Assembly method of SIP packaging bottom welding device

Abstract

The invention relates to an assembling method of an SIP packaging bottom welding device, and belongs to the field of electronic assembling. Solder paste is printed at the welding end of the bottom of the device, a supporting copper sheet is attached to the welding end, and the copper sheet is combined with the device in a reflow soldering mode. And then printing solder paste on the printed board bonding pad, pasting the pre-processed device on the printed board bonding pad through a chip mounter, and finally welding the device through reflow soldering. The supporting copper sheet is welded to the bottom of the SIP device in advance, so that a certain gap is always kept between the device and the printed board in the reflow soldering process, the height of the whole welding structure is not increased too much, bubbles and cavities of welding spots can be reduced, and the reliability of the SIP device is improved. And meanwhile, the whole structure is changed into four alloy layers formed between the device and the supporting copper sheet and between the supporting copper sheet and the bonding pad from an original double alloy layer formed by the welding flux, the component and the bonding pad, so that the welding strength of the whole welding structure of the device is improved.

Description

Technical Field

[0001] The invention belongs to the field of electronic assembly, and in particular relates to an assembly method for a SIP package bottom welding device. Background Art

[0002] With the increasing demand for miniaturization and micro-miniaturization of electronic products, printed circuit board assemblies and component packaging are gradually showing a trend of high density and integration. SIP packaged devices are currently the most advanced form of electronic device packaging. They assemble and integrate multiple IC chips or other different types of components on a package substrate to form a system with specific functions. Due to their extremely high assembly density and functional integration, they have been more widely used in the electronic product market in recent years. However, such components have high requirements for welding technology. The bottom of the device is only supported by the surface tension of a small amount of solder. During the reflow process, the weight of the device is easy to squeeze the bottom solder paste, causing tin bridging; while the practice of reducing the bottom solder leads to too thin solder joints, and the solder joint strength cannot meet the requirements of high reliability; and the practice of implanting BGA solder balls at the bottom of the device leads to the overall size of the device being too high, affecting the product volume. Therefore, a welding method is urgently needed to solve the above problems. Summary of the invention

[0003] 1. Technical issues to be resolved

[0004] The technical problem to be solved by the present invention is how to provide a method for assembling a SIP package bottom welding device to solve the problem of bridging and insufficient solder joint strength when the device is welded.

[0005] (II) Technical solution

[0006] In order to solve the above technical problems, the present invention provides a method for assembling a SIP package bottom welding device, the method comprising the following steps:

[0007] S1. Place the device with the bottom surface facing up on the component fixture.

[0008] Placing the device on a device fixture with the soldering end facing upward;

[0009] S2. Print solder paste on the bottom of the device

[0010] Covering the bottom solder end surface of the device with a metal stencil, and manually printing solder paste on the bottom solder end using a scraper;

[0011] S3. Solder the supporting copper sheet at the bottom of the device

[0012] Place the supporting copper sheet on the solder paste and keep the supporting copper sheet at the center of the solder paste at the solder end. Place the device fixture and the device in a hot air reflow oven for reflow soldering. Heat and melt the solder paste, and finally solder the device and the supporting copper sheet together.

[0013] S4, PCB solder paste printing

[0014] The printed circuit board to be soldered is fixed in the screen printer. The steel mesh is set with an opening area according to the size of the pad on the surface of the printed circuit board. Then it is placed in the screen printer and aligned with the printed circuit board. The solder paste is printed on the pad of the printed circuit board using the printer.

[0015] S5. Mount the device on the printed circuit board

[0016] Place the device in the material tray, use the automatic placement machine to pick up the device from the middle position, place it on the corresponding position of the printed circuit board, and put the device down when the bottom support copper sheet is pressed into the solder paste, so that the device falls on the welding center position of the printed circuit board;

[0017] S6, Reflow soldering:

[0018] Put the mounted components and printed circuit boards into the hot air reflow oven to complete the soldering of the components.

