Metal shell component installation method

Abstract

The invention belongs to the technical field of component installation, and particularly relates to a metal shell component installation method. Comprising the steps that a printed board is prepared, component pins are trimmed and cleaned, the upper surface of the printed board is provided with a grounding bonding pad and a mounting through hole, and the diameter of a grounding bonding pad avoiding area is larger than that of the mounting through hole; the mounting through hole is metalized, the bottom of the mounting through hole is designed with a single-sided bonding pad, and the mounting bonding pad is not manufactured at the position close to the bottom of the component; mounting an insulating spacer at the top of a pin of the to-be-mounted metal shell component; coating solder on the grounding bonding pad; pins of a metal shell component to be installed are inserted into the installation through holes of the printed board; fixing the metal shell component on the grounding bonding pad in a reflow soldering mode; filling welding flux into the mounting through hole and carrying out lead pin welding; and removing the soldering flux on the board surface of the printed board and the mounting through hole area, and baking and drying in a baking oven to finish assembly. The components are good in grounding and heat dissipation performance, and the installation reliability of the type of products is improved.

Description

Technical Field

[0001] This invention belongs to the field of component mounting technology, and specifically relates to a method for mounting metal-cased components. Background Technology

[0002] SMT (Surface Mount Technology) is a new type of electronic product assembly technology that mounts surface-mount components onto circuit boards. Specifically, it involves applying adhesive or solder paste to the pads of the circuit board using a fixture, then attaching the component leads to the pads, and finally soldering them using methods such as reflow soldering to achieve mechanical and electrical connections. However, through-hole components still have a wide range of applications in the electronics industry due to their high mounting strength and ease of handling and wiring. Most circuit boards are hybrid boards containing both through-hole and surface-mount components. The structure of through-hole components makes them difficult to solder using SMT technology, often requiring additional soldering operations after the surface-mount components are installed, causing significant inconvenience to production.

[0003] Furthermore, high-reliability applications place specific installation requirements on some pin-type components, such as metal-cased components with bottom leads (e.g., TO-packaged transistors, metal-packaged relays, voltage modules, filters, crystal oscillators, etc.). The restricted processes for high-reliability products explicitly state that "metal-cased components should be insulated from adjacent printed conductors and other conductive components during installation" and "component installation should not obstruct solder flow to the pads on the soldering end face of the metallized vias being soldered." Additionally, large-mass components should not be secured solely with silicone rubber. Moreover, there are requirements to avoid solder buildup that could cause short circuits between the pins and the component's metal casing during installation. Therefore, these components often require custom-designed mounting brackets or additional fastening measures to ensure assembly and usability, severely hindering the overall assembly quality and efficiency of the product.

[0004] In summary, there is an urgent need for a new method for mounting metal-cased components to achieve highly reliable through-hole mounting of metal-cased components with bottom leads to printed circuit boards. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a method for mounting metal housing components, the method comprising:

[0006] S1: Prepare the printed circuit board and clean it. The upper surface of the printed circuit board has a large grounding pad. The grounding pad and the printed circuit board have mounting through holes. The diameter of the grounding pad avoidance area is larger than that of the mounting through holes. The mounting through holes are metallized and have a single-sided pad design at the bottom. No mounting pads are made near the bottom of the components.

[0007] S2: Install insulating pads on the top of the pins of the metal-cased component to be installed;

[0008] S3: Apply solder to the ground pad to form a solder layer; the solder application operation of the ground pad is performed simultaneously with the solder application operation of other surface mount components on the printed circuit board;

[0009] S4: Insert the pins of the metal-cased component to be installed into the mounting through holes of the printed circuit board.

[0010] S5: Use reflow soldering to fix the base of the metal housing component on the grounding pad; the reflow soldering operation of the metal housing component is performed simultaneously with the reflow soldering operation of other surface mount components on the printed circuit board;

[0011] S6: Fill the mounting through hole with solder and perform pin welding;

[0012] S7: Remove flux from the surface of the printed circuit board and the mounting via area, and bake dry in an oven to complete the assembly.

[0013] Preferably, multiple vent holes penetrating the printed circuit board are provided next to the mounting through holes, and the vent holes are located inside the grounding pad avoidance area.

[0014] Furthermore, the vent holes are evenly distributed around the mounting through holes, with a quantity of 3 to 5 holes and a diameter of 10 to 50 μm.

