Alkaline resistor printed circuit board with metal edging in blind slot and preparation method thereof

Abstract

The present invention discloses an alkaline resistor printed circuit board with metal edging in a blind groove and a preparation method thereof, comprising the following steps: providing a resistor substrate and a copper clad core board, and cutting the resistor substrate and the copper clad core board into the size specifications required for production; milling the resistor substrate to obtain a blind groove, and metalizing the blind groove; plating an edging copper layer on the side of the blind groove, performing photo imaging, etching, and plating a side protective layer on the blind groove to obtain a resistor substrate with an edging copper layer blind groove; pressing the resistor substrate with the edging copper layer blind groove and the copper clad core board through a semi-cured sheet to obtain a composite board; performing photo imaging, copper plating, tin plating, and etching on the composite board to obtain an alkaline resistor printed circuit board. The present invention is used to solve the technical problem of no mature manufacturing process when a printed circuit board is combined with blind grooves, resistors, and side edges, thereby achieving the purpose of producing a printed circuit board with a blind groove + resistor + metal edging design.

Description

Technical Field

[0001] The invention relates to the technical field of printed circuit boards, and in particular to an alkaline resistor printed board with metal edging in a blind slot and a preparation method thereof. Background Art

[0002] As PCB (Printed Circuit Board) develops towards small size, light weight, three-dimensional installation and high connection reliability, flexible printed circuit boards are developing rapidly and are beginning to develop towards rigid-flexible printed circuit boards. Therefore, rigid-flexible printed circuit boards are one of the main growth points of the PCB industry in the future.

[0003] Blind slot design is also one of the common product types of printed circuit boards. Blind slots are mainly used to install components, fix products, improve the overall integration of products, and shield signals. The traditional lamination glue blocking process of blind slot printed circuit boards uses glue blocking materials to prevent the glue flow of the interlayer bonding sheet, so that the glue flow is blocked, thereby ensuring that the circuit at the bottom of the blind slot is intact and there is no glue overflowing to the surface of other circuits to affect circuit welding.

[0004] As printed circuit boards develop towards integration and miniaturization, printed circuit boards with built-in resistors come into being. Alloys are used as resistor materials to achieve the required resistance values. Since most active metals are alkali-resistant but not acid-resistant, when resistors are designed on printed circuit boards, they need to be processed specifically according to their characteristics. Acid is used to make the circuit, and strong alkali is used to etch the copper to make a separate resistor.

[0005] Metal side edge is a common method used in the industry to make shielding, which uses the principle of connecting the side edge with the ground to ensure the process network is covered. However, from the production perspective, the design of metal side edge requires protective measures to be taken during the production process to prevent the side edge from being attacked, so the side edge is often produced in a fully covered form.

[0006] When a PCB board is combined with blind slots, resistors and side edges, it is necessary to realize and integrate various features separately. Currently, there is no mature manufacturing process that can realize metallization of different blind slot sides or metallization of all sides while realizing blind slot and resistor manufacturing. Summary of the invention

[0007] In order to overcome the shortcomings of the prior art, the present invention provides an alkaline resistor printed circuit board with metal edging in a blind groove and a preparation method thereof, which is used to solve the technical problem that there is no mature manufacturing process when the printed circuit board is combined with blind grooves, resistors and side edges, thereby achieving the purpose of manufacturing a printed circuit board with a blind groove + resistor + metal edging design.

[0008] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing an alkaline resistor printed circuit board with metal edging in a blind slot comprises the following steps:

[0010] Providing a resistor substrate and a copper clad core board, and cutting the resistor substrate and the copper clad core board into the size specifications required for production;

[0011] Milling the resistor substrate to obtain a blind groove, and metalizing the blind groove;

[0012] Plating a copper layer on the side of the blind groove, performing photo-imaging, etching, and plating a side protection layer on the blind groove to obtain a resistor substrate with a copper layer blind groove;

[0013] The resistor substrate with the blind groove of the copper layer and the copper clad core board are pressed together through a prepreg to obtain a composite board;

[0014] The composite board is subjected to photoimaging, copper plating, tin plating and etching to obtain the alkaline resistor printed board.