[0019] (III) Beneficial effects

[0020] The present invention provides a method for assembling a SIP package bottom welding device. The method for assembling a SIP package bottom welding device does not increase too much height of the overall welding structure, but is also conducive to reducing the formation of bubbles and voids in the solder joints. At the same time, the overall structure is transformed from a double alloy layer formed by the original solder, components and pads to a four alloy layer formed by the device and the supporting copper sheet, and between the supporting copper sheet and the pad, thereby improving the welding strength of the overall welding structure of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a process flow chart of the present invention;

[0022] Figure 2 A schematic diagram of placing the device of the present invention on a fixing device;

[0023] Figure 3 This is a structural diagram of the supporting copper sheet of the present invention;

[0024] Figure 4 This is a schematic diagram of the local solder joint structure of the device after soldering;

[0025] Figure 5 It is a schematic diagram of the structure of the device after welding of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, content and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below in conjunction with the drawings and examples.

[0027] The purpose of the present invention is to provide a method for assembling SIP bottom-sealed welding devices, which is used to solve the problem of bridging and insufficient solder joint strength during device welding, while raising the height of the device to a reasonable range, thereby improving reliability without affecting product volume.

[0028] The present invention prints solder paste on the solder end at the bottom of the device, attaches a supporting copper sheet to the solder end, and combines the copper sheet with the device by reflow soldering. Then, the solder paste is printed on the printed circuit board pad, and the pre-processed device is attached to the printed circuit board pad by a placement machine, and finally the device is soldered by reflow soldering. The present invention solders the supporting copper sheet at the bottom of the SIP device in advance, so that a certain gap is always maintained between the device and the printed circuit board during the reflow soldering process, which does not increase too much height to the overall welding structure, and is conducive to reducing the formation of bubbles and voids in the solder joints. At the same time, the overall structure is transformed from the original double alloy layer formed by the solder, the components and the pad to the four alloy layers formed by the device and the supporting copper sheet, and the supporting copper sheet and the pad, thereby improving the welding strength of the overall welding structure of the device.

[0029] The present invention provides a method for assembling a SIP package bottom welding device, comprising the following steps:

[0030] S1. Place the device with the bottom surface facing upward on the component fixture:

[0031] The device is placed on a device fixture made of synthetic stone with the soldering end facing upward. The fixture can be used to fix only a single device or to fix multiple devices at one time in an array.

[0032] S2. Print solder paste at the bottom of the device:

[0033] Cover the bottom solder end surface of the device with a metal mesh, and the opening area of ​​the metal mesh is 80% of the bottom solder end area of ​​the device. Use a scraper to print solder paste on the bottom solder end manually;

[0034] The metal stencil used for printing solder paste on the device is made of stainless steel, and the holes in the metal stencil are cut by laser.

[0035] S3, solder the supporting copper sheet at the bottom of the device:

[0036] Place the supporting copper sheet on the solder paste and keep it in the center of the solder paste at the solder end. Place the device fixture and the device in a hot air reflow oven for reflow soldering. Melt the solder paste by heating and finally weld the device and the supporting copper sheet together.

[0037] S4, PCB solder paste printing:

[0038] The printed circuit board to be soldered is fixed in the screen printer. The steel mesh is set with an opening area according to the size of the pad on the surface of the printed circuit board. Then it is placed in the screen printer and aligned with the printed circuit board. The solder paste is printed on the pad of the printed circuit board using the printer.

[0039] S5. Mounting the device on the printed circuit board:

[0040] Place the device in the material tray, use the automatic placement machine to pick up the device from the middle position, place it on the corresponding position of the printed circuit board, and put down the device when the bottom supporting copper sheet is pressed into the solder paste so that the device falls on the welding center position of the printed circuit board.

[0041] S6, Reflow soldering:

[0042] Put the mounted components and printed circuit boards into the hot air reflow oven to complete the reflow soldering of the components;

[0043] Furthermore, the device fixing device described in step S1 is a device that is resistant to high temperatures and can fix the device. The fixing device can only fix a single component, or can be an array device that fixes multiple components at one time.

[0044] Furthermore, the thickness of the stencil used for printing solder paste of the device in step S2 is 0.1mm to 0.12mm, the opening area of ​​the stencil is 80% of the metal area of ​​the solder end of the device, and the material of the stencil is stainless steel, wherein the opening of the stencil is achieved by laser cutting, and after cutting, electrochemical polishing is performed to increase the smoothness of the opening.

