BGA component assembly and rework

BGA component assembly and rework

Because PBGA is moisture sensitive, preconditioning should be taken prior to assembly. It is recommended that all packages be fully assembled and reflowed within 24 hours. Excessive removal of the device from the antistatic bag can damage the device. CBGA is not sensitive to moisture, but care needs to be taken.

 

The solder paste should be carefully selected because solder paste composition is not always ideal for BGA assembly, especially for PBGA assembly. The supplier must be assured that its solder paste will not form solder joint holes. Similarly, if using water-soluble solder paste, pay attention to choose the package type.

 

However, due to the invisible BGA solder joints, the solder paste application must be carefully observed. The accuracy of solder paste coating, especially for CBGA, will directly affect the assembly pass rate. General allow SMD device assembly rate of qualified low, because it is fast and cheap rework, and BGA devices have no such advantage. To increase the initial pass rate, many high-volume assemblers of BGA purchased inspection systems and complex rework equipment. Detecting solder paste application and component placement prior to reflow reduces costs more than testing after reflow because testing is difficult after reflow and the equipment needed is expensive.

 

The BGA reflow process is the same as the SMD reflow process, but BGA reflow requires precision temperature control and an ideal temperature profile for each component. In addition, most BGA devices can be automatically aligned on the pad during reflow. Therefore, from a practical point of view, it is possible to assemble a BGA using an SMD-assembled device.

 

The big advantage of BGA assembly is that if the assembly method is correct, the pass rate is higher than the traditional device. This is because it has no leads, simplifying component handling and therefore reducing the likelihood of device damage.

 

A third type of BGA package is a carrier-tape ball grid array package (TBGA), which is now increasingly used in high-performance components that require lighter and thinner devices. On polyimide tapes, TBGA I / O leads can be more than 700. TBGA can be processed using standard screen printing paste and conventional IR reflow soldering methods.

 

The two most common BGA packages are plastic BGA (PBGA) and ceramic BGA packages (CBGA). The PBGA has an easy-to-solder ball with a typical diameter of 0.762 mm. During solder reflow (typically 215 ° C), these solder balls collapse into 0.406 mm solder joints between the package and the PCB. CBGA is used in the components and printed boards without melting ball (in fact, its melting point is much higher than the reflow temperature), solder ball diameter of 0.889mm, the height remains unchanged.

 

    Ballistic Array (BGA) devices have undeniable advantages. However, some of the problems in this technique still need further discussion, not immediately, because of the difficulty of trimming the soldered ends. BGA interconnect integrity can only be tested using X-ray or electrical test circuitry, but both are expensive and time-consuming.