks at the four corners of the core board. The targets are symmetrically distributed at the four corners of the core board, and the center of the circle is 1.2-1.5 times the thickness of the core board from the edge; Step 3: AOI inspection: Use optical inspection equipment to identify defects in the inner layer pattern and screen out open circuits, short circuits and poorly etched core boards; Step 4: Target hole drilling: Synchronously drill the original hot melt positioning holes and the newly added four corner target holes; Step 5: Browning: Roughen the copper surface of the core board through chemical treatment, and the roughness of the copper surface is controlled at 0.8-1.2μm; Step 6: Melt curing: After laminating the prepreg and the core board, perform local hot pressing curing at high temperature to melt the prepreg and fill the four corner target holes to form a solidified connection structure that runs through the core boards; Step 7: Layer deviation detection: Use X-RAY equipment to detect the target hole area at the four corners. The inter-layer displacement of ≤0.1mm is qualified. Step 8: Lamination and layer addition: The qualified multilayer boards are laminated at 380-395℃ and 3-5 kg / cm² pressure for 15-30 seconds.

[0008] Furthermore, the tolerance of the target hole center distance in step 2 is ≤±0.05mm, the diameter of the circular shooting target is 3.175mm, and the tolerance of the target hole diameter is ±0.02mm.

[0009] Furthermore, in step 4, the diameter of the original positioning hole is 2.0-2.5 mm, and the diameter of the newly added target hole is 2.4-3.8 mm.

[0010] Furthermore, the prepreg in step six is ​​made of polypropylene, has a melt viscosity of 500-800 Pa·s, and has a cured thickness of 0.5-1.2 mm after filling the target hole.

[0011] Furthermore, the cured connection structure comprises at least three interlocking nodes between layers, the spacing error between each node is ≤0.1 mm, and the density of the semi-cured sheet at the node after curing is ≥1.8 g / cm³.

[0012] Furthermore, the grayscale contrast threshold of the X-RAY detection in step seven is set to 60-80%, and the interlayer displacement is automatically calculated by an image algorithm to generate an offset vector diagram.

[0013] Furthermore, during the lamination process in step eight, the heating rate is controlled at 3-5°C / min, and the holding time is 30-50 minutes.

[0014] Furthermore, the interlayer bonding force of the cured connection structure is ≥10 N / cm, and the thermal expansion coefficient matches ±1.5 ppm / °C of the core board material.

[0015] Furthermore, the hot melt pressure head of the voltage press adopts a zoned temperature control design, and the temperature of the target hole areas at the four corners is 5-10°C higher than that of the central area.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention achieves physical interlocking by filling the solidification structure with target holes at the four corners. The target hole diameter tolerance is controlled at ±0.02mm, thereby reducing the interlayer displacement. The three interlocking nodes set in the solidification connection structure can disperse shear stress and increase shear strength, thereby ensuring the fixation stability between layers without the need for rivets, meeting the manufacturing requirements of multi-layer PCB boards.

[0017] The present invention adopts a zoned temperature-controlled pressing technology to compensate for the curing delay caused by edge heat dissipation, thereby improving the uniformity of the filling thickness of the prepreg.

[0018] The present invention reduces copper consumption by 15% through a rivet-free design and avoids metal debris pollution generated by traditional riveting processes. DETAILED DESCRIPTION

[0019] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below in conjunction with specific implementation methods. Example 1

[0020] A rivet-free fixing and pressing method using an electric press comprises the following steps: Step 1: Cutting: Cut the large copper clad laminate into PNL specification core boards according to the engineering design size; Step 2: Inner layer pattern production: According to the customer's pattern requirements, the required inner layer pattern is completed through the inner layer pre-treatment, coating, exposure, development, etching, and film stripping sub-processes. Circular shooting targets are set within the range of the hot melt blocks at the four corners of the core board. The targets are symmetrically distributed at the four corners of the core board, and the distance between the center of the circle and the edge of the core board is 1.2-1.5 times the thickness of the board. Step 3: AOI inspection: Use optical inspection equipment to identify defects in the inner layer pattern, screen out open circuits, short circuits and poorly etched core boards, and keep qualified boards for use; Step 4: Target hole drilling: The original hot melt positioning hole and the newly added four corner target holes are drilled simultaneously, where the aperture ratio of the original positioning hole and the newly added target hole is 1:1.2-1.5, and the axial deviation of the target hole is less than 0.05mm; Step 5: Browning: Roughen the copper surface of the core board through chemical treatment, and the roughness of the copper surface is controlled at 0.8-1.2μm; Step 6: Melt curing: After laminating the prepreg and the core board, perform local hot pressing curing at a temperature of 120-150℃ to melt the prepreg and fill the four corner target holes to form a solidified connection structure that penetrates the core boards. The shear strength of the solidified connection structure is ≥1.5N / mm². Step 7: Layer deviation detection: Use X-RAY equipment to detect the target hole area at the four corners, and the inter-layer displacement is ≤0.1mm; Step 8: Lamination and layer addition: The qualified multilayer boards are laminated at 380-395℃ and 3-5 kg / cm² pressure for 15-30 seconds.

