CN114828436B - Method for solving problem of jump plating at fixed position of PCB (printed circuit board) caused by battery effect - Google Patents

Abstract

The invention discloses a method for solving the problem of the jump plating of a fixed position of a PCB board caused by a battery effect, which comprises the following steps: providing a production plate, wherein a solder mask window opening position to be subjected to nickel-gold plating treatment and oxidation resistance treatment is arranged on the production plate so that PAD is exposed, and nonmetal holes and metalized holes are formed in the production plate; the PADs include a first PAD connected to a non-metallized well, a second PAD connected to a metallized well, and/or a third PAD not connected to a well; wherein, the first PAD is treated by nickel-plating gold, the second PAD connected with the metallized hole is treated by nickel-plating gold or oxidation-resistant treatment simultaneously with the metallized hole, and the third PAD with the distance from the metallized hole smaller than 20ml is treated by nickel-plating gold simultaneously with the metallized hole; after the film is stuck on the production plate, windowing is carried out at the position corresponding to the non-metallized hole and the position to be subjected to nickel-gold plating treatment; carrying out electroless nickel-gold plating treatment on the production plate; and (5) performing antioxidation treatment on the production plate after film stripping. The method effectively solves the jump plating problem of PAD in the prior art.

Description

A method for solving skip plating at fixed position of PCB board caused by battery effect

Technical Field

The invention relates to the technical field of printed circuit board manufacturing, and in particular to a method for solving skip plating at a fixed position of a PCB board caused by a battery effect.

Background Art

In the printed circuit board industry, many surface treatment processes are applied, such as organic protective film OSP, ENIG, immersion silver, immersion tin, etc. However, ENIG immersion gold surface treatment is prone to nickel-gold-free plating, that is, skip plating; it is affected by many factors such as PCB board materials, pre-treatment capabilities, load, surface tension, and wettability. Especially for the selective surface treatment (ENIG+OSP), the phenomenon of nickel-gold-free plating is more common.

In a specific production, during a selective surface treatment (ENIG+OSP), the fixed point skipped nickel-gold plating failed; no improvement was seen in the test by optimizing the parameters, such as extending the activation time, increasing the nickel tank load, reconfiguring the gold tank and nickel tank, etc., but the original fixed position still skipped plating; fixed point skip plating has one thing in common: the pads connected to the skipped pads are not independent PADs, but are connected to PTH holes or NPTH holes.

The plugged vias connected to PAD skip plating as above are sliced and analyzed. Of course, this type of plugging is related to our factory's own process or customer requirements. Here we just compare and illustrate the common characteristics of skip plating - the holes are not completely filled, and the semi-plugged via design or the plugging process itself leads to incomplete filling.

The following explains the reasons for skip plating based on the reaction principle of ENIG:

Chemical nickel reaction:

①H ₂ PO ₂ ^- +H ₂ O→H ₂ PO ₃ ^- +2H ⁺ +2e ^-

Oxidation of hypophosphite releases electrons ……………… anodic reaction

②Ni ²⁺ +2e ^－ →Ni

Nickel ions gain electrons and are reduced to metallic nickel... cathode reaction

③2H ⁺ +2e ^－ →H ₂ ↑

Hydrogen ions gain electrons and are reduced to hydrogen gas... cathode reaction

④H ₂ PO ₂ ^- +e ^- →P+2OH ^-

Hypophosphite gets electrons and releases phosphorus... cathodic reaction

⑤Overall reaction formula:Ni ²⁺ +H ₂ PO ₂ ^－ +H ₂ O→H ₂ PO ₃ ^－ +2H ⁺ +Ni

The reaction of chemical nickel is a reaction that relies on activated Pd to catalyze the plating. When nickel plating begins, it relies on the self-catalyzed redox reaction of the nickel metal itself.

Here, the way we react nickel is to deposit a unit sub-layer of Pd on the copper surface using a replacement method. The basis of the reaction between Cu and Pd ²⁺ is a replacement reaction, and the ionization trend is Cu>Pd.

