A method for manufacturing a PCB

Abstract

The present invention relates to a method for manufacturing a PCB. By controlling the selection of raw materials, pre-treatment is performed before solder masking, a high-temperature curing process is added before surface treatment, ion cleaning is performed before packaging, an ultrasonic cleaning step is added for HDI boards with tiny holes, and the shape processing, electrical measurement, and shape detection processes are optimized. The residues of various ions can be effectively reduced, and undesirable problems such as ion migration after mounting components on the PCB can be avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of PCBs, and in particular relates to a method for manufacturing a PCB. Background Art

[0002] With the rapid development of the electronics industry and the increasing requirements for long-term functional stability, the integration of electronic products is getting higher and higher, the functional life is getting longer and longer, the density of components on circuit boards is increasing, the wiring is becoming more and more dense, the spacing between lines is getting smaller and smaller, and the degree of environmental adaptation is becoming more and more extensive. These phenomena are more obvious in the fields of aerospace, automotive circuit boards, high-end communication boards, high-end medical equipment, etc. The surface ion contamination of traditional printed circuit boards (PCBs) is too high or not clean enough, and it can no longer meet the special requirements of existing high-end products. Because the ion contamination of the PCB surface is too high or not clean enough, it will affect the propagation of electrical signals, and ion migration may occur during use, and in severe cases, it will cause short circuits and burn boards. Therefore, the detection of the ion contamination of the product itself is a key step, and its detection standards are gradually improving.

[0003] Different surface treatment methods, different ink types, different treatment levels, etc. have different effects on the ionic contamination of the PCB surface. Therefore, in the actual PCB cleaning process, in addition to the problem of difficulty in achieving low ionic contamination, different cleaning process flows need to be formulated based on the actual production test results of the factory, which are complex to operate and have limited adaptability. Therefore, it is urgent to find a more suitable method to reduce ionic contamination of PCBs to ensure that the products produced meet industry standards and the quality requirements of high-end circuit boards. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a method for manufacturing a PCB, which can effectively control the ion contamination source during the PCB manufacturing process and reduce the ion contamination degree in the PCB.

[0005] The purpose of the present invention is achieved by the following technical means:

[0006] A method for manufacturing a PCB comprises the following steps:

[0007] The circuit-fabricated substrate is taken and solder resisted; after the solder resist is completed, the substrate is cured at 145-165° C.; and after curing, surface treatment is performed.

[0008] The PCB manufacturing method according to the present invention has at least the following beneficial effects:

[0009] The solder resist process in the PCB manufacturing process generally bakes the solder resist ink (mainly composed of polymer resin) at a low temperature (75±5°C), and then forms a semi-liquid and semi-solid solder resist layer through exposure and development. The surface treatment process after solder resist generally includes one or more of tin spraying, gold immersion, OSP, tin immersion, silver immersion, nickel-palladium-gold, electric hard gold, and electric gold finger. In this surface treatment process, the plate, especially the semi-liquid and semi-solid solder resist layer on the plate, needs to contact with various chemical solutions, so that more contaminated ions remain. The present invention fully cures the semi-liquid and semi-solid solder resist layer by adding a high-temperature curing process after solder resist and before surface treatment, which can further solidify and smooth the surface of the solder resist layer, reduce the solder resist ink in the solder resist layer from adsorbing chemical solutions during the surface treatment process, thereby reducing the residual ion pollution and avoiding excessive ion pollution.

[0010] In some embodiments of the present invention, the method for manufacturing the PCB more specifically includes the following steps:

[0011] S1: cutting;

[0012] S2: Make inner layer circuit;

[0013] S3: browning;

[0014] S4: lamination;

[0015] S5: half gong;

[0016] S6: drilling;

[0017] S7: copper deposition, board plating;

[0018] S8: making outer circuit;

[0019] S9: solder mask;

[0020] S10: Curing at 145-165°C;

[0021] S11: surface treatment;

[0022] S12: Shape processing.

[0023] In some embodiments of the present invention, the curing can be carried out by UV baking, and the energy of UV baking is 1500-3500 MJ / cm 2 .