[0015] As a preferred embodiment of the present invention, when performing optical imaging, etching and plating a side protection layer on the blind groove, it includes:

[0016] Adhere a dry film on the copper-clad layer of the resistor substrate and perform optical imaging to obtain a first circuit pattern;

[0017] Etching the copper clad layer according to the first circuit pattern to expose the resistor film underneath, and then etching the resistor film to remove the dry film;

[0018] Plating a side protection layer on the blind groove, attaching a dry film at the resistor position and performing optical imaging to obtain a second circuit pattern;

[0019] After etching the core board of the resistor substrate according to the second circuit pattern, the dry film is removed to obtain the resistor substrate with blind grooves of the edge-wrapped copper layer.

[0020] As a preferred embodiment of the present invention, when the composite board is subjected to photoimaging, copper plating, tin plating and etching, the method includes:

[0021] Drilling through holes on the copper-clad core board of the composite board and metallizing the through holes;

[0022] After the composite board is subjected to full-board electroplating to increase copper, a dry film is attached and optical imaging is performed to obtain a third circuit pattern;

[0023] Copper plating and tin plating are performed on the composite board, a dry film is attached again, and optical imaging is performed to obtain a fourth circuit pattern;

[0024] Stripping the tin according to the fourth circuit pattern to expose the copper plating layer underneath, and etching part of the exposed copper plating layer;

[0025] Etching is performed according to the third circuit pattern, and the remaining exposed copper plating layer is etched at the same time. After the etching is completed, the remaining tin and dry film are removed to obtain the alkaline resistor printed circuit board.

[0026] As a preferred embodiment of the present invention, when obtaining the alkaline resistor printed board, it includes:

[0027] The blind groove and the edge position of the composite board are stripped of tin to obtain the exposed copper plating layer in the blind groove and the edge position, and after etching 60-80% of the exposed copper plating layer, etching is performed according to the third circuit pattern, and the remaining 20-40% of the exposed copper plating layer is etched at the same time.

[0028] As a preferred embodiment of the present invention, when obtaining the alkaline resistor printed board, it also includes:

[0029] Using an acidic solution to remove tin from the composite board;

[0030] Using a strong oxidizing solution to etch according to the third circuit pattern and to etch the exposed copper plating layer;

[0031] A strong alkaline solution was used to remove the dry film on the composite board.

[0032] As a preferred embodiment of the present invention, when etching the core plate of the resistor substrate according to the second circuit pattern, it includes:

[0033] Determining whether the side protection layer is connected to the board surface of the resistor substrate;

[0034] If so, determine whether there is a connection exceeding 0.1 mm;

[0035] If so, a dry film mask is used to protect the side protection layer;

[0036] If the side protection layer is not connected to the board surface of the resistor substrate or the connection is less than 0.1 mm, the edge groove is filled with glue to protect the side protection layer.

[0037] As a preferred embodiment of the present invention, the tinning process parameters are: when the copper thickness is 4OZ-6OZ, the tinning current density is 10-14ASF, and the tinning time is 5-10 minutes; when the copper thickness is 7OZ-9OZ, the tinning current density is 15-20ASF, and the tinning time is 7-9 minutes; when the copper thickness is 9OZ-12OZ, the tinning current density is 16-20ASF, and the tinning time is 10-15 minutes.

[0038] As a preferred embodiment of the present invention, the side plated protective layer is a side gold plated layer.

[0039] As a preferred embodiment of the present invention, the process parameters of the side gold-plated layer are: current density is 5-6ASF, time is 120-150 seconds, and the thickness of the gold-plated layer is 0.045-0.095 μm.

[0040] An alkaline resistor printed circuit board with metal edging in blind slots is prepared by the above method.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) The present invention further protects the blind slot by plating a side protection layer on the blind slot and using a dry film mask or glue filling according to the connection between the side protection layer and the resistor substrate surface, thereby achieving effective protection of the blind slot;

[0043] (2) The present invention can realize the production of printed circuit boards with blind slot + resistor + metal edging design;

[0044] (3) The preparation method provided by the present invention is easy to operate and highly feasible.