Anodic reaction: Cu→Cu ²⁺ +2e ^-

Cathode reaction: Pd ²⁺ +2e ^- →Pd

Overall reaction: Cu+Pd2 ⁺ →Cu2 ⁺ +Pd

From the above reaction principle of chemical nickel, it can be seen that the deposition of Pd plays the role of a catalyst in the whole reaction; it accelerates the chemical reaction between nickel and copper; without the catalytic effect of Pd, the reaction between nickel and copper is difficult to proceed.

According to a large number of laboratory tests, the main reason for the skipping of the pad connected to the plugged hole or the hole covered under the dry film is that the micro-etching bath solution enters the hole during the main line pre-treatment, causing the electrode potential of Cu to change; the micro-etching bath solution contains relatively more Cu ²⁺ ions. Due to the entry of Cu ²⁺ ions in the hole, the electrode potential of the Cu pad, which serves as the cathode, will partially show the characteristics of Cu ²⁺ , reducing the ionization trend of Cu metal. Cu ²⁺ cannot be oxidized because it cannot lose electrons, so Pd ²⁺ cannot get electrons to be reduced. When the Pad that cannot be plated with Pd is in the nickel bath, it will of course not be plated, and the situation of not being able to plate nickel and gold will also occur. If the more holes such a Pad is connected to and the more solutions enter, the more obvious the potential effect will be, and even the fixed Pad will not be able to be plated with nickel and gold, that is, the problem of skipping plating will occur.

Summary of the invention

In view of the above-mentioned existing technical defects, the present invention provides a method for solving the skipping plating at a fixed position of a PCB board caused by the battery effect, which effectively solves the skipping plating problem of PAD in the prior art.

In order to solve the above technical problems, the present invention provides a method for solving the skip plating of a fixed position of a PCB board caused by a battery effect, comprising the following steps:

S1. Provide a production board with a solder mask layer, wherein a solder mask window position to be treated with nickel-gold and anti-oxidation treatment is provided on the production board, so that the PAD at the corresponding position of the solder mask window position is exposed, and the production board is provided with a non-metallized hole and a metallized hole; the PAD includes a first PAD connected to the non-metallized hole, a second PAD connected to the metallized hole and/or a third PAD not connected to the hole; wherein the first PAD is treated with nickel-gold, the second PAD connected to the metallized hole needs to be treated with nickel-gold or anti-oxidation treatment at the same time as the metallized hole, and the third PAD less than 20 mils away from the metallized hole needs to be treated with nickel-gold at the same time as the metallized hole;

S2. According to the above-mentioned surface treatment design, after the film is attached to the production board, windows are opened on the film corresponding to the non-metallized holes and the positions to be treated with nickel and gold;

S3, chemically immerse the production board in nickel and gold;

S4. After film removal, anti-oxidation treatment is performed on the PAD and metallized holes on the production board that have not been treated with nickel-gold immersion.

Furthermore, before step S1, the following steps are also included:

S01, making non-metallized holes and metallized holes on the production board;

S02, performing a resin ink plugging process on at least one metallized hole of the production board to form a plugged hole;

S03. Curing the resin ink by baking, wherein the baking includes a low temperature section with a temperature of ≤100°C and a high temperature section with a temperature of greater than 100°C, and the heating rate in the low temperature section is controlled at 0.4-0.5°C/min, and the heating rate in the high temperature section is controlled at 0.8-1.0°C/min

S04. Make the outer layer circuit and solder mask layer on the production board in sequence.

Furthermore, in step S03, a segmented baking method is adopted, and the segmented baking conditions are as follows: first segment: temperature 50°C, time 30 min; second segment: temperature 65°C, time 30 min; third segment: temperature 75°C, time 30 min; fourth segment: temperature 85°C, time 30 min; fifth segment: temperature 100°C, time 30 min; sixth segment: temperature 120°C, time 30 min; seventh segment: temperature 150°C, time 50 min.

Furthermore, in step S02, after plugging the holes, the resin ink is initially cured by exposure.

Furthermore, in step S02, when the plug hole needs to be made into a semi-plug hole, the resin ink on one side of the plug hole is fully exposed, and an exposure film is designed on the other side of the plug hole, and the exposure film is provided with a light-transmitting hole with an aperture smaller than the aperture of the plug hole in the middle of the corresponding plug hole, and then the unexposed resin ink is removed by development to form a semi-plug hole.