[0024] In some embodiments of the present invention, the curing temperature is 150-160°C, and the corresponding UV baking energy is 2500-3500 MJ / cm 2 .

[0025] In some embodiments of the present invention, the cutting process in step S1 is the process of cutting the original copper-clad laminate into plates that can be produced on the production line. The plates are selected to have low ion contamination, especially those that meet the requirements of ROHS and REACH standards, preferably halogen-free plates (the content of any one of fluorine, chlorine, bromine, and iodine is less than 900ppm, and the total element content is less than 1500ppm). By screening the plates, ion adhesion can be significantly reduced, and ion contamination can be reduced from the source.

[0026] In some embodiments of the present invention, in step S9, the solder resist is formed by screen printing or coating solder resist ink, baking the plate at a low temperature (75±5°C), exposing and developing, and exposing the solder resist layer to expose the pads and holes to be soldered; the solder resist ink is made of SO4 2- Lower ink, SO4 2- Concentration <2.0 μg / square inch; Preferably, the solder resist ink is a halogen-free solder resist ink. The inventors found that solder resist ink is the main source of sulfate ions. By selecting a solder resist ink with a lower sulfate ion content, the ion contamination can be further reduced. At the same time, the inventors found that halogens in solder resist inks promote the release of sulfates. Therefore, by selecting a halogen-free solder resist ink, the release of sulfates can be reduced, thereby reducing ion contamination.

[0027] Chloride ions, bromide ions, fluoride ions, etc. are common ion pollutions on PCBs. These halogen ions mainly come from the residues of solder resist ink. The present invention can reduce the pollution of these halogen ions to PCBs by controlling the types of solder resist ink.

[0028] In some embodiments of the present invention, an ultrasonic cleaning step is further included before step S9 (after step S8), and the power of the ultrasonic wave is 0-10 kW, preferably 8-10 kW. Through ultrasonic cleaning, ink residues in the production of the outer layer circuit and other processes are reduced, and ion contamination is reduced.

[0029] In some embodiments of the present invention, in step S12, the shape processing is performed by gong plate, that is, the shape processing is performed by a CNC milling machine. By performing shape processing by gong plate, the roughness of the edge of the plate can be reduced, thereby reducing ion residue.

[0030] In some embodiments of the present invention, after step S12, the steps of electrical testing and appearance inspection are also included, wherein the electrical testing is to conduct electrical performance inspection by powering on to detect whether there is an open circuit or a short circuit. In the electrical testing and appearance inspection steps, the inspector wears sulfur-free gloves to contact the PCB; and the PCB board is wrapped with sulfur-free paper during the inspection process. The inventors have found that the electrical testing and appearance inspection steps can also cause ion contamination to the PCB. The present invention can further reduce ion contamination by controlling the gloves worn by the inspector during the inspection process and the paper used to wrap the board.

[0031] In some embodiments of the present invention, a packaging step is included after the electrical measurement and appearance inspection steps, and an ion cleaning step is included after the electrical measurement and appearance inspection steps and before the packaging step. In the ion cleaning process, an ion cleaning agent with strong adsorption and cleaning capabilities is used, and the ion cleaning process can be assisted by ultrasound.

[0032] In some embodiments of the present invention, the ion cleaning step is performed by sequentially using an aqueous solution containing an ion cleaning agent, cold water, and hot water. The mass concentration of the ion cleaning agent solution is 5-15%, and the temperature is 60-70°C; the conductivity of the ion cleaning agent is 1-2μs / cm; the type of ion cleaning agent can be selected according to actual conditions, for example, ETC-168B can be used. The temperature of cold water cleaning is 10-30°C, and the temperature of hot water cleaning is 55-65°C; the time of cold water and hot water cleaning is twice or more than the cleaning time of the ion cleaning agent.

[0033] In some embodiments of the present invention, the ion cleaning is performed by spraying. In actual operation, the PCB can be controlled to pass through a spray cleaning line containing an ion cleaning agent solution, cold water and hot water in sequence at a speed of 1.0 to 2.0 m / min.

