Reinforcing method of FPC (Flexible Printed Circuit)

Abstract

The invention belongs to the field of FPCs (Flexible Printed Circuit), and particularly discloses a reinforcing method of an FPC. According to the method, the boundary dimension of an FR4 reinforcing plate is designed to be 1.2 mm larger than the boundary dimension of a to-be-reinforced area on an FPC, then the FR4 reinforcing plate and the to-be-reinforced area on the FPC are sequentially attached and solidified to obtain a stacked plate, finally the stacked plate is sequentially subjected to rough punching and fine punching with the single-side allowance being 0.05-0.2 mm, and the FR4 reinforcing plate and the to-be-reinforced area on the FPC are sequentially subjected to rough punching and fine punching with the single-side allowance being 0.05-0.2 mm. And an FPC reinforcing product with the FR4 reinforcing plate having the same boundary dimension as the to-be-reinforced area on the FPC is obtained. According to the method, the defects of scraps and burrs generated in a conventional punching method can be overcome, the size precision and the qualified rate of products are improved, and the yield of the products and the machining quality stability of the products are improved.

Description

Technical Field

[0001] The invention belongs to the field of FPC, and in particular relates to a method for reinforcing an FPC. Background Art

[0002] With the continuous development of circuit board assembly technology, FR4 reinforcement board (material with flame retardant grade of FR-4) is often used to reinforce FPC (Flexible Printed Circuit) during the current assembly process to improve the strength of the plug-in part on the FPC, thereby improving the yield and efficiency of the assembled product. In the design of assembling the FR4 reinforcement board with the FPC, the area on the FR4 reinforcement board and the FPC that needs to be reinforced are equal in size. For example, if the area on the FPC that needs to be reinforced is the FPC unit, the size of the FR4 reinforcement board needs to be consistent with the maximum size of the FPC unit, and the dimensional accuracy is required to reach + / -0.05mm. Generally, the FR4 reinforcement board and the FPC are bonded through the adhesive layer to form a stacked board, and then the whole is punched to obtain the product to achieve the reinforcement of the FPC. However, during the punching process, due to the characteristics of the FR4 reinforcement material, after the FR4 reinforcement and the FPC are punched together, the product is prone to debris and burrs of the FR4 reinforcement board, which reduces the dimensional accuracy of the product and affects the quality of the assembled product. Especially when the thickness of the FR4 reinforcement board is greater than 0.3mm, the product will have more serious FR4 reinforcement board debris and burrs, resulting in unqualified product dimensions and reduced product yield. In order to improve the serious burr defects, the FR4 reinforcement board debris and burrs after punching can be manually repaired to meet the size requirements as much as possible; however, the repair is time-consuming and labor-intensive, and the repair effect is unstable, the dimensional accuracy is not high, and the product cannot be repaired if the debris damages the product, and the size will be unqualified and the product will be scratched again. Summary of the invention

[0003] In view of the defects involved in the above-mentioned prior art, the present invention provides a method for reinforcing an FPC.

[0004] To achieve the above purpose, the following technical solutions are specifically included:

[0005] A method for reinforcing an FPC comprises the following steps:

[0006] (1) Using hot pressing adhesive to bond the FR4 reinforcing plate to the area to be reinforced on the FPC, and after curing, to obtain a laminated plate; the outer dimensions of the FR4 reinforcing plate are greater than the outer dimensions of the area to be reinforced on the FPC by more than 1.2 mm;

[0007] (2) punching the FR4 reinforcing plate on the stacked plate, wherein the single-side allowance of the punching is 0.05-0.2 mm, to obtain a rough punched product;

[0008] (3) Punching the FR4 reinforcing plate on the rough punched product so that the outer dimensions of the FR4 reinforcing plate on the rough punched product are consistent with the outer dimensions of the area to be reinforced on the FPC, thereby obtaining an FPC reinforcing plate.