Furthermore, the aperture of the light-transmitting hole is 4 mils smaller than the aperture of the plug hole.

Furthermore, the anti-oxidation treatment adopts OSP surface treatment.

Furthermore, in step S1, the third PAD which is more than 20 mils away from the metallized hole is treated with nickel-gold immersion or anti-oxidation treatment.

Furthermore, in step S2, the film is applied as a dry film.

Furthermore, the production board is a multi-layer board in which an inner core board and an outer copper foil are pressed together by a semi-cured sheet, and the multi-layer board has been subjected to drilling, copper deposition and full-board electroplating processes in sequence.

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

1. First, a window is opened on the film at the position corresponding to the non-metallized hole, and a hollowing process is performed so that the micro-etching liquid remaining in the non-metallized hole can be washed away when the nickel-gold is etched, so as to avoid the micro-etching liquid from penetrating into the non-metallized hole after the film is attached and causing a potential difference, thereby solving the problem of skip plating of the PAD connected to the non-metallized hole.

2. Design the PAD connected to the metallized hole to be treated with nickel-gold or anti-oxidation treatment at the same time as the metallized hole, that is, use the same surface treatment method. This can avoid the problem that the PAD cannot be nickel-gold coated due to the potential difference between the two due to different surface treatments, and avoid the potential difference caused by the micro-etching solution penetrating into the metallized hole after the film is applied.

3. For an independent PAD, when the distance between it and the metallized hole is less than 20 mils, if it is designed to be anti-oxidation treated, considering the selective process capability of the cover film, the metallized hole will have the problem of gold penetration when the nickel-gold immersion treatment is performed, thereby affecting the anti-oxidation treatment of the PAD. Therefore, in the present invention, it is also designed to adopt the same nickel-gold immersion surface treatment method as the metallized hole.

4. When there is a plugged hole on the board, it is necessary to extend the baking time of the low-temperature section and reduce the heating rate after the ink plugging to improve the quality of the plugged hole. Therefore, in the present invention, the heating rate of the low-temperature section is reduced to 0.4-0.5°C/min, which is only half of the heating rate conventionally used in the prior art, to avoid cracks in the plugged hole during baking, resulting in the infiltration of micro-etching solution in the later stage, thereby causing a potential difference that affects the nickel-gold surface treatment of the PAD.

5. When the plug hole is a semi-plug hole, one side of the plug hole is fully exposed, and an exposure film is designed on the other side. In the exposure film, a light-transmitting hole with an aperture smaller than the corresponding plug hole is designed in the middle position, so that the ink in the middle of the plug hole in this side is exposed and cured, while the ink around it is not exposed and cured. At this time, the uncured ink in the hole is removed by development. Since the size of the uncured hole is smaller, the amount of ink removed during development can be reduced to reduce the depth of the depression here. First, it reduces the amount of micro-etching solution entering the hole in the later stage. Second, it is convenient to wash away the micro-etching solution in the pit during nickel-gold treatment, and solve the problem of PAD jump plating caused by potential difference.

DETAILED DESCRIPTION

In order to more fully understand the technical content of the present invention, the technical solution of the present invention will be further introduced and illustrated in conjunction with specific embodiments below.

Example 1

A circuit board method shown in this embodiment can solve the problem of skipping plating at a fixed position of a PCB board caused by the battery effect, and includes the following processing steps in sequence:

(1) Cutting: Cut the core board according to the panel size of 520mm×620mm. The thickness of the core board is 0.5mm, and the thickness of the copper layer on both surfaces of the core board is 0.5oz.

(2) Inner layer circuit production (negative film process): Inner layer pattern transfer, use a vertical coating machine to coat the photosensitive film, the film thickness of the photosensitive film is controlled to 8μm, and a fully automatic exposure machine is used to complete the exposure of the inner layer circuit with a 5-6 grid exposure ruler (21 grid exposure ruler). After development, the inner layer circuit pattern is formed; inner layer etching, the exposed and developed core board is etched to etch the inner layer circuit, and the inner layer line width is measured to be 3mil; inner layer AOI, and then check the inner layer circuit for defects such as open short circuits, circuit gaps, and circuit pinholes. Defective products are scrapped, and non-defective products are sent to the next process.