[0034] In some embodiments of the present invention, the PCB board is an HDI board (a high-density interconnect manufacturing type printed circuit board with plugged holes), and an ultrasonic cleaning step is further included after the ion cleaning step and before the packaging step; the power of the ultrasonic wave is 0 to 10 kW, preferably 8 to 10 kW. The HDI board has a high line distribution density and has holes with a small aperture. After the surface treatment, when the ordinary method is used for cleaning, due to the small aperture of the hole, the wetting ability of the cleaning liquid in the hole is insufficient, resulting in more ionic contaminants remaining in the hole. By ultrasonic cleaning, the ionic contaminants in the hole can be effectively removed.

[0035] In some embodiments of the present invention, the PCB board is an HDI board, and the HDI board has a plug hole, and the plug hole is blocked by resin. In the case of a plug hole, after various processes, the plug hole is easily blocked by ink, and the ink is easy to crack, so that the solution will remain in the crack, that is, ion residue. By blocking the plug hole with resin, the resin will not crack, thereby reducing ion contamination.

[0036] In some embodiments of the present invention, the water used in the aforementioned cleaning steps such as ultrasonic cleaning and ion cleaning is DI water (ultrapure water).

[0037] In some embodiments of the present invention, if there is a marking line made with a paint pen on the PCB, the marking line is wiped clean with alcohol before testing.

[0038] In some embodiments of the present invention, the PCB manufacturing process also includes the step of making an ET stamp (a stamp used to prove that the PCB has passed the test and has no problems) and / or a LOT number (product batch number). The step of making the ET stamp and / or the LOT number can be arranged before the electrical testing and appearance inspection steps according to actual conditions, for example, after the solder mask, before the electrical testing and appearance inspection steps. The method of making the ET stamp is marking or drawing lines, and the method of making the LOT number is laser printing. By controlling the method of making the ET stamp and / or the LOT number, ion residues can be further reduced.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] The present invention analyzes different factors that affect surface ion contamination through DOE (experimental design) test scheme and on-site simulation test, thereby improving the PCB manufacturing process and reducing the ion contamination of the PCB. By controlling the selection of raw materials, pre-treatment before solder mask, adding a high-temperature curing process before surface treatment, ion cleaning before packaging, adding an ultrasonic cleaning step for HDI boards with tiny holes, optimizing the shape processing, electrical measurement, and shape detection processes, the residue of various ions can be effectively reduced, and undesirable problems such as ion migration after mounting components on the PCB can be avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is the ion contamination degree under different ultrasonic powers in Example 4. DETAILED DESCRIPTION

[0042] In order to more clearly illustrate the technical solution of the present invention, the following examples are listed. Unless otherwise stated, the raw materials, reactions and treatment methods shown in the examples are common raw materials on the market and technical methods well known to those skilled in the art.

[0043] Example 1

[0044] A method for manufacturing a PCB without plugging holes comprises the following steps:

[0045] (1) Cutting materials: select halogen-free sheets (content of any one element of fluorine, chlorine, bromine, and iodine < 900 ppm), and total element content < 1500 ppm). After testing, the ion contamination of halogen-free sheets is 2.83 μg / square inch;

[0046] (2) Making inner layer circuits;

[0047] (3) Browning;

[0048] (4) Lamination;

[0049] (5) half gong;

[0050] (6) Drilling;

[0051] (7) Copper plating and plate plating;

[0052] (8) making an outer layer circuit to obtain a PCB substrate with a completed circuit;

[0053] (9) Outer layer AOI (automatic optical inspection of outer layer circuits);

[0054] (10) Solder mask: After ultrasonic cleaning in DI water, use halogen-free solder mask ink (SO4 2- <2.0μg / square inch), the solder mask is made by low temperature baking at 75℃, exposure and development;

[0055] (11) Curing: UV baking of PCB, UV energy is about 2786MJ / cm 2 , temperature is about 155℃;

[0056] (12) Surface treatment: specifically, surface tin spraying;

[0057] (13) Shape processing, the processing method is gong plate;

[0058] (14) Use sulfur-free paper to wrap the panels and send them to electrical testing and appearance inspection. During the electrical testing and appearance inspection, the inspectors should wear logistics gloves to touch the panels;

[0059] (15) The plate is passed through a spray cleaning line containing an ion cleaning agent solution (the ion cleaning agent is ETC-168B, with a concentration of 10 wt %, about 60° C., and a conductivity of 2.175 μs / cm), cold water (room temperature) and hot water (about 60° C.) at a rate of about 2.0 m / min, and spray cleaning is performed. The cleaning time is 2.5 min, and the total time of cold water and hot water cleaning is twice the cleaning time of the ion cleaning agent;

[0060] (16) Packaging.

