Non-flitch pin welding method

Abstract

The invention discloses a non-flitch pin welding method, which belongs to the field of welding, and comprises the following steps of: removing soldering tin of a device and a bonding pad to ensure that the heights of the welding ends of the device are consistent, and cleaning a soldering flux on the device by using a cleaning agent; performing silk-screen printing on the soldering paste in the middle of the bonding pad by using a steel mesh; the soldering paste is melted into solder balls, and soldering tin on each bonding pad is melted; redundant soldering flux on the printed board is cleaned up, so that the solder balls at the bonding pad end are bright, no soldering flux is left, and no fiber exists; a steel mesh is used for screen printing of soldering paste, so that each solder ball is provided with the soldering paste, and the soldering paste is uniform and free of tip pulling; placing the cleaned device on the soldering tin, positioning the device into the welding hole according to the positioning pin of the device, and enabling the welding end of the device to be in contact with the soldering paste; welding the device, and checking pins of the device before welding, so that the distances from the periphery of the device to the printed board are consistent. The method solves the problem of device factory returning and ball mounting, and can save the cost.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and more specifically, to a method for soldering leads without a board. Background Technology

[0002] FMC sockets are a type of stepped terminal block. In conventional soldering methods, the height of the terminal is typically increased by attaching solder pads to the soldering terminals, followed by soldering using standard silkscreen solder paste. However, conventional soldering methods often present the following problems: 1) When the solder pads on the device solder terminals melt at high temperatures, they cannot flow evenly to both sides of the device, often resulting in one side of the device solder terminal having more solder and the other side having less solder; 2) After the device is soldered, the solder will flow to the upper part of the terminal, resulting in a cold solder joint after the device is soldered; 3) The existing process technology cannot install solder pads during rework; 4) During rework, only a new socket can be replaced, and the cost of a new socket is high, so the rework cost is high. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for soldering unmounted pins, which solves the problem of returning devices to the factory for ball repositioning and can save costs.

[0004] The objective of this invention is achieved through the following solution: A method for soldering unmounted pins includes the following steps: Step S1: Remove the solder from the components and pads. After cleaning, ensure that the height of the component solder ends is consistent. After the components have cooled, use a cleaning agent to clean the flux off the components. Step S2: Use a stencil to screen print the solder paste onto the center of the pads, ensuring that the solder paste does not form spikes or brittle lines. Step S3: Melt the solder paste into solder balls. The solder on each pad is melted, and the solder on each pad is of uniform size with no excess solder powder. Step S4: Clean the excess flux off the printed circuit board so that the solder balls at the pad ends are bright and free of flux residue and fibers. Step S5: Use a stencil to screen print solder paste, ensuring that each solder ball has solder paste on it, and that the solder paste is even and without spikes; Step S6: Place the cleaned component onto the solder and position it into the solder hole according to the positioning pin of the component, so that the solder end of the component contacts the solder paste. Step S7: Solder the components. Before soldering, check the component pins to ensure that the components are at the same height from the printed circuit board.

[0005] Furthermore, in step S1, during the cleaning process, an electric arc lamp at a temperature of 330 degrees Celsius is used to remove the solder from the device and the pads.

[0006] Furthermore, in step S1, after cleaning, it is ensured that there are no excess fibers on the devices and pads.

[0007] Furthermore, in step S2, a steel mesh screen with a 0.7mm opening and a depth of 0.3mm is specifically used.

[0008] Furthermore, in step S5, a steel mesh screen with a 0.7mm opening and a depth of 0.35mm is specifically used.

[0009] Furthermore, in step S6, the contact between the device solder tip and the solder paste is specifically ensured that the device solder tip does not extend beyond 10% of the solder pad.

[0010] Furthermore, step S6 also includes a sub-step: adding a layer of solder resist to the cured solder paste to allow the solder at the device end to extend better onto the pins, making the device soldering more reliable.