[0021] Among them, the tolerance of the target hole center spacing in step 2 is ≤±0.05mm, the diameter of the circular shooting target is 3.175mm, and the target hole diameter tolerance is ±0.02mm.

[0022] Among them, the aperture of the original positioning hole in step 4 is 2.0-2.5 mm, and the aperture of the newly added target hole is 2.4-3.8 mm.

[0023] The prepreg in step six is ​​made of polypropylene with a melt viscosity of 500-800 Pa·s and a cured thickness of 0.5-1.2 mm after filling the target hole.

[0024] The cured connection structure includes at least three interlocking nodes between layers, the spacing error between each node is ≤0.1mm, and the density of the semi-cured sheet at the node after curing is ≥1.8g / cm³.

[0025] Among them, the grayscale contrast threshold of the X-RAY detection in step 7 is set to 60-80%, and the inter-layer displacement is automatically calculated by the image algorithm to generate the offset vector diagram.

[0026] In the step eight, during the lamination process, the heating rate is controlled at 3-5°C / min, and the holding time is 30-50 minutes.

[0027] The interlayer bonding strength of the cured connection structure is ≥10N / cm, and the thermal expansion coefficient matches the core board material at ±1.5ppm / °C.

[0028] Among them, the hot melt pressure head of the voltage press adopts a zoned temperature control design, and the temperature of the four corner target hole areas is 5-10℃ higher than that of the central area. Example 2

[0029] The manufacturing process of 6-layer high-frequency PCB for 5G base station is as follows: 1. Cutting and material preparation: A 0.2mm-thick FR-4 high-TG (Tg ≥ 180°C) core board was selected and cut to a PNL-specified 610mm x 508mm board according to the project design. The copper foil surface roughness (Rz) was controlled within 3μm to meet the requirements of high-frequency signal transmission.

[0030] 2. Inner layer graphics production and target setting: Laser direct imaging (LDI) technology is used to fabricate the inner-layer circuitry, achieving a line width / line spacing accuracy of ±5μm. Circular targets (diameter 3.175mm ± 0.02mm) are symmetrically placed at the four corners of the core board. The distance from the center of the circle to the board edge is 1.3 times the board thickness (i.e., 0.26mm). The center spacing tolerance of the target holes is controlled to ±0.03mm. The target area is covered with an anti-oxidation coating to prevent browning that may affect positioning accuracy.

[0031] 3. AOI inspection: The inner layer graphics are inspected by AOI equipment with a grayscale contrast threshold of 75% to screen out qualified products.

[0032] 4. High-precision target hole processing: A CNC drill was used to simultaneously machine the original positioning holes (2.5mm diameter) and the newly added four corner target holes (3.0mm diameter), with an aperture ratio of 1:1.2. The target hole axial deviation was ≤0.04mm, and the hole wall roughness was ≤15μm, ensuring uniform filling of the subsequent prepreg.

[0033] 5. Browning treatment and surface roughening: The copper surface was treated with a sulfuric acid-hydrogen peroxide browning solution, achieving an oxide layer thickness of 0.6 μm and a surface roughness of Ra = 1.0 μm. The post-treatment peel strength test showed a value of ≥ 1.2 N / mm, meeting the bonding requirements for high-frequency substrates.

[0034] 6. Target hole melting and solidification interlocking: A 2116 polypropylene prepreg (melt viscosity 650 Pa·s) containing 58% resin was laminated to the core board and locally hot-pressed using a four-zone temperature-controlled hot press (155°C in the corners and 145°C in the center). The prepreg melted and filled the target holes, forming three interlocking joints (with a spacing tolerance of 0.08mm). After curing, the density reached 1.85g / cm³ and the shear strength reached 1.8N / mm². Infrared thermal imaging monitoring showed a temperature difference of ≤3°C in the four corners, and a cured thickness uniformity tolerance of ±0.1mm.

