Laminating and glue filling method for multi-layer printed circuit board

Abstract

The invention discloses a multilayer printed circuit board pressing and glue filling method, and particularly relates to the technical field of multilayer circuit board pressing, and the method comprises the following specific steps: S1, selecting liquid resin oil with the same performance as a prepreg; s2, liquid resin oil is printed in the middle of the inner-layer circuit board in a silk-screen mode, after printing, standing is carried out, so that the liquid resin oil completely fills the circuit, and then low-temperature baking is carried out, so that the liquid resin oil reaches a semi-solidified state; s3, stacking the inner-layer circuit board, the prepreg and the outer-layer copper foil according to a specific sequence and direction to form a to-be-pressed body; and S4, the to-be-pressed body formed in the step S3 is put into a pressing machine to be pressed. According to the method, the liquid resin oil is used for replacing traditional PP filling glue, the liquid resin oil can be filled into the gap in the middle of the inner-layer circuit board by means of the good flowability of the liquid resin oil, the inner-layer circuit board is filled and leveled up, the glue filling effect is improved, and the technical difficulty of lamination production of the multi-layer circuit board is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of multi-layer circuit board lamination, and more particularly to a method for laminating and filling glue on a multi-layer printed circuit board. Background Art

[0002] Screen printing glue filling for multilayer circuit boards (PCBs) is a process in which glue is applied to specific areas of the board using screen printing technology during the manufacturing process. A screen printer is used to apply glue to designated areas of the board. Screen printing offers the advantage of precise control over the placement and shape of the glue, making it suitable for a variety of complex patterns and designs. Traditionally, the glue needs to be cured after printing, typically using heat or UV irradiation. The cured glue provides excellent mechanical strength and electrical properties, ensuring that the board does not experience glue detachment or electrical shorts during use. Some ultra-thick copper multilayer PCBs utilize relatively thick copper layers in the conductive layer. These specialized PCBs are characterized by a typical layer count of 4 to 12, an inner substrate copper foil thickness of 350 μm (10 oz) or greater, and high quality and reliability requirements. Ultra-thick copper multilayer PCBs offer excellent current-carrying capacity and heat dissipation, and are primarily used in network energy, communications, automotive, high-power power supplies, and clean energy solar energy, thus possessing broad market development prospects.

[0003] However, during the lamination process for these types of PCBs, the issue of filling between inner layer lines requires consideration. The thicker the copper, the more difficult it is to fill between inner layer lines. Due to the deeper gaps between lines, multiple prepregs with good flowability are required to meet the required resin filling volume, assuming the same residual copper content. Even with this approach, insufficient resin filling can occur, leading to problems such as lamination voids, wrinkled copper surfaces, and uneven board thickness distribution. For thick copper core boards with asymmetric inner layer residual copper content, using multiple sheets of PP filling cannot achieve the required board thickness uniformity, resulting in serious quality issues in subsequent production processes.

[0004] The current industry practice is to use PP (prepreg) with a high glue content for filling. However, due to the limitations of inner layer wiring, residual copper rate and copper thickness, as well as the number of PP sheets used (dielectric layer thickness), the filling is prone to unevenness, affecting quality. Poor filling can also lead to functional problems such as board explosion and delamination. Summary of the Invention

[0005] In order to overcome the above-mentioned defects of the prior art, the present invention provides a method for laminating and filling multi-layer printed circuit boards, using liquid resin oil instead of traditional PP filling. The good fluidity of the liquid resin oil itself is utilized to enable it to fill the gap in the middle of the inner circuit board, fill the inner circuit board, improve the filling effect, reduce the difficulty of lamination production technology, and solve the problems arising from the above-mentioned background technology.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for laminating and filling glue on a multi-layer printed circuit board, comprising the following specific steps:

[0007] S1. Select liquid resin oil with the same performance as prepreg;

[0008] S2. Use silk screen printing to print liquid resin oil in the middle of the inner circuit board. After printing, let it stand to allow the liquid resin oil to completely fill the circuit. Then bake it at low temperature to make the liquid resin oil reach a semi-solidified state.