[0045] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 - is a step diagram of a method for preparing an alkaline resistor printed circuit board with metal edging in a blind slot according to an embodiment of the present invention;

[0047] Figure 2 - is a diagram of the preparation process of a resistor substrate with a blind groove of a copper layer with an edge covering according to an embodiment of the present invention;

[0048] Figure 3 - is a schematic structural diagram of an alkaline resistor printed circuit board with metal edging in a blind slot according to an embodiment of the present invention.

[0049] Explanation of the accompanying drawings: 1. resistor substrate; 2. copper-clad core board; 3. core board; 4. copper-clad layer; 5. resistor film; 6. prepreg. DETAILED DESCRIPTION

[0050] The present invention provides a method for preparing an alkaline resistor printed circuit board with metal edging in a blind slot, such as Figure 1 and Figure 3 As shown, the following steps are included:

[0051] Step S1: providing a resistor substrate 1 and a copper clad core board 2, and cutting the resistor substrate 1 and the copper clad core board 2 into sizes required for production;

[0052] Step S2: milling a groove on the resistor substrate 1 to obtain a blind groove, and metalizing the blind groove;

[0053] Step S3: plating a copper layer on the side of the blind groove, performing photo-imaging, etching, and plating a side protective layer on the blind groove to obtain a resistor substrate 1 with a copper layer blind groove;

[0054] Step S4: The resistor substrate 1 with the blind groove of the copper layer and the copper clad core board 2 are pressed together through the prepreg 6 to obtain a composite board;

[0055] Step S5: performing photo-imaging, copper plating, tin plating and etching on the composite board to obtain an alkaline resistor printed board.

[0056] Conventional resistor thin film circuit production designs usually have two layers of metal covering layers for signal shielding to avoid signal loss and non-concentration, so the resistor thin film layer is usually set in the inner layer design. When there is a step circuit design, that is, there are multiple levels of circuits on the same printed circuit board, and there are interconnections between the circuits, this is a blind slot design in the industry. If the design has both resistor thin film circuits and step circuits, the combination of circuit production and structural design must take into account the realization of the structure while ensuring circuit production. In fact, the design involving circuit shielding requires metal on the side to ensure maximum signal concentration. Therefore, it is of great significance to realize the production of printed circuit boards with blind slots + resistors + metal edging designs. The preparation method of the alkaline resistor printed board provided by the present invention can effectively realize the production of printed circuit boards with blind slots + resistors + metal edging designs.

[0057] Furthermore, optical imaging must go through the steps of pre-treatment, film attachment, exposure and development. The specific process of pre-treatment consists of pickling → overflow water washing → grinding plate → pressurized water washing → HF water washing → intermediate inspection → micro-etching → overflow water washing → drying. Its purpose is to remove the oxide on the surface of the copper foil and expose the copper surface with certain activity between the dry film and the copper foil interface. The factors that affect the bonding force include contact surface area, contact angle and interfacial chemical force (including intermolecular van der Waals force, polar bond force, etc.). For this, it is necessary to create a certain surface micro-roughness through pre-treatment to ensure good adhesion between the dry film and the copper foil surface.

[0058] It is best to attach the film to the PCB board immediately after pre-treatment. If the placement time exceeds 4 hours, it should be cleaned again before attaching the film. The process of attaching the film consists of setting the dry film → turning on the power switch → adjusting the temperature → adjusting the pressure → starting to attach the film → cutting the film → standing still and other sub-processes.

[0059] Notes on film attachment:

[0060] (1) Before attaching the film, the substrate must be placed in an oven at 110±5℃ for 10min~15min to remove moisture from the board surface and the holes to ensure that the board surface is dry before attaching the film;

[0061] (2) After the film is attached, the substrate needs to be left to cool for more than 15 minutes before exposure. The purpose is to make the dry film completely adhere to the board surface and make it completely hardened.

[0062] The exposure process consists of turning on the main power → opening the cooling water and air valve → turning on the main power → entering the main operation interface → entering the light source system → energy setting → vacuuming → degassing → exposure → taking the plate → standing still and other sub-processes.