[0035] 7. X-RAY layer deviation detection and compensation: An X-ray machine with a grayscale contrast threshold of 70% was used to inspect the four corner target holes. The resulting offset vector diagram showed a maximum interlayer displacement of 0.07 mm. An AI algorithm automatically adjusted subsequent lamination parameters to compensate for the cumulative offset to ≤ 0.05 mm.

[0036] 8. High temperature and high pressure pressing and adding layers: Lamination was performed at 385°C and 4.5kg / cm² (approximately 4.36atm) pressure, with a heating rate of 4°C / min and a dwell time of 40 minutes. The interlayer bonding strength after lamination was tested to be ≥12N / cm, and the coefficient of thermal expansion (CTE) matched the core board to an error of ±1.2ppm / °C. The Z-axis expansion coefficient of the final six-layer board was ≤0.8%, meeting the stability requirements for 5G high-frequency signal transmission.

[0037] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A rivet-free fixing and pressing method using an electric press, characterized in that: The following steps are involved: Step 1: Cutting: Cut the large copper clad laminate into PNL specification core boards according to the engineering design size; Step 2: Inner layer pattern production: According to the customer's pattern requirements, the required inner layer pattern is completed through the inner layer pre-treatment, coating, exposure, development, etching, and film stripping sub-processes, and circular shooting targets are set within the range of the hot melt blocks at the four corners of the core board. The targets are symmetrically distributed at the four corners of the core board, and the center of the circle is 1.2-1.5 times the thickness of the core board from the edge; Step 3: AOI inspection: Use optical inspection equipment to identify defects in the inner layer pattern and screen out open circuits, short circuits and poorly etched core boards; Step 4: Target hole drilling: Synchronously drill the original hot melt positioning holes and the newly added four corner target holes; Step 5: Browning: Roughen the copper surface of the core board through chemical treatment, and the roughness of the copper surface is controlled at 0.8-1.2μm; Step 6: Melt curing: After laminating the prepreg and the core board, perform local hot pressing curing at high temperature to melt the prepreg and fill the four corner target holes to form a solidified connection structure that runs through the core boards; Step 7: Layer deviation detection: Use X-RAY equipment to detect the target hole area at the four corners. The inter-layer displacement of ≤0.1mm is qualified. Step 8: Lamination and layer addition: The qualified multilayer boards are laminated at 380-395℃ and 3-5 kg / cm² pressure for 15-30 seconds.

2. The rivet-free fixing and pressing method of an electric press according to claim 1, characterized in that: The target hole center distance tolerance in step 2 is ≤±0.05mm, the diameter of the circular target is 3.175mm, and the target hole diameter tolerance is ±0.02mm.

3. The rivet-free fixing and pressing method of an electric press according to claim 1, characterized in that: In the fourth step, the diameter of the original positioning hole is 2.0-2.5 mm, and the diameter of the newly added target hole is 2.4-3.8 mm.

4. The rivet-free fixing and pressing method of an electric press according to claim 1, characterized in that: The prepreg in step six is ​​made of polypropylene, has a melt viscosity of 500-800 Pa·s, and has a cured thickness of 0.5-1.2 mm after filling the target hole.

5. The rivet-free fixing and pressing method of an electric press according to claim 1, characterized in that: The cured connection structure comprises at least three interlocking nodes between layers, the spacing error between each node is ≤0.1 mm, and the density of the semi-cured sheet at the node after curing is ≥1.8 g / cm³.

6. The rivet-free fixing and pressing method of an electric machine according to claim 1, characterized in that: In step seven, the grayscale contrast threshold of the X-RAY detection is set to 60-80%, and the inter-layer displacement is automatically calculated by an image algorithm to generate an offset vector diagram.

7. The rivet-free fixing and pressing method using an electric press according to claim 1, characterized in that: During the lamination process in step eight, the heating rate is controlled at 3-5°C / min, and the holding time is 30-50 minutes.

8. The rivet-free fixing and pressing method using an electric press according to claim 1, characterized in that: The interlayer bonding force of the cured connection structure is ≥10N / cm, and the thermal expansion coefficient matches ±1.5ppm / °C of the core board material.

9. The rivet-free fixing and pressing method of an electric press according to claim 1, characterized in that: The hot melt pressure head of the voltage press adopts a zoned temperature control design, and the temperature of the target hole area at the four corners is 5-10°C higher than that of the central area.