[0015] Preferably, the area of ​​the grounding pad is larger than that of the metal housing component, accommodating excess solder on the grounding pad, so that the overflow solder at the edge of the metal housing component forms a climbing wetting angle with the housing, thereby ensuring high welding strength.

[0016] Preferably, during the installation of metal-cased components, after the pins protrude from the printed circuit board, the wall of the mounting through hole and the pins maintain a gap of 0.2~0.4mm.

[0017] Preferably, the leads of the metal-cased components are trimmed before installation to ensure that the leads of the metal-cased components protrude 1.5±0.6mm above the surface of the printed circuit board after installation.

[0018] Preferably, the insulating pad is a polytetrafluoroethylene (PTFE) ring sheet, the thickness of the insulating pad is 0.15~0.3mm, which is less than the sum of the thickness of the grounding pad and the solder layer; the outer diameter of the insulating pad is 2~5mm, which is less than the avoidance area of ​​the grounding pad; the inner diameter of the insulating pad is equal to the pin diameter.

[0019] Preferably, in step S6, the method of filling the mounting through-hole with solder is manual soldering or wave soldering.

[0020] Preferably, when cleaning components, a mixture of acetone and gasoline in a ratio of 3:2 and anhydrous ethanol are used for surface cleaning to ensure that the metal-cased components have good solderability.

[0021] The beneficial effects of this invention are as follows:

[0022] This invention solves the technical challenge of reflow soldering and surface mount mounting of metal-cased components with bottom leads. Similar to other components on the printed circuit board (PCB), the components in this invention are mounted and fixed using reflow soldering, resulting in high mounting strength, good grounding and heat dissipation performance, and eliminating the need for custom-made mounting brackets. Solder application and reflow soldering are performed synchronously with surface mount components on the PCB, without requiring additional mounting steps. Large-area grounding pads ensure mounting strength, and venting holes on the PCB ensure good solder filling of metallized holes during pin through-hole soldering. The use of insulating pads avoids the risk of short circuits between signal pins and the metal casing due to solder buildup during reflow soldering and through-hole soldering. This improves the mounting reliability of this type of product, is simple and efficient to operate, and is suitable for the widespread application and mass production of this type of component. Attached Figure Description

[0023] Figure 1 This is a diagram illustrating the installation effect of the metal casing components in this invention.

[0024] Figure 2 This is a magnified view of a portion of the soldering of the component pins in this invention;

[0025] Figure 3 This is a metal-cased component with a bottom lead wire in this invention;

[0026] In the diagram: 1. Grounding pad; 2. Solder layer; 3. Solder; 4. Lead; 5. Insulating pad; 6. Vent hole; 7. Mounting through hole; 8. Printed circuit board. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] This invention proposes a method for mounting metal-cased components, such as... Figure 1 , Figure 2 As shown, the method includes the following:

[0029] S1: Prepare the printed circuit board 8 and clean it. The upper surface of the printed circuit board 8 is provided with a large grounding pad 1. A mounting through hole 7 is provided through the grounding pad 1 and the printed circuit board 8, and the diameter of the avoidance area of ​​the grounding pad 1 is larger than that of the mounting through hole 7. The mounting through hole 7 is metallized and has a single-sided pad design at the bottom. No mounting pad is made near the bottom of the component.

[0030] In some preferred embodiments of the present invention, before the metal housing components are installed, their bottom mounting surfaces and pins should be soaked and cleaned with a 3:2 mixture of acetone and gasoline, and then rinsed with anhydrous ethanol to ensure good solderability.

[0031] In this invention, such as Figure 3 As shown, the components are metal-cased components with bottom leads, and their surfaces should have good solderability. The printed circuit board material is not limited and can be FR4, Rogers 5800, or other substrates.

[0032] In this invention, the outer dimensions of the grounding pad are larger than the bottom dimensions of the component housing to accommodate excess solder that overflows during soldering, and to form a solder accumulation wetting angle on the side wall of the housing, thereby improving the mounting strength of the component.

[0033] The present invention can meet the solder filling requirements during the soldering process of component pins for surface mount mounting by setting vent holes.

[0034] The mounting holes for component leads are designed with single-sided pads and are metallized. No mounting pads are made near the bottom of the component.

[0035] S2: Install insulating pads 5 on the top of the pins of the metal-cased component to be installed.

