A method for bleed printing of PCB boards

Abstract

The application discloses a screen printing method for a PCB (Printed Circuit Board), and belongs to the technical field of screen printing. The screen printing method comprises the following steps: cutting a first steel sheet by means of a laser cutting technique based on the position of screen printing on the PCB, so as to form a plurality of first through holes arranged at intervals; cutting a second steel sheet by means of the laser cutting technique based on the position of screen printing on the PCB and the position of a bump on the PCB, so as to form a position-avoiding hole and a plurality of second through holes; arranging the first steel sheet on the second steel sheet and aligning; placing a screen structure on the PCB, inserting the bump into the position-avoiding hole, placing solder paste on the first steel sheet, and brushing tin by means of a doctor blade, so that the solder paste is screen printed on the solder pad of the PCB through the first through hole and the second through hole, and the screen structure is taken away from the direction perpendicular to the PCB. The screen printing method for the PCB provided by the application can not only realize the tin brushing of the PCB with the bump, but also avoid the influence of the solder paste on the bump.

Description

Technical Field

[0001] This invention belongs to the field of screen printing technology, and more specifically, relates to a stencil printing method for PCB boards. Background Technology

[0002] With the continuous improvement and maturation of SMT (Surface Mount Technology), its application in the electronics industry is becoming increasingly widespread. Among these technologies, screen printing, the front-end process, is one of the most crucial and is receiving increasing attention. Screen printing technology primarily utilizes perforated steel sheets to print a certain amount of solder paste onto the PCB pads, preparing for component placement and reflow soldering. The quality of this printing directly affects the entire SMT process and thus the product quality, making it extremely important.

[0003] Screen printing technology mainly includes two steps: alignment of the stencil and the PCB board, and soldering (using a squeegee). Currently, this technology is primarily designed for PCB boards with a smooth, stepless surface and no other components. As electronic products become increasingly integrated, the number and density of components mounted on PCB boards are also increasing. For PCB boards with other materials already mounted on the surface or with raised bumps due to pre-treatment, the stencil cannot be perfectly aligned. To avoid these areas, one solution is to create clearance holes in the stencil corresponding to these areas. Simultaneously, the soldering process avoids these areas, preventing solder from leaking through the clearance holes and affecting the bumps with solder paste.

[0004] However, on existing PCBs, the areas that need soldering and the bumps that need to be avoided are often intertwined (i.e., there are areas that need soldering in multiple directions around the bumps). This means that even after the stencil is aligned with the PCB, the squeegee cannot avoid soldering certain areas (the squeegee will still pass through the avoidance holes no matter which direction it is soldering from), which in turn causes the bumps in the avoidance holes to be affected by the solder paste (the solder paste enters the avoidance holes). Summary of the Invention

[0005] In view of the above-mentioned defects or improvement needs of the prior art, the present invention provides a stencil printing method for PCB boards, which aims to not only achieve tinning of PCB boards with bumps, but also avoid the bumps being affected by solder paste.

[0006] This invention provides a stencil printing method for PCB boards, the stencil printing method comprising:

[0007] Based on the location of the missing print on the PCB board, the first steel sheet is cut using laser cutting technology to form multiple spaced first through holes;

[0008] Based on the location of the missing print on the PCB board and the location of the bumps on the PCB board, the second steel sheet is cut using laser cutting technology to form a clearance hole and multiple second through holes, which are arranged at intervals.

[0009] The first steel sheet is arranged on the second steel sheet and aligned to ensure that the multiple first through holes and the multiple second through holes correspond one-to-one, thereby obtaining a wire mesh structure.

[0010] The wire mesh structure is placed on the PCB board, the bumps are inserted into the clearance holes, solder paste is placed on the first steel sheet, and tin is brushed on with a scraper. The solder paste is printed onto the pads of the PCB board through the first and second through holes, and the wire mesh structure is removed from a direction perpendicular to the PCB board.

[0011] Optionally, the step of arranging and aligning the first steel sheet on the second steel sheet to ensure that the plurality of first through holes and the plurality of second through holes correspond one-to-one, thereby obtaining a wire mesh structure, includes:

[0012] Apply adhesive to the un-holeed area of ​​the second steel sheet, align the first steel sheet and the second steel sheet using a pick and place machine, and apply a certain pressure to bond the first steel sheet and the second steel sheet together, ensuring that the multiple first through holes and the multiple second through holes correspond one-to-one;

[0013] The wire mesh structure is obtained by allowing it to stand still for a unit of time.