[0045] Furthermore, the SIP package bottom welding process method is characterized in that the solder paste in step S2 uses Sn63Pb37 solder.

[0046] Furthermore, the thickness of the supporting copper sheet in step S3 is 1 mm, and the shape of the supporting copper sheet is determined according to the shape of the soldering end of the device, and can be a rectangle with an arc or a circle.

[0047] The size of the supporting copper sheet is 90% of the bottom solder terminal area of ​​the device.

[0048] Furthermore, in the step S4, the thickness of the steel mesh used for printing solder paste on the printed board is 0.12 mm to 0.15 mm, and the opening size of the steel mesh covers 70% to 90% of the pad area.

[0049] Furthermore, in step S5, the chip mounter uses a pressure of 1.5N to press the device onto the printed circuit board.

[0050] Furthermore, in step S6, the peak temperature of the reflow soldering is 225° C. to 230° C.

[0051] Embodiment 1:

[0052] In order to clearly illustrate the implementation of the printed steel mesh design of the QFN package bottom special-shaped pad proposed in the present invention, the specific implementation steps will be described below in conjunction with the accompanying drawings.

[0053] (1) The device is placed on a component fixture made of synthetic stone with the solder end facing upward. First, a stencil with an opening size of 80% of the pad area and a thickness of 0.10 mm to 0.12 mm is used to cover the solder end of the device and solder paste is printed on the solder end manually using a scraper;

[0054] (2) Use a placement machine to mount a support copper sheet with an area of ​​90% of the solder end area of ​​the SIP package device on the solder paste of the solder end, and keep the support copper sheet in the center of the solder paste of the solder end. Place the fixture and device in a hot air reflow oven for reflow soldering. By heating and melting the solder paste, the device and the support copper sheet are finally soldered together.

[0055] (3) Fix the printed circuit board to be soldered in the screen printer, use a steel mesh with an opening size of 70% to 90% of the pad area and a thickness of 0.12 mm to 0.15 mm to cover the printed circuit board, and use a scraper to print solder paste on the pad on the surface of the printed circuit board;

[0056] (4) Place the components on the material tray and use the automatic placement machine to pick up the components from the middle position. Set the placement pressure of the placement machine to 1.5 N. Press the solder paste into the solder copper sheet at the bottom of the component and put the component down so that it falls in the center of the soldering position.

[0057] (5) Place the mounted components and printed circuit boards into a hot air reflow oven to complete the soldering of the components;

[0058] Embodiment 2:

[0059] A method for assembling a device soldered at the bottom of a SIP package, comprising the following steps:

[0060] Place the device with the bottom side facing upward on the component fixture;

[0061] Printing solder paste on the bottom solder end of the device;

[0062] Soldering a supporting copper sheet at the bottom of the device;

[0063] Printing solder paste on printed circuit boards;

[0064] Mounting components on the printed circuit board;

[0065] Reflow soldering is performed on the printed circuit board on which the device is mounted;

[0066] Furthermore, the component fixing device described in step (1) is a device that is resistant to high temperatures and can fix the components. The fixing device can fix only a single component, or can fix multiple components at one time in an array.

[0067] Furthermore, the thickness of the stencil used for printing solder paste of the device in step (2) is 0.1 mm to 0.12 mm, the opening area of ​​the stencil is 80% of the metal area of ​​the solder end of the device, and the material of the stencil is stainless steel, wherein the opening of the stencil is achieved by laser cutting, and after cutting, electrochemical polishing is performed to increase the smoothness of the opening.

[0068] Furthermore, the solder paste in step (2) and step (4) is Sn63Pb37 solder.

[0069] Furthermore, the thickness of the supporting copper sheet in step (3) is 1 mm, and the shape of the supporting copper sheet is determined according to the shape of the soldering end of the device, which can be a rectangle with an arc or a circle. The size of the supporting copper sheet is 90% of the bottom soldering end area of ​​the device.

