Film for improving tablet standing effect generated by bonding pad

Abstract

The utility model relates to a film for improving the tombstone effect generated by a bonding pad, which comprises a light-transmitting area and a plurality of bonding pad shading areas used for manufacturing the bonding pad of a PCB (Printed Circuit Board), and the light-transmitting area and the bonding pad shading areas are distributed on the film according to the design of the PCB; the circuit board further comprises a buffer shading area, the buffer shading area surrounds the bonding pad shading area and is connected with the bonding pad shading area, the partial edge, away from the bonding pad shading area, of the buffer shading area is connected with the wiring shading area, and the area, connected with the wiring shading area, of the buffer shading area is a first buffer shading area. The area, not connected with the wiring shading area, of the buffering shading area is a second buffering shading area; and the isolation light-transmitting area is positioned between any two adjacent second buffer shading areas and is connected with any two adjacent second buffer shading areas. According to the utility model, by designing the area of the buffer shading area in the film, the size of the windowing area of the bonding pad is ensured to be consistent, thereby preventing the bonding pad from generating a tombstone effect.

Description

Technical Field

[0001] The utility model relates to the field of PCB production and manufacturing, in particular to a film for improving the tombstone effect produced by a soldering pad. Background Art

[0002] Film is a special transparent film, usually made of transparent plastic materials such as polyester or polyimide, which can withstand the high temperature and chemical treatment of the photolithography process. It is printed with precise circuit patterns. These patterns are made by laser printing or other high-precision printing technologies and correspond to the copper lines, pads, traces and other conductive elements on the PCB.

[0003] A pad is a circular, square, or other shaped metalized area on a PCB board. It is used to solder the pins of electronic components. The pad is usually made of copper and is connected to the circuit on the PCB. It is the interface for establishing electrical connection between electronic components and the PCB.

[0004] The production process before soldering pads is generally that the designer defines the size and shape of each pad in the PCB design software, outputs the design information to the film, and then coats a layer of photoresist on the PCB substrate. The film is then covered on the PCB board coated with photoresist. Next, ultraviolet light is used to irradiate the photoresist through the film. The exposed PCB board is placed in a developer to wash away the unexposed photoresist to expose the copper layer. The copper layer other than the pads and traces is then removed. After a series of cleaning and pretreatment, the PCB board is coated with solder mask ink. After the solder mask ink is cured, the pads are opened to expose the pads, and finally soldering is performed.

[0005] The main reason why inconsistent pad sizes lead to the tombstoning effect is that during the reflow soldering process, the solder paste melts into liquid solder, which flows on the pad due to surface tension and gravity. If the pad areas are inconsistent, the flow dynamics of the liquid solder on the larger pad will be stronger than on the smaller pad, causing the solder to flow from the smaller pad to the larger pad, resulting in insufficient solder on the smaller pad and a tombstoning effect. At the same time, pads of different areas have different thermal conductivity characteristics during heating. Larger pads may absorb heat faster, causing the solder to melt earlier on the pad, resulting in uneven solder flow and ultimately a tombstoning effect.

[0006] There are many ways to improve the tombstoning effect, including: controlling solder paste: precisely controlling the amount of solder paste printed, ensuring uniformity on the pad, and selecting the appropriate solder paste type to improve solder wettability and stability; optimizing soldering parameters: adjusting the reflow soldering heating rate, peak temperature, and time to optimize the soldering process, maintaining furnace temperature uniformity to avoid local overheating or uneven cooling, etc. However, none of these methods mention ensuring consistent pad size to prevent the tombstoning effect, so a solution to improve the tombstoning effect on pads is urgently needed. Utility Model Content

[0007] In view of the problem that the above-mentioned technology does not mention how to avoid the tombstone effect by ensuring the consistency of the pad area size, the utility model provides a film film for improving the tombstone effect of the pad, the film film includes a light-transmitting area and a plurality of pad light-shielding areas for making PCB board pads, the light-transmitting area and the pad light-shielding area are distributed on the film film according to the design of the PCB board; it also includes a buffer light-shielding area, the buffer light-shielding area surrounds the pad light-shielding area and is connected to the pad light-shielding area, the edge of the buffer light-shielding area away from the pad light-shielding area is connected to the trace light-shielding area, the area where the buffer light-shielding area is connected to the trace light-shielding area is a first buffer light-shielding area, and the area where the buffer light-shielding area is not connected to the trace light-shielding area is a second buffer light-shielding area; it also includes an isolation light-transmitting area, the isolation light-transmitting area is located between any two adjacent second buffer light-shielding areas and is connected to any two adjacent second buffer light-shielding areas.

[0008] As a further improvement of the present invention, the width of the first buffer shading area is set to a uniform width, the width of the second buffer shading area is also set to a uniform width, and the width of the first buffer shading area is smaller than the width of the second buffer shading area.

[0009] As a further improvement of the present invention, a transition zone is provided between the second buffer shading zone and the first buffer shading zone, and the width of the transition zone is set to a uniformly changing width, and the uniformly changing width is that the width of the second buffer shading zone gradually decreases to the width of the first buffer shading zone.