[0014] Optionally, the unit time is 4-6 hours.

[0015] Optionally, the step of arranging and aligning the first steel sheet on the second steel sheet to ensure that the plurality of first through holes and the plurality of second through holes correspond one-to-one, thereby obtaining a wire mesh structure, includes:

[0016] Multiple limiting strips are arranged on the outer edge of one side of the second steel sheet, and the multiple limiting strips form a U-shaped structure;

[0017] The first steel sheet is inserted parallel to the U-shaped structure to ensure that the multiple first through holes and the multiple second through holes correspond one-to-one, thereby obtaining a wire mesh structure.

[0018] Optionally, before removing the screen printing structure from a direction perpendicular to the PCB board, the stencil printing method includes:

[0019] The first steel sheet is pulled outward a unit distance in a direction parallel to the PCB board, causing the corresponding first and second through holes to be misaligned, thereby moving the solder paste in each of the first steel sheets to the second steel sheet.

[0020] Optionally, the unit distance satisfies the following conditions;

[0021] M < L < N;

[0022] Wherein, L is the unit distance, M is the diameter of the second through hole, and N is the minimum distance between the second through hole and the clearance hole in the direction of pulling out the first steel sheet.

[0023] Optionally, at least one of the second through holes has a diameter smaller than the corresponding diameter of the first through hole.

[0024] Optionally, the thickness of the first steel sheet and the second steel sheet is 60-100 μm.

[0025] The beneficial effects of the technical solution provided by the embodiments of the present invention are as follows:

[0026] According to the stencil printing method for PCB boards provided in this embodiment of the invention, when stencil printing on a PCB board with bumps, firstly, based on the stencil printing position on the PCB board, a first steel sheet is cut using laser cutting technology to form multiple spaced first through holes. Secondly, based on the stencil printing position and the position of the bumps on the PCB board, a second steel sheet is cut using laser cutting technology to form clearance holes and multiple second through holes, which are spaced apart. Then, the first steel sheet is placed on the second steel sheet and aligned to ensure a one-to-one correspondence between the multiple first through holes and the multiple second through holes, thereby obtaining a screen mesh structure. The screen mesh structure is placed on the PCB board, the bumps are inserted into the clearance holes, solder paste is placed on the first steel sheet, and solder is applied using a squeegee. The solder paste is stenciled onto the pads of the PCB board through the first and second through holes, and the screen mesh structure is removed from a direction perpendicular to the PCB board.

[0027] Since multiple second through-holes correspond one-to-one with multiple first through-holes, and the clearance holes and each second through-hole are arranged alternately, the area above the clearance holes is the non-hole position of the first steel plate. This means the first steel plate covers the clearance holes, preventing solder paste from entering the clearance holes and affecting the bumps even when tinning the first steel plate. Additionally, solder paste can enter the PCB board through the first and second through-holes. Next, tinning is performed on the PCB. Solder paste is placed on the first steel plate and applied using a scraper. The solder paste is then transferred onto the PCB board through the first and second through-holes, completing the tinning process. Furthermore, the first steel plate covers the bumps, preventing solder paste from entering the clearance holes and affecting the bumps, thus not interfering with the tinning process.

[0028] In other words, the stencil printing method for PCB boards provided by the embodiments of the present invention can not only achieve the tinning of PCB boards with bumps, but also avoid the bumps being affected by solder paste. Attached Figure Description

[0029] Figure 1 This is a flowchart of a PCB board stencil printing method provided in an embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of the structure of the first steel sheet provided in an embodiment of the present invention;

[0031] Figure 3 This is a schematic diagram of the structure of the first type of second steel sheet provided in the embodiments of the present invention;

[0032] Figure 4 This is a schematic diagram of the wire mesh structure provided in an embodiment of the present invention;

[0033] Figure 5 This is a flowchart of another stencil printing method for PCB boards provided in an embodiment of the present invention;

[0034] Figure 6 This is a schematic diagram of the structure of the second type of second steel sheet provided in the embodiments of the present invention;

[0035] Figure 7 This is a schematic diagram of the structure of the third type of second steel sheet provided in the embodiments of the present invention.

[0036] The symbols in the diagram represent the following meanings:

[0037] 1. First steel plate; 11. First through hole; 2. Second steel plate; 21. Alternating hole; 22. Second through hole; 23. Limiting strip. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0039] Figure 1 This is a flowchart of a PCB board stencil printing method provided by an embodiment of the present invention, such as... Figure 1 As shown, the stencil printing method includes:

[0040] S101. Based on the location of the missing print on the PCB board, the first steel sheet 1 is cut using laser cutting technology to form multiple spaced first through holes 11 (see...). Figure 2 ).