[0011] The beneficial effects of this invention include: This invention solves the technical problem of poor soldering caused by different solders, which makes the devices unrepairable, and also solves the problem of procuring new devices for long-term use. At the same time, it also solves the problem of repeated use of old devices and the problem of returning devices to the factory for ball repositioning. Statistics show that about 10% of newly soldered devices need to be repaired. In addition, considering the practical need for long-term use of new devices, the application of the technical solution of this invention can significantly save costs. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a flowchart illustrating the steps of the method in an embodiment of the present invention; Figure 2 This is a schematic diagram showing the distance between the device pins and the printed circuit board when the device is mounted on the board, with a distance of approximately 0.3 mm between the device pins and the printed circuit board. Figure 3 This is a schematic diagram showing the solder state of the device after it has been screen-printed on a 0.3mm thick steel mesh. Figure 4 This is a schematic diagram showing the state of solder paste after it has melted at high temperatures and the flux has been cleaned. Figure 5 A schematic diagram illustrating the process of reprinting solder paste onto molten solder paste; Figure 6This is a schematic diagram showing the appearance of the device after soldering. Figure 7 This is a magnified diagram of the solder joints of the device pins. Figure 8 This is a schematic diagram of the morphology of the device as observed in X-ray after soldering. Detailed Implementation

[0014] All features disclosed in all embodiments of this specification, or steps in all methods or processes implied in the disclosure, may be combined and / or extended or replaced in any way, except for mutually exclusive features and / or steps.

[0015] The specific implementation process of this invention is as follows: Given the background situation, the inventors of this invention discovered that: when new devices arrive, solder pads are already applied to the device. After the device completes one in-flow soldering cycle, the solder pads melt, and the device is then desoldered through rework. This causes the solder in the original solder pads to separate from the leads and pads, resulting in inconsistent solder paste on the device. If the device needs to be reused, it needs to be re-soldered, increasing the steps and soldering costs. For example, after reworking and desoldering the device, the solder pads on the device leads have become connected to the solder on the pads, resulting in uneven solder on the terminals and pads. Therefore, the original solder pads cannot be reused. After desoldering, all the solder on the device and the printed circuit board needs to be removed. After removing the solder, the height of the device terminals is 0.3mm from the height of the printed circuit board. How to solder the device terminals to the soldering terminals at a height of 0.3mm becomes a technical problem to be solved. After creative thinking, this invention proposes the following solution, such as... Figure 1 As shown, it specifically includes: Step S1: Remove the solder from the components and pads. After cleaning, ensure that the solder joints of the components are at the same height. After the components have cooled, use a cleaning agent to clean the flux off the components, ensuring that there are no fibers or other foreign objects on the components and pads. When cleaning, an electric arc iron at a temperature of 330 degrees Celsius can be used to remove the solder from the components and pads.

[0016] Step S2: Use a stencil to screen print all the solder paste onto the center of the pads, ensuring no solder paste spikes or bridging. Specifically, use a stencil with a 0.7mm opening and a 0.3mm depth. The purpose of this solder paste screen printing is twofold: first, to compensate for any height differences caused by the solder blocks installed at the factory; and second, to ensure that the solder paste is evenly distributed on each pad on the printed circuit board.

[0017] Step S3: Melt the solder paste into solder balls. All the solder on each pad should be melted, and the size of the solder on each pad should be uniform with no excess solder powder.

[0018] Step S4: Clean the excess flux off the printed circuit board so that the solder balls at the pad ends are shiny and free of flux residue and fibers.

[0019] Step S5: Use a stencil to screen print solder paste, ensuring each solder ball is coated with solder paste evenly and without spikes. Specifically, use a stencil with a 0.7mm opening and a depth of 0.35mm. The purpose of screen printing another layer on top of the cured solder paste is to compensate for printing defects from the first screen printing.

[0020] Step S6: Place the cleaned device onto the solder, positioning it into the solder hole according to the device's positioning pins, ensuring the device's solder tip contacts the solder paste, and that the solder tip does not extend more than 10% beyond the solder pad. Add a layer of solder resist on the cured solder paste to allow the solder at the device end to extend better onto the pins, making the device soldering more reliable.

