FPC expansion and contraction management method

Abstract

The application discloses a kind of FPC expansion and contraction management methods, including the selection and processing of copper foil substrate, laser, plasma treatment, copper plating, etching, paste pressure CVL, punching, grinding plate, ink, baking, gold, PI pressure and cutting shape, by each process in the FPC production process is controlled, including the selection of material, the processing of material, parameter control in each process, can effectively improve the expansion and contraction in the FPC production process, avoid due to expansion and contraction and cause FPC's defect, ensure the stability of product, can avoid due to FPC expansion and contraction and need rework or repair, improve the production efficiency of FPC.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flexible circuit boards, in particular to a FPC expansion and contraction control method. BACKGROUND

[0002] Flexible printed circuit board (FPC), as an important branch of printed circuit board (PCB), is a kind of flexible printed circuit board with high reliability and excellent flexibility, which is made of polyimide or polyester film as insulating substrate. Flexible printed circuit board (FPC) has the advantages of high wiring density, ultra-thin, ultra-light, foldable, flexible assembly and other advantages. It can be moved and stretched anywhere in the main space, and it is easy to realize the integration of component assembly and wire connection. At present, the application of FPC almost involves all electronic information products, including consumer electronics, communication equipment and automotive products in a wide range of fields.

[0003] The expansion and contraction of flexible circuit board (FPC) may cause the following hazards: in terms of electrical performance, expansion and contraction may cause changes in line spacing, and subtle changes in line may cause signal transmission interruption or errors; changes in line length and width will affect the resistance value, thereby affecting the performance and stability of the circuit. In terms of assembly and connection, the expansion and contraction of FPC may cause the pins of the installed electronic components to be unable to accurately align, affecting the efficiency and quality of assembly, for example, the connector cannot be tightly connected with the FPC, resulting in poor contact; during the welding process, the expansion and contraction may cause uneven bonding of the solder pad and solder, resulting in problems such as virtual welding and false welding, reducing the reliability of welding. In terms of product reliability, internal stress generated by expansion and contraction may concentrate in certain parts, which may cause fatigue damage to the circuit board under long-term action, thereby shortening the service life of the product; expansion and contraction may damage the insulating layer of the circuit board, reduce the insulation performance, and increase the risk of leakage and short circuit. In addition, due to the quality problems caused by expansion and contraction, the generation of waste products will increase, and the production cost will increase. FPCs with expansion and contraction problems need to be reworked or repaired, which will consume a lot of time and manpower, and reduce the overall production efficiency. In summary, the expansion and contraction of flexible circuit board will have adverse effects on the electrical performance, assembly and connection, reliability and production process of the product, so effective measures must be taken to control and reduce the occurrence of expansion and contraction during design, production and use.

[0004] Therefore, the present application is developed based on the deep thinking and active research on the improvement of the flexible circuit board expansion and contraction. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the prior art and provide a FPC expansion and contraction control method that can improve the expansion and contraction of FPC.

[0006] In order to achieve the above purpose, the solution of the present application is:

[0007] A FPC expansion control method, comprising the following steps:

[0008] S1, after baking the copper foil substrate, the temperature is returned to improve the dimensional stability of the substrate, remove the moisture in the copper foil substrate, reduce the size change caused by the evaporation of moisture in the subsequent processing process;

[0009] S2, laser, select laser energy, avoid excessive energy leading to excessive heating of the substrate, control the laser speed, ensure uniform distribution of heat;

[0010] S3, plasma treatment, clean and activate the surface of the substrate after laser, remove the surface contaminants, oxides and organic impurities, improve the surface properties and wettability, and enhance the bonding force between materials;

[0011] S4, copper plating, control the current density, avoid excessive current leading to local overheating and stress concentration, control the plating time, ensure the uniform thickness of the copper plating layer, control the composition of the plating solution, ensure the stability of the plating solution performance;

[0012] S5, etching, control the concentration of etching solution, keep the concentration of etching solution stable and appropriate, avoid concentration fluctuation leading to uneven etching rate, control etching temperature and time, prevent excessive etching or insufficient etching caused by size change, ensure uniform stirring of etching solution during etching process, make etching reaction proceed uniformly; balance the line distribution, make the line evenly distributed on the FPC;

[0013] S6, paste CVL, control the paste temperature, avoid excessive temperature leading to excessive expansion of the substrate and CVL, or low temperature leading to poor adhesion; adjust the pressure to ensure the tight fit of CVL and substrate, reduce the gap and uneven stress; control the paste time to ensure sufficient time for the adhesive to fully cure;

[0014] S7, punching, control the punching speed, avoid excessive heat generated by fast punching speed, control the punching pressure, uniformly apply pressure to prevent material deformation caused by uneven pressure;