[0009] In the method of the present invention, the outer dimensions of the FR4 reinforcing plate are first designed to be larger than the outer dimensions of the area to be reinforced on the FPC by more than 1.2 mm, and then the FR4 reinforcing plate and the area to be reinforced on the FPC are sequentially bonded and cured to obtain a stacked plate, and finally the stacked plate is sequentially subjected to rough punching and fine punching with a single-side margin of 0.05-0.2 mm to obtain an FPC reinforced product whose outer dimensions of the FR4 reinforcing plate are consistent with those of the area to be reinforced on the FPC. The method of the present invention can overcome the FR4 reinforcing plate debris and burr defects generated in conventional punching methods, improve the dimensional accuracy and qualified rate of the product, and improve the yield rate of the product and the stability of product processing quality.

[0010] Preferably, in step (1), after lamination, the peeling force of the FR4 reinforcement plate is ≥ 0.56 kgf / cm 2 .

[0011] The area to be reinforced on the FPC is generally based on the unit on the FPC as a whole. The FR4 reinforcement board is bonded to the area to be reinforced on the FPC using hot pressing adhesive. The hot pressing adhesive used needs to meet the requirement that the peeling force of the FR4 reinforcement board is ≥0.56kgf / cm 2 , to ensure the firmness of the FR4 reinforcement board and FPC and prevent the FR4 reinforcement board from falling off.

[0012] Preferably, the thickness of the FR4 reinforcement plate in step (1) is 0.3-0.55 mm.

[0013] The material of the FR4 reinforcing plate of the present invention is not particularly limited, and any conventional commercially available reinforcing plate may be used, such as a FR4 reinforcing plate made of common glass fiber material.

[0014] Generally speaking, the thicker the reinforcing plate is, the higher the reinforcing effect on FPC is. However, the punching difficulty increases, and it is more likely to cause FR4 reinforcing plate debris and burr defects, and the required punching energy is higher. Generally speaking, when the thickness of the FR4 reinforcing plate is 0.3-0.55mm, it is a thicker reinforcing plate, and the reinforcing plate has a greater reinforcing effect on FPC. It can also adapt to the general punching energy intensity of the production workshop. When the punching method of the present invention is used, the FR4 reinforcing plate debris and burr defects can be effectively avoided in the punched product.

[0015] Preferably, in step (1), the thickness of the FPC is 0.05-0.6 mm.

[0016] Preferably, in step (2), the single-side margin of punching is 0.1-0.15 mm.

[0017] The single-side allowance of punching will significantly affect the impact force on the FR4 reinforcing plate on the stacked plate during the punching process, and further affect the defects and dimensional accuracy of the product after punching. In the method of the present invention, when the single-side allowance of punching is 0.05-0.2mm, the impact during the punching process is stable and moderate, and the defects of FR4 reinforcing plate debris and burrs can be basically overcome. It is further preferred that the single-side allowance of punching is 0.1-0.15mm, at this time, not only can the defects of FR4 reinforcing plate debris and burrs of the product be overcome, but also the dimensional accuracy of the product is higher.

[0018] Preferably, in step (3), the Cpk index of the FPC reinforcement product is greater than 0.9.

[0019] Further preferably, in step (3), the Cpk index of the FPC reinforcement product is greater than 1.33, and further preferably the Cpk index is 1.67-2.1.

