Method for improving warpage of high-frequency and high-speed mixed-pressing copper-block-embedded PCB (Printed Circuit Board)

Abstract

The invention discloses a method for improving warpage of a high-frequency and high-speed mixed-pressing copper-block-embedded PCB (Printed Circuit Board), relates to a PCB manufacturing technology, and provides a scheme aiming at the problem of high warpage rate in the prior art. Material pre-balancing: carrying out low-temperature vacuum baking on the resin material; the copper block is subjected to micro-arc oxidation treatment, and a ceramic film layer is generated on the surface of the copper block; the method comprises the following steps: pre-mixing a high-elastic-modulus filler to a resin material according to PCB structure simulation calculation to adjust the comprehensive CTE of the overall material of the PCB, so that the difference of the comprehensive CTE of the overall PCB in X, Y and Z directions is controlled within a threshold value; step-by-step lamination: heating from room temperature to a resin softening point at a first heating rate, carrying out heat preservation pressing, and heating from the resin softening point to a complete curing temperature at a second heating rate; gradually pressurizing in three sections in the process from the softening point of the resin to the complete curing temperature; and discharging: after the curing is finished, linearly controlling the temperature to be reduced to the discharging temperature under low pressure, and completing the discharging step. The method has the advantage that the PCB warping condition is effectively improved.

Description

Technical Field

[0001] The invention relates to PCB manufacturing technology, and in particular to a method for improving warping of a high-frequency and high-speed mixed-pressure buried copper block PCB board. Background Art

[0002] In the process of modern electronic equipment developing towards miniaturization and high performance, the demand for high-frequency and high-speed mixed-pressure buried copper block PCB boards has increased sharply. However, the manufacturing of such PCB boards faces severe challenges, and the problem of board warping is prominent. On the one hand, high frequency and high speed require the use of special resin materials with low dielectric constant and low loss tangent, which are greatly different from the thermal expansion coefficient (CTE) of conventional materials. On the other hand, due to the huge difference in CTE between the metal and the surrounding resin materials of the buried copper block, during the PCB processing thermal process (such as lamination, curing, and welding), due to the inconsistent thermal expansion and cooling contraction of each layer and material, huge internal stress is generated, causing the PCB board to bend and deform toward the copper block side, seriously affecting the manufacturability and performance of the PCB, reducing product yield, increasing production costs, and limiting the upgrading and development of related electronic equipment. Summary of the invention

[0003] The object of the present invention is to provide a method for improving the warping of a high-frequency and high-speed mixed-pressure buried copper block PCB board, so as to solve the problems existing in the above-mentioned prior art.

[0004] The method for improving the warping of a high-frequency, high-speed, mixed-pressure, buried copper block PCB board described in the present invention comprises the following steps:

[0005] The steps of material pre-balancing are as follows: the resin material is subjected to low-temperature vacuum baking; the copper block is subjected to micro-arc oxidation treatment to form a ceramic film layer on the surface of the copper block; based on the PCB structure simulation calculation, a high elastic modulus filler is pre-mixed into the resin material to adjust the overall material comprehensive CTE of the PCB board, so that the overall CTE of the PCB board in the X, Y, and Z directions is controlled within the threshold value;

[0006] Step-by-step lamination steps: heating from room temperature to the resin softening point at a first heating rate and pressing at the temperature, heating from the resin softening point to the complete curing temperature at a second heating rate; during the process from the resin softening point to the complete curing temperature, gradually increasing the pressure in three stages;

[0007] Out-of-baking step: After curing is completed, the temperature is linearly controlled to drop to the out-of-baking temperature under low pressure to complete the out-of-baking step.

[0008] The method for improving the warping of high-frequency, high-speed, mixed-pressure buried copper block PCB boards described in the present invention has the advantage that, after detection by a high-precision three-dimensional measuring instrument, the maximum warping value of the improved PCB board is sharply reduced from 1%-1.5% (percentage of board length) commonly seen in traditional processes to less than 0.2%, ensuring that the component mounting accuracy is within ±0.05mm, greatly reducing the welding defect rate, and improving the reliability of product electrical connections. The one-time yield of the product is increased to more than 92%, reducing the loss of scrapping due to board warping, shortening the production cycle by about 25%, and saving material and rework costs. At the same time, the heat dissipation performance of the PCB is guaranteed due to the optimization of the combination of copper blocks and resins, the thermal resistance is reduced by 20%-30%, the equipment operation stability is enhanced, and the service life is extended. DETAILED DESCRIPTION

[0009] The method for improving the warping of high-frequency and high-speed mixed-pressure buried copper block PCB boards described in the present invention is applicable to electronic products such as communication base station RF modules, high-end server motherboards, and precision medical electronic equipment that have extremely high requirements for the electrical performance, heat dissipation performance, and flatness of PCB boards. Ensure that the PCB board can operate stably under high-frequency and high-speed signal transmission conditions, and that the warping does not affect component welding, signal integrity, and equipment reliability. The specific steps are as follows:

[0010] Material pre-equalization step: pre-treat the resin materials and copper blocks with different CTEs respectively. The resin material is baked at low temperature vacuum before lamination, the temperature is set to 80℃-100℃, the vacuum degree is maintained at 50Pa-80Pa, and the duration is 4-6 hours to remove water vapor, stabilize the molecular structure, and reduce the subsequent thermal expansion and contraction. The copper block adopts a micro-arc oxidation process to generate a ceramic film layer with a thickness of about 2μm-5μm on its surface. This film layer not only enhances the bonding force between the copper block and the resin, but also has its own certain thermal insulation properties, buffers thermal shock, reduces the heat conduction rate, and alleviates the stress concentration caused by the rapid heating and cooling of the copper block. According to the simulation calculation of the PCB structure, a small amount of high elastic modulus filler is pre-mixed with different CTE materials in a certain proportion, and the comprehensive CTE of the overall material is adjusted so that the difference in the X, Y, and Z directions is controlled within 8ppm / ℃, which weakens the cause of board warping from the root. The high elastic modulus filler can be selected from nano-silicon dioxide, with a particle size of 30nm-50nm and an addition amount of 1%-3% (mass fraction).