[0009] S3, stacking the inner circuit board, the prepreg, and the outer copper foil in a specific order and direction to form a body to be pressed;

[0010] S4, placing the body to be pressed formed in step S3 into a press, and bonding the inner circuit board, the prepreg, and the outer copper foil together through melt flow solidification of the prepreg;

[0011] S5, disassembling the pressed body to obtain a multilayer printed circuit board;

[0012] S6. The obtained multi-layer printed circuit board is subjected to edge milling and edge grinding, and then quality inspection is performed.

[0013] In a preferred embodiment, the TG value of the liquid resin oil selected in step S1 is the same as the TG value of the prepreg.

[0014] In a preferred embodiment, the size of the prepreg is precisely cut according to the number of layers, thickness and design requirements of the circuit board, and the thickness of the prepreg is consistent with the thickness of the dielectric layer required in the multi-layer printed circuit board.

[0015] In a preferred embodiment, before performing step S2, the inner layer circuit board is cleaned and etched to remove oil and impurities, and a precise circuit pattern is etched out. Then, a blackening or browning treatment is performed to make the copper surface fuzzy, increase the roughness, form an organic oxide layer, and enhance the adhesion with the semi-cured sheet.

[0016] In a preferred embodiment, in step S3, positioning pins or an optical positioning system are used to ensure that the circuit patterns of each layer are accurately aligned.

[0017] In a preferred embodiment, the pressing process in step S4 is carried out in the following steps in sequence: S4.1 Pre-pressing: contacting the multilayer board surface to remove the air between the multilayer board layers; S4.2. Medium pressure: the semi-cured sheet melts and the viscosity becomes smaller. The pressure applied in the initial stage promotes the molten resin to flow, wet the bonding surface and fill the gap, and at the same time drives away the volatiles generated when the semi-cured sheet melts, preventing the core board from wrinkling due to excessive pressure in the initial stage; S4.3. Full pressure: the pressure applied when the semi-cured sheet melts and has low viscosity, to ensure that the resin flows and fills completely, and the volatiles of the semi-cured sheet are completely discharged, until the resin is cured to complete the bonding of the core board and the semi-cured sheet, making them become one; S4.4. Pressure reduction: after the semi-cured sheet is completely cured, a certain pressure is applied in the cooling stage to prevent the internal stress of the multilayer board from being released sharply during the cooling process, resulting in board bending and warping defects.

[0018] In a preferred embodiment, the quality inspection in step S6 includes both a visual inspection and electrical performance testing. The visual inspection primarily checks for obvious surface defects on the circuit board, such as delamination, bubbles, and copper foil scratches. The electrical performance testing examines key circuit board characteristics, such as conductivity, insulation, and impedance matching, to ensure they meet design requirements. For multi-layer circuit boards, X-ray inspection equipment is also used to check the alignment between the layers.

[0019] In a preferred embodiment, the milling in step S6 is to remove excess copper foil and glue flow from the side of the multilayer printed circuit board, and the edge grinding is to perform chamfering and beveling on the multilayer printed circuit board to remove peaks and burrs on the edge of the multilayer printed circuit board.

[0020] The technical effects and advantages of the present invention are as follows:

[0021] 1. The present invention uses liquid resin oil to replace traditional PP filler. The good fluidity of the liquid resin oil itself is used to enable it to be filled into the circuit in the middle of the inner circuit board, filling the inner circuit board and improving the filler effect, thereby reducing the technical difficulty of pressing production. There is no need to consider functional issues such as copper thickness, residual copper rate, PP filler content, and whether the lack of glue will cause board explosion and delamination.

[0022] 2. The present invention uses a liquid resin oil material with the same TG value as the prepreg, which can ensure that the fluidity of the liquid resin oil is not too large, thereby avoiding oil leakage during low-temperature baking, and can also improve the compatibility between the liquid resin oil and the prepreg. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Flowchart of the present invention. DETAILED DESCRIPTION

[0024] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0025] Refer to the instruction manual Figure 1 The present invention provides a method for laminating and filling a multilayer printed circuit board, comprising the following specific steps:

[0026] S1. Select liquid resin oil with the same performance as the prepreg, that is, the TG value of the selected liquid resin oil should be the same as the TG value of the prepreg (TG value refers to the glass transition temperature). The fluidity of the liquid resin oil should not be too large, otherwise there will be oil flow during the baking process. The performance of the material and the prepreg should be compatible, otherwise there will be a risk of delamination. The bonding strength between the material and the prepreg should be good.

