Method for improving reliability of BGA packaging device

Abstract

The invention discloses a method for improving the reliability of a BGA (Ball Grid Array) packaging device. The method comprises the following steps of: 1, creating a welding area for being matched and welded with a weldable cushion block at the bottom of a BGA substrate; 2, a weldable cushion block is configured; and step 3, welding the two sides of the weldable cushion block with the BGA substrate and the PCB respectively by using welding flux. According to the invention, the weldable cushion blocks with the same height as the solder balls are added between the four corners of the BGA substrate and the PCB, the upper surfaces of the cushion blocks are in high-strength physical hard connection with the BGA substrate through the solder, and the lower surfaces of the cushion blocks are in high-strength physical hard connection with the PCB through the solder. The welding cushion block can effectively bear thermal stress caused by factors such as mismatching of thermal expansion coefficients between the BGA substrate and the PCB, and the thermal stress originally borne by a normal BGA welding ball is greatly reduced, so that the reliability of a BGA packaging device is improved, and the fatigue failure of a welding point of the welding ball of the BGA packaging device is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor integrated circuit packaging, and relates to a method for improving the reliability of a BGA packaging device. Background Art

[0002] With the rapid development of wireless communication technology, people's demand for intelligent electronic devices is increasing. Consumers are pursuing product functions while also putting forward higher requirements for their appearance, performance, size, portability, etc. Therefore, semiconductor integrated circuit packaging technology is facing unprecedented challenges, and it is urgent to study high-integration, high-density electronic packaging devices (such as BGA packaging devices, etc.) to meet the needs of products. Ball grid array (BGA) packaging technology is currently a relatively advanced and commonly used chip packaging technology, but with the continuous improvement of packaging density and circuit scale, BGA packaging size is getting larger and larger. The fatigue failure of solder joints of large-size BGA packaging devices under thermal stress has attracted more and more attention. How to ensure the reliability of BGA packaging devices during use and improve the fatigue failure resistance of BGA packaging device solder joints is currently a hot research topic.

[0003] In the current prior art, in order to reduce the fatigue failure of solder ball joints caused by external environmental influences such as thermal cycles, vibrations or shocks during the service of BGA packaged devices, a method of adding fillers between the bottom of the BGA packaged device and the PCB printed circuit board is used to improve the reliability of the BGA packaged device and increase the fatigue life of the solder ball joints. Although this method improves the reliability of the BGA packaged device to a certain extent, it is not convenient to dismantle and repair the BGA packaged device in the event of solder joint fatigue failure due to the presence of the bottom filler. In view of the problem of difficult dismantling and rework in the existing methods for improving the reliability of BGA packaged devices, the present invention proposes a method for improving the reliability of BGA packaged devices by adding a solderable pad between the bottom of the BGA packaged device and the PCB printed circuit board. Summary of the invention

[0004] In order to overcome the deficiencies of the prior art, the present invention provides a method for improving the reliability of a BGA packaging device.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for improving the reliability of a BGA packaged device comprises the following steps:

[0007] Step 1: Based on the maximum equivalent stress point in the BGA solder ball distribution, create a soldering area on the bottom of the BGA substrate for matching soldering with the solderable pad;

[0008] Step 2: Configure the weldable pad;

[0009] Step 3: Use solder to solder the two sides of the solderable pad to the BGA substrate and the PCB printed circuit board respectively to form a BGA package device.

[0010] Furthermore, the location and number of maximum equivalent stress points are obtained based on the simulation tool analysis.

[0011] Furthermore, the height of the solderable pad is equal to the diameter of the BGA solder ball.

[0012] Furthermore, the welding area between the weldable pad and the welding region is at least three times the vertical projection area of ​​the BGA solder ball.

[0013] Furthermore, the BGA substrate has a rectangular structure, and the welding area is arranged at a right angle to the bottom surface of the BGA substrate.

[0014] Furthermore, the BGA solder balls are distributed in a rectangular array, the center of the rectangular array of the BGA solder balls coincides with the center of the BGA substrate, the maximum equivalent stress points of the BGA solder balls are located at the four corners of the rectangular array, the number of the welding areas is four, and they are respectively located at the four right angles of the BGA substrate.

[0015] Furthermore, the weldable pad has a triangular prism structure.

[0016] Furthermore, the material of the BGA substrate is alumina, the material of the PCB printed circuit board is a high-frequency composite material board RA300B of ceramic filler and PTFE resin, the material of the weldable pad is alumina, the material of the BGA solder ball is Sn10Pb90, and the material of the solder is Sn63Pb37.

