Method for repairing full-array three-dimensional stacked packaging printed board assembly

Abstract

The invention relates to the technical field of electronic assembly, in particular to a repair method of a full-array three-dimensional stacked package printed board assembly, which realizes desoldering and assembly soldering of stacked devices on the full-array three-dimensional stacked package printed board assembly by optimizing a heating mode and increasing monitoring of process temperature and heating time. The problems of insufficient soldering, reliability reduction and the like caused by multiple times of heating of surrounding devices in an existing repair method are effectively avoided; and the welding spot quality and the repair efficiency of the repaired printed board assembly part are improved.

Description

Technical Field

[0001] The invention relates to the technical field of electronic assembly, and in particular to a rework method for a full array three-dimensional stacked package printed circuit board assembly. Background Art

[0002] With the continuous development of electronic technology, electronic products are developing rapidly in miniaturization and high integration, which puts forward higher requirements for electronic assembly technology, and new high-density assembly technology is constantly emerging. One of the successful paths of three-dimensional stacking technology is to use the method of CSP to stack the crystal core, and the other is to achieve it by stacking the packaged devices during the PCB assembly process, that is, the three-dimensional stacking printed circuit board assembly packaging technology, which is widely used in both military and civilian fields.

[0003] In the field of military communication systems, with the continuous improvement of frequency bands and integration, the design density of chip-type active phased array antennas is getting higher and higher, and the device spacing is getting smaller and smaller, making it more and more difficult to repair and replace faulty devices. Various studies have shown that the remelting of solder joints will lead to the coarsening of the intermetallic compound grains at the welding interface, which reduces the reliability of the solder joints. Therefore, the rework of printed circuit board assemblies generally adopts local heating to avoid the remelting of solder joints of components that do not need to be repaired. At present, the rework methods for BGA packaged devices on printed circuit board assemblies in the industry include hot air rework workstation rework, infrared rework workstation rework, manual hot air gun rework, etc., all of which belong to local heating rework methods. At the same time, in order to ensure the reworkability of subsequent assemblies, the design does not arrange devices within a certain distance around the BGA packaged devices. For example, the aerospace industry standard QJ165C requires that "a 5mm gap should be left around the grid array device for the reflow nozzle to facilitate the removal and replacement of the device"; if the surrounding devices cannot be avoided, the surrounding devices must be removed or thermal insulation materials must be attached for thermal insulation protection before rework. However, for printed circuit board assemblies with a full array three-dimensional stacked packaging design, on the one hand, the spacing between adjacent devices is only 1mm to 2mm, or even smaller. The traditional rework method can no longer guarantee that the solder joints of the surrounding devices near the rework position will not remelt during the rework process. At the same time, the solder joints far away from the rework position are not melted, which is very likely to cause cold solder joints and cause rework failure. On the other hand, due to the three-dimensional stacking structure, the thickness of the device increases, the heat transfer path increases, and the heat required for melting the solder at the solder joints is greater. Traditional rework methods use thermal convection and thermal radiation to transfer heat, which are easily blocked in the case of fine spacing, resulting in reduced heat transfer efficiency and affecting rework production efficiency. In addition, if the first device fails and is reworked, the solder joints of the second device will definitely remelt, that is, the existing rework methods cannot achieve graded solder joint desoldering and welding.

[0004] At present, the above problems have not been solved. For device failures on full array three-dimensional stacked package printed circuit board assemblies, the only options are scrapping, or sacrificing some performance indicators and accepting them in concession, or sacrificing product reliability and using the rework station rework method, that is, using hot air or infrared rework stations to heat the rework position, after the solder joints of the reworked devices are melted, remove the faulty devices, and then place solder paste, mount normal devices, use the rework station to weld normal devices, and after the electrical test is qualified, increase the strict screening test to eliminate the faults; or use the heating platform overall heating method, that is, using the heating platform to heat the full array three-dimensional stacked package printed circuit board assembly as a whole, after the solder joints of the reworked devices are melted, remove the faulty devices, and then place solder paste, mount normal devices, and then heat the whole and weld normal devices. None of the above methods can take into account both product yield and reliability at the same time.

[0005] In view of the above-mentioned defects, the inventors of the present invention finally obtained the present invention after a long period of research and practice. Summary of the invention

[0006] The purpose of the present invention is to solve the problem that the existing rework method of a full array three-dimensional stacked package printed circuit board assembly cannot take into account both the rework yield and reliability, and provide a rework method of a full array three-dimensional stacked package printed circuit board assembly.