[0061] Example 2

[0062] A method for manufacturing a PCB, which is different from Example 1 in that the ion contamination of the halogen-free plate selected in step (1) is 2.84 μg / square inch, and the UV energy in step (11) is 3000 MJ / cm 2 In step (15), the temperature of the ion cleaning agent solution and hot water is 65° C., the concentration of the ion cleaning agent is 15 wt %, the conductivity is 1.86 μs / cm, and the cleaning time is 4 min.

[0063] Example 3

[0064] A method for manufacturing a PCB, which is different from Example 1 in that the ion contamination of the halogen-free plate selected in step (1) is 2.33 μg / square inch, and the UV energy in step (11) is 2700 MJ / cm 2 In step (15), the temperature of the ion cleaning agent solution and hot water is 65° C., the concentration of the ion cleaning agent is 15 wt %, the conductivity is 1.86 μs / cm, and the cleaning time is 4 min.

[0065] Example 4

[0066] A method for manufacturing an HDI board (a PCB with solder mask plug holes) comprises the following steps:

[0067] (1) Cutting materials: select halogen-free sheets (content of any one element of fluorine, chlorine, bromine, and iodine < 900 ppm), and total element content < 1500 ppm). After testing, the ion contamination of halogen-free sheets is 2.83 μg / square inch;

[0068] (2) Making inner layer circuits;

[0069] (3) Browning;

[0070] (4) stacking the multi-layer sheets together in order for lamination;

[0071] (5) half gong;

[0072] (6) Drilling: drilling holes in the board to form conductive holes that connect the internal circuits of each layer of board;

[0073] (7) Copper deposition and board plating to form a conductive copper layer on the surface of the via hole.

[0074] (8) Making outer circuits;

[0075] (9) Outer layer AOI;

[0076] (10) Solder mask: After ultrasonic cleaning in DI water, use halogen-free solder mask ink (SO4 2- <2.0μg / square inch), and then the solder mask layer is made by low temperature baking at 75℃, exposure and development; in the solder mask process, the via hole is plugged with solder mask ink to form a 0.3mm solder mask plug hole;

[0077] (11) Curing: UV baking of PCB, UV energy is about 2786MJ / cm 2 , temperature is about 155℃;

[0078] (12) Surface treatment: specifically, surface tin spraying;

[0079] (13) Shape processing, the processing method is gong plate;

[0080] (14) Use sulfur-free paper to wrap the panels and send them to electrical testing and appearance inspection. During the electrical testing and appearance inspection, the inspectors should wear logistics gloves to touch the panels;

[0081] (15) The plate is sequentially passed through a spray cleaning line of an ion cleaning agent solution (the ion cleaning agent is ETC-168B, with a concentration of 10 wt %, about 60° C., and a conductivity of 2.175 μs / cm), cold water (room temperature), and hot water (about 60° C.) at a rate of about 2.0 m / min for spray cleaning. The cleaning time is 2.5 min, wherein the total time of cold water and hot water cleaning is twice the cleaning time of the ion cleaning agent.

[0082] (16) Ultrasonic cleaning was performed in DI water with an ultrasonic power of 0 to 10 kW;

[0083] (17) Packaging.

[0084] Comparative Example 1

[0085] The difference between the preparation method of this comparative example and that of Example 1 is that the preparation method of Comparative Example 1 does not include step (11).

[0086] Comparative Example 2

[0087] The difference between the preparation method of this comparative example and that of Example 4 is that the preparation method of Comparative Example 2 does not include step (15).

[0088] Comparative Example 3

[0089] The difference between the preparation method of this comparative example and that of Example 4 is that the ion cleaning agent in step (15) is replaced with 816# ion cleaning agent, and the ultrasonic cleaning step in step (16) is not performed.