(3) Lamination: The browning speed is based on the browning thickness of the bottom copper. The core board, prepreg, and outer copper foil are laminated in sequence as required. Then, appropriate lamination conditions are selected according to the Tg of the sheet material to laminate the laminated board to form a production board.

(4) Drilling: Based on the existing drilling technology, drilling processing is performed on the production board according to the design requirements.

(5) Copper plating: A thin layer of copper is deposited on the board surface and hole wall by chemical copper plating. The backlight test is level 10, and the thickness of the copper plating in the hole is 0.5μm.

(6) Full-board electroplating: Full-board electroplating is performed for 120 minutes at a current density of 18 ASF to thicken the hole copper and the board surface copper layer to form a metallized hole.

(7) Drilling: Based on the existing drilling technology, drilling is performed on the production board according to the design requirements to produce non-metallized holes.

(8) Production of outer circuits (positive film process): Transfer of outer pattern, using fully automatic exposure machine and positive circuit film, with 5-7 grid exposure ruler (21 grid exposure ruler) to complete the exposure of outer circuit, after development, the outer circuit pattern is formed on the production board; electroplating of outer pattern, and then copper plating and tin plating on the production board respectively, setting the electroplating parameters according to the required copper thickness, copper plating is 1.8ASD current density electroplating for 60 minutes on the whole board, tin plating is 1.2ASD current density electroplating for 10 minutes, tin thickness is 3-5μm; then stripping, etching and tin stripping are carried out in turn, and the outer circuit is etched on the production board, and the copper thickness of the outer circuit is greater than or equal to 70μm; outer layer AOI, using automatic optical inspection system, by comparing with CAM data, detect whether the outer circuit has defects such as open circuit, gap, incomplete etching, short circuit, etc.

(9) Solder mask and silk screen characters: After the solder mask ink is silk screen printed on the surface of the production board, it is sequentially subjected to pre-curing, exposure, development and thermal curing treatments to solidify the solder mask ink into a solder mask layer; specifically, a "UL mark" is added to the solder mask ink on the TOP surface and the characters on the TOP surface, thereby coating a layer on the circuits and substrates that do not require soldering to prevent bridging between circuits during soldering, provide a permanent electrical environment and resist chemical corrosion, and at the same time beautify the appearance.

In the above, the solder mask is opened to expose the PAD (i.e., pad) on the production board to be treated with nickel-gold and anti-oxidation. Of course, the non-metallized holes and metallized holes that need surface treatment on the production board are also exposed.

Among them, the exposed PAD generally includes a first PAD connected to the non-metallized hole (for example, a PAD arranged around the non-metallized hole or a PAD arranged next to the non-metallized hole), a second PAD connected to the metallized hole and/or a third PAD not connected to the hole (i.e., an independent PAD); in addition, in order to improve the quality of the subsequent surface treatment and solve the problem of skip plating, the surface treatment of each PAD and the metallized hole is redesigned and selected, as follows:

1. The first PAD is treated with nickel-plated gold. Whether the dry film applied during the later localized gold treatment covers the non-metallic holes on the large copper surface will directly affect the gold treatment, resulting in the failure of nickel-plated gold treatment on the first Pad connected to it. For this reason, the non-metallic holes in the board and the edge of the board in the dry film need to be hollowed out, so that the micro-etching liquid remaining in the hole during the pre-treatment can be washed away during nickel-plated gold treatment, avoiding the potential difference caused by the micro-etching liquid in the hole affecting the gold treatment.

2. Currently, the gold-plated PAD connected to the metallized hole treated with OSP has the risk of skipping plating at a fixed position. When designing the surface treatment method of the PAD, the client should make the metallized hole connected to the PAD the same surface treatment method, that is, the second PAD connected to the metallized hole needs to be treated with nickel-plated gold or anti-oxidation treatment at the same time as the metallized hole.