[0017] In summary, the present invention is beneficial in that:

[0018] The present invention adds solderable pads with the same height as the solder balls between the four corners of the BGA substrate and the PCB printed circuit board. The upper surface of the pad is physically hard-connected with the BGA substrate through solder, and the lower surface of the pad is physically hard-connected with the PCB printed circuit board through solder. The solderable pads can effectively bear the thermal stress caused by factors such as the mismatch of thermal expansion coefficients between the BGA substrate and the PCB printed circuit board, greatly reducing the thermal stress that the normal BGA solder balls should originally bear, thereby improving the reliability of the BGA packaged device and reducing the fatigue failure of the solder joints of the BGA packaged device solder balls. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1The diagram is a schematic diagram of the BGA packaged device of the present invention after being welded to a weldable triangular prism-shaped pad.

[0020] Figure 2 Schematic diagram of the welding area at the four corners of the bottom of the BGA package substrate.

[0021] Figure 3 A schematic diagram of a triangular prism-shaped weldable spacer.

[0022] Figure 4 This is a schematic diagram of the key solder joints of the solder balls of BGA packaged devices.

[0023] Markings in the figure:. DETAILED DESCRIPTION

[0024] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0025] The present invention provides a BGA packaging device, referring to Figure 1 , including a BGA package shell, a BGA solder ball and a solderable pad. The BGA package shell includes a BGA substrate and a PCB printed circuit board. The BGA substrate is arranged on the top of the PCB printed circuit board. The BGA substrate and the PCB printed circuit board form a gap of a set height. The BGA solder ball is arranged in the gap. The BGA solder ball is respectively welded with the BGA substrate and the PCB printed circuit board. The height of the gap is the diameter of the BGA solder ball.

[0026] It also includes a weldable pad, which is arranged between the BGA substrate and the PCB printed circuit board, and the top and bottom of the weldable pad are respectively welded to the bottom surface of the BGA substrate and the top surface of the PCB printed circuit board.

[0027] The present invention also provides a method for improving the reliability of the above-mentioned BGA packaging device, comprising the following steps:

[0028] Step 1: Create an area on the bottom of the BGA substrate for soldering with solderable pads.

[0029] The location and number of the maximum stress points of the device are obtained by using a simulation tool, wherein the above process is based on the method disclosed in the BGA thermal fatigue simulation report in the field, which is a direct reference to the prior art and will not be described in detail.

[0030] A weldable area is set at the position of the maximum stress point or a position close to the maximum stress point, and the height of the weldable area is consistent with the height of the solder ball.

[0031] In this embodiment, preferably, refer to Figure 2 The BGA substrate has a rectangular structure, and the BGA solder balls are set to be distributed in a rectangular array to match the rectangular structure of the substrate. Under this distribution setting, the BGA solder balls at the four corners of the rectangle are farthest from the center of the BGA substrate and the PCB printed circuit board. During the temperature rise and fall cycle, the linear expansion distance at the four corners is the largest, and the solder joints at the four corners are subjected to the greatest thermal stress, which makes them more prone to failure. Therefore, the four right angles on the bottom surface of the BGA substrate are set as areas for welding with solderable pads.

[0032] Step 2: Make a weldable spacer with set size, material and performance parameters.

[0033] The height of the solderable pad is set to be consistent with the diameter of the BGA solder ball.

[0034] Preferably, refer to Figure 3 In this embodiment, the weldable pad is set to a triangular prism, and its shape under the vertical projection perspective coincides with the four right-angle shapes of the BGA substrate; however, it should be noted that the triangular prism shape is only one of the cases listed in this patent. No matter what shape is used in the actual design and any graphic deformation made on the basis of the graphic, it falls within the protection scope of the patent of this invention.

[0035] The horizontal area of ​​the solderable pad under the vertical projection angle is determined by the size of the blank area at the four corners of the BGA substrate, the diameter of the BGA solder ball, the key solder balls of the BGA device (i.e., the four solder balls planted at the four corners closest to the BGA substrate, refer to Figure 4 ) is determined by the maximum equivalent stress on the solder joint.

[0036] Specifically, for the stress resistance effect brought by the horizontal area of ​​the weldable pad, relevant mechanical simulation analysis was performed based on the Ansys WorkBench mechanical simulation platform, and the simulation comparison results are shown in Table 1.