[0027] S2. First, clean and etch the inner circuit board to remove oil and impurities, etch out a precise circuit pattern, and then perform a blackening or browning treatment to make the copper surface fuzzy, increase the roughness, form an organic oxide layer, and enhance the bonding strength with the prepreg;

[0028] Next, the liquid resin oil is printed on the middle of the inner circuit board by silk screen printing. After printing, it is left to stand to allow the liquid resin oil to completely fill the circuit. It is then baked at low temperature to make the liquid resin oil reach a semi-solidified state. Among them, the silk screen mesh selection method is as follows: for example, for a 6OZ thick copper plate, the copper thickness is 0.21mm, and the line spacing after etching is 10mil. In order to ensure good filling of this small spacing, the silk screen mesh is generally selected as 36T or 32T, so that a larger amount of resin glue is used during printing.

[0029] The resin oil used in this step is a resin-type connecting material made by dispersing and dissolving synthetic resin or semi-synthetic resin with drying vegetable oil, high-boiling point mineral oil, etc. Liquid resin oil is liquid at room temperature and solidifies at a slightly higher temperature. The solidified resin oil can fill the gaps in the inner layer circuit board to achieve the effect of filling the inner layer circuit;

[0030] Compared with the existing technology, the present invention uses liquid resin oil instead of traditional PP filler. By utilizing the fluidity of the liquid resin oil, it can fill the gaps in the inner layer circuit board, which can reduce the difficulty of the pressing production technology. There is no need to consider copper thickness, residual copper rate, PP filler content selection, whether the lack of glue will cause the board to explode and delaminate, and other functional quality problems.

[0031] S3. The inner circuit board, prepreg, and outer copper foil are stacked in a specific order and direction to form a body to be pressed. During this process, positioning pins or an optical positioning system are required to ensure that the circuit patterns of each layer are accurately aligned.

[0032] The size of the prepreg is precisely cut according to the number of layers, thickness and design requirements of the circuit board, and the thickness of the prepreg is consistent with the thickness of the dielectric layer required in the multi-layer printed circuit board.

[0033] S4, placing the body to be pressed formed in step S3 into a press, and bonding the inner circuit board, the prepreg, and the outer copper foil together through melt flow solidification of the prepreg;

[0034] The lamination process is carried out in the following steps: S4.1. Pre-pressing (0-10 minutes): Contact the multilayer board surface to remove air between the multilayer boards to prevent the formation of bubbles. During this stage, the temperature is raised from room temperature to 140-170°C and maintained for 5 minutes. The pressure is set to 80 PSI and maintained for 10 minutes.

[0035] S4.2. Medium Pressure (10-21 minutes): The prepreg melts and its viscosity decreases. The pressure applied at the initial stage promotes the flow of molten resin to wet the bonding surface and fill the gap. It also drives away volatiles produced by the prepreg melting and prevents core board wrinkling caused by excessive pressure at the initial stage. During this stage, the temperature is increased at a rate of 6.25°C / min-10°C / min to 220°C, and the pressure is increased at a rate of 85 PSI / min to 250 PSI.

[0036] S4.3. Full Pressing (Minutes 21-61): Pressure is applied while the prepreg is molten and has a low viscosity, ensuring complete resin flow and filling and the complete expulsion of volatiles from the prepreg. This is followed by the resin solidifying and bonding the core and prepreg together. During this stage, the temperature is increased at a rate of 5°C / min to 240°C, and the pressure is increased at a rate of 75 PSI / min to 400 PSI.