[0036] The component leads are insulated from the housing by an insulating medium. During installation, solder buildup on the insulating medium should be avoided to prevent short circuits between the component leads and the housing. Therefore, this invention uses insulating pads to prevent short circuits between signal leads and the metal housing caused by excess solder.

[0037] The material of the insulating pad is not limited; any material with good insulation, thermal stability, and ease of processing is acceptable. Polytetrafluoroethylene (PTFE) discs are preferred. The PTFE disc thickness is 0.15~0.3mm, slightly smaller than the sum of the thickness of the copper foil and solder layer of the grounding pad; the outer diameter is 2~5mm, slightly smaller than the clearance area of ​​the grounding pad; and the inner diameter is equal to the lead diameter.

[0038] In some preferred embodiments of the present invention, the insulation treatment is not limited to gaskets; other measures such as dispensing can also be used to achieve the same effect. Furthermore, insulating gaskets are used for signal pins, but are not mandatory for grounding pins.

[0039] The diameter of the grounding pad avoidance area is larger than that of the mounting through hole because there is no grounding pad at the mounting location of the insulating gasket (PTFE disc), i.e., grounding pad copper foil avoidance treatment has been performed.

[0040] S3: Apply solder to the ground pad 1 to form a solder layer 2; the solder application operation of the ground pad is performed synchronously with the solder application operation of other surface mount components on the printed circuit board.

[0041] In this invention, the solder is not limited, and the same solder as that used in other areas of the printed circuit board is selected. Reflow mounting and fixing of the component's metal casing to the printed circuit board is achieved by applying solder to the grounding pads of the printed circuit board.

[0042] The solder application method on the grounding pad is the same as that for other components on the board, and can be performed at the same time, simplifying the component processing operation process on the printed circuit board.

[0043] S4: Insert the pin 4 of the metal housing component to be installed into the mounting through hole 7 of the printed circuit board 8.

[0044] For metal-cased components, corresponding to the component pins, there are metallized mounting through holes to ensure the soldering of the pins when the components are mounted flat on the printed circuit board.

[0045] Before installing metal-cased components, the leads need to be trimmed to ensure that after the leads of the metal-cased components to be installed are inserted into the mounting holes of the printed circuit board, the leads protrude 1.5±0.6mm above the surface of the printed circuit board.

[0046] After the pins emerge, the mounting hole wall should maintain a gap of 0.2~0.4mm with the pins to ensure good filling and wetting of the solder.

[0047] S5: Use reflow soldering to fix the base of the metal housing component on the grounding pad 1; the reflow soldering operation of the metal housing component is performed simultaneously with the reflow soldering operation of other surface mount components on the printed circuit board.

[0048] The soldering method of this invention is not limited and can be performed by manual soldering, wave soldering, laser soldering, etc. The solder application and reflow soldering operations can be performed simultaneously with other surface-mount components on the board.

[0049] S6: Fill the mounting through hole 7 with solder 3 and perform pin soldering.

[0050] In some preferred embodiments of the present invention, a plurality of vent holes 6 penetrating the printed circuit board are provided next to the mounting through hole 7, and the vent holes 6 are located below the grounding pad avoidance area. Preferably, the vent holes are evenly distributed, with a quantity of 3 to 5, and a diameter of 10 to 50 μm.

[0051] Vent holes are used to expel gas from the bottom of components during solder filling of through-holes, preventing interference with solder wetting and filling within the mounting holes. No custom mounting brackets are required, meeting the installation requirements of high-reliability product restricted processes, which state that "component mounting should not obstruct solder flow to the pads on the soldering end face of the metallized hole being soldered."

[0052] S7: Remove flux from the surface of the printed circuit board 8 and the mounting through-hole area, and bake it in an oven to dry, thus completing the assembly.

[0053] In some preferred embodiments of the present invention, the metal housing component installation process is as follows:

[0054] (1) Trim the component leads and clean the appearance with a mixture of acetone, gasoline, and anhydrous ethanol. The trimming length is described in the solution description.

[0055] (2) Install insulating pads on the signal pins.

[0056] (3) Apply solder paste to the mounting pads on the printed circuit board using the same method as for other components, and insert the components into the through-holes. This can be done by printing or dotting, ensuring an appropriate application area and amount of solder to guarantee that the lead penetration after soldering is not less than 70%.

