BGA repair of the critical step assembly problem
Set up temperature curve
Clean the mounting position
Most manufacturers agree that spherical array (BGA) devices have undeniable advantages. But some problems with this technique are still to be discussed further, rather than implemented immediately, because it is difficult to trim the weld ends. The interconnection integrity of BGA can only be tested by X-ray or electrical test circuit methods, but both methods are expensive and time consuming. Designers need to understand the performance characteristics of BGA, much like earlier SMDS. The PCB designer must know how to modify the design accordingly when the manufacturing process changes. For manufacturers, there is the challenge of dealing with different types of BGA packages and changes in the final process. In order to increase yield, the assembler must consider establishing a new set of standards for handling BGA devices. In the end, perhaps the key to a more cost-effective assembly lies with the BGA returner.
The two most common types of BGA packages are plastic BGA(PBGA) and ceramic BGA(CBGA). The PBGA has fusible solder balls, usually 0.762mm in diameter, which collapse into a 0.406mm high solder joint between the package and the PCB during reflow soldering (usually 215℃). CBGA is the use of a non-fusion ball (in fact, its melting point is much higher than the temperature of reflow soldering) on components and printed boards. The diameter of the ball is 0.889mm and the height remains the same.
The third type of BGA package is the on-board ball grid array package (TBGA), which is increasingly used in high-performance components that require lighter, thinner devices. TBGA can have more than 700 I/O leads on the polyimide carrier. TBGA can be processed using standard screen printing solder paste and traditional infrared reflow soldering. The great advantage of BGA assembly is that, if the assembly method is correct, the pass rate is higher than that of traditional devices. This is because it has no leads, simplifying the handling of the component and therefore reducing the possibility of damage to the device: with tin-absorbing webbing, residual solder paste can be safely and effectively removed. The BGA reflow process is the same as the SMD reflow process, but BGA reflow requires precise temperature control and the establishment of an ideal temperature curve for each component. In addition, most BGA devices are able to align themselves on the pad during reflow soldering. Therefore, from a practical point of view, the BGA can be assembled with the same equipment used to assemble SMDS. However, since the solder joints of the BGA are not visible, the application of the solder paste must be carefully observed. The accuracy of solder paste coating, especially for CBGA, will directly affect the assembly pass rate. SMD devices are generally allowed to be assembled with a low pass rate because they are quickly and cheaply repaired, whereas BGA devices do not have the same advantage. To improve initial acceptance, many high-volume BGA assemblers have purchased testing systems and sophisticated repair equipment. Testing paste coating and component mounting before reflow is more cost-effective than testing after reflow, which is difficult and requires expensive equipment. Choose solder paste carefully, as the composition of solder paste is not always ideal for BGA assembly, especially for PBGA assembly. Suppliers must be assured that their solder paste will not form solder joint holes. Similarly, if water-soluble solder paste is used, care should be taken to select the type of package. Since PBGA is sensitive to moisture, pretreatment is required prior to assembly. It is recommended that all packages be fully assembled and reflow welded within 24 hours. If the device leaves the antistatic bag for a long time, the device will be damaged. CBGA is not sensitive to moisture, but care is still needed. The basic steps for repairing a BGA are the same as those for repairing a traditional SMD
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