[0010] As a further improvement of the present invention, the width of the first buffer shading area is set to 0.5 mil.

[0011] As a further improvement of the present invention, the width of the second buffer shading area is set to 2 mil.

[0012] As a further improvement of the present invention, the width of the isolated light-transmitting area is set to be a uniform width.

[0013] As a further improvement of the present invention, the width of the isolated light-transmitting area is set to be ≥8 mil.

[0014] The beneficial effect of the present invention is that compared with the prior art, the present invention provides a film for improving the tombstone effect of solder pads by designing a buffer shading area in the film to ensure that when windows are opened for solder pads on a PCB board, the areas of the opened solder pads are consistent, thereby avoiding the tombstone effect of components on the solder pads. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic diagram of the structural principle of the film part of the utility model.

[0016] Figure 2 For this utility model Figure 1 A local enlarged view of area A.

[0017] The main component symbols are described as follows:

[0018] 1. Transparent area; 2. Pad light-shielding area; 3. First buffer light-shielding area; 4. Second buffer light-shielding area;

[0019] 5. Wiring shading area; 6. Transition area; 7. Isolation and light-transmitting area. DETAILED DESCRIPTION

[0020] In order to more clearly illustrate the present invention, the present invention will be further described below with reference to the accompanying drawings.

[0021] In the following description, general examples are provided to provide a deeper understanding of the present invention. Obviously, the embodiments described are only a portion of the present invention, not all of it. It should be understood that the specific embodiments described are intended only to illustrate the present invention and are not intended to limit the present invention.

[0022] It should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the existence of features, integers, steps, operations, elements or components, but do not exclude the existence or addition of one or more other features, integers, steps, operations, elements, components or their combinations.

[0023] See also Figure 1 and Figure 2The utility model discloses a film for improving the monument effect of solder pads. The film includes a light-transmitting area and a plurality of solder pad light-shielding areas for making solder pads on a PCB board. The light-transmitting area and the solder pad light-shielding area are distributed on the film according to the design of the PCB board; the film also includes a buffer light-shielding area, which surrounds the solder pad light-shielding area and is connected to the solder pad light-shielding area. The edge of the buffer light-shielding area away from the solder pad light-shielding area is connected to the trace light-shielding area, wherein the area where the buffer light-shielding area is connected to the trace light-shielding area is a first buffer light-shielding area, and the area where the buffer light-shielding area is not connected to the trace light-shielding area is a second buffer light-shielding area; the film also includes an isolation light-transmitting area, which is located between any two adjacent second buffer light-shielding areas and is connected to any two adjacent second buffer light-shielding areas.

[0024] After the PCB is coated with photoresist, it is covered with film. The PCB covered by the light-transmitting area of ​​the film does not have copper circuits, pads, traces and other conductive parts. In the subsequent exposure process, ultraviolet rays are irradiated onto the photoresist through the light-transmitting area of ​​the film, causing this part of the photoresist to undergo chemical changes and become insoluble in the developer. In the light-shielding area of ​​the film, the pad light-shielding area is used to cover the pads on the PCB board, the buffer light-shielding area is used to cover the edge of the pad light-shielding area on the PCB board and the area surrounding the pad light-shielding area, and the trace light-shielding area is used to cover the traces on the PCB board. This area blocks the ultraviolet rays in the subsequent exposure, so that the photoresist does not undergo chemical reaction and is washed away by the developer, exposing the pads and traces, and etching away the copper layer outside the pads and traces. Then, a layer of solder mask ink is coated on the PCB board. After the solder mask ink is cured, windows are opened for the corresponding pads on the PCB board according to the positions of the pad shading areas in the film. The buffer shading area is set to prevent the window opening position from being offset due to the tolerance of PCB production when the pad is windowed, and the solder mask ink on the pad cannot be completely removed, resulting in a smaller pad area, and ultimately causing the solder mask ink to still partially cover the pad, or the window opening offset causes the window to be opened on the trace, resulting in inconsistent sizes of the two pads to produce a tombstone effect. By designing the buffer shading area of ​​the film to surround the pad shading area, when the solder mask layer is windowed at the position of the film pad shading area, the buffer shading area can offset the tolerance of PCB production and manufacturing so that the windows are all opened on the copper layer reserved in the buffer shading area, thereby ensuring that the pad area exposed after the window opening is consistent.

[0025] See also Figure 2In the present invention, the width of the first buffer shading area is set to a uniform width, the width of the second buffer shading area is also set to a uniform width, a transition area is set between the second buffer shading area and the first buffer shading area, and the width of the transition area is set to a uniformly changing width. The uniformly changing width is that the width of the second buffer shading area gradually decreases to the width of the first buffer shading area; the width of the first buffer shading area is set to 0.5 mil, and the width of the second buffer shading area is set to 2 mil.

[0026] Because a layer of solder mask ink is subsequently covered on the PCB board, and then the pad is windowed according to the size of the pad shading area in the film, the width of the buffer shading area is limited. On the one hand, it is to keep the copper layer exposed and avoid the copper layer exposure at the routing within a certain production tolerance when the pad window is opened. On the other hand, it is a design arrangement under a certain known tolerance to reduce the use of materials and thus save costs, so that the area of ​​the windowed pad is as similar as possible, thereby avoiding the tombstoning effect caused by inconsistent pad area size during the soldering process.

