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CN-122028331-A - FPC high multilayer board explosion board improvement method

CN122028331ACN 122028331 ACN122028331 ACN 122028331ACN-122028331-A

Abstract

The invention discloses a method for improving a high-multilayer board explosion board of an FPC, and relates to the technical field of FPC manufacturing. The method comprises the steps of covering film selection, covering film pretreatment, pure glue selection, substrate selection, combined pretreatment, interlayer structure design, steel sheet treatment, pressing process optimization and the like, wherein a covering film with a peeling force of more than 1.0kg/cm < 2 >, a pretreatment mode with preferential middle roughening are adopted, ion-resistant pure glue is selected, through the pretreatment of middle roughening or browning, a frosted steel sheet without holes and a thick steel sheet glue are selected, the steel sheet is subjected to plasma treatment, pressing parameters are optimized, and a quick pressing/pressure transmitting mode is adapted. According to the invention, through multi-dimensional collaborative design, interlayer binding force is improved, stress concentration and moisture absorption risk are reduced, the FPC high-multilayer board passes double 85+reflow and PCT severe tests, the problem of high explosion rate of the FPC multilayer board in the prior art is solved, and the FPC high-multilayer board is particularly suitable for four-layer and more multilayer boards, and has strong practicability.

Inventors

  • PAN HUI
  • ZHANG YUNCHENG
  • DONG ZHIMING

Assignees

  • 厦门弘信电子科技集团股份有限公司

Dates

Publication Date
20260512
Application Date
20260228

Claims (10)