[0020] The process capability index refers to the degree to which the process capability meets the requirements of the product quality standard (specification range, etc.). The present invention uses the Cpk index to represent the process capability index of the method of the present invention. Cpk refers to the size of the deviation between the process mean value (μ) and the product standard specification (M). It is usually represented by the smaller of the upper deviation value of customer satisfaction minus the mean value and the mean value minus the lower deviation value, divided by 3σ. Under normal circumstances, the overall standard deviation σ of the distribution of quality characteristic values ​​is unknown, so the sample standard deviation s can be used instead. The judgment criteria of Cpk index are as follows: (1) Grade A++, Cpk ≥ 2.0, excellent, cost reduction can be considered; (2) Grade A+, 2.0> Cpk ≥ 1.67, excellent, should be maintained; (3) Grade A, 1.67> Cpk ≥ 1.33, good, good capability, stable status, but efforts should be made to upgrade to Grade A+; (4) Grade B, 1.33> Cpk ≥ 1.0, fair, fair status, slight variation in process factors will lead to risk of defective products, various resources and methods should be used to upgrade to Grade A; (5) Grade C, 1.0> Cpk ≥ 0.67, poor, many process defects, and capability must be improved; (6) Grade D, 0.67> Cpk, unacceptable, poor capability, and redesign of the process should be considered. The method of the present invention can achieve a Cpk index greater than 0.9, and more preferably a Cpk index greater than 1.33. At this time, the process capability index of the method of the present invention reaches A+ level, which can prove that the FPC reinforcement method of the present invention can significantly improve the quality stability of product processing, the quality of the product and the yield of the product. In addition, the method of the present invention can omit the process of manual modification, save time and cost, and produce more efficiently.

[0021] Compared with the prior art, the present invention has the following beneficial effects: in the method of the present invention, the outer dimensions of the FR4 reinforcing plate are first designed to be larger than the outer dimensions of the area to be reinforced on the FPC by more than 1.2 mm, and then the FR4 reinforcing plate and the area to be reinforced on the FPC are sequentially bonded and cured to obtain a stacked plate, and finally the stacked plate is sequentially subjected to rough punching and fine punching with a single-side margin of 0.05-0.2 mm to obtain an FPC reinforced product whose outer dimensions of the FR4 reinforcing plate are consistent with those of the area to be reinforced on the FPC. The method of the present invention can overcome the FR4 reinforcing plate debris and burr defects generated in conventional punching methods, improve the dimensional accuracy and qualified rate of the product, and improve the yield rate of the product and the stability of product processing quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the structure in which the FR4 reinforcement plate in Example 1 fits the unit shape of the FPC.

[0023] Figure 2 This is a schematic diagram of the dimensions of the target FPC reinforcement product designed in Example 1.

[0024] Figure 3 This is a schematic diagram of the structure of the stacked plate during the fine punching and rough punching processes designed in Example 1.

[0025] Figure 4 Schematic diagram of the change in the structural dimensions of the laminated plate during the fine punching and rough punching processes designed in Examples 1-4.

[0026] Figure 5 Schematic diagram of the laminated structure of the FPC reinforcement product prepared in Example 1.

[0027] Figure 6 This is a physical effect diagram of the FPC reinforcement product prepared in Example 1.

[0028] Figure 7 The Cpk index of the measured dimensions at two locations with a designed diameter of 0.96 mm on the FPC reinforcement product in Examples 1-4 and the box plot analysis comparison results are shown.

[0029] Figure 8 This is a diagram showing the Cpk index of the actual measured dimensions at the designed length of 6.49 mm on the FPC reinforcement product in Examples 1-4 and the box plot analysis and comparison results.

[0030] Fig. 9 This is a diagram showing the Cpk index of the actual measured dimensions at the designed length of 8.3 mm on the FPC reinforcement product in Examples 1-4 and the box plot analysis and comparison results.

[0031] Fig.10This is a diagram showing the Cpk index of the actual measured dimensions at the designed length of 5.7 mm on the FPC reinforcement product in Examples 1-4 and the box plot analysis and comparison results.

[0032] Fig.11 This is a photo of the actual effect of the FPC reinforcement product in Comparative Example 1. DETAILED DESCRIPTION

[0033] In order to better illustrate the purpose, technical scheme and advantages of the present invention, the present invention will be further described below through specific examples. The test methods used in the examples and / or comparative examples are conventional methods unless otherwise specified; the materials, reagents, etc. used can be obtained from commercial channels unless otherwise specified.