[0021] Step S7: Solder the components. Before soldering, check the component pins to ensure that the components are at the same height from the printed circuit board.

[0022] It should be noted that after desoldering, the excess solder on the device pins must first be removed. After removal, the coplanarity of the device should be checked. Specifically, the pins on the device should be visually inspected to see if the excess solder paste has been removed and to see if the non-soldering ends of the pins are in the cavity. Then, the device should be placed on the corresponding pads to check the coplanarity of the device. This step is to check before the printed circuit board is tinned.

[0023] It should be noted that the technical solution of this invention can also use parameters such as a stencil opening of 0.75 mm, a ball center spacing of 1.27 mm, and a stencil thickness of 3 mm. A layer of solder is first screen-printed on the pads. After melting the screen-printed solder paste, another layer of solder paste is screen-printed on the melted solder. The purpose of the screen-printed solder paste is to compensate for the height difference of the solder blocks installed at the factory and to ensure that the solder paste on each pad on the printed circuit board is uniform. The purpose of screen-printing another layer on the cured solder paste is to compensate for any printing defects that may have occurred during the first screen-printing.

[0024] During the welding process, the technical solution of this invention uses two stencil screen printings. The first screen printing is to fill the defect of no solder block on the pins in the old device. The second screen printing is to increase the thickness of the solder paste and to increase the flux, so as to increase the fluidity of the solder on the device solder end and the solder pad, and make the device solder end better welded.

[0025] Figure 2 This is a schematic diagram showing the distance between the device pins and the printed circuit board when the device is mounted on the board, with a distance of approximately 0.3 mm between the device pins and the printed circuit board. Figure 3This is a schematic diagram showing the solder state after the component is screen-printed on a 0.3mm thick stencil; the solder should be uniform in size and free of spikes, burrs, etc. Figure 4 This is a schematic diagram showing the state of solder paste after it has melted at high temperature and the flux has been cleaned. The solder paste should be uniform in size on the pads after melting, with no excess material. Figure 5 To reprint solder paste diagrams on the molten solder paste, it is required that the solder paste be of uniform size and that no excess solder paste be printed out during the secondary stencil demolding process. Figure 6 This is a schematic diagram showing the appearance of the device after soldering. Figure 7 This is a magnified diagram of the solder joints of the device pins. Figure 8 This is a schematic diagram of the device's morphology as observed in X-ray after soldering. Each pin is well soldered to the pad, and the solder balls are of consistent size and shape.

[0026] In summary, the embodiments of the present invention have the following advantages: 1) Soldering problems of device terminal solder blocks, especially stepped soldering terminals, are solved; 2) Solder creeping up the terminals of devices at high temperatures causes cold solder joints; 3) Solder creeping problems of device solder joints when device leads are not coplanar; 4) Soldering problems of leaded and lead-free printed circuit boards.

[0027] It should be noted that, within the scope of protection defined in the claims of this invention, the following embodiments can be combined and / or extended or replaced in any logical manner from the above specific embodiments, such as the disclosed technical principles, disclosed technical features or implicitly disclosed technical features.

[0028] Example 1 A method for soldering unmounted pins includes the following steps: Step S1: Remove the solder from the components and pads. After cleaning, ensure that the height of the component solder ends is consistent. After the components have cooled, use a cleaning agent to clean the flux off the components. Step S2: Use a stencil to screen print the solder paste onto the center of the pads, ensuring that the solder paste does not form spikes or brittle lines. Step S3: Melt the solder paste into solder balls. The solder on each pad is melted, and the solder on each pad is of uniform size with no excess solder powder. Step S4: Clean the excess flux off the printed circuit board so that the solder balls at the pad ends are bright and free of flux residue and fibers. Step S5: Use a stencil to screen print solder paste, ensuring that each solder ball has solder paste on it, and that the solder paste is even and without spikes; Step S6: Place the cleaned component onto the solder and position it into the solder hole according to the positioning pin of the component, so that the solder end of the component contacts the solder paste. Step S7: Solder the components. Before soldering, check the component pins to ensure that the components are at the same height from the printed circuit board.