[0041] S102. Based on the location of the missing print on the PCB board and the location of the bumps on the PCB board, the second steel sheet 2 is cut using laser cutting technology to form a clearance hole 21 and multiple second through holes 22. The clearance hole 21 and multiple second through holes 22 are arranged at intervals (see...). Figure 3 ).

[0042] S103. Arrange the first steel sheet 1 on the second steel sheet 2 and align them to ensure that the multiple first through holes 11 and the multiple second through holes 22 correspond one-to-one, thereby obtaining a wire mesh structure (see...). Figure 4 ).

[0043] S104. Place the screen mesh structure on the PCB board, insert the bumps into the clearance holes 21, place solder paste on the first steel sheet 1, and brush tin with a scraper. The solder paste is printed onto the pads of the PCB board through the first through hole 11 and the second through hole 22. Remove the screen mesh structure from the direction perpendicular to the PCB board.

[0044] According to the stencil printing method for PCB boards provided in this embodiment of the invention, when stencil printing on a PCB board with bumps, firstly, based on the stencil printing position on the PCB board, a first steel sheet 1 is cut using laser cutting technology to form multiple spaced first through holes 11. Secondly, based on the stencil printing position and the position of the bumps on the PCB board, a second steel sheet 2 is cut using laser cutting technology to form clearance holes 21 and multiple second through holes 22, which are spaced apart. Then, the first steel sheet 1 is placed on the second steel sheet 2 and aligned to ensure a one-to-one correspondence between the multiple first through holes 11 and the multiple second through holes 22, thereby obtaining a screen mesh structure. The screen mesh structure is placed on the PCB board, the bumps are inserted into the clearance holes 21, solder paste is placed on the first steel sheet 1, and solder is applied using a squeegee. The solder paste is stenciled onto the pads of the PCB board through the first through holes 11 and the second through holes 22. The screen mesh structure is then removed from a direction perpendicular to the PCB board.

[0045] Since the multiple second through holes 22 correspond one-to-one with the multiple first through holes 11, and the avoidance holes 21 and the second through holes 22 are arranged alternately, the area above the avoidance holes 21 is the non-hole position of the first steel plate 1. That is, the first steel plate 1 covers the avoidance holes 21, so even if the first steel plate 1 is tinned, the solder paste will not enter the avoidance holes 21 and affect the bumps. In addition, the solder paste can enter the PCB board through the first through holes 11 and the second through holes 22. Next, the PCB is tinned, that is, solder paste is placed on the first steel plate 1 and tinned with a scraper. The solder paste is printed onto the PCB board through the first through holes 11 and the second through holes 22, thus completing the tinning. In addition, the first steel plate 1 covers the bumps, and the solder paste will not enter the avoidance holes 21 and affect the bumps, thus not affecting the tinning.

[0046] In other words, the stencil printing method for PCB boards provided by the embodiments of the present invention can not only achieve the tinning of PCB boards with bumps, but also avoid the bumps being affected by solder paste.

[0047] It is easy to understand that the stencil printing method provided by the present invention does not require slotting directly on the steel sheet (the steel sheet is thin and slotting is costly). It involves drilling holes on the existing steel sheet and combining two steel sheets, which reduces production costs and can effectively prevent solder paste from affecting the bumps on the PCB board.

[0048] In one implementation of the present invention, a first steel sheet 1 is arranged and aligned on a second steel sheet 2 to ensure that a plurality of first through holes 11 and a plurality of second through holes 22 correspond one-to-one, thereby obtaining a wire mesh structure, including:

[0049] a. Apply adhesive to the un-holeed area of ​​the second steel sheet 2, and align the first steel sheet 1 and the second steel sheet 2 using a pick and place machine, and apply a certain pressure to bond the first steel sheet 1 and the second steel sheet 2 together, ensuring that the multiple first through holes 11 and the multiple second through holes 22 correspond one-to-one.

[0050] b. Allow the material to stand still for a given time to obtain the wire mesh structure.

[0051] In the above embodiments, the first steel sheet 1 and the second steel sheet 2 can be precisely bonded by the pick and place machine, which not only ensures the connection strength of the first steel sheet 1 and the second steel sheet 2, but also ensures the alignment accuracy of the first through hole 11 and the second through hole 22.