[0034] Example 1

[0035] A method for reinforcing an FPC comprises the following steps:

[0036] (1) Reinforcement design: Based on the unit shape of the FPC (there are multiple units on the FPC), the size of the FR4 reinforcement board is designed to be 1.5 mm larger than the unit size of the FPC, as shown in the attached figure. Figure 1 As shown in the figure; one of the units is used as a detailed description of the target product dimensions, as shown in the attached Figure 2 As shown, the dimensions of the FR4 reinforcement board in the product are the same as those of the unit;

[0037] (2) Attaching the reinforcing plate: The FPC as a whole includes the FCCL and the cover surface, with an overall thickness of 105 μm. There are multiple units on the FPC. Using the alignment mark on the FPC as a reference, the FR4 reinforcing plate (thickness 460 μm) is attached to the FPC using hot pressing adhesive;

[0038] (3) Pressing the reinforcing plate: Use a fast press machine to bond the FR4 reinforcing plate to the FPC through high temperature, high pressure and time, and the peeling force of the FR4 reinforcing plate should be ≥ 0.56kgf / cm 2 The hot pressing temperature is 180℃±10℃, the hot pressing pre-pressing time is 10±5s, the hot pressing pressing time is 120±10s, and the hot pressing set pressure is 18±3kgf / cm 2 , the thickness of the final hot-pressed adhesive layer is 40 μm;

[0039] (4) Post-baking of the reinforcing plate: Use an oven to cure the hot pressing adhesive between the reinforcing plate and the FPC at high temperature and time to obtain a laminated plate; wherein the baking temperature is 157±3°C and the baking time is 2h;

[0040] (5) Rough punching: Based on the outer dimensions of the target product, design the die cutting position dimensions on the FR4 reinforcement plate, and make the die cutting position dimension 0.1mm larger than the target product dimension on one side. For example, the distance between one side of the target product and the die cutting position is 0.1mm. See the attached Figure 3-4 As shown in the schematic diagram; according to the designed size and using a mechanical punching machine with a punching force of not less than 30T, punching is performed. Because there is a punching margin of 0.1mm in this punching, the final shape of the entire area of ​​the FR4 reinforcement plate has not been punched out;

[0041] (6) Fine punching: Based on the size of the target product, design the size of the die cutting position on the FR4 reinforcement plate. Design the size of the die cutting position to be the same as the size of the target product. Figure 3-4 As shown, the punching is performed according to the designed size so that the shape of the FR4 reinforcement board is aligned with the shape of the unit on the FPC to obtain the final FPC reinforcement product. The stacking structure diagram and thickness dimensions of the product are shown in the attached Figure 5 shown.

[0042] The actual effect picture is as attached Figure 6 As shown in the figure, it can be observed that the product after punching in this embodiment has no burrs and no FR4 reinforcement plate debris. The actual measured dimensions of the final product are detected, and the actual measured dimension data are analyzed by calculating the Cpk index and box plot. The results are shown in the attached figure. Figure 7-9 .

[0043] Embodiment 2-4

[0044] The only difference between Examples 2-4 and Example 1 is that the single-side punching allowance is different. The punching allowances of Examples 2-4 are 0.15mm, 0.05mm, and 0.2mm respectively. The size design of the rough punching and fine punching of each embodiment is shown in the attached figure. Figure 4 As shown, the Cpk index and box plot analysis results of the measured dimensional data of the FPC reinforcement products of each embodiment are as follows Figure 7-9 and Table 1.

[0045] Table 1 (Dimensional accuracy + / -0.05mm)

[0046]

[0047]

[0048] Figure 7-10As shown in Table 1, the measured size data of the FPC reinforcement product can be analyzed through the Cpk index and the box plot. When the punching allowance is 0.05-0.2mm, the Cpk index can be greater than 0.9. It is further preferred that when the punching allowance is 0.1-0.15mm, the Cpk index is greater than 1.67, and the Cpk index can reach A+ level, with high processing size accuracy and high processing stability; and the box plot result is biased towards the median, which also indicates that the product processing stability is high. Therefore, the FPC reinforcement method of the present invention can significantly improve the quality stability of product processing, the quality of the product, and the yield of the product.