[0027] See also Figure 1 In the present invention, an isolation light-transmitting area is provided in the light-transmitting area. This isolation light-transmitting area is located between the second buffer light-shielding areas of two adjacent pads. The width of the isolation light-transmitting area is set to be uniform and consistent, and its size is set to be greater than or equal to 8 mils. The isolation light-transmitting area is provided to ensure sufficient spacing between pads, and this spacing still meets the electrical safety spacing requirements to prevent short circuits.

[0028] Example 1:

[0029] Before the film was improved, the film did not have a buffer shading area, only a pad shading area and a trace shading area. When the pad needs to be windowed after the solder mask ink is applied, the size of the window is based on the size of the pad shading area in the film. With this size of windowing and within a certain manufacturing tolerance, the copper layer of the pad cannot be fully exposed, and part of the copper layer will still be covered by the solder mask layer. This is especially true for a pair of pads with different numbers of pad connections or a combination of one connecting to copper foil and the other to copper wire. When the window is opened, it will reach the trace, resulting in a significant difference in pad area. Therefore, in the subsequent soldering operation, the large difference in pad area will lead to different melting rates of the solder paste, which will eventually lead to the phenomenon of component tombstones on the pads.

[0030] After the film is improved, the buffer shading area of ​​the film is divided into a first buffer shading area and a second buffer shading area. The first buffer shading area is located between the pad shading area and the trace shading area, and the width of the first buffer shading area remains uniform and the width is limited to 0.5 mil. The second buffer shading area is not connected to the trace shading area but only to the pad shading area, and the width of the second buffer shading area remains consistent and the width is limited to 2 mil. At the same time, a transition zone is set between the first buffer shading area and the second buffer shading area, and the width of the transition zone changes uniformly from the width of the second buffer shading area to the width of the first buffer shading area. This design opens windows in accordance with the size of the pad's shading area in the film when the pad needs to be windowed after the subsequent coating of solder mask ink. Although there will still be manufacturing tolerances when opening windows in this size, the window can be opened to the copper layer in the buffer shading area within the manufacturing tolerances, and the window can be avoided from being opened on the traces, thereby ensuring the area of ​​the pad. This not only ensures that the area of ​​the pad is consistent, but also avoids opening the window on the traces as much as possible, resulting in an excessively large pad area. Opening windows in this size can solve the tombstone effect caused by different pad sizes. Regardless of whether a pair of pads has different numbers of connections or a pair of pads connected to copper foil and copper wire respectively, the tombstone effect will not occur due to excessive differences in pad area when the pads are windowed.

[0031] The advantage of the present invention is that a buffer shading area is designed at the edge of the pad shading area of ​​the film to cope with production tolerances, thereby effectively controlling the consistency of the pad window area and avoiding the occurrence of the tombstone effect.

[0032] The above disclosures are only a few specific embodiments of the present invention, but the present invention is not limited thereto. Any changes that can be conceived by those skilled in the art should fall within the scope of protection of the present invention.

Claims

1. A film for improving the tombstone effect of a soldering pad, characterized in that: The film includes a light-transmitting area and a plurality of pad light-shielding areas for making PCB pads, and the light-transmitting area and the pad light-shielding areas are distributed on the film according to the design of the PCB board; The invention also includes a buffer light shielding area, wherein the buffer light shielding area surrounds the pad light shielding area and is connected to the pad light shielding area, and a portion of the edge of the buffer light shielding area away from the pad light shielding area is connected to the trace light shielding area, wherein the area where the buffer light shielding area is connected to the trace light shielding area is a first buffer light shielding area, and the area where the buffer light shielding area is not connected to the trace light shielding area is a second buffer light shielding area; It also includes an isolation light-transmitting area, which is located between any two adjacent second buffer light-shielding areas and connected to the any two adjacent second buffer light-shielding areas.

2. The film for improving the tombstone effect of a soldering pad according to claim 1, characterized in that: The width of the first buffer light-shielding area is set to be uniform, the width of the second buffer light-shielding area is also set to be uniform, and the width of the first buffer light-shielding area is smaller than the width of the second buffer light-shielding area.

3. The film for improving the tombstone effect of a soldering pad according to claim 2, characterized in that: A transition zone is provided between the second buffer shading zone and the first buffer shading zone, and a width of the transition zone is set to a uniformly varying width, where the uniformly varying width is a width of the second buffer shading zone gradually decreasing to a width of the first buffer shading zone.

4. The film for improving the tombstone effect of a soldering pad according to claim 2, characterized in that: The width of the first buffer light shielding area is set to 0.5 mil.

5. The film for improving the tombstone effect of a soldering pad according to claim 2, characterized in that: The width of the second buffer shading area is set to 2 mil.

6. The film for improving the tombstone effect of a soldering pad according to claim 1, characterized in that: The width of the isolated light-transmitting area is set to be uniform.

7. The film for improving the tombstone effect of a soldering pad according to claim 6, characterized in that: The width of the isolated light-transmitting area is set to be ≥8 mil.

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