3. When selecting the surface treatment method for PAD, attention should be paid to the process capability of dry film covering. The process capability of dry film selection is: the distance from PAD to the hole needs to be greater than 20 mils. When the distance between it and the metallized hole is less than 20 mils, and it is designed to be anti-oxidation treated and requires dry film covering, considering the selective process capability of the cover film, the metallized hole will have the problem of gold penetration when the nickel-gold immersion treatment is performed, which will affect the anti-oxidation treatment of the PAD. Therefore, in this embodiment, the third PAD with a distance less than 20 mils from the metallized hole is designed to be treated with nickel-gold immersion at the same time as the metallized hole.

(10) Film pasting: A dry film is pasted on the production board, and windows are opened on the dry film at the positions of non-metallized holes and metallized holes and PADs to be treated with nickel and gold according to the selected surface treatment methods of the above-mentioned PADs and metallized holes. The metallized holes and PADs that need anti-oxidation treatment are covered by the dry film.

(11) Nickel and gold treatment: The copper surface of the dry film window opening is chemically deposited with a nickel layer and a gold layer of a certain required thickness. The thickness of the nickel layer is 3-5μm; the thickness of the gold layer is 0.05-0.1μm.

(12) Anti-oxidation treatment: The dry film on the production board is removed, and then an anti-oxidation treatment is performed on the production board, thereby forming an anti-oxidation protective film on the PAD and metallized holes that have not been treated with nickel-gold immersion. The thickness of the protective film is 0.2-0.5 μm; the anti-oxidation treatment is preferably an OSP surface treatment.

(13) Electrical test: Test the electrical conductivity of the finished board. The test method used for this board is: flying probe test.

(14) Molding: According to the existing technology and the design requirements, the circuit board is manufactured with a shape tolerance of +/-0.05mm.

(15) FQC: Inspect the appearance of the circuit board according to the customer's acceptance standards and our inspection standards. If there are any defects, repair them in time to ensure that we provide customers with excellent quality control.

(16) FQA: Re-test the circuit board’s appearance, hole copper thickness, dielectric layer thickness, green oil thickness, inner layer copper thickness, etc. to see if they meet customer requirements.

(17) Packaging: According to the packaging method and packaging quantity required by the customer, the circuit boards are sealed and packed with desiccant and humidity card before shipment.

Example 2

The circuit board method shown in this embodiment is basically the same as the method described in Embodiment 1, except that between steps (7) and (8), a step of plugging the metallized hole to form a full plugged hole or a half plugged hole is included, which is specifically as follows:

(71) plugging: performing a resin ink plugging process on at least one metallized hole of the production board to form a plugged hole;

(72) Baking: The resin ink is cured by baking, wherein the baking includes a low temperature section with a temperature of ≤100°C and a high temperature section with a temperature of greater than 100°C, and the heating rate in the low temperature section is controlled at 0.4-0.5°C/min, while the heating rate in the high temperature section is controlled at 0.8-1.0°C/min. In this step, a segmented baking method is adopted, and the segmented baking conditions are as follows: first section: temperature 50°C, time 30 min; second section: temperature 65°C, time 30 min; third section: temperature 75°C, time 30 min; fourth section: temperature 85°C, time The first stage is to heat the production board from room temperature to 50°C for 30 minutes at the heating rate of the low temperature stage, and then heat it to 65°C for 30 minutes. In this way, the temperature is gradually increased to 100°C and kept for 30 minutes. Then, the temperature is increased to 120°C at the heating rate of the high temperature stage and kept for 30 minutes. Finally, the temperature is increased to 150°C and kept for 50 minutes.

In a specific implementation case, after plugging the holes, the resin ink is first initially cured by exposure to prevent the resin ink from flowing out of the plugged holes before being baked and cured.

In a specific implementation case, when the plug hole in step (71) needs to be made into a semi-plug hole, the resin ink on one side of the plug hole is fully exposed, and an exposure film is designed on the other side of the plug hole, and the exposure film is provided with a light-transmitting hole with an aperture smaller than the aperture of the plug hole in the middle of the corresponding plug hole, and then the unexposed resin ink is removed by development to form a semi-plug hole; preferably, the aperture of the light-transmitting hole is 4 mils smaller than the aperture of the plug hole.

