CN112752438A

CN112752438A - FPC hole plating method

Info

Publication number: CN112752438A
Application number: CN202011452768.4A
Authority: CN
Inventors: 刘美才; 钟胜祥; 吴永进
Original assignee: Xiamen Bolion Tech Co ltd
Current assignee: Xiamen Bolion Tech Co ltd
Priority date: 2020-12-11
Filing date: 2020-12-11
Publication date: 2021-05-04

Abstract

The invention relates to a hole plating method for an FPC (flexible printed circuit), which comprises the following steps of: s10, after drilling holes in the double-sided base material FCCL, performing PTH treatment to deposit a thin copper layer on the copper surface and the hole wall; s20, pasting a dry film on one surface of the FCCL; s30, placing for a preset time, and then directly entering a developing section to enable a developing solution to react with the dry film to form a uniform annular dry film-free area taking the hole as the center; s40, cleaning in a water washing section after the developing section, cleaning the dissolved dry film, and drying the product in a drying section; s50, after drying, carrying out whole-face exposure on the dry film surface, and tearing off the protective film of the dry film; s60, attaching a dry film to the side, not attached with the dry film, of the FCCL, and then repeating the steps S30, S40 and S50; s70, thickening the hole copper through electroplating copper to enable the hole copper to reach the required thickness. By adopting the method, the alignment is not needed, the skill requirement of manual alignment is reduced, the precision can be extremely high, and the actual measurement precision reaches +/-10 um.

Description

FPC hole plating method

Technical Field

The invention relates to the technical field of FPC, in particular to a FPC hole plating method.

Background

In recent years, electronic products, particularly consumer electronic products, have been developed to be light and small. As a component of electronic products, such as circuit boards, the density of the circuits is also required to be higher and higher due to the same requirement. This requires more lines per unit area, and thus the line width/pitch of the circuit board is also required to be smaller.

The thinner line width/line distance is required to be matched with a thinner copper layer, and the double-sided board/multilayer board can ensure the reliability of the performance of the via hole only when the thickness requirement of the metal layer in the via hole meets the corresponding requirement due to the fact that the via hole needs to be metallized, and theoretically, the thicker the thickness, the higher the reliability. This therefore creates a contradiction: thin surface copper is needed for manufacturing a thin circuit, the hole copper is required to be thick to ensure reliability, and the hole copper and the surface copper are thickened in the same proportion in the common copper electroplating process.

In order to solve the problems, the common practice in the circuit board industry is to apply a lead-in hole plating process, i.e., a dry film is attached to the surface of a product to play a role in resisting electroplating, and the area of a hole is left for electroplating and thickening. Therefore, the requirement that the surface copper cannot be thickened when the hole copper is thickened can be met, and a thinner circuit can be manufactured on the premise that the reliability of the hole copper is guaranteed.

However, the process also has some problems, such as high alignment difficulty, and once a large offset occurs in the alignment during hole plating, the potential hazards of short circuit and the like are easily caused during subsequent circuit fabrication.

Disclosure of Invention

The invention aims to provide a hole plating method for an FPC (flexible printed circuit) to solve the problems. Therefore, the invention adopts the following specific technical scheme:

an FPC hole plating method can comprise the following steps:

s10, after drilling holes in the double-sided base material FCCL, performing PTH treatment to deposit a thin copper layer on the copper surface and the hole wall;

s20, pasting a dry film on one surface of the FCCL;

s30, placing for a preset time, and then directly entering a developing section to enable a developing solution to react with the dry film to form a uniform annular dry film-free area taking the hole as the center;

s40, cleaning in a water washing section after the developing section, cleaning the dissolved dry film, and drying the product in a drying section;

s50, after drying, carrying out whole-face exposure on the dry film surface, and tearing off the protective film of the dry film;

s60, attaching a dry film to the side, not attached with the dry film, of the FCCL, and then repeating the steps S30, S40 and S50;

s70, thickening the hole copper through electroplating copper to enable the hole copper to reach the required thickness.

Further, in step S10, the thickness of the deposited copper layer is 0.5-1 μm.

Further, between the steps S10 and S20, there is further included the step of: the thickness of the hole wall and the surface copper on the FCCL original copper layer is increased to 3-5 microns through electroplating copper thickening in a short time.

Further, in step S30, the predetermined time is 0.5 to 4 hours.

Further, in step S30, the acting time of the developer and the dry film is adjusted by controlling the developing speed, so as to control the size of the annular dry film-free region.

By adopting the technical scheme, the invention has the beneficial effects that:

1. the effect of uniform ring-opening is achieved by means of uniform reaction of the developing solution and the dry film;

2. controlling the size of the pore ring by the reaction time of the liquid medicine and the dry film;

3. the requirement of manual alignment skills is reduced, and meanwhile, the precision can be extremely high, and the actual measurement precision reaches +/-10 um.

Drawings

To further illustrate the various embodiments, the invention provides the accompanying drawings. The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the embodiments. Those skilled in the art will appreciate still other possible embodiments and advantages of the present invention with reference to these figures. Elements in the figures are not drawn to scale and like reference numerals are generally used to indicate like elements.