[0037] S4.4. Pressure reduction (61-124 minutes): After the semi-cured sheet is completely cured, a certain amount of pressure is applied during the cooling stage to prevent the internal stress of the multilayer board from being released rapidly during the cooling process, which may cause board bending and warping defects. In this stage, the temperature is first reduced to 210°C at a rate of 3°C / min, maintained at 210°C for 80 minutes, then reduced to 140°C at a rate of 3.5°C / min and maintained for 9 minutes, and finally reduced to 100°C at a rate of 8°C / min; the pressure in this stage is first maintained at 400PSI for 80 minutes, then reduced to 300PSI at a rate of 10PSI / min, and then maintained at 300PSI for 19 minutes, and finally reduced to 100PSI at a rate of 40PSI / min, and maintained at this pressure for 10 minutes until the pressing is completed.

[0038] S5. Demolish the pressed body to obtain a multilayer printed circuit board.

[0039] S6. The obtained multi-layer printed circuit board is subjected to milling and grinding. The purpose of milling is to remove the excess copper foil and glue flow on the side of the multi-layer printed circuit board. The purpose of grinding is to perform chamfering and beveling on the multi-layer printed circuit board to remove the peaks and burrs on the edge of the multi-layer printed circuit board.

[0040] Next, quality inspections are conducted. These inspections include visual inspection and electrical performance testing. The visual inspection primarily checks for obvious surface defects on the circuit board, such as delamination, bubbles, and copper foil scratches. The electrical performance test assesses key indicators such as the board's conductivity, insulation, and impedance matching to ensure it meets design requirements. For multi-layer circuit boards, X-ray inspection equipment is also used to check the alignment between the layers.

[0041] Finally: The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for laminating and filling a multilayer printed circuit board, characterized in that: The specific steps include: S1. Select liquid resin oil with the same performance as prepreg; S2. Use silk screen printing to print liquid resin oil in the middle of the inner circuit board. After printing, let it stand to allow the liquid resin oil to completely fill the circuit. Then bake it at low temperature to make the liquid resin oil reach a semi-solidified state. S3, stacking the inner circuit board, the prepreg, and the outer copper foil in a specific order and direction to form a body to be pressed; S4, placing the body to be pressed formed in step S3 into a press, and bonding the inner circuit board, the prepreg, and the outer copper foil together through melt flow solidification of the prepreg; S5, disassembling the pressed body to obtain a multilayer printed circuit board; S6. The obtained multi-layer printed circuit board is subjected to edge milling and edge grinding, and then quality inspection is performed.

2. The method for laminating and filling a multilayer printed circuit board according to claim 1, wherein: The TG value of the liquid resin oil selected in step S1 is the same as the TG value of the prepreg.

3. The method for laminating and filling a multilayer printed circuit board according to claim 1, wherein: The size of the prepreg is precisely cut according to the number of layers, thickness and design requirements of the circuit board, and the thickness of the prepreg is consistent with the thickness of the dielectric layer required in the multi-layer printed circuit board.

4. The method for laminating and filling a multilayer printed circuit board according to claim 1, wherein: Before performing step S2, the inner layer circuit board is cleaned and etched to remove oil and impurities, and a precise circuit pattern is etched out. Then, a blackening or browning treatment is performed to make the copper surface fuzzy, increase the roughness, form an organic oxide layer, and enhance the bonding strength with the prepreg.

5. The method for laminating and filling a multilayer printed circuit board according to claim 1, wherein: In step S3, positioning pins or an optical positioning system are used to ensure that the circuit patterns of each layer are accurately aligned.

6. The method for laminating and filling a multilayer printed circuit board according to claim 1, wherein: The pressing process in step S4 is carried out in the following steps in sequence: pre-pressing, medium pressing, full pressing, and pressure reduction.

7. The method for laminating and filling a multilayer printed circuit board according to claim 1, characterized in that: The quality inspection in step S6 includes appearance inspection and electrical performance testing.

8. The method for laminating and filling a multi-layer printed circuit board according to claim 1, characterized in that: The edge milling in step S6 is to remove excess copper foil and adhesive on the side of the multilayer printed circuit board, and the edge grinding is to perform chamfering and beveling on the multilayer printed circuit board to remove peaks and burrs on the edge of the multilayer printed circuit board.

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