[0015] S8, grinding, reduce the grinding pressure, control the grinding speed, use multi-stage grinding, gradually adjust the grinding amount, control the temperature during grinding process to avoid excessive temperature leading to changes in the properties of the substrate material;

[0016] S9, ink, uniformly coat the ink to avoid excessive thickness difference;

[0017] S10, baking, use a hot air circulation oven to ensure uniform temperature distribution in the baking chamber;

[0018] S11, chemical gold plating, control the temperature and concentration of the chemical gold plating solution, avoid excessive temperature fluctuation; control the concentration of each component in the gold plating solution;

[0019] S12, PI pressing, control the pressing pressure to ensure uniform distribution of pressure throughout the pressing area, so that the PI is closely attached to the substrate; control the pressing time to ensure sufficient pressing time for the PI material to fully solidify and fuse;

[0020] S13, punching the outer shape, baking the FPC before punching, designing the punching path to make the punching path symmetrical; control the punching speed to avoid excessive impact force caused by excessive speed to cause material deformation; control the punching pressure to complete the punching without excessive extrusion of the material; maintain the temperature stability of the punching.

[0021] Further, in step S12, the PI is selected to have a low coefficient of thermal expansion and stable performance, and the PI material is subjected to incoming inspection to ensure uniform thickness and no defects; the pressing temperature is accurately controlled to avoid uneven expansion or shrinkage caused by excessive or insufficient temperature;

[0022] Further, steps S1 to S5 are all roll-to-roll processing, the copper foil substrate of step S1 uses a whole roll of copper foil, and the leading and trailing films are each 8m long.

[0023] Further, between the plasma treatment of step S3 and the copper plating process of step S4, there is also a black shadow process, before the black shadow, the FPC is pre-baked to remove moisture and internal stress; after the black shadow process is completed, slow cooling or annealing treatment is performed to reduce internal stress.

[0024] Further, between the copper plating of step S4 and the etching process of step S5, there is also an exposure process, a glass film is used, and the leading and trailing films are each 8m long.

[0025] Further, before the CVL is attached in step S6, the CVL is pretreated, and the waste area arrow points forward in the feeding direction.

[0026] Further, the present application further comprises a swelling and shrinking test step, 30PNL are taken from the first section, the middle section and the last section of the whole roll of product, respectively, and marked as 1-30 for the first section, 31-60 for the middle section, and 61-90 for the last section. The data of each PNL are collected and monitored, and correspond to the corresponding mark order.

[0027] After adopting the above scheme, the FPC swelling and shrinking control method can effectively improve the swelling and shrinking amount in the FPC production process by controlling each process in the FPC production process, including the selection of materials, the treatment of materials, and the parameter control in each process. It can avoid the defects of FPC caused by swelling and shrinking, ensure the stability of the product, avoid the need for rework or repair due to FPC swelling and shrinking, and improve the production efficiency of FPC. DETAILED DESCRIPTION

[0028] In order to further explain the technical solutions of the present application, the present application will be described in detail below through specific examples.

[0029] The present application discloses a kind of FPC expansion control method, it includes the following steps:

[0030] S1, using oven to the copper foil substrate is baked 120 DEG C, 4 hours, back temperature 3 hours.Copper foil substrate is baked to reduce the risk of expansion.In addition, baking can also improve the dimensional stability, remove moisture in copper foil substrate, so as to improve the accuracy and accuracy of laser processing.

[0031] S2, laser, select appropriate laser energy, avoid excessive energy to cause substrate excessive heating and produce larger expansion;Control the speed of laser, reasonable control the scanning speed of laser, to ensure that heat is evenly distributed, reduce the expansion caused by local thermal stress.

[0032] S3, plasma treatment, clean and activate the surface of substrate after laser, remove surface contaminants, oxides and organic impurities, etc., improve surface energy, enhance the bonding force between materials, after plasma treatment, the properties of FPC surface are improved, which helps to better control the expansion of materials in subsequent processes.

[0033] S4, copper plating, control current density, select appropriate current density, avoid excessive current to cause local overheating and stress concentration, cause expansion;Control plating time, ensure that the thickness of copper plating layer is uniform, not too thick or too thin;Control the composition of plating solution, detect and supplement the composition of main salt, additive and other components in plating solution before copper plating, to ensure the stability of plating solution performance.

[0034] S5, etching, control the concentration of etching solution, keep the stability and appropriateness of etching solution concentration, avoid concentration fluctuation to cause uneven etching rate, cause expansion;Control the temperature and time of etching, prevent size change caused by excessive etching or insufficient etching, ensure that etching solution is uniformly stirred in etching process, so that etching reaction proceeds uniformly;Balance the distribution of lines, make the lines evenly distributed on FPC, avoid the expansion caused by local stress concentration.