FIG. 1 is a flow chart of a FPC hole plating method of the present invention;

fig. 2 is a schematic diagram of the FPC performing step S10;

fig. 3 is a schematic diagram of the FPC performing step S20;

fig. 4 is a schematic diagram of the FPC performing step S30;

fig. 5 is a schematic diagram of the FPC performing step S50;

fig. 6 is a schematic diagram of the FPC performing step S60;

fig. 7 is a schematic diagram of the FPC performing step S70.

Detailed Description

The invention will now be further described with reference to the accompanying drawings and detailed description.

As shown in fig. 1, an FPC hole plating method may include the steps of:

s10, after drilling holes on the double-sided base material FCCL, PTH treatment is carried out to deposit a thin copper layer (for example, 0.5-1 micron) on the copper surface and the hole walls, as shown in FIG. 2. Drilling and PTH are conventional processes and will not be described here. And depositing a thin copper layer to enable the originally non-conductive hole wall to have the conductive characteristic and serve as an initial conductive layer for thickening the copper layer by subsequent electroplating.

S20. attaching a dry film (e.g., via a film-attaching machine) on one side (e.g., the reverse side) of the FCCL, as shown in fig. 3. The dry film may be commercially available, for example, dupont FX 930. In one embodiment, the parameters of the dry film pasting are as follows: the temperature is 100-110 ℃, the pressure is 4.5-5.5 kg, and the speed is 1.2-1.8 m/min.

Preferably, between the steps S10 and S20, there may be further included the steps of: the thickness of the hole wall and the surface copper on the FCCL copper layer is increased to 3-5 microns by electroplating copper (i.e. flash plating) for a short time. This ensures that the copper thickness is maintained to a sufficient level to ensure conductivity even after the surface layer of copper is oxidized and cleaned.

S30, standing for a preset time (for example, 0.5-4 hours), and then directly entering a developing section. Because the protective film layer on the dry film is reserved, at the moment, the developing solution can permeate to the side with the dry film from the side without the dry film through the via hole, the developing solution reacts with the dry film, and the unexposed dry film is gradually and uniformly dissolved by taking the hole as the center in the developing process, so that a uniform annular dry film-free area taking the hole as the center can be formed, as shown in fig. 4. An operator can adjust the action time of the developing liquid medicine and the dry film by controlling the developing speed, and then the size of the annular dry film-free area is controlled, so that the annular dry film-free area meets the design requirement. After the dry film is pasted and the dry film and the copper layer are kept stand for a period of time, the dry film and the copper layer can be combined more tightly, and the phenomenon that developing liquid medicine permeates from the combination position of the dry film and the copper layer to influence the uniformity of a dry film-free area on the periphery of the hole is avoided.

And S40, cleaning in a water washing section after the developing section, cleaning the dissolved dry film, and drying the product in a drying section. The washing and drying are conventional processes and will not be described here.

S50, after drying, carrying out whole-face exposure on the dry film surface, and tearing off the protective film of the dry film, as shown in figure 5.

S60, a dry film is attached to one side (e.g., the front side) of the FCCL to which the dry film is not attached, and then steps S30, S40, and S50 are repeated as shown in fig. 6. At this time, both ends of the hole of the FCCL have uniform annular dry film-free areas which take the hole as the center, namely, the alignment of the film in the original pattern copper plating process is realized. Compared with the original alignment mode, the method reduces the skill requirement of manual alignment, and can achieve extremely high precision, and the actual measurement precision reaches +/-10 um.

S70, thickening the hole copper through electroplating copper to reach the required thickness, as shown in figure 7. The thickness of the copper plating can be realized by adjusting the copper plating time. The electrolytic copper plating process is well known and will not be described here.

The invention achieves the effect of uniform hole rings by means of uniform reaction of the developing liquid medicine and the dry film, and controls the size of the hole rings through the reaction time of the liquid medicine and the dry film; compared with the traditional hole plating method, the method reduces the skill requirement of manual alignment, and simultaneously can achieve extremely high precision, and the actual measurement precision reaches +/-10 um.

While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. A FPC hole plating method is characterized by comprising the following steps:

s10, after drilling holes in the FCCL, performing PTH treatment, and depositing a thin copper layer on the copper surface and the hole wall;

s20, pasting a dry film on one surface of the FCCL;

2. The FPC hole plating method of claim 1, wherein in step S10, the thickness of the copper layer deposited is 0.5 to 1 μm.

3. The FPC via plating method of claim 2, further comprising, between steps S10 and S20, the steps of: the thickness of the hole wall and the surface copper on the FCCL original copper layer is increased to 3-5 microns through electroplating copper thickening in a short time.

4. The FPC hole plating method according to claim 1, wherein in step S30, the predetermined time is 0.5 to 4 hours.

5. The FPC plating method according to claim 1, wherein in step S30, the action time of the developer solution and the dry film is adjusted by controlling the developing speed, thereby controlling the size of the annular dry film-free region.