[0063] In the above step S3, if Figure 2 As shown, when performing photo-imaging, etching and plating side protection layer on blind grooves, it includes:

[0064] A dry film is attached to the copper-clad layer 4 of the resistor substrate 1 and optical imaging is performed to obtain a first circuit pattern;

[0065] After etching the copper clad layer 4 according to the first circuit pattern to expose the resistor film 5 underneath, the resistor film 5 is further etched to remove the dry film;

[0066] Plating a side protection layer on the blind slot, attaching a dry film to the resistor position and performing optical imaging to obtain a second circuit pattern;

[0067] After etching the core board 3 of the resistor substrate 1 according to the second circuit pattern, the dry film is removed to obtain the resistor substrate 1 with blind grooves of the edge-wrapped copper layer.

[0068] Furthermore, the resistor substrate 1 includes a core board 3 , copper clad layers 4 respectively disposed on the upper and lower surfaces of the core board 3 , and a resistor film 5 located between the copper clad layers 4 and the core board 3 .

[0069] Furthermore, since the resistor film 5 cannot be alkaline passivated, an acid solution is used for etching.

[0070] The present invention embeds the resistor film 5 inside the printed circuit board, which has the following advantages:

[0071] (1) It can effectively improve the electrical performance of the printed circuit board. The appropriate matching resistance value can be selected according to the characteristic impedance value required by the specific circuit. The embedded resistance technology is used to integrate it into the termination of the transmission signal, so that the distance from the resistor to the signal line is shortened to the shortest, and the best matching effect is obtained. At the same time, due to the reduction of the through hole and the lead-out and lead-in wires, signal crosstalk, noise and electromagnetic interference can be reduced;

[0072] (2) It can improve the reliability of the printed circuit board. By burying the resistor inside the printed circuit board, the number of pads and soldering points can be reduced, and the influence of external conditions on the resistor can be avoided, such as mechanical vibration, shock, moisture, pollution, corrosive gas, etc.

[0073] (3) It can effectively promote the development of printed circuit boards towards high density. By burying the passive components that occupy a large amount of the printed circuit board surface area inside, it can reduce the number of vias and connecting wires while increasing the design surface area of ​​the printed circuit board, increasing the wiring freedom of the printed circuit board, shortening the length of the interconnecting wires, and reducing the number of layers and size of the printed circuit board, which is conducive to improving the density of the printed circuit board.

[0074] In the above step S5, when the composite board is subjected to photoimaging, copper plating, tin plating and etching, it includes:

[0075] Drilling through holes on the copper-clad core board 2 of the composite board and metalizing the through holes;

[0076] After the composite board is subjected to full-board copper plating, a dry film is attached and optical imaging is performed to obtain a third circuit pattern;

[0077] The composite board is copper plated and tin plated, a dry film is attached again, and optical imaging is performed to obtain a fourth circuit pattern;

[0078] Stripping the tin according to the fourth circuit pattern to expose the copper plating layer below, and etching part of the exposed copper plating layer;

[0079] Etching is performed according to the third circuit pattern, and the remaining exposed copper plating layer is etched at the same time. After the etching is completed, the remaining tin and dry film are removed to obtain an alkaline resistor printed circuit board.

[0080] The purpose of full-board copper electroplating is to protect the newly deposited thin copper layer and prevent the thin copper layer from being oxidized and corroded by acid. Therefore, the thin copper layer is thickened to a certain extent by electroplating, thereby improving the corrosion resistance of the copper layer.

[0081] In the present invention, the bath liquid used for full-board copper electroplating mainly contains copper sulfate and sulfuric acid, and adopts a high-acid, low-copper formula, thereby ensuring the uniformity of the thickness distribution of the board surface during electroplating and the deep plating capability for deep holes and small holes.

[0082] Furthermore, the present invention adopts an acidic tin plating process, which is mainly composed of stannous salts, sulfuric acid and organic additives. The process has the characteristics of high current efficiency, fast deposition speed, good leveling performance, lasting bright appearance, strong resistance to alkali corrosion, etc.

[0083] Furthermore, in the present invention, when copper and tin are plated on the composite board, an acidic copper sulfate plating solution is used for copper plating;

[0084] Furthermore, the acidic copper sulfate plating solution includes copper sulfate (CuSO4), sulfuric acid (H2SO4), hydrochloric acid (mainly chloride ions) and organic additives, etc. The acidic copper sulfate plating solution has the advantages of good dispersibility and deep plating ability, high current efficiency and low cost.

[0085] Furthermore, the copper-clad core board 2 includes a core board 3 and copper-clad layers 4 respectively arranged on the upper and lower surfaces of the core board 3 .