[0070] Furthermore, in the step (4), the thickness of the steel mesh used for printing solder paste on the printed board is 0.12 mm to 0.15 mm, and the opening size of the steel mesh covers 70% to 90% of the pad area.

[0071] Furthermore, in the step (5), the chip mounter uses a pressure of 1.5N to press the device onto the printed circuit board.

[0072] Furthermore, the peak temperature of the reflow soldering in step (6) is 225°C to 230°C.

[0073] The present invention discloses a method for assembling a bottom welding device of a SIP package, which does not increase too much height of the overall welding structure, but is also conducive to reducing the formation of bubbles and voids in the solder joints. At the same time, the overall structure is transformed from a double alloy layer formed by the original solder, the component and the pad to a four alloy layer formed by the component and the supporting copper sheet, and between the supporting copper sheet and the pad, thereby improving the welding strength of the overall welding structure of the device.

[0074] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for assembling a SIP package bottom welding device, characterized in that: The method comprises the following steps: S1. Place the device with the bottom surface facing up on the component fixture. Placing the device on a device fixture with the soldering end facing upward; S2. Print solder paste on the bottom of the device Covering the bottom solder end surface of the device with a metal stencil, and manually printing solder paste on the bottom solder end using a scraper; S3. Solder the supporting copper sheet at the bottom of the device Place the supporting copper sheet on the solder paste and keep the supporting copper sheet at the center of the solder paste at the solder end. Place the device fixture and the device in a hot air reflow oven for reflow soldering. Heat and melt the solder paste, and finally solder the device and the supporting copper sheet together. S4, PCB solder paste printing The printed circuit board to be soldered is fixed in the screen printer. The steel mesh is set with an opening area according to the size of the pad on the surface of the printed circuit board. Then it is placed in the screen printer and aligned with the printed circuit board. The solder paste is printed on the pad of the printed circuit board using the printer. S5. Mount the device on the printed circuit board Place the device in the material tray, use the automatic placement machine to pick up the device from the middle position, place it on the corresponding position of the printed circuit board, and put the device down when the bottom support copper sheet is pressed into the solder paste, so that the device falls on the welding center position of the printed circuit board; S6, Reflow soldering: Put the mounted components and printed circuit boards into the hot air reflow oven to complete the soldering of the components.

2. The method for assembling a SIP package bottom welding device according to claim 1, characterized in that: The device fixing device in step S1 is a device that is resistant to high temperatures and can fix the device. The device only fixes a single component or fixes multiple components at one time in an array manner.

3. The method for assembling a SIP package bottom welding device as claimed in claim 2, characterized in that: The device fixing device is made of synthetic stone.

4. The method for assembling a SIP package bottom welding device according to claim 1, characterized in that: In S2, the thickness of the stencil used for printing solder paste of the device is 0.1 mm to 0.12 mm, and the opening area of ​​the stencil is 80% of the metal area of ​​the soldering terminal of the device.

5. The method for assembling a SIP package bottom welding device as claimed in claim 4, characterized in that: The mesh plate is made of stainless steel, the holes of the mesh plate are cut by laser, and electro-polishing is performed by electrochemical method after cutting.

6. The method for assembling a SIP package bottom welding device as claimed in claim 4, characterized in that: The solder paste in step S2 is Sn63Pb37 solder.

7. The method for assembling a SIP package bottom welding device according to claim 1, characterized in that: The thickness of the supporting copper sheet in step S3 is 1 mm, the shape of the supporting copper sheet is determined according to the shape of the soldering terminal of the device, and the size of the supporting copper sheet is 90% of the area of ​​the bottom soldering terminal of the device.

8. The method for assembling a SIP package bottom welding device as claimed in claim 1, characterized in that: The thickness of the steel mesh used for printing solder paste on the printed board in step S4 is 0.12 mm to 0.15 mm, and the opening size of the steel mesh covers 70% to 90% of the pad area.

9. The method for assembling a SIP package bottom welding device according to claim 1, characterized in that: In step S5, the chip mounter uses a pressure of 1.5N to press the device onto the printed circuit board.

10. The method for assembling a SIP package bottom welding device according to claim 1, characterized in that: The peak temperature of the reflow soldering in step S6 is 225° C. to 230° C.

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