[0049] Comparative Example 1

[0050] Compared with Example 1, the blanking allowance in this comparative example is 0, and the specific process is as follows:

[0051] (1) Reinforcement design: Based on the unit shape of the FPC (there are multiple units on the FPC), the size of the FR4 reinforcement board is designed to be 1.5 mm larger than the unit size of the FPC;

[0052] (2) Attaching the reinforcing plate: The FPC as a whole includes the FCCL and the cover surface, with an overall thickness of 105 μm. There are multiple units on the FPC. Using the alignment mark on the FPC as a reference, the FR4 reinforcing plate (thickness 460 μm) is attached to the FPC using hot pressing adhesive;

[0053] (3) Pressing the reinforcing plate: Use a fast press machine to bond the FR4 reinforcing plate to the FPC through high temperature, high pressure and time, and the peeling force of the FR4 reinforcing plate should be ≥ 0.56kgf / cm 2 The hot pressing temperature is 180℃±10℃, the hot pressing pre-pressing time is 10±5s, the hot pressing pressing time is 120±10s, and the hot pressing set pressure is 18±3kgf / cm 2 , the thickness of the final hot-pressed adhesive layer is 40 μm;

[0054] (4) Post-baking of the reinforcing plate: Use an oven to cure the hot pressing adhesive between the reinforcing plate and the FPC at high temperature and time to obtain a laminated plate; wherein the baking temperature is 157±3°C and the baking time is 2h;

[0055] (5) Rough punching: Based on the size of the target product, the size of the die cutting position on the FR4 reinforcement board is designed to be the same as the size of the target product. According to the designed size and using a mechanical punching machine with a punching force of not less than 30T, the shape of the FR4 reinforcement board is aligned with the shape of the unit on the FPC to obtain the final FPC reinforcement product.

[0056] The actual effect diagram of the comparative product is shown in the attached Fig.11As shown, it can be observed that the comparative example does not design the punching margin, and the product after punching has obvious burrs, and there are also FR4 reinforcing plate debris in the product, which is obviously unqualified. It can be seen that the reinforcement method of the present invention can overcome the defects of the conventional method that the product after punching has obvious burrs and FR4 reinforcing plate debris, and improve the yield of the product.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for reinforcing an FPC, characterized in that: The steps include: (1) Using hot pressing adhesive to bond the FR4 reinforcing plate to the area to be reinforced on the FPC, and after curing, to obtain a laminated plate; the outer dimensions of the FR4 reinforcing plate are greater than the outer dimensions of the area to be reinforced on the FPC by more than 1.2 mm; (2) punching the FR4 reinforcing plate on the stacked plate, wherein the single-side allowance of the punching is 0.05-0.2 mm, to obtain a rough punched product; (3) Punching the FR4 reinforcing plate on the rough punched product so that the outer dimensions of the FR4 reinforcing plate on the rough punched product are consistent with the outer dimensions of the area to be reinforced on the FPC, thereby obtaining an FPC reinforced product.

2. The FPC reinforcement method according to claim 1, characterized in that: In step (2), the single-side allowance of punching is 0.1-0.15 mm.

3. The FPC reinforcement method according to claim 1, characterized in that: In step (1), after lamination, the peeling force of the FR4 reinforcement plate is ≥ 0.56 kgf / cm 2 .

4. The FPC reinforcement method according to claim 1, characterized in that: The thickness of the FR4 reinforcement plate in step (1) is 0.3-0.55 mm.

5. The FPC reinforcement method according to claim 1, characterized in that: In step (1), the thickness of the FPC is 0.05-0.6 mm.

6. The FPC reinforcement method according to claim 1, characterized in that: In step (3), the Cpk index of the FPC reinforcement product is greater than 0.9.

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