[0052] For example, the unit time is 4-6 hours, thereby ensuring a strong bond.

[0053] Figure 5 This is a flowchart of another PCB board stencil printing method provided by an embodiment of the present invention, such as... Figure 5 As shown, the stencil printing method includes:

[0054] S501. Based on the location of the missing print on the PCB board, the first steel sheet 1 is cut using laser cutting technology to form multiple spaced first through holes 11.

[0055] S502. Based on the location of the missing print on the PCB board and the location of the bumps on the PCB board, the second steel sheet 2 is cut by laser cutting technology to form a clearance hole 21 and multiple second through holes 22, which are arranged at intervals.

[0056] S503. Multiple limiting strips 23 are arranged on the outer edge of one side of the second steel sheet 2, forming a U-shaped structure (see...). Figure 6 ).

[0057] In the above embodiment, the limiting strip 23 plays a role in the insertion and pulling out of the first steel sheet 1, thereby ensuring the positioning accuracy between the first steel sheet 1 and the second steel sheet 2.

[0058] S504. Insert the first steel sheet 1 in parallel into the U-shaped structure to ensure that the multiple first through holes 11 and the multiple second through holes 22 correspond one-to-one, thereby obtaining the wire mesh structure.

[0059] S505. Place the screen mesh structure on the PCB board, insert the bumps into the clearance holes 21, place solder paste on the first steel sheet 1, and brush tin with a scraper. The solder paste is printed onto the pads of the PCB board through the first through hole 11 and the second through hole 22.

[0060] S506. Pull the first steel sheet 1 outward along the direction parallel to the PCB board by a unit distance, so that the corresponding first through hole 11 and second through hole 22 are misaligned, thereby moving the solder paste in each of the first steel sheets 1 to the second steel sheet 2.

[0061] In the above embodiment, by pulling the first steel sheet 1, the solder paste in each of the first through holes 11 on the first steel sheet 1 can be taken away during the pulling process, avoiding the problem of excessive solder paste thickness caused by the two steel sheets being missing, thereby reducing the solder paste thickness, so that the thickness of the solder paste missing on the PCB board is the same as the thickness of the second steel sheet 2.

[0062] It's easy to understand that when the solder paste is misprinted and the height is too high, on the one hand, after the components are mounted, the solder paste is prone to creeping onto the surface of the components, resulting in poor soldering. On the other hand, after the components are mounted, the solder is prone to overflowing onto the surrounding metal pads, causing a short circuit between the two pads, which may affect the performance of the PCB board.

[0063] In this embodiment, the unit distance satisfies the following conditions;

[0064] M < L < N;

[0065] Where L is the unit distance, M is the diameter of the second through hole 22; N is the distance from the second through hole 22 in the direction of pulling out the first steel sheet 1. Figure 6 In the middle, the minimum distance between the second through hole 22 located above the avoidance hole 21 and the avoidance hole 21.

[0066] In the above embodiment, by pulling a unit distance, not only can a portion of the solder paste be removed, but also the removed solder paste can be prevented from being re-printed into the relief hole 21 and affecting the bump when the unit distance is too large.

[0067] S507. Remove the silkscreen structure from a direction perpendicular to the PCB board.

[0068] In this embodiment, the diameter of at least one second through hole 22 is smaller than the diameter of the corresponding first through hole 11 (see...). Figure 7 ).

[0069] In the above embodiment, the diameter of the second through hole 22 located below is smaller than the diameter of the first through hole 11, so that the through hole of the stencil is regarded as a funnel shape with "larger at the top and smaller at the bottom", achieving the effect of a stepped stencil, thereby allowing more solder paste in the direction perpendicular to the PCB board, ensuring the accuracy and quality of the stencil printing.

[0070] It is easy to understand that when the size of the solder paste stencil is small, the solder paste may not be able to enter the via or may only partially enter the via during the soldering process. By setting the via to a funnel shape that is "larger at the top and smaller at the bottom", more solder paste can be placed at the top of the stencil, thereby ensuring the accuracy and quality of the stencil printing.

[0071] For example, each first through hole 11 and each second through hole 22 can be square or circular, and the present invention does not limit this.

[0072] For example, the thickness of the first steel sheet 1 and the second steel sheet 2 can be 60-100 μm.

[0073] It should be noted that the thickness of the first steel sheet 1 and the second steel sheet 2, as well as the size and position of the first through hole 11, the second through hole 22, and the clearance hole 21, can be determined according to the PCB board's printing conditions. Therefore, the screen mesh structure that can be prepared by this invention can be selected according to different scenarios.