  1. 1. The FPC multilayer board explosion improvement method is characterized by comprising the following steps of: S1, selecting a cover film, wherein the cover film is a cover film with a peeling force of more than 1.0kg/cm <2 >, and has excellent high temperature resistance, moisture absorption resistance and interlayer bonding stability, the cover film is subjected to high temperature of 265-270 ℃ reflow soldering for 10S within 5min after double-85 testing, interlayer separation does not occur after 5 times of repetition, and meanwhile, the thermal expansion coefficient of the cover film is matched with that of an FPC substrate and copper foil, and the difference value is controlled within 5ppm/° C; S2, surface pretreatment of the cover film selected in the step 1, wherein the surface pretreatment is to perform any one or any combination of roughening, microetching or sand blasting on one surface of the adhesive layer, the copper etching amount is controlled to be 0.8-1.2 mu m in the roughening treatment, the surface of the adhesive layer of the cover film forms a uniformly distributed micro-roughness structure, the peeling force between the cover film and the substrate after the pretreatment is greater than 0.9kg/cm <2 >, and the peeling force variation coefficient is controlled to be within 5%; s3, selecting the pure rubber, namely selecting the ion-resistant pure rubber, wherein the moisture absorption rate of the ion-resistant pure rubber is controlled below 0.1% after double-85 test for 5H, and meanwhile, the glass transition temperature of the ion-resistant pure rubber is higher than 200 ℃; s4, selecting a substrate, wherein the moisture absorption rate of the selected substrate is controlled below 0.2% after double-85 test is performed for 5H, the thermal decomposition temperature is higher than 300 ℃, for more than four layers of multi-layer boards, the interlayer adhesive layer of the substrate needs to be modified epoxy resin adhesive with high bonding strength, the thickness of the adhesive layer is controlled to be 80-100 mu m, and meanwhile, the thermal expansion coefficient of the substrate needs to be coordinated with that of a covering film and a copper foil; S5, combined pretreatment, namely pretreating the substrate or the copper foil in a manner of roughening, browning or microetching, combining the pretreated substrate or the copper foil with pure rubber, wherein the stripping force of the combined pure rubber is more than 1.0kg, and the rate of reduction of the stripping force after double-85 test for 12H is not more than 8%; S6, designing an interlayer structure, namely adopting an interlayer structure of interlayer thin glue and outer layer thick glue for four or more layers of the multilayer boards, wherein the thickness of the interlayer glue is 80-100 mu m, and the thickness of the outer layer glue is 120-150 mu m; And S7, optimizing a lamination process, namely setting lamination parameters to be 90-130KG of lamination pressure, 90-150S of lamination time and 180 ℃ of lamination temperature, and simultaneously, enabling the pressure fluctuation range in the lamination process not to exceed +/-5 KG.
  2. 2. The method for improving the FPC multilayer board explosion board according to claim 1, wherein the FPC multilayer board comprises a steel sheet, step S8 is further included before the lamination process of step S7 is optimized, the steel sheet is a frosted steel sheet without holes, the thickness of the steel sheet is 0.1 mm-0.3 mm, the hardness of the steel sheet is HV 200-HV 250, plasma pretreatment is conducted on the steel sheet, active groups are introduced into the surface of the steel sheet through plasma treatment, steel sheet glue with the thickness of 150-200 mu m is selected, and the elastic modulus of the steel sheet glue is controlled to be 1.5-2.5 GPa.
  3. 3. The method for improving the FPC multilayer board explosion board according to claim 2 is characterized in that the edge of the steel sheet is designed in a circular arc transition mode, the radius of a round angle is 0.5 mm-1 mm, the bonding area of the steel sheet and the FPC adopts a combination mode of local dispensing and integral pressing, high-strength glue is pre-dispensed on the edge and central key stress points of the steel sheet, the dispensing diameter is 1 mm-2 mm, the dispensing interval is 4 mm-6 mm, and integral pressing is carried out, so that local reinforced bonding is formed between the steel sheet and a covering film.
  4. 4. The method for improving the explosion panel of the FPC multilayer board according to claim 1, wherein the high FPC multilayer board comprises a steel sheet, a plurality of blind holes are formed in the steel sheet, the blind holes do not penetrate through the steel sheet, the inner walls of the blind holes are coated with a hydrophobic coating, the hydrophobic coating is made of polytetrafluoroethylene or fluorine modified resin, the thickness of the coating is 5-10 mu m, and the contact angle is larger than 110 degrees.
  5. 5. The method for improving the explosion board of the FPC multi-layer board according to claim 1, wherein grid-shaped copper layers are distributed during wiring, grid intervals are 1 mm-2 mm, and grid line widths are 0.1 mm-0.2 mm.
  6. 6. The method for improving the explosion of the FPC multilayer board according to claim 1, further comprising the step S9 after the step S7, and after lamination, performing slow cooling treatment, namely, after lamination, placing the FPC high multilayer board in a slow cooling furnace for gradual cooling, wherein the cooling rate is 5-8 ℃ per minute, gradually cooling from 180 ℃ to room temperature, and controlling the temperature difference in the slow cooling process within +/-3 ℃.
  7. 7. The method for improving the explosion board of the FPC multilayer board according to claim 6, further comprising the steps of S10, post-treatment and detection reinforcement, wherein a vacuum degassing procedure is added after reflow soldering, treatment is carried out for 30min under the conditions of 200 ℃ and minus 0.08MPa, trace moisture and gas remained between layers are discharged, interlayer bonding force on-line detection is increased, an ultrasonic scanning microscope is adopted to carry out 100% detection on each batch of high FPC multilayer boards after the lamination procedure, detection precision is 5 mu m, 5% of each batch of high FPC multilayer boards are extracted for accelerated aging test, the conditions of reflow soldering for 10 times after double 85 test for 120H are adopted, the reliability of the high FPC multilayer boards after long-term use is verified, the qualification standard is no explosion board and layering phenomenon, and the peeling force reduction rate is less than or equal to 10%.
  8. 8. The method for improving the FPC multilayer board explosion board according to claim 1, wherein the cover film in the step S1 at least comprises a PI film layer and an adhesive layer, the thickness of the PI film layer is 25-50 mu m, the surface of the PI film layer is pretreated by plasma, active groups such as hydroxyl groups and carboxyl groups are introduced to improve the interface binding force with the adhesive layer, the adhesive layer is used for realizing firm bonding with a substrate and copper foil, the thickness of the adhesive layer is 15-25 mu m, modified epoxy resin with high bonding strength is used as a base adhesive, 5-8% of isocyanate curing agent and 2-3% of silane coupling agent are added to the adhesive layer, and meanwhile, 3-5% of nano calcium carbonate filler is mixed to improve the initial peeling force to more than 1.2kg/cm < 2 >, the crosslinking degree in the curing process of the adhesive layer is more than or equal to 85%, a compact three-dimensional network structure is formed, the molecular weight of the adhesive layer is distributed between 1000-3000, and the molecular weight distribution width (PDI) is less than or equal to 2.5.
  9. 9. The method for improving the explosion board of the FPC multi-layer board as claimed in claim 8, wherein after the PI film layer is compounded with the adhesive layer, edges are sealed by edge sealing adhesive, the width is 0.5 mm-1 mm, a surface protection coating is designed on the PI film layer by the cover film, the surface protection coating is a fluorine modified resin coating or a silicon coating, the thickness of the surface protection coating is 2um-5um, the surface protection coating forms a hydrophobic barrier, and the contact angle is more than or equal to 110 degrees.
  10. 10. The method for improving the FPC multilayer board explosion plate of claim 9, wherein the step S2 is characterized in that a vacuum drying process is added after the pretreatment of a covering film, the drying is carried out for 60-90 min under the conditions of 120 ℃ and minus 0.09MPa, the combined pretreatment of the step S5 is carried out after 2H baking by nitrogen or plasma cleaning, the treatment power is controlled to be 100-150W and the treatment time is controlled to be 30-60S when the plasma cleaning is adopted, the combined surface of the pure glue and the substrate is preferably treated in a plasma and microetching compound pretreatment mode, the surface greasy dirt and the oxide layer are removed by plasma cleaning, and then the microetching is carried out slightly, wherein the microetching amount is 0.5-0.8 mu m.