[0035] S6, paste pressure CVL, control the temperature of paste pressure, select appropriate temperature range, avoid excessive temperature to cause excessive expansion of substrate and CVL, or too low temperature to cause poor adhesion;Adjust the pressure, uniformly apply appropriate pressure, to ensure that CVL is closely attached to the substrate, reduce the gap and uneven stress;Control the time of paste pressure, ensure enough time for the adhesive to fully cure, but not too long to affect production efficiency and cause unnecessary size change.

[0036] S7, punching, controlling the punching speed to avoid excessive heat generated by too fast punching speed; controlling the punching pressure to apply uniform and appropriate pressure to prevent material deformation caused by uneven pressure.

[0037] S8, grinding plate, reducing the grinding plate pressure, controlling the grinding plate speed, using multi-section grinding plate, gradually adjusting the grinding amount, controlling the temperature during the grinding plate process to avoid excessive temperature leading to changes in the properties of the substrate material.

[0038] S9, ink, uniformly applying ink to avoid excessive thickness difference, as different thickness of ink may have different shrinkage levels during baking.

[0039] S10, baking, using a hot air circulation oven to bake, ensuring uniform temperature distribution in the baking cavity to avoid excessive expansion of the substrate and ink caused by excessive temperature, or incomplete solidification of the ink caused by insufficient temperature.

[0040] S11, chemical gold plating, controlling the temperature and concentration of the chemical gold plating solution to stabilize the temperature within a suitable range and avoid excessive temperature fluctuations; while controlling the concentration of each component in the gold plating solution to ensure uniformity and stability of the reaction. During the chemical gold plating process, the size change of the FPC is detected in real time, and once the expansion and contraction exceeds the allowed range, the process parameters are adjusted in time.

[0041] S12, PI pressing, selecting PI material with low thermal expansion coefficient and stable performance, conducting incoming inspection on the PI material to ensure uniform thickness and no defects; accurately controlling the pressing temperature to avoid uneven expansion or contraction caused by excessive or insufficient temperature; controlling the pressing pressure to ensure uniform pressure distribution in the entire pressing area, making the PI closely adhere to the substrate, reducing voids and stress concentration; controlling the pressing time to ensure sufficient pressing time for the PI material to fully solidify and fuse, but not too long to prevent excessive heat effect.

[0042] S13, punching the outer shape, baking the FPC before punching, designing the punching path to be symmetrical to reduce expansion and contraction caused by uneven stress; controlling the punching speed to avoid excessive impact force caused by too fast speed leading to material deformation; controlling the punching pressure to ensure moderate pressure to complete the punching without excessive extrusion of the material; maintaining stable temperature during punching to reduce the impact of temperature changes on material properties and size.

[0043] The FPC expansion and contraction control method can effectively improve the expansion and contraction amount during FPC production process by controlling each process, including material selection, material treatment, and parameter control in each process, to avoid FPC defects caused by expansion and contraction, ensure product stability, avoid the need for rework or repair due to FPC expansion and contraction, and improve FPC production efficiency.

[0044] In order to provide production efficiency, the steps S1 to S5 all adopt roll-to-roll processing, the copper foil substrate of step S1 adopts a whole roll of copper foil, and the substrates of steps S2-S5 are all pulled by guide films at the head and tail of the roll, and the front and rear guide films are each 8 m. If the length of the pulling film is too short, although the middle MD expansion and contraction data is stable, the etching first and last MD (roll transmission direction) direction expansion and contraction data is different, the etching first is small and the last is large, and there is a T-shaped first and last MD, and the end expansion and contraction is obvious.

[0045] Table 1 is a specific implementation table of the expansion and contraction control project of the present application:

[0046]

[0047] Expansion and contraction monitoring and comparison: take 30 PNL from the first section, the middle section and the last section of the whole roll of product, mark 1-30 as the first section, 31-60 as the middle section, and 61-90 as the last section, collect and monitor the data of each PNL and correspond to the corresponding mark order. After comparing the expansion and contraction conditions of the existing FPC process and the process of the present application, it can be concluded that the FPC expansion and contraction of the present application is obviously better than that of the FPC made by the existing process, and the yield of the FPC of the present application is much higher than that of the FPC made by the existing process.

[0048] The above examples do not limit the product form and style of the present application, and any appropriate changes or modifications made by any ordinary skilled person in the art shall be considered as not departing from the scope of the patent of the present application.