[0037]

[0038] Table 1

[0039] The tensile strength of Sn63Pb37, a tin-lead solder commonly used in BGA packaging devices, is about 52MPa. Referring to Table 1, it can be seen that when the area of ​​the welding area at each of the four corners is 3 times or more of the vertical projection area of ​​the BGA solder ball, the maximum equivalent stress on the BGA solder ball is less than half of the tensile strength of Sn63Pb37 tin-lead solder used in conventional welding. Therefore, when the area of ​​the welding area at each of the four corners reaches 3 times or more of the projection area of ​​the BGA solder ball, a better stress resistance effect can be obtained.

[0040] Preferably, in the above-mentioned mechanical simulation analysis, the material of the BGA substrate is alumina, with a size of 18mm×18mm×2.8mm, the PCB printed circuit board adopts a high-frequency composite material board RA300B with ceramic filler and PTFE resin, with a size of 30mm×30mm×1.8mm, the material of the BGA solder ball is Sn10Pb90, the solder ball array is 17×17, the distance between adjacent solder balls is 1mm, the solder ball diameter is 0.5mm, the material of the weldable pad is alumina, and the tin-lead solder composition used for welding the BGA substrate to the PCB printed circuit board is Sn63Pb37; referring to the IPC-9701 standard, the temperature cycle range set during the simulation analysis is -55℃~+125℃, the heating and cooling rate is 10℃ / min, the high and low temperature insulation time of each cycle is 15min, and the number of simulation cycles is 5 times.

[0041] In other embodiments, the material of the weldable pad is not limited to alumina. When selecting the material of the weldable pad, the following two aspects may be considered: on the one hand, the performance parameters of the BGA substrate material used in the design of the BGA packaged device shall be considered; on the other hand, the performance parameters of the PCB printed circuit board material to be mounted when the BGA packaged device is actually used shall be considered. Specifically, the thermal expansion coefficient, material density, Young's modulus and other aspects may be considered. The actual selection may be made based on the user's specific application scenario. However, it should be noted that no matter what material is selected as the material of the weldable pad, it shall fall within the protection scope of the patent of this invention.

[0042] Step 3: Use solder to solder the solderable pad to the BGA substrate and PCB printed circuit board. In order to simplify the relevant process steps, it is required that the welding between the solderable pad and the BGA package shell can be performed simultaneously with the BGA solder ball planting work. The finished schematic diagram of the BGA package device after welding is as follows: Figure 1 shown.

[0043] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

Claims

1. A method for improving the reliability of a BGA packaged device, characterized in that: The following steps are involved: Step 1: Based on the maximum equivalent stress point in the BGA solder ball distribution, create a soldering area on the bottom of the BGA substrate for matching soldering with the solderable pad; Step 2: Configure the weldable pad; Step 3: Use solder to solder the two sides of the solderable pad to the BGA substrate and the PCB printed circuit board respectively to form a BGA package device.

2. A method for improving the reliability of a BGA packaged device according to claim 1, characterized in that: The location and number of maximum equivalent stress points are obtained based on simulation tool analysis.

3. A method for improving the reliability of a BGA packaged device according to claim 1, characterized in that: The height of the solderable pad is equal to the diameter of the BGA solder ball.

4. A method for improving the reliability of a BGA packaged device according to claim 1, characterized in that: The welding area between the weldable pad and the welding region is at least three times the vertical projection area of ​​the BGA solder ball.

5. A method for improving the reliability of a BGA packaged device according to claim 1, characterized in that: The BGA substrate is in a rectangular structure, and the welding area is arranged at a right angle to the bottom surface of the BGA substrate.

6. A method for improving the reliability of a BGA packaged device according to claim 5, characterized in that: The BGA solder balls are distributed in a rectangular array, the center of the rectangular array of the BGA solder balls coincides with the center of the BGA substrate, the maximum equivalent stress points of the BGA solder balls are located at the four corners of the rectangular array, and the number of the welding areas is four, which are respectively located at the four right angles of the BGA substrate.

7. A method for improving the reliability of a BGA packaged device according to claim 6, characterized in that: The weldable pad is in a triangular prism structure.

8. A method for improving the reliability of a BGA packaged device according to claim 1, characterized in that: The material of the BGA substrate is alumina, the material of the PCB printed circuit board is a high-frequency composite material board RA300B of ceramic filler and PTFE resin, the material of the weldable pad is alumina, the material of the BGA solder ball is Sn10Pb90, and the material of the solder is Sn63Pb37.

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