[0086] Furthermore, when obtaining the alkaline resistor printed circuit board, it includes:

[0087] The blind slots and the edge positions of the composite board are stripped of tin to obtain the exposed copper plating layer in the blind slots and the edge positions. After etching 60-80% of the exposed copper plating layer, etching is performed according to the third circuit pattern, and the remaining 20-40% of the exposed copper plating layer is etched at the same time.

[0088] Furthermore, when obtaining the alkaline resistor printed circuit board, it also includes:

[0089] Use acidic solution to remove tin from composite board;

[0090] Using a strong oxidizing solution to etch according to the third circuit pattern and to etch the exposed copper plating layer;

[0091] Use a strong alkaline solution to remove the dry film on the composite board.

[0092] In the above step S3, when etching the core board 3 of the resistor substrate 1 according to the second circuit pattern, it includes:

[0093] Determine whether the side protection layer is connected to the board surface of the resistor substrate 1;

[0094] If so, determine whether there is a connection exceeding 0.1 mm;

[0095] If so, use dry film masking to protect the side edges;

[0096] If the side protection layer has no connection with the board surface of the resistor substrate 1 or the connection is less than 0.1 mm, the edge groove is filled with glue to protect the side protection layer.

[0097] Furthermore, the use of dry film edge masking can effectively ensure that the etching solution does not contact the side protection layer in the case of a connection exceeding 0.1 mm.

[0098] Furthermore, the edge groove is filled with glue, which can effectively ensure that no etching solution flows into the side of the side protection layer during the etching process when there is no connection or the diameter does not exceed 0.1 mm.

[0099] In the above step S5, the tinning process parameters are: when the copper thickness is 4OZ-6OZ, the tinning current density is 10-14ASF, and the tinning time is 5-10 minutes; when the copper thickness is 7OZ-9OZ, the tinning current density is 15-20ASF, and the tinning time is 7-9 minutes; when the copper thickness is 9OZ-12OZ, the tinning current density is 16-20ASF, and the tinning time is 10-15 minutes.

[0100] Furthermore, the present invention uses stannous sulfate as a tin source to obtain a tin coating containing Cu6Sn5 intermetallic compounds on the copper surface. By performing electrochemical tests on the tin coating, the tin coating obtained by using the above process parameters and stannous sulfate as a tin source can effectively protect the copper layer.

[0101] In the above step S3, the side plated protective layer is a side plated gold layer.

[0102] Furthermore, the process parameters of the side gold plating layer are: current density is 5-6ASF, time is 120-150 seconds, and the thickness of the gold plating layer is 0.045-0.095μm.

[0103] The present invention adopts a gold-plated layer as a side protection layer, thereby utilizing the characteristics of gold such as good electrical conductivity, small contact resistance and good chemical stability to achieve good electrical connection performance and realize effective protection of the side of the blind slot.

[0104] The present invention can obtain a gold-plated layer with good performance through the above-mentioned process parameters.

[0105] The alkaline resistor printed circuit board with metal edging in the blind slot provided by the present invention is prepared by the above method.

[0106] Compared with the prior art, the present invention has the following beneficial effects:

[0107] (1) The present invention further protects the blind slot by plating a side protection layer on the blind slot and using a dry film mask or glue filling according to the connection between the side protection layer and the resistor substrate surface, thereby achieving effective protection of the blind slot;

[0108] (2) The present invention can realize the production of printed circuit boards with blind slot + resistor + metal edging design;

[0109] (3) The preparation method provided by the present invention is easy to operate and highly feasible.

[0110] The above-mentioned embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and substitutions made by technicians in this field on the basis of the present invention shall fall within the scope of protection required by the present invention.