[0007] In order to achieve the above object, the present invention discloses a repair method for a full array three-dimensional stacked package printed circuit board assembly, comprising the following steps:

[0008] S1, placing a thermocouple of a temperature monitoring device near the solder joint of the repaired device and fixing it;

[0009] S2, placing a thermal insulation pad and a heat transfer pad on a heating platform, and then placing the printed circuit board assembly on the thermal insulation pad and the heat transfer pad;

[0010] S3, set the temperature value of the heating platform, turn on the heating function, and use the thermocouple to monitor the temperature of the repair position in real time. After the temperature monitored by the thermocouple reaches the expected temperature for a certain period of time, remove the faulty component to be repaired and record the total heating time;

[0011] S4, remove the printed circuit board assembly from the heating platform, clean the pads at the rework location, and clean them in time;

[0012] S5, pre-place solder paste on the pads at the rework location and mount normal components;

[0013] S6, placing a thermal insulation pad and a heat transfer pad on a heating platform, and then placing the printed circuit board assembly on the thermal insulation pad and the heat transfer pad;

[0014] S7, set the temperature value of the heating platform, turn on the heating function, turn off the heating after heating is completed, cool naturally, and complete the repair.

[0015] In step S1, the measurement accuracy of the thermocouple of the temperature monitoring device is better than ±1°C, and the measurement range of the temperature monitoring device is 0°C to 350°C.

[0016] In step S2, a thermal insulation pad is placed at a position corresponding to the component that does not need to be repaired, and the material of the thermal insulation pad is a non-metallic material with poor thermal conductivity.

[0017] In the step S2, a heat transfer pad is placed at a position corresponding to the device to be repaired, and the material of the heat transfer pad is a metal material with good thermal conductivity.

[0018] In step S2, the heating platform is any one of a flat heating platform, an infrared heating platform, and a hot air heating platform, the temperature control accuracy is ±1°C, the heating capacity is adjustable from 100°C to 400°C, and the size of the heating platform is larger than the size of the printed circuit board assembly.

[0019] In step S2, the direction and position of the printed circuit board assembly need to be controlled when it is placed to ensure that the position of the device to be repaired is opposite to the position of the bottom heat transfer pad. When the device to be repaired is the first device, the printed circuit board assembly is placed forward, and when the device to be repaired is the second device, the printed circuit board assembly is placed reversely.

[0020] In step S3, the total heating time is the time from when the heating platform starts the heating function to when the device to be repaired is removed from the printed circuit board assembly.

[0021] In step S7, the temperature value of the heating platform is the same as the temperature value of the heating platform in step S3, and the heating time is the same as the total heating time in step S3.

[0022] The thermal insulation pad has the same size as the heat transfer pad and is 0 mm to 5 mm larger than the reworked device. The thickness of the thermal insulation pad is 5 mm to 10 mm.

[0023] The product faced by the present invention is a full-array structure, with a spacing of 1 to 2 mm between adjacent devices. The heat conduction method of hot air convection or infrared thermal radiation has a very slow heat transfer efficiency due to the presence of obstruction, and also because the spacing is too small, the traditional thermal insulation tape protection method cannot completely avoid the remelting of the solder joints of the surrounding devices. The present invention uses a heat transfer pad to increase the heat conduction efficiency to achieve a heating effect, and at the same time uses a thermal insulation pad to reduce the heat transfer efficiency to achieve a thermal insulation effect, thereby achieving the rework of the printed circuit board assembly with a full-array structure.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: the rework method of a full-array three-dimensional stacked package printed circuit board assembly proposed in the present invention realizes local heating of the rework position of the printed circuit board assembly by adding a thermal insulation pad and a heat transfer pad between the heating platform and the printed circuit board assembly, and controls the welding temperature and time at the same time, effectively controls the temperature of the solder joints of the surrounding devices during the rework of the full-array three-dimensional stacked package printed circuit board assembly, ensures that the rework work is completed smoothly, and avoids the remelting of the solder joints of the surrounding devices; in addition, the step-by-step desoldering and welding of multi-layer solder joints can be realized by changing the placement direction of the printed circuit board assembly, effectively avoiding the risks of cold solder joints and reduced solder joint reliability caused by rework, and at the same time, for multiple reworked products, it is only necessary to keep the welding temperature and time consistent to realize the rework work at the same position, which greatly improves the consistency of the rework work and improves the yield rate and production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the structure of a full array three-dimensional stacked package printed circuit board assembly of an embodiment;

[0026] Figure 2 It is a schematic cross-sectional structure diagram of a full array three-dimensional stacked package printed circuit board assembly of an embodiment;

[0027] Figure 3 It is a schematic diagram of the position of the full array three-dimensional stacked package printed circuit board assembly on the heating platform of Example 1;

[0028] Figure 4 Schematic diagram of the position of the full array three-dimensional stacked package printed circuit board assembly on the heating platform of Example 2.