The technical solutions provided by the embodiments of the present invention are introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the embodiments of the present invention. The description of the above embodiments is only applicable to help understand the principles of the embodiments of the present invention. At the same time, for those skilled in the art, according to the embodiments of the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting the present invention.

Claims (8)

1. A method for solving skip plating at a fixed position of a PCB board caused by a battery effect, characterized in that it comprises the following steps: S01, making non-metallized holes and metallized holes on the production board; S02, performing a resin ink plugging process on at least one metallized hole of the production board to form a plugged hole; after plugging the hole, the resin ink is firstly cured by exposure; when the plugged hole needs to be made into a semi-plugged hole, the resin ink on one side of the plugged hole is fully exposed, and an exposure film is designed on the other side of the plugged hole, and the exposure film is provided with a light-transmitting hole with an aperture smaller than the aperture of the plugged hole in the middle of the corresponding plugged hole, and then the unexposed resin ink is removed by development to form a semi-plugged hole; S03, curing the resin ink by baking; S04, making outer circuits and solder resist layers on the production board in sequence; S1. Provide a production board with a solder mask layer, wherein a solder mask window position to be treated with nickel-gold and anti-oxidation treatment is provided on the production board, so that the PAD at the corresponding position of the solder mask window position is exposed, and a non-metallized hole and a metallized hole are provided on the production board; the PAD includes a first PAD connected to the non-metallized hole, a second PAD connected to the metallized hole, and a third PAD not connected to the hole; wherein the first PAD is treated with nickel-gold, the second PAD connected to the metallized hole needs to be treated with nickel-gold or anti-oxidation treatment at the same time as the metallized hole, and the third PAD less than 20 mils away from the metallized hole needs to be treated with nickel-gold at the same time as the metallized hole; S2. According to the above-mentioned surface treatment design, after the film is attached to the production board, windows are opened on the film corresponding to the non-metallized holes and the positions to be treated with nickel and gold; S3, chemically immerse the production board in nickel and gold; S4. After film removal, anti-oxidation treatment is performed on the PAD and metallized holes on the production board that have not been treated with nickel-gold immersion. 2. The method for solving the skip plating problem of a fixed position of a PCB board caused by a battery effect according to claim 1 is characterized in that, in step S03, the baking includes a low temperature section with a temperature ≤ 100°C and a high temperature section with a temperature greater than 100°C, and the heating rate in the low temperature section is controlled at 0.4-0.5°C/min, and the heating rate in the high temperature section is controlled at 0.8-1.0°C/min. 3. The method for solving the skip plating problem of a fixed position of a PCB board caused by a battery effect according to claim 2 is characterized in that, in step S03, a segmented baking method is adopted, and the segmented baking conditions are as follows: first segment: temperature 50°C, time 30 min; second segment: temperature 65°C, time 30 min; third segment: temperature 75°C, time 30 min; fourth segment: temperature 85°C, time 30 min; fifth segment: temperature 100°C, time 30 min; sixth segment: temperature 120°C, time 30 min; seventh segment: temperature 150°C, time 50 min. 4. The method for solving skip plating at a fixed position of a PCB board caused by a battery effect according to claim 1, wherein the aperture of the light-transmitting hole is 4 mils smaller than the aperture of the plug hole. 5. The method for solving skip plating at a fixed position of a PCB board caused by a battery effect according to claim 1, wherein the anti-oxidation treatment adopts OSP surface treatment. 6. The method for solving skip plating at a fixed position of a PCB board caused by a battery effect according to claim 1, characterized in that, in step S1, a third PAD which is more than 20 mils away from the metallized hole is treated with nickel-gold immersion or anti-oxidation treatment. 7. The method for solving skip plating at a fixed position of a PCB board caused by a battery effect according to claim 1, characterized in that in step S2, a dry film is used for the film. 8. The method for solving skip plating at a fixed position of a PCB board caused by a battery effect according to claim 1 is characterized in that the production board is a multi-layer board in which an inner core board and an outer copper foil are pressed together by a prepreg, and the multi-layer board has undergone drilling, copper deposition and full-board electroplating processes in sequence.