Claims

1. A method for preparing an alkaline resistor printed circuit board with metal edging in a blind slot, characterized in that: The following steps are involved: Providing a resistor substrate and a copper clad core board, and cutting the resistor substrate and the copper clad core board into the size specifications required for production; Milling the resistor substrate to obtain a blind groove, and metalizing the blind groove; Plating a copper layer on the side of the blind groove, performing photo-imaging, etching, and plating a side protective layer on the blind groove to obtain a resistor substrate with a copper layer blind groove; The resistor substrate with the blind groove of the copper layer and the copper clad core board are pressed together through a prepreg to obtain a composite board; Performing photoimaging, copper plating, tin plating and etching on the composite board to obtain the alkaline resistor printed board; Wherein, when performing optical imaging, etching and plating a side protection layer on the blind groove, it includes: Adhere a dry film on the copper-clad layer of the resistor substrate and perform optical imaging to obtain a first circuit pattern; Etching the copper clad layer according to the first circuit pattern to expose the resistor film underneath, and then etching the resistor film to remove the dry film; Plating a side protection layer on the blind groove, attaching a dry film at the resistor position and performing optical imaging to obtain a second circuit pattern; After etching the core board of the resistor substrate according to the second circuit pattern, the dry film is removed to obtain the resistor substrate with blind grooves of the edge-wrapped copper layer.

2. The method for preparing the alkaline resistor printed circuit board with metal edging in the blind slot according to claim 1, characterized in that: When the composite board is subjected to photoimaging, copper plating, tin plating and etching, it includes: Drilling through holes on the copper-clad core board of the composite board and metallizing the through holes; After the composite board is subjected to full-board electroplating to increase copper, a dry film is attached and optical imaging is performed to obtain a third circuit pattern; Copper plating and tin plating are performed on the composite board, a dry film is attached again, and optical imaging is performed to obtain a fourth circuit pattern; Stripping the tin according to the fourth circuit pattern to expose the copper plating layer underneath, and etching part of the exposed copper plating layer; Etching is performed according to the third circuit pattern, and the remaining exposed copper plating layer is etched at the same time. After the etching is completed, the remaining tin and dry film are removed to obtain the alkaline resistor printed circuit board.

3. The method for preparing the alkaline resistor printed circuit board with metal edging in the blind slot according to claim 2, characterized in that: When obtaining the alkaline resistor printed board, it includes: The blind groove and the edge position of the composite board are stripped of tin to obtain the exposed copper plating layer in the blind groove and the edge position. After etching 60-80% of the exposed copper plating layer, etching is performed according to the third circuit pattern, and the remaining 20-40% of the exposed copper plating layer is etched at the same time.

4. The method for preparing the alkaline resistor printed circuit board with metal edging in the blind slot according to claim 2 or 3, characterized in that: When obtaining the alkaline resistor printed board, it also includes: Using an acidic solution to remove tin from the composite board; Using a strong oxidizing solution to etch according to the third circuit pattern and to etch the exposed copper plating layer; A strong alkaline solution was used to remove the dry film on the composite board.

5. The method for preparing an alkaline resistor printed circuit board with metal edging in a blind slot according to claim 1, characterized in that: When etching the core board of the resistor substrate according to the second circuit pattern, the method includes: Determining whether the side protection layer is connected to the board surface of the resistor substrate; If so, determine whether there is a connection exceeding 0.1 mm; If so, a dry film mask is used to protect the side protection layer; If the side protection layer is not connected to the board surface of the resistor substrate or the connection is less than 0.1 mm, the edge groove is filled with glue to protect the side protection layer.

6. The method for preparing an alkaline resistor printed circuit board with metal edging in a blind slot according to claim 2, characterized in that: The tinning process parameters are: when the copper thickness is 4OZ-6OZ, the tinning current density is 10-14ASF, and the tinning time is 5-10 minutes; when the copper thickness is 7OZ-9OZ, the tinning current density is 15-20ASF, and the tinning time is 7-9 minutes; when the copper thickness is 9OZ-12OZ, the tinning current density is 16-20ASF, and the tinning time is 10-15 minutes.

7. The method for preparing an alkaline resistor printed circuit board with metal edging in a blind slot according to claim 1, characterized in that: The side protection layer is a side gold-plated layer.

8. The method for preparing an alkaline resistor printed circuit board with metal edging in a blind slot according to claim 7, characterized in that: The process parameters of the side gold-plated layer are: current density is 5-6ASF, time is 120-150 seconds, and the thickness of the gold-plated layer is 0.045-0.095 μm.

9. An alkaline resistor printed circuit board with metal edging in a blind slot, characterized in that: Prepared by the method according to any one of claims 1 to 8.

Images