[0074] In summary, the stencil printing method for PCB boards provided by this invention has the following advantages:

[0075] 1. The combined steel sheet forms a "two-in-one" structure that can avoid and protect the bumps on the PCB board without affecting the solder leakage of the PCB board.

[0076] 2. Forming a "two-in-one" combined steel sheet, so that the through-hole of the stencil is regarded as a funnel shape with "larger at the top and smaller at the bottom", so as to accurately obtain more solder paste and achieve the effect of stepped stencil.

[0077] 3. This stencil printing method uses simple materials and does not require expensive additional equipment or complex, original steel sheets, thus saving costs. Furthermore, it effectively avoids the problem of excessive solder paste during stencil printing.

[0078] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for bleed printing of PCB boards, characterized by, The printing method comprises: Based on the position of the missed printing on the PCB board, the first steel sheet (1) is cut by laser cutting technology, thereby forming a plurality of first through holes (11) arranged at intervals; Based on the position of the missed printing on the PCB board and the position of the bump on the PCB board, the second steel sheet (2) is cut by laser cutting technology, thereby forming an avoidance hole (21) and a plurality of second through holes (22), the avoidance hole (21) and the plurality of second through holes (22) are arranged at intervals; The first steel sheet (1) is arranged on the second steel sheet (2) and aligned to ensure that the plurality of first through holes (11) and the plurality of second through holes (22) correspond one by one, thereby obtaining a silk screen structure, the first steel sheet (1) forms a cover for the avoidance hole (21); The silk screen structure is placed on the PCB board, the bump is inserted into the avoidance hole (21), solder paste is placed on the first steel sheet (1), and tin is brushed by a doctor blade, the solder paste is printed on the solder pad of the PCB board through the first through hole (11) and the second through hole (22), and the silk screen structure is taken away from the direction perpendicular to the PCB board.

2. A method for bleed printing of PCB board as claimed in claim 1 wherein, The first steel sheet (1) is arranged on the second steel sheet (2) and aligned to ensure that the plurality of first through holes (11) and the plurality of second through holes (22) correspond one by one, thereby obtaining a silk screen structure, comprising: Glue is applied at the unperforated part of the second steel sheet (2), and the first steel sheet (1) and the second steel sheet (2) are aligned by a chip mounter, and a certain pressure is applied to bond the first steel sheet (1) and the second steel sheet (2), to ensure that the plurality of first through holes (11) and the plurality of second through holes (22) correspond one by one; Rest for a unit time, thereby obtaining the silk screen structure.

3. A method for bleed printing of a PCB board according to claim 2, characterized in that, The unit time is 4-6h.

4. The method for bleed printing of a PCB board according to claim 1, wherein, The first steel sheet (1) is arranged on the second steel sheet (2) and aligned to ensure that the plurality of first through holes (11) and the plurality of second through holes (22) correspond one by one, thereby obtaining a silk screen structure, comprising: A plurality of limiting strips (23) are arranged on the outer edge of one side of the second steel sheet (2), and the plurality of limiting strips (23) form a U-shaped structure; The first steel sheet (1) is inserted into the U-shaped structure in parallel to ensure that the plurality of first through holes (11) and the plurality of second through holes (22) correspond one by one, thereby obtaining a silk screen structure.

5. A method for bleed printing of PCBs according to claim 4, characterized in that, Before the silk screen structure is taken away from the direction perpendicular to the PCB board, the printing method comprises: The first steel sheet (1) is pulled out by a unit distance in a direction parallel to the PCB board, so that the corresponding first through hole (11) and the second through hole (22) are misaligned, thereby moving the solder paste in each first steel sheet (1) to the second steel sheet (2).

6. A method for bleed printing of a PCB board according to claim 5, wherein, The unit distance satisfies the following conditions; M < L < N; Wherein, L is the unit distance, M is the diameter of the second through hole (22); N is the minimum distance between the second through hole (22) and the avoidance hole (21) in the direction of pulling out the first steel sheet (1).

7. A method for bleed printing of PCBs according to any one of claims 1-6, characterized in that, At least one of said second through holes (22) has a diameter smaller than the diameter of the corresponding first through hole (11).

8. A method for bleed printing of PCBs according to any one of claims 1-6, characterized in that, The first steel sheet (1) and the second steel sheet (2) have a thickness of 60-100 μm.

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