[0090] PCB test:

[0091] The PCB samples treated by Examples 1 and 4 and Comparative Examples 1 to 3 were tested for ion contamination.

[0092] The test method for ionic contamination is: using the test method of IPC-TM650-2.3.28 (A / B), using 75% isopropyl alcohol and 25% DI water to boil the board in a constant temperature water bath at 80°C for 1 hour, and the total amount of ions extracted is the ionic contamination. The results are shown in Table 1.

[0093] Table 1 Test results of PCB samples after treatment in Examples 1, 4 and Comparative Examples 1 to 3

[0094] Ionic contamination (μg / square inch) Example 1 5.35 Example 4 1.65～8.13 Comparative Example 1 11.32 Comparative Example 2 12.42 Comparative Example 3 10.57

[0095] The test results of Examples 2 and 3 are similar to those of Example 1. The ion contamination degree of Example 4 under different ultrasonic powers is as follows: Figure 1 shown.

[0096] From the above table and Figure 1 It can be seen that Example 1 can significantly reduce the ionic contamination of the PCB by adding a curing step after the solder mask process, compared with the comparative example 1 without curing, and the ionic contamination is reduced by 52.73%; and for the HDI board with tiny solder mask plug holes, the ionic contamination can be effectively reduced by performing ion cleaning before packaging, and the ionic contamination is reduced from 12.42μg / square inch when not cleaned to 8.13μg / square inch; if an ultrasonic cleaning step is added, the ionic contamination can be further reduced. In addition, by controlling the ionic cleaning agent, the use of a specific ionic cleaning agent has a greater impact on reducing the ionic contamination.

[0097] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0098] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for manufacturing a PCB, characterized in that: The method comprises the following steps: taking a substrate on which circuit manufacturing has been completed, and performing solder resist on the substrate; curing the substrate at 145-165° C. after the solder resist is completed; and performing surface treatment after curing; The method for manufacturing the PCB comprises the following steps: S1: cutting; S2: Make inner layer circuit; S3: browning; S4: lamination; S5: half gong; S6: drilling; S7: copper deposition, board plating; S8: making outer circuit; S9: solder mask; S10: curing at 145-165° C.; the curing is UV baking of the PCB; S11: surface treatment; S12: shape processing; After step S12, the steps of electrical testing and appearance inspection are also included. During the electrical testing and appearance inspection, the inspection personnel wear sulfur-free gloves to contact the PCB, wherein the electrical testing is to turn on the power to check the electrical performance to detect whether there is an open circuit or a short circuit; after the electrical testing and appearance inspection steps, an ion cleaning step is also included, and the ion cleaning step is to use an ion cleaning agent aqueous solution, cold water and hot water for cleaning in sequence; the cleaning temperature of the ion cleaning agent aqueous solution is 60-70°C, the cold water cleaning temperature is 10-30°C, and the hot water cleaning temperature is 55-65°C; the mass concentration of the ion cleaning agent aqueous solution is 5-15%; the model of the ion cleaning agent is ETC-168B; The ion cleaning step also includes an ultrasonic cleaning step.

2. The method for manufacturing a PCB according to claim 1, characterized in that: The curing temperature is 150-160°C.

3. The method for manufacturing a PCB according to claim 1, characterized in that: The cutting in step S1 is the process of cutting the original copper clad laminate into plates that can be produced on a production line. The plates are halogen-free plates, and the content of any one of fluorine, chlorine, bromine and iodine in the halogen-free plates is less than 900 ppm, and the total content of fluorine, chlorine, bromine and iodine is less than 1500 ppm.

4. The method for manufacturing a PCB according to claim 1, characterized in that: In step S9, the solder resist is formed by screen printing or coating solder resist ink, and then exposed and developed to form a solder resist layer that exposes the pads and holes to be soldered; SO4 2- Concentration <2.0 μg / square inch.

5. The method for manufacturing a PCB according to claim 4, characterized in that: The solder resist ink is a halogen-free solder resist ink.

6. The method for manufacturing a PCB according to claim 1, characterized in that: In step S12, the shape processing method is gong plate.

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