[0029] Example 2 Based on Example 1, in step S1, during the cleaning process, an electric arc furnace at a temperature of 330 degrees Celsius is used to remove the solder from the device and the pads.

[0030] Example 3 Based on Example 1, in step S1, after cleaning, ensure that there are no excess fibers on the device and the pad.

[0031] Example 4 Based on Example 1, in step S2, a steel mesh screen with a 0.7mm opening and a depth of 0.3mm is specifically used.

[0032] Example 5 Based on Example 1, in step S5, a steel mesh screen with a 0.7mm opening and a depth of 0.35mm is specifically used.

[0033] Example 6 Based on Example 1, in step S6, the contact between the device solder tip and the solder paste is specifically such that the device solder tip does not extend more than 10% of the solder pad.

[0034] Example 7 Based on Example 1, step S6 further includes a sub-step: adding a layer of solder resist to the cured solder paste to allow the solder at the device end to extend better to the pins, making the device soldering more reliable.

[0035] The above description is merely the technical principles and preferred embodiments used in this invention. Those skilled in the art will understand that this invention is not limited to the specific embodiments described herein. Various obvious changes, adjustments, and substitutions can be made by those skilled in the art without departing from the scope of protection of this invention. Therefore, although the invention has been described in detail through the above embodiments, this invention is not limited to the above embodiments. Many other equivalent embodiments may be included without departing from the principles and concept of this invention, and the scope of this invention is determined by the scope of the appended claims.

Claims

1. A method for soldering unmounted pins, characterized in that, Includes the following steps: Step S1: Remove the solder from the components and pads. After cleaning, ensure that the height of the component solder ends is consistent. After the components have cooled, use a cleaning agent to clean the flux off the components. Step S2: Use a stencil to screen print the solder paste onto the center of the pads, ensuring that the solder paste does not form spikes or brittle lines. Step S3: Melt the solder paste into solder balls. The solder on each pad is melted, and the solder on each pad is of uniform size with no excess solder powder. Step S4: Clean the excess flux off the printed circuit board so that the solder balls at the pad ends are bright and free of flux residue and fibers. Step S5: Use a stencil to screen print solder paste, ensuring that each solder ball has solder paste on it, and that the solder paste is even and without spikes; Step S6: Place the cleaned component onto the solder and position it into the solder hole according to the positioning pin of the component, so that the solder end of the component contacts the solder paste. Step S7: Solder the components. Before soldering, check the component pins to ensure that the components are at the same height from the printed circuit board.

2. The method for soldering unmounted pins according to claim 1, characterized in that, In step S1, during the cleaning process, an electric arc lamp at a temperature of 330 degrees Celsius is used to remove the solder from the device and the pads.

3. The method for soldering unmounted pins according to claim 1, characterized in that, In step S1, after cleaning, ensure that there are no excess fibers on the devices and pads.

4. The method for soldering unmounted pins according to claim 1, characterized in that, In step S2, a steel mesh screen with a 0.7mm opening and a depth of 0.3mm is specifically used.

5. The method for soldering unmounted pins according to claim 1, characterized in that, In step S5, a steel mesh screen with a 0.7mm opening and a depth of 0.35mm is specifically used.

6. The method for soldering unmounted pins according to claim 1, characterized in that, In step S6, the contact between the device solder tip and the solder paste is specifically ensured that the device solder tip does not extend beyond 10% of the solder pad.

7. The method for soldering unmounted pins according to claim 1, characterized in that, Step S6 also includes a sub-step: adding a layer of solder resist to the cured solder paste to allow the solder at the device end to extend better onto the pins, making the device soldering more reliable.

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