Claims

1. A method for controlling the expansion and contraction of an FPC, characterized in that: The following steps are involved: S1. Bake the copper foil substrate and then return it to the temperature to improve the dimensional stability of the substrate, remove moisture from the copper foil substrate, and reduce dimensional changes caused by moisture evaporation during subsequent processing; S2. Laser: Select the laser energy to avoid excessive heating of the substrate due to excessive energy, and control the laser speed to ensure even heat distribution; S3, plasma treatment, cleans and activates the surface of the substrate after laser treatment, removes surface pollutants, oxides and organic impurities, improves surface properties and strengthens the bonding force between materials; S4, copper plating, control the current density to avoid local overheating and stress concentration caused by excessive current, control the electroplating time to ensure uniform thickness of the copper plating layer, and control the plating solution composition to ensure stable plating solution performance; S5, etching, control the concentration of the etching solution, keep the concentration of the etching solution stable and appropriate, avoid concentration fluctuations that lead to uneven etching rate, control the temperature and time of etching, prevent dimensional changes caused by over-etching or under-etching, ensure that the etching solution is evenly stirred during the etching process, so that the etching reaction proceeds evenly; balance the circuit distribution so that the circuit is evenly distributed on the FPC; S6. Laminating the CVL. Control the laminating temperature to avoid excessive expansion of the substrate and CVL due to excessive temperature, or loose bonding due to low temperature. Adjust the pressure to ensure a tight fit between the CVL and the substrate, reducing gaps and uneven stress. Control the laminating time to ensure sufficient time for the adhesive to fully cure. S7, Punching, control the punching speed to avoid excessive heat generated by punching too fast, control the punching pressure, apply pressure evenly to prevent uneven pressure from causing material deformation; S8, grinding, reduce grinding pressure, control grinding speed, use multi-stage grinding, gradually adjust grinding volume, control the temperature during grinding to avoid excessive temperature causing changes in substrate material properties; S9, ink, apply ink evenly to avoid large differences in ink thickness; S10, baking, using a hot air circulation oven to ensure uniform temperature distribution in the baking chamber; S11, chemical gold plating, control the temperature and concentration of the chemical gold plating solution to avoid excessive temperature fluctuations; control the concentration of each component in the gold plating solution; S12, PI lamination, control the lamination pressure to ensure that the pressure is evenly distributed in the entire lamination area, so that the PI and the substrate are tightly fitted; control the lamination time to ensure that there is enough time for the PI material to fully solidify and fuse; S13. Punching the shape: Bake the FPC before punching and design the punching path to make it symmetrical. Control the punching speed to avoid excessive impact force caused by excessive speed, which may lead to material deformation. Control the punching pressure to complete the punching without over-extruding the material. Keep the punching temperature stable.

2. The FPC expansion and contraction control method according to claim 1, wherein: In step S12, PI materials with low thermal expansion coefficient and stable performance are selected, and incoming PI materials are inspected to ensure that their thickness is uniform and free of defects; the pressing temperature is precisely controlled to avoid uneven expansion or contraction caused by excessively high or low temperatures.

3. The FPC expansion and contraction control method according to claim 1, wherein: The steps S1 to S5 are all processed by roll-to-roll. The copper foil substrate of step S1 is a whole roll of copper foil. The substrate of steps S2-S5 is pulled by guide films at the front and rear rolls. The front and rear guide films are 8m each.

4. The FPC expansion and contraction control method according to claim 1, wherein: There is a black shadow process between step S3 plasma treatment and step S4 copper plating process. Before the black shadow process, the FPC is pre-baked to remove moisture and internal stress.

5. The FPC expansion and contraction control method according to claim 1, wherein: There is also an exposure process between step S4 copper plating and S5 etching process, using glass film, and the front and rear rolls are pulled by guide films, with the front and rear pulling films each being 8m.

6. The FPC expansion and contraction control method according to claim 1, wherein: Step S6: Pre-process the CVL before laminating the CVL, with the arrow in the waste area pointing forward in the board feeding direction.

7. The FPC expansion and contraction control method according to claim 1, wherein: It also includes an expansion and contraction test step, taking 30 PNL from the first, middle and last sections of the entire roll of product, marking 1-30 as the first section, 31-60 as the middle section, and 61-90 as the last section, collecting and monitoring the data of each PNL and corresponding to its corresponding marking order.

8. The FPC expansion and contraction control method according to claim 1, wherein: Step S12: After preheating the PI pressing machine, evenly apply a layer of thermosetting adhesive film on the substrate, accurately align the PI film on the adhesive film, set the temperature to 180°C, the pressure to 20 MPa, and the time to press for 45 minutes. After pressing is completed, naturally cool for 30 minutes.

Images