[0057] (4) Select the appropriate reflow profile based on the solder paste used and perform reflow soldering.

[0058] (5) Use appropriate methods for through-hole soldering. Solder should fill at least 85% of the hole height and wet the hole well.

[0059] (6) Remove the flux from the board surface and mounting hole area using an appropriate cleaning solution and method, and bake it in an oven to dry it, and complete the assembly.

[0060] In summary, this invention achieves a method for reflow soldering and fixing metal-cased components with bottom leads to a printed circuit board (PCB) by designing a PCB structure with a large-area grounding pad and vent holes. The large-area grounding pad on the PCB enables reflow mounting and fixing of the metal casing to the PCB (simultaneously with surface-mount components). The pin pad is designed as a single-sided metallized via with vent holes to meet solder filling requirements during pin soldering. The insulating gasket prevents short circuits between signal pins and the metal casing caused by excess solder, thus achieving highly reliable through-hole mounting of metal-cased components with bottom leads. This invention is characterized by low cost, strong applicability, and high reliability, making it suitable for mass production.

[0061] The above-described embodiments further illustrate the purpose, technical solution, and advantages of the present invention. It should be understood that the above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the present invention within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for mounting metal-cased components, characterized in that, Includes the following steps: S1: Prepare the printed circuit board, trim the component leads and clean it. The upper surface of the printed circuit board has a large area of ​​mounting ground pads. Through the ground pads and the printed circuit board, there are mounting through holes for the corresponding component leads. The diameter of the ground pad avoidance area is larger than that of the mounting through holes. The mounting through holes are metallized and have a single-sided pad design at the bottom. No mounting pads are made near the bottom of the components. S2: Install an insulating pad on top of the pins of the metal-cased component to be installed; the insulating pad is used to prevent short circuits at the junction of the pins and the housing due to solder overflow and accumulation on the grounding pad; S3: Apply solder to the ground pad to form a solder layer; the solder application operation of the ground pad is performed simultaneously with the solder application operation of other surface mount components on the printed circuit board; S4: Insert the pins of the metal-cased component to be installed into the mounting through holes of the printed circuit board. S5: Use reflow soldering to fix the base of the metal housing component on the grounding pad; the reflow soldering operation of the metal housing component is performed simultaneously with the reflow soldering operation of other surface mount components on the printed circuit board; S6: Fill the mounting through hole with solder and perform pin welding; S7: Remove flux from the surface of the printed circuit board and the mounting via area, and bake dry in an oven to complete the assembly.

2. The method for mounting metal housing components according to claim 1, characterized in that, Multiple vent holes that penetrate the printed circuit board are provided next to the mounting through holes, and the vent holes are located inside the grounding pad avoidance area.

3. The method for mounting metal housing components according to claim 2, characterized in that, The vent holes are evenly distributed around the mounting through holes, with a quantity of 3 to 5 and a diameter of 10 to 50 μm.

4. The method for mounting metal housing components according to claim 1, characterized in that, The grounding pad has a larger area than the metal casing components, accommodating excess solder on the grounding pad. This allows the overflow solder at the edges of the metal casing components to form a climbing wetting angle with the casing, ensuring high solder strength.

5. The method for mounting metal housing components according to claim 1, characterized in that, During the installation of metal-cased components, after the pins protrude from the printed circuit board, a gap of 0.2~0.4mm should be maintained between the wall of the mounting through hole and the pins.

6. The method for mounting metal housing components according to claim 1, characterized in that, Trim the leads of metal-cased components before installation to ensure that the leads protrude 1.5±0.6mm above the printed circuit board surface after installation.

7. The method for mounting metal housing components according to claim 1, characterized in that, The insulating pad is a polytetrafluoroethylene (PTFE) ring sheet with a thickness of 0.15~0.3mm, which is less than the sum of the thickness of the grounding pad and the solder layer; the outer diameter of the insulating pad is 2~5mm, which is less than the clearance area of ​​the grounding pad; the inner diameter of the insulating pad is equal to the pin diameter.

8. The method for mounting metal housing components according to claim 1, characterized in that, In step S6, the method of filling the mounting through hole with solder is manual soldering or wave soldering.

9. The method for mounting metal housing components according to claim 1, characterized in that, When cleaning components, use a 3:2 mixture of acetone and gasoline, along with anhydrous ethanol, for surface cleaning to ensure that the metal-cased components have good solderability.

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