Description

FPC high multilayer board explosion board improvement method Technical Field The invention relates to the technical field of FPC manufacturing, in particular to an FPC multi-layer board explosion board improvement method. Background Along with the development of electronic equipment towards light weight and high performance, FPCs are increasingly widely applied, and in particular in the fields of display modules and the like, the reliability requirements of customers on high multi-layer (four layers and more) FPCs are continuously improved. Some customers require that after newly adding FPC double 85 test, reflow (Reflow) non-conventional test projects are directly carried out within 5min, the double 85 test is used for testing the reliability of the FPC multilayer board in a high-temperature and high-humidity environment, the test conditions are that the FPC multilayer board is placed in the environment for testing 5H (part of expansion test is 12H) under the environment of 85 ℃ high temperature and 85% relative humidity, and the FPC multilayer board belongs to the accelerated aging test of the FPC multilayer board. The Reflow is directly performed within 5min after the double 85 test to simulate the full-flow extreme scene from storage (high temperature and high humidity) to assembly (Reflow soldering high temperature) of the FPC, the structural stability of the FPC is verified when the FPC is subjected to the extreme high temperature in a moisture absorption state, the high temperature can soften the interlayer adhesive layer of the FPC, meanwhile, the moisture generated by moisture absorption is vaporized and expanded, and layering, foaming or board explosion can be directly caused if the interlayer binding force is insufficient, so that the Reflow test is a core test for evaluating the thermal stress resistance and the moisture absorption collaborative breaking capability of the FPC. In the testing process, the FPC is subjected to high-temperature reflow soldering in a wet state, so that layering board explosion phenomenon is easily caused by the problems of insufficient interlayer binding force, stress concentration, moisture absorption and the like, and the product qualification rate and the use reliability are seriously affected. In the prior art, the problem of explosion of the FPC multilayer board is mainly concentrated on more than four layers of high multilayer boards, and the more the number of layers is, the larger the stress is, the higher the risk of moisture absorption explosion is, meanwhile, the peeling strength of the traditional covering film is lower, the design of steel sheet holes is easy to cause moisture absorption, the problem of explosion of the board is aggravated by factors such as improper pretreatment mode, unreasonable pressing process parameters and the like, and the prior art lacks a system, and a comprehensive FPC multilayer board explosion improvement scheme, so that the severe testing requirements of customers cannot be met. In view of this, the present invention was developed by taking into consideration many drawbacks and inconveniences caused by the board explosion problem of the conventional high multilayer board for FPC, and actively researching and modifying the test. Disclosure of Invention The invention aims to solve the technical problem of high bursting rate of an FPC (flexible printed circuit) high-multilayer board in the prior art, and provides the FPC high-multilayer board bursting improvement method which can improve bonding force between FPC layers and avoid layered bursting caused by stress concentration, so that the FPC high-multilayer board can meet the testing condition of directly passing Reflow within 5min after double 85 testing. In order to achieve the above object, the solution of the present invention is: an FPC multilayer board explosion board improvement method comprises the following steps: S1, selecting a cover film, wherein the cover film is a cover film with a peeling force of more than 1.0kg/cm <2 >, and has excellent high temperature resistance, moisture absorption resistance and interlayer bonding stability, the cover film is subjected to high temperature of 265-270 ℃ reflow soldering for 10S within 5min after double-85 testing, interlayer separation does not occur after 5 times of repetition, and meanwhile, the thermal expansion coefficient of the cover film is matched with that of an FPC substrate and copper foil, and the difference value is controlled within 5ppm/° C; S2, surface pretreatment of the cover film selected in the step 1, wherein the surface pretreatment is to perform any one or any combination of roughening, microetching or sand blasting on one surface of the adhesive layer, the copper etching amount is controlled to be 0.8-1.2 mu m in the roughening treatment, the surface of the adhesive layer of the cover film forms a uniformly distributed micro-roughness structure, the peeling force between the cover film and the subs