[0011] Steps for step-by-step lamination: Design a gradient temperature rise and segmented pressure-maintaining lamination curve. In the initial stage of temperature rise, the temperature rises from room temperature to the softening point of the resin at a rate of 0.8℃ / min-1℃ / min, depending on the type of resin, generally 120℃-140℃. Keep warm for 15-20 minutes to promote the initial uniform flow of the resin. Then slowly rise to the full curing temperature at 0.5℃ / min, generally 170℃-190℃. In the process from the softening point of the resin to the full curing temperature, gradually increase the pressure in three stages. The pressure of the initial stage is set to 30%-40% of the final pressure, the pressure of the middle stage is set to 60%-70% of the final pressure, and the final stage directly uses the final pressure, such as 0.8MPa-1MPa. Ensure that the resin fully fills the gaps between the layers at different temperature stages, especially the parts that tightly wrap the copper block.

[0012] Steps of taking out of the oven: After curing, the temperature is linearly cooled to below 80°C for 40-60 minutes before being taken out of the oven. High-precision temperature control is used throughout the process, with a temperature control accuracy of ±2°C to suppress sudden changes in thermal stress. Vacuum-assisted lamination is introduced, and the vacuum degree is maintained at 60Pa-90Pa throughout the process, which can remove air between layers, avoid residual bubbles forming local weak points that aggravate board warping, and ensure that the interlayer structure of the PCB is dense and uniform.

[0013] For those skilled in the art, various other corresponding changes and deformations can be made according to the technical solutions and concepts described above, and all of these changes and deformations should fall within the protection scope of the claims of the present invention.

Claims

1. A method for improving the warping of high-frequency and high-speed mixed-pressure buried copper block PCB board, characterized in that: The following steps are involved: The steps of material pre-equalization are as follows: the resin material is subjected to low-temperature vacuum baking; the copper block is subjected to micro-arc oxidation treatment to form a ceramic film layer on the surface of the copper block; According to the simulation calculation of PCB structure, pre-mix high elastic modulus filler into the resin material to adjust the comprehensive CTE of the whole material of PCB board, so that the difference of the comprehensive CTE of the whole PCB board in X, Y and Z directions is controlled within the threshold; Step-by-step lamination steps: heating from room temperature to the resin softening point at a first heating rate and pressing at the temperature, heating from the resin softening point to the complete curing temperature at a second heating rate; during the process from the resin softening point to the complete curing temperature, gradually increasing the pressure in three stages; Out-of-baking step: After curing is completed, the temperature is linearly controlled to drop to the out-of-baking temperature under low pressure to complete the out-of-baking step.

2. According to the method for improving the warping of high-frequency and high-speed mixed-pressure buried copper block PCB board according to claim 1, it is characterized in that: The thickness of the ceramic film layer is 2 μm-5 μm.

3. According to the method for improving the warping of high-frequency and high-speed mixed-pressure buried copper block PCB board according to claim 1, it is characterized in that: The temperature of the low-temperature vacuum baking is set to 80°C-100°C, the vacuum degree is maintained at 50Pa-80Pa, and the duration is 4-6 hours.

4. According to claim 1, a method for improving warping of a high-frequency, high-speed, mixed-pressure buried copper block PCB board is characterized in that: The threshold value of the overall PCB board's comprehensive CTE difference in the X, Y, and Z directions is 8ppm / ℃.

5. According to claim 1, a method for improving warping of a high-frequency, high-speed, mixed-pressure buried copper block PCB board is characterized in that: The high elastic modulus filler is nano silicon dioxide.

6. A method for improving warping of a high-frequency, high-speed, mixed-pressure buried copper block PCB board according to claim 5, characterized in that: The particle size of the nano silicon dioxide is 30nm-50nm, and the added amount is 1%-3% by mass.

7. The method for improving warping of a high-frequency, high-speed, mixed-pressure buried copper block PCB board according to claim 1, characterized in that: The first heating rate is 0.8°C / min-1°C / min; the second heating rate is 0.5°C / min; and the heat preservation and pressing time is 15-20 minutes.

8. The method for improving warping of a high-frequency, high-speed, mixed-pressure buried copper block PCB board according to claim 1, characterized in that: The three-stage gradual pressure increase is specifically as follows: the pressure of the initial stage is set to 30%-40% of the final pressure, the pressure of the middle stage is set to 60%-70% of the final pressure, and the final stage directly uses the final pressure.

9. The method for improving warping of a high-frequency, high-speed, mixed-pressure buried copper block PCB according to claim 1, characterized in that: The specific steps of taking out the furnace are: linearly cooling the temperature to below 80°C over 40 minutes to 60 minutes, maintaining the temperature control accuracy of ±2°C throughout the process, and maintaining the vacuum degree at 60Pa-90Pa.