Today, Datafeng Xiaobian will introduce the analysis of common problems related to BGA repair, let's have a look ~
Analysis of common problems in BGA repair
Warp of chip:
After welding defects appear in BGA, if disassembly and planting ball welding is carried out, a total of at least 5 times of thermal shock such as SMT reflow, disassembly, pad cleaning, planting ball and welding have been experienced, which is close to the limit life. Statistics show that 5% of BGA chips will eventually have warpage stratification. Therefore, it is necessary to pay attention to control the heat of chips in these links. Reduce the temperature and heating time as much as possible in the process of disassembly, pad cleaning and ball planting.
The hot air workstation uses local heating of the upper and lower parts simultaneously to complete the BGA welding. Due to the thermal expansion and cold contraction properties of PCB material and the gravity effect of PCB itself, greater thermal stress will be generated in the BGA area of PCB, which will lead to warping and deformation of PCB to a certain extent in the repair process. Although the support plays a certain role, But PCB deformation still exists. In severe cases, this deformation will cause the contact between the external connection point and the pad to be minimized, resulting in BGA quadrangle welding spot bridging, intermediate welding air welding and other welding defects. Therefore, the temperature should be controlled as much as possible. Since the heating area at the bottom of the workstation is large, under the condition of ensuring the maximum curve temperature and reflux time, increasing the preheating time and increasing the heating temperature at the bottom, while reducing the heating temperature at the top, will greatly reduce the thermal deformation of PCB. The other is to pay attention to the position and height of the bottom support.
Welding open circuit:
The reasons for the welding open circuit are complicated, and the PCB warping described above is one of them. In addition, there are several factors that may lead to open circuit. It is important to check whether the welding curve is correct. The incorrect curve will lead to the reflux time is too short or the temperature is too low, and the tin ball and solder paste are not sufficiently reflux to cause open circuit. Whether because of the use of solder paste rather than solder paste as welding auxiliary material, the possibility of open circuit will be reduced by the use of solder paste reflux process, this is because the solder paste has lower requirements for coplanar; Whether PCB and chip are not dried before welding and so on.
Welding short circuit:
PCB warping is one of the reasons leading to short circuit welding. Other reasons are whether the thickness of the net plate opening and the amount of solder paste printed are appropriate. If the solder paste is too thick and uneven, it is very easy to produce short circuit. Whether PCB and chip drying, if not drying, popcorn phenomenon may cause short circuit; Whether the solder resistance film is damaged when cleaning the pad? If the solder resistance is damaged, it is easy to lead to short circuit; The other thing is whether the temperature curve is correct.
At present, the production process of BGA is stable, and each company is improving the technological level and strengthening the management, and the defect rate of BGA is gradually decreasing. Each company appropriately trains the repair technicians, adopts the appropriate repair equipment, understands the key processes of BGA repair, and constantly summarize the repair experience, optimize the repair process and improve the repair process. All of these contribute to a stable and efficient repair.
Well, all the above content is about the BGA repair table common problems analysis, hope to help you ~
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