Key Points of SMT Assembly Process for BGA Components

April 16 [Tue], 2019, 17:07
The advent of BGA (ball grid array) definitely decreases assembly defects when SMT (surface mount technology) / SMD (surface mount device) practitioners find QFP (quad flat package) with pitch of 0.3mm incapable of ensuring SMT quality achievement. From the perspective of system theory, because the reduction of process technology difficulty level leads problems solved as quickly as possible and makes product quality more easily controlled, compatible with the concept of modern manufacturing, although BGA components inspection is not easy to be implemented. This article will discuss and analyze SMT assembly process of BGA components in all directions based on practical volume production.
Key Points of SMT Assembly Process for BGA Components

• Pretreatment

Although some components with BGA packages are not so sensitive to humidity, all the components are advised to go through baking at a temperature of 125°C because no negative impact has been witnessed on low-temperature baking. That also works for bare PCBs (printed circuit boards) that are ready to go through SMT assembly. After all, moisture can be first eliminated with soldering balls defects going down and solderability improving.

• Solder Paste Printing

In accordance with my assembly experience, solder paste printing is generally easy to be implemented on BGA components with a pitch of more than 0.8mm and QFP components with a pitch of 0.5mm. Sometimes, however, an issue might be encountered that tin needs to be compensated through manual operation since some solder balls haven't received sufficient solder paste printing, which leads soldering to be displaced or short circuits to occur.

Nevertheless, I don't think solder paste is more easily printed on BGA components with a pitch of 0.8mm than on QFP components with a pitch of 0.5mm. I believe that lots of engineers have been aware of the difference between horizontal printing and vertical printing on QFP with a pitch of 0.5mm, which can be explained from the perspective of mechanics. Thus, some printers are capable of providing 45° printing function. Based on the opinion that printing plays an essential role in SMT assembly, sufficient attention is suggested to being paid.

• Placement and Mounting

Based on practical assembly experience, because physical characteristics lead BGA components to feature high manufacturability, they are more easily to be mounted than QFP components with a pitch of 0.5mm. However, the main problem we have to face up with during SMT assembly process is that vibration usually occurs on components when large-scale nozzle with rubber ring is used to get components placed on circuit board with a size of more than 30mm. Based on analysis, it can be believed that it takes place as a result of too high pressure within nozzle due to excessive mounting strength and it can be eliminated after agreeable modifications.

• Soldering

Reflow soldering with hot air is a non-intuitive process during SMT assembly process or it can be defined as a special technology. Although BGA components share equivalent time and temperature curve of soldering with standard curve, it differs from majority of traditional SMDs in terms of reflow soldering. Solder joints of BGA components are under components, between component body and PCB, which determines that BGA components are much more affected on solder joints than traditional SMDs since pins of the latter are placed at periphery of component body. At least, they are directly exposed in hot air. Thermal resistance calculation and practices indicate that solder balls in central area of BGA component body suffer from thermal postponing, slow temperature rising and a low maximum temperature.

• Inspection

Due to physical structures of BGA components, visual inspection fails to meet inspection demands of hidden solder joints of BGA components so X-ray inspection is called for to make soldering defects such as voids, short circuits, missing soldering balls, air holes etc. The only disadvantage of X-ray inspection is its high cost.

• Rework

Along with a wide range of applications of BGA components, plus the popularity of electronics products for personal telecommunications, BGA rework has become increasingly significant. However, compared with QFP components, BGA components can never be used again once they are disassembled from circuit board.

Now that BGA packaging technology has become a mainstream in SMT assembly, its technology difficulty level can never be neglected and key points mentioned in this article should be carefully and correctly analyzed with issues rationally solved. When selecting a electronic contract manufacturer or assembler, professional manufacturing line should be picked up together with full-scale assembly capabilities and assembly equipment.

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ALLPCB features specialized SMT assembly line containing solder paste printer, chip mounter, on-line and off-line AOI equipment, reflow soldering oven, AXI equipment and BGA rework station. The automatic assembly procedure provided by ALLPCB is capable of dealing with BGA components with a pitch as low as 0.4mm. All the services and products provided by us are compatible with regulations of ISO9001:2008 system, which is a solid foundation for customers' expectation achievement. Contact us for more information about our SMT capabilities for BGA components. Or, you may click below button to request FREE and non-obligation PCBA quote!
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