[0029] The numbers in the figure represent:

[0030] 1-printed circuit board; 2-first solder ball; 3-first device; 31-first faulty device; 4-second solder ball; 5-second device; 51-second faulty device; 6-thermocouple; 7-insulation pad; 8-heat transfer pad; 9-heating platform. DETAILED DESCRIPTION

[0031] The above and other technical features and advantages of the present invention are described in more detail below in conjunction with the accompanying drawings.

[0032] Example 1

[0033] like Figure 1As shown, it is a schematic diagram of the structure of the full array three-dimensional stacked package printed circuit board assembly of this embodiment, the first device 3 has a size of 15mm*15mm and a thickness of 8mm; the first solder ball 2 is made of Sn63Pb37 material with a ball diameter of 0.6mm; the second device 5 has a size of 15mm*15mm and a thickness of 5mm; the second solder ball 4 is made of Sn63Pb37 material with a ball diameter of 0.6mm; the spacing between adjacent first devices 3 on the printed circuit board assembly is 2mm, and the spacing between adjacent second devices 5 is 2mm; the size of the thermal insulation pad 7 and the heat transfer pad 8 are 16mm*16mm and a thickness of 5mm, wherein the thermal insulation pad 7 is made of epoxy resin board, and the heat transfer pad 8 is made of brass alloy; the thermocouple 6 is a 1.2mm K-type thermocouple, and the temperature monitoring device has a range of 350°C; the heating platform 9 is a hot plate heating platform, and the temperature control accuracy is ±1°C, which can be heated to 350°C; Figure 3 As shown, it is a schematic diagram of the position of the full array three-dimensional stacked package printed circuit board assembly on the heating platform of this embodiment. The first device 3 is confirmed to be faulty and needs to be repaired.

[0034] A method for repairing a full array three-dimensional stacked package printed circuit board assembly has the following operating steps:

[0035] Step S1: Place a thermocouple of the temperature monitoring device near the solder joint of the repaired device and fix it. The thermocouple is placed at the following position: Figure 3 As shown;

[0036] Step S2: placing the heat insulating pad and the heat transfer pad on the heating platform, and then placing the printed circuit board assembly forward on the heat insulating pad 7 and the heat transfer pad 8, ensuring that the position of the heat transfer pad 8 corresponds to the position of the first faulty component 31;

[0037] Step S3: Set the temperature of the heating platform to 240°C, turn on the heating function, and use the thermocouple to monitor the temperature of the repair position in real time. After the temperature monitored by the thermocouple reaches above 183°C for 25 seconds, remove the first device 3 and the second device 5 assembly, and record the total heating time as 352 seconds.

[0038] Step S4: remove the printed circuit board assembly from the heating platform 9, clean the solder pads at the repair position, and clean them in time;

[0039] Step S5: pre-place solder paste on the pad at the repair position, and mount a normal first device 3 and second device 5 assembly;

[0040] Step S6: placing the thermal insulation pad 7 and the heat transfer pad 8 on the heating platform 9, and then placing the printed circuit board assembly on the thermal insulation pad 7 and the heat transfer pad 8;

[0041] Step S7: Set the temperature of the heating platform to 240° C., turn on the heating function, and after 352 seconds, turn off the heating and allow natural cooling to complete the normal welding of the first device 3 and the second device 5 assembly.

[0042] Example 2

[0043] The structure of the full array three-dimensional stacked package printed circuit board assembly of this embodiment is consistent with that of embodiment 1, except that Figure 4 As shown, the faulty device is the second device 5, which needs to be repaired.

[0044] A method for repairing a full array three-dimensional stacked package printed circuit board assembly has the following operating steps:

[0045] Step S1: Place a thermocouple of the temperature monitoring device near the solder joint of the repaired device and fix it. The thermocouple is placed at the following position: Figure 4 As shown;

[0046] Step S2: placing the heat insulating pad 7 and the heat transfer pad 8 on the heating platform, and then placing the printed circuit board assembly on the heat insulating pad and the heat transfer pad in reverse, ensuring that the position of the heat transfer pad 8 corresponds to the position of the second faulty component 51;

[0047] Step S3: Set the temperature of the heating platform 9 to 240°C, turn on the heating function, and use the thermocouple to monitor the temperature of the repair position in real time. After the temperature monitored by the thermocouple reaches above 183°C for 25 seconds, remove the printed circuit board assembly and quickly remove the faulty component 51. Record the total heating time as 236 seconds.

[0048] Step S4: Clean the solder pads at the repair position of the printed circuit board assembly and clean them in time;

[0049] Step S5: pre-place solder paste on the pad at the rework location, mount a normal second device on the upper end surface of the first device, and fix the normal second device using red glue or other auxiliary methods;

[0050] Step S6: placing the heat insulating pad 7 and the heat transfer pad 8 on the heating platform, and then placing the printed circuit board assembly on the heat insulating pad 7 and the heat transfer pad 8 in reverse;

[0051] Step S7: Set the temperature of the heating platform 9 to 240° C., turn on the heating function, and after 236 seconds, turn off the heating, cool naturally, and complete the normal welding of the second device.

[0052] By adopting the above process method, local heating of the repair position of the printed circuit board assembly can be achieved, and the welding temperature and time can be controlled at the same time, so as to effectively control the temperature of the solder joints of the surrounding devices when the full array three-dimensional stacked package printed circuit board assembly is repaired, so as to ensure the smooth completion of the rework work and avoid the remelting of the solder joints of the surrounding devices; at the same time, the step-by-step desoldering and welding of the multi-layer solder joints can be achieved, so as to effectively avoid the risks of cold solder joints and reduced reliability of solder joints caused by rework, greatly improve the consistency of the rework work, and improve the yield rate and production efficiency.

[0053] The above description is only a preferred embodiment of the present invention, which is only illustrative and not restrictive of the present invention. Those skilled in the art understand that many changes, modifications, and even equivalences may be made to the present invention within the spirit and scope defined by the claims of the present invention, but all of them will fall within the scope of protection of the present invention.

Claims

1. A method for repairing a full array three-dimensional stacked package printed circuit board assembly, characterized in that: The following steps are involved: S1, placing a thermocouple of a temperature monitoring device near the solder joint of the repaired device and fixing it; S2, placing a thermal insulation pad and a heat transfer pad on a heating platform, and then placing the printed circuit board assembly on the thermal insulation pad and the heat transfer pad; S3, set the temperature value of the heating platform, turn on the heating function, and use the thermocouple to monitor the temperature of the repair position in real time. After the temperature monitored by the thermocouple reaches the expected temperature for a certain period of time, remove the faulty component to be repaired and record the total heating time; S4, remove the printed circuit board assembly from the heating platform, clean the pads at the rework location, and clean them in time; S5, pre-place solder paste on the pads at the rework location and mount normal components; S6, placing a thermal insulation pad and a heat transfer pad on a heating platform, and then placing the printed circuit board assembly on the thermal insulation pad and the heat transfer pad; S7, set the temperature value of the heating platform, turn on the heating function, turn off the heating after heating is completed, cool naturally, and complete the repair.

2. A method for repairing a full array three-dimensional stacked package printed circuit board assembly as claimed in claim 1, characterized in that: In step S1, the measurement accuracy of the thermocouple of the temperature monitoring device is better than ±1°C, and the measurement range of the temperature monitoring device is 0°C to 350°C.

3. The method for repairing a full array three-dimensional stacked package printed circuit board assembly as claimed in claim 1, characterized in that: In step S2, a thermal insulation pad is placed at a position corresponding to the component that does not need to be repaired, and the material of the thermal insulation pad is a non-metallic material with poor thermal conductivity.

4. The method for repairing a full array three-dimensional stacked package printed circuit board assembly as claimed in claim 1, characterized in that: In the step S2, a heat transfer pad is placed at a position corresponding to the device to be repaired, and the material of the heat transfer pad is a metal material with good thermal conductivity.

5. The method for repairing a full array three-dimensional stacked package printed circuit board assembly as claimed in claim 1, characterized in that: In step S2, the heating platform is any one of a flat heating platform, an infrared heating platform, and a hot air heating platform, the temperature control accuracy is ±1°C, the heating capacity is adjustable from 100°C to 400°C, and the size of the heating platform is larger than the size of the printed circuit board assembly.

6. A method for repairing a full array three-dimensional stacked package printed circuit board assembly as claimed in claim 1, characterized in that: In step S2, the direction and position of the printed circuit board assembly need to be controlled when it is placed to ensure that the position of the device to be repaired is opposite to the position of the bottom heat transfer pad. When the device to be repaired is the first device, the printed circuit board assembly is placed forward, and when the device to be repaired is the second device, the printed circuit board assembly is placed reversely.

7. The method for repairing a full array three-dimensional stacked package printed circuit board assembly as claimed in claim 1, characterized in that: In step S3, the total heating time is the time from when the heating platform starts the heating function to when the device to be repaired is removed from the printed circuit board assembly.

8. The method for repairing a full array three-dimensional stacked package printed circuit board assembly as claimed in claim 1, characterized in that: In step S7, the temperature value of the heating platform is the same as the temperature value of the heating platform in step S3, and the heating time is the same as the total heating time in step S3.

9. A method for repairing a full array three-dimensional stacked package printed circuit board assembly as claimed in claim 1, characterized in that: The thermal insulation pad has the same size as the heat transfer pad and is 0 mm to 5 mm larger than the reworked device. The thickness of the thermal insulation